JP5332078B2 - Beam output controller - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To certainly control the light quantity of a plurality of beams through simple structure. <P>SOLUTION: A selection part 62 of beams to be corrected generates a selection signal Pcng0 of the beams to be corrected showing the order of the output quantity correction process of each of the beams. A switching signal generation part 65 of APC lighting beam generates the switching signal Pcng0 of APC lighting beam having a clock corresponding to the beam. A reference signal generation part 68 counts the switching signal of APC lighting beam, switches a switching device 85 on the basis of a select signal SEL from an APC timing control part 67 and outputs reference signals of corresponding colors in time division. A counting processing part 66 and the APC timing control part 67 cooperate to generate a beam-corresponding clock in which a correction timing is so adjusted that the correction process of a following beam is stopped for a predetermined term immediately after switching a reference value and the correction process of the stopped beam is begun after the predetermined term elapses, and further output the switching signal Pcng of APC lighting beam to an output value control part 52. <P>COPYRIGHT: (C)2007,JPO&amp;INPIT

Description

  The present invention relates to a beam output control device used in a multi-beam optical scanning device that writes predetermined information such as an image on a scanned object using a plurality of beams. More specifically, the present invention relates to a mechanism for individually controlling the output value of each beam so as to be maintained at a target value.

  For example, as in an image forming apparatus employing an electrophotographic system, a scanned object such as a photosensitive member is scanned with a beam whose output is controlled in accordance with predetermined information, whereby the scanned object is scanned on the scanned object. A technique for writing the information is known.

  For example, in an electrophotographic image forming apparatus using laser light in recent years, individual light sources and photosensitive drums are provided for four colors of black, cyan, magenta, and yellow for colorization, and emitted from each light source. There is known a tandem system that performs drawing on a corresponding photosensitive drum and simultaneously controls the light emission output of these light sources.

  Recently, for example, a laser diode capable of emitting n light beams from one chip is used for one photosensitive drum, for example, in order to increase the writing speed of information and perform high-density recording. A multi-beam technique (in a narrow sense) in which the number of beams is increased and a plurality of beams are simultaneously scanned has been proposed. In addition, a mechanism for adopting this method in the above-described tandem method is also considered.

  A scanning device that scans a plurality of beams in synchronization like the tandem method and the multi-beam method is referred to as a multi-beam method in a broad sense in the present specification.

  By the way, when scanning the object to be scanned with a beam, since it is necessary to scan with the beam output amount (power) stabilized, automatic output amount control (APC: Automatic Power Control) is performed. Usually, the automatic output amount control monitors the output amount of the beam with a detector, and shows information indicating the output amount of the beam obtained from the detector and reference information (so-called reference signal) according to the target output amount. By comparison, feedback control is performed so that the output amount of the beam is always maintained at the target output amount.

  When using multiple beams, it is necessary to take into account the characteristic variations of each beam and refer to the individual reference values, and to perform automatic output amount control for each. Various things have been proposed.

  Further, in a tandem configuration using a plurality of scanned objects, scanning is performed with an output amount corresponding to the variation in characteristics of the scanned objects even if the characteristics of each beam used for the same scanned object are uniform. Since there is a need, a mechanism for executing the automatic output amount control for each of the scanned objects with reference to individual reference values is also required. In particular, when a multicolor image is formed, the target light amount may be different for each color (that is, for each photoconductor), so individual control is required for each color. In addition, if there is a characteristic variation among the beams used for the same scanning object, a mechanism for executing automatic output amount control in consideration of this beam variation is also required.

  Various mechanisms for executing the automatic output amount control when using a plurality of beams are considered. For example, the most primitive idea is to provide a drive circuit, light receiving element, and control circuit corresponding to the number of light emitting elements, and supply a reference signal corresponding to the target light intensity corresponding to each beam to each control circuit. However, it is conceivable to perform automatic output amount control independently for each drive circuit and light emitting element. However, in this case, it is necessary to provide each independently, and there is a problem that the circuit scale and the number of elements become enormous.

  In general, this type of apparatus includes a light source unit (light source control unit) provided with a light emitting element and a drive circuit, a CPU for performing control, an image memory for storing image data, and the like. In many cases, the configuration is independent of the device control unit. In this case, in order to control the drive circuit of the light source control unit, it is necessary to connect the light source control unit and the device control unit with reference signal lines or various control lines.

  Therefore, when automatic output amount control is executed in a multi-beam system configuration, the number of connection lines increases, resulting in complication of the overall configuration, and appropriate changes due to variations among various signals transmitted through the connection lines. There is also a problem that it is difficult to control. For example, a reference signal corresponding to a target light amount corresponding to each beam is supplied from the apparatus control unit to the light source control unit through an independent signal line, and the light source control unit performs the reference when the automatic output amount control process is executed. Although it is conceivable to use a signal, the number of reference signal lines increases.

  For this reason, a mechanism for individually controlling the output value of each beam to be maintained at the target value while solving these problems has been proposed (see, for example, Patent Documents 1 to 3).

JP 2001-024273 A JP 2001-150726 A JP 2003-248368 A

  For example, in the mechanisms described in Patent Documents 1 and 2, a plurality of light emitting elements (for example, semiconductor lasers) are driven in a time division manner, and the light output of each light emitting element is detected in a time division manner with a single light receiving element. In addition, an APC control unit (output amount control unit) including a comparator that compares a reference value corresponding to each light emitting element and the light receiving output of the light receiving element is provided for each light emitting element, and the detected light receiving output and On the basis of the reference value (specifically, so that both coincide with each other), a mechanism for separately controlling the light output of the corresponding light emitting element has been proposed.

  That is, the mechanisms described in Patent Documents 1 and 2 monitor the optical output of a plurality of beams in a time division manner, and detect the optical output value detected in the time division and the reference for each beam corresponding to the optical output value. Automatic output amount control is performed by comparing values individually.

  In the mechanism described in Patent Document 3, the controller unit generates a plurality of duty signals for controlling a plurality of semiconductor lasers, and generates duty signals that are arranged on the time axis and output to the scanning unit. The scanning unit includes a plurality of drive circuits for individually driving the plurality of semiconductor lasers, a duty voltage circuit for converting each duty signal into a voltage, and a duty corresponding to each drive circuit from each duty signal. A configuration is proposed that includes a reference voltage circuit that detects a signal and inputs the duty voltage output from the duty voltage circuit to the corresponding drive circuit as a reference voltage in synchronization with the detected duty signal.

  That is, the number of transmission lines is reduced by serially transmitting the bias voltage and the reference value of the light amount control with signals having different frequencies and duties, and converting them into analog voltages to perform light amount control. In this technique, the bias voltage and the reference voltage are discriminated from the difference in frequency, and the voltage value is controlled by the duty.

  However, in the mechanisms described in Patent Documents 1 and 2, although the driving of the light emitting element (including automatic output amount control for the light emitting element) and the detection of the light output are performed in a time-sharing manner, the control including the comparator is performed. The circuit is individually provided so as to correspond to each beam, and the reference signal corresponding to the target light quantity corresponding to each beam is still transmitted individually to each control circuit.

  For this reason, when the controller unit and the scanning unit are configured independently, the number of reference signal lines increases, resulting in a complicated overall configuration, and appropriate due to the mutual variation of various signals transmitted through each connection line. The problem that makes it difficult to perform proper control cannot be solved.

  On the other hand, in the mechanism described in Patent Document 3, since signals are transmitted serially with signals having different frequencies and duties, a plurality of frequencies must be used in order to recognize each beam by a frequency difference. Since a circuit for duty adjustment is required, the circuit scale is greatly increased and complicated. In addition, since each beam is recognized by a frequency difference, a clock signal is always required, and if the clock signal is transmitted together with the image data, there is a possibility of adversely affecting each other due to crosstalk with the image signal.

  The present invention has been made in view of the above circumstances, and even when the light source control unit and the apparatus control unit are configured independently, the light quantity control of a plurality of light beams is performed with a simple configuration and reliably. The purpose is to provide a mechanism that can do this.

  In the beam output control device according to the present invention, first, for the output amount correction processing unit provided on the light source control unit side, each reference value set corresponding to each of the plurality of beams is set to the output amount of the plurality of beams. Import in time division according to the correction processing order. When the light source control unit and the apparatus control unit are configured independently, the reference signal line between the controller unit and the scanning unit is a signal line (typically a single signal) that is less than the number of beams in time division. The number of output amount control units that perform transmission amount correction processing using each reference value in a time-sharing manner is smaller than the number of beams (typically in a single output amount control unit) Is possible).

  In this case, a signal indicating the output amount correction processing order of a plurality of beams (referred to as a correction target beam selection signal) and a lighting signal for lighting each of the plurality of beams are transmitted from the controller unit to the scanning unit. The output amount correction processing unit takes in a reference signal transmitted in time division according to a correction target beam selection signal indicating the output amount correction processing order, and outputs an output amount correction for the beam corresponding to the output amount correction processing order. Execute the process.

  For this reason, first, as the output control device on the scanning unit side, each reference value set corresponding to each of a plurality of beams is taken in a time division manner according to the output amount correction processing order of the plurality of beams, and output amount correction is performed. An output amount correction processing unit for executing processing is provided.

  Further, as a beam output control device on the controller unit side that generates various signals for executing output amount correction processing so that the output value of each of the plurality of beams becomes a value indicated by a reference value on the scanning unit side, A correction target beam selection unit that generates and outputs a correction target beam selection signal indicating an output amount correction processing order for each of the plurality of beams, and each reference value set corresponding to each of the plurality of beams is corrected. A reference signal generation unit that performs time division conversion so as to correspond to the output amount correction processing order of a plurality of beams represented by a correction target beam selection signal output from the target beam selection unit, and lights each of the plurality of beams And a lighting beam setting unit that generates and outputs a correction timing signal for the purpose.

  At this time, if the reference signal is captured in a time-sharing manner, there is a possibility that the reference signal does not reach a predetermined value within the correctable period for the beam to be corrected in consideration of the response speed of the control system. If the output amount correction process is executed during a period in which the reference signal does not reach the predetermined value (referred to as a settling period), a problem arises because an appropriate output cannot be guaranteed for the beam. In other words, when trying to capture the reference signal in a time-sharing manner, the settling time until the reference signal after switching becomes stable due to the difference between the reference values before and after switching (difference between the reference value before switching and the reference value after switching). A period is required, and if the correction process is executed within this settling period, a harmful effect occurs.

  Note that the “beam to be corrected” here is out of the information writing range within the scanning period, the correction timing for executing the output amount correction processing is set at what point in time, the relationship with the object to be scanned, etc. There are various forms. For example, when all the beams are handled independently, there may be cases where each of the beams is one by one, there may be cases where the scanning target is different (not limited to one, but there may be a plurality of beams) within one scanning period, or the scanning period. There are also cases in which each object is scanned (not limited to one but may be a plurality of beams).

  In the present invention, in order to solve the problem related to the settling period, the fixed period after switching is set as the stop period, or the light beam corresponding to the fixed period after switching is corrected so that the output is not appropriate. Duplicate force correction processing is performed, and the correction processing order is adjusted so that the difference in the reference signals at the time of switching is as small as possible.

  That is, in the first beam output control device, the output amount correction processing unit stops the subsequent beam output amount correction processing for a predetermined period immediately after the reference value switching between the reference value switching, After a predetermined period, the correction timing is adjusted so as to start the output amount correction process for the beam that has been stopped.

  In other words, by assigning a predetermined period immediately after switching of the reference value to the stop period, it waits for the reference signal to reach the predetermined value during the stop period, and executes the output amount correction process after the reference signal reaches the predetermined value. This ensures that all beams have the proper output. The technique employed by the first beam output control device is called a settling period stop technique.

  In this case, with respect to the lighting beam setting unit, when generating and outputting a correction timing signal for lighting each of the plurality of beams, a predetermined period immediately after the switching of the reference value between the switching of the reference value is followed The beam output amount correction processing is stopped, and after a predetermined period, a beam-corresponding clock is generated with the correction timing adjusted so that the output amount correction processing for the stopped beam can be started. The lighting beam setting signal is output to the output amount control unit.

  Further, in the second beam output control device, the output amount correction processing unit executes the subsequent beam output amount correction processing for a predetermined period immediately after the reference value switching between the reference value switchings. Even after the period has elapsed, the correction timing is adjusted so that the output amount correction processing is repeated (repeatedly) again for the beam corresponding to the predetermined period.

  That is, similar output amount correction processing is executed for the same beam in both a predetermined period immediately after the reference value is switched and a period corresponding to the predetermined period (referred to as an overlapping period). The technique adopted by the second beam output control device is called a settling period overlapping technique.

  In the first half of the output amount correction process during the predetermined period, there is a possibility that the output is not appropriate, but it waits for the reference signal to reach a predetermined value during this stop period, and the overlap after the reference signal reaches the predetermined value By executing the same output amount correction process for the same beam again during the period, it is ensured that all the beams have an appropriate output.

  In this case, with respect to the lighting beam setting unit, when generating and outputting a correction timing signal for lighting each of the plurality of beams, a predetermined period immediately after the switching of the reference value between the switching of the reference value is followed The output amount correction processing is executed for the beam of the beam, and after a predetermined period, the beam-corresponding clock is generated with the correction timing adjusted so that the output amount correction processing for the subsequent beam can be performed again. The lighting beam setting signal is output to the output amount control unit.

  In the third beam output control device, when each reference value set corresponding to each of the plurality of beams is handled in a time-sharing manner, the difference between the reference values before and after switching (the reference value before switching) A rank adjustment unit for determining the output amount correction processing order of a plurality of beams is provided so that the difference from the reference value after switching becomes smaller. The output amount correction processing unit captures each reference value set corresponding to each of the plurality of beams in a time-sharing manner according to the adjusted output amount correction processing order, and outputs the output amount for the beam corresponding to the acquired reference value. Perform correction processing.

  By reducing the difference in the reference signal at the time of switching by time division, the reference signal can reach a predetermined value within the correctable period for the beam to be corrected. If the reference signal does not reach the predetermined value within the correctable period for the beam to be corrected even if the correction processing order is adjusted, the settling period stopping method or the settling period overlapping method described above may be applied. .

  The point of the present invention is that each reference value for each beam can be acquired in a time division manner in accordance with the correction processing order, and the adverse effects caused by the regular period that can occur when the reference signal is acquired by the time division are prevented. As long as this is done, various methods can be used as the specific mechanism for executing output amount correction processing according to the correction processing order using each reference value acquired in time division. . That is, as long as each reference signal corresponding to each target output value is handled in a time-sharing manner and the output amount correction process is executed for each beam, various forms can be adopted.

  In particular, it is free to drive the light-emitting elements and the circuit configuration for detecting the output value of each beam. The drive circuit and the light-receiving element are provided corresponding to the number of light-emitting elements. It is also possible to adopt a configuration in which automatic output amount control is independently performed for the light emitting elements.

  Even in this case, the output amount control unit including a comparator for comparing the reference value corresponding to each of the light emitting elements and the light receiving output of the light receiving element is not different from the beam, and the number is smaller than the number of beams (typically One example). In addition, the transmission line between the controller unit and the scanning unit related to the output amount correction processing includes a correction target beam selection signal indicating the output amount correction processing order of the plurality of beams, and lighting for lighting each of the plurality of beams. Three systems of a signal and a reference signal line for transmitting the reference signal in time division may be used.

  However, in this case, since the scale of the light receiving element and the drive circuit increases, preferably, a plurality of light emitting elements are driven in a time-sharing manner as in the mechanisms described in Patent Documents 1 and 2, and the light output of each light emitting element Is preferably detected in a time division manner with a single light receiving element.

  In this case, the number of laser drive units, light receiving elements, and drive circuits is one, and these are used in a time-sharing manner in accordance with each of a plurality of beams, whereby the output amount correction processing for each beam can be executed. In this case, since it is necessary to drive corresponding ones of a plurality of beams in a time division manner in accordance with a reference signal captured in a time division manner, each of the plurality of beams output from the lighting beam setting unit is turned on. For the lighting signal for this, it is necessary to use a switching signal for sequentially lighting each of the plurality of beams in time series (in a time division manner).

  According to the present invention, each reference value for each beam is captured in a time-sharing manner in accordance with the correction processing order, and a fixed period after switching is set as a stop period, or an appropriate amount of light beam corresponding to the fixed period after switching is set. The output amount correction processing is executed repeatedly so as to correct the lost portion of the output, or the correction processing order is adjusted so that the difference in the reference signal at the time of switching is as small as possible.

  Accordingly, the number of signal lines for reference values and the number of output amount control units that execute output amount correction processing using each reference value in a time division manner can be made smaller than the number of beams. In addition, it is possible to prevent adverse effects caused by the reference signal sizing period that may occur when the reference signal is taken in by time division.

  Even when the light source control unit and the device control unit are configured independently, the light quantity control of multiple light beams can be realized with a simple configuration by reducing the number of reference value signal lines, and the time division reference signal By taking a mechanism for preventing adverse effects that may occur at the time of taking-in, it is possible to reliably perform light quantity control for all of the plurality of light beams.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

<Schematic configuration of image forming apparatus>
FIG. 1 is a diagram showing an outline of a configuration example of an image forming apparatus according to the present invention. In order to enable full-color image formation, the image forming apparatus 1 sequentially applies an image that has been color-separated with single-color toners of yellow (Y), magenta (M), cyan (C), and black (K) onto a sheet. To superimpose, each latent image is scanned and exposed on a plurality of photoconductors corresponding to each color of yellow, magenta, cyan, and black by an image signal corresponding to an image separated by an optical scanning device, and each single color image is developed. The full-color toner image formed by sequentially transferring each single-color image onto the intermediate transfer member is collectively transferred onto the recording medium.

  Specifically, the image forming apparatus 1 includes an image output unit 10 and an optical scanning device 20. The image output unit 10 includes three transport rollers 12A to 12C, an endless transfer belt 14 wound around the transport rollers 12A to 12C, and a transfer roller 16 disposed to face the transport roller 12C with the transfer belt 14 interposed therebetween. And an image forming section 18 for each color (represented with reference elements Y, M, C, and K, respectively).

  In order to form a yellow (Y) monochromatic image on the side of the transfer belt 14 along the moving direction of the transfer belt 14 when the transfer belt 14 is driven to rotate (direction of arrow A in FIG. 1A). An image forming unit 18Y for forming a monochrome image of magenta (M), an image forming unit 18C for forming a monochrome image of cyan (C), and a monochrome image of black (K). For this purpose, image forming portions 18K are sequentially arranged at substantially equal intervals.

  Although not shown in detail in FIG. 1, each image forming unit 18 includes a photosensitive drum 19 that is arranged so as to be orthogonal to the moving direction of the transfer belt 14 and rotates in the direction of arrow B in the drawing. Further, as shown in the image forming unit 18Y, the photosensitive drum 19 is formed on the photosensitive drum 19 by the charger 18a for charging the photosensitive drum 19 and the optical scanning device 20 around each photosensitive drum 19. A developing unit 18b that develops the electrostatic latent image with toner of a predetermined color (Y, M, C, K) to form a toner image, and a transfer that transfers the toner image formed on the photosensitive drum 19 to the transfer belt 14. A cleaner 18d and a cleaner 18d for removing the toner remaining on the photosensitive drum 19 are sequentially arranged. The transfer unit 18c is disposed to face the photosensitive drum 19 with the transfer belt 14 interposed therebetween.

  The toner images of different colors formed on the photosensitive drums 19 of the individual image forming units 18 are respectively transferred to the transfer belt 14 so as to overlap each other on the belt surface of the transfer belt 14. As a result, a color toner image is formed on the transfer belt 14, and the formed color toner image is transferred between the conveying roller 12C and the transfer roller 16 in the moving direction (direction of arrow C in FIG. 1). Transferred to the material 22. Then, the transfer material 22 is sent to a fixing device (not shown), and the transferred toner image is fixed. As a result, a color image (full color image) is formed on the transfer material 22.

  An optical scanning device 20 is disposed in the vicinity of the image forming units 18Y, 18M, 18C, and 18K. The optical scanning device 20 includes a light source 24 that emits a plurality of light beams, a motor 46, and a polygon mirror (rotating polygonal mirror) 28 that is rotationally driven by the motor 46.

  The optical scanning device 20 includes two lenses 33 and 34 constituting an fθ lens 32 having power only in the main scanning direction on the optical path on the light beam emission side of the rotary polygon mirror 28, and a plurality of beam lights. Are separated into a group of predetermined light beams, and a cylindrical mirror 38 is provided.

  In FIG. 1, the single separation mirror 36 is shown, but the separation mirror 36 can also be constituted by a combination of a plurality of separation mirrors as shown in FIG.

