JP4534829B2 - Light control device - Google Patents

Description

  The present invention relates to a light amount control device, and more particularly to a light amount control device that is used in an optical scanning device that scans a surface to be scanned with a plurality of light beams and performs light amount control of each light beam.

  In recent years, in an image forming apparatus adopting an electrophotographic method, a high-speed (high frequency) image clock signal, a polygon mirror that rotates at high speed, and a request for high-speed image formation and high resolution of a formed image, An optical scanning device including a laser driver that modulates a laser beam at high speed is employed.

  In addition, in an image forming apparatus employing an electrophotographic system, multicolor image formation has been put into practical use, and in order to increase the speed of multicolor image formation, a plurality of light beams are separated and scanned on different photoreceptors. Various image forming apparatuses that form full-color images have been proposed.

  In an optical scanning device for increasing the speed of image formation, increasing the resolution of formed images, and creating multicolor images, the number of light emitting points that emit laser beams is increased, and images are scanned by simultaneously scanning multiple laser beams. A technique for forming the above has been proposed. For example, by using a laser diode (hereinafter referred to as “LD”) capable of emitting n laser beams from one chip, the rotational speed of the polygon mirror is changed to an LD that emits one beam. Compared to 1 / n, the speed of scanning on the photosensitive member can be reduced, so that the frequency of the image clock signal can also be reduced.

  In particular, a vertical cavity surface emitting laser (hereinafter referred to as “VCSEL”) can be easily arrayed and can form a large number of light emitting points on a single chip. It is useful as a light source with

  Incidentally, in an electrophotographic image forming apparatus using a laser, automatic light amount control (hereinafter referred to as “APC”) of a laser beam is performed in order to scan with a stable light amount of the laser beam. Usually, APC monitors the amount of light emitted from a laser beam with a light amount detection sensor such as a monitor photodiode (hereinafter referred to as “MPD”), converts the current value corresponding to the monitored light amount into a voltage, and sets the target light amount. This is performed by performing feedback control so that the light quantity of the LD becomes the target light quantity by comparing with a reference voltage according to the above.

  In image forming apparatuses that require high speed, high resolution, and high image quality, the number of laser beams of the light source mounted in the optical scanning apparatus is increased and the amount of light is corrected during the non-image forming period within one scanning period. Must be done. In this case, as the number of laser beams increases, the number of laser beams for controlling the amount of light also increases. However, it is substantially difficult to arrange MPDs for the number of laser beams due to space restrictions and the like. With the MPD, it is desirable to control the light amounts of all the laser beams in time series.

  In particular, when a multicolor image is formed, the target light amount may be different for each color, so individual light amount control is required for each color.

  For this reason, it is conceivable that each color has a reference signal having a reference voltage value corresponding to the target light quantity corresponding to each color and is used by switching the reference signal during APC execution, but the number of signals increases. Therefore, it is not preferable.

Therefore, a technique for reducing the number of transmission lines by serially transmitting the LD bias voltage and the light intensity control reference voltage value using signals with different frequencies and duties, and converting them into analog voltages to control the light intensity is proposed. (For example, refer to Patent Document 1). 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.
JP 2003-248368 A

  However, when serially transmitting signals with different frequencies and duties, it is necessary to use a plurality of frequencies in order to recognize the discrimination of each color by a frequency difference, and a circuit for adjusting the duty is required for each frequency. Therefore, the circuit scale is greatly complicated.

  In addition, since each color is recognized by a frequency difference, it must be a clock signal. Therefore, if the clock signal is transmitted together with image data, there is a risk of adversely affecting each other due to crosstalk with the image signal.

  The present invention has been made in consideration of the above-described facts, and an object of the present invention is to provide a light amount control device capable of performing light amount control of a plurality of light beams with a simple configuration.

In order to achieve the above object, the present invention provides a light source that has a plurality of light emitting points and emits a light beam by lighting each light emitting point, and a plurality of light beams emitted from the light source are a plurality of color groups. In a light quantity control device for controlling the light quantity of each of the plurality of light beams, each of which is used in an optical scanning device having a scanning optical system that classifies and guides and scans the surface to be scanned corresponding to each color. Light detection means for detecting each light quantity of the plurality of light beams; color group selection means for outputting a selection signal representing a color group of the light beam corresponding to each color from a plurality of light emitting points of the light source; outputs a switching signal for sequentially lighting the each light emitting point in a time series, when switching the color groups of the selection signal the color group selection means outputs, analog values of the reference voltage corresponding to the target light A lighting switching means for stopping an output of said switching signal during a predetermined given time as a time to avoid instability when converting the signal, for each of the plurality of color groups, the target amount of light A target light amount output means for outputting a value, and based on the detected light amount, the switching signal, the selection signal, and the target light amount, each of the plurality of light emitting points is time-sequentially such that each light amount becomes a target light amount. And a light amount control means for sequentially controlling the light amounts of the plurality of light beams.

