JP2018041938A - Light source driving device, image forming apparatus, and light intensity control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light source driving device that can reduce the time required for adjustment of an optical pulse.SOLUTION: A light source driving device comprises: smoothing means 36 that smooths a signal detected by optical pulse detection means; first current value adjustment means 40 that adjusts a first current value on the basis of the signal smoothed by the smoothing means; second current value adjustment means 50 that adjusts a second current value on the basis of the signal smoothed by the smoothing means; control means 60 that performs adjustment of at least either one of the first current value or the second current value while dividing the adjustment into plurality; and characteristic changing means 55 that changes the characteristic of the smoothing means when the adjustment of the first current value or the second current value is divided into plurality and performed.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a light source driving device, an image forming apparatus, and a light amount control method.

  In an electrophotographic image forming apparatus, an exposure device using a laser diode or LED as a light source exposes a photosensitive drum based on image data to form a latent image. The developing roller supplies toner while rotating together with the photosensitive drum, thereby creating a toner image by attaching the toner to the photosensitive drum by electrostatic force.

  Since a light source used in such an electrophotographic image forming apparatus emits light by a driving current, it is preferable to form a rectangular light pulse whose driving current waveform corresponds to a pixel (referred to as a dot or a pixel). . However, the optical pulse does not follow the waveform of the drive current due to a delay in responsiveness such as an oscillation delay of the light source. For this reason, the light pulse emitted so as to correspond to the pixel is not rectangular and the amount of light emitted to the pixel is smaller than the target.

  OV (overshoot) control and UD (undershoot) control are known as techniques for improving such a shortage of light quantity (see, for example, Patent Document 1). Patent Document 1 discloses a semiconductor laser control device that adjusts an overshoot current according to a change in drive current and adjusts an undershoot current according to a change in drive current.

  However, the conventional OV control and UD control have a problem that the adjustment time for determining the optimum value of the OV value and the UD value becomes long. That is, since the OV value and the UD value influence each other, it is difficult to simultaneously adjust the optimum value of the OV value and the UD value. For this reason, it is necessary to adjust the OV value and the UD value separately, and the adjustment time becomes long. If the adjustment time is long, it takes time to adjust the light amount when starting up the image forming apparatus or during process control.

  In view of the above problems, an object of the present invention is to provide a light source driving device that can shorten the time required for adjusting a light pulse.

  The present invention relates to a light source driving device that adds a first current value to a rising edge of a driving current for driving a light source, outputs the driving current obtained by subtracting a second current value from the falling edge, and emits a light pulse to the light source. A smoothing means for smoothing the signal detected by the light pulse detecting means, and a first current value for adjusting the first current value based on the signal smoothed by the smoothing means. Adjusting means; second current value adjusting means for adjusting the second current value based on the signal smoothed by the smoothing means; at least the first current value or the second current value; Control means for performing one adjustment in a plurality of times, and a characteristic change for changing the characteristics of the smoothing means when the first current value or the second current value is adjusted in a plurality of times. Means.

  It is possible to provide a light source driving device that can shorten the time required for adjusting the light pulse.

It is an example of the figure explaining the outline of the determination method of OV value in this embodiment. 1 is an example of a schematic configuration diagram of an image forming apparatus. FIG. 3 is an example of a diagram illustrating the formation of a toner image. It is an example of the schematic block diagram of an optical scanning device. It is an example of the hardware block diagram of a light source drive device. It is an example of the functional block diagram explaining the function of a drive control circuit. It is an example of the figure which shows a light pulse and integrated light quantity. It is an example of the figure for demonstrating the effectiveness of OV control and UD control conventionally known. It is an example explaining the drive current and light pulse with respect to a continuous dot when the light quantity of OV control and UD control is not appropriate. It is an example of the figure explaining the light pulse of a subsequent dot when the light quantity of OV control and UD control is not appropriate. It is an example of the figure explaining the determination method of rough adjustment OV value. It is an example of the figure explaining the determination method of rough adjustment UD value. It is an example of the figure explaining the determination method of optimal OV value. It is an example of the figure explaining the determination method of the optimal UD value. It is an example of the flowchart figure which shows the procedure in which a drive control circuit determines the optimal OV value and the optimal UD value. It is an example of the flowchart figure which shows the procedure of optimal OV adjustment. It is an example of the flowchart figure which shows the procedure of optimal UD adjustment. It is an example of the figure which illustrates a rough adjustment filter and a fine adjustment filter typically. It is an example of the figure which compares and demonstrates the influence which a rough adjustment filter and a fine adjustment filter have on PD voltage. It is an example of the flowchart figure which shows the procedure which determines the optimal UD value and the optimal OV value by fine adjustment after determination of the coarse adjustment OV value by rough adjustment. It is an example of the flowchart figure which shows the procedure which determines the optimal OV value and the optimal UD value by fine adjustment after the coarse adjustment UD value is determined.

  Hereinafter, a light source control device for carrying out the present invention and a light amount control method performed by the light source control device will be described with reference to the drawings.

  FIG. 1 is an example of a diagram for explaining an outline of a method for determining an optimum OV value and an optimum UD value according to this embodiment. The light source driving device of the present embodiment determines the optimum OV value and the optimum UD value in a plurality of times. Also, when adjusting in multiple times, a coarse filter and a fine filter are used properly.

  FIG. 1A schematically shows the determination of the coarse OV value and the coarse UD value using the coarse filter, and FIG. 1B shows the optimum OV value and the optimal UD using the fine filter. The determination of the value is shown schematically. The coarse adjustment filter and the fine adjustment filter smooth the detection value of a PD (Photo Detector) that detects the light intensity of the laser diode that emits the light pulse.

  In the determination of the coarse adjustment OV value, the light source driving device gradually increases the OV value 1 while the UD initial value 2I is set, and measures the integrated light quantity of the light pulse. The OV value when the integrated light amount becomes equal to or greater than the target integrated light amount is determined to be the coarse adjustment OV value 1 rp.

  In the determination of the coarse adjustment UD value, the light source driving device gradually increases the UD value 2 in a state where the coarse adjustment OV value 1rp is set, and measures the integrated light quantity of the light pulse. The UD value when the integrated light quantity becomes equal to or less than the target integrated light quantity is determined as the coarse adjustment UD value 2 rp.

  The light source driving device switches from the coarse filter to the fine filter. In determining the optimum OV value, the OV value 1 is gradually increased in a state where the coarse adjustment UD value 2rp is set, and the integrated light quantity of the light pulse is measured. The OV value when the integrated light quantity becomes equal to or greater than the target integrated light quantity is determined to be the optimum OV value 1 op.

  In the determination of the optimum UD value, the light source driving device gradually increases the UD value 2 while the optimum OV value 1op is set, and measures the integrated light quantity of the light pulse. The UD value when the integrated light quantity becomes equal to or less than the target integrated light quantity is determined to be the optimal UD value 2op.

  Since the relation of “rise speed of the coarse filter> rise speed of the fine filter” is established, the determination of the coarse OV value and the coarse UD value is completed in a short time. In the determination of the optimum OV value and the optimum UD value, it is possible to determine the optimum OV adjustment and the optimum UD adjustment with high accuracy by the fine adjustment filter.

  In this way, by shortening the adjustment time at the time of coarse adjustment and increasing the adjustment time at the time of fine adjustment to increase the accuracy, the OV value and the UD value can be optimally adjusted and the overall adjustment time can be shortened. it can.

<Terminology>
An optical pulse refers to light whose intensity changes to a rectangular shape. The light pulse may be repeatedly formed or may be formed once. In addition, the same pattern may be repeated periodically.

  A light source is an element having a function of outputting light. It may be called a light emitting element or the like. Specifically, it is a laser diode (semiconductor diode), LED, or the like.

  The lighting interval is the lighting cycle of the light pulse. For example, the lighting interval of a lighting pattern in which light pulses are continuously lit is zero, the lighting interval of a lighting pattern in which every other light pulse is lit is 1, and lighting in which a light pulse is lit every n times. The lighting interval of the pattern is n.

Smoothing is a process of reducing the divergence value when there is a divergence value in continuous data. As an example, data may be averaged, data that is significantly different from other data may be removed, or the value of other data may be approximated.
<Configuration example>
FIG. 2 is an example of a schematic configuration diagram of the image forming apparatus. FIG. 2 is an example of a schematic configuration diagram of the image forming apparatus 2000. The image forming apparatus 2000 is a tandem multicolor printer that forms a full color image by superimposing four colors (black K, cyan C, magenta M, and yellow Y). The image forming apparatus 2000 includes an optical scanning device 2010 having a function as an exposure device, four photosensitive drums (2030a, 2030b, 2030c, 2030d) sensitive to light, four cleaning units (2031a, 2031b, 2031c, 2031d), There are four charging devices (2032a, 2032b, 2032c, 2032d), four developing rollers (2033a, 2033b, 2033c, 2033d), and four toner cartridges (2034a, 2034b, 2034c, 2034d).

