JP2011152744A - Optical scanner, image forming apparatus, control method, and program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical scanner reducing a noise level by shifting the timing of noise occurrence, and also to provide an image forming apparatus, a control method and a program. <P>SOLUTION: The image forming apparatus is equipped with: a semiconductor laser having a plurality of laser diodes configured to attain blinking control of light-on and light-off, based on image data. The rising edges of image data corresponding to the rising timing of lighting of each laser diode of the semiconductor laser, and the falling edges of image data corresponding to the falling timing of lighting of the laser diode, are detected. When the difference between the number of detected simultaneously rising edges of the image data and the number of detected simultaneously falling edges of the image data is a preset number or more, the rising timing of the simultaneously rising edges and the falling timing of the simultaneously falling edges are controlled. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention is mounted on an image forming apparatus that forms an image by transferring a visible image (image) of a latent image formed by scanning a photoconductor with laser beams emitted from a plurality of light sources onto a recording sheet. The present invention relates to an optical scanning device, an image forming apparatus, a control method, and a program.

  In recent years, with the increase in image formation speed and image quality of electrophotographic image forming apparatuses (printers, copiers), the productivity of exposure units that scan a photoreceptor with a laser beam to form a latent image Has been regarded as important. The productivity of the exposure unit corresponds to the number of exposure lines per unit time when the photosensitive member is scanned with a laser beam. In order to increase the productivity of the exposure unit, exposure is performed for one scan by increasing the rotation speed of the polygon motor that rotates the polygon mirror that reflects the laser beam emitted from the light source to the photoreceptor and increasing the number of polygon mirror surfaces. It is conceivable to increase the number of laser beams.

  However, the rotational speed of the polygon motor is approaching the limit from the technical aspect, and with the increase in the rotational speed of the polygon motor, there are adverse effects such as a rise in temperature of the polygon motor, noise during driving, and an increase in cost. Yes. In addition, increasing the number of polygon mirror surfaces reduces the scanning angle of the laser beam with respect to the photosensitive member, so that it is necessary to increase the optical path length in order to obtain the same exposure width, which increases the size and cost of the image forming apparatus. Invite the rise. For this reason, in recent years, a multi-beam laser diode has been developed as a light source mounted on an exposure unit of an image forming apparatus, and the number of beams is further increased from 2 beams to 4 beams. Hereinafter, in the background art and the problem to be solved by the invention described later, description will be made on the premise of a multi-beam laser diode.

  In this multi-beam trend, the development of surface emitting laser diodes (hereinafter referred to as VCSELs) that are more suitable for multi-beams has been developed from the conventional edge emitter laser diodes that are lasers. It has been put into practical use (for example, see Patent Document 1). An example in which a multi-beam semiconductor laser is used in an image forming apparatus will be described below with reference to FIG.

  FIG. 12 is a diagram illustrating a configuration of a multi-beam semiconductor laser and a driver circuit of an image forming apparatus according to a conventional example.

  In FIG. 12, the image forming apparatus includes a semiconductor laser LD1000, driver circuits 1 and 1001 to driver circuits 8 and 1008, and a photodiode PD1. The semiconductor laser LD1000 includes laser diodes LD1 to LD8 in a package. The cathode terminals of the laser diodes LD1 to LD8 become a common terminal and are grounded. The anode terminals of the laser diodes LD1 to LD8 are connected to the driver circuits 1 and 1001 to the driver circuits 8 and 1008, respectively, and a lighting current is supplied from the connected driver circuit.

  Since the driver circuits 1 and 1001 to the driver circuits 8 and 1008 have the same configuration, the driver circuits 1 and 1001 will be described as a representative. The photodiode PD1 is installed at a position where the emitted light of the laser diodes LD1 to LD8 or a part thereof is irradiated in order to monitor the light quantity of the laser diodes LD1 to LD8. The anode terminal of the photodiode PD1 is grounded. A bias voltage connected to the power supply Vcc through the resistor R1 is applied to the cathode terminal of the photodiode PD1. The cathode terminal of the photodiode PD1 becomes a monitor output and is connected to the + input terminal of the error amplifier OP1.

  A reference voltage Vref is applied to the negative input terminal of the error amplifier OP1. The output terminal of the error amplifier OP1 is input to the analog switch SW1. A control signal (cont1 signal) is input from a controller (not shown) to a control terminal that controls the operation of the analog switch SW1. The output of the analog switch SW1 is connected to one terminal of the capacitor C1 and further inputted as a control signal for the constant current source CC1. The other terminal of the capacitor C1 is grounded.

  The constant current source CC1 supplies a current corresponding to the applied voltage from its output. The output of the constant current source CC1 is connected to each emitter terminal of the PNP transistors Q10 and Q11. The collector terminal of the PNP transistor Q10 becomes the output of the driver circuit 1001, and is connected to the anode terminal of the laser diode LD1. One end of a resistor RD1 is connected to the collector terminal of the PNP transistor Q11. The other end of the RD1 resistor is grounded. A data signal (data1 signal) is input to the base terminal of the PNP transistor Q10 via the inverter Q12 and to the base terminal of the PNP transistor Q11 via the buffer Q13.

  Next, the operation of the driver circuits 1 and 1001 will be described. First, both the cont1 signal and the data1 signal are output Hi by a controller (not shown) so as to enter the auto power control (APC) mode of the laser diode LD1. Lo is output from the cont2 signal to the cont8 signal and the data2 signal to the data8 signal. Since the data1 signal is Hi, the output of the inverter Q12 becomes Lo, and the PNP transistor Q10 is turned ON. Conversely, the PNP transistor Q11 is turned OFF.

  When the PNP transistor Q10 is turned on, the laser diode LD1 is turned on by the current supplied from the constant current source CC1. When the light quantity of the laser diode LD1 increases, the output current of the photodiode PD1 increases and the voltage input to the error amplifier OP1 decreases. The output of the photodiode PD1 is compared with the reference voltage Vref by the error amplifier OP1, and as a result, the output voltage of the error amplifier OP1 decreases. Since the output voltage of the error amplifier OP1 decreases, the output current of the constant current source CC1 also decreases. When the output current of the constant current source CC1 is also reduced, the light amount of the laser diode LD1 is also reduced.

  As described above, the driver circuits 1 and 1001 constitute a negative feedback circuit, and the laser diode LD1 is lit with a constant light amount so that the output voltage of the photodiode PD1 and the reference voltage Vref are the same voltage. It will be. The same applies to the APC modes of the other laser diodes LD2 to LD8.

  Next, a description will be given of a print mode in which a visible image (developed image) of a latent image formed by scanning a photoconductor of an image forming apparatus with a laser beam is transferred to a recording sheet. In the print mode, a controller (not shown) outputs Lo to the cont1 signal to the cont8 signal, and image data for printing is output to the data1 signal to the data8 signal. Since the cont1 signal is Lo, the analog switch SW1 is turned OFF. For this reason, the voltage in the APC mode is held by the capacitor C1. Since the voltage of the capacitor C1 is applied to the control terminal of the constant current source CC1, the output of the constant current source CC1 has the same current value as in the APC mode.

  When the data1 signal is Hi, the PNP transistor Q10 is turned on, so that the laser diode LD1 is lit. When the data1 signal is Lo, the PNP transistor Q10 is turned off, so that the laser diode LD1 is turned off. As a result, the laser diode can be blinked and driven in accordance with the image data supplied to the semiconductor laser drive circuit, and image exposure of the photoreceptor is performed. Further, it is known that a semiconductor laser is lit with a constant light amount at the same current value in the same environment. Thereby, it becomes possible to light with a constant light amount equivalent to the APC mode at the time of lighting.

