JP2018008488A - Light source drive device, image formation apparatus and light amount control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light source drive device in which a light source forms an appropriate amount of an optical pulse.SOLUTION: A light source drive device which adds a first current value to rising of a drive current of driving a light source and causes the light source to emit an optical pulse by outputting the drive current obtained by subtracting a second current value from falling, includes first current value determination means which outputs the drive current in a first lighting pattern and determines the first current value on the basis of the integrated light amount of the optical pulse. The first current value determination means drives the light source with the drive current obtained by subtracting the second current value with which the falling time of the optical pulse becomes equal to or less than a threshold.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). In Patent Document 1, the second auxiliary is used by using a lighting pattern signal that shortens the time during which the supply of the predetermined current is stopped, compared to the lighting pattern signal used when setting the value of the first auxiliary driving current Iov. An optical drive circuit that sets the value of the drive current Iud is disclosed.

  However, in the conventional OV control and UD control, there is a problem that it is difficult to obtain a target light amount at the time of high-speed lighting accompanying high resolution and high speed of an image. For example, in the case of continuous dots, the light amount of each dot may not affect the target light amount, and may affect the image quality.

  An object of the present invention is to provide a light source driving device in which a light source forms a light pulse with an appropriate light amount.

  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. The driving current is output in a first lighting pattern, and the first current value determining means for determining the first current value based on the integrated light quantity of the light pulse is provided. The current value determining means drives the light source with the drive current from which the second current value at which the fall time of the light pulse is equal to or less than a threshold is reduced.

  It is possible to provide a light source driving device in which a light source forms a light pulse with an appropriate amount of light.

It is an example of the figure explaining the outline of the determination method of OV value in this embodiment. It is an example of the figure explaining the outline of the determination method of UD 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 OV value. It is an example of the figure explaining the determination method of 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. FIG. 10 is an example of a flowchart showing a procedure for determining an optimum OV value and an optimum UD value by the drive control circuit (Example 2). It is an example of the figure explaining determination of the group of the optimal OV value and the optimal UD value.

  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.

<Outline of determination of OV value 1 and UD value 2>
The light source driving apparatus according to the present embodiment determines an optimum OV value by using the optimum OV value.

  FIG. 1 is an example of a diagram illustrating an outline of a method for determining an optimal OV value in the present embodiment. FIG. 1 shows the drive current 4. The light source driving device of the present embodiment turns on the light source for every M dots with the driving current 4 in which the gradually increasing OV value 1 is set in a state where the predetermined UD initial value 2I is set.

The predetermined UD initial value 2I is determined so that the fall time of the optical pulse is less than or equal to the threshold value. That is, the value is sufficiently large so that the falling of the optical pulse is not lost. That is, the drive current 4 that does not slow down the rise time of the light pulse is obtained. The driving current 4 because it has a spacing of M _OV-number fraction of a dot, even UD initial value 2I is sufficiently large, the UD initial value 2I has no influence on the rise of the optical pulses of the subsequent dot. In this state, the light source driving device determines the optimum OV value 1 op as follows.
(1) The light source driving device measures the integrated light quantity when the OV value 1 is zero (FIG. 1A).
(2) The light source driving device increases the OV value 1 by a predetermined amount and measures the integrated light amount (FIG. 1B).
(3) The light source driving device increases the OV value 1 by a predetermined amount and measures the integrated light amount (FIG. 1C).
(4) The light source driving device increases the OV value 1 by a predetermined amount and measures the integrated light amount (FIG. 1 (d)).

  Hereinafter, when the UD value is gradually increased while the UD initial value 2I remains constant and the light source driving device measures the integrated light amount, the optimum OV value 1op at which the measured integrated light amount is equal to or greater than the target integrated light amount is determined. Since the falling edge of the optical pulse is not blurred, it can be estimated that the rising edge of the optical pulse whose measured integrated light quantity is the same as the target integrated light quantity is not blurred. Therefore, an optical pulse having a shape close to a rectangle is obtained as one optical pulse. With the drive current 4 in which the optimum OV determined in this way is set, the light amount of each continuous dot can be brought close to the target light amount.

  As a result, the OV value 1 is optimized (since the optimum OV value is obtained), and then the UD value 2 is optimized.