  The image forming apparatus 2000 includes a transfer belt 2040, a transfer roller 2042, a fixing roller 2050, a paper feed roller 2054, a registration roller pair 2056, a paper discharge roller 2058, a paper feed tray 2060, a paper discharge tray 2070, a communication control device 2080, a density. Detector 2245. Further, four home position sensors (2246a, 2246b, 2246c, 2246d) so as to detect the rotation of the respective photosensitive drums (2030a, 2030b, 2030c, 2030d), a printer control device 2090 that controls the above-mentioned units in an integrated manner, etc. It has.

  Hereinafter, when the four photosensitive drums (2030a, 2030b, 2030c, 2030d) are not distinguished, they are collectively referred to as the photosensitive drum 2030. When the four charging devices (2032a, 2032b, 2032c, 2032d) are not distinguished, they are collectively referred to as a charging device 2032. When the four developing rollers (2033a, 2033b, 2033c, 2033d) are not distinguished, they are collectively referred to as a developing roller 2033.

  The communication control device 2080 controls bidirectional communication with a host device (for example, PC: Personal Computer) via a network or the like. For example, a network card such as Ethernet (registered trademark).

  The printer control device 2090 is an information processing device, a microcomputer, or the like, and includes a CPU, a ROM that stores a program written in code readable by the CPU, and various data used when the program is executed, RAM, which is a general purpose memory, an AD conversion circuit for converting analog data into digital data, and the like. The printer control device 2090 controls each unit in response to a print job execution request from the host device and sends image data (image information) included in the print job to the optical scanning device 2010.

  The photosensitive drum 2030a, the charging device 2032a, the developing roller 2033a, the toner cartridge 2034a, and the cleaning unit 2031a operate as a set of devices for forming a single color (for example, black K) image. Such a set of apparatuses may be referred to as an image forming station, and the black image forming station may be referred to as a “K station” for convenience in the following.

  Similarly, the photoconductor drum 2030b, the charging device 2032b, the developing roller 2033b, the toner cartridge 2034b, and the cleaning unit 2031b operate as a set of devices relating to, for example, cyan C image formation, and form an image of cyan. Is sometimes referred to as “C station” for the sake of convenience.

  The photosensitive drum 2030c, the charging device 2032c, the developing roller 2033c, the toner cartridge 2034c, and the cleaning unit 2031c operate as a set of devices for forming magenta M images, for example. Then, for convenience, it may be referred to as “M station”.

  The photosensitive drum 2030d, the charging device 2032d, the developing roller 2033d, the toner cartridge 2034d, and the cleaning unit 2031d operate as a set of devices related to the yellow Y image forming device 2000, and an image forming station that forms a yellow image is described below. Then, for convenience, it may be referred to as “Y station”. Hereinafter, when the toner color is not limited, the image forming station is also simply referred to as a “station”.

  Each photosensitive drum 2030 has a photosensitive layer formed on the surface thereof. That is, the surface of each photoconductor drum 2030 is a surface to be scanned. Each photosensitive drum 2030 is rotated in the direction of the arrow (clockwise) within the plane of FIG. 2 by a rotation mechanism.

  In FIG. 2, in the three-dimensional orthogonal coordinate system of the X axis, the Y axis, and the Z axis, the direction along the longitudinal direction of each photosensitive drum 2030 is the Y axis direction, and the arrangement direction of the four photosensitive drums 2030 is aligned. This direction will be described as the X-axis direction.

  Each charging device 2032 uniformly charges the surface of the corresponding photosensitive drum 2030. Based on the multicolor image information (black image information, cyan image information, magenta image information, yellow image information) from the host device, the optical scanning device 2010 applies a light beam modulated for each color to the corresponding charged light beam. The light is emitted to the surface of the photosensitive drum 2030. As a result, on the surface of each photoconductive drum 2030, the charge is lost only in the portion where the light is emitted, and a latent image corresponding to the image information is formed on the surface of each photoconductive drum 2030. The latent image formed here moves in the direction of the corresponding developing roller 2033 as the photosensitive drum 2030 rotates. A more detailed configuration of the optical scanning device 2010 will be described later.

  By the way, in each photoconductor drum 2030, an area where image information is written is called an “effective scanning area”, an “image forming area”, an “effective image area”, or the like.

  The toner cartridge 2034a stores black toner, and the toner is supplied to the developing roller 2033a. The toner cartridge 2034b stores cyan toner, and the toner is supplied to the developing roller 2033b. The toner cartridge 2034c stores magenta toner, and the toner is supplied to the developing roller 2033c. The toner cartridge 2034d stores yellow toner, and the toner is supplied to the developing roller 2033d.

  As each developing roller 2033 rotates, the toner from the corresponding toner cartridge is thinly and uniformly applied to the surface thereof. Then, when the toner on the surface of each developing roller 2033 comes into contact with the surface of the corresponding photosensitive drum 2030, the toner moves only to the portion where the light is emitted on the surface and adheres thereto. That is, each developing roller 2033 causes toner to adhere to the latent image formed on the surface of the corresponding photosensitive drum 2030 to make it visible. Here, the toner-attached image (toner image) moves in the direction of the transfer belt 2040 as the photosensitive drum 2030 rotates.

  The toner images of yellow Y, magenta M, cyan C, and black K are sequentially transferred onto the transfer belt 2040 at a predetermined timing, and are superimposed to form a color image.

  Recording paper is stored in the paper feed tray 2060. A paper feed roller 2054 is disposed in the vicinity of the paper feed tray 2060, and the paper feed roller 2054 takes out the recording paper one by one from the paper feed tray 2060 and conveys it to the registration roller pair 2056. The registration roller pair 2056 feeds the recording paper toward the gap between the transfer belt 2040 and the transfer roller 2042 at a predetermined timing. As a result, the color image on the transfer belt 2040 is transferred to the recording paper. The recording sheet transferred here is sent to the fixing roller 2050.

  In the fixing roller 2050, heat and pressure are applied to the recording paper, whereby the toner is fixed on the recording paper. The recording paper fixed here is sent to the paper discharge tray 2070 via the paper discharge roller 2058 and is sequentially stacked on the paper discharge tray 2070 functioning as a paper discharge unit.

  Each cleaning unit removes toner (residual toner) remaining on the surface of the corresponding photosensitive drum 2030. The surface of the photosensitive drum 2030 from which the residual toner has been removed returns to the position facing the corresponding charging device 2032 again.

  The density detector 2245 is disposed on the −X side of the transfer belt 2040. The home position sensor 2246a detects a rotation home position in the photosensitive drum 2030a. The home position sensor 2246b detects the home position of rotation in the photosensitive drum 2030b. The home position sensor 2246c detects the home position of rotation in the photosensitive drum 2030c. The home position sensor 2246d detects the rotation home position in the photosensitive drum 2030d.

  In addition, four potential sensors (2247a, 2247b, 2247c, 2247d) are arranged respectively facing the four photosensitive drums 2030, and each potential sensor stores the surface potential information of the opposing photosensitive drum 2030. Detect.

<About the structure around the photosensitive drum>
FIG. 3 is an example for explaining the formation of a toner image. Around the photosensitive drum 2030, a cleaning unit 2031, a charging device 2032, an optical scanning device 2010, a developing unit 2035, a transfer unit 2045, and a separating unit 2046 are arranged. The image forming apparatus also sets an image processing unit that performs necessary image processing on print data, a data reception unit that receives print data from a host device (such as a personal computer or a scanner), and various operation modes of a laser printer. An operation key for operation, an operation panel for displaying various information, and the like are included.

  A laser beam modulated by the optical scanning device 2010 based on image data is emitted to the photosensitive drum 2030 to the photosensitive drum uniformly charged by the charging device 2032, thereby forming an electrostatic latent image on the photosensitive drum. . Next, the developing unit 2035 attaches toner to the photosensitive drum 2030 to form a toner image as a developer image. Next, the transfer unit 2045 transfers the toner image on the photosensitive drum from a paper supply unit to a recording medium (printing paper) 2047 that is fed between the photosensitive drum and the transfer unit 2045 through a paper feed path. Next, the separation unit 2046 separates the recording medium 2047 onto which the toner image has been transferred from the photosensitive drum and conveys the recording medium 2047 to the fixing unit 2051.