  Further, when the data1 signal is Hi, the PNP transistor Q11 is turned off. When the data1 signal is Lo, the PNP transistor Q11 is turned on, so that the current supplied from the constant current source CC1 is applied to the resistor RD1. As a result, the current supplied from the constant current source CC1 is constant without being affected by the status of the data1 signal.

  In general, high-speed driving of a constant current circuit (especially, operation at a frequency of several tens of MHz, which is a frequency for performing laser diode blinking driving during image formation) is difficult. According to the configuration shown in FIG. 12, the PNP transistors Q10 and Q11 require high-speed operation, but the constant current source CC1 does not require high-speed operation, so that image formation is facilitated. The same applies to the printing modes corresponding to the other laser diodes LD2 to LD8.

  As described above, by converting the electrical image signal (image data) supplied to the semiconductor laser driving circuit into the optical pulse signal of the semiconductor laser, the photosensitive member is scanned with the laser beam to form a latent image. Image formation is performed by performing exposure.

JP 2006-116716 A

  As described above, the number of exposure laser beams has been increased in order to cope with the recent increase in speed and image quality of image forming apparatuses. However, there is an adverse effect that unnecessary radiation increases as the number of beams increases. Is starting to occur. The cause of the increase in unnecessary radiation will be described below.

  The semiconductor laser driving circuit performs blinking driving of a laser diode in accordance with image data supplied to the semiconductor laser driving circuit in order to expose the photosensitive member with a laser beam. The frequency at which this blinking driving is performed is several tens of MHz. It becomes. Further, the current for turning on the laser diode requires a steep rise and fall in order to stabilize exposure.

  Here, for example, a VCSEL (surface emitting laser diode suitable for multi-beam) will be described as an example of the laser diode. Since VCSEL has a large parasitic capacitance, it has a current component that flows through the parasitic capacitance when the current rises or falls. Since the current component flowing in the parasitic capacitance does not contribute to the laser emission, the charging time for the parasitic capacitance is a delay in the rise of the laser emission amount with respect to the signal for driving the VCSEL. An increase in the delay amount of the rise of the amount of light emitted from the laser appears as a thinned exposed pixel, which causes image degradation.

  Therefore, in order to reduce the delay amount of the rise of the laser light emission amount, a method of shortening the charging time by supplying a large current to the parasitic capacitance can be considered. The operation waveform of the VCSEL in this case is shown in FIG. In FIG. 13, the vertical axis of (a) indicates the forward voltage Vf of the VCSEL, and the horizontal axis indicates time t. The vertical axis of (b) indicates the forward current If of the VCSEL, and the horizontal axis indicates time t. The vertical axis of (c) indicates the output light amount P, and the horizontal axis indicates time t. As a current necessary for actually reducing the delay time to around 1 nsec, a current that is several to a dozen times as large as the current at the time of normal lighting of the VCSEL flows, and this current causes unnecessary radiation. .

  Although unnecessary radiation is generated due to high-speed and steep switching (lighting / extinguishing) of the VCSEL, there are the following problems. In the past, unnecessary radiation was negligible, but due to the ease with which the multi-beam characteristic of VCSELs can be achieved, as the number of laser light sources increases due to multi-beaming, unnecessary radiation is an important issue that cannot be ignored. Has been. Further, when the rise / fall timings of image signals that determine blinking of a plurality of laser light sources overlap due to the increase in the number of beams, a rapid increase in the drive current of the laser diode becomes a problem. As a result, unnecessary radiation becomes a problem.

  An object of the present invention is to provide an optical scanning apparatus, an image forming apparatus, a control method, and a program capable of reducing unnecessary radiation.

  In order to achieve the above object, the present invention provides an optical scanning apparatus for forming a latent image on the image carrier by scanning and exposing the image carrier with a light beam, the latent image on the image carrier. A light source having a plurality of light emitting elements each emitting a light beam, and a plurality of light emitting elements that are simultaneously turned on in the light source, are configured to be capable of blinking control of turning on and off based on image data for forming an image And control means for performing control for delaying or speeding up the light emission timing of at least one light emitting element with respect to light emission timings other than the at least one light emitting element.

  According to the present invention, the control for delaying or advancing the light emission timing of at least one light emitting element among the plurality of light emitting elements that are simultaneously turned on in the light source is performed with respect to the light emission timing other than at least one light emitting element. Therefore, it is possible to reduce unnecessary radiation generated at the time of rising. This makes it possible to reduce the noise level by shifting the timing of noise generation.

1 is a configuration diagram illustrating a configuration example of an image forming apparatus according to a first embodiment of the present invention. It is the schematic which shows the typical structure of the exposure unit of an image forming apparatus. 1 is a schematic diagram showing a configuration centering on an exposure unit and a control system of an image forming apparatus. 1 is a diagram illustrating a configuration of a multi-beam semiconductor laser and a driver circuit of an image forming apparatus. 2A and 2B are diagrams illustrating image data input in the image forming apparatus, in which FIG. 1A is a diagram illustrating image data input for one scan on the photosensitive drum, and FIG. 2B is a diagram illustrating a pixel structure; FIG. 1 is a diagram illustrating a configuration of an image processing circuit of an image forming apparatus. FIG. 7 is a sequence diagram for explaining the operation of the image processing circuit in FIG. 6. 6 is a flowchart illustrating processing of an image forming apparatus according to a second embodiment of the present invention. It is a figure which shows the image signal input and image signal output at the time of performing the process of FIG. 8, (a) is a figure which shows image signal input, (b) is a figure which shows image signal output. 10 is a flowchart illustrating processing of an image forming apparatus according to a third embodiment of the present invention. 3 is a flowchart illustrating processing of the image forming apparatus. 3 is a flowchart illustrating processing of the image forming apparatus. It is a figure which shows the image signal input and image signal output at the time of performing the process of FIG. 10a-FIG. 10c, (a) is a figure which shows image signal input, (b) is a figure which shows image signal output. . It is a figure which shows the structure of the multi-beam semiconductor laser and driver circuit of the image forming apparatus which concerns on a prior art example. It is a figure which shows the operation | movement waveform of the laser diode of a surface emitting structure, (a) is a figure which shows the forward voltage of VCSEL, (b) is a figure which shows the forward current of VCSEL, (c) is an output light quantity. FIG.

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

[First Embodiment]
FIG. 1 is a configuration diagram illustrating a configuration example of an image forming apparatus according to a first embodiment of the present invention.

  In FIG. 1, an image forming apparatus includes an image forming unit 1 that forms an image (monochrome image / color image) on recording paper by an electrophotographic method, an image reading unit 2 that reads an image from a document, and a document that is supplied to the image reading unit 2. A document feeder 3 for feeding is provided. The image forming unit 1 includes cassette sheet feeding units 4 and 5, a manual sheet feeding unit 6, an intermediate transfer belt 13, and photosensitive drums 14, 15, 16, and 17 installed for each color (magenta, cyan, yellow, and black). , A fixing device 35, exposure units 41, 42, 43, 44, and the like. In the following description, the image forming unit 1 will be mainly described, and descriptions of the image reading unit 2 and the document feeding unit 3 will be omitted.