  The cylindrical mirror 38 has the image forming unit for each color for each color of Y, M, C, and K so that the light beams of each group for each color separated by the separation mirror 36 enter the corresponding image forming unit 18. 18 (referred to as 38Y, 38M, 38C, and 38K, respectively). The cylindrical mirror 38 has power only in the sub-scanning direction, and further has a surface tilt correction function that conjugates the outer peripheral surfaces of the rotary polygon mirror 28 and the photosensitive drum 19 in the sub-scanning direction. .

  The light beam emitted from the light source 24 is deflected and reflected by the rotary polygon mirror 28, and then enters the separation mirror 36 through the fθ lens 32. The separation mirror 36 uses the color-specific cylindrical mirrors 38Y, 38M, A predetermined number is separated and reflected toward 38C and 38K. The light beams emitted from the separation mirrors 36 are reflected by the cylindrical mirrors 38 so that the imaging positions in the sub-scanning direction coincide with the photosensitive drums 19, and corresponding image forming units 18Y, 18M, and 18C for respective colors. , 18K are incident on the photosensitive drums 19 respectively.

  Here, the light beam incident on the photosensitive drum 19 moves on the outer peripheral surface of the rotating photosensitive drum 19 at a substantially constant speed, and the imaging position in the main scanning direction is the outer peripheral surface of the photosensitive drum 19. It is refracted by the fθ lens 32 so as to coincide with the upper side.

<Configuration of optical scanning device>
FIG. 2 is a diagram illustrating a detailed configuration example of the scanning optical system of the optical scanning device 20. In FIG. 1, the separation mirror 36 is shown as having a single configuration, but here, the separation mirror 36 is shown by a combination of a plurality of mirrors. Here, FIG. 2A is a plan view showing an overall outline of the optical scanning device 20, and FIG. 2B is a diagram illustrating the incident path to the photosensitive drum 19, with reference to FIG. It is sectional drawing on the ZZ line.

  The light source 24 is provided on the circuit board 30, and the light source 24 is attached to the housing 20 a of the optical scanning device 20.

  On the circuit board 30, an LD control unit 50, which is an example of a light source control unit including a laser drive circuit for driving and controlling the light source 24 and an output amount correction processing circuit, is configured. By 31, it connects with the apparatus control part provided in the apparatus exterior.

  The incident optical system 26 between the light source 24 and the polygon mirror 28 includes a collimator lens 26a, a half mirror 26b, and a cylindrical lens 26c in the order of the optical path. A part of the light beam emitted from the light source 24 is reflected by the half mirror 26b.

  A plurality of light beams emitted from the light source 24 are converted into parallel luminous fluxes by the collimator lens 26a arranged on the beam emission side of the light source 24, and then a single rotating polyhedral surface on which a plurality of reflecting surfaces are formed. The light enters the same reflecting surface of the mirror 28 and enters the separation mirror 36 through the fθ lens 32. Here, the separation mirror 36 includes a plurality of reflection mirrors (flat mirrors) in order to separate the light beam that has passed through the fθ lens 32 into Y, M, C, and K groups.

  The polygon mirror 28 rotates at a high speed in the direction of arrow D in FIG. 2 (rotates at a constant speed with high accuracy) by the driving force of the motor 46 (see FIG. 1) being transmitted to the same reflecting surface. The incident light beams are each deflected and scanned along the main scanning direction. As a result, the light beam is scanned in the direction of arrow E in FIG.

  In addition, the optical scanning device 20 includes a pickup mirror 40 on the beam emission side of the fθ lens 32 at a position corresponding to an end portion (SOS: Start Of Scan) of the scanning range of the light beam, A main scanning synchronization sensor (hereinafter referred to as SOS sensor) 42 for detecting the light beam reflected by the pickup mirror 40 is provided on the light beam emission side of the pickup mirror 40. In the configuration shown in the figure, the scanning start signal SOS is output with a light beam corresponding to black.

  Of the light beams scanned by the polygon mirror 28, the light beam at the position corresponding to the scanning start end is reflected by the pickup mirror 40 and enters the SOS sensor 42. The SOS sensor 42 outputs a signal corresponding to the incidence of the light beam, and can detect the scanning start timing for each scanning. The scanning start signal SOS that is an output signal of the SOS sensor 42 synchronizes the image writing timing in the scanning direction.

  Further, the optical scanning device 20 includes a condenser lens 44 and a light amount detection sensor 45 that functions as a light detection unit in the light reflection direction of the half mirror 26b. The light beam emitted from the light source 24 is reflected by the half mirror 26 b and enters the light amount detection sensor 45 before entering the polygon mirror 28. The light amount detection sensor 45 receives the incident light beam and outputs a current corresponding to the amount of received light. That is, the light amount of the light beam can be measured by the light amount detection sensor 45.

  As the light source 24 used in the present embodiment, an image can be formed by increasing the number of light emitting points that emit a laser beam and simultaneously scanning a plurality of light beams. By using a laser diode (LD) capable of emitting n light beams (laser light) from one chip, the rotational speed of the polygon mirror 28 is 1 / n compared to a laser diode emitting one beam. Thus, the scanning speed on the photosensitive drum 19 can be reduced, and the frequency of the image clock can be reduced.

  As such a laser diode having a plurality of light emitting points, a VCSEL (vertical cavity surface emitting laser) is used in the present embodiment. A VCSEL is useful as a laser light source having a plurality of light emitting points because a large number of laser light source portions can be formed on a single chip relatively easily.

  In the electrophotographic image forming apparatus 1 using a laser light source, automatic light beam output amount correction processing (APC) is performed in order to stably scan the light beam. When a VCSEL is used as the light source 24, since the emission direction of the light beam is perpendicular to the semiconductor substrate, it does not have a back beam. Therefore, unlike the edge-emitting laser light source, a monitor photodiode ( Since it is difficult to have an MPD), a light amount detection sensor 45 is provided outside the package, and a light beam emitted from the light source 24 is separated by a half mirror 26b and incident on the light amount detection sensor 45 to emit light from the light source 24. The light quantity is detected, a current value corresponding to the detected light quantity is converted into a voltage, and the target light quantity is controlled by comparing with a reference voltage corresponding to the target light quantity.

  Since the number of light beams emitted from the VCSEL is very large (for example, 32), providing the light quantity detection sensors 45 for the number of light beams necessitates separation of the emitted beams, and the arrangement space and cost of the sensors. In this embodiment, one light quantity detection sensor 45 is arranged, each light beam is driven to light in time series, APC control is executed, and each light beam is set to a predetermined light quantity. To be.

<Configuration example of multiple beams>
FIG. 3 is a diagram illustrating a configuration example of a plurality of light beams emitted from the light source 24. Here, the light source 24 will be described as having a configuration having 32 light emitting points. From the light source 24, 32 light beams are emitted in four groups for forming Y, M, C, and K monochromatic images. Note that the light source 24 is not limited to the VCSEL, and a configuration in which 32 laser diodes (LDs) 25 are composed of a plurality of LD arrays, or a configuration in which 32 light beams are emitted from a single package by being integrated. Good. For convenience, including the VCSEL, the individual light emitting sources will be referred to as laser diodes 25 even in a single package.

  As described above, in this embodiment, a VCSEL is used. As an example, a VCSEL including 32 light emitting sources (laser diodes 25) arranged in a two-dimensional manner of 4 × 8 is used. When a multi-beam light source such as the VCSEL is used, it is possible to use a plurality of beams for one color. The following two can be taken.

  For example, as shown in the figure, it is assumed that the laser diodes 25 are arranged in a 4 × 8 matrix and 32 light beams are used. Each laser diode 25 is represented by (column number-row number) so as to distinguish the column and the row.

  In the first example shown in FIG. 3A, a total of 8 laser diodes 25 ((1 row × 4 columns)) in the first row and the second row ((1 The groups (-1) to (4-1) and (1-2) to (4-2)) are groups in charge of the black (K) color. Similarly, a total of eight (2 rows × 4 columns) laser diodes 25 ((1-3) to (4-3) and (1-4) to (4-4) in the third row and the fourth row ) Is a group in charge of cyan (C) color, and a total of 8 laser diodes 25 ((1-5) to (4-5) in the 5th and 6th rows). ) And (1-6) to (4-6)) are responsible for the magenta (M) color, and a total of 8 lasers (2 rows × 4 columns) in the 7th and 8th rows. A group of diodes 25 ((1-7) to (4-7) and (1-8) to (4-8)) is a group in charge of yellow (Y) color. Therefore, in the first example, eight light beams are scanned on one photosensitive drum 19.

  On the other hand, in the second example shown in FIG. 3B, a total of 8 laser diodes 25 (for 1 row × 8 columns) in the first row ((1-1) are used in 4 rows × 8 columns. ) To (8-1)) are groups in charge of the black (K) color. Similarly, a group of a total of 8 laser diodes 25 ((1-2) to (8-2)) in the second row is a group responsible for cyan (C) color, A group of eight laser diodes 25 ((1-3) to (8-3)) in total in the third row is a group in charge of magenta (M) color, and the fourth row A group of eight (1 row × 8 columns) laser diodes 25 ((1-4) to (8-4)) is a group in charge of yellow (Y) color. Therefore, also in the second example, eight light beams are scanned on one photosensitive drum 19.

  In the present embodiment, a case where the light source 24 having the 4 × 8 laser diode 25 is used to scan the photosensitive drums 19 for each color with eight light beams is described, but the present invention is not limited thereto. It is sufficient that one light beam corresponds to at least each color. Therefore, the light source 24 can be a light source 24 such as a VCSEL having at least four laser diodes 25.

<Output amount correction processing system; Basic>
FIG. 4 is a functional block diagram for explaining an outline of a control system for performing the output amount correction process of the light beam. Here, FIG. 4 is a diagram for explaining a basic configuration example, and shows two comparative examples and a basic configuration example adopted by the present embodiment.

  In this configuration, first, the number of light beams from the light source 24 mounted in the optical scanning device 20 is increased. In this case, as the number of light beams increases, the number of light beams for which output amount correction processing is performed also increases. At this time, providing a light amount detection sensor (monitor photo diode: MPD) for each light beam causes restrictions in arrangement space and cost. Therefore, in the present embodiment, a mechanism is employed in which the light emission points are turned on in time series and the light amounts of all the light beams are detected in a time division manner with a single light amount detection sensor. In response to this, the APC control system of the beam output control device compares the light quantity of each light beam output in time division with the reference signal Vref indicating the reference light quantity, thereby correcting the light quantity so that they match. Run.

  Here, as shown in FIG. 3, when a VCSEL that performs APC control by turning on light in time series is used as shown in FIG. That is, as in Comparative Example 1 shown in FIG. 4A, an output amount including a reference voltage generation circuit (not shown) for each color that outputs a reference voltage signal (Vref) in a time division manner for each beam. The correction processing unit (light quantity control unit) 52 and the color-specific laser driving unit 51 are used. In this case, the circuit configuration becomes complicated by the use of each circuit for each color.

  On the other hand, as shown in FIGS. 4B and 4C, color-specific reference signals are generated based on color-specific light amount setting data (reference data) DVref supplied from the image control unit 56, and time-division is performed. Is provided with a reference signal generation unit 68 for outputting light amount setting data DVref (or analog reference signal Vref) on the image control unit 56 side or the LD control unit 50 side. It is conceivable to adopt a configuration in which the laser driving unit 51 is controlled using the reference signal Vref expressed by

  That is, a reference signal having a reference voltage value corresponding to a target light amount corresponding to each color can be output in a time-sharing manner for each color group of the beam, and the reference signal can be switched and used when APC is executed. Conceivable.

  Note that the difference between the configuration employed in Comparative Example 2 shown in FIG. 4B and this embodiment shown in FIG. 4C is that the reference signal generator 68 is placed in the LD controller 50 on the scanning unit side. It is placed in the image control unit 56 on the part side. In the configuration of Comparative Example 2 in which the reference signal generation unit 68 is mounted on the LD control unit 50 side, the output amount correction is performed after time-division conversion of the color-specific light amount setting data DVref by the reference signal generation unit 68 of the LD control unit 50. Since the configuration is transferred to the processing unit 52, a reference signal line between the controller unit and the scanning unit is required for each color.

  In contrast, in the configuration of the present embodiment in which the reference signal generation unit 68 is mounted on the image control unit 56 on the controller unit side, the light amount setting data DVref for each color is stored in the reference signal generation unit 68 of the image control unit 56. Since the configuration is such that after division conversion, it is passed to the output amount correction processing unit 52 on the LD control unit 50 side, there is an advantage that a single reference signal line can be provided between the controller unit and the scanning unit.

  In other words, when the output amount correction processing unit 52 on the scanning unit side captures the reference signal in a time-sharing manner, the controller unit side (in this example, the image control unit 56 in the previous stage) preliminarily receives each of the plurality of beams. Each reference value set correspondingly is prepared, and a configuration is adopted in which the number of reference signal lines is reduced by adopting a configuration in which time-division is given to the output amount correction processing unit 52 according to the output amount correction processing order. It is good.

  However, even if the configuration of the present embodiment shown in FIG. 4C is adopted, if the photosensitive drum 19 is different, it is necessary to individually set the target light amount value according to the environmental conditions and characteristic variations. For example, when a multicolor image is formed, the target light amount must be different for each photosensitive drum 19 (that is, for each color), and individual output amount correction processing is performed for each color. is necessary.

  Since a single package like VCSEL has the same light emission characteristics, the reference voltage difference when switching and outputting the reference voltage signal corresponding to each light beam within the same color is small, but the colors are different. The reference voltage difference becomes large. In this case, if time is required for the regular period after switching the reference voltage corresponding to the color in relation to the response speed of the control system, if the light amount correction is executed until it stabilizes, the first several times when switching the color group The normal light amount correction cannot be executed for the beam. Further, when the target light amount difference for each color is large, if the light amount correction process is executed after being stabilized, it takes time until the light becomes stable, which causes a problem that the APC control time becomes long.

  The same can be said for a light source having a plurality of light emitting points with different characteristics, such as a combination of individual laser diodes. That is, even within the same group, the reference voltage difference may increase if the diodes are different due to characteristic variations of the laser diodes. In this case, the reference signal is not stabilized within a specified time (period required for light amount correction of one laser diode), and as a result, normal light amount correction cannot be performed for the laser diode after switching, and the target light amount is not reached. Problems can arise. In addition, when the target light amount difference is large, if the light amount correction process is executed after being stabilized, it takes time to stabilize, so that the APC control time becomes long.

  To solve these problems, it may be possible to make the control system response fast so that the reference signal instantaneously reaches a stable voltage after switching. However, increasing the control response speed reduces the margin for noise. This may cause a problem that the target light quantity is not stable.

  For this reason, in the present embodiment, by devising the configuration and processing timing of the APC control system, when the target light quantity of each beam is different, each light beam can be configured with a simple configuration without increasing the response speed of the control system. Adopt a mechanism that can control the amount of light with high accuracy and reliability. Hereinafter, this point will be mainly described in detail.

<Output amount correction processing system; detailed example>
FIG. 5 is a diagram illustrating a detailed configuration example of a control system for performing the output amount correction process of the light beam. As shown in FIG. 5, the output amount correction processing system of the image forming apparatus 1 is a central control that controls the operation of the optical scanning apparatus 20 shown in FIG. 2 and the entire image forming apparatus 1 in which the optical scanning apparatus 10 is mounted. And a device control unit 54 which is an example of a controller unit including the unit 70. In addition, as the light source 24, it is assumed that 32 laser diodes 25 are used for each color in the state of the second example shown in FIG. 3B.

  The optical scanning device 20 includes, as a functional unit that drives and controls the light source 24, an LD control unit 50 that is a control functional unit on the scanning unit (optical scanning device 20) side that includes a laser driving unit 51 and an output amount correction processing unit 52. ing. The laser drive unit 51 and the output amount correction processing unit 52 are connected to each other. The LD control unit 50 including the laser drive unit 51 and the output amount correction processing unit 52 is connected to a device control unit 54 that is separate from the optical scanning device 20 by the cable 31.

  Examples of signals transmitted via the cable 31 include a scanning start signal SOS from the SOS sensor 42, a reference signal Vref for output amount correction processing, and an APC lighting beam switching signal Pcng which is an example of a lighting beam setting signal. And a correction target beam selection signal Psel0 or group selection signal Psel, which is an example of a light emission order signal indicating the light emission order (that is, the light intensity correction order), and n-bit color-specific video signals VIDEO_Y, VIDEO_M, VIDEO_C, VIDEO_K, and the like. .

  The device control unit 54 controls the operation of the optical scanning device 20, and includes an image control unit 56 that is responsible for overall control relating to images and a central control unit 70 that controls the entire device. From 70, image data indicating the formed image and various data such as the resolution of the image to be formed and the target light quantity for each color are input to the image control unit 56. The image control unit 56 includes an image processing unit 58 that processes image data of an image to be formed and an APC control unit 60 that generates various signals used for the light amount correction processing used by the output amount correction processing unit 52. Has been.

  The output amount correction processing section 52 of the LD control section 50 and the APC control section 60 of the apparatus control section 54 are main elements of the beam output control apparatus 2 according to the present invention. The output amount correction processing unit 52 and the APC control unit 60 may be configured by various circuit members, respectively. For example, each may be provided by a single package semiconductor IC.

  The image processing unit 58 converts input image data into image data of each color of YMCK and outputs it. Specifically, the image processing unit 58 controls (turns on / off) lighting and extinguishing of each laser diode 25 (see FIG. 3) constituting the light source 24 based on the input image data. A lighting signal (video signals VIDEO_Y, VIDEO_M, VIDEO_C, VIDEO_K)) is generated and output to the laser driving unit 51 in synchronization with the scanning start signal SOS.

  The laser driver 51 can output a light beam modulated based on the image data from each laser diode 25 by turning on / off each laser diode 25 based on this lighting signal. The light beam modulated based on the image data output from each laser diode 25 is scanned by the optical scanning device 20 and irradiated to the photosensitive drum 19, so that the photosensitive drum 19 has eight lines. Images are written simultaneously.

  The APC control unit 60 is for giving an instruction when the output amount correction processing unit 52 controls the amount of light of each laser diode 25 of the light source 24, and correction processing order data transferred from the central control unit 70. Light quantity correction order for determining a light quantity correction order (APC control order for color groups) based on (in this example, color group data Dsel0) and light quantity setting data DVref_Y, DVref_M, DVref_C, DVref_K indicating the target light quantity setting value of each color group Each light emitted from the light emitting points (laser diodes 25) of the light source 24 based on the adjustment unit 61 and the information (color group data Dsel) after the light amount correction order adjustment output from the light amount correction order adjustment unit 61. And a correction target beam selection unit 62 that outputs a correction target beam selection signal Psel0 indicating the beam selection order.

  For example, when the correction target beam selection unit 62 adjusts the correction order for each group without adjusting the correction order in the same group, the light source 24 emits a plurality of light sources 24 based on the color group data Dsel. It can function as a color group selection unit that outputs a group selection signal Psel representing a color group of a light beam corresponding to each color emitted from a point (laser diode 25). In the following description, it is assumed that the correction target beam selection unit 62 is the color group selection unit 62 unless otherwise specified.

  The correction target beam selection unit 62 selects a color group corresponding to each color based on the color group data Dsel from the light amount correction order adjustment unit 61, and sets the lighting order within each color group and the lighting order for each color group. The data for this is output as a group selection signal Psel. For example, regarding the lighting order for each color group, the order signal “1” for Y color, “2” for M color, “3” for C color, and “4” for K color. Is output. The group selection signal Psel may be a parallel connection such as a data bus, but is preferably a serial connection in consideration of the number of signal lines.

  The APC controller 60 outputs a switching signal (APC lighting beam switching signal Pcng) for sequentially lighting each of the laser diodes 25, which are a plurality of light emitting points of the light source 24, in time series. 64 and a reference signal generation unit 68 which is an example of a target light quantity output unit.

  The APC lighting beam switching unit 64 indicates an APC lighting beam switching signal generation unit 65 that generates the APC lighting beam switching signal Pcng0, a count processing unit 66 that counts the APC lighting beam switching signal, and count arrival of the counting processing unit 66. An APC timing control unit 67 that adjusts the APC control timing with reference to the count arrival signal CNtarv and outputs the APC lighting beam switching signal Pcng is provided. The counting processing unit 66 counts the APC lighting beam switching signal Pcng0 output from the APC lighting beam switching signal generation unit 65 or the APC lighting beam switching signal Pcng that has been gated by the APC timing control unit 67.