  The fixing unit 2051 includes a heating roller that is rotated and heated to a predetermined fixing temperature, a pressure roller that contacts the heating roller and rotates together with the heating roller, a heater that heats the heating roller to a predetermined fixing temperature, and the like. I have. Then, the recording medium on which the toner image is transferred is conveyed while being heated and pressurized by a heating roller and a pressure roller, and the toner image is fixed on the recording medium, thereby forming an image.

  Further, the cleaning unit 2031 removes residual toner by neutralizing the photosensitive drum on which the toner image has been transferred. Thereafter, image formation by the charging device 2032 or the like is performed again.

  FIG. 4 is an example of a schematic configuration diagram of the optical scanning device 2010. The optical scanning device 2010 mainly includes a writing control unit 11, a light source driving device 12, a light source 13, a synchronization detection sensor 14, and a polygon mirror 15. FIG. 4 shows main elements of the present embodiment, and elements other than those shown are omitted.

  The write control unit 11 is realized by hardware such as ASIC or FPGA. The print data acquired from the host device is converted into raster data (bitmap data) by RIP (Raster Image Processor) processing. The image data read by a scanner or the like is raster data. These raster data are subjected to image area separation, color conversion, γ conversion, and the like, and are further subjected to pseudo halftone processing such as dither processing and error diffusion processing, so that 8-bit image data has pixel presence / absence (1 , 0) is converted into screen data.

  The writing control unit 11 outputs a polygon control signal for controlling the rotation speed of the polygon mirror 15 to the polygon mirror 15. Further, the writing control unit 11 outputs a DATA signal indicating timing (pixel clock) corresponding to the pixel and a lighting control signal for requesting lighting in accordance with the timing when there is a pixel to the light source driving device 12. To do.

  The light source driving device 12 turns on or off the light source 13 according to the DATA signal and the lighting control signal from the writing control unit 11. The light source driving device 12 is realized by an information processing device such as an ASIC, FPGA, or microcomputer. The light source driving device 12 performs lighting control of the light source 13 for each scanning line in the main scanning direction based on the DATA signal and the lighting control signal. That is, the light source 13 is turned on when the lighting control signal is turned on, and the light source 13 is turned off when the lighting control signal is turned off.

  When the light source 13 is, for example, an LD 21 (laser diode), the light source driving device 12 is an LD driver. That is, it has a circuit for generating a constant current, an auto power control circuit for keeping the light output constant, a circuit for controlling turning on and off, and the like, and outputs a driving current 4 for driving the LD 21 to the light source 13. That is, the light source driving device 12 has a function of outputting a controlled pulsed driving current 4.

  Further, as will be described later, the light source driving device 12 adds a current corresponding to the OV value 1 to the pulsed driving current 4 and subtracts the current corresponding to the UD value 2 so that a preferable light pulse can be obtained. 4 is output. In addition, it has a function of performing control for determining the optimum OV value 1 op and the optimum UD value 2 op.

  The light source 13 includes an LD 21 and a PD 22 (Photo Detector). The LD 21 emits a laser beam 25 as a front beam toward the polygon mirror 15 and emits a back beam (laser beam) 26 toward the PD 22. This back beam 26 is used in determining the optimum OV value 1 op and the optimum UD value 2 op.

  The laser beam 25 emitted toward the polygon mirror 15 is reflected by the polygon mirror 15 rotating at an angular velocity corresponding to the resolution of the image forming apparatus, and forms an image on the photosensitive drum through the fθ lens, the reflection mirror, and the synchronous reflection mirror. . The broken arrow in the figure indicates the laser beam 25.

  As the polygon mirror 15 rotates, the imaging position on the photosensitive drum moves in the direction of the arrow in the figure. The direction of the arrow is the direction of the cylindrical generatrix that is the shape of the photosensitive drum 2030, and is the main scanning direction of the image.

  The laser beam 25 reflected by the polygon mirror 15 is incident on a synchronous reflection mirror 27 disposed on the scanning line of the photosensitive drum 2030 in the vicinity of a position outside the image forming area. The synchronous reflection mirror 27 reflects the incident laser beam 25 to the synchronous detection sensor 14. The synchronization detection sensor 14 has, for example, a PD, and generates a synchronization signal that is a pulse output when the laser beam 25 is incident. In the configuration shown in the figure, the synchronous reflection mirror 27 is disposed on the scanning start side of the photosensitive drum 2030 on the scanning line. However, synchronous reflection mirrors may be arranged at both ends of the photosensitive drum 2030 on the scanning line.

  The photosensitive drum is scanned once on one surface of the polygon mirror 15, and this is detected by a synchronization signal. That is, the write control unit 11 is notified of the timing at which one scan in the main scanning direction starts by the synchronization signal. The writing control unit 11 can set an effective scanning period that is a period for writing an image on the photosensitive drum 2030 based on the synchronization signal. That is, an effective scanning period is set between the acquisition of the synchronization signal and the next acquisition of the synchronization signal, and the DATA signal and the lighting control signal are generated based on the image data.

  The back beam 26 emitted from the LD 21 is incident on the PD 22 of the light source 13, and the PD 22 outputs a PD voltage (a light amount feedback control signal described later) proportional to the intensity of the back beam 26 to the light source driving device 12. As a result, the light source driving device 12 can perform light amount feedback control.

  Note that the LD 21 of the light source 13 in FIG. 4 may be called a semiconductor laser. The general LD 21 is an edge emitting laser, but a surface emitting laser such as a VCSEL (Vertical Cavity Surface Emitting LASER) may be used. The light source 13 may be an LED. In this case, scanning with the polygon mirror 15 can be made unnecessary by arranging a plurality of LEDs corresponding to the resolution. Further, a plurality of LDs 21 may be arranged for each color light source 13. Each LD 21 of such a light source 13 is called a channel (CH).

  The configuration of FIG. 4 relates to single-color image data, and a color image forming apparatus performs similar scanning for each of CMYK image data.

  FIG. 5 is an example of a hardware configuration diagram of the light source driving device 12. The light source driving device 12 includes a drive control circuit 31, four DACs (Digital Analog Converter) 32, an adder 34, a subtractor 35, one ADC (Analog Digital Converter) 33, and a filter 36.

  The drive control circuit 31 outputs a drive current 4 from which a rectangular light pulse is obtained. Further, the drive control circuit 31 acquires the PD voltage detected by the PD 22 as a light amount feedback control signal, and determines the optimum OV value 1op and the optimum UD value 2op.

  The drive control circuit 31 receives the DATA signal and the lighting control signal from the writing control unit 11 and controls the driving current 4 for lighting the LD 21. The lighting timing is controlled by the DATA signal, and the UD control signal, the OV control signal, the bias control signal, and the light amount control signal are output by the lighting control signal.

  For example, when the DATA signal means lighting, a UD control signal, an OV control signal, a bias control signal, and a light amount control signal are output. When the lighting control signal does not mean lighting, only the bias control signal is output.

  The light amount control signal is a signal for outputting a reference current when the LD 21 is turned on. That is, it is a signal for outputting a current in a state where neither OV control nor UD control is performed. This is a signal corresponding to the current on the upper side of the pulsed drive current 4.

  The bias control signal is a signal for always outputting a constant current to the LD 21 of the light source 13. This is a signal corresponding to the current at the bottom of the pulsed drive current 4. The current flowing by the bias control signal is a current for improving the light emission response of the LD 21. The LD 21 does not emit light unless a current equal to or greater than the threshold value flows. However, by always flowing a current slightly smaller than the threshold value, it is possible to shorten the time until the LD 21 emits light rather than flowing a current exceeding the threshold value from zero.

  The OV control signal is a signal corresponding to the OV value 1 when the drive current 4 rises, and the UD control current is a signal corresponding to the UD value 2 when the drive current 4 falls. Therefore, in this embodiment, the optimum OV control signal and UD control signal are determined. The OV control signal is output for a shorter time than the light amount control signal when the drive current rises. For example, 1/2, 1/3, 1/4, 1/5, etc. of the light quantity control signal. The UD control signal is output for a shorter time than the light amount control signal when the drive current falls. For example, 1/2, 1/3, 1/4, 1/5, etc. of the light quantity control signal. The OV control signal and the UD control signal may not be the same.

  The UD control signal, the OV control signal, the bias control signal, and the light amount control signal are input to the DAC 32 and converted from a digital value to an analog value. This analog value is the current value of the drive current 4. That is, the UD control signal is converted into a UD current, the OV control signal is converted into an OV current, the bias control signal is converted into a bias current, and the light amount control signal is converted into an LD current. The reference LD current and bias current are added to each other by an adder 34 to form a pulsed drive current 4. Further, when the OV current is applied by the adder 34, an OV-controlled drive current 4 is formed. The UD current is subtracted by a subtractor 35 to form a UD controlled drive current 4.