  In the light quantity control device according to the present invention, the light detection means detects each light quantity of the plurality of light beams, and the light quantity control means controls each light quantity of the plurality of light beams. At this time, the lighting switching means outputs a switching signal for sequentially lighting each of the plurality of light emitting points in time series. The color group selection means selects a light beam corresponding to each color from a plurality of light emitting points of the light source, and outputs a selection signal representing a color group for determining the lighting order at the time of light quantity control. The target light amount output means counts a switching signal for sequentially lighting each of the plurality of light emitting points in time series, and outputs a target light amount value for each of the plurality of color groups based on the counted value. Accordingly, a target light amount value for each of a plurality of color groups can be output. Therefore, the light amount control means sequentially turns on each of the plurality of light emitting points in time series so that each light amount becomes the target light amount based on the detected light amount, the switching signal, the selection signal, and the target light amount. The amount of light of each beam is controlled. As a result, the light amount can be controlled only by three kinds of signal outputs of the switching signal by the lighting switching means, the signal indicating the target light amount, and the selection signal indicating the color group, and the configuration is simple without increasing the number of signal lines. It becomes possible to control the amount of light.

  The target light amount output unit has a target light amount value corresponding to the color group, and outputs a target light amount value corresponding to the color group based on the selection signal.

  Each of the plurality of color groups may behave differently on the scanned surface depending on the exposure amount of the light beam. For example, in an image forming apparatus that employs an electrophotographic system, the photosensitive member may be deflected and scanned, and in this case, the sensitivity may be different for each color. Therefore, the target light quantity output means has a target light quantity value corresponding to the color group, and outputs the target light quantity value corresponding to the color group based on the selection signal, thereby obtaining the target light quantity value corresponding to each color. The light quantity of the light beam can be controlled with high accuracy.

  The lighting switching means stops outputting the switching signal for a predetermined time when the color group of the selection signal output from the color group selection means is switched.

  The light quantity control device outputs a target light quantity value for each color group, but the target light quantity value is not immediately stable in the actual circuit configuration even if the change in the target light quantity value for each color group is slight. There is. Therefore, the output of the switching signal is stopped during a predetermined time. By doing so, when the color group is switched, the light amount control of the light beam is stopped, and the light amount control for the unstable target light amount value is not executed, so that the occurrence of a light amount error can be avoided. .

  As described above, according to the present invention, based on the detected light amount, the switching signal, the selection signal, and the target light amount, each of the plurality of light emitting points is sequentially turned on in time series so that each light amount becomes the target light amount. There is an effect that the light amount can be controlled with a simple configuration without increasing the number of signal lines only by the signal output for controlling the light amounts of the plurality of light beams.

  Hereinafter, an example of an embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 shows an image forming apparatus 10 as an image forming apparatus according to the present invention. The image forming apparatus 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. It has.

  On the side of the transfer belt 14, an image is formed to form a black (K) single-color image along the moving direction of the transfer belt 14 when the transfer belt 14 is driven to rotate (direction of arrow A in FIG. 1). Part 18K, image forming part 18C for forming a cyan (C) monochrome image, image forming part 18M for forming a magenta (M) monochrome image, and image for forming a yellow (Y) monochrome image The forming portions 18Y are sequentially arranged at substantially equal intervals.

  Although not shown in detail in FIG. 1, each image forming unit 18 includes a photoconductor drum 19 that is arranged so as to be orthogonal to the moving direction of the transfer belt 14, and around each photoconductor drum 19. Further, an electrostatic latent image formed on the photosensitive drum 19 by a charger for charging the photosensitive drum 19 and an optical scanning device 20 (details will be described later) of a predetermined color (K or C or M or Y). A developing device for developing with toner to form a toner image, a transfer device for transferring the toner image formed on the photosensitive drum 19 to the transfer belt 14, and a cleaning device for removing the toner remaining on the photosensitive drum 19 are sequentially provided. Arranged and configured.