  The APC control unit 60 selects a light beam corresponding to each color from the laser diode 25 which is a plurality of light emitting points of the light source 24, and corrects the group selection signal Psel for selecting the APC lighting order during the output amount correction processing. The target beam selection unit 62 outputs the target beam. In addition, the APC lighting beam switching signal Pcng for controlling the execution of APC is output from the APC lighting beam switching unit 64 in synchronization with the scanning start signal SOS, and the reference signal Vref is generated by the reference signal generation unit 68. The output amount is corrected to the output amount correction processing unit 52.

  Specifically, the APC lighting beam switching signal generation unit 65 of the APC lighting beam switching unit 64 is supplied with the scanning start signal SOS from the SOS sensor 42 and the master clock CLK0 from the central control unit 70. The APC lighting beam switching signal generation unit 65 counts the master clock CLK0 in synchronization with the scanning start signal SOS and corresponds to a time (for example, about 4 μsec) required to perform the output amount correction processing for one beam. This is converted into a clock signal CLK having a period, and this is output to the count processing unit 66 and the APC timing control unit 67 as an APC lighting beam switching signal Pcng0.

  The count processing unit 66 and the APC timing control unit 67 cooperate to generate the APC lighting beam switching signal Pcng by shaping the APC lighting beam switching signal Pcng0 from the APC lighting beam switching signal generation unit 65, and the reference signal A select signal SEL for controlling the generation unit 68 is generated.

  In addition, the count processing unit 66 and the APC timing control unit 67 cooperate with each other from the reference signal generation unit 68 so as to conform to the color group order indicated by the group selection signal Psel output from the correction target beam selection unit 62. The reference signal generator 68 is controlled by the select signal SEL so that the color-specific reference signal Vref is output in a time division manner. As a result, the reference signal generation unit 68 interlocks in the order of the color groups indicated by the group selection signal Psel output from the correction target beam selection unit 62, and the light amount setting data for each color that can generate the reference signal Vref for each color. The DVref is supplied to the output amount correction processing unit 52 in a time division manner.

  The output amount correction processing unit 52 includes a photoelectric conversion current signal (light amount detection signal) Si corresponding to the scanning start signal SOS from the SOS sensor 42 provided in the optical scanning device 20 and the amount of light received from the light amount detection sensor 45. Is entered.

  Further, the reference signal Vref corresponding to the target light amount of the output amount correction process is input to the output amount correction processing unit 52 from the APC control unit 60 of the apparatus control unit 54. The reference signal Vref is sent to the output amount correction processing unit 52 by an analog signal in a predetermined range, digital data of a predetermined number of bits, a pulse width modulation signal (PWM), or the like. For example, when receiving as digital data, the output amount correction processing unit 52 converts the value of the input digital reference signal Vref into an analog voltage value by a digital-analog converter or the like.

  The output amount correction processing unit 52 converts the photoelectric conversion current signal Si input from the light amount detection sensor 45 into a voltage signal. A reference signal Vref, which is a target value of the light amount of each beam, is input to the output amount correction processing unit 52 as a target value of the light amount of each beam from the device control unit 54 as an external controller, and is supplied to the photoelectric conversion current signal Si from the light amount detection sensor 45. The corresponding voltage signal is compared with the light amount target value corresponding to each beam indicated by the reference signal Vref so that the voltage signal obtained by converting the output from the light amount detection sensor 45 matches the corresponding reference signal Vref. The light quantity of each beam of each laser diode 25 of the light source 24 is adjusted.

  That is, the output amount correction processing unit 52 compares the reference signal Vref and the monitor voltage based on the photoelectric conversion current signal Si corresponding to the amount of light received from the light amount detection sensor 45, and the result is set so that the difference signal becomes zero. That is, the amount of light emitted from each laser diode 25 is increased / decreased with respect to the laser drive unit 51 so that the monitor voltage substantially matches the reference voltage, and the amount of light is adjusted so that the light beam becomes a predetermined amount of light. Thereafter, by holding the control value after the light amount adjustment, control is performed so that a light beam having a predetermined light amount is obtained from the laser diode 25. This light amount adjustment is performed during a period during which APC execution is permitted (correctable period). This correctable period is set at least outside the image area in one scanning period.

  By the way, in this embodiment, since only one light quantity detection sensor 45 is provided for the light source 24, the light quantity adjustment of each laser diode 25 is not performed at the same time but is performed by lighting individually in a time division manner. .

  In the present embodiment, the tandem type full-color image forming apparatus 1 uses an image forming unit 18 including four photosensitive drums 19 corresponding to yellow, magenta, cyan, and black. In this case, the amount of exposure light is often different for each photosensitive drum 19 corresponding to each color due to temperature difference or usage frequency difference depending on the arrangement position of the photosensitive drum 19, and the light emission output amount correction processing of the laser diode 25 is performed for each color. Must be done independently.

  For this reason, in the present embodiment, the laser diodes 25 are sequentially turned on based on the image data while writing the image on the photosensitive drum 19 while increasing or decreasing the light amount of the light beam for each color. Therefore, the output amount correction processing unit 52 needs to perform output amount correction processing using different target values (reference signal Vref) for each color as well as within the same color.

  If a light source 24 having uniform characteristics such as VCSEL is used, there is little variation within the same color and the reference voltage difference corresponding to each light beam is small. Therefore, the reference signal Vref is not necessarily switched for each light beam. Good. On the other hand, in order to perform output amount correction processing using different target values (reference signal Vref) for each color, it is necessary to output the reference signal Vref for each color. If a signal line is used for each reference signal Vref, the number of signal lines increases and the apparatus configuration becomes complicated. Therefore, in the present embodiment, a mechanism is adopted in which the number of signal lines is reduced by sequentially outputting the reference signal Vref corresponding to each color while selecting the lighting order of the laser diodes 25 in the light source 24.

  That is, only one light amount detection sensor 45 is provided for a plurality (32 in this example) of laser diodes 25 of the light source 24, and therefore, one light amount detection sensor 45 outputs all light beams. When correction processing is performed, output amount correction processing cannot be performed for a plurality of beams at the same time. Therefore, output amount correction processing is individually performed for each light beam. In this case, in order to perform output amount correction processing for all the light beams, at least in the region outside the image forming area, all the light beams are turned on in time series, and the light emission amount of each light beam is detected by the light amount detection sensor 45. Each light beam is controlled to a predetermined light amount.

  For example, the output signal supplied from the APC control unit 60 to the output amount correction processing unit 52 selects the APC lighting beam switching signal Pcng for switching the laser diode 25 to be APC and the APC lighting order corresponding to each color. Are composed of a group selection signal Psel output from the correction target beam selector 62 and a reference signal Vref output from the reference signal generator 68 in a time-division manner for each color. These are timing pulses that can execute APC control in a region outside the image forming area in synchronization with the scanning start signal SOS from the SOS sensor 42 (see FIG. 9 described later).

  When the APC control is executed, one of the laser diodes 25 in the light source 24 is turned on by the APC lighting beam switching signal Pcng in synchronization with the scanning start signal SOS and outside the image forming area, and the amount of light is changed to the APC lighting beam. The target light amount is controlled to be the value of the reference signal Vref that switches according to the count value of the switching signal Pcng. Accordingly, the output amount correction processing unit 52 switches the reference signal Vref while switching the laser diode 25 that is turned on for light amount adjustment in the light source 24, and adjusts the light amount of each laser diode 25.

  Here, in order to execute APC control in the area outside the image forming area, for example, a first method for completing APC control of all color groups in the area outside the image forming area within one scanning period, and a plurality of scanning periods Any one of the second methods for completing the APC control of all the color groups using each of the areas outside the image forming area can be taken.

  Further, in the second method, the APC control for one or a plurality of color groups is completed in the image forming area in each scanning period, and the APC control for all the color groups is completed by the combination thereof, In the image forming area within the period, the APC control for one color group is completed, and the APC control for all color groups is completed by the combination, that is, the APC control (light quantity correction) for each color group is switched for each scan. Any of the methods (performing one group of light amount correction in one scan) can be adopted, but the latter is easier to control.

<Operation of light quantity correction order adjustment unit>
FIG. 6 is a diagram for explaining the basic operation of the light quantity correction order adjustment unit 61. The light quantity correction order adjustment unit 61 can normally output the color group data Dsel0 transferred from the central control unit 70 as it is as the color group data Dsel. However, as a feature point of the present embodiment, the reference signal When performing light amount correction using time division, the light amount correction order is determined so that the difference between the reference signals indicating adjacent target light amount setting values becomes as small as possible. That is, the light quantity correction order adjustment unit 61 calculates a target light quantity difference that is continuously adjusted, that is, a difference (adjacent difference) between the light quantity setting data DVref (reference signal Vref) before and after switching of each target light quantity used in time division. The light quantity correction order is determined so as to be as small as possible.

  In particular, in the configuration of the present embodiment in which each image forming unit 18 (specifically, the photosensitive drum 19 in detail) is cascaded to form a color image, the same image forming unit is used. Even if the difference between the reference signals Vref for the laser diodes 25 used for the image 18 is small, the target light amount is generally different for each image forming unit 18 (photosensitive drum 19). When the light amount correction (APC control) control is continuously performed for the group corresponding to the above, the light amount correction order is determined so that the difference between the reference signals indicating the target light amount setting values of the adjacent color groups becomes as small as possible.

  For example, the light amount correction order adjusting unit 61 includes a comparison unit (not shown) that compares the light amount setting data DVref for each group from the central control unit 70. The comparison means calculates the difference between the light amount setting data DVref for each group and the light amount setting data DVref for the other group, and adjacently uses the light amount setting data DVref (that is, the reference signal Vref) sequentially in time division. The use order of the light quantity setting data DVref (that is, the reference signal Vref), that is, the color group order of the light quantity correction is determined so that the maximum value of the difference is as small as possible.

  In this case, a correction order that minimizes the maximum value of the difference between adjacent areas may be selected, or any correction order that does not exceed a certain threshold value TH1 (APC control). Order) may be determined. That is, the light quantity correction order is adjusted so that the APC control order is equal to or less than a preset threshold value TH1.

  Here, the “threshold value TH1” is a difference between reference signals corresponding to a target light amount difference that can be changed and tracked in one cycle. “Change tracking in one cycle is possible” means that the reference signal after switching can reach a stable value before the light amount correction processing in that cycle is started.

  If any correction order that does not exceed a certain threshold TH1 can be determined, the correction order is adopted. If there is no correction order that does not exceed the threshold TH1, the difference between adjacent points is determined. It is preferable to select a correction order that minimizes the maximum value of.

  When a correction order that does not exceed the threshold value TH1 can be selected, the reference signal Vref is corrected to the next correction in one cycle after switching, even if the correction order that minimizes the maximum difference between adjacent values is not necessarily used. This is because the light quantity correction can be executed after the target reference signal level is stabilized, that is, the reference signal can be changed and tracked within one cycle, and there is no inconvenience.

  On the other hand, when the correction order that does not exceed the threshold value TH1 cannot be selected, the reference voltage settling period after switching is selected by selecting the correction order that exceeds the threshold value TH1 but minimizes the maximum difference between adjacent values. Is shortened as much as possible, and the entire correction period can be shortened by shortening the period of the adaptation process (details will be described later, which are the stop method and the overlap method) as much as possible.

  When correcting the light amount by switching the reference signal Vref in time division, the difference between the reference signals giving the target light amount setting value at the time of each correction is calculated, so that the difference between adjacent reference signals becomes small, that is, at the time of sequential processing The light quantity correction order is determined so as to reduce the target light quantity difference, and the respective light sources are sequentially turned on to control the light quantity detection result to the set target light quantity.

  In this way, by adjusting the light amount correction order, even if the difference between adjacent reference signals is large in a certain processing order, it becomes possible to perform stable light amount correction by adjusting the processing order. .

  For example, as shown in FIG. 6 (A1), the light amount setting data DVref for each color (that is, the target light amount value indicated by the reference signal Vref) is in the order of Y → K → C → M (a little for each beam in the group). When the correction processing order indicated by the correction target beam selection signal Psel0 is Y → M → C → K →..., As shown in FIG. When the light amount setting data DVref is time-divided in the correction processing order and passed to the output amount correction processing unit 52, the maximum difference Δmax between adjacent values is the maximum Y-color light amount setting data DVref_Y and the minimum K Since this is a difference from the light quantity setting data DVref_K for color, it is very large and the settling period after switching becomes long. On the other hand, if the change is made in the order of Y → C → M → K →..., For example, as shown in FIG. The settling period after switching can be shortened.

  The same can be said even when there is a characteristic variation for each beam within the group. For example, as shown in FIG. 6 (B1), the light amount setting data DVref (that is, the target light amount value indicated by the reference signal Vref) of each beam is in the order of 1 → 8 → 6 → 4 → 2 → 7 → 5 → 3. In some cases, as shown in FIG. 6 (B2), the case where the correction processing order indicated by the correction target beam selection signal Psel0 is 1 → 2 → 3 → 4 → 5 → 6 → 7 → 8.

  In this case, when the light amount setting data DVref is time-divided in the correction processing order and passed to the output amount correction processing unit 52, the maximum difference Δmax between adjacent values becomes the maximum light amount setting data DVref_1 and the minimum light amount. Since it becomes the difference of the setting data DVref_3, it is very large and the settling period after switching becomes long. On the other hand, as shown in FIG. 6 (B3), for example, as shown in FIG. 6 (B3), the order of 1 → 6 → 2 → 5 → 3 → 7 → 4 → 8 →. Therefore, the maximum value Δmax of the difference between adjacent ones can be made smaller, and the settling period after switching can be shortened.

  Note that “one cycle” is equal to or shorter than the light amount correction period required for one beam (laser diode 25) when performing light amount correction for a plurality of color groups within one scanning period. As shown in FIG. 6C1, within the correctable period Tc for one beam, the reference signal Vref is reached before the beam is actually turned on, for example, before reaching the H level period of the APC lighting beam switching signal Pcng. This is because it is only necessary to stabilize.

  Further, when the light amount correction for each group is performed for each scanning period, it is a pause period provided between the light amount correction periods Tg of each group. As shown in FIG. 6C2, a rest period Trest such as an image area is provided between the correctable periods of each group, and the correction for the last beam of the previous group (for Y color in this example) is completed. After that, the reference signal Vref for the next group only needs to be stabilized before the correction for the first beam of the next group (in this example, for M color) is started. This is because the signal Vref only needs to be stabilized.

  The difference in the reference signal corresponding to the threshold value TH1, that is, the target light amount difference that can be changed and tracked in one cycle, is related to the change tracking after the switching of the reference signal, and this corresponds to the response speed of the control system. Closely inseparable. Therefore, the threshold value TH1 is a value determined by the analog response speed of the output amount correction processing circuit, and the reference signal Vref_pre of the correction target laser diode 25_pre immediately before switching is executed by the APC execution of the correction target laser diode 25_back immediately after switching. This is the maximum difference between the reference signal Vref_back and the reference signal Vref_pre that can be set to the target light amount of the laser diode 25_back.

  When the light amount correction of the next correction target laser diode 25 is performed continuously without providing an idle time (rest period) after the light amount correction of each correction target laser diode 25, it is difficult to provide a reference voltage settling period. In fact, as shown in FIG. 6 (C 1), the reference signal needs to be stabilized to the reference signal Vref for the next laser diode 25 within the light amount correction period Tc for one laser diode 25.

  On the other hand, as shown in FIG. 6 (D1), when the idle time Tv is provided after the light amount correction of the last laser diode 25 to be corrected, this idle time is estimated as also estimated from FIG. 6 (C2). By using Tv, the reference signal Vref for the next laser diode 25 can be stabilized. That is, the threshold TH1 (maximum value of the difference between adjacent areas) can be adjusted depending on how much free time Tv is provided. In other words, by adjusting the idle time Tv according to the threshold value TH1 (maximum value of the difference between adjacent areas), it is possible to solve the problem of performing the light amount correction during an unstable period of the reference signal Vref. .

  The same applies to the case where the same reference signal Vref is given in the same group and the individual reference signal Vref is given for each group. That is, the maximum value of the reference signal difference that can be set as the target light amount after the end of light amount correction of the previous group and before execution of APC of the next group becomes the threshold value TH1.

  In this case, as shown in FIG. 6 (D2), when the light amount correction of the next correction target group is performed continuously without providing a free time after the light amount correction of each correction target group, the reference voltage settling period is set. In practice, the reference signal is stabilized to the reference signal Vref for the next laser diode 25 within the light amount correction period for one laser diode 25, as shown in FIG. 6C2. There is a need.

  On the other hand, as will be described in detail later, when a vacant time is provided after the light amount correction of each correction target group, the vacant time can be used to stabilize the reference signal Vref for the next group. That is, even when the color group is switched, the threshold value TH1 (maximum value of the difference between adjacent areas) can be adjusted depending on how much free time is provided. In other words, the problem of executing light amount correction during an unstable period of the reference signal Vref can be solved by adjusting the idle time according to the threshold value TH1 (maximum value of the difference between adjacent areas).

  In this case, one correction cycle is defined by the sum of the period required for light amount correction for all the laser diodes 25 in the group and the free time between groups. In such APC control for each group, differences between adjacent groups in successive groups (in the order of Y → M → C → K, Y → M, M → C, C → K, K → Y). However, if the target light amount difference is equal to or less than the threshold TH1, the light amount can be corrected in one correction cycle.

  When there is a difference between adjacent values exceeding the threshold value TH1, in that portion, as estimated from FIG. 6 (D2), the light amount correction is executed when the reference signal Vref is not stable. Therefore, for all the groups and all the laser diodes 25, it is necessary to take necessary measures to execute the light amount correction after the reference signal Vref is stabilized. Specifically, the problem of executing light amount correction during an unstable period of the reference signal Vref is set by further setting an idle time according to the threshold value TH1 (maximum value of the difference between adjacent areas). Can do.

<Configuration example of APC lighting beam switching unit, reference signal generation unit, and output amount correction processing circuit>
FIG. 7 is a circuit block diagram illustrating a detailed configuration example of the APC control unit 60. Here, in particular, the APC lighting beam switching unit 64, the reference signal generation unit 68, and the counting processing unit 66 are shown in detail. FIG. 8 is a diagram for explaining the operation of the counting processing unit 66.

  The APC lighting beam switching signal generator 65 includes a counter (COUNT) 71 that counts the number of pulses of the master clock CLK0. The counter 71 counts the master clock CLK0 supplied from the central control unit 70 in synchronization with the scanning start signal SOS supplied from the SOS sensor 42, and is preset from the active edge time point of the scanning start signal SOS. Is converted into a frequency-divided clock signal CLK having a period corresponding to the time required for executing the output amount correction processing for one beam, and this is output as an APC lighting beam switching signal Pcng0 To do.

  The APC timing control unit 67 is configured to generate the APC lighting beam switching signal Pcng and the APC lighting beam switching signal output timing signal (hereinafter referred to as APC timing setting signal LOAD) to be supplied to the combining unit 72. Part 74. The synthesizer 72 receives an APC lighting beam switching signal Pcng0 having a clock having a period corresponding to the time required to perform the output amount correction processing of one beam from the counter 71 of the APC lighting beam switching unit 64. So connected.

  The setting unit 74 considers a time sufficient to stably supply the reference voltage according to the reference signal Vref output from the reference signal generation unit 68 for the output amount correction processing unit 52 to perform the output amount correction processing. Referring to the counting result from the counter 76 (here, the count arrival signal CNtarv), a period for adjusting all (eight in this example) laser diodes 25 in one color group (for example, eight clock signals CLK) A rectangular signal that becomes active (in this example, H level) during the period is generated as the APC timing setting signal LOAD.

  It becomes inactive (= L) when the light quantity correction processing end of one color group is indicated (the count value of one color laser diode 25, 8 in this example), and is active for APC control of the next color after a predetermined period (= H). How much the inactive period is set will be described later.

  The synthesizing unit 72 is a signal obtained by logically synthesizing the clock signal CLK (APC lighting beam switching signal Pcng0) input from the counter 71 of the APC lighting beam switching unit 64 and the APC timing setting signal LOAD input from the setting unit 74. Is output as an APC lighting beam switching signal Pcng.

  The counting processing unit 66 is a counter that counts the number of pulses of the APC lighting beam switching signal Pcng (which may be the APC lighting beam switching signal Pcng0 from the counter 71) input from the combining unit 72 of the APC lighting beam switching unit 64. COUNT) 76, the count result CNTout of the counter 76, the count arrival signal CNTarv, and the color group data Dsel from the light quantity correction rank adjustment unit 61, the reference signal generation unit 68 selects the reference signal Vref corresponding to the color. And a decoder 78 for generating a select signal SEL to be provided.