  In the image forming unit 1, the exposure units 41, 42, 43, and 44 are disposed above the photosensitive drums 14, 15, 16, and 17, respectively, and have the configuration shown in FIG. 2 (configuration other than the photosensitive drum). The exposure operation is performed using a multi-beam (8-beam) semiconductor laser. Details will be described later with reference to FIGS. The exposure units 41, 42, 43, and 44 respectively apply a laser beam LM based on a magenta component image, a cyan component image, a yellow component image, and a black component image to the photosensitive drums 14, 15, 16, and 17, respectively. LC, LY, and LB are exposed to form an electrostatic latent image.

  The photosensitive drums 14, 15, 16, and 17 are image carriers on which electrostatic latent images are formed by exposure by the exposure units 41, 42, 43, and 44, respectively, and are intermediate along the rotation direction of the intermediate transfer belt 13. The transfer belt 13 is arranged on the upper surface of the horizontal portion at equal intervals. Around the photosensitive drums 14, 15, 16, and 17, developing units 23, 24, 25, and 26, primary chargers 27, 28, 29, and 30, cleaners 31, 32, 33, and 34 are arranged, respectively. Yes.

  The primary chargers 27, 28, 29, and 30 uniformly charge the surfaces of the photosensitive drums 14, 15, 16, and 17, respectively. The developing units 23, 24, 25, and 26 develop and visualize the electrostatic latent images formed on the photosensitive drums 14, 15, 16, and 17 with toner, respectively. The cleaners 31, 32, 33, and 34 respectively remove the toner adhering to the photosensitive drums 14, 15, 16, and 17 after the toner image is transferred from the photosensitive drums 14, 15, 16, and 17 to the intermediate transfer belt 13. Remove.

  The image forming apparatus can set either a single-side mode in which an image is formed on one side of a recording sheet or a double-side mode in which an image is formed on both sides of a recording sheet from an operation unit (not shown). First, image formation in the single-side mode will be described. Exposure of a laser beam (light beam) LM based on the image of the magenta component is started on the uppermost photosensitive drum 14, and an electrostatic latent image is formed on the photosensitive drum 14. This electrostatic latent image is visualized by magenta toner supplied from the developing unit 23. Next, exposure of the laser beam LC based on the cyan component image is started on the photosensitive drum 15, and an electrostatic latent image is formed on the photosensitive drum 16. This electrostatic latent image is visualized by cyan toner supplied from the developing device 24.

  Next, after a predetermined time has elapsed from the start of exposure of the laser beam LC to the photosensitive drum 15, the exposure of the laser beam LY based on the yellow component image is started on the photosensitive drum 16, and the electrostatic latent image is applied to the photosensitive drum 16. Form an image. This electrostatic latent image is visualized by yellow toner supplied from the developing device 25. Next, after a predetermined time has elapsed from the start of exposure of the laser beam LY to the photosensitive drum 16, the exposure of the laser beam LB based on the black component image is started on the photosensitive drum 17, and the electrostatic latent image is applied to the photosensitive drum 17. Form an image. This electrostatic latent image is visualized by black toner supplied from the developing device 26.

  The intermediate transfer belt 13 is an endless belt having a substantially triangular cross section that is stretched around the drive roller 13a, the secondary transfer counter roller 13b, and the tension roller 13c. The intermediate transfer belt 13 is rotated clockwise (circulation drive) in the drawing. Inside the intermediate transfer belt 13, transfer chargers 90, 91, 92, and 93 are disposed corresponding to the photosensitive drums 14, 15, 16, and 17, respectively. Further, a secondary transfer roller 40 is disposed opposite the secondary transfer counter roller 13b with the intermediate transfer belt 13 interposed therebetween. A contact portion between the secondary transfer roller 40 and the secondary transfer counter roller 13b forms a secondary transfer portion T2.

  In the process in which the intermediate transfer belt 13 rotates in the clockwise direction in the drawing, the transfer regions that are the contact portions between the photosensitive drums 14, 15, 16, and 17 and the transfer chargers 90, 91, 92, and 93, respectively. Are sequentially passed by the intermediate transfer belt 13. As a result, magenta, cyan, yellow, and black toner images are superimposed and transferred onto the intermediate transfer belt 13.

  On the other hand, when the recording paper S to be imaged is automatically fed, the manual paper feeding unit 6 is used to manually feed the recording paper S from the tray 4a of the cassette paper feeding unit 4 or the tray 5a of the cassette paper feeding unit 5. Are fed from the tray 6a to the secondary transfer portion T2. After the sheet is fed from the uppermost recording sheet S in order by the pickup roller 7 from the corresponding sheet feeding unit, only the uppermost recording sheet S is separated by the pair of separation rollers including the feed roller 8A and the retard roller 8B, and the rotation stops. Is sent to the registration roller pair 12.

  The recording paper S fed from any of the paper feed cassettes 4 and 5 is relayed by the transport roller pair 9, 10, and 11 and sent to the registration roller pair 12. The recording paper S sent to the registration roller pair 12 is temporarily stopped when the leading edge of the recording paper hits the nip portion of the registration roller pair 12 to form a predetermined loop. By forming this loop, the skew state of the recording paper S is corrected. The recording sheet S whose skew state has been corrected is sent to the secondary transfer region T2 by the registration roller pair 12 that starts to rotate at the timing of aligning the position of the toner image on the intermediate transfer belt 13 and the leading end of the recording sheet. The toner image is transferred onto the recording paper.

  The recording sheet S that has passed through the secondary transfer region T2 is sent to the fixing device 35 by the intermediate transfer belt 13. The recording paper S is heated by the fixing roller 35A and pressurized by the pressure roller 35B in the process of passing through the nip portion formed by the fixing roller 35A and the pressure roller 35B in the fixing device 35, and is applied to the recording paper. The toner image is fixed. The recording sheet S that has been subjected to the fixing process after passing through the fixing device 35 is sent to the discharge roller pair 37 by the conveying roller pair 36 and further discharged onto the discharge tray 38 outside the apparatus.

  FIG. 2 is a schematic diagram showing a schematic configuration of the exposure unit 41 of the image forming apparatus.

  FIG. 2 shows an exposure unit 41 installed corresponding to the photosensitive drum 14 on which a magenta toner image is formed. The exposure unit 41 includes a laser diode 111, a collimator lens 112, an aperture 113, a cylindrical lens 114, a laser scanner motor 115, a rotary polygon mirror (polygon mirror) 116, an imaging optical system (fθ lens) 117, and a folding mirror 118. Yes. Illustration and description of the exposure units 42, 43, and 44 corresponding to the cyan photosensitive drum 15, the yellow photosensitive drum 16, and the black photosensitive drum 17 are omitted.

  The laser beam (light beam: divergent light beam) emitted from the laser diode 111 (light source) is made into a substantially parallel light beam by the collimator lens 112, and after the light beam is limited by the stop 113, it has a predetermined refractive power only in the sub-scanning direction. The light enters the cylindrical lens 114 having the same. Of the substantially parallel light beam incident on the cylindrical lens 114, the light beam in the main scanning section is emitted as it is in a substantially parallel light beam state. Of the substantially parallel light beam incident on the cylindrical lens 114, the light beam in the sub-scan section is converged and rotated by the laser scanner motor 115 to the deflecting surface (reflecting surface) 116a of the rotary polygon mirror 116 constituting the optical deflector. The image is formed almost as a line image.