  As described with reference to FIG. 4, a part of the laser beam (back beam 26) emitted from the LD 21 lit by the drive current 4 is incident on the PD 22, and the PD 22 is a PD proportional to the intensity of the back beam 26. The voltage is output to the light source driving device 12. The PD voltage is input to the filter 36, smoothed by the filter 36, and then input to the ADC 33. The filter 36 is a low-pass filter that cuts a high-frequency signal. The ADC 33 converts the PD voltage from an analog value to a digital value. This digital value is input to the drive control circuit 31 as a light amount feedback control signal.

The drive control circuit 31 controls the smoothing strength of the filter 36 by the filter control signal. Specifically, the filter 36 has a cutoff frequency changed to at least one of binary values by a filter control signal. The smoothing strength of the coarse filter is smaller than the smoothing strength of the fine filter. The filter 36 is called a digital filter, and may be configured by a general-purpose information processing device such as a microcomputer even if it is configured by a logic circuit. For example, if the output signal is Y and the input signal is X, the filter 36 calculates the output Y by the following differential equation.
Y (n) = a0 × X (n) + a1 × X (n-1) + a2 × X (n-2) +…
An and the like are coefficients. When at least one of the coefficient and the number of terms is changed, the cutoff frequency is changed. That is, the drive control circuit 31 switches the filter by switching a predetermined coefficient for cutting the high frequency component of the PD voltage as a coarse adjustment filter and a predetermined coefficient for cutting the high frequency component of the PD voltage as a fine adjustment filter. Set to 36. If the coefficient such as an is set to a value other than zero, the number of effective terms can be increased.

  Although the above difference equation is for FIR, the filter 36 may be any of FIR, IIR or active filter.

  The coarse adjustment of the coarse filter means rough adjustment, and means that high accuracy is not required for the smoothed PD voltage. The fine adjustment of the fine adjustment filter means fine adjustment, and means that the accuracy of the PD voltage is preferably high. In the present embodiment, it is sufficient that the PD voltage of the fine filter is more accurate than the PD voltage of the coarse filter. Specifically, the cutoff frequency of the coarse filter is higher than the cutoff frequency of the fine filter. As a result, the PD voltage rises faster in the coarse filter, and the PD voltage rises slower in the fine filter, but the accuracy of the PD voltage is improved.

  Note that the coarse filter and the fine filter may have the same configuration or different configurations. If different, a coarse adjustment filter and a fine adjustment filter may be realized depending on the configuration.

  Further, the filter 36 may be divided into a coarse filter and a fine filter as hardware, and the input destination of the PD voltage may be switched to either the coarse filter or the fine filter by a changeover switch.

  The drive control circuit 31 uses the light amount feedback control signal to determine the coarse adjustment OV value 1rp, the coarse adjustment UD value 2rp, the optimum OV value 1op, and the optimum UD value 2op.

  FIG. 4 shows an example in which the LD 21 of the light source 13 is one, but when there are a plurality of LDs 21, there are as many light quantity control signals, bias control signals, OV control signals, and UD control signals as the number of LDs 21.

<Functions of control drive circuit>
FIG. 6 is an example of a functional block diagram illustrating the function of the drive control circuit 31. The drive control circuit 31 includes a control unit 60, an OV value determination unit 40, and a UD value determination unit 50. The control unit 60 controls the overall procedure for determining the optimum OV value 1 op and the optimum UD value 2 op. That is, the control unit 60 controls whether the optimum OV value is determined once or twice or more and whether the optimum UD value is determined once or twice or more. Further, it instructs the OV value determination unit 40 and the UD value determination unit 50 about the lighting interval M during rough adjustment and fine adjustment. Further, the cutoff frequency of the filter 36 is switched between rough adjustment and fine adjustment.

  The OV value determination unit 40 includes a current control unit 41, an integrated light amount calculation unit 42, a comparison unit 53, and an optimum OV value determination unit 44. Each of these functions is realized by each circuit included in the drive control circuit 31. Alternatively, it is realized by the CPU executing a program and cooperating with the hardware resources of the drive control circuit 31. Further, the OV value determination unit 40 includes a storage unit 49 in which the UD initial value 2I, the target integrated light amount 46, and the coarse adjustment UD value 2rp are stored. The storage unit 49 is realized by a storage device such as a RAM or a flash memory of the drive control circuit 31.

  The current control unit 41 gradually increases the OV current and outputs the drive current 4 to the light source 13 in order to determine the coarse adjustment OV value 1 rp and the optimum OV value 1 op. The bias control signal and the light amount control signal may be constant.

  The integrated light quantity calculation unit 42 acquires the light quantity feedback control signal and calculates the integrated light quantity. The integrated light amount is an integrated value of the light amount per unit time. For example, the amount of light is integrated using the time for which the drive current 4 for 10 dots of image data is formed as a unit time.

  The comparison unit 43 compares the integrated light amount calculated by the integrated light amount calculation unit 42 with the target integrated light amount, and feeds back the comparison result to the current control unit 41 and the optimum OV value determination unit 44. Since the OV value 1 gradually increases, the integrated light amount also gradually increases. Therefore, when “integrated light amount <target integrated light amount”, the current control unit 41 increases the OV value 1 and outputs the drive current 4. The current control unit 41 ends the output of the drive current 4 when “integrated light quantity ≧ target integrated light quantity”.

  When notified from the comparison unit 43 that “integrated light amount ≧ target integrated light amount”, the optimum OV value determination unit 44 acquires the OV value 1 at that time from the current control unit 41. The acquired OV value 1 is the coarse adjustment OV value 1 rp or the optimum OV value 1 op. The optimum OV value determination unit 44 stores the coarse adjustment OV value 1rp and the optimum OV value 1op in the storage unit 59 of the UD value determination unit 50.

  The UD value determination unit 50 includes a current control unit 51, an integrated light amount calculation unit 52, a comparison unit 53, and an optimal UD value determination unit 54. Each of these functions is realized by each circuit included in the drive control circuit 31. Alternatively, it is realized by the CPU executing a program and cooperating with the hardware resources of the drive control circuit 31. Further, the UD value determining unit 50 includes a storage unit 59 in which the coarse adjustment OV value 1rp, the optimum OV value 1op, the target integrated light amount 46, and the optimum UD value 2op are stored. The storage unit 59 is realized by a storage device such as a RAM or a flash memory of the drive control circuit 31.

  The current control unit 51 gradually increases the UD current using the coarse adjustment OV value 1 rp or the optimum OV value 1 op, and outputs the drive current 4 to the light source 13. The bias control signal and the light amount control signal may be constant. The integrated light amount calculation unit 52 is the same as the OV value determination unit 40.

  The comparison unit 53 compares the integrated light amount calculated by the integrated light amount calculation unit 52 with the target integrated light amount, and feeds back the comparison result to the current control unit 51 and the optimum UD value determination unit 54. Since the UD value 2 gradually increases, the integrated light amount also gradually decreases. Therefore, when “integrated light quantity> target integrated light quantity”, the current control unit 51 increases the UD value 2 and outputs the drive current 4. The current control unit 51 ends the output of the drive current 4 when “integrated light quantity ≦ target integrated light quantity”.

  When notified from the comparison unit 53 that “integrated light amount ≦ target integrated light amount”, the optimum UD value determining unit 54 acquires the UD value 2 at that time from the current control unit 51. The acquired UD value 2 is the coarse UD value 2rp or the optimum UD value 2op. The optimal UD value determination unit 54 stores the coarse adjustment UD value 2rp in the storage unit 49 of the OV value determination unit 40 and stores the optimal UD value 2op in the storage unit 59 of the UD value determination unit 50.

  The filter switching unit 55 outputs a filter control signal to the filter 36 in response to an instruction from the control unit 60, and switches whether the filter 36 operates as a coarse filter or a fine filter (the coarse filter and the fine filter are switched). Switch). When determining the coarse adjustment OV value 1 rp and the coarse adjustment UD value 2 rp, the filter 36 is a coarse adjustment filter. When the coarse tuning OV value 1rp and the coarse tuning UD value 2rp are determined, the filter switching unit 55 switches the filter 36 to the fine tuning filter. When the determination of the optimal OV value and the determination of the optimal UD value is completed, the filter 36 is switched to an image forming filter that is an image forming filter. The image forming filter may be the same as the fine adjustment filter, or may be designed as a filter at the time of image formation.

  When the optimum OV value 1op and the optimum UD value 2op are thus determined, the drive control circuit 31 can output the drive current 4 to the light source 13 using the optimum OV value 1op and the optimum UD value 2op.

<About integrated light intensity>
The drive control circuit 31 uses the integrated light amount obtained by integrating the light amount feedback control signal per unit time as the magnitude of the light pulse emitted from the LD 21 of the light source 13. This integrated light quantity will be described.