FIG. 2 is an example of a diagram illustrating an outline of a method for determining the UD value 2 in the present embodiment. FIG. 2 shows the drive current 4. The light source driving device repeats the control to turn on the light source for each dot with the driving current 4 in which the gradually increasing UD value 2 is set while the optimum OV value 1 op is set.
(1) The light source driving device measures the integrated light quantity when the UD value 2 is zero (FIG. 2A).
(2) The light source driving device increases the UD value 2 by a predetermined amount and measures the integrated light amount (FIG. 2B).
(3) The light source driving device increases the UD value 2 by a predetermined amount and measures the integrated light amount (FIG. 2C).
(4) The light source driving device increases the UD value 2 by a predetermined amount and measures the integrated light amount (FIG. 2D).

  Hereinafter, when the integrated light quantity is measured by gradually increasing the UD value 2 while maintaining the optimal OV value 1 op, the UD value 2 is determined so that the measured integrated light quantity is equal to or less than the target integrated light quantity. In a state where the UD value 2 is small, the falling of the light pulse is reduced, so that the surplus light amount is included in the off-lighting interval and the subsequent dots. However, when the UD value 2 is gradually increased, the surplus light amount decreases, and the optimum UD value 2op can be determined in which the surplus light amount hardly influences the integrated light amount even when the light is turned on every other dot. That is, the drive current 4 with a small falling edge of the optical pulse can be obtained. Since the OV value 1 is optimized, the rise of the light pulse is sufficiently small. Therefore, the light amount of the subsequent dots when the dot interval is short can be made close to the target light amount by such a drive current 4.

  Thus, by obtaining the optimum OV value 1 op and the optimum UD value 2 op, an optical pulse having a small rounding at both the rising and falling edges of the optical pulse can be obtained. Considering the case of obtaining the optimal UD value 2op first, when the light is lit at an interval of 1 dot, the UD value easily affects the rise of the optical pulse by affecting the OV value of the subsequent dots. The UD value 2op is susceptible to the OV initial value (provisionally set). For this reason, when, for example, 1 by 1 is lit at the optimum OV value 1 op determined next, it may be necessary to determine the optimum UD value 2 op again. In the present embodiment, the optimum UD value 2op is obtained after the optimum OV value 1op, so that each can be appropriately determined.

<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 pattern is a lighting rule of a light pulse having periodicity. For example, there are a pattern in which light pulses are continuously formed, a pattern in which every other light pulse is formed, a pattern in which every other light pulse is formed, a pattern formed every nth, etc. .

<Configuration example>
FIG. 3 is an example of a schematic configuration diagram of the image forming apparatus. FIG. 3 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. 3 by a rotation mechanism.

  In FIG. 3, 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. 4 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. 5 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. 5 shows main elements of this 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. Further, it has a function of performing control to determine the optimum OV value 1 op and the UD value 2.

  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 detection 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 detection signal. That is, the writing control unit 11 is notified of the timing at which one scan in the main scanning direction starts by the synchronization detection 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 detection signal. That is, an effective scanning period is set between the acquisition of the synchronization detection signal and the next acquisition of the synchronization detection 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 current (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. 5 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. 5 relates to single-color image data, and the color image forming apparatus performs similar scanning for each of the CMYK image data.

  FIG. 6 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, and one ADC (Analog Digital Converter) 33.

  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 current 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 a UD control signal, an OV control signal, a bias control signal, and a light amount control signal that are predetermined by the lighting control signal are output.

  For example, when the lighting control 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 LD21 current. The reference LD 21 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. 5, a part of the laser beam emitted from the LD 21 lit by the driving current 4 is incident on the PD 22, and the PD 22 outputs the PD current to the light source driving device 12. The light source driving device 12 converts the input PD current from an analog value to a digital value by the ADC 33. This digital value is input to the drive control circuit 31 as a light amount feedback control signal.

  The drive control circuit 31 determines the optimal OV value 1op and the optimal UD value 2op using the light amount feedback control signal.

  FIG. 6 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.

  FIG. 7 is an example of a functional block diagram illustrating the function of the drive control circuit 31. The drive control circuit 31 includes an OV value determining unit 40 and a UD value determining unit 50. 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 optimal 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 has a storage unit 49 in which the UD initial value 2I and the target integrated light quantity 46 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 optimum OV value 1op using the UD initial value 2I. 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 optimum OV value 1 op. The optimum OV value determination unit 44 stores 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. The UD value determining unit 50 includes a storage unit 59 in which the optimum OV value 1 op and the target integrated light amount 46 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 and outputs the drive current 4 to the light source 13 in order to determine the optimal UD current using the optimal OV value 1op. 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. 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 optimum UD value 2op. The optimal UD value determination unit 54 stores the optimal UD value 2op in the storage unit 59 of the UD value determination unit 50.