  A laser beam (light beam) deflected and reflected by the deflecting surface 116a of the rotary polygon mirror 116 is passed through a folding mirror 118 by an imaging optical system (fθ lens) 117 having fθ characteristics, and a photosensitive member as a scanning surface. An image is formed on the drum surface of the drum 14. In this case, the rotating polygon mirror 116 is rotated in the direction of arrow A by the laser scanner motor 115, and the drum surface of the photosensitive drum 14 is scanned in the direction of arrow B (main scanning direction). Information recording (formation of an electrostatic latent image) is performed.

  FIG. 3 is a schematic diagram showing a configuration (optical scanning device) centering on the exposure unit 41 and the control system of the image forming apparatus.

  In FIG. 3, the image forming unit 1 of the image forming apparatus includes a laser driver 120, a sequence controller 121, an image processing controller 122, a FIFO memory 123, an image processing circuit 124, and a BD sensor 125. The laser driver 120, the sequence controller 121, the image processing controller 122, the FIFO memory 123, and the image processing circuit 124 correspond to the image processing means of the present invention.

  3 shows the photosensitive drum 14 and the exposure unit 41 for forming an image of a magenta component, the photosensitive drum 15 for forming an image of other color components (cyan, yellow, black), Illustrations and descriptions of 16, 17 and exposure units 42, 43, 44 are omitted.

  The laser driver 120 includes driver circuits 1 and 101 to driver circuits 8 and 108 shown in FIG. The laser driver 120 outputs a blinking signal to the laser diode 111 based on the control signal output from the sequence controller 121 and the image data output from the image processing circuit 124, and controls the blinking of the laser diode 111. The laser diode 111 is turned on and off in response to the blinking signal, and the light-modulated laser beam (light beam) is directed to the rotating polygonal mirror 116 via the collimator lens 112, the diaphragm 113, and the cylindrical lens 114 (see FIG. 2). Irradiate.

  The laser beam applied to the rotary polygon mirror 116 is reflected as a laser beam (deflection beam) whose angle is continuously changed by the deflection surface 116 a as the rotary polygon mirror 116 rotates. The laser beam reflected by the rotating polygonal mirror 116 is subjected to correction of distortion and the like by a lens group (not shown), and scans in the main scanning direction of the photosensitive drum 14 via the folding mirror 118.

  As described with reference to FIG. 1, the photosensitive drum 14 is charged in advance by the primary charger 27 and is rotationally driven in the direction of the arrow, and is sequentially exposed by scanning with a laser beam to form an electrostatic latent image. The The electrostatic latent image formed on the photosensitive drum 14 is developed with toner by the developing unit 23 to become a visible image (toner image). The developed visible image is transferred onto a recording sheet by a transfer charger 90. The recording sheet on which the visible image has been transferred is conveyed to the fixing device 35, and after being fixed, is discharged outside the apparatus.

  In addition, a BD sensor 125 is disposed in the vicinity of the scanning start position in the main scanning direction (or a position corresponding to the scanning start position) on the side of the photosensitive drum 14 in the axial direction. A BD (Beam Detector) sensor 125 detects a laser beam reflected by each deflecting surface 116a of the rotary polygon mirror 116 prior to scanning each line of the photosensitive drum 14, and outputs a BD signal. The BD signal is input to the sequence controller 121 as a scanning start reference signal for the photosensitive drum 14 in the main scanning direction.

  The sequence controller 121 outputs the following signals so as to synchronize the writing start position in the main scanning direction of each line of the photosensitive drum 14 (position where formation of an electrostatic latent image is started by exposure) with reference to the BD signal. Generate. That is, timing signals (control signals) to be output to the FIFO memory 123 and the laser driver 120 are generated.

  Further, the sequence controller 121 performs the following control by executing a program. The light emission timing of at least one light-emitting element among a plurality of light-emitting elements that are simultaneously turned on in a light source having a plurality of light-emitting elements that emit a light beam (laser beam) is delayed with respect to light emission timings other than at least one light-emitting element. Control to speed up or speed up. Details of the control will be described later.

  The image processing controller 122 has a format unique to the image forming unit 1 for image data supplied from the image reading unit 2 in the image forming apparatus or image data supplied from an external device (such as a personal computer). Apply image processing. Further, the image processing controller 122 stores the image data after image processing in a FIFO (First In First Out) memory 123. The image processing circuit 124 converts the image data (video signal) output from the FIFO memory 123 into a blinking signal for turning on and off the laser diodes LD1 to LD8 (see FIG. 4) of the semiconductor laser LD100.

  FIG. 4 is a diagram illustrating a configuration of a multi-beam (8-beam) semiconductor laser and a driver circuit of the image forming apparatus.

  4, the image forming apparatus includes a semiconductor laser LD100 (VCSEL: light source), driver circuits 1 and 101 to driver circuits 8 and 108, and a photodiode PD1. The semiconductor laser LD100 includes laser diodes LD1 to LD8 (a plurality of light emitting elements) in a package. The cathode terminals of the laser diodes LD1 to LD8 become a common terminal and are grounded. The anode terminals of the laser diodes LD1 to LD8 are connected to the driver circuits 1 and 101 to the driver circuits 8 and 108, respectively, and a lighting current is supplied from the connected driver circuit.

  Since the driver circuits 1 and 101 to the driver circuits 8 and 108 have the same configuration, the driver circuits 1 and 101 will be described as a representative. The PD1 photodiode is installed at a position where the emitted light of the laser diodes LD1 to LD8 or a part thereof is irradiated in order to monitor the light amount of the laser diodes LD1 to LD8. The anode terminal of the photodiode PD1 is grounded. A bias voltage connected to the power supply Vcc through the resistor R1 is applied to the cathode terminal of the photodiode PD1. The cathode terminal of the photodiode PD1 serves as a monitor output and is connected to the + input terminal of the error amplifier OP111.

  A reference voltage Vref is applied to the negative input terminal of the error amplifier OP111. The output terminal of the error amplifier OP111 serves as a control signal for the constant current source Q111 and is input to the constant current source Q111. The constant current source Q111 supplies a current corresponding to the applied voltage from the power source Vcc to the output of the constant current source Q111. The output of constant current source Q111 is connected to the collector terminal of NPN transistor Q112. The emitter terminal of the NPN transistor Q112 becomes the output of the driver circuits 1 and 101 and is connected to the anode terminal of the laser diode LD1.

  A control signal (cont1 signal) is input to the base terminal of the NPN transistor Q112. The cont1 signal is generated and supplied by the sequence controller 121 of FIG. The emitter terminal of the NPN transistor Q112 is also connected to one terminal of the analog switch SW111. The cont1 signal is input to the central control terminal that controls the operation of the analog switch SW111. The other terminal of the analog switch SW111 is connected to one terminal of the sample and hold capacitor C111, and is further connected to the control terminal of the constant voltage power supply Q113. The other terminal of the sample hold capacitor C111 is grounded.

  The output of constant voltage power supply Q113 is connected to the collector terminal of NPN transistor Q114. The emitter terminal of the NPN transistor Q114 is also the output of the driver circuits 1 and 101, and is connected to the anode terminal of the laser diode LD1. A data signal (data1 signal) is input to the base terminal of the NPN transistor Q114. The data1 signal is supplied from the FIFO memory 123 of FIG.