  FIG. 7 is an example of a diagram illustrating the light pulse 3 and the integrated light quantity. In FIG. 7A, the LD 21 is repeatedly lit at intervals of one dot. Such lighting is referred to as “1by1” lighting. 1 by 1 refers to a lighting pattern in which the interval between lighting is 1 dot. The integrated light amount is obtained by calculating the light amount of the light pulse 3 that is repeatedly turned on in this way as an integrated value per unit time.

  Assuming that the integrated light quantity per unit time when the light is always on is 1, in FIG. 7A, since the LD 21 repeats lighting and extinguishing at intervals of one dot, the integrated light quantity per unit time becomes ½. However, this integrated light quantity is the case of the ideal light pulse 3 in which the light pulse 3 has a rectangular shape. In other words, there is a possibility that an ideal light pulse 3 is obtained when the integrated light quantity becomes 1/2 when the light is lit at 1 by 1. Although it is not easy for the drive control circuit 31 to reproduce the light pulse 3 of one dot by sampling the light intensity with time, it can be determined whether the light amount per dot is appropriate by measuring the integrated light amount. .

  FIG. 7B is a diagram illustrating the light pulse 3 having a 1by3 lighting pattern in which the LD 21 repeats lighting at intervals of three dots. When the light pulse 3 is an ideal rectangular wave, the integrated light amount becomes 1/4. FIG. 7C is a diagram showing a light pulse 3 having a 1by9 lighting pattern in which the LD 21 repeats lighting at intervals of 9 dots. When the light pulse 3 is an ideal rectangular wave, the integrated light amount is 1/10. As described above, the target integrated light amount varies depending on the value of M of the lighting pattern of 1 byM.

  The drive control circuit 31 turns on the LD 21 at 1 byM (M: an integer equal to or larger than 1), and acquires a light amount feedback control signal. Then, the optimum OV value 1 op and the optimum UD value 2 op are determined so that a target integrated light quantity of 1 byM can be obtained.

  In the present embodiment, a lighting pattern (1byM1) for determining the coarse adjustment OV value 1rp and the coarse adjustment UD value 2rp at the time of the rough adjustment, and a lighting pattern (1byM1) at the time of determining the optimal OV value 1op and the optimal UD value 2op at the time of the fine adjustment. 1byM2), there is a relationship of M1> M2. As a result, the coarse adjustment OV value 1 rp and the coarse adjustment UD value 2 rp can be determined at an early stage while the influence of the subsequent dots is small in the coarse adjustment, and the optimum OV is set so that the rise and fall of the light pulse of the subsequent dots is not lost in the fine adjustment. A value 1 op and an optimal UD value 2 op can be determined.

<About OV value 1 and UD value 2>
The effectiveness of the premise OV control and UD control will be described with reference to FIG. That is, FIG. 8 is an example of a diagram for explaining the effectiveness of conventionally known OV control and UD control. 8A shows the drive current 4 in which OV control and UD control are not performed, and FIG. 8B shows the light pulse 3 when the light source 13 is driven by the drive current 4 in FIG. 8A. Show.

  As shown in FIG. 8B, even when a pulsed drive current 4 is applied as a characteristic of the LD 21, the optical pulse 3 does not become a rectangular wave due to the influence of the response delay such as the oscillation delay of the LD 21. That is, there is a delay until the rise reaches a maximum value. Furthermore, there is a delay until the light level becomes zero due to the rise. The falling edge in the light pulse 3 is caused by the time taken for the potential of the light source 13 to transition from the light-on potential to the light-off potential.

  Therefore, a technique for shaping the drive current 4 by OV control and UD control so as to obtain an optical pulse 3 close to a rectangular wave is known. FIG. 8C shows the drive current 4 subjected to OV control and UD control, and FIG. 8D shows the light pulse 3 when the light source 13 is driven by the drive current 4 of FIG. 8C. . The OV control is to give an overshoot when the drive current 4 rises and output a current larger than the light amount control current. The UD control means that an undershoot is given when the drive current 4 falls and a current smaller than the bias control current is output.

  As shown in FIG. 8D, it can be seen that the rising round of the optical pulse 3 is improved by the OV control, and the falling round of the optical pulse 3 is improved by the UD control.

  When the LD 21 is lit, the heat is generated and the temperature changes. For this reason, the drive control circuit 31 is controlled so that the amount of light at the time of lighting is constant by auto power control control.

  As described above, the light pulse 3 can be made close to a rectangular wave by the OV control and the UD control. However, the light amount of the subsequent dots when the continuous dots or the distance between the dots is short as described below may not be the target light amount. It was. This will be described below.

<Light pulse in continuous dots>
FIG. 9 is an example for explaining the drive current 4 and the light pulse 3 for the continuous dots when the light amounts of the OV control and the UD control are not appropriate. The drive control circuit 31 calculates an integrated light amount by a light amount feedback control signal when the LD 21 is driven by the drive current 4. Further, the OV value 1 and the UD value 2 can be determined so that an integrated light amount comparable to the target integrated light amount can be obtained. Therefore, as shown in FIG. 9A, the integrated light quantity of one isolated dot can be appropriately determined.

  However, since the drive control circuit 31 makes a determination based on the integrated light quantity, there is a possibility that the rising and the falling of the dot will be smooth even if the integrated light quantity is appropriate. This is because since the determination is based on the integrated light quantity, it cannot be determined whether or not the shape of the light pulse 3 is appropriate.

  The optical pulse 3 in FIG. 9A is an example when the OV value 1 and the UD value 2 are smaller than ideal values. Since the target integrated light amount is obtained in a state where the rising edge is reduced and the falling edge is reduced, an excessive light amount 201 is generated at the falling portion of the light pulse 3.

  FIG. 9B shows the light pulse 3 in the case where continuous dots are formed with the drive current 4 in FIG. 9A. As shown in FIG. 9B, neither the continuous dot 1 nor the dot 2 can obtain an appropriate amount of light. First, since the surplus light amount 201 is emitted to the dot 2 at the dot 1, the integrated light amount becomes insufficient. In addition, in dot 2, the excessive light amount 201 that should have been emitted to dot 1 is emitted to dot 2, so the integrated light amount becomes excessive.

  Thus, if there is a rounding in the light pulse 3 at the time of falling, the difference in the integrated light quantity occurs between isolated dots and continuous dots. Since there is a difference in the integrated light quantity per unit area between isolated dots and continuous dots, there is a possibility that uneven density or the like may occur.

  Therefore, even if the integrated light amount of one dot is appropriate, in the case of continuous dots, the target light amount may not be obtained for each dot.

<Light quantity of subsequent dots when the dot interval is short>
Next, a description will be given of the optical pulse 3 when the OV value 1 is increased in order to reduce the rising round and the UD value 2 is increased in order to reduce the falling round. In this case, the succeeding dot is affected by the UD control of the previous dot, and the rising edge is rounded.

  FIG. 10 is an example for explaining the light pulse 3 of the succeeding dot when the light amounts of the OV control and the UD control are not appropriate. Since the OV value 1 is set to reduce the rising round and the UD value 2 is set to reduce the falling round, the light pulse 3 of the dot 1 becomes rectangular. However, when the dot interval is close at the time of high-speed lighting (in the figure, 1 by 1), the subsequent dots, dots 2 and 3, are affected by the UD control of the dot 1 and the rising edge is rounded.

  Therefore, for example, even if the OV value 1 and the UD value 2 at which the integrated light quantity becomes the target integrated light quantity is determined in a pattern with a wide interval such as 1by9, the quality of the light pulse 3 is deteriorated during high-speed lighting with a short dot interval. May occur. When the quality of the light pulse 3 is poor, there is a possibility that density unevenness may occur due to dot blurring (decrease in adhesion, deformation of shape, etc.) and a difference in integrated light quantity per unit area.

<Determination of OV value 1 and UD value 2 of this embodiment>
Conventionally, it has been known that setting the OV value 1 and the UD value 2 is effective, but as described with reference to FIG. 10, the OV value 1 and the UD value 2 affect each other. In the present embodiment, as described below, first, the coarse OV value 1 rp and the coarse UD UD with a lighting pattern (at least M1 = 2 dots or more) that does not affect the OV value 1 and UD value 2 in the coarse gradation. The value 2rp is determined. In the fine adjustment after the rough adjustment, the optimum OV value 1op and the optimum UD value 2op are adjusted with M2 = 1 dot. Even in a state where the OV value 1 and the UD value 2 have an influence on each other, a more appropriate optimum OV value and optimum UD value can be determined by fine adjustment.