  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. 8 is an example of a diagram illustrating the light pulse 3 and the integrated light quantity. In FIG. 8A, the LD 21 is repeatedly lit at intervals of 1 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. 8A, since the LD 21 repeats turning on and off 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 difficult for the drive control circuit 31 to reproduce the light pulse 3 of one dot by temporally sampling the light intensity, it is determined whether or not the light amount per dot is appropriate by measuring the integrated light amount. it can.

  FIG. 8B is a diagram showing a 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. 8C 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, the lighting pattern (1byM _OV ) when determining the optimal OV value 1op and the lighting pattern (1byM _UD ) when determining the optimal UD value 2op satisfy M _OV <M _UD . Thereby, the optimum OV value 1op can be determined in a state where the rising edge of the light pulse is not easily affected by the UD initial value 2I. Further, the optimum UD value 2op can be determined so that the trailing edge light pulse does not fall.

<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. 9 is an example of a diagram for explaining the effectiveness of conventionally known OV control and UD control. FIG. 9A shows the drive current 4 in which OV control and UD control are not performed, and FIG. 9B shows the light pulse 3 when the light source 13 is driven by the drive current 4 in FIG. 9A. Show.

  As shown in FIG. 9B, 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. 9C shows the drive current 4 subjected to OV control and UD control, and FIG. 9D shows the light pulse 3 when the light source 13 is driven by the drive current 4 of FIG. 9C. . 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. 9D, 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. 10 is an example of a diagram illustrating 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. 10A, 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. 10A is an example in the case where 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. 10B shows the light pulse 3 in the case where continuous dots are formed with the drive current 4 of FIG. As shown in FIG. 10B, 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. Further, in dot 2, the surplus light amount 201 that should have been emitted with respect to dot 1 and the surplus light amount 201 that has been emitted with respect to dot 2 are emitted, so that 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 the integrated light quantity per unit area is different between isolated dots and continuous dots, density unevenness 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 distance between dots 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. 11 is an example of a diagram for explaining the light pulse 3 of the subsequent 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 unevenness of density or the like may occur due to dot blurring or 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 found that setting OV value 1 and UD value 2 is effective, but a method for determining appropriate OV value 1 and UD value 2 has not been known. In the present embodiment, a determination method for appropriately determining the OV value 1 and the UD value 2 as follows is provided.

  FIG. 12 is an example of a diagram illustrating a method for determining the optimum OV value 1 op. 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 1byM _OV. Here, the _MOV is preferably at least 2 (2 dots or more). As the _MOV 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. _{Therefore, M OV} may be to some extent large. 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 with a large UD value 2 such that the shape of the falling light pulse 3 is rectangular, the dot interval is large, so there is little possibility that the UD value 2 will affect the light pulse of the subsequent dots. Therefore, an appropriate optimum OV value 1 op can be determined.

  12A shows the optical pulse 3 when the OV value 1 is zero, and FIGS. 12B to 12D 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 an OV value of 1 in FIG.

  When the integrated light quantity calculation unit 42 calculates the integrated light quantity in each of FIGS. 12A to 12D, 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 quantity should be about the same as the target integrated light quantity when the light pulse 3 becomes rectangular as shown in FIG. Accordingly, the drive control circuit 31 can determine the optimum OV value 1op by gradually increasing the OV value 1 and comparing the integrated light amount with the target integrated light amount.

  Since the drive current 4 having the optimum OV value 1 op 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.

FIG. 13 is an example of a diagram illustrating a method for determining the optimum UD value 2op. 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 optimum OV value 1op. Lighting pattern is a 1byM _UD, in this embodiment the _{M UD} = 1. That is, the UD value 2 is determined so that the integrated light quantity becomes the target integrated light quantity in high-speed lighting with a small dot interval. 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. There is a possibility that the light amount value of the subsequent dots rises and the integrated light amount becomes larger than the target integrated light amount, but the influence of the rising of the light pulse 3 of the subsequent dots disappears as the UD value 2 gradually increases. Note that M _UD = 2 or more, but M _UD <M _ov .

  FIG. 13A shows the optical pulse 3 when the UD value 2 is zero, and FIGS. 13B to 13D show the optical pulse 3 when the UD value 2 is gradually increased. In any case, the OV value 1 is the optimum OV value 1 op. 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, the maximum UD value 2 that does not reduce the rising edge of the light pulse 3 of the subsequent dot can be determined.