  Next, the operation of the driver circuits 1 and 101 will be described. First, Hi is output to the cont1 signal and Lo is output to the data1 signal by the sequence controller 121 of FIG. 3 so that the auto power control (APC) mode of the laser diode LD1 is set. Lo is also output to the cont2 signal to the cont8 signal and the data2 signal to the data8 signal. First, since the cont1 signal is Hi, the NPN transistor Q112 is turned ON, and the analog switch SW111 is also turned ON. Since the data1 signal is Lo, the NPN transistor Q114 is turned OFF.

  When the NPN transistor Q112 is turned on, the laser diode LD1 is turned on by the current supplied from the constant current source Q111. When the light quantity of the laser diode LD1 increases, the output current of the photodiode PD1 increases and the voltage input to the error amplifier OP111 decreases. The output of the photodiode PD1 is compared with the reference voltage Vref by the error amplifier OP111, and the output voltage of the error amplifier OP111 decreases. Since the output voltage of the error amplifier OP111 decreases, the output current of the constant current source Q111 also decreases. When the output current of the constant current source Q111 is also reduced, the light amount of the laser diode LD1 is also reduced.

  As described above, the driver circuits 1 and 101 constitute a negative feedback circuit, and the laser diode LD1 is lit with a constant light amount so that the output voltage of the photodiode PD1 and the reference voltage Vref are the same voltage. It becomes.

  At this time, the emitter voltage of the NPN transistor Q112, that is, the output of the driver circuits 1 and 101 is accumulated in the sample hold capacitor C111 via the analog switch SW111 and further input to the constant voltage power supply Q113. The constant voltage power supply Q113 outputs a voltage having the same potential as the input voltage. Since the NPN transistor Q114 to which a voltage is applied from the constant voltage power supply Q113 is turned off by the data1 signal, the voltage of the constant voltage power supply Q113 is not applied elsewhere.

  Since Lo is input to the cont2 signal to the cont8 signal and the data2 signal to the data8 signal, the outputs of the driver circuits 2 and 102 to 8 and 108 are not input to the laser diodes LD2 to LD8. Therefore, the laser diodes LD2 to LD8 are turned off.

  Next, the laser diode LD2 moves to the APC mode. The sequence controller 121 in FIG. 3 changes the cont1 signal from Hi to Lo, and the cont1 signal from Lo to Hi. Lo is output to the other cont3 signal to cont8 signal and data1 signal to data8 signal. First, since the cont2 signal is Hi, the NPN transistor Q122 of the driver circuits 2 and 102 is turned ON, and the analog switch SW121 is also turned ON. Since the data2 signal is Lo, the NPN transistor Q124 is turned off.

  When the NPN transistor Q122 is turned on, the laser diode LD2 is turned on by the current supplied from the constant current source Q121. When the light quantity of the laser diode LD2 increases, the output current of the photodiode PD1 increases and the voltage input to the error amplifier OP121 decreases. The output of the photodiode PD1 is compared with the reference voltage Vref by the error amplifier OP121, and the output voltage of the error amplifier OP121 decreases. Since the output voltage of the error amplifier OP121 decreases, the output current of the constant current source Q121 also decreases. When the output current of the constant current source Q121 also decreases, the light amount of the laser diode LD2 also decreases.

  As described above, the driver circuits 2 and 102 constitute a negative feedback circuit, and the LD2 laser diode is lit with a constant light amount so that the output voltage of the photodiode PD1 and the reference voltage Vref are the same voltage. It becomes.

  At this time, the emitter voltage of the NPN transistor Q122, that is, the output of the driver circuits 2 and 102 is accumulated in the sample-and-hold capacitor C121 via the analog switch SW121 and further input to the constant voltage power supply Q123. The constant voltage power supply Q123 outputs a voltage having the same potential as the input voltage. Since the transistor Q124 to which the voltage is applied by the constant voltage power supply Q123 is turned off by the data2 signal, the voltage of the constant voltage power supply Q123 is not applied elsewhere.

  In addition, since Lo is input as the cont1 signal, the laser diode LD1 is turned off and the analog switch SW111 is also turned off as in the laser diodes LD3 to LD8. Therefore, the voltage in the APC mode is held in the sample hold capacitor C111. As described above, APC of the laser diodes LD3 to LD8 is sequentially performed.

  Next, in the OFF mode, Lo is input to the cont1 signal to the cont8 signal and Lo is input to the data1 signal to the data8 signal, so that all the laser diodes LD1 to LD8 are turned off.

  Next, a printing mode (a mode in which an electrostatic latent image is formed by irradiating a photosensitive drum with a laser beam, and a toner image obtained by developing the electrostatic latent image with toner is transferred onto a recording sheet via an intermediate transfer belt. ). In the print mode, Lo is output to the cont1 signal to the cont8 signal by the sequence controller 121 of FIG. 3, and image data for printing is output to the data1 signal to the data8 signal. The image data is converted into blinking signals of the eight laser diodes LD1 to LD8 of the semiconductor laser LD1000 by the driver circuits 1 and 101 to driver circuits 8 and 108, respectively.

  Since the cont1 signal is Lo, the NPN transistor Q112 and the analog switch SW111 are turned OFF. As a result, the hold voltage is applied to the constant voltage power supply Q113 by the sample hold capacitor C111 that holds the voltage in the APC mode. The constant voltage power supply Q113 outputs the same voltage in the print mode as in the APC mode and applies it to the collector terminal of the NPN transistor Q114.

  When the data1 signal is Hi, the NPN transistor Q114 is turned on, so that the output voltage of the constant voltage power supply Q113, that is, the voltage in the APC mode is applied to the laser diode LD1, so that the laser diode LD1 is lit. When the data1 signal is Lo, the NPN transistor Q114 is turned off, so that the laser diode LD1 is turned off.

  With the above-described control, the laser data LD1 to LD8 in the semiconductor laser LD100 can be driven to blink by the image data output from the data1 signal to the data8 signal, and the image exposure on the photosensitive drum is performed.

  In addition, by driving the VCSEL (laser diodes LD1 to LD8 in the semiconductor laser LD100) with a constant voltage circuit including the constant voltage power supply Q113, it is possible to drive a rapid current at the time of rising and falling. As a result, high-speed printing on recording paper becomes possible.

  5A and 5B are diagrams illustrating image data input in the image forming apparatus. FIG. 5A is a diagram illustrating image data input for one scan on the photosensitive drum, and FIG. 5B is a pixel diagram. FIG.

  In FIG. 5A, one pixel in the image data (image signal) input from the image processing circuit 124 to the laser driver 120 for one scan of the photosensitive drum by the semiconductor laser LD100 is one pixel. Show. N_beam indicated by the vertical arrow in the figure is the number of data scanned at one time. In this embodiment, N_beam corresponds to the number of laser beams, and thus there are 8 rows. N_horizon indicated by a horizontal arrow in the figure indicates data in the scanning direction.

  FIG. 5B shows 3 × 3 pixels. One pixel is composed of ten pixel pieces in the scanning direction. Furthermore, one pixel piece has a length of 10 μm or less in the scanning direction, and is difficult to visually recognize. Image data (image signal) operates in units of pixel pieces. That is, the operation clock of the image data (image signal) has a frequency determined by the period of the pixel piece larger than the pixel frequency.

  FIG. 6 is a diagram illustrating a configuration of the image processing circuit 124 of the image forming apparatus.