  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 to the transfer material 22 fed between the transport roller 12 </ b> C and the transfer roller 16. 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.

  As shown in FIG. 2, the optical scanning device 20 includes a light source 24 including 32 laser diodes (LD) 25 as light emitting points (FIG. 5), and Y, M, C, K are emitted from the light source 24. Thirty-two light beams are emitted in four groups for forming each monochrome image. The light source 24 may have a configuration in which 32 LDs are composed of a plurality of LD arrays, or may be a configuration in which 32 light beams are emitted from a single package.

  In this embodiment, a vertical cavity surface emitting laser (VCSEL) having a 4 × 8 LD 25 is used as the light source 24. In the present embodiment, the light source 24 has eight LDs 25 in the first row (in FIG. 5, the columns and the rows are represented as (1-1) to (8-1) in order to distinguish each LD 25). ) Is a group in charge of K color. Similarly, eight LDs 25 in the second row (indicated as (1-2) to (8-2) in FIG. 5) are groups in charge of the C color, and eight LDs in the third row. LD25 (indicated as (1-3) to (8-3) in FIG. 5) is a group in charge of M color, and eight LD25s in the fourth row ((1-4) in FIG. 5). ~ (8-4)) is the group responsible for the Y color. Therefore, in this embodiment, eight light beams are scanned on one photosensitive drum 19.

  In this embodiment, the case where the light source 24 having the 4 × 8 LD 25 is used will be described. However, in the present invention, it is sufficient that at least one light beam corresponds to each color. Therefore, a light source 24 such as a VCSEL having at least four LDs 25 can be used as the light source 24.

  The 32 light beams emitted from the light source 24 are converted into parallel luminous fluxes by the collimator lens 26 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. Each is incident on the same reflecting surface of the mirror 28. The rotary polygon mirror 28 is rotated at a high speed in the direction of arrow B in FIG. 2 (rotated at a constant speed with high accuracy) by being transmitted with the driving force of the motor 46 (FIG. 1), and is incident on the same reflecting surface. The 32 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 C in FIG.

  On the light beam exit side of the rotary polygon mirror 28, fθ lenses 32 and 34 (collectively, fθ lens 33) having power only in the main scanning direction are arranged, and the light deflected and reflected by the rotary polygon mirror 28. The beam is refracted by the fθ lenses 32 and 34 so that the beam moves on the outer peripheral surface of the photosensitive drum at a substantially constant speed, and the imaging position in the main scanning direction coincides with the outer peripheral surface of the photosensitive drum. A separation mirror 36 (see also FIG. 1) is arranged on the light beam emission side of the fθ lenses 32 and 34, and a plurality of (32 in this example) light beams incident on the separation mirror 36 are separated from the separation mirror 36. Is reflected to the side where the corresponding image forming unit 18 is located.

  As shown in FIG. 1, cylindrical mirrors 38K, 38C, 38M, and 38Y having power only in the sub-scanning direction are disposed in the vicinity of the image forming units 18K, 18C, 18M, and 18Y. The light beams emitted from the separation mirrors 36 are respectively reflected by the cylindrical mirrors 38 so that the imaging positions in the sub-scanning direction coincide with the photosensitive drums 19, and are respectively reflected on the photosensitive drums 19 of the corresponding image forming units 18. Irradiated. The cylindrical mirror 38 also 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.

  Further, as shown in FIG. 2, on the beam exit side of the fθ lenses 32 and 34, a pickup mirror 40 is located at a position corresponding to an end portion (SOS: Start Of Scan) of the scanning range of the light beam. The SOS sensor 42 is disposed on the light beam emission side of the pickup mirror 40. Of the light beams scanned by the rotary polygon mirror 28, the light beam at a 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 according to the incidence of the light beam, and can detect the scanning start timing for each scanning. The output timing of the image in the scanning direction is synchronized by the output signal of the SOS sensor 42 (hereinafter referred to as SOS signal).

  A half mirror 43 is provided between the collimator lens 14 and the cylindrical lens 16, and a part of the light beam emitted from the light source 24 is reflected by the half mirror 43. A light amount detection sensor 44 (MPD) is provided in the light reflection direction of the half mirror 43, and the light beam reflected by the half mirror 43 enters the light amount detection sensor 44. The light amount detection sensor 44 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 44.