  The counting processing unit 66 counts the number of pulses of the APC lighting beam switching signal Pcng0 by the counter 76, and based on the counting result and the color group data Dsel, the APC lighting beam output from the APC lighting beam switching signal generation unit 65 is output. The color group of the beam switching signal Pcng0 is detected.

  In the present embodiment, the light source 24 sequentially turns on 32 laser diodes 25. At this time, the counter 76 and the decoder 78 of the counting processing unit 66 are grouped into eight groups (corresponding to color classification in this example). That is, as shown in FIG. 8A, the counter 76 counts the clock of the APC lighting beam switching signal Pcng, and every time the count value increases by “8”, the counter 76 counts the eighth clock. The count arrival signal CNTarv is output while holding the count value at that time.

  In FIG. 8A, a predetermined reference voltage settling period Tst is provided for every eight clocks of the APC lighting beam switching signal Pcng, and the clock output is stopped during this period. This point will be described later.

  As shown in FIG. 8B, a selection signal “1” representing one color is generated with the count values “1” to “8”, and the selection signal is sequentially changed until the selection signal becomes “4”. When the counter is incremented and the selection signal “1” to “4” is cyclically output, the counter 76 holds the immediately preceding count value during the stop period, so the decoder 78 restarts the counting operation. Since the select signal SEL cannot be switched to the next color unless it is after, the effect (details will be described later) of providing the stop period cannot be enjoyed. In this embodiment, as shown in FIG. Does not adopt processing.

  As shown in FIGS. 8A and 8C, the decoder 78 first decodes the count result of the counter 76 to count the count values “1” to “8” as the select signal SEL. The selection signal SEL_1 representing the first color is output until the count arrival signal CNTarv is received, and after the count arrival signal CNtarv is received, the selection signal SEL_2 representing the second color is switched to, and the selection signals ‘9’ to ‘16’ are further switched. Until the count value is counted and the next count arrival signal CNtarv is received, the selection signal SEL_2 representing the second color is output, and such processing is sequentially incremented until the selection signal SEL_4 representing the fourth color is obtained. The selection signals SEL_1 to SEL_4 are cyclically output.

  Here, when the light quantity correction order adjustment unit 61 outputs the color group data Dsel0 transferred from the central control unit 70 as it is as the color group data Dsel as usual, the decoder 78 particularly outputs the color group data Dsel. The referenced decoding process is unnecessary. This is because the color group selection operation of the correction target beam selection unit 62 and the selection operation of the reference signal Vref for each color in the reference signal generation unit 68 always correspond to a predetermined order.

  For example, “1” to “8 (a; up to count arrival signal CNtarv output / same below)”, “1”, “8 (b; after count arrival signal CNtarv output / same below)” and “9” to “2”, “16 (b)” and “17” to “24 (a)” “3”, “24 (b)” and “25” to “32” for “16 (a)” When the selection signal (select signal SEL) of “4” is cyclically output with respect to (a) ”,“ 1 ”and M colors for the Y color indicated by the group selection signal Psel (order signal for each color group) Thus, each color is surely handled in the order of Y → M → C → K so as to be linked with “2” for “C”, “3” for C color, and “4” for K color.

  However, in the present embodiment, the light amount correction order adjustment unit 61 determines the light amount correction order so that the difference between the target light amount setting values of adjacent color groups is as small as possible when performing APC control for each color group continuously. Therefore, the light quantity correction order is not necessarily in the order of Y → M → C → K.

  Therefore, in the selection operation of the reference signal generation unit 68, “1” is Y, “2” is M, “3” is C, “4” based on the select signal SEL (any one of 1, 2, 3, 4). "Is associated with K, and when the reference signal Vref for each color is selected, the color group of the reference signal Vref output from the reference signal generator 68 in a time division manner and the color group by the correction target beam selector 62 are displayed. The result of selection is not consistent.

  In order to avoid this problem, the decoder 78 of the present embodiment refers to the color group data Dsel supplied from the light quantity correction order adjustment unit 61, and “1” to “8”, “9” to “16”, “ 17 ”to“ 24 ”,“ 25 ”to“ 32 ”(selection signals for the respective count values (considering (a) until the count arrival signal CNtarv is output and (b) after the count arrival signal CNTarv is output)) Decoding processing is performed so that SEL surely corresponds to the color group order indicated by the color group data Dsel.

  For example, as shown in FIG. 8D, if the color group data Dsel indicates that the order is “M → K → Y → C”, then the decoder 78 has “1” to “8 (a ) ”For M color“ 2 ”,“ 8 (b) ”and“ 9 ”to“ 16 (a) ”for K color“ 4 ”,“ 16 (b) ”and“ 17 ” “3”, “24 (b)” for “Y” to “24 (a)” and “3” selection signal for C color for “25” to “32 (a)” ( The select signal SEL) is output cyclically.

  The reference signal generation unit 68 includes registers 82 and 84 configured by two-stage flip-flop circuits (latches) provided for each color (represented with reference elements Y, M, C, and K for each color). And a switcher (multiplexer MUX) 85 for switching the color-specific signal from each register 84.

  In each register 82 in the first stage, light amount setting data DVref of each color based on 10-bit data is individually input from the central control unit 70 to the data input terminal D, and a write signal WR is input to each clock terminal CLK (in the drawing). Are commonly input to the terminal of the triangle mark). Each register 82 in the first stage receives and holds the light amount setting data DVref when the write signal WR is input.

  Further, in each register 84 in the second stage, the output signal from the non-inverted output terminal Q of the register 82 corresponding to the first stage is supplied to the data input terminal D, and the APC timing setting signal LOAD is supplied to the clock terminal CLK as a read signal. The output signal from the non-inverted output terminal Q is input to the switch 85. Each register 84 in the second stage receives the value of the reference signal held in the corresponding register 82 in the first stage in synchronization with the active edge when the APC timing setting signal LOAD is input. Read and hold (see FIG. 11 described later).

  In practice, for the first setting, an initial setting pulse is added to the APC timing setting signal LOAD to convert it to a load signal, and then input to the clock terminal CLK of the register 84. In this way, the required light amount setting data DVref can be taken into the register 84 before the APC timing setting signal LOAD is issued and the light amount correction is executed, and the light amount is appropriately corrected from the first color at the start of the correction process. Can be implemented.

  The select signal SEL from the decoder 78 is inputted to the control input terminal CNT of the switch 85. The output side of the switch 85 is connected to the output amount correction processing unit 52 of the optical scanning device 20 via the interface unit. The switch 85 selects and outputs the value of the reference signal held in any one of the registers 84 in the second stage according to the select signal SEL input to the control input terminal CNT.

  As described above, even when the light amount correction order adjustment unit 61 adjusts the light amount correction order, the decoder 78 ensures that the color group indicated by the select signal SEL corresponds to the color group indicated by the color group data Dsel. Since the decoding process is performed, the color group indicated by the color group data Dsel output from the correction target beam selection unit 62 and the color group of the selected reference signal Vref output from the switch 85 are surely determined. To be consistent.

  The output signal from the switch 85 is a 10-bit digital signal. Therefore, when the digital signal is transmitted as it is to and from the output amount correction processing unit 52 of the optical scanning device (ROS) 20, the output signal is directly connected as shown in the upper part on the right side of the drawing. . When the output amount correction processing unit 52 performs control by analog signal processing, the connection is made via a digital / analog (D / A) converter 86 as shown in the middle part of the interface unit on the right side of the figure. Further, when the reference signal Vref is transmitted by PWM modulation, it is connected via the PWM converter 88 as shown in the lower part of the interface part.

  Note that the tip of the PWM converter 88 is connected to a PWM circuit provided in the output amount correction processing unit 52 as it is, or a filtering circuit 89 is provided for connection to the circuit of the output amount correction processing unit 52 that performs analog processing. There is also a case of connecting via The output destination signal of the switch 85 may be any signal as long as it corresponds to the correspondence of the output amount correction processing unit 52, and any of these may be used.

  As described above, each laser diode 25 of the light source 24 is controlled by the output amount correction processing unit 52 so that the light emission amount becomes a predetermined light amount, and the APC lighting beam switching unit 64, the correction target beam selection unit 62, and Lighting control is performed based on each signal from the reference signal generator 68.

  The overall operation of the APC control unit 60 configured as described above will be briefly described as follows. The light amount setting data DVref is input to the first-stage register 82 of the reference signal generation unit 68 as 10-bit digital data for each color of yellow, magenta, cyan, and black, and one stage corresponding to each color by the write signal WR. Set in the eye register 82.

  Thereafter, when the APC timing setting signal LOAD is input to the second-stage register 84 of the reference signal generation unit 68, the light amount setting data DVref corresponding to each color is set in the register 84 corresponding to each color and is supplied to the switch 85. Light amount setting data DVref for each color is input. At this time, it is also possible to set the next light quantity setting data DVref in the first-stage register 82.

  The initial value of the select signal SEL of the switch 85 is a selection signal indicating the first color (for example, yellow) in the light quantity correction order adjusted by the light quantity correction order adjustment unit 61, and initially corresponds to the first color. Light amount setting data DVref_1 is output from the switch 85. For example, if the first color is yellow, the light amount setting data DVref_Y is output from the switch 85.

  In synchronization with the input of the APC timing setting signal LOAD to the register 84 of the reference signal generation unit 68, the count processing unit 66 starts a count operation and sets the number of switching of the APC lighting beam switching signal Pcng0 (such as a rising edge). Count.

  When the count value reaches a predetermined number (8 in this example) corresponding to the number of all laser diodes 25 in one group, the counter 76 outputs a count arrival signal CNtarv and stops the counting operation. Based on the count result CNTout output from the counter 76, the decoder 78 switches the select signal SEL used by the switch 85 to the selection signal for the second color. In response to this, the switch 85 outputs light amount setting data DVref_2 corresponding to the second color. For example, if the second color is magenta, the light amount setting data DVref_M is output from the switch 85.

  By repeating such an operation, the switch 85 uses the light amount setting data DVref supplied to the output amount correction processing unit 52 in accordance with the light amount correction order adjusted by the light amount correction order adjusting unit 61, and the light amount setting data DVref_1. Select and output in order of → DVref_2 → DVref_3 → DVref_4. For example, if the first color is yellow, the second color is magenta, the third color is cyan, and the fourth color is black, the switch 85 selects and outputs the light amount setting data DVref_Y → DVref_M → DVref_C → DVref_K in this order. To do.

<Output amount correction processing timing: Basic>
FIGS. 9 and 10 are diagrams illustrating a basic example of the timing of each signal (output amount correction processing timing) when lighting control of each laser diode 25 of the light source 24 is performed. Here, FIG. 9A is a diagram for explaining the output amount correction processing period of the laser diode 25, FIG. 9B is a characteristic diagram of the reference signal Vref in the output amount correction processing section 52, and FIG. FIG. 9D is a characteristic diagram of the APC lighting beam switching signal Pcng, and FIG. 9E is a layout diagram of the laser diode 25. FIG. 9D is a characteristic diagram of the APC timing setting signal LOAD indicating output timing with respect to the APC lighting beam switching signal Pcng. . FIG. 10 is a diagram for explaining the necessity of stopping the clock of the APC lighting beam switching signal Pcng when switching color groups.

  In the following description, as the output amount correction processing of each laser diode 25 of the light source 24, 32 out of the image area within one scanning period and before the detection of the scanning start signal SOS, that is, in the image non-recording area. Each of the laser diodes 25 is adjusted so as to have a target light amount (see FIG. 9E).

  As shown in FIG. 5E, in the light source 24, among the 4 × 8 laser diodes 25, the eight laser diodes 25 ((1-1) to (8-1)) in the first row are K color, Eight laser diodes 25 ((1-2) to (8-2)) in the second row are C color, and eight laser diodes 25 ((1-3) to (8-3)) in the third row are M. The eight laser diodes 25 ((1-4) to (8-4)) in the fourth row are responsible for the Y color.

  Each of these 32 laser diodes 25 is sequentially turned on in a light amount correction order so that the difference in target light amount setting values of adjacent color groups becomes as small as possible when performing APC control for each color group. Adjust the light intensity. For example, the light quantity correction order indicated by the color group data Dsel0 is yellow → magenta → cyan → black, and when the light quantity correction is performed in this order, the difference in the target light quantity setting values of adjacent color groups is a predetermined value. When the threshold value is not more than the threshold value, the entire light amount is corrected by performing APC control in yellow → magenta → cyan → black.

  First, basic color group data Dsel0 for setting a beam to be used for each color of yellow, magenta, cyan, and black and light amount setting data DVref for each color are sent from the central control unit 70 to the light amount correction order adjusting unit 61. Transferred. The color group data Dsel0 may be set in advance according to the specifications of the image forming apparatus 1, or may be set by an external input unit or the like.

  The light quantity correction order adjustment unit 61 determines the light quantity correction order so that the difference between the target light quantity setting values of adjacent color groups is as small as possible when performing APC control for each color group continuously.

  Here, the order of light quantity correction indicated by the color group data Dsel0 is yellow → magenta → cyan → black, and when the light quantity correction is performed in this order, the difference between the target light quantity setting values of adjacent color groups is predetermined. The description will be continued on the assumption that it is equal to or less than the threshold value. In this case, the light amount correction order adjustment unit 61 outputs the color group data Dsel0 to the correction target beam selection unit 62 as it is.

  The correction target beam selection unit 62 collects the light beams for each color at the time of APC execution so that the light beams used for each color are continuously turned on, and further, APC is executed sequentially for each color group in time series. Determine the order of the light beams to be lit.

  The optical scanning device 20 forms a latent image on the photosensitive drum 19 by scanning the light beam emitted from the light source 24 in the main scanning direction with the scanning start signal SOS detected by the SOS sensor 42 as a reference.

  As shown in FIG. 9A, the APC control is executed in a non-image area within one scanning period from the image area where the image is formed until the scanning start signal SOS which is the reference for scanning the next line is output. Is done. When this APC control is executed, the light beam selected by the correction target beam selection unit 62 is lit in time series in each color group for each color group determined by the correction target beam selection unit 62, and the APC is performed for each light beam. Control is executed.

  In this example, the light quantity correction order indicated by the color group data Dsel0 is yellow → magenta → cyan → black. Even if the light quantity correction is performed in this order, the difference between the target light quantity setting values of adjacent color groups is a predetermined value. Since it is less than or equal to the threshold value, the order of APC control for each color group is the order of yellow → magenta → cyan → black. First, in the yellow group, each of the Y laser diodes 25 (1-4) to 25 (8-4) is sequentially turned on. Similarly, in the magenta group, each of the eight laser diodes 25 (1-3) to 25 (8-3) of M color is sequentially turned on, and in the cyan group, the eight laser diodes 25 of C color are turned on. Each of (1-2) to 25 (8-2) is sequentially turned on, and each of the eight K-color laser diodes 25 (1-1) to 25 (8-1) is sequentially turned on in the black group. Let

  The APC lighting beam switching signal generator 65 synchronizes with the scanning start signal SOS at a predetermined timing (Ta) after the end of the image area shown in FIG. 9A, as shown in FIG. A lighting beam switching signal Pcng0 is generated.

  The APC timing control unit 67 gates the APC lighting beam switching signal Pcng0 output from the APC lighting beam switching signal generation unit 65 with the APC timing setting signal LOAD as shown in FIG. A signal group consisting of 8 pulse signals for each color of C and K is continuously output four times (for each of Ta, Tb, Tc and Td), and this is output as an APC lighting beam switching signal Pcng. To the unit 52.

  As shown in FIG. 9B, as the light amount setting data DVref serving as a reference for the output amount correction processing, first, the light amount corresponding to yellow is synchronized with the APC timing setting signal LOAD generated by the APC timing control unit 67. Setting data DVref_Y is output from the reference signal generator 68 (Ta).

  In the output amount correction processing unit 52, each of the laser diodes 25 (1-4) to 25 (8-4) is sequentially sequentially synchronized with the APC lighting beam switching signal Pcng with reference to the light amount setting data DVref_Y corresponding to yellow. Turn on and execute APC control.

  At this time, the counting processing unit 66 counts the number of pulses of the APC lighting beam switching signal Pcng0 with the counter 76, detects the color group of the APC lighting beam switching signal Pcng0 based on the counting result, and generates the reference signal generation unit 68. When the select signal SEL for controlling the reference signal is generated, the color group of the reference signal Vref output from the reference signal generator 68 is controlled.

  In the output amount correction processing unit 52, the group selection signal supplied from the correction target beam selection unit 62 in synchronization with the APC lighting beam switching signal Pcng in conjunction with the time-division output of the reference signal Vref for each color. Each of the laser diodes 25 for forming each color set by Psel is turned on sequentially.

  In the output amount correction processing unit 52, the reference signal obtained by converting the value of the light amount setting data DVref (see FIG. 9B) corresponding to the target light amount for each color input in a time division manner from the reference signal generation unit 68 into an analog signal. Vref is acquired in time series, the reference signal Vref is compared with the voltage of the output signal of the light quantity detection sensor 45, and APC control (output amount correction processing) is executed so that they match.

  For example, the counter 76 first counts the number of switching of the APC lighting beam switching signal Pcng (rising edge or the like), and when it reaches a predetermined count value, the decoder 78 changes the select signal SEL for the second color (for example, magenta). That is, in this example, since the number of beams used for yellow is eight, the decoder 78 changes the select signal SEL to the second color (for example, magenta) when the number of switching of the APC lighting beam switching signal Pcng0 of the counter 76 becomes eight. The counter 76 stops the count operation and outputs the count arrival signal CNTarv. The counter 76 holds the count value at that time (here, the number of switching = 8).

  When the select signal SEL is switched to a selection signal corresponding to the second color (for example, magenta), the switch 85 of the reference signal generator 68 outputs the light amount setting data DVref_M corresponding to magenta as the reference signal Vref (Tb). . The output amount correction processing unit 52 sequentially sets each of the laser diodes 25 (1-3) to 25 (8-3) in synchronization with the APC lighting beam switching signal Pcng with reference to the light amount setting data DVref_M corresponding to magenta. Turn on and execute APC control.

  At this time, the counter 76 of the count processing unit 66 again counts the number of switching of the APC lighting beam switching signal Pcng as described above, and when it reaches a predetermined count value, the decoder 78 converts the selection signal SEL to the third color (for example, cyan). ) That is, in this example, since the number of beams used for magenta is 8, the decoder 78 changes the select signal SEL to the third color (for example, cyan) when the number of switching of the APC lighting beam switching signal Pcng0 of the counter 76 becomes 8. The counter 76 stops the count operation and outputs the count arrival signal CNTarv. The counter 76 holds the count value at that time (here, the number of switching = 16).

  When the select signal SEL is switched to a selection signal corresponding to the third color (for example, cyan), the switch 85 of the reference signal generator 68 outputs the light amount setting data DVref_C corresponding to cyan as the reference signal Vref (Tc). . In the output amount correction processing unit 52, each of the laser diodes 25 (1-2) to 25 (8-2) is sequentially sequentially synchronized with the APC lighting beam switching signal Pcng with reference to the light amount setting data DVref_C corresponding to cyan. Turn on and execute APC control.

  At this time, the counter 76 of the count processing unit 66 again counts the number of switching of the APC lighting beam switching signal Pcng as described above, and when it reaches a predetermined count value, the decoder 78 sets the select signal SEL to the fourth color (for example, black). ) That is, in this example, since the number of beams used for cyan is eight, the decoder 78 changes the select signal SEL to the fourth color (for example, black) when the number of switching of the APC lighting beam switching signal Pcng0 of the counter 76 becomes eight. The counter 76 stops the count operation and outputs the count arrival signal CNTarv. The counter 76 holds the count value at that time (here, the number of switches = 24).

  When the select signal SEL is switched to a selection signal corresponding to the fourth color (for example, black), the switch 85 of the reference signal generation unit 68 outputs the light amount setting data DVref_K corresponding to black as the reference signal Vref (Td). . The output amount correction processing unit 52 sequentially sets each of the laser diodes 25 (1-1) to 25 (8-1) in synchronization with the APC lighting beam switching signal Pcng with reference to the light amount setting data DVref_K corresponding to black. Turn on and execute APC control.

  At this time, the counter 76 of the counting processing unit 66 again counts the number of switching of the APC lighting beam switching signal Pcng as described above, and tries to change the reference signal Vref for the next color when a predetermined count value is reached. In this example, since the number of beams used for black is eight, when the number of switching of the APC lighting beam switching signal Pcng of the counter 76 is further added to 32, it is determined that the APC control of all the light beams is completed. The counter 76 outputs a count arrival signal CNTarv. At this time, the counter 76 once resets the count output. The count value (here, the number of switching) is cleared to zero (Te).

  In order to determine that the APC control of all the light beams has been completed, the total number of light beams of the VCSEL to be used may be stored in advance in a memory or the like and set in the counter 76, an external input means, etc. It may be set by.