  In FIG. 6, DI_ 0 to DI_ 7 are image signal inputs accompanying the image reading of the document input from the image reading unit 2 to the image processing circuit 124 of the image forming unit 1. Image signal inputs DI_0, DI_1, DI_2, DI_3, DI_4, DI_5, DI_6, and DI_7 are D flip-flop circuits (hereinafter referred to as “circuits”) Q100, Q110, Q120, Q130, Q140, Q150, Q160, and Q170. Each is connected.

  The Q outputs of the D flip-flops Q100 to Q170 are inverted and input to one input terminal of each of the AND circuits Q101, Q111, Q121, Q131, Q141, Q151, Q161, and Q171. Further, the image signal inputs DI_0 to DI_7 are input to the other input terminals of the AND circuits Q101 to Q171, respectively.

  The outputs of the AND circuit Q101, the AND circuit Q111, the AND circuit Q121, and the AND circuit Q131 are input to the adder Q142. The output of the AND circuit Q141 and the output of the adder Q142 are input to the adder Q152. The output of the AND circuit Q151 and the output of the adder Q152 are input to the adder Q162. The output of the AND circuit Q161 and the output of the adder Q162 are input to the adder Q172.

  The outputs of adders Q142, Q152, Q162, and Q172 are input to one input terminals of comparators Q143, Q153, Q163, and Q173, respectively. A threshold value (comparison value data) Q180 is input to the other input terminals of the comparators Q143, Q153, Q163, and Q173. The outputs of comparators Q143 to Q173 are input to one input terminals of AND circuits Q144, Q154, Q164, and Q174, respectively. The outputs of the AND circuits Q141 to Q171 are input to the other input terminals of the AND circuits Q144 to Q174, respectively.

  Outputs of AND circuits Q144 to Q174 are input to selector terminals of selectors Q146, Q156, Q166, and Q176, respectively. DI_4 to DI_7 are input to one input terminals of the selectors Q146 to Q176, respectively. Q outputs of D flip-flops Q145, Q155, Q165, and Q175 are input to the other input terminals of the selectors Q146 to Q176, respectively. Image signal inputs DI_4 to DI_7 are input to D inputs of the D flip-flops Q145 to Q175, respectively.

  The outputs of selectors Q146 to Q176 are connected to the D inputs of D flip-flops Q149, Q159, Q169, and Q179, respectively. DI_0 to DI_3 are input to the D inputs of the D flip-flops Q109, Q119, Q129, and Q139, respectively. The Q outputs of the D flip-flops Q109 to Q179 become image signal outputs DO_0 to DO_7, respectively, and are input to the driver circuits 1 and 101 to the driver circuits 8 and 108 in FIG. The same clock determined by the pixel piece described in FIG. 5 is input to the clock terminal of each D flip-flop.

  FIG. 7 is a sequence diagram for explaining the operation of the image processing circuit of FIG.

  In FIG. 7, the operation of the image processing circuit of FIG. 6 will be described. The first pixel is OFF, and the image signal (image data) inputs DI_0 to DI_7 are delayed by one clock by the D flip-flops Q109 to Q179 in FIG. 6 to become image signal (image data) outputs DO_0 to DO_7. Next, in the second pixel, the image signal inputs DI_0 to DI_7 are all ON.

  The rising edge of light emission of the laser diode is detected from the image signal input DI_0 by a rising edge detection circuit (detection means) constituted by the D flip-flop Q100 and the AND circuit Q101 of FIG. The output of this rising edge detection circuit is indicated by Q101 in FIG. Similarly, Q111, Q121, Q131, Q141, Q151, Q161, and Q171 in FIG. 7 indicate rising detection signals of the image signal inputs DI_1 to DI_7, respectively.

  Next, the adder Q142 in FIG. 6 adds the outputs of the rising edge detection signals Q101, Q111, Q121, and Q131, and calculates the number of rising edges at the same time. Next, the comparator Q143 compares the output of the adder Q142 with the output of the threshold value Q180, and outputs Hi when the number of edges rising simultaneously is 4 or more. The AND circuit Q144 generates a delay permission signal when the number of simultaneously rising edges is 4 or more, that is, when the image signal inputs DI_0 to DI_3 are rising edges and the image signal input DI_4 is also a rising edge. This delay permission signal is indicated by Q144 in FIG.

  Next, the adder Q152 in FIG. 6 adds the output of the adder Q142 and the output of the rising edge detection signal Q141, and calculates the number of rising edges at the same time. Next, the comparator Q153 compares the output of the adder Q152 with the output of the threshold value Q180, and outputs Hi when the number of edges rising simultaneously is 4 or more. The AND circuit Q154 generates a delay permission signal when the number of simultaneously rising edges is 4 or more, that is, when the image signal inputs DI_0 to DI_4 are rising edges and the image signal input DI_5 is also a rising edge. This delay permission signal is indicated by Q154 in FIG.

  Next, the adder Q162 in FIG. 6 adds the output of the adder Q152 and the output of the rising edge detection signal Q151, and calculates the number of rising edges at the same time. Next, the comparator Q163 compares the output of the adder Q162 with the output of the threshold value Q180, and outputs Hi when the number of edges rising simultaneously is 4 or more. The AND circuit Q164 generates a delay permission signal when the number of edges rising simultaneously is 4 or more, that is, when the image signal inputs DI_0 to DI_5 are rising edges and the image signal input DI_6 is also a rising edge. This delay permission signal is indicated by Q164 in FIG.

  Next, the adder Q172 adds the output of the adder Q162 and the output of the rising edge detection signal Q161, and calculates the number of rising edges at the same time. Next, the comparator Q173 compares the output of the adder Q172 with the output of the threshold value Q180, and outputs Hi when the number of edges rising simultaneously is 4 or more. The AND circuit Q174 generates a delay permission signal when the number of simultaneously rising edges is 4 or more, that is, when the image signal inputs DI_0 to DI_6 are rising edges and the image signal input DI_7 is also a rising edge. This delay permission signal is indicated by Q174 in FIG.

  The delay permission signals generated by the AND circuits Q144, Q154, Q164, and Q174 in FIG. 6 are selection signals for the selectors Q146, Q156, Q166, and Q176, respectively. The selectors Q146 to Q176 select and output the image signal inputs DI_4 to DI_7, respectively, when the delay permission signal is Lo. When the delay permission signal is Hi, the selectors Q146 to Q176 respectively select and output the signals delayed by one clock by the D flip-flops Q145, Q155, Q165, and Q175 for the image signal inputs DI_4 to DI_7.

  The D flip-flops Q109, Q119, Q129, and Q139 in FIG. 6 delay the image signal inputs DI_0 to DI_3 by one clock and output them as image signal outputs DO_0 to DO_3. The D flip-flops Q149, Q159, Q169, and Q179 delay the outputs of the selectors Q146, Q156, Q166, and Q176 by one clock, and output them as image signal outputs DO_4 to DO_7.

  At the rise of the second pixel in FIG. 7, the image signal outputs DO_0 to DO_3 rise simultaneously, but the image signal outputs DO_4 to DO_7 rise with a delay of one clock of the pixel piece. Similarly, at the rise of the fourth pixel, the image signal outputs DO_0, DO_2, DO_3, and DO_4 rise simultaneously, but the image signal output DO_6 rises with a delay of one clock of the pixel piece.

  As described above, the image signal output (image data) that rises at the same time is up to four lines, and it is possible to reduce unnecessary radiation generated when the laser diode of the semiconductor laser rises.