  The light amount detection sensor 44 corresponds to the light detection means of the present invention.

  As shown in FIG. 3, the optical scanning device 20 has a laser drive circuit 50 and a light amount control circuit 52 mounted on a circuit board 30 on which the light source 24 shown in FIG. 2 is mounted. The control circuits 52 are connected to each other. Further, the SOS signal from the SOS sensor 26 is input to the device control unit 54.

  The circuit board 30 including the laser drive circuit 50 and the light amount control circuit 52 is connected to the apparatus control unit 54 by the cable 31. The device control unit 54 controls the operation of the optical scanning device 20 and is connected to a controller 70 that controls the operation of the entire image forming apparatus on which the optical scanning device 10 is mounted. The image data and various data such as the resolution of the image to be formed and the target light amount for each color are input.

  The apparatus control unit 54 includes an image control unit 56 that is responsible for overall control of images. 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. The image processing unit 58 converts the input image data into YMCK color image data (VIDE_Y, VIDEO_M, VIDEO_C, VIDEO_K in FIG. 3) and outputs the converted data.

  The image processing unit 58 generates a lighting signal (in FIG. 3, VIDEO_Y, VIDEO_M, VIDEO_C, VIDEO_K) that turns on / off the LD 32 based on the input image data, and synchronizes with the SOS signal. Output to the laser drive circuit 50. The laser drive circuit 50 can output a light beam modulated based on image data from each LD 32 by lighting each LD 32 based on this lighting signal. The light beam modulated based on the image data output from each LD 32 is scanned by the optical scanning device 10 and applied to the photosensitive member, so that images of eight lines are simultaneously written on the photosensitive member.

  The APC control unit 60 is for instructing the light amount control circuit 52 to control the light amount of each LD 25 of the light source 24. The APC lighting beam switching unit 62, the color group selecting unit 64, and the reference signal generating unit Means 66 is included. These APC lighting beam switching means 62, color group selection means 64, and reference signal generation means 66 are connected to the light quantity control circuit 52.

  The APC lighting beam switching means 62 in the above embodiment corresponds to the lighting switching means of the present invention, the color group selection means 64 corresponds to the color group selection means of the present invention, and the reference signal generation means 66 is the target of the present invention. Corresponds to the light output means. The light quantity control circuit 52 corresponds to the light quantity control means of the present invention.

  The APC control unit 60 selects a light beam corresponding to each color from a plurality of light emitting points of the light source, and outputs a color group selection signal for selecting an APC lighting order at the time of light quantity control. Further, in synchronization with the SOS signal, an APC lighting beam switching signal for controlling the execution of APC and a reference signal (Vref signal) are generated and output to the light quantity control circuit 52.

  Here, an output current corresponding to the amount of light received from the light amount detection sensor 44 is input to the light amount control circuit 52. In addition, a value of a reference voltage corresponding to a light amount targeted for light amount control is input from the APC control unit 60 to the light amount control circuit 52. In the light quantity control circuit 52, the input reference voltage value is converted into a voltage value by a digital-analog converter or the like. The light quantity control circuit 52 compares the reference voltage with the monitor voltage based on the output current corresponding to the received light quantity from the light quantity detection sensor 44, and the result is set so that the difference signal becomes zero, that is, The amount of light emitted from the LD 32 is increased or decreased with respect to the laser drive circuit 40 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 LD 32. This light amount adjustment is performed in a period during which APC execution is permitted.

  By the way, in the present embodiment, since only one light amount detection sensor 44 is provided for the light source 24, the light amount adjustment of each LD 25 is not performed at the same time, but is performed individually. Further, in the present embodiment, the laser drive circuit 50 is based on image data while increasing or decreasing the amount of light beam for each color due to a temperature difference in the image forming apparatus, a variation in sensitivity of each photoconductor, or the like. The LD 25 is turned on to write an image on the photoconductor. Therefore, the light quantity control circuit 52 requires light quantity control using different target values for each color.

  However, in order to perform light amount control using different target values for each color, it is necessary to output a reference signal for each color. If a signal line is used for each reference signal, the number of signal lines increases and the apparatus configuration becomes complicated. Therefore, in the present embodiment, the number of signal lines is reduced by sequentially outputting the reference signals corresponding to the respective colors while selecting the lighting order of the LDs 25 in the light source 24.