  When the integrated light quantity calculation unit 52 calculates the integrated light quantity in each of FIGS. 13A to 13D, the integrated light quantity gradually decreases because the trailing edge becomes small. Further, since the OV value 1 is optimal, there is almost no rise, and when the light pulse 3 becomes rectangular as shown in FIG. 13D, the integrated light amount should be about the same as the target integrated light amount. Therefore, the drive control circuit 31 can determine the optimum UD value 2op by gradually increasing the UD value 2 and comparing the integrated light amount with the target integrated light amount.

  The optimum UD value 2op is determined so that the falling of the light pulse and the rising of the light pulse 3 of the succeeding dot are not slowed in a state where the lighting interval is short. Easy to control the amount of light.

  As described above, the drive control circuit 31 of this embodiment can determine the optimum OV value 1op by gradually increasing the OV value 1 with a sufficiently large UD value 2. Further, the optimal UD value 2op can be determined by gradually increasing the UD value 2 in the 1by1 lighting pattern using the optimal OV value 1op.

<Operation procedure>
FIG. 14 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. 14 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.
First, the drive control circuit 31 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 OV value determination unit 40 performs optimum OV adjustment (S102). Details will be described with reference to FIG. The OV value determination unit 40 performs optimal OV adjustment until the determination of the optimal OV value 1op for all channels is completed (S103).

  Next, in order to perform optimal UD adjustment, the drive control circuit 31 sets a lighting channel (S104).

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

<< Optimal OV adjustment >>
FIG. 15 is an example of a flowchart showing a procedure for optimal OV 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 turns on a periodic illumination pattern of 1byM _ov (S202). The initial OV value 1 is zero.

  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). As a result, the OV value 1 can be determined with a small rise.

  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 optimal OV value determination unit 44 determines the current OV control signal to the optimal OV value 1op (S206). .

Thus, to set the UD initial value 2I in a sufficiently large value, by a sufficiently large dot spacing periodic lighting pattern of 1ByM _OV, the rectangular optical pulses 3 to determine the best OV value 1op can get.

<< Optimal UD adjustment >>
FIG. 16 is an example of a flowchart illustrating a procedure for optimal UD adjustment. First, the current control unit 51 acquires the optimal OV value 1op from the optimal 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 1 (S302). The initial UD value 2 is zero.

  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.

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

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

<Summary>
As described above, it is possible to determine the OV value 1 and the UD value 2 at which the target integrated light quantity can be obtained even in the continuous dots and the subsequent dots that are lit at high speed.

In Example 1, _{M OV} was fixed in the lighting pattern in determining the optimum OV value 1op (1byM _OV). In this _embodiment, it will be described a drive control circuit 31 can determine the optimum OV value 1op while changing the _{M OV.}

  The hardware configuration diagram and functional block diagram of the optical scanning device 2010 are the same as those in the first embodiment.

  FIG. 17 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 (second embodiment). In the description of FIG. 17, differences from FIG. 14 are mainly described.

First, OV value determination unit 40 sets the _{M OV} (S100). The initial value of M _OV is 2. Rather than maintaining a constant M _OV in this embodiment, variably controls the M _OV.

  Next, the drive control circuit 31 sets a lighting channel (CH) (S101).

  Next, the OV value determination unit 40 performs optimum OV adjustment (S102). The content of the optimum OV adjustment may be the same as that in the first embodiment. The OV value determination unit 40 performs optimal OV adjustment until the determination of the optimal OV value 1op for all channels is completed (S103). The processing in steps S104 to S106 of the migration may be the same as that in the first embodiment.

Next, the UD value determination unit 50 increases the _MOV by one (S107).

_Then, until _{M OV} is greater than 10 for example (No in S108), the process returns to step S103, the optimum OV value 1op and optimum UD value 2op is determined.

When M _OV becomes larger than 10 (Yes in S108), the UD value determining unit 50 determines one optimal OV value 1op and optimal UD value 2op from a plurality of sets of optimal OV value 1op and optimal UD value 2op. (S109). In addition, 10 is an example and may be less than 10 or more than 10.

FIG. 18 is an example of a diagram illustrating determination of a set of an optimal OV value 1 op and an optimal UD value 2 op. For example, as shown in FIG. 18, UD value determination unit 50 _calculates the inclination of the optimum OV value 1op and optimum UD value 2op for _{M OV.} UD value determination unit 50 to each of the slope of the optimum OV value 1op and optimum UD value 2OP, calculated in each _{M OV.} It can be estimated that the optimum OV value 1op and the optimum UD value 2op in which the absolute value of the slope is less than the threshold value are stable. The UD value determining unit 50 determines to adopt the first optimal OV value 1op and optimal UD value 2op, in which the slopes of the optimal OV value 1op and the optimal UD value 2op are both less than the threshold. In FIG. 18, when M _OV = 5, the optimal OV value 1op is stable, and when M _OV = 4, the optimal UD value 2op is stable, the optimal OV value determining unit 44 and the optimal UD value determining unit 54 are optimal with M _OV = 5. An OV value of 1 op and an optimum UD value of 2 op are employed.