  As described above in detail, according to the present embodiment, the rising edge of the image data corresponding to the lighting rising timing of each laser diode of the semiconductor laser is detected. When the number of simultaneously rising edges of the detected image data is greater than or equal to a preset number, control is performed to delay the rising timing of the simultaneously rising edges of the image data.

  Therefore, it is possible to reduce unnecessary radiation generated at the rising edge of the image data corresponding to the rising timing of lighting of the laser diode. This makes it possible to reduce the noise level by shifting the timing of noise generation.

[Second Embodiment]
The image forming apparatus according to the second embodiment of the present invention includes a multi-beam (8-beam) semiconductor laser, and the points described with reference to FIGS. 8 and 9 with respect to the first embodiment. Is different. In the first embodiment, the method for realizing the present invention by hardware has been described. In the present embodiment, a method for realizing the present invention by software will be described. Since the other elements of the present embodiment are the same as the corresponding ones of the first embodiment (FIGS. 1, 2, and 3), description thereof is omitted.

  FIG. 8 is a flowchart showing the operation of the image forming apparatus according to the present embodiment.

  In FIG. 8, N_subpix is the number of the pixel piece in the scanning direction, n is the channel of the laser beam that is scanned simultaneously, RiseCount is the number of edges that rise simultaneously, FallCount is the number of edges that fall simultaneously, Data is the image data for each pixel piece Show. In this embodiment, a process for a multi-beam (8-beam) semiconductor laser will be described as in the first embodiment. This process is executed by a CPU (not shown) of the sequence controller 121 of the image forming apparatus based on a program (program code).

  When the sequence controller 121 of the image forming apparatus starts this processing (step S501), initial setting (N_subpix = 0) (step S502), initial setting (n = 0, RiseCount = 0, FallCount = 0) (step S503). I do. Next, the sequence controller 121 determines whether or not the image data (image signal) in the N_subpix row and the n-th column is a rising edge (step S504). If it is not a rising edge, the process proceeds to step S508. In the case of the rising edge, the sequence controller 121 increments RiseCount (step S505).

  Next, the sequence controller 121 determines whether RiseCount is greater than 4 (step S506). If RiseCount is less than 4, the process proceeds to step S508. If RiseCount is larger than 4, that is, if the overlapping of rising edges is larger than 4, the sequence controller 121 performs processing for delaying the rising edges (step S507), and proceeds to step S508.

  Next, the sequence controller 121 determines whether the image data (image signal) in the N_subpix row and the n-th column is a falling edge (step S508). If it is not a falling edge, the process proceeds to step S512. In the case of the falling edge, the sequence controller 121 increments FallCount (step S509).

  Next, the sequence controller 121 determines whether FallCount is greater than 4 (step S510). If FallCount is less than 4, the process proceeds to step S512. If FallCount is greater than 4, that is, if the falling edge overlap is greater than 4, the sequence controller 121 performs a process of delaying the falling edge (step S511), and proceeds to step S512.

  Next, the sequence controller 121 increments n (step S512). Next, the sequence controller 121 determines whether n is less than 8 (step S513). If n is less than 8, that is, if the processing for the eight beams of the semiconductor laser is not completed, the process returns to step S504. When n reaches 8, that is, when the processing for the eight beams of the semiconductor laser is completed, the sequence controller 121 increments N_subpix (step S514).

  Next, the sequence controller 121 determines whether N_subpix is less than N_subpix_max (step S515). If N_subpix is less than N_subpix_max, that is, if the processing for all the pixels of one scan is not completed, the process returns to step S503. When N_subpix reaches N_subpix_max, that is, when the processing for all the pixels of one scan is completed, this processing for the image data of one scan ends.

  FIG. 9 is a diagram illustrating image signal input and image signal output when the processing of FIG. 8 is performed. (A) is a diagram illustrating image signal input, and (b) is a diagram illustrating image signal output. is there.

  9, before the processing of FIG. 8 is indicated by image signal inputs DI_0 to DI_7, and after the processing of FIG. 8 is indicated by image signal outputs DO_0 to DO_7. At the rise of the second pixel, the image signal outputs DO_0 to DO_3 rise simultaneously, but the image signal outputs DO_4 to DO_7 rise with a delay of one clock of the pixel piece. At the fall of the third pixel, the image signal outputs DO_0 to DO_3 fall simultaneously, but the image signal outputs DO_4 to DO_7 fall with a delay of one clock of the pixel piece.

  Similarly, at the rise of the fourth pixel, the image signal outputs DO_0, DO_2, DO_3, and DO_4 rise simultaneously, but the image signal output DO_6 rises with a delay of one clock of the pixel piece. At the falling edge of the fifth pixel, the image signal outputs DO_0, DO_2, DO_3, and DO_4 fall simultaneously, but the image signal output DO_6 falls with a delay of one clock of the pixel piece.

  As described above in detail, according to the present embodiment, rising / falling edges of image data corresponding to lighting rising / falling timings of the respective laser diodes of the semiconductor laser are detected. When the number of edges rising / falling simultaneously in the detected image data is greater than or equal to a preset number, control is performed to delay the rising / falling timing of the edges rising / falling simultaneously in the image data.

  Accordingly, the image data rising or falling at the same time is up to four lines as described above, and it is possible to reduce unnecessary radiation generated not only at the time of rising of the image data but also at the time of falling. This makes it possible to reduce the noise level by shifting the timing of noise generation.

[Third Embodiment]
The image forming apparatus according to the third embodiment of the present invention includes a multi-beam (8-beam) semiconductor laser, and the points described with reference to FIGS. 10 and 11 with respect to the first embodiment. Is different. In the first embodiment, the method for realizing the present invention by hardware has been described. In the present embodiment, a method for realizing the present invention by software will be described. Since the other elements of the present embodiment are the same as the corresponding ones of the first embodiment (FIGS. 1, 2, and 3), description thereof is omitted.

  10a, 10b, and 10c are flowcharts showing processing of the image forming apparatus.

  In FIG. 10a, N_subpix represents the number of pixel pieces in the scanning direction, N_beam represents the channel of the laser beam that is scanned simultaneously, and EdgeCount represents the difference between the rising edge and the falling edge. That is, when the value of EdgeCount is positive, the number of rising edges is large, and when it is negative, the number of falling edges is large. Others are the same as in the second embodiment. In this embodiment mode, processing for a multi-beam (16 beam) semiconductor laser will be described. This process (FIGS. 10a, 10b, and 10c) is executed by a CPU (not shown) of the sequence controller 121 of the image forming apparatus based on a program (program code).

  When starting this processing (step S601), the sequence controller 121 of the image forming apparatus performs initial settings (N_subpix = 0, N_beam = 0, RiseCount = 0, FallCount = 0) (steps S602 and S603). Next, the sequence controller 121 determines whether or not the image data (image signal) in the N_subpix row and the n-th column is a rising edge (step S604). If it is not a rising edge, the process proceeds to step S606. In the case of the rising edge, the sequence controller 121 increments RiseCount (step S605), and proceeds to step S6060.

  Next, the sequence controller 121 determines whether or not the image data (image signal) in the N_subpix row and the n-th column is a falling edge (step S606). If it is not a falling edge, the process proceeds to step S608. In the case of the falling edge, the sequence controller 121 increments FallCount (step S607), and proceeds to step S6060.