  In the actual apparatus, when the APC control of all the light beams is completed, the above-described operation is repeated from the beginning. Thereby, during the exposure operation, the APC control is not stopped, and the light amount correction of any one of the light sources is always performed. In this example, when Y.fwdarw.M.fwdarw.C.fwdarw.K ends, the process proceeds to the Y APC operation.

  When the target light quantity between the color groups is set separately in this way, the target light quantity may become very large if the difference in change over time or the characteristic of each color in the photosensitive drum 19 is large.

  Although it is possible to have a plurality of output amount correction processing circuits and to perform drive control for each group, the output signal of one light quantity detection sensor 45 is used after being photoelectrically converted and time-divisionally used. In a simple system configuration corresponding to a tandem configuration that performs APC, it is wasteful to have a plurality of output amount correction processing circuits. In the present embodiment, since the single light amount correction processing unit 52 is configured to correct the light amount of each color group, the above-described problem can be solved.

  On the other hand, it is desirable that the output amount correction processing unit 52 be designed so as to reduce the response speed as much as possible and suppress the influence of high-frequency noise generated from image data or the like. Accordingly, when the light amount of each color group is corrected by one output amount correction processing unit 52, the control response speed may become a bottleneck if the target light amount fluctuation of each color group is large.

  That is, it may happen that the reference signal Vref is not stabilized within a specified time (in this example, one clock required for light amount correction of one laser diode 25). As a result, for the first few laser diodes 25 at the time of color group switching, normal light amount correction cannot be executed, and there is a possibility that the target light amount may not be reached. In order to solve this problem, it is conceivable to increase the control response speed, but on the other hand, there is a possibility that the margin for noise is reduced and the target light quantity is not stable.

  As a method of correcting the light amount of each color group with one output amount correction processing unit 52 while solving the problem of control response speed, the inventor of the present application uses the APC lighting beam switching signal Pcng after switching after switching the color group. A fixed period is set as a stop period, the output amount correction process is performed repeatedly so as to correct the amount of light beam corresponding to the fixed period after switching is lost, or the reference signal at the time of switching It has been found that it is effective to adjust the correction processing order so that the difference becomes as small as possible.

  For example, when the reference signal Vref is switched in units of color groups, the APC lighting beam switching signal is stopped for a predetermined time when the reference signal Vref is switched, and the APC lighting beam switching signal is switched after the reference signal Vref is completely switched to a desired value. It has been found that outputting Pcng is effective.

  For example, the output amount correction processing unit 52 first obtains a reference voltage obtained by converting the value of the light amount setting data DVref corresponding to the target light amount for each color input from the reference signal generation unit 68 into an analog signal. The output amount correction processing unit 52 executes output amount correction processing based on the reference voltage and the voltage of the output signal of the light amount detection sensor 45.

  At this time, as shown in FIG. 10, even if the change in the target light amount value for each color group is slight, in the actual circuit configuration, the reference signal Vref is switched to the next color and then completely set to the desired value. In some cases, a delay occurs until the target light amount is stabilized, that is, the target light amount value is not immediately stabilized.

  For example, when switching the lighting of the eighth laser diode 25 (8-4) of Y color to the lighting of the first laser diode 25 (1-3) of M color which is the next color, the flip-flop circuit The rise or fall of the reference voltage becomes smooth without being steep due to the registers 82 and 84 configured by (latch) and the like, and a delay when the light amount setting data DVref is converted into an analog signal.

  This delay period is referred to as a reference voltage settling period Tst. When the output amount correction process for the next color is started in the reference voltage settling period Tst in which the reference signal Vref is not stable, the light amount of the light beam that performs APC control at the beginning of the next color However, it becomes impossible to control to the target light quantity. As the entire APC control, an incomplete period exists.

  Therefore, the APC lighting beam switching signal Pcng is stopped for a predetermined time during the reference voltage settling period Tst in which the APC control of the next color is expected to be incomplete (T1 to T2, T3 to T4, T5 to T6 in FIG. 9). If the clock of the APC lighting beam switching signal Pcng is output after the reference signal Vref is completely switched to the desired value, the output amount of the light beam is corrected within the reference voltage settling period Tst. Since the process is stopped and the output amount correction process for the unstable target light amount value is not executed, the occurrence of a light amount error can be avoided.

  That is, since the APC control for the next color is not started before the reference signal Vref is stabilized, it can be expected that the light quantity can be reliably controlled to a predetermined amount. Such a method is referred to as a settling period stop method.

  Alternatively, if the APC control is executed during the reference voltage settling period Tst in which the APC control of the next color is expected to be incomplete, and the APC control is executed repeatedly for the same beam, it becomes unstable. Since the amount of execution of the output amount correction process for the target light amount value can be corrected by the subsequent APC control for the same color, the occurrence of a light amount error can be avoided and the light amount can be reliably controlled to a predetermined amount. It is expected to be possible. Such a method is called a settling period overlapping method.

  Further, the cause of the incomplete APC control is that the reference signal Vref corresponding to each laser diode 25 (in this example, especially for each color group) is used in a time-sharing manner for each laser diode 25 (in this example, particularly in the color group). This is because when the APC control is performed in time division, the difference between the reference signals Vref (in this example, the difference between the reference signals Vref for each color group) is large.

  Accordingly, the light quantity correction order (APC control for each laser diode 25 is performed so that the reference signal Vref for each laser diode 25 is output in a time division order in which the difference between adjacent target light quantities used in time division becomes smaller. If the order is adjusted, it is expected that the occurrence of the light quantity error can be reduced by reducing the cause of the incomplete APC control. Such a method is referred to as a light amount correction order adjustment method.

  Here, as an idea when realizing the settling period stopping method and the settling period overlapping method, the active output of the APC lighting beam switching signal Pcng is stopped for a predetermined period corresponding to the settling period every time the color group is switched. Alternatively, the APC control may be performed repeatedly for the same beam of the same color for a predetermined period for interpolating the settling period, but various methods may be used for setting the stop period and the overlap period. .

  For example, any one of the first method for stabilizing the APC control by freely setting the stop period and the overlap period, the method for setting the stop period and the overlap period in a certain unit, and a combination thereof are adopted. Can do. In the latter method, the second method for stabilizing APC control in units of output amount correction processing for one light beam and the method for stabilizing APC control in units of output amount correction processing for color groups. Either of these can be adopted.

  Further, in the method using the output amount correction processing for the color group as a unit, as a combination with the method of completing the APC control of all the color groups in the area outside the image forming area within one scanning period (of course, within one scanning period) As a combination of the third method for stabilizing APC control in units of output amount correction processing for color groups in a non-image period) and a method for switching APC control for each color group for each scan, Any of the fourth methods for stabilizing the APC control in units of one scanning period assigned to the output amount correction process can be employed.

  When the first method is used, the stop period and the overlap period can be freely set, so that there is a degree of freedom, but it is necessary to determine in advance as the stable period of the reference signal in the output amount correction processing unit 52. The setting process can be complicated. On the other hand, when using a method of setting a stop period or an overlap period in units having a relationship with the output amount correction processing period as in the second to fourth methods, how many units are used? The setting is simple.

  In the second method of the second to fourth methods, the APC lighting beam switching is performed in accordance with the number of clocks set as a stop period or an overlap period in the second method based on output amount correction processing for one light beam. While it is necessary to adjust the signal Pcng and the group selection signal Psel, in the third and fourth methods using the output amount correction processing for the color group as a unit, it is only necessary to adjust the group selection signal Psel. The fourth method is easier to control than the third method.

  Hereinafter, the settling period stop method, the settling period overlap method, and the light amount correction rank adjustment method to which the second to fourth methods for setting the stop period and the overlap period in a certain unit will be described in detail.

<Settling period stop method with 1 beam unit>
FIG. 11 is a time chart related to the output amount correction processing, and is a diagram for explaining a second method (part 1) for stabilizing APC control in units of output amount correction processing for one beam. 11A shows the light amount setting data DVref input to the switch 85, FIG. 11B shows the select signal SEL supplied from the APC timing controller 67 to the switch 85, and FIG. The light quantity setting data DVref output from the switch 85 in a time division manner is shown. 11D shows an APC lighting beam switching signal Pcng0, FIG. 11E shows an APC timing setting signal LOAD, FIG. 11F shows an APC lighting beam switching signal Pcng, and FIG. 11G shows an output amount correction process. The reference signal Vref in an analog state by the unit 52 is shown.

  This second method (part 1) is a mode in which the output of the APC lighting beam switching signal Pcng is stopped for several cycles in units of one beam during the reference voltage settling period Tst. In the example shown in FIG. 9, the instability of the control result due to the execution of the APC control during the reference voltage settling period Tst is avoided. Specifically, the eighth color of the M color is from the lighting of the eighth laser diode 25 (8-4) of Y color to the lighting of the first laser diode 25 (1-3) of C color which is the next color. During the lighting of the first laser diode 25 (1-2) of the C color, which is the next color, from the lighting of the eighth laser diode 25 (8-2) of the C color, During the lighting of the first laser diode 25 (1-1) of K color, the APC lighting beam switching signal Pcng is not output for a certain period (the reference voltage settling period Tst in FIG. 9).

  When the color group is switched, the output of the APC in the output amount correction processing unit 52 is stopped by stopping the output of the clock signal for the APC lighting beam switching signal Pcng during a period in which the reference voltage difference is large and the APC control may be unstable. The control is not performed, and it waits for the analog response of the reference signal Vref to stabilize.

  Specifically, the count processing unit 66 and the APC timing control unit 67 cooperate to set the APC lighting beam switching signal Pcng0 (see FIG. 11D) input from the APC lighting beam switching signal generation unit 65 and the setting. The APC timing setting signal LOAD (see FIG. 11E) output from the unit 74 is logically synthesized to generate an APC lighting beam switching signal Pcng (see FIG. 11F).

  Specifically, after the setting unit 74 activates the APC timing setting signal LOAD for a predetermined color and then receives the count arrival signal CNtarv from the counting processing unit 66, the setting unit 74 inactivates the APC timing setting signal LOAD. Thereafter, when the APC timing setting signal LOAD is activated for the next color, the clock signal CLK is output for a predetermined time (for example, several clocks) sufficient to stably supply the reference signal Vref. Stop.

  For example, as shown in FIG. 11E, when the APC control of a certain color group is completed and the reference voltage settling period Tst starts (Ts), the counter 76 outputs the count arrival signal CNtarv and stops the counting operation. The count value (for example, 8) at that time is held. The APC timing control unit 67 outputs the APC lighting beam switching signal Pcng for the next color by gating the APC lighting beam switching signal Pcng0 with the APC timing setting signal LOAD in units of output amount correction processing for one light beam. Is stopped for a certain period (here, equivalent to the reference voltage settling period TstTs to Te).

  Thereafter, when the reference voltage settling period Tst elapses (Te), the counter 76 restarts the counting operation from the held count value (8 in this example). For example, if the information of the reference voltage settling period Tst is for 3 clocks, it is counted as 9, 10, 11.

  The decoder 78 generates the select signal SEL based on the count result CNTout output from the counter 76 and the count arrival signal CNTarv. Therefore, when the reference voltage settling period Tst starts (Ts), the select signal SEL is Switch to “2” for selecting light amount setting data DVref for color (M color in this example). As a result, the reference signal generation unit 68 switches the light amount setting data DVref to the output amount correction processing unit 52 from the light amount setting data DVref_Y for Y color to the light amount setting data DVref_M for M color.

  Therefore, the reference signal generation unit 68 can change the light amount setting data DVref to data for the next color at the time when the reference voltage settling period Tst starts. Further, the APC timing control unit 67 performs the output amount correction process for all the laser diodes 25 (eight in this example) in the color group for the next color after the reference voltage settling period Tst has elapsed (Te). The APC lighting beam switching signal Pcng having the number of clocks can be output to the output amount correction processing unit 52 side.

  The count processing unit 66 and the APC timing control unit 67 cooperate to stop the correction process of the subsequent beam for a predetermined period immediately after the reference value switching, and correct the stop beam correction process after the predetermined period has elapsed. After generating a beam-corresponding clock whose timing is adjusted, the APC lighting beam switching signal Pcng is output to the output amount control unit 52.

  As the APC lighting beam switching signal Pcng, the light amount setting data DVref for the next color is output from the reference signal generation unit 68 before the clock for the next color is output after the reference voltage settling period has elapsed. The processing unit 52 can wait for the reference signal Vref to become stable before starting the light amount correction for the next color.

  That is, the APC lighting beam switching signal Pcng is output during the period until the signal voltage stabilizes when the value of the light amount setting data DVref output from the reference signal generation unit 68 is converted into an analog signal in the output amount correction processing unit 52. No input is made to the force correction processing unit 52.

  Thus, the output amount correction processing unit 52 uses each clock of the APC lighting beam switching signal Pcng supplied after generating a stable analog reference signal Vref without making the response of the control system high speed. The output amount correction process can be executed in a time division manner for all the laser diodes 25 in the color group. Since there is no need to increase the control response speed, a large margin for noise can be secured, and the target light quantity can be reliably stabilized.

  By adopting such a settling period stopping method, a plurality of light beams emitted from one light source 24 are separated and scanned on different photosensitive drums 19 of the image forming unit 18 provided for each color. When forming a full-color image, the output amount correction processing of a plurality of beams corresponding to each color can be stably executed in a time division manner without increasing the control signal with a simple configuration.

  However, in the settling period stop method in units of one beam, a stop period is provided in units of output amount correction processing for one light beam. After this stop period, all (8 in this example) lasers for the next color are used. Since it is necessary to generate a signal group of eight pulse signals as the APC lighting beam switching signal Pcng for the next color in order to execute the output amount correction processing for the diode 25, the APC timing setting signal LOAD and the APC lighting beam switching are switched. The generation of the signal Pcng needs to be performed in cooperation with each other, and the count processing unit 66 and the APC timing control unit 67 need to refer to each other's output result, and have high accuracy in consideration of gate delay and the like. It is necessary to manage the timing.

<Combination of settling period stop method and light intensity correction order adjustment method>
FIG. 12 is a diagram for explaining a combination method of the second method (part 1) to which the settling period stop method is applied and the light amount correction order adjustment method.

  In the tandem configuration in which a color image is formed using the image forming unit 18 (photosensitive drum 19) for each color as in the image forming apparatus 1 of the present embodiment, the second settling period stopping method as described above is applied. When the above method (part 1) is executed, the light amount setting data DVref indicating the target light amount corresponding to each color is generated due to variations in characteristics of the photosensitive drum 19 or differences in changes of the photosensitive drum 19 over time. In general, the light amount setting data DVref (reference signal Vref) indicating the target light amount of each color group is set in a time-sharing manner, that is, the light amount setting data DVref (for each color) every time the color group to be processed is switched. When the reference signal Vref) is switched, the reference voltage settling period Tst is almost certainly required. Therefore, the total processing time takes longer as long as the stop period is provided.

  Therefore, as to how much the stop period corresponding to the inactive period of the APC timing setting signal LOAD is set, the difference between adjacent points when the reference signal Vref indicating the target light amount of each color group is set in a time division manner is used. It is preferable to decide accordingly. If the difference between adjacent pixels is large, the period until the reference signal Vref is stabilized after switching the color group to be processed (reference voltage settling period Tst) becomes long, so the inactive period (stop period) needs to be set long. . In some cases, there is a possibility that all light quantity corrections cannot be executed for all color groups in a non-image area within one scanning period.

  For example, as shown in FIG. 12A, when the light amount correction is executed in the order of Y → M → C → K according to the order indicated by the color group data Dsel0, the reference signals Vref_C and K for the C color When the difference from the reference signal Vref_K for color is significantly larger than the difference between other adjacent colors, when switching from C color to K color, when switching from Y → M, M → C, K → Y In comparison, the reference voltage settling period Tst becomes considerably long. As a result, if the light amount correction is performed after the reference signal Vref is stabilized, the corresponding stop period must be set to be considerably long, and the APC control time is increased accordingly, and the non-image area within one scanning period In some cases, it becomes impossible to complete the light amount correction for all the laser diodes 25.

  On the other hand, if the light amount correction order is determined by the light amount correction order adjustment unit 61 so that the difference between adjacent areas becomes smaller than the order indicated by the color group data Dsel0, the reference voltage settling period is reached. Tst can be made shorter, and in some cases, if not all, the reference signal is stable in the order in which the difference between adjacent neighbors becomes almost zero, that is, within a specified time (a period required for light amount correction of one laser diode). You may be able to select a combination that has the order you want.

  In determining the correction order at this time, the maximum value of the adjacent difference, which is the difference before and after switching of the reference signal Vref used in time division, is made as small as possible. More specifically, an order is selected so that the maximum value Δmax of the difference between adjacent values becomes smaller than a predetermined threshold value Δs.

  First, the light quantity correction order adjusting unit 61 sets the target light quantity value of each color of Y / M / C / K in the initial correction order (Y → M → C → K →...) Indicated by the color group data Dsel0. The difference Δ between the corresponding light quantity setting data DVref (reference signal Vref) is obtained according to the following equation (1).

  Next, the light quantity correction order adjustment unit 61 compares the adjacent differences ΔV1 to ΔV4 of the reference signal Vref with the threshold value ΔVs, and if all of the adjacent differences ΔV1 to ΔV4 are equal to or less than the threshold value Δs, the APC control order is set. The color group data Dsel0 is passed to the color group selection unit 62 as it is as color group data Dsel. On the other hand, if any of the adjacent differences ΔV1 to ΔV4 exceeds the threshold value Δs, the light amount correction order adjustment unit 61 determines that the APC control order (light amount correction order) needs to be changed.

  In the case of four colors, there are 24 combinations of control of the reference signal Vref, so the maximum inter-adjacent difference ΔVn = Δmax in each combination is obtained, and any one of the APC orders that is equal to or less than the threshold value ΔVs may be selected. . At this time, if the maximum ΔVn = Δmax is greater than or equal to the threshold value ΔVs in all the combinations, first, the combination having the minimum Δmax is selected.

  As a result, even if there is a large difference between the target light amounts of the four colors, the single output amount correction processing unit 52 can efficiently execute the APC control.

  For example, when the reference signal Vref of each color before the order change is as shown in FIG. 12A, the light amount correction is performed in the order of Y → K → M → C →... As shown in FIG. If executed, the difference Δ of the light amount setting data DVref (reference signal Vref) corresponding to the target light amount value of each color of Y / M / C / K is expressed by the following equation (2).

  Thereby, the maximum value Δmax of the difference between adjacent ones can be made smaller than the case where the light amount correction is executed in the order of Y → M → C → K → Y, and the entire stop period can be shortened accordingly. it can. Even if the light amount correction is executed after the reference signal Vref is stabilized, the stop period can be shortened, so that the light amount correction for all the laser diodes 25 can be completed within the non-image region within one scanning period. Become.

  Further, by adjusting the order, there may be a combination having an order in which the difference between adjacent neighbors becomes almost zero. For example, as shown in FIG. 12C, if the reference signals Vref for Y and C are of the same level, Y → C → M → K → Y as shown in FIG. If the light amount correction is performed in order, the entire processing period can be further shortened by not providing the stop period at the time of switching when the difference between adjacent areas becomes substantially zero. Accordingly, the light amount correction period allocated per group can be increased, and as a result, the light amount correction period allocated to one laser diode 25 can be increased.

  If the reference voltage settling period Tst falls within the light quantity correction period assigned to one laser diode 25, it is not necessary to provide a stop period. Therefore, the light quantity correction sequence can be adjusted to increase the light quantity correction period. Doing so means that the control response speed can be reduced, and a large margin for noise can be obtained, which is an advantageous direction for stabilizing the target light quantity.

  In addition, when combining the settling period stop method in units of one beam and the light amount correction order adjustment method, the stop period can be adjusted in units of one beam, so that the extreme method is not limited to the order of color groups. It is also possible to adjust the light amount correction order so that the difference between adjacent beams becomes as small as possible for all the beams in the group. Of course, in this case, since the output amount correction processing unit 52 side also needs to select the correction target beam in conjunction with the order after the adjustment, the light amount correction order adjustment unit 62 uses the light amount correction order adjustment unit 61. It is necessary to supply the correction target beam selection signal Psel0 representing the adjusted correction order to the output amount correction processing unit 52.

  In order to perform fine control such as providing a stop period when switching to a certain light beam and not providing a stop period when switching to a certain light beam, it is not possible to perform such simple repetitive control as described above. It is necessary to adopt a circuit configuration that can freely set whether or not to provide a stop period for each color group or for each laser diode 25 in the color group. I will omit the explanation.