  Alternatively, the optimum OV value determination unit 44 may adopt an average of the optimum OV values 1op after the slope of the optimum OV value 1op becomes less than the threshold value. The optimal UD value determination unit 54 determines to adopt the average of the optimal UD values 2op after the slope of the optimal UD value 2op becomes less than the threshold.

In the first embodiment, one M _OV is determined in advance to determine the optimal OV value 1 op, and then the optimal UD value 2 op is determined with a 1 by 1 lighting pattern. However, _{M OV} when determining the optimum OV value 1op is not necessarily optimal. In this _embodiment, since the calculated optimum OV value 1op and optimum UD value 2OP by changing the _{M OV,} by estimating the appropriate Mov, you can determine the optimum OV value 1op and optimum UD value 2OP.

<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.

For example, although the OV value is gradually increased in the determination of the optimal OV value 1op, the integrated light amount is calculated using a plurality of OV values, and the OV value that provides the integrated light amount closest to the target integrated light amount is determined as the optimal OV value 1op. May be. The same applies to the determination of the optimal UD value 2op.
In this embodiment, the optimal UD value 2op is determined after determining the optimal OV value 1op. However, the optimal OV value 1op may be determined after the optimal UD value 2op. In this case, the optimal OV value is determined by gradually increasing the UD value with respect to an appropriate OV initial value, and the optimal OV value is determined by gradually increasing the OV value 1 using the optimal UD value 2op. 1 op is determined.

  Further, the optimal OV value 1 op and the optimal UD value 2 op may be determined by changing the output time of the OV control signal and the UD control signal. Further, after determining the optimal UD value 2op, the optimal OV value 1op may be determined again.

  Further, the configuration example in FIG. 7 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.

  In addition, the lighting pattern at the time of determining the optimal OV value 1op is an example of the first lighting pattern, and the lighting pattern at the time of determining the optimal UD value 2op is an example of the second lighting pattern. The OV current or OV value is an example of a first current value, the UD current or UD value is an example of a second current value, and the OV value determination unit 40 is an example of a first current value determination unit. The UD value determining unit 50 is an example of a second current value determining unit.

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

JP 2014-229691 A

Claims (10)

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,
The driving current is output in a first lighting pattern, and has a first current value determining means for determining the first current value based on an integrated light quantity of the light pulse,
The first current value determining means drives the light source with the drive current from which the second current value at which the fall time of the light pulse is equal to or less than a threshold is reduced.   2. The light source driving according to claim 1, wherein the first lighting pattern has a lighting interval such that the second current value at which the falling time of the light pulse is equal to or less than a threshold does not affect the rising of the light pulse. apparatus. The drive current to which the first current value determined by the first current value determining means is added is output in a second lighting pattern having a lighting interval shorter than the first lighting pattern, and the light pulse Second current value determining means for determining the second current value based on the integrated light quantity of
The light source driving device according to claim 1, comprising:   The first current value determining means outputs the drive current with the second current value reduced by changing the first current value in the first lighting pattern, which is about the same as the target integrated light amount. The light source driving device according to claim 1, wherein the first current value at which an integrated light amount is obtained is determined.   The second current value determination means changes the second current value by changing the second current value by changing the drive current to which the first current value determined by the first current value determination means is added. The light source driving device according to claim 3, wherein the second current value that is output in a pattern and that obtains an integrated light amount that is approximately equal to the target integrated light amount is determined.   The light source driving device according to claim 1, wherein the first lighting pattern is a lighting pattern having a lighting interval of 2 dots or more.   The light source driving device according to claim 1, wherein the second lighting pattern is a lighting pattern having a lighting interval of 1 dot. The first current value determining means determines the first current value by changing the lighting interval of the first lighting pattern,
The second current value determining means determines the second current value for each of the first current values,
The light source driving device according to claim 3, wherein the first current value and the second current value that are stable with respect to a change in lighting interval of the first lighting pattern are employed. 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
A first current value determining means for outputting the drive current in a first lighting pattern;
Determining the first current value based on an integrated light quantity of the light pulse, and
The first current value determining means is a light amount control method for driving the light source with the drive current from which the second current value at which the fall time of the light pulse is equal to or less than a threshold is reduced. A light source driving device according to any one of claims 1 to 8,
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.

Images