  Next, the sequence controller 121 increments N_beam (step S608). Next, the sequence controller 121 determines whether or not N_beam is 16 (step S609). If N_beam is less than 16, that is, if the processing for 16 beams is not completed, the process returns to step S604. When N_beam is 16, that is, when processing for 16 beams is completed, the sequence controller 121 obtains a difference between RiseCount, which is the number of edges that rise simultaneously, and FallCount, which is the number of edges that fall simultaneously. That is, EdgeCount is calculated (step S610).

  Next, the processing proceeds to a rising edge processing subroutine (step S611), and further proceeds to a falling edge processing subroutine (step S612). Details of the rising edge processing subroutine will be described later with reference to FIG. 10b, and details of the falling edge processing subroutine will be described later with reference to FIG. 10c. Next, the sequence controller 121 increments N_subpix (step S613).

  Next, the sequence controller 121 determines whether N_subpix is less than N_subpix_max (step S614). If N_subpix is less than N_subpix_max, that is, if the processing for all pixels in one scan is not completed, the process returns to step S603. When N_subpix reaches N_subpix_max, that is, when the process for all the pixels of one scan is completed, the process for the image data of one scan ends (step S615).

  In FIG. 10b, the rising edge processing subroutine (step S611 in FIG. 10a) will be described. When starting the rising edge process (step S621), the sequence controller 121 determines whether EdgeCount is greater than 4 (step S622). If EdgeCount is not greater than 4, the sequence controller 121 determines that the rising edge overlap is not greater than 4, and ends this process (step S623).

  If EdgeCount is greater than 4, that is, if the rising edge overlap is greater than 4, the sequence controller 121 makes the following determination. That is, it is determined whether or not the image data in the N_subpix row and the n_beam column is a rising edge (step S624). If it is not a rising edge, the process proceeds to step S628. When it is a rising edge, the sequence controller 121 determines whether or not the rising edge in the column of the pixel piece immediately before the main scanning direction is larger than 4 (step S625).

  If the rising edge in the row of pixel pieces immediately before the main scanning direction is larger than 4, the sequence controller 121 performs a delay process of rising (step S627), and proceeds to step S628. If the rising edge in the row of pixel pieces immediately before in the main scanning direction is not larger than 4, an operation for speeding up the rising is performed (step S626) and the process proceeds to step S628. Next, the sequence controller 121 decrements EdgeCount (step S628), returns to step S622, and performs the above-described process again.

  With reference to FIG. 10c, the falling edge processing subroutine (step S612 in FIG. 10a) will be described. When the sequence controller 121 starts the falling edge process (step S631), the sequence controller 121 determines whether EdgeCount is smaller than −4 (step S632). If EdgeCount is not smaller than −4, the sequence controller 121 determines that the falling edge overlap is not larger than 4 and ends this processing (step S633).

  If EdgeCount is smaller than −4, that is, if the overlapping edge of the falling edge is larger than 4, the sequence controller 121 makes the following determination. That is, it is determined whether or not the image data in the N_subpix row and the n_beam column is a falling edge (step S634). If it is not a falling edge, the process proceeds to step S638. When it is a falling edge, the sequence controller 121 determines whether or not the falling edge in the column of the pixel piece immediately before the main scanning direction is larger than 4 (step S635).

  If the falling edge in the row of pixel pieces immediately before the main scanning direction is larger than −4, the sequence controller 121 performs the falling delay process (step S637), and proceeds to step S638. If the falling edge in the row of pixel pieces immediately before in the main scanning direction is not greater than −4, the sequence controller 121 performs an operation of speeding up the falling (step S636), and proceeds to step S638. Next, the sequence controller 121 decrements EdgeCount (step S638), returns to step S632, and performs the above-described processing again.

  11A and 11B are diagrams illustrating image signal input and image signal output when the processes of FIGS. 10a to 10c are performed. FIG. 11A is a diagram illustrating image signal input, and FIG. 11B is a diagram illustrating image signal output. FIG.

  In FIG. 11, before processing in FIGS. 10 a to 10 c is indicated by image signal inputs DI_ 0 to DI_ 15, and after processing in FIGS. 10 a to 10 c is indicated by image signal outputs DO_ 0 to DO_ 15. At the rise of the second pixel, the image signal outputs DO_0 to DO_3 rise at the same time, but the image signal outputs DO_4 to DO_7 rise earlier by one clock of the pixel piece. The image signal outputs DO_8 to DO_11 rise with a delay of one clock of the pixel piece, and the image signal outputs DO_12 to DO_15 rise with a delay of two clocks of the pixel piece.

  At the fall of the third pixel, the image signal outputs DO_0 to DO_3 rise at the same time, but the image signal outputs DO_8 to DO_11 fall earlier by one clock of the pixel piece. The image signal outputs DO_12 to DO_15 rise with a delay of one clock of the pixel piece.

  In the fourth pixel, since the image signal outputs DO_0 to DO_3 and DO_8 to DO_15 are rising and the image signal outputs DO_4 to DO_7 are falling, the rising and falling of four data are canceled out. For this reason, the image signal outputs DO_0 to DO_11 rise and fall simultaneously, but the image signal outputs DO_12 to DO_15 rise earlier by one clock of the pixel piece (control to advance timing).

  As described above in detail, according to the present embodiment, rising / falling edges of image data corresponding to lighting rising / falling timings of the respective laser diodes of the semiconductor laser are detected. When the number of edges rising / falling simultaneously in the detected image data is greater than or equal to a preset number, control for delaying or advancing the rising / falling timing of the simultaneously rising / falling edges of the image data is performed. .

  If the number of beams allowed to rise / fall at the same time is small compared to the total number of beams in a semiconductor laser (multiple beams), the phase is shifted more than the original ideal timing if the timing is shifted only by delay processing. . Therefore, the above-described timing control can reduce unnecessary radiation with only the minimum necessary processing. This makes it possible to reduce the noise level by shifting the timing of noise generation. It is also possible to prevent image degradation.

  In the first to third embodiments described above, when the difference between the number of simultaneously rising edges of image data and the number of simultaneously falling edges of image data is equal to or greater than a preset number, Take control. Control for delaying or advancing the rising timing of the rising edges of the image data simultaneously and the falling timing of the edges of the image data falling simultaneously.

  In addition, when the number of image data edges that delay the rise / fall timing or the number of image data edges that advance the rise / fall timing is a preset number, the following control is performed. Control for delaying the timing or control for advancing the timing is performed again for the edges of the image data of a preset number or more.

  In addition, the amount of pixel pieces constituting the image data for performing control for advancing or delaying the rising / falling timing is 10 μm or less.

[Other Embodiments]
In the first to third embodiments, the present invention is exemplified by an image forming apparatus having a structure in which a photosensitive drum is irradiated with a laser beam emitted from a laser diode of a semiconductor laser via a rotating polygon mirror (polygon mirror). Although mentioned, it is not limited to this. The present invention can also be applied to an image forming apparatus having a structure in which a photosensitive drum is irradiated with a laser beam emitted from a laser diode of a semiconductor laser via a oscillating mirror (galvanomirror).

  The present invention can also be realized by executing the following processing. That is, software (program) that realizes the functions of the above-described embodiments is supplied to a system or apparatus via a network or various storage media, and a computer (or CPU, MPU, or the like) of the system or apparatus reads the program. It is a process to be executed.

14-17 Photosensitive drums 41-44 Exposure units 101-108 Driver circuit 120