<< Determination of optimal OV and UD values by coarse adjustment >>
FIG. 11 is an example of a diagram illustrating a method of determining the coarse adjustment OV value 1rp. The current control unit 41 of the OV value determination unit 40 outputs the drive current 4 to the light source 13 while gradually increasing the OV value 1 using the UD initial value 2I. The UD initial value 2I is a UD value 2 at which the fall time of the optical pulse 3 is equal to or less than a threshold value. The fall time is, for example, the time until the light quantity value becomes 1 / n (natural number) from the peak. The UD initial value 2I can be experimentally determined by a person in charge of the image forming apparatus. The UD initial value 2I can take the value of the bias control current at the maximum, but may be the same as the bias control current.

  The lighting pattern is 1 by M1. Here, the coarse tone M1 is preferably at least 2 (2 dots or more). The figure is an example of M1 = 3, but it may be 2 or more. As M1 is larger, the influence of the UD initial value 2I on the rise of the light pulse 3 of the subsequent dot can be reduced. For example, based on the UD initial value 2I, the person in charge or the like decides so that the rise time of the light pulse 3 is less than or equal to the threshold value. The rise time is the time from when the signal reaches 10% of the peak value until it reaches 90%. Even if the UD value 2 is large so that the shape of the falling light pulse 3 is rectangular, if the dot interval is large, the possibility that the UD value 2 affects the light pulse of the subsequent dots is reduced. Therefore, an appropriate coarse adjustment OV value 1 rp can be determined.

  FIG. 11A shows the optical pulse 3 when the OV value 1 is zero, and FIGS. 11B to 11D show the optical pulse 3 when the OV value 1 is gradually increased. In any case, the UD value 2 is the UD initial value 2I. It can be seen that as the OV value 1 increases, the rounding of the rising edge of the optical pulse 3 decreases. For example, the optical pulse 3 has a rectangular shape with the OV value 1 in FIG.

  When the integrated light quantity calculation unit 42 calculates the integrated light quantity in each of FIGS. 11A to 11D, the integral light quantity gradually increases because the rounding at the rise is reduced. Further, since the trailing edge is sufficiently small, the integrated light amount should be approximately the same as the target integrated light amount when the light pulse 3 becomes rectangular as shown in FIG. Accordingly, the drive control circuit 31 can determine the coarse adjustment OV value 1rp by gradually increasing the OV value 1 and comparing the integrated light amount with the target integrated light amount.

  Since the light pulse 3 having the coarse tone OV value 1 rp determined in this way is a rectangular wave, the light amount of each dot of the continuous dots becomes the target light amount, and the influence on the image quality can be reduced. However, these are the results of the coarse adjustment, and since the coarse adjustment OV value 1rp is determined by the UD initial value 2I, the preferable optimum OV value 1op is determined by the fine adjustment after the coarse adjustment UD value 2rp is determined. .

  FIG. 12 is an example of a diagram illustrating a method of determining the coarse adjustment UD value 2rp. The current control unit 51 of the UD value determination unit 50 outputs the drive current 4 to the light source 13 while gradually increasing the UD value 2 using the coarse adjustment OV value 1rp. The lighting pattern is 1 by M1, but M1 during coarse adjustment is set to 2 or more.

  When the UD value 2 is small, the fall of the light pulse is reduced, but since the UD value 2 is small, there is no possibility that the integrated light amount of the subsequent dots becomes smaller than the target integrated light amount. Since M1 at the time of coarse adjustment is a relatively large value, the influence on the subsequent dot rise is not large. Note that M1 may be 2 or more, and M1 at the time of adjusting the coarse adjustment OV value 1rp may be the same as or different from M1 at the time of adjustment of the coarse adjustment UD value 2rp.

  12A shows the optical pulse 3 when the UD value 2 is zero, and FIGS. 12B to 12D show the optical pulse 3 when the UD value 2 is gradually increased. In either case, the OV value 1 is the coarse adjustment OV value 1 rp. It can be seen that as the UD value 2 increases, the trailing edge of the light pulse 3 decreases, and for example, the light pulse 3 has a rectangular shape with a UD value 2 of FIG. That is, it is possible to determine the maximum UD value 2 at which the UD value 2 does not cause the rising of the light pulse 3 of the subsequent dot.

  When the integrated light quantity calculation unit 52 calculates the integrated light quantity in each of FIGS. 12A to 12D, the integrated light quantity gradually decreases because the trailing edge is reduced. Also, since the OV value 1 is optimal, there is almost no rise, and when the light pulse 3 becomes rectangular as shown in FIG. 12D, the integrated light amount should be approximately the same as the target integrated light amount. Therefore, the drive control circuit 31 can determine the coarse adjustment UD value 2rp by gradually increasing the UD value 2 and comparing the integrated light amount with the target integrated light amount. However, these are the results of coarse adjustment, and the light amount of each dot of the subsequent dots during high-speed lighting is adjusted by fine adjustment.

<< Determination of optimal OV and UD values by fine adjustment >>
FIG. 13 is an example of a diagram illustrating a method for determining the optimum OV value 1 op. In the description of FIG. 13, differences from FIG. 11 are mainly described. The optimum OV adjustment at the time of fine adjustment differs from the coarse adjustment in the following two points.
(i) M2 = 1 in 1 by M2 of the lighting pattern.
(ii) The UD value 2 is the coarse adjustment UD value 2 rp determined by the optimum UD adjustment for coarse adjustment.

  Since M2 is 1, the optimum OV value 1op can be determined so that the integrated light quantity at the time of high-speed lighting becomes the target integrated light quantity. Further, since the UD value 2 is the coarse UD value 2rp, the optical pulse is more appropriate (for example, close to a rectangular wave) by the coarse UD value 2rp obtained by the coarse adjustment than when the UD initial value 2I is used. Can be determined easily.

FIG. 14 is an example of a diagram illustrating a method for determining the optimum UD value 2op. In the description of FIG. 14, differences from FIG. 12 are mainly described. The optimum UD adjustment at the time of fine adjustment differs from the coarse adjustment in the following two points.
(i) M2 = 1 in 1 by M2 of the lighting pattern.
(ii) The OV value 1 is the optimum OV value 1 op determined by the fine tuning optimum OV adjustment.

  Since M2 is 1, the optimal UD value 2op can be determined so that the waveform of the subsequent dots during high-speed lighting is a rectangular wave. Further, since the OV value 1 is the optimum OV value 1op determined by fine adjustment, the optimum UD value 2op that can obtain a more appropriate optical pulse (eg, close to a rectangular wave) is determined by the optimum OV value 1op obtained by fine adjustment. It becomes easy to do.

<Operation procedure>
FIG. 15 is an example of a flowchart illustrating a procedure in which the drive control circuit 31 determines the optimum OV value 1op and the optimum UD value 2op. The process of FIG. 15 is executed before one job is executed, for example. However, when the image forming engine is adjusted, the adjustment is performed following the image forming engine adjustment. The adjustment of the image forming engine is control for generating a pattern for adjusting an image forming condition on the transfer belt 2040, reading the pattern with a potential sensor, a density sensor, or the like, and feeding back to the image forming engine. By this control, the density of the toner image is appropriately adjusted. Since the state of the image forming engine changes, the light amount is corrected according to the state after adjustment.
<< Determination of coarse OV value 1rp, coarse UD value 2rp >>
First, the control unit 60 determines the coarse adjustment OV value 1 rp and the coarse adjustment UD value 2 rp. The filter 36 at this time is a coarse adjustment filter. If necessary, the control unit 60 controls the filter switching unit 55 to set the filter 36 as a coarse adjustment filter.

  The control unit 60 sets a lighting channel (CH) (S101). The lighting channel corresponds to each LD 21 when the light source 13 is a multi-beam having a plurality of LDs 21. As the number of LDs 21 increases, the scanning time of the photosensitive drum can be reduced.

  Next, the control unit 60 determines the coarse adjustment OV value 1 rp by the OV value determination unit 40. The control unit 60 instructs the OV value determination unit 40 about the lighting interval M1 during rough adjustment. The OV value determination unit 40 performs optimum OV adjustment for coarse adjustment (S102). Details will be described with reference to FIG. The OV value determination unit 40 performs optimum OV adjustment until the determination of the coarse adjustment OV value 1rp of all channels is completed (S103).

  Next, the control unit 60 determines the coarse adjustment UD value 2rp by the UD value determination unit 50. The control unit 60 instructs the UD value determination unit 50 about the lighting interval M1 during rough adjustment.

  The controller 60 sets a lighting channel in order to perform optimum UD adjustment for coarse adjustment (S104).

  The UD value determination unit 50 performs optimum UD adjustment for coarse adjustment (S105). Details will be described with reference to FIG. The UD value determination unit 50 performs the optimum UD adjustment until the determination of the coarse adjustment UD value 2rp of all channels is completed (S106).