  In such a stopping method, by stopping the APC lighting beam switching signal Pcng, the number of outputs of the APC lighting beam switching signal Pcng is equal to the number of APC beams, which is in a one-to-one relationship. In this case, there is an advantage that the degree of freedom of circuit configuration is increased, such as beam switching can be performed by a state machine using the APC lighting beam switching signal Pcng as a trigger.

<Method of overlapping settling periods in units of one beam>
13 and 14 are diagrams illustrating a second method (part 2) for stabilizing the APC control in units of output amount correction processing for one beam. Here, each diagram in FIG. 13 corresponds to each diagram in FIG. 11. FIG. 14 is a diagram for explaining a circuit modification example for realizing the second method (part 2).

  As can be seen from the comparison between FIG. 11 and FIG. 13, this second method (No. 2) outputs the clock signal CLK for the APC lighting beam switching signal Pcng during the reference voltage settling period Tst, and then this reference. The second method (part 1) is different in that the clock signal CLK for the APC lighting beam switching signal Pcng is output again for the group in the period corresponding to the voltage settling period Tst.

  When the color group is switched, a clock signal for the APC lighting beam switching signal Pcng is output and the APC control is performed in the output amount correction processing unit 52 during a period in which the reference voltage difference is large and instability can occur in the APC control. In order to compensate for the instability of the APC control during this period, the APC lighting beam switching signal Pcng (corresponding clock signal) is output again for the same light beam, so that the output amount correction processing unit 52 performs the APC control. It is carried out again. That is, the output amount correction processing unit 52 performs light amount correction by performing APC control for a plurality of cycles for the laser diode 25 corresponding to the reference voltage settling period Tst.

  In order to generate a pulse signal adapted to such a settling period overlapping method, for example, the operation of the correction target beam selection unit 62 and the APC timing control unit 67 and the configuration of the count processing unit 66 may be devised.

  First, the APC timing control unit 67, based on the information of the reference voltage settling period Tst set in the setting unit 74, not only the reference voltage settling period Tst but also after the reference voltage settling period elapses. The APC timing setting signal LOAD is adjusted so that a predetermined number of clocks are output from the APC lighting beam switching signal Pcng so as to supplement the clock.

  The combining unit 72 of the APC timing control unit 67 also receives the clock signal CLK (APC lighting beam switching signal Pcng0) input from the counter 71 of the APC lighting beam switching unit 64 and the APC timing setting input from the setting unit 74. A signal obtained by logically synthesizing gate pulses Gate1 indicating all groups of the signal LOAD is output as an APC lighting beam switching signal Pcng.

  As illustrated in FIG. 14, the count processing unit 66 adds a count value holding unit 77 including a latch that holds a count value at that time immediately before the counter 76 starts a counting operation. For example, the count value holding unit 77 clears the held data to zero, and then takes in the count value of the counter 76 using the count arrival signal CNTarv from the APC timing control unit 67 as a trigger.

  Further, the counter 76 starts the counting operation after loading the count value held in the count value holding unit 77 immediately before starting the counting operation when the color group is switched or after the reference voltage settling period elapses. change. For example, the count value holding unit 77 clears the count value at the start of counting to zero as an initial setting, and then the counter 76 detects both edges of the APC timing setting signal LOAD from the APC timing control unit 67. Synchronously with this, the count value of the count value holding unit 77 is taken in, and the counting operation is restarted from this count value.

  Further, the beam selection unit 62 for correction uses the data for setting the lighting order in each color group adapted to the settling period overlapping method based on the information of the reference voltage settling period Tst set in the APC timing control unit 67, and the color Data for setting the lighting order for each group is generated and output to the output amount correction processing unit 52 as the group selection signal Psel.

  As a result, as shown in FIG. 13, when the APC control of a certain color group is completed and the reference voltage settling period Tst starts (Ts1), the count value holding unit 77 counts the count value of the counter 76 at this time (main In the example, 8) is captured. In the reference voltage settling period Tst, the counter 76 first loads the count value (8 in this example) held in the count value holding unit 77 and then continues the counting operation. For example, if the information of the reference voltage settling period Tst is for 3 clocks, it is counted as 9, 10, 11.

  The decoder 78 generates the select signal SEL based on the count result CNTout output from the counter 76 and the count arrival signal CNTarv. At this time, the select signal SEL is used for the next color (M color in this example). Switch to “2” for selecting the light amount setting data DVref. As a result, the reference signal generation unit 68 switches the light amount setting data DVref to the output amount correction processing unit 52 from the light amount setting data DVref_Y for Y color to the light amount setting data DVref_M for M color.

  Thereafter, when the reference voltage settling period Tst elapses (Te1 = Ts2), the counter 76 again loads the count value (8 in this example) held in the count value holding unit 77 and then continues. The counting operation is continued.

  Therefore, after the reference voltage settling period Tst elapses, the APC lighting beam having the number of clocks for performing output amount correction processing for all the laser diodes 25 (eight in this example) in the color group for the next color again. The switching signal Pcng can be output to the output amount correction processing unit 52 side.

  Further, based on the information of the reference voltage settling period Tst set in the APC timing control unit 67, the same laser diode 25 is sequentially turned on for the reference voltage settling period Tst and the overlap period in each color group. As is done, the correction target beam selection unit 62 adjusts the lighting order according to the correction target beam selection signal Psel0. For example, if the reference voltage settling period Tst is 3 clocks, (1-3), (2-3), (3-3) corresponding to the reference voltage settling period Tst after shifting from Y color to M color. Is set first, and thereafter (1-3), (2-3), (3-3) are set again, and then (4-3), (5-3), (6-3), (7-3) and (8-3) are set.

  The synthesizing unit 72 of the APC timing control unit 67 logically synthesizes the APC lighting beam switching signal Pcng0 input from the counter 71 of the APC lighting beam switching unit 64 with a gate pulse Gate1 indicating all groups of the APC timing setting signal LOAD. Gate and pass to the output amount correction processing unit 52 as the APC lighting beam switching signal Pcng.

  That is, the correction target beam selection unit 62, the count processing unit 66, and the APC timing control unit 67 cooperate to execute the output amount correction process for the subsequent beam for a predetermined period immediately after the reference value switching, and the predetermined period has elapsed. After that, a beam-corresponding clock whose adjustment timing is adjusted so that the output amount correction process for the subsequent beam can be performed again is generated, and then the APC lighting beam switching signal Pcng is output to the output amount control unit 52. .

  In the period until the signal voltage is stabilized when the value of the light amount setting data DVref output from the reference signal generation unit 68 is converted into an analog signal in the output amount correction processing unit 52, the APC lighting beam switching signal Pcng is output. Since it is input to the correction processing unit 52, the output amount correction processing unit 52 executes an output amount correction process for the next color.

  Further, after the stable analog reference signal Vref is generated, the color group of the next color is used by using each clock of the APC lighting beam switching signal Pcng supplied to all the laser diodes 25 in the color group of the next color again. The output amount correction processing can be executed in a time division manner for all of the laser diodes 25.

  A period (referred to as an overlap period) (Ts2 to Te2) corresponding to the first “reference voltage settling period Tst” after the elapse of the reference voltage settling period Tst (Ts1 to Te1) is the reference voltage settling period Tst (Ts1 to Te1). The light amount correction can be performed again for the laser diode 25 that has been subjected to the light amount correction. In short, for the plurality of laser diodes 25 corresponding to the reference voltage settling period Tst (Ts1 to Te1), the light quantity correction is performed by performing APC control for a plurality of cycles.

  Even if the response of the control system is not made high-speed, all the laser diodes 25 in the color group of the next color are used by using each clock of the APC lighting beam switching signal Pcng supplied after generating a stable analog reference signal Vref. The point that the output amount correction process can be executed in a time-sharing manner is the same as in the second method (part 1) employing the settling period stop method. Since there is no need to increase the control response speed, a large margin for noise can be secured, and the target light quantity can be reliably stabilized.

  Even if such a settling period overlapping method is adopted, a plurality of light beams emitted from one light source 24 are separated and scanned on different photosensitive drums 19 of the image forming unit 18 provided for each color. When forming a full-color image, the output amount correction processing of a plurality of beams corresponding to each color can be stably executed in a time division manner without increasing the control signal with a simple configuration.

  However, in the settling period overlapping method in which one beam unit is used, an overlap period is provided in units of output amount correction processing for one light beam. Therefore, after the reference voltage settling period Tst, all of the next colors (eight in this example) In order to execute the output amount correction process for the laser diode 25), it is necessary to generate a signal group including eight pulse signals as the APC lighting beam switching signal Pcng for the next color. Therefore, the APC timing setting signal LOAD and the generation of the APC lighting beam switching signal Pcng need to be performed in cooperation, and the count processing unit 66 and the APC timing control unit 67 operate with reference to the output results of the other party. Therefore, it is necessary to manage timing with high accuracy in consideration of gate delay and the like.

  Further, for example, after the light amount correction processing for the Y color, the counter 76 once counts 9, 10, and 11 to perform the light amount correction processing for the M color, and then again with the counter 76, 9 , 10, and 11 to perform the light quantity correction processing for M color, etc., and the light quantity in the same group indicated by the group selection signal Psel (correction target beam selection signal Psel0) issued from the correction target beam selection unit 62 Linkage with correction order is required. Compared to the stop method described above, it is disadvantageous in that complex timing control is required.

  Although the explanation using the figure is omitted, the second method (part 2) to which the settling period duplication method is applied can be combined with the light quantity correction rank adjustment method, and the settling period stop method is applied. The same effect as that obtained by combining the second method (part 1) with the light amount correction order adjustment method can be obtained.

<Method for overlapping settling periods in units of one beam; modification>
FIGS. 15 and 16 are diagrams for explaining a modification of the second method (part 2) for stabilizing the APC control in units of output amount correction processing for one beam. Here, each drawing in FIG. 15 corresponds to each drawing in FIG. FIG. 16 is a diagram for explaining a circuit change example for realizing this modification.

  In this modified example, like the method of FIG. 13, the second method (part 1) is that the clock signal CLK for the APC lighting beam switching signal Pcng is also output during the reference voltage settling period Tst. Different. However, as can be seen from a comparison between FIG. 13F and FIG. 15F, there is a difference in beam selection for correction in the reference voltage settling period Tst.

  That is, the correction target beam selection unit 62 sets the lighting order within each color group adapted to the settling period overlapping method based on the information of the reference voltage settling period Tst set in the APC timing control unit 67, and the color When the data for setting the lighting order for each group is generated and output to the output amount correction processing unit 52 as the group selection signal Psel (correction target beam selection signal Psel0), correction is performed within the reference voltage settling period Tst. The target beam is fixed to the first light beam after switching.

  When the color group is switched, the clock signal for the APC lighting beam switching signal Pcng is output and the beam to be corrected is fixed in the output amount correction processing unit 52 during a period when the reference voltage difference is large and instability in the APC control can occur. In the illustrated example, the APC control is performed with the reference voltage being fixed to 1-3, and after the reference voltage becomes stable, the beam is sequentially switched to the next correction target beam. That is, the output amount correction processing unit 52 performs light amount correction by performing APC control for a plurality of cycles for one laser diode 25 corresponding to the reference voltage settling period Tst.

  In order to generate a pulse signal adapted to such a settling period overlapping method, for example, the operation of the correction target beam selection unit 62 and the APC timing control unit 67 and the configuration of the count processing unit 66 may be devised.

  First, the APC timing control unit 67 sets the APC timing to stop the count-up operation in the counting processing unit 66 during the reference voltage settling period Tst based on the information of the reference voltage settling period Tst set in the setting unit 74. Adjust the signal LOAD.

  The APC timing control unit 67 outputs the clock signal CLK (APC lighting beam switching signal Pcng0) input from the counter 71 of the APC lighting beam switching unit 64 as the APC lighting beam switching signal Pcng as it is. In effect, the combining unit 72 is unnecessary.

  As shown in FIG. 16, the counting processing unit 66 receives the APC timing setting signal LOAD input to the counter 76 in order to temporarily stop the counting operation of the counter 76 during the reference voltage settling period Tst. The counter 76 counts up when the APC timing setting signal LOAD is High (active) and does not count up (Disable) when it is Low (inactive).

  Further, the correction target beam selection unit 62 sets the lighting order for each color group based on the information of the reference voltage settling period Tst set in the APC timing control unit 67, and the first beam after switching for the reference voltage settling period Tst. Is output to the output amount correction processing unit 52.

  As a result, as shown in FIG. 15, when the APC control of a certain color group is completed and the reference voltage settling period Tst starts (Ts), the counter 76 outputs the count arrival signal CNtarv and counts at that time. The result CNTout (8 in the illustrated example) is held.

  The decoder 78 generates the select signal SEL based on the count result CNTout output from the counter 76 and the count arrival signal CNTarv. At this time, the select signal SEL is used for the next color (M color in this example). Switch to “2” for selecting the light amount setting data DVref. As a result, the reference signal generation unit 68 switches the light amount setting data DVref to the output amount correction processing unit 52 from the light amount setting data DVref_Y for Y color to the light amount setting data DVref_M for M color.

  Even after the start of the reference voltage settling period Tst, the APC lighting beam switching signal Pcng is output to the output amount correction processing unit 52, but within the reference voltage settling period Tst, the correction target beam is selected by the correction target beam selection signal Psel0. Since the first beam after switching is fixed to the first beam (1-3 in this example), the output amount correction processing unit 52 uses the APC lighting beam for the first beam (1-3) that has entered the reference voltage settling period Tst. The light amount correction is repeatedly performed based on the clock of the switching signal Pcng.

  Thereafter, when the reference voltage settling period Tst elapses (Te), the counter 76 restarts the count-up operation. In this example, since the counter 76 holds “8” as the counting result CNTout, the counter 76 counts up from “9”.

  In response to this, the correction target beam selection unit 62 returns the correction target beam selection signal Psel0 to the normal selection cycle. In this example, settings are made such as (1-3), (2-3), (3-3),. The overlap period after the elapse of the reference voltage settling period Tst is effectively one clock for (1-3).

  Even during the reference voltage settling period Tst, the clock of the APC lighting beam switching signal Pcng (= APC lighting beam switching signal Pcng0) remains output, and the output amount correction processing unit 52 selects the first beam after switching the reference signal Vref. The light quantity correction is performed as a correction coping beam, waiting for the reference signal Vref to become stable, and the correction coping beam is sequentially switched from the stable state.

  That is, the correction target beam selection unit 62, the count processing unit 66, and the APC timing control unit 67 cooperate to execute the output amount correction process repeatedly for the subsequent first beam for a predetermined period immediately after the reference value switching. After the elapse of the period, the APC lighting beam switching signal Pcng is generated after generating a beam-corresponding clock whose correction timing is adjusted so that the output amount correction process can be executed by returning to the normal correction target beam selection operation. Is output to the output amount control unit 52.

  In the period until the signal voltage is stabilized when the value of the light amount setting data DVref output from the reference signal generation unit 68 is converted into an analog signal in the output amount correction processing unit 52, the APC lighting beam switching signal Pcng is output. Since it is input to the correction processing unit 52, the output amount correction processing unit 52 executes an output amount correction process for the next color. At this time, the correction target beam is fixed to one beam immediately after switching, which is different from the method of FIG. In short, for one laser diode 25 corresponding to the reference voltage settling period Tst (Ts to Te), APC control is performed for a plurality of cycles to perform light amount correction.

  After the stable analog reference signal Vref is generated, the normal correction target beam selection operation returns to the APC lighting beam switching signal Pcng supplied to all the laser diodes 25 in the color group of the next color. Using each clock, output amount correction processing is executed in a time-sharing manner for all laser diodes 25 in the color group of the next color.

  Even if the response of the control system is not made high-speed, all the laser diodes 25 in the color group of the next color are used by using each clock of the APC lighting beam switching signal Pcng supplied after generating a stable analog reference signal Vref. The point that the output amount correction process can be executed in a time-sharing manner is the same as in the second method (part 1) employing the settling period stop method. Since there is no need to increase the control response speed, a large margin for noise can be secured, and the target light quantity can be reliably stabilized.

  Even if such a variation of the settling period overlapping method is adopted, a plurality of light beams emitted from one light source 24 are separated on different photosensitive drums 19 of the image forming unit 18 provided for each color. When a full color image is formed by scanning, the output amount correction processing of a plurality of beams corresponding to each color can be stably executed in a time division manner without increasing the control signal with a simple configuration.

  Compared to the modes shown in FIGS. 13 and 14, the counter 76 controls the count-up operation using the APC timing setting signal LOAD and the correction target beam selection command by the correction target beam selection unit 62. For example, the count value holding unit 77 and the synthesizing unit 72 are unnecessary, and there is an advantage that the circuit configuration can be made compact.

<Settling period stopping method within one scanning period for each color group; Part 1>
17 and 18 complete all light amount correction within one scanning period, and perform APC control in units of color groups, that is, in units of output amount correction processing for all laser diodes 25 in the color groups. It is a figure explaining the 1st example of the 3rd method (the 1) which aims at stabilization. Here, FIG. 17 is a time chart related to the output amount correction processing, and FIG. 18 is a diagram for explaining a circuit change example for enabling the output of each pulse signal shown in FIG.

  The first example of the third method (part 1) shows a first example of an aspect in which the output of the APC lighting beam switching signal Pcng is stopped in units of color groups during the reference voltage settling period Tst. In the example shown in FIG. 17, in order to avoid instability of the control result due to execution of APC control during the reference voltage settling period Tst, the APC lighting beam switching signal is switched for a certain period when switching between the previous color and the next color. The point of stopping without outputting Pcng is the same as the second method (part 1), but there is a difference in setting of the stop period, and the stop period is set for each color group.

  By doing so, it is possible to provide a more stable period than the actual reference voltage settling period Tst. Specifically, after the light amount correction is executed for 8 clocks of the APC lighting beam switching signal Pcng0, a stop period of 8 clocks of the APC lighting beam switching signal Pcng0 is set, and then, 8 clocks of the APC lighting beam switching signal Pcng0. The amount of light of the next color is corrected in minutes.

  In order to generate a pulse signal adapted to such a method for stopping the settling period in units of color groups, the configuration shown in FIG. 7 may be used. For example, the configuration of the count processing unit 66 and the APC timing control unit 67 It can also be dealt with by devising the operation.

  First, the combining unit 72 of the APC timing control unit 67 receives the clock signal CLK (APC lighting beam switching signal Pcng0) input from the counter 71 of the APC lighting beam switching unit 64 and the APC timing setting input from the setting unit 74. A signal obtained by logically combining the signal LOAD is output as an APC lighting beam switching signal Pcng.

  As shown in FIG. 18, the count processing unit 66 adds a count value holding unit 77 configured by a latch or the like that holds a count value at that time immediately before the counter 76 starts the counting operation. This is the same as the circuit configuration corresponding to the second method (part 2) shown in FIG. The counter 76 counts the APC lighting beam switching signal Pcng0.

  The count value holding unit 77 clears the held data to zero, and then takes in the count value of the counter 76 at the time of color group switching. For example, not the count arrival signal CNtarv from the APC timing control unit 67 but the falling edge of the APC timing setting signal LOAD from the APC timing control unit 67 is used as a trigger to capture the count value of the counter 76.

  The counter 76 starts the counting operation after loading the count value held in the count value holding unit 77 immediately before starting the counting operation after the reference voltage settling period has elapsed. For example, in synchronization with the rising edge of the APC timing setting signal LOAD from the APC timing control unit 67, the count value of the count value holding unit 77 is taken in, and the counting operation is restarted from this count value.

  The APC timing control unit 67 generates the APC timing setting signal LOAD by inverting the output logic using the count arrival signal CNtarv from the counter 76 as a trigger.

  As a result, when the APC control of a certain color group is completed and the reference voltage settling period Tst starts (Ts), the APC timing control unit 67 uses the count arrival signal CNtarv from the counter 76 as a trigger to trigger the APC timing setting signal. LOAD is made inactive (= L). The count value holding unit 77 takes in the count value (8 in this example) of the counter 76 at that time. When the reference voltage settling period Tst is entered, the counter 76 continues the counting operation.

  The decoder 78 generates the select signal SEL based on the count result CNTout output from the counter 76 and the count arrival signal CNTarv. At this time, the select signal SEL is used for the next color (M color in this example). Switch to “2” for selecting the light amount setting data DVref. As a result, the reference signal generation unit 68 switches the light amount setting data DVref to the output amount correction processing unit 52 from the light amount setting data DVref_Y for Y color to the light amount setting data DVref_M for M color.

  Thereafter, when 8 clocks have elapsed (Te), the counter 76 outputs a count arrival signal CNTarv indicating the arrival of the next 8 clocks. In response to this, the APC timing control unit 67 activates the APC timing setting signal LOAD. The counter 76 continues the counting operation after reloading the count value (8 in this example) held in the count value holding unit 77 in synchronization with the active edge of the APC timing setting signal LOAD. .

  Thereafter, by repeating the same process, a timing pulse having one group as a stop period as shown in FIG. 17 is obtained. The APC timing setting signal LOAD may be controlled by a simple toggle operation using the count arrival signal CNtarv, and the counter 76 and the count value holding unit 77 only need to operate in conjunction with this, so the control is simple. It is.

  Therefore, the reference signal generation unit 68 can change the light amount setting data DVref to data for the next color at the time when the reference voltage settling period Tst starts. Further, the APC timing control unit 67 performs the output amount correction process for all the laser diodes 25 (eight in this example) in the color group for the next color after the reference voltage settling period Tst has elapsed (Te). The APC lighting beam switching signal Pcng having the number of clocks can be output to the output amount correction processing unit 52 side.

  As the APC lighting beam switching signal Pcng, the reference signal generation unit 68 outputs the light quantity setting data DVref for the next color before the clock for the next color is output after the reference voltage settling period having all the clock periods for the color groups has elapsed. Thus, the output amount correction processing unit 52 can wait for the reference signal Vref to become sufficiently stable before starting the light amount correction for the next color. In the output amount correction processing unit 52, when the value of the light amount setting data DVref output from the reference signal generation unit 68 is converted into an analog signal, the light amount correction for 8 clocks until the signal voltage is stabilized, that is, for one color group. During the period corresponding to the period, the APC lighting beam switching signal Pcng is not input to the output amount correction processing unit 52.

  Thereby, the output amount correction processing unit 52 uses each clock of the APC lighting beam switching signal Pcng supplied after generating a stable analog reference signal Vref using a sufficiently long reference voltage settling period Tst, Output amount correction processing can be executed in a time-sharing manner for all laser diodes 25 in the color group of the next color.

  By adopting such a settling period stop method in units of color groups, a plurality of light beams emitted from one light source 24 are separated on different photosensitive drums 19 of the image forming unit 18 provided for each color. Thus, when a full color image is formed by scanning each, the output amount correction processing of a plurality of beams corresponding to each color can be stably executed by time division without increasing the control signal with a simple configuration.

  In addition, the counting processing unit 66 and the APC timing control unit 67 need to refer to each other's output results, but actually, since the stop period is set in units of color groups, as described above. The control can be easily performed by a simple toggle operation using the count arrival signal CNTarv.

<Method for stopping settling period within one scanning period for each color group; Part 2>
19 and 20, all light quantity correction is completed within one scanning period, and APC control is performed in units of color groups, that is, in units of output amount correction processing for all laser diodes 25 in the color group. It is a figure explaining the 2nd example of the 3rd method (the 1) which aims at stabilization. Here, FIG. 19 is a time chart related to the output amount correction processing, and FIG. 20 is a diagram for explaining an example of circuit modification for enabling output of each pulse signal shown in FIG.

  In the second example, the output of the APC lighting beam switching signal Pcng is stopped in units of color groups during the reference voltage settling period Tst. In the description of the first example, the stop period is set to one color group (8 clocks). However, as shown in FIG. 19, the difference is that a plurality of stop periods can be set.

  In order to generate a pulse signal adapted to such a method for stopping the settling period in units of color groups, as shown in FIG. 20, a slight modification may be added to the configuration of the first example shown in FIG. . Specifically, the counter 76 captures the count value of the count value holding unit 77 with a pulse obtained by slightly delaying the count arrival signal CNTarv by the delay circuit (DT) 177. When the setting unit 74 receives the count arrival signal CNTarv from the counter 76, the setting unit 74 sets the APC timing setting signal LOAD to inactive (= L), and then sets the APC timing when a predetermined number of count arrival signals CNtarv are input. The operation of making the signal LOAD active (= H) is repeated.

  For example, the count value holding unit 77 clears the held data to zero, and then takes in the count value of the counter 76 at the time of color group switching. For example, not the count arrival signal CNtarv from the APC timing control unit 67 but the falling edge of the APC timing setting signal LOAD from the APC timing control unit 67 is used as a trigger to capture the count value of the counter 76.

  As a result, when the APC control of a certain color group is completed and the reference voltage settling period Tst starts (Ts), the APC timing control unit 67 uses the count arrival signal CNtarv from the counter 76 as a trigger to trigger the APC timing setting signal. LOAD is made inactive (= L). The count value holding unit 77 takes in the count value (8 in this example) of the counter 76 in synchronization with the inactive edge of the APC timing setting signal LOAD. In the reference voltage settling period Tst, the counter 76 first loads the count value (8 in this example) held in the count value holding unit 77 based on the output of the delay circuit 177, and then continues. Continue counting.

  The decoder 78 generates the select signal SEL based on the count result CNTout output from the counter 76 and the count arrival signal CNTarv. At this time, the select signal SEL is used for the next color (M color in this example). Switch to “2” for selecting the light amount setting data DVref. As a result, the reference signal generation unit 68 switches the light amount setting data DVref to the output amount correction processing unit 52 from the light amount setting data DVref_Y for Y color to the light amount setting data DVref_M for M color.

  Thereafter, for example, if the information of the reference voltage settling period Tst is for two groups, first, when eight clocks have elapsed (Te1), the counter 76 generates a count arrival signal CNtarv indicating the arrival of the next eight clocks. Output. In response to this, the counter 76 loads the count value (8 in this example) held in the count value holding unit 77 based on the output of the delay circuit 177 and then continues the counting operation.

  When 8 clocks have elapsed (Te2), the counter 76 outputs a count arrival signal CNtarv indicating arrival of the next 8 clocks. The setting unit 74 of the APC timing control unit 67 counts the number of count arrival signals CNtarv from the counter 76. When two groups have elapsed as the stop period, that is, the second count arrival signal CNtarv is after Ts. When it becomes, the APC timing setting signal LOAD is made active (= H). The count value holding unit 77 captures the count value (16 in this example) of the counter 76 at that time in synchronization with the inactive edge of the APC timing setting signal LOAD.

  Thereafter, by repeating the same processing, a timing pulse having two groups as a stop period as shown in FIG. 19 is obtained.

  The APC timing setting signal LOAD may be controlled by a simple operation using the count arrival signal CNtarv, and the counter 76 and the count value holding unit 77 only need to operate in conjunction with this, so the control is simple. is there. There is an advantage that the stop time can be easily adjusted in units of groups. Other points are the same as in the first example. In the configuration of the second example as well, by setting one group for the setting gate, one group can be set as the stop period as in the configuration of the first example.

<Method for overlapping settling periods within one scanning period for each color group>
21 and 22 complete all light amount correction within one scanning period, and perform APC control in units of color groups, that is, in units of output amount correction processing for all laser diodes 25 in the color group. It is a figure explaining the 3rd method (the 2) which aims at stabilization. Here, FIG. 21 is a time chart related to the output amount correction processing, and FIG. 22 is a diagram for explaining a circuit change example for enabling output of each pulse signal shown in FIG.

  In the third method (No. 2), the APC lighting beam switching signal Pcng is output also in the reference voltage settling period Tst, and thereafter, APC control is performed also in a period corresponding to the reference voltage settling period Tst. This is the mode of execution. In order to generate a pulse signal adapted to such a settling period overlapping method in units of color groups, it is basically preferable to employ the configuration shown in FIG. However, the operation of the synthesizer 72 is modified so that a clock is output as the APC lighting beam switching signal Pcng during the reference voltage settling period Tst.

  That is, since the APC lighting beam switching signal Pcng is also output during the reference voltage settling period Tst, the combining unit 72 of the APC timing control unit 67 receives the clock signal CLK (APC) input from the counter 71 of the APC lighting beam switching unit 64. A signal obtained by logically synthesizing the lighting beam switching signal Pcng0) and gate pulses Gate1 indicating all groups of the APC timing setting signal LOAD input from the setting unit 74 is output as the APC lighting beam switching signal Pcng.

  By doing so, it is possible to output a clock for executing the light amount correction for the next color even during the stop period in FIG. 19 shown as the operation of the third method (part 2). Then, the APC control is performed for a plurality of cycles to correct the light amount.

  Even when the settling period overlapping method using such color groups as a unit is adopted, a plurality of light beams emitted from one light source 24 are separated on different photosensitive drums 19 of the image forming unit 18 provided for each color. Thus, when a full color image is formed by scanning each, the output amount correction processing of a plurality of beams corresponding to each color can be stably executed by time division without increasing the control signal with a simple configuration.

  The count processing units 66 and 67 may perform the same operation regardless of whether the predetermined color group period corresponding to the reference voltage settling period Tst is a stop period or an overlap period. The reference voltage settling period Tst is switched between the stop period and the overlap period by changing the pulse used by the combining unit 72 of the APC timing control unit 67 to the APC timing setting signal LOAD or setting the APC timing. It can be realized by switching to the gate pulse Gate1 indicating all groups of the signal LOAD, and the setting is simple.

<Combination of settling period stop method or settling period overlap method within one scanning period in units of color group and light amount correction order adjustment method>
FIG. 23 is a diagram for explaining a combination method of the third method (part 1) to which the settling period stopping method is applied (part 1), the third method (part 2) to which the settling period overlap method is applied, and the light amount correction rank adjustment method. is there. As in the case of combining the second method (part 1), which is a settling period stop method for one beam unit, with the light amount correction order adjustment method, the settling period stop method for applying within one scanning period for each color group is applied. The third method (part 1) and the third method (part 2) to which the settling period overlapping method is applied can also be combined with the light amount correction rank adjustment method.

  In this case, the light quantity correction order is set so that the difference between adjacent ones becomes as small as possible for all the beams of all groups without being taken in the color group order as in the case where the second technique (part 1) is combined with the light quantity correction order adjusting method. Instead of adjusting, the light amount correction order is adjusted in color group units within one scanning period so that the difference between adjacent units in color group units is as small as possible. Interlocking with the selection operation can be facilitated.

  In addition, when performing detailed control such as setting a stop period or overlap period when switching to a certain color group, and not setting a stop period or overlap period when switching to a certain color group, the stop period or overlap period is set for each group. Although it is necessary to adopt a circuit configuration in which whether or not to provide can be freely set, it may be handled in units of color groups, and the circuit configuration and control are simpler than in the case of controlling each beam.

  For example, while adopting a circuit configuration as shown in FIG. 20, the setting unit 74 controls the timing at which the APC timing setting signal LOAD is activated in accordance with whether or not a stop period or an overlap period is provided. Thus, it is possible to easily control whether to provide a stop period or an overlap period for each color group.

  For example, when the Y color and C color reference signals Vref are substantially the same, as shown in FIG. 23A, when the light amount correction is executed in the order of Y → M → C → K, Since there is a difference between adjacent areas at the time of switching, the setting unit 74 logically inverts the APC timing setting signal LOAD by a toggle operation every time the count arrival signal CNTarv from the counter 76 is received.

  On the other hand, as shown in FIG. 23 (B), if the light amount correction order adjustment unit 61 is modified to execute light amount correction in the order of Y → C → M → K, when switching from Y → C, Since the adjacent difference is zero, when the setting unit 74 receives the count arrival signal CNTarv from the counter 76, the setting unit 74 once inactivates the APC timing setting signal LOAD. By setting to, the APC timing setting signal LOAD is immediately activated. This effectively makes the stop period zero when switching from Y to C. In addition, when other M → Y, C → K, and K → M are switched, a stop period for one group can be provided by instructing the setting gate for one group. Even if this is done, the maximum value of the difference between adjacent points is not changed.

  In any case, in the case where a stop period is provided, the synthesis unit 72 performs logic synthesis on the APC lighting beam switching signal Pcng0 from the APC lighting beam switching signal generation unit 65 (counter 71) with the APC timing setting signal LOAD. Then, it may be passed to the output amount correction processing unit 52 as the APC lighting beam switching signal Pcng. Thus, the APC lighting beam switching signal Pcng without a clock is passed to the output amount correction processing unit 52 during the inactive period of the APC timing setting signal LOAD.

  When providing an overlap period, the combining unit 72 uses the APC lighting beam switching signal Pcng0 from the APC lighting beam switching signal generation unit 65 (counter 71) as an APC timing setting signal input from the setting unit 74. What is necessary is just to carry out logic synthesis | combination with the gate pulse Gate1 which shows all the groups of LOAD, and to pass to the output amount correction process part 52 as APC lighting beam switching signal Pcng. By doing so, the APC lighting beam switching signal Pcng in which the clock exists even during the inactive period of the APC timing setting signal LOAD is passed to the output amount correction processing unit 52.

<Settling period stop method for each scanning period in color group unit>
24 and 25, the light amount correction of one color group is performed within one scanning period, and the output amount correction processing for all laser diodes 25 in the color group is performed in units of color groups. It is a figure explaining the 4th method which aims at stabilization of APC control. Here, FIG. 24 is a diagram for explaining a circuit configuration example for generating various pulse signals for executing the fourth hand. FIG. 25 is an example of a time chart (A: basic example / B: modified example) related to output amount correction processing.

  The fourth method shows a mode in which the output of the APC lighting beam switching signal Pcng is stopped during the reference voltage settling period Tst when one scanning period is assigned to one group of light amount correction processing periods. The difference from the third method (part 1) is that all light amount correction is completed within one scanning period, or the light amount correction of one color group is performed within one scanning period, and the scanning period is equal to the number of color groups. Is used to complete all the light amount corrections, and therefore, a correction corresponding to this difference may be added.

  As shown in FIG. 24, first, the counting processing unit 66 and the APC timing control unit 67 are based on the configuration shown in FIG. 20 described above with respect to all the laser diodes 25 in one color group for each scanning period. To change the amount of light so that it can be corrected.

  For example, as shown in FIG. 24, the setting unit 74 of the APC timing control unit 67 sets the output start timing after the active edge of the scanning start signal SOS of the APC lighting beam switching signal Pcng for each color group. The APC lighting beam switching signal Pcng0 having the clocks necessary for executing the light amount correction for all the laser diodes 25 is generated.

  This output start timing is such that the light amount correction is executed in the non-image area within one scanning period from the time when the scanning start signal SOS that is the reference for scanning the next line is output from the image area that forms the image. A predetermined time after the image area.

  The setting unit 74 activates the APC timing setting signal LOAD at the output start timing. As a result, the clock of the APC lighting beam switching signal Pcng is supplied to the counter 76, and the counter 76 starts counting. At this time, the counter 76 first starts the counting operation after loading the count value held in the count value holding unit 77 with the pulse obtained by delaying the APC timing setting signal LOAD by the delay circuit 177 as a trigger. Since this is the first time, “0” is loaded, and counting is started as 1, 2,.

  The count value holding unit 77 may be removed and the count operation may be stopped.

  When the counter 76 finishes counting the number of clocks (eight in this example) required for light amount correction for all the laser diodes 25 in the group, the counter arrival signal CNtarv is sent to the setting unit 74 of the APC timing control unit 67. Output. In response to this, the setting unit 74 inactivates the APC timing setting signal LOAD. Thereby, the APC timing control unit 67 temporarily stops the supply of the clock in the APC lighting beam switching signal Pcng to the counter 76. The count value holding unit 77 takes in the count value (8 in this example) of the counter 76 at the time of inactivity.

  The decoder 78 generates the select signal SEL based on the count result CNTout output from the counter 76 and the count arrival signal CNTarv. At this time, as in the basic example shown in FIG. Is switched to “2” for selecting the light amount setting data DVref for the next color (M color in this example). As a result, the reference signal generation unit 68 switches the light amount setting data DVref to the output amount correction processing unit 52 from the light amount setting data DVref_Y for Y color to the light amount setting data DVref_M for M color.

  It should be noted that, by making necessary circuit modifications, the reference signal Vref can be changed at the start time of the image area as in the modification shown in FIG.

  Thereafter, at the next output start timing, the setting unit 74 activates the APC timing setting signal LOAD. As a result, the clock supply of the APC lighting beam switching signal Pcng to the counter 76 is resumed, and the counter 76 resumes the counting operation. At this time, the counter 76 first starts the counting operation after loading the count value held in the count value holding unit 77 with the pulse obtained by delaying the APC timing setting signal LOAD by the delay circuit 177 as a trigger. Here, “8” is loaded, and counting is restarted as 9, 10,.

  When the counter 76 finishes counting the number of clocks (eight in this example) required for light amount correction for all the laser diodes 25 in the group, the counter arrival signal CNtarv is sent to the setting unit 74 of the APC timing control unit 67. Output. In response to this, the setting unit 74 inactivates the APC timing setting signal LOAD. Thereby, the APC timing control unit 67 temporarily stops the supply of the clock in the APC lighting beam switching signal Pcng to the counter 76. The count value holding unit 77 takes in the count value (8 in this example) of the counter 76 at the time of inactivity.

  The decoder 78 generates the select signal SEL based on the count result CNTout output from the counter 76 and the count arrival signal CNtarv. At this time, the select signal SEL is used for the next color (C color in this example). Switch to “3” for selecting the light amount setting data DVref. As a result, the reference signal generation unit 68 switches the light amount setting data DVref for the output amount correction processing unit 52 from the light amount setting data DVref_M for M color to the light amount setting data DVref_C for C color.

  By repeating such an operation, the APC lighting beam switching signal Pcng having eight clocks for performing light amount correction for all the laser diodes 25 of one color group is sequentially output amount corrected every scanning period. It is supplied to the processing unit 52.

  In synchronization with each scanning start signal SOS, a period (SOS search period) in which the scanning start signal SOS is detected (searched), an image area, and a non-image area are arranged in order, and the non-image area is used for light amount correction. Since it can be used, the light amount correction is executed by performing light amount correction for one color group in one scanning period without continuously performing light amount correction for a plurality of color groups within one scanning period. A period other than the non-image area can be assigned to the reference voltage settling period Tst in which the reference signal Vref becomes stable.

  For example, since the target light amount can be generated by the output amount correction processing unit 52 during printing (that is, the image area), the target light amount is generated in a sufficient time even if the response speed is slow. be able to.

  Therefore, as with the second method and the third method, each time a color group is switched, it is automatically provided without performing timing control that actively performs stop processing or duplication processing. By using the SOS search period and image area to be used as the reference voltage settling period Tst, the settling period stop method can be practically executed.

  In particular, in this example, the decoder 78 outputs the select signal SEL for switching to the light amount setting data DVref for the next color to the switch 85 of the count processing unit 66 immediately after completing the light amount correction of the previous group. Both the SOS search period and the image area can be reliably used as the reference voltage settling period Tst, and there is an advantage that almost all the period until reaching the non-image area can be assigned to the reference voltage settling period Tst.

  Further, the entire non-image area within each scanning period (specifically, after the image area period until the start of the SOS search period) can be assigned to the light amount correction period of each color group, and for all color groups within one scanning period. The response of the control system can be made lower than in the case of executing the light amount correction. By making the response of the control system slow, it becomes possible to obtain a larger margin for noise, so that extremely stable light quantity correction can be realized.

  For example, when the light source 24 is configured by a combination of individual laser diodes 25 instead of a VCSEL, the target light amount corresponding to each laser diode 25 is different even within the same group due to variation in characteristics. Therefore, it is necessary to perform light amount correction using the light amount setting data DVref (reference signal Vref) corresponding to the above in a time division manner.

  In this case, if the light amount correction of each color group is executed using the whole of each non-image area in each scanning period, the correction period per one (for each laser diode 25) can be increased, Accordingly, the margin for the difference between adjacent reference signals Vref is increased, so that it is not necessary to actively provide a stop period each time the reference signal Vref corresponding to each laser diode 25 is switched. This can be dealt with by setting a stop period only for those signals where the difference between adjacent reference signals Vref is large and not stable within one correction period, and then performing light quantity correction.

  Of course, if the light amount correction order is determined by the light amount correction order adjustment unit 61 so that the difference between adjacent target light amounts used in time division becomes as small as possible, even within the same group, within the correction period per unit. It is also possible to avoid the combination of orders that are not stable as much as possible, and set a stop period only for those that cannot be dealt with by changing the order, and then perform the light amount correction to deal with it. As a result, the number of stop period setting points can be reduced, the light amount correction period for each laser diode 25 can be lengthened, and the margin for the adjacent difference can be further increased.

  Even in the same group, when the reference signal Vref is individually switched, it is necessary to make a necessary change to the configuration of the reference signal generation unit 68 so as to be adapted to the switching, but the specific circuit configuration of the change I will omit the explanation.

<Combination with light quantity correction order adjustment method / setting period stop method and settling period overlap method>
FIG. 26 to FIG. 28 illustrate a fourth method to which the settling period stop method for each scanning period in color groups is applied and a combination method of the light amount correction rank adjustment method or the settling period stop method and the settling period overlap method. It is a figure to do. Here, FIG. 26 and FIG. 27 are timing charts related to the light amount correction, and FIG. 28 is a diagram illustrating a circuit modification example adapted to the combination with the settling period overlapping method.

  Also in the fourth method, by adjusting the light amount correction order in color group units so that the difference between adjacent units in color group units is as small as possible, the output amount correction processing unit 52 selects the correction target beam. It becomes possible to easily link.

  Moreover, the settling period stop method and the settling period overlap method can be combined in units of scanning periods. Although the reference voltage settling period Tst already exists within one scanning period, the settling period stopping technique and the settling period overlapping technique are applied in units of scanning periods.

  The basic idea is the same as shown in FIG. First, the light amount correction order adjusting unit 61 corresponds to the target light amount values of the respective colors Y / M / C / K in the initial correction order (Y → M → C → K) indicated by the color group data Dsel0. A difference Δ between the light amount setting data DVref (reference signal Vref) is obtained according to the equation (1).

  Next, the light quantity correction order adjustment unit 61 compares the adjacent differences ΔV1 to ΔV4 of the reference signal Vref with the threshold value ΔVs, and if all of the adjacent differences ΔV1 to ΔV4 are equal to or less than the threshold value Δs, the APC control order is set. The color group data Dsel0 is passed to the color group selection unit 62 as it is as color group data Dsel. On the other hand, if any of the adjacent differences ΔV1 to ΔV4 exceeds the threshold value Δs, the light amount correction order adjustment unit 61 determines that the APC control order (light amount correction order) needs to be changed.

  In the case of four colors, there are 24 combinations of control of the reference signal Vref, so the maximum inter-adjacent difference ΔVn = Δmax in each combination is obtained, and any one of the APC orders that is equal to or less than the threshold value ΔVs may be selected. . At this time, if the maximum ΔVn = Δmax is greater than or equal to the threshold value ΔVs in all the combinations, first, the combination having the minimum Δmax is selected.

  Further, when Δmax is equal to or greater than the threshold value ΔVs, a target light amount cannot be generated in the reference voltage settling period Tst within one scanning period. Therefore, in the next scanning period, the settling period stopping method and the settling period overlapping method are used. Apply. Furthermore, if the target light amount difference is still large enough, a plurality of APC non-execution cycles are assigned.

  As a result, even if there is a large difference between the target light amounts of the four colors, the single output amount correction processing unit 52 can efficiently execute the APC control. For example, when the reference signal Vref of each color before the order change is as shown in FIG. 26, the light amount correction is executed in the order of Y → K → M → C →... As shown in FIG. In this case, the difference Δ of the light amount setting data DVref (reference signal Vref) corresponding to the target light amount value of each color of Y / M / C / K is expressed by Equation (2).

  Thereby, the maximum value Δmax of the difference between adjacent ones can be made smaller than the case where the light amount correction is executed in the order of Y → M → C → K → Y, and the entire stop period can be shortened accordingly. it can. Even if the light amount correction is executed after the reference signal Vref is stabilized, the stop period can be shortened, so that the light amount correction for all the laser diodes 25 can be completed within the non-image region within one scanning period. Become.

  Further, when the target light amount difference is so large that the change in the light amount correction order is insufficient, for example, as shown in FIG. 27A, the clock output of the APC lighting beam switching signal Pcng is stopped in the next scanning period. Thus, the entire scanning period is assigned to a cycle in which APC is not performed. Even if the correction order is changed, if Δmax still exceeds the threshold value ΔVs, the APC control is not performed completely for one scanning period, and the process waits until the reference signal Vref becomes stable.

  After the correction process order is changed so that the target light quantity difference is reduced in the light quantity correction order adjustment unit 61, the reference light quantity difference between the color groups corresponding to the different photosensitive drums 19 is considerably large and is still continuous. If the target light amount difference is greater than or equal to the threshold value, the light amount correction in the light amount correction cycle in the next scanning period is skipped, that is, one scanning period is skipped, waiting for analog follow-up of the reference signal Vref, and the transition of the reference light amount The light amount correction is performed after completion.

  Such stop processing in units of scanning periods can be easily realized by suspending the setting unit 74 from activating the APC timing setting signal LOAD even at the output start timing of the next scanning period. . In short, the activation of the APC timing setting signal LOAD is held for one scanning period. If the target light amount difference is still large enough, it may be held for a plurality of consecutive scanning periods.

  Alternatively, when the target light amount difference is so large that the change of the light amount correction order is insufficient, the clock output of the APC lighting beam switching signal Pcng in the next scanning period is output as shown in FIG. In this scanning period, the processing order may be assigned so that the APC control is performed again for the same group. Even if the correction order is changed, if Δmax still exceeds the threshold value ΔVs, the APC control is performed by overlapping one cycle. Also in this case, in the later APC control, it is possible to wait for the reference signal Vref to become stable.

  After the correction process order is changed so that the target light quantity difference is reduced in the light quantity correction order adjustment unit 61, the reference light quantity difference between the color groups corresponding to the different photosensitive drums 19 is considerably large and is still continuous. When the target light amount difference is equal to or greater than the threshold value, light amount correction is executed in the light amount correction cycle within each scanning period for the scanning period until the analog tracking of the reference signal Vref is completed, and the transition of the reference light amount is not performed. Even after completion, the light amount correction is performed again in the light amount correction cycle within the scanning period. The correction is continued N times until the analog tracking of the reference signal Vref is completed. In short, the light amount correction processing is performed on the same group a plurality of times until the target light amount can be set.

  In the stop process, the light quantity correction process is performed after reaching the target light quantity, so that the light quantity correction process is performed only once after the reference signal Vref becomes stable. The light amount correction process is always performed even at the timing of the light amount correction process in each scanning period until the analog tracking is completed, and the light amount correction process is performed even after reaching the target light amount, that is, the target light amount can be set. The difference is that the light amount correction processing is performed on the same group a plurality of times continuously for the same group.

  In order to obtain a circuit configuration adapted to such overlapping processing in units of scanning periods, the configuration shown in FIG. 24 may be modified. Specifically, as shown in FIG. 28, the count value holding unit 77 has a two-stage configuration, and the output values of the respective count value holding units 77a and 77b are selected according to whether or not the overlap processing is performed. A selection unit 77c is provided. Note that the configuration may be such that the count value holding unit 77a at the previous stage is removed and the count operation is stopped, and only the count value holding unit 77b at the first stage is provided.

  The selection unit 77c passes the count value of the previous count value holding unit 77a to the counter 76 when not performing the duplication processing, and passes the count value of the subsequent count value holding unit 77b to the counter 76 when performing the duplication processing. hand over.

  In this way, in the state shown in FIG. 27B, once counted as 25 to 32, it can be counted again as 25 to 32 in the next scanning period, and the decoder 78 counts the counting result of the counter 76. The select signal SEL adapted to such processing order can be supplied to the switch 85.

  Each of the stop method and the overlap method has an advantage that the light amount correction process can be controlled in a short time even if the minimum value of the target light amount between the groups is a certain value or more. Thereby, even if there is a large difference in the target light amounts of the four colors, the single light amount correction processing unit 52 can efficiently perform the light amount correction process.

  As mentioned above, although this invention was demonstrated using embodiment, the technical scope of this invention is not limited to the range as described in the said embodiment. Various changes or improvements can be added to the above-described embodiment without departing from the gist of the invention, and embodiments to which such changes or improvements are added are also included in the technical scope of the present invention.

  Further, the above embodiments do not limit the invention according to the claims (claims), and all combinations of features described in the embodiments are not necessarily essential to the solution means of the invention. Absent. The embodiments described above include inventions at various stages, and various inventions can be extracted by appropriately combining a plurality of disclosed constituent elements. Even if some constituent requirements are deleted from all the constituent requirements shown in the embodiment, as long as an effect is obtained, a configuration from which these some constituent requirements are deleted can be extracted as an invention.

  For example, in the above-described embodiment, APC control in a four-tandem tandem configuration in which four image forming units 18 are arranged in cascade for four colors (Y, M, C, K) so as to make the image forming apparatus 1 compatible with full color. As described above, the number of image forming units 18 may be configured to be, for example, a triple structure by removing the image forming units 18 for black, or may further add image forming units 18 for other colors. When the monochrome image forming apparatus 1 is used, the image forming unit 18 that uses black toner as a developer and the image forming unit 18 that uses waste toner as a developer may be provided independently. it can.

  In short, if the object to be scanned (photosensitive drum 19 in the previous example) has a different configuration, the plurality of beams emitted from the light source 24 as described above are grouped into a plurality of light beams (light emitting points). ) In a time-sharing manner, scanning each scanning body, in the process, sequentially detecting the light output of each light beam, and each reference value set for each light beam and the corresponding same light beam As long as a mechanism for controlling the light output of the light beam to be a value indicated by the reference value based on the comparison result is adopted, the mechanism of each embodiment described above is appropriately used. It can be adopted.

  In any case, with regard to the APC control (output amount correction processing) described above, any of the above-described embodiments is applicable to any one that includes a plurality of image forming units 18 (that is, the photosensitive drums 19). This mechanism can be adopted as appropriate.

  Of course, the configuration is not limited to a configuration including a plurality of scanned objects such as the photosensitive drum 19, and the output amount of each beam becomes a target value for an apparatus that writes predetermined information to the scanned body using a plurality of beams. By adopting the mechanism of each of the above-described embodiments as appropriate, the reference values for each beam are fetched in a time-sharing manner according to the correction processing order, and the problem between the regular intervals that may occur after switching is improved. What is necessary is just to take the mechanism to do.

1 is a diagram illustrating an outline of a configuration example of an image forming apparatus according to the present invention. It is a figure which shows the detailed structural example of the scanning optical system of an optical scanning device. It is a figure which shows the structural example of the several light beam which a light source radiate | emits. It is a functional block diagram explaining the outline of the control system for implementing the output amount correction process of a light beam. It is a figure which shows the detailed structural example of the control system for implementing the output amount correction process of a light beam. It is a figure explaining the basic operation | movement of a light quantity correction order adjustment part. It is a circuit block diagram which shows the detailed structural example of an APC control part. It is a figure explaining operation | movement of a count process part. It is a figure explaining the basic example of the timing (output amount correction process timing) of each signal at the time of lighting control of each laser diode of a light source. It is a figure explaining the necessity to stop the clock of APC lighting beam switching signal Pcng at the time of switching of a color group. It is a figure explaining the 2nd method (the 1) which aims at stabilization of APC control in the unit of output amount amendment processing to one beam. It is a figure explaining the combination method of the 2nd method (the 1) to which the settling period stop method is applied, and the light quantity correction order adjustment method. It is a figure explaining the 2nd method (the 2) which aims at stabilization of APC control in the unit of output amount amendment processing to one beam. It is a figure explaining the circuit structural example for implement | achieving a 2nd method (the 2). It is a figure explaining the modification of the 2nd method (the 2) which aims at stabilization of APC control in the unit of output amount amendment processing to one beam. It is a figure explaining the example of a circuit structure for implement | achieving the modification of a 2nd method (the 2). It is a figure explaining the 1st example of the 3rd method (the 1) which makes all the light quantity corrections complete within one scanning period, and stabilizes APC control per color group. It is a figure explaining the example of a circuit change for implement | achieving the 1st example of the 3rd method (the 1). It is a figure explaining the 2nd example of the 3rd method (the 1) which makes all light quantity corrections complete within one scanning period, and stabilizes APC control per color group. It is a figure explaining the example of a circuit change for implement | achieving the 2nd example of the 3rd method (the 1). It is a figure explaining the 3rd method (the 2) which makes all the light quantity corrections complete within one scanning period, and stabilizes APC control per color group. It is a figure explaining the example of a circuit change for implement | achieving a 3rd method (the 2). It is a figure explaining the 3rd method (the 1) which applied the settling period stop method, the 3rd method (the 2) which applied the settling period duplication method, and the combination method of the light quantity correction order adjustment method. It is a figure explaining the example of a circuit change for implement | achieving the 4th method which makes light quantity correction | amendment of one color group within one scanning period, and stabilizes APC control per color group. It is an example of the time chart (A: basic example / B: modification) related to the output amount correction process of the 4th method. It is a figure explaining the combination method of the 4th method and the light quantity correction order adjustment method. It is a figure explaining the combination method of the 4th method, the light quantity correction order adjustment method, the settling period stop method, and the settling period overlap method. It is a figure explaining the example of a circuit change for implement | achieving the combination method of the 4th method, the light quantity correction order adjustment method, and the settling period overlap method.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 2 ... Beam output control apparatus, 10 ... Image output part, 18 ... Image forming part, 19 ... Photosensitive drum (an example of to-be-scanned body), 20 ... Optical scanning apparatus, 24 ... Light source, 42 ... SOS sensor 45 ... light quantity detection sensor 50 ... LD control unit 51 ... laser drive unit 52 ... output amount correction processing unit 54 ... device control unit 56 ... image control unit 58 ... image processing unit 60 ... APC Control unit 61 ... Light quantity correction order adjustment unit 62 62 Color group selection unit 62 ... Correction target beam selection unit 64 64 APC lighting beam switching unit 65 65 APC lighting beam switching signal generator 66 66 Count processing unit 67 ... APC timing control unit, 68 ... reference signal generation unit, 70 ... central control unit

Claims (14)

In the process of writing predetermined information on the scanned object by scanning the scanned object with a plurality of beams, the output values of the plurality of beams are compared with the reference values set for the plurality of beams. A beam output control device that executes an output amount correction process based on the comparison result so that the output value of each of the plurality of beams becomes a value indicated by the reference value;
While uptake in a time sharing each reference value set in correspondence with each of the plurality of beams in accordance with the output amount correction processing order of the plurality of beams, said immediately after the switching of the reference value between the switching of the reference value The time required for the reference value to stabilize is corrected so that the subsequent output amount correction processing for the beam is stopped, and after the time has elapsed, the output amount correction processing for the stopped beam is started. A beam output control device comprising an output amount correction processing unit for adjusting timing. In the process of writing predetermined information on the scanned object by scanning the scanned object with a plurality of beams, the output values of the plurality of beams are compared with the reference values set for the plurality of beams. A beam output control device that executes an output amount correction process based on the comparison result so that the output value of each of the plurality of beams becomes a value indicated by the reference value;
While uptake in a time sharing each reference value set in correspondence with each of the plurality of beams in accordance with the output amount correction processing order of the plurality of beams, said immediately after the switching of the reference value between the switching of the reference value The time required for the reference value to stabilize is corrected so that the output amount correction process for the subsequent beam is executed, and after the time has elapsed, the output amount correction process for the subsequent beam is performed again. A beam output control device comprising an output amount correction processing unit for adjusting timing. In the process of scanning the same scanned object with a plurality of beams and scanning the scanned object,
The output amount correction processing unit executes the output amount correction processing for all the beams in a period other than a period in which the information within one scanning period is written on the scanned object, and for each of the scanned objects. after switching of the reference value set, that all of the plurality of beams for scanning the same scanning subjects is so as to correspond to the time, it executes control Kiho positive timing before relating to the time The beam output control apparatus according to claim 1, wherein: The output amount correction processing unit executes the output amount correction processing for all the beams that scan the same scanned object in a period other than a period in which the information in the scanning period is written on the scanned object. The output amount correction processing is executed using a different scanning period for each of the scan objects, and the output amount correction processing in the next scanning period is executed after the output amount correction processing in each scanning period is executed. A reference value for capturing is acquired, and a period from the start of the output amount correction process in the next scanning period is assigned to the time for stopping the output amount correction process of the subsequent beam. The beam output control device according to claim 1. The output amount correction processing unit executes the output amount correction processing for all the beams that scan the same scanned object in a period other than a period in which the information in the scanning period is written on the scanned object. The output amount correction processing is executed using a different scanning period for each of the scan objects, and the output amount correction processing in the next scanning period is executed after the output amount correction processing in each scanning period is executed. A reference value for performing the output amount correction processing in the next scanning period is assigned to the time for stopping the output amount correction processing of the subsequent beam, and the reference after switching value, in units of one scan period, the time or subsequent scanning period for stopping the power compensation processing for all of the beams for subsequent scanning period Nitsu Beam power control device according to claim 1 or 2, characterized in that to set the time to be applied to re-output amount correction processing of the beam of Te. The output amount correction processing unit adjusts the plurality of reference values set to correspond to each of the plurality of beams so that a difference between the reference values before and after switching becomes smaller when handling the reference values in a time division manner. In accordance with the order of beam output amount correction processing, each reference value set corresponding to each of the plurality of beams is acquired in a time-sharing manner, and output amount correction processing is performed for the beam corresponding to the acquired reference value. U
Beam power control device according to claim 1 or 2, characterized and this. The output amount correction processing unit, when a maximum value of differences between reference values before and after switching in the output amount correction processing order after adjustment exceeds a predetermined threshold, the reference between the switching of the reference values The time required for the reference value to stabilize immediately after the value switching is to stop the output amount correction process for the subsequent beam, and after the time has elapsed, the output amount correction for the beam that has been stopped. The beam output control apparatus according to claim 6 , wherein the correction timing is adjusted so as to start processing. The output amount correction processing unit, when a maximum value of differences between reference values before and after switching in the output amount correction processing order after adjustment exceeds a predetermined threshold, the reference between the switching of the reference values The time required for the reference value to stabilize immediately after the value switching is performed by performing the output amount correction process for the subsequent beam. After the time has elapsed, the output amount for the subsequent beam is again obtained. The beam output control device according to claim 6 , wherein the correction timing is adjusted so that the correction process is executed again. In the process of writing predetermined information on the scanned object by scanning the scanned object with a plurality of beams, the output values of the plurality of beams are compared with the reference values set for the plurality of beams. And a beam output control device that generates various signals for executing output amount correction processing so that the output value of each of the plurality of beams becomes a value indicated by the reference value based on the comparison result. And
A correction target beam selection unit that generates and outputs a correction target beam selection signal indicating an output amount correction processing order for each of the plurality of beams;
Each reference value set corresponding to each of the plurality of beams corresponds to the output amount correction processing order of the plurality of beams represented by the correction target beam selection signal output from the correction target beam selection unit. A reference signal generator for time-division conversion and output,
When generating and outputting a correction timing signal for lighting each of the plurality of beams, the time required for the reference value immediately after switching of the reference value between the switching of the reference value is as follows: And a lighting beam setting unit that adjusts the correction timing to stop the output amount correction processing of the subsequent beam and start the output amount correction processing for the beam that has been stopped after the time has elapsed. A beam output control device characterized by that. In the process of writing predetermined information on the scanned object by scanning the scanned object with a plurality of beams, the output values of the plurality of beams are compared with the reference values set for the plurality of beams. And a beam output control device that generates various signals for executing output amount correction processing so that the output value of each of the plurality of beams becomes a value indicated by the reference value based on the comparison result. And
A correction target beam selection unit that generates and outputs a correction target beam selection signal indicating an output amount correction processing order for each of the plurality of beams;
Each reference value set corresponding to each of the plurality of beams corresponds to the output amount correction processing order of the plurality of beams represented by the correction target beam selection signal output from the correction target beam selection unit. A reference signal generator for time-division conversion and output,
When generating and outputting a correction timing signal for lighting each of the plurality of beams, the time required for the reference value immediately after switching of the reference value between the switching of the reference value is as follows: A lighting beam setting unit that executes an output amount correction process for the subsequent beam and adjusts the correction timing so that the output amount correction process for the subsequent beam is performed again after the time has elapsed. A beam output control device characterized by that. When handling by time division each reference value set in correspondence with each of the prior SL plurality of beams, so that the difference in the reference values before and after the switching becomes smaller, the power compensation processing order of the plurality of beams It has a rank adjustment unit to decide ,
The correction target beam selection unit generates and outputs a correction target beam selection signal indicating the output amount correction processing order for each of the plurality of beams based on the output amount correction processing order determined by the order adjustment unit. Ru
Beam power control device according to claim 9 or 10, characterized and this. The beam output control apparatus according to claim 11 , wherein the order adjustment unit determines the output amount correction processing order so that a maximum value of a difference between reference values before and after switching is minimized. The order adjusting unit scans the same scanned object with a plurality of the beams and scans the plurality of scanned objects with respect to the reference value set for each of the scanned objects. The beam output control apparatus according to claim 11 , wherein the output amount correction processing order is determined for each scanning body. The lighting beam setting unit of claims 11 to 13, characterized by including the lighting beam switching function of generating and outputting a switching signal for sequentially turned in time series each of said plurality of beams The beam output control apparatus of any one of Claims.

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