  That is, the output signal from the APC control unit 60 includes an APC lighting beam switching signal for switching the LD 25 to be APC, a color group selection signal for selecting an APC lighting order corresponding to each color, and a reference signal (Vref signal). ) And. One of the LDs 25 in the light source 24 is turned on by the APC lighting beam signal, and is controlled to a target light amount that is a reference voltage value that is switched according to the count value of the APC lighting beam switching signal. Accordingly, the light quantity control circuit 52 adjusts the light quantity of each LD 25 by switching the reference signal while switching the LD 25 that is lit to adjust the light quantity in the light source 24.

  As shown in FIG. 4, the APC lighting beam switching means 62 of the APC control unit 60 receives a clock from the controller 70 (clock having a period corresponding to the time required for performing the light amount control of one beam (for example, about 4 μs)). ) Is entered. The APC lighting beam switching means 62 includes a combining unit 72 and a setting unit 74. The combining unit 72 outputs a signal obtained by combining the input clock signal and the setting signal from the setting unit 74 as an APC lighting beam switching signal.

  The setting unit 74 has a predetermined time (for example, a time corresponding to several clocks) sufficient to stably supply a reference voltage corresponding to the reference signal output from the reference signal generation unit 66 so that the light amount control circuit 52 controls the light amount. ) And a time for adjusting the LD 25 for one color (for example, a time corresponding to 8 clocks) are generated. Note that the setting unit 74 indicates the end of one color when the count value from the counter 76 described later indicates the end of one color (the count value of the LD 25 for one color, which is 8 in the present embodiment). The output may be prohibited.

  The color group selection means 64 selects a color group corresponding to each color, and outputs data for setting the lighting order in each color group and the lighting order for each color group as a color group selection signal. The color group selection signal 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 reference signal generating means 66 is connected so that an APC lighting beam switching signal is input. The reference signal generator 66 includes a counter 76 and a decoder 78. The counter 76 is for counting the number of pulses of the input APC lighting beam switching signal. The result is output as count data in the decoder 78.

  In the present embodiment, the light source 24 sequentially turns on 32 LDs 25. At this time, the colors are classified every eight. That is, the counter 76 and the decoder 78 of the reference signal generating means 66 first generate a selection signal “1” representing one color with the count values “1” to “8”, and select the selection signal “4”. "1" to "4", and the selection signals "1" to "4" are cyclically output. The selection signals “1” to “4” correspond to each color of YMCK.

  The output side of the decoder 78 is connected to the control side of the switch 80. The output side of the switch 80 is connected to the light quantity control circuit 52, and the input side is connected to the controller 70 via registers 82 and 84 such as flip-flop circuits. The reference signal generation means 66 is supplied with the reference signal value (DATA in FIG. 4) of each color based on 10-bit data from the controller 70, and the first-stage registers 82Y and 82M for each color. , 82C, and 82K, and second stage registers 82Y, 82M, 82C, and 82K are connected to each of them.

  A write signal (WR in FIG. 4) is inputted to the first-stage registers 82Y to 82K, and the value of the reference signal is written at the input. A read signal (LOAD in FIG. 4) is input to the second-stage registers 84Y to 84K, and the value of the reference signal held in the first-stage registers 82Y to 82K at that input. Is read. The output sides of the second stage registers 84Y to 84K are connected to the switch 80, respectively, and the second stage registers 84Y to 84Y are controlled by a control signal (signal from the decoder 78) input to the switch 80. The value of the reference signal held in any one of 84K is output.

  In FIG. 4, as an example of the output side of the switch 80, the type of control of the optical scanning device 20 (indicated as ROS in FIG. 4) is given. That is, the output signal from the switch 80 is a 10-bit digital signal. Therefore, when the digital signal is transmitted as it is in the optical scanning device 20, the output signal is connected as it is (connection in the upper part of FIG. 4). Further, when the optical scanning device 20 performs control by analog signal processing, the connection is made through the digital-analog converter 86 (connection of the middle part in FIG. 4). Furthermore, when transmitting a reference signal by PWM modulation, it connects via the PWM converter 88 (connection of the lower part of FIG. 4). Note that the tip of the PWM converter 88 may be connected to a PWM circuit as it is, or may be connected to a circuit of the optical scanning device 20 that performs analog processing. The output destination of the switch 80 may be any of these.