  Next, the control unit 60 controls the filter switching unit 55 to switch the filter 36 from the coarse filter to the fine filter (S107).

<< Determination of optimal OV value 1op and optimal UD value 2op >>
When the filter 36 is switched from the coarse filter to the fine filter, the control unit 60 determines the optimal OV value 1op and the optimal UD value 2op.

  Steps S108 to S113 in FIG. 15 are the same as steps S101 to S106. However, the control unit 60 instructs the OV value determination unit 40 about the lighting interval M2 at the time of fine adjustment, and instructs the UD value determination unit 50 about the lighting interval M2 at the time of fine adjustment.

  In FIG. 15, the optimum OV value 1op and the optimum UD value 2op are determined in two stages of coarse adjustment and fine adjustment, but at least one of coarse adjustment and fine adjustment is performed twice or more (that is, a total of three stages). The final optimal OV value 1 op and the optimal UD value 2 op may be determined. Further, the optimal adjustment of the OV value 1 may be performed three times or more, and the optimal adjustment of the UD value 2 may be performed three times or more. When the adjustment is performed three times or more, it is only necessary that the lighting interval M after the second time is shorter than the first time (first time), and the lighting interval M may be gradually shortened every time the adjustment is repeated.

<Optimal OV adjustment>
FIG. 16 is an example of a flowchart illustrating a procedure for optimal OV adjustment. The procedure for optimal OV adjustment is the same for coarse adjustment and fine adjustment.

<< Optimal OV adjustment for coarse adjustment >>
First, the current control unit 41 reads the UD initial value 2I from the storage unit 49, and sets the UD initial value 2I as a UD control signal (S201). It is assumed that the bias current signal and the light amount control signal are predetermined.

  Next, the current control unit 41 is turned on with a periodic lighting pattern of 1 by M1 (S202). The initial OV value 1 is zero. Moreover, M1 at the time of rough adjustment is 2 or more.

  The integrated light quantity calculation unit 42 integrates the light quantity feedback control signal to calculate the integrated light quantity (S203).

  The comparison unit 43 determines whether or not the integrated light amount is equal to or greater than the target integrated light amount (S204). Thereby, it is possible to determine the OV value 1 that reduces the rounding of the rise of the light pulse.

  When the determination in step S204 is No (No in S204), the current control unit 41 increases the OV control signal by a predetermined amount and turns on the LD 21 (S205). Therefore, the OV value 1 can be gradually increased.

  If the determination in step S204 is Yes (Yes in S204), it can be estimated that the optical pulse 3 has become a rectangular wave, so the optimum OV value determination unit 44 determines the current OV control signal to be the coarse OV value 1rp (S206). ).

  As described above, the UD initial value 2I is set to a sufficiently large value, and the dot interval of the periodic lighting pattern of 1byM1 is increased to some extent, so that the coarsely-tuned OV value at which the rectangular light pulse 3 can be obtained. 1 rp can be determined. Since fine adjustment is performed later, it is not necessary to determine the coarse adjustment OV value 1rp with high accuracy.

<Optimal UD adjustment>
FIG. 17 is an example of a flowchart showing a procedure for optimal UD adjustment. The procedure for optimal UD adjustment is the same for coarse adjustment and fine adjustment.

<< Optimal UD adjustment for coarse adjustment >>
First, the current control unit 51 acquires the coarse adjustment OV value 1rp from the optimum OV value determination unit 44 and sets it as an OV control signal (S301). It is assumed that the bias current signal and the light amount control signal are predetermined. In the case of the multi-beam LD 21, the optimum OV value 1 op determined for each LD 21 is set.

  Next, the current control unit 51 turns on with a periodic lighting pattern of 1 by M1 (S302). The initial UD value 2 is zero. M1 at the time of rough adjustment is 2 or more.

  The integrated light amount calculation unit 52 integrates the light amount feedback control signal to calculate the integrated light amount (S303).

  The comparison unit 53 determines whether or not the integrated light quantity is equal to or less than the target integrated light quantity (S304). As a result, the UD value 2 can be determined in which the trailing edge is reduced.

  When the determination in step S304 is No (No in S304), the current control unit 51 increases the UD control signal by a predetermined amount and turns on the LD 21 (S305). Therefore, the UD value 2 can be gradually increased.

  When the determination in step S304 is Yes (Yes in S304), since it can be estimated that the optical pulse 3 has become a rectangular wave, the optimal UD value determination unit 54 determines the current UD control signal to be the coarse UD value 2rp (S306). ).

  Such control makes it possible to determine the maximum UD value 2 in which the UD value 2 hardly causes the rising of the light pulse 3 of the subsequent dot without making the UD value 2 excessive. Since fine adjustment is performed later, it is not necessary to determine the coarse adjustment OV value 1rp with high accuracy.

  In the case of multi-beams, the coarse adjustment OV value 1 rp and the coarse adjustment UD value 2 rp may have a set value for each channel, or may be an average value of all channels.

<< Optimal OV adjustment for fine adjustment >>
The procedure of the optimum OV adjustment at the time of fine adjustment is the same as that in FIG. However, in step S201, the current control unit 41 sets the coarse adjustment UD value 2rp determined by the UD value determination unit 50 as a UD value (S201).

  Further, the current control unit 41 is lit with a periodic lighting pattern of 1 by M2 (S202), but M2 at the time of fine adjustment is 1. The subsequent procedure may be the same as in rough adjustment. By adjusting with the lighting cycle of 1 by 1, the optimum OV value 1 op in which the light waveform of the subsequent dots during high-speed lighting is close to a rectangular wave can be obtained.

<< Optimal UD adjustment for fine adjustment >>
The procedure of the optimum UD adjustment at the time of fine adjustment is the same as that in FIG. However, in step S301, the current control unit 41 sets the optimum OV value 1op determined by the OV value determination unit 40 as an OV value (S301).

  Further, the current control unit 41 lights up with a periodic lighting pattern of 1 by M2 (S302), but M2 at the time of fine adjustment is 1. The subsequent procedure may be the same as in rough adjustment.

  By adjusting with a lighting cycle of 1 by 1, the optimal UD value 2op in which the light waveform of the subsequent dots during high-speed lighting is close to a rectangular wave can be obtained. Further, the optical pulse can be set to the minimum value that makes the rectangular wave without making the UD value an excessive control value.

<About filters>
FIG. 18 is an example of a diagram schematically illustrating the coarse adjustment filter and the fine adjustment filter. FIG. 18A shows the cutoff frequency fc1 of the coarse filter and the filter output for the time-series signal. Since a rapid change in signal is suppressed by the low-pass filter, when a time-series signal (for example, a constant value) is input, the rise is slow.

  FIG. 18B shows the cutoff frequency fc2 of the fine adjustment filter and the filter output for the time-series signal. There is a relationship of fc1> fc2 between the cutoff frequency fc2 of the fine tuning filter and the cutoff frequency fc1 of the coarse tuning filter.

For the rise time tr and the cut-off frequency fc, tr∝1 / fc
There is a relationship. Accordingly, the rise time of the fine filter is longer than the rise time of the coarse filter. On the other hand, since the high-frequency filter cuts the high-frequency signal more than the coarse-tone filter, a more accurate signal can be obtained.

  FIG. 19 is an example of a diagram for comparing and explaining the influence of the coarse filter and the fine filter on the PD voltage. FIG. 19A shows the PD voltage obtained by the coarse filter, and FIG. 19B shows the PD voltage obtained by the fine filter. The pre-filter PD voltage is a signal obtained by converting the intensity of the back beam into the PD voltage by the PD 22, and the post-filter PD voltage is a signal obtained by smoothing the pre-filter PD voltage by the filter 36. The status indicates an operation performed by the drive control circuit 31.

  The pre-filter PD voltage has a waveform equivalent to an optical pulse, and the post-filter PD voltage becomes a constant voltage after the rise time has elapsed due to smoothing. As described with reference to FIG. 18, the rising speed differs between the coarse adjustment filter and the fine adjustment filter by the filter 36 (for example, cutoff frequency). In the status of FIG. 19, the rise time is described as “PD stabilization time”.

  The integrated light quantity calculation units 42 and 52 start sampling the filtered PD voltage after waiting for the PD stabilization time for each channel. The PD stabilization time differs between the coarse adjustment filter and the fine adjustment filter, but is constant for the coarse adjustment filter and constant for the fine adjustment filter. Therefore, the integrated light quantity calculation units 42 and 52 wait for a predetermined time after the channel is switched.

  After waiting, the integrated light quantity calculation units 42 and 52 perform sampling during the sampling time period and measure it as the integrated light quantity. The sampling time is common to the coarse adjustment filter and the fine adjustment filter, and is determined in advance. The integrated light quantity is obtained from the filtered PD voltage sampled at the sampling time, and based on this, the coarse adjustment OV value 1rp, the coarse adjustment UD value 2rp, the optimum OV value 1op, and the optimum UD value 2op are determined.

  (i) Since the rise of the PD voltage after filtering is accelerated by increasing the cutoff frequency of the filter 36 during coarse adjustment, sampling can be started at an early stage. Thereby, the time required to determine the coarse adjustment OV value 1 rp and the coarse adjustment UD value 2 rp can be shortened.

  (ii) At the time of fine adjustment, the accuracy of the filtered PD voltage can be improved by reducing the cut-off frequency of the filter 36.

  By preparing the coarse adjustment filter and the fine adjustment filter in this way, the overall adjustment time can be shortened even if the optimum OV value 1 op and the optimum UD value 2 op are determined in two stages. That is, at the time of coarse adjustment, the rise of the PD voltage is accelerated by increasing the cutoff frequency of the filter 36, but there is a possibility that high frequency component noise is included in the PD voltage. However, it is sufficient that the approximate OV value and UD value can be determined during rough adjustment. Since the cut-off frequency of the filter 36 is reduced during fine adjustment, the optimum OV value 1 op and the optimum UD value 2 op can be determined so as to obtain a target integrated light quantity.

<When only OV or UD value is determined during coarse adjustment>
In the above embodiment, the coarse adjustment OV value 1rp is determined and the coarse adjustment UD value 2rp is determined at the time of the rough adjustment. However, only the coarse adjustment OV value 1rp may be determined at the rough adjustment, or the coarse adjustment UD. Only the value 2rp may be determined.

  FIG. 20 is an example of a flowchart showing a procedure for determining the optimum UD value and the optimum OV value by fine adjustment after the coarse adjustment OV value by coarse adjustment.

  Steps S101 to S103 are the same as those in FIG. However, after that, the UD value determination unit 50 does not determine the coarse adjustment UD value 2rp by the coarse adjustment.

  When the coarse tuning OV value 1rp is determined, the filter switching unit 55 switches the filter 36 to the fine tuning filter (S107).

  Next, in steps S111 to S113, the optimum UD value 2op is determined using the coarse adjustment OV value 1rp. In steps S108 to S110, the optimum OV value 1op is determined using the optimum UD value 2op.

  As described above, if the coarse adjustment OV value 1rp is determined in the coarse adjustment, the fine adjustment can perform the optimal UD adjustment using the coarse adjustment OV value 1rp, and the optimal OV value 1op using the optimal UD value 2op. Can be determined. Therefore, since the OV value is adjusted twice and the UD value is adjusted once, the optimum value can be determined by the adjustment operation at least three times.

  In addition, as shown in FIG. 21, the optimum UD adjustment may be performed first with coarse adjustment. FIG. 21 is an example of a flowchart illustrating a procedure for determining the optimum OV value and the optimum UD value by fine adjustment after the coarse adjustment UD value is determined.

  First, the OV value determination unit 40 does not determine the coarse adjustment OV value 1rp by coarse adjustment. First, in steps S104 to S106, the coarse adjustment UD value 2rp is determined. The processing is the same as steps S104 to S106 in FIG. The OV value 1 when determining the coarse adjustment UD value 2rp is a predetermined OV initial value.

  When the coarse adjustment UD value 2rp is determined, the filter switching unit 55 switches the filter 36 to the fine adjustment filter (S107).

  Next, in steps S108 to S110, the optimum OV value 1op is determined using the coarse adjustment UD value 2rp. In steps S111 to S113, the optimum UD value 2op is determined using the optimum OV value 1op.

  As described above, if the coarse UD value 2rp is determined in the coarse adjustment, the fine tune can perform the optimal OV adjustment using the coarse UD value 2rp, and the optimal UD value 2op using the optimal OV value 1op. Can be determined. Therefore, since the OV value is adjusted once and the UD value is adjusted twice, the optimum value can be determined by the adjustment operation at least three times.

<Summary>
Since the light source driving device 12 of the present embodiment determines the UD value 2 after the determination of the OV value 1, the OV value 1 and UD value 2 that can obtain the target integrated light quantity even in the continuous dots and the subsequent dots that are lit at high speed. Can be determined.

  Further, when determining at least one of the OV value 1 or the UD value 2 in a plurality of times, in the determination of the first OV value 1 or the UD value 2, the filter cutoff frequency is large, so the coarsely adjusted OV value in a short time. 1 rp and coarse tone UD value 2 rp can be determined. In the second determination of the OV value 1 or the UD value 2, since the filter cutoff frequency is small, the optimal OV value 1op and the optimal UD value 2op can be determined with higher accuracy.

<Other application examples>
The best mode for carrying out the present invention has been described above with reference to the embodiments. However, the present invention is not limited to these embodiments, and various modifications can be made without departing from the scope of the present invention. And substitutions can be added.

  Further, the configuration example in FIG. 6 and the like is divided according to main functions in order to facilitate understanding of processing by the light source driving device. The present invention is not limited by the way of dividing the processing unit or the name. Further, the processing of the light source driving device can be divided into more processing units according to the processing content. Moreover, it can also divide | segment so that one process unit may contain many processes.

  The filter 36 is an example of a smoothing unit, the OV value determining unit 40 is an example of a first current value adjusting unit, and the UD value determining unit 50 is an example of a second current value adjusting unit. The unit 60 is an example of a control unit, the filter switching unit 55 is an example of a characteristic changing unit, the PD 22 is an example of a detection unit, the OV value is an example of a first current value, and the UD value is a second value. It is an example of the current value.

DESCRIPTION OF SYMBOLS 11 Write control part 12 Light source drive device 13 Light source 40 OV value determination part 41 Current control part 42 Integrated light quantity calculation part 43 Comparison part 44 Optimum OV value determination part 46 Target integrated light quantity 50 UD value determination part 60 Control part

Japanese Patent Laid-Open No. 2015-103680

Claims (8)

A light source driving device that adds a first current value to a rising edge of a driving current for driving a light source, outputs the driving current obtained by subtracting a second current value from the falling edge, and emits a light pulse to the light source,
Smoothing means for smoothing the signal detected by the light pulse detection means;
First current value adjusting means for adjusting the first current value based on the signal smoothed by the smoothing means;
Second current value adjusting means for adjusting the second current value based on the signal smoothed by the smoothing means;
Control means for performing at least one adjustment of the first current value or the second current value in a plurality of times;
Characteristic changing means for changing the characteristics of the smoothing means when the first current value or the second current value is adjusted in a plurality of times, and
A light source driving device. When the control means adjusts the first current value divided into a plurality of times, the characteristic changing means increases the smoothing strength of the smoothing means in the adjustment after the initial adjustment at least,
2. When the control means adjusts the second current value in a plurality of times, the characteristic changing means increases the smoothing strength of the smoothing means in an adjustment after at least an initial adjustment. The light source driving device according to 1. The control means adjusts the first current value in two steps,
The light source driving apparatus according to claim 2, wherein the control unit adjusts the second current value once. The control means adjusts the first current value in two steps,
The light source driving apparatus according to claim 2, wherein the control unit adjusts the second current value in two steps. The first current value adjusting means adjusts the first current value based on an integrated light amount of the signal when the drive current is output at a predetermined lighting interval.
When the first current value is adjusted in two steps, the first current value adjusting means adjusts the drive current in the second adjustment more than at least the lighting interval of the drive current in the first adjustment. The light source driving device according to claim 3 or 4, wherein the lighting interval is shortened. The second current value adjusting means adjusts the second current value based on an integrated light amount of the signal when the driving current is output at a predetermined lighting interval.
When the second current value is adjusted in two steps, the second current value adjusting means is configured to adjust the driving current in the second adjustment more than the lighting interval of the driving current in the first adjustment. The light source driving device according to claim 4, wherein the lighting interval is shortened. A light amount control method for a light source driving device that emits a light pulse to the light source by adding the first current value to the rising edge of the driving current for driving the light source and outputting the driving current obtained by subtracting the second current value from the falling edge. Because
Smoothing means smoothing the signal detected by the light pulse detection means;
A first current value adjusting means adjusting the first current value based on the signal smoothed by the smoothing means;
A second current value adjusting unit adjusting the second current value based on the signal smoothed by the smoothing unit;
A step in which the control means adjusts at least one of the first current value or the second current value in a plurality of times;
When the characteristic changing means adjusts the first current value or the second current value divided into a plurality of times, changing the characteristic of the smoothing means;
A method for controlling the amount of light. A light source driving device according to any one of claims 1 to 6,
A developing unit for developing the latent image formed by the light source driving device with toner;
An image forming apparatus having a paper feed unit and a paper discharge unit.

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