  Thus, each LD 25 of the light source 24 is controlled by the APC lighting beam switching means 62, the color group selection means 64, and the reference signal generation means 66 when the light quantity control circuit 52 controls the emitted light quantity to be a predetermined light quantity. It is turned on based on the signal.

  Next, the operation of the present embodiment will be described with reference to FIGS. In the following description, as the light quantity control of each LD 25 of the light source 24, each is adjusted so that the target light quantity is obtained for 32 LD 25 outside the image area before the detection of the SOS signal, that is, in the image non-recording area. (See FIG. 5B).

  As shown in FIG. 5 (E), the light source 24 includes 8 LDs 25 ((1-1) to (8-1)) in the first row of 4 × 8 LDs 25 in the K color and the second row. 8 LD25 ((1-2) to (8-2)) is C color, 8 LD25 ((1-3) to (8-3)) in the 3rd row is M color, 8 in the 4th row The LD 25 ((1-4) to (8-4)) takes charge of the Y color. Each of these 32 LDs 25 is sequentially turned on to adjust the amount of light.

  In the following description, the light quantity is controlled by sequentially turning on the light in the order of YMCK. That is, each of the eight Y-color LDs 25 (1-4) to 25 (8-4) is sequentially turned on, and each of the eight M-color LDs 25 (1-3) to 25 (8-3) is turned on. Sequentially turn on each of the eight C-color LD25 (1-2) to 25 (8-2) and turn on each of the eight K-colored LD25 (1-1) to 25 (8-1). Each is turned on sequentially.

  First, the light quantity control circuit selects a color group corresponding to each color in accordance with a color group selection signal output from the color group selection means, and sets the lighting order within each color group and the lighting order for each color group. In this embodiment, each color group includes ((1-1) to (8-1)) K color, ((1-2) to (8-2)) C color, ((1-3) to (8-3)) is M color, ((1-4) to (8-4)) is Y color, and the lighting order within each group is K color (1-1), (2-1 ), ..., (7-1), (8-1), C color is (1-2, (2-2), ..., (7-2), (8-2), M color (1-3), (2-3), ..., (7-3), (8-3), Y color is (1-4), (2-4), ..., (7 -4) and (8-4), and the lighting order for each color group is set to be the order of Y, M, C, and K colors.

  As shown in FIG. 5D, the APC lighting beam switching means 62 generates an APC lighting beam switching signal so as to continuously output a signal group consisting of eight pulse signals for each color of YMCK four times. The generated APC lighting beam switching signal is output.

  At this time, the reference signal generation means 66 counts the number of pulses of the APC lighting beam switching signal, and detects the color group when the APC lighting beam switching signal output from the APC lighting beam switching means 62 is output. That is, the color group is detected by counting the pulse signal by the counter 76. In the light amount control circuit, the LDs for forming each color set by the color group selection signal are sequentially turned on. That is, when executing APC for Y color, each of the eight LDs 25 (1-4) to 25 (8-4) for Y color is sequentially turned on and M color is selected by the color group selection signal. Each of the eight M-color LD25 (1-3) to 25 (8-3) is turned on sequentially, and each of the eight C-color LD25 (1-2) to 25 (8-2) is turned on. Control is performed so that each of the eight K-color LDs 25 (1-1) to 25 (8-1) is sequentially lit.

  At the same time, the reference signal generating means 66 first outputs a reference signal corresponding to the Y color, and the value of the reference voltage of the corresponding color is output according to the measured number of pulses of the APC lighting beam switching signal. Thus, the switch 80 is switched. Here, the switch 80 is switched in the order of the registers 84Y, 84M, 84C, 84K. Therefore, the reference signal generation unit 66 outputs a reference voltage value corresponding to the target light amount in the order of YMCK colors.

  As shown in FIG. 5C, the light quantity control circuit 52 can obtain a reference voltage obtained by converting the value of the reference voltage corresponding to the target light quantity for each color input from the reference signal generating means 66 into an analog signal. . The light amount control circuit 52 executes light amount control based on the reference voltage and the voltage of the output signal of the light amount detection sensor 44.

  As shown in FIG. 5A, in the present embodiment, when the color is switched, that is, from the lighting of the eighth LD 25 (8-4) of the Y color, the first of the M color that is the next color. During the lighting of the LD 25 (1-3), the APC lighting beam switching signal is not output for a certain period and is stopped. This is predetermined as a stable period of the reference signal in the light quantity control circuit 52.

  That is, the light amount control circuit 52 converts the reference voltage value corresponding to the target light amount for each color input from the reference signal generation unit 66 into an analog signal, but the rising or falling of the reference voltage is not steep. Therefore, if the light amount control is performed during the period, the control result becomes unstable. In order to avoid this, the light amount control is prohibited for a certain period (in FIG. 5, Vref settling time). Similarly, during the lighting of the first LD 25 (1-2) of the C color, which is the next color, from the lighting of the eighth LD 25 (8-3) of the M color, the eighth 25 (8-2) of the C color. ) From the lighting of the first LD 25 (1-1) of K color, it stops without outputting the APC lighting beam switching signal for a certain period.

  Specifically, the APC lighting beam switching means 62 combines the input clock signal (see FIG. 6A) and the setting signal output from the setting unit 74 (see FIG. 6B) to generate the APC. A lighting beam switching signal (see FIG. 6C) is generated. As a result, the light quantity control circuit 52 does not output the APC lighting beam switching signal until the signal stabilizes when the reference voltage value is converted into an analog signal (see FIG. 6D). As a result, the light quantity control circuit 52 can generate a stable reference voltage.

  As described above, according to the present embodiment, an image forming apparatus that forms a full-color image by separating a plurality of light beams emitted from one light source onto different photoconductors and scanning the respective light beams with a simple configuration. The light quantity control of a plurality of beams corresponding to each color can be performed without increasing the control signal.

1 is a block diagram illustrating a schematic configuration of an image forming apparatus according to an embodiment of the present invention. 1 is a schematic configuration diagram of an optical scanning device according to an embodiment of the present invention. It is a schematic block diagram of the control system for controlling the light quantity of LD of the optical scanning device which concerns on embodiment of this invention. It is a block diagram which shows schematic structure of an APC control part. It is explanatory drawing of light quantity control of LD of an optical scanning device, (A) is explanatory drawing of stopping an APC lighting beam switching signal at the time of color switching, (B) is explanatory drawing of the light quantity control period of LD, (C ) Is a characteristic diagram of a reference voltage in the light quantity control circuit, (D) is a characteristic diagram of an APC lighting beam switching signal, and (E) is an LD arrangement diagram. It is a time chart related to light quantity control, (A) shows a clock, (B) shows a setting signal, (C) shows an APC lighting beam switching signal, and (D) shows a reference voltage signal in the light quantity control circuit.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Image forming apparatus 18 ... Image forming part 19 ... Photosensitive drum 20 ... Optical scanning device 24 ... Light source 26 ... Collimator lens 28 ... Rotating polygon mirror 30 ... Circuit board 36 ... Separation mirror 43 ... Half mirror 44 ... Light quantity detection sensor 50 ... Laser drive circuit 52 ... Light quantity control circuit 58 ... Image processing section 60 ... APC control section 62 ... APC lighting beam switching means 64 ... Color group selection means 66 ... Reference signal generation means 70 ... Controller

Claims (2)

A light source having a plurality of light emitting points and emitting a light beam by lighting each light emitting point, and a plurality of light beams emitted from the light source are classified on a scanned surface corresponding to each color for each of a plurality of color groups And a scanning optical system for guiding and deflecting scanning, and a light quantity control device for controlling the light quantity of each of the plurality of light beams.
A light detecting means for detecting each light quantity of the plurality of light beams;
Color group selection means for outputting a selection signal representing a color group of a light beam corresponding to each color from a plurality of light emitting points of the light source;
A switching signal for sequentially lighting each of the plurality of light emitting points in time series is output, and when the color group of the selection signal output by the color group selection unit is switched, the value of the reference voltage corresponding to the target light amount is set. Lighting switching means for stopping the output of the switching signal for a predetermined time as a time for avoiding instability when converting to an analog signal ;
Target light quantity output means for outputting a target light quantity value for each of the plurality of color groups;
Based on the detected light amount, the switching signal, the selection signal, and the target light amount, each of the plurality of light emitting points is sequentially lit in time series so that each light amount becomes a target light amount. A light amount control means for controlling the amount of light respectively;
A light quantity control device comprising:   The target light amount output unit has a target light amount value corresponding to the color group, and outputs a target light amount value corresponding to the color group based on the selection signal. Light quantity control device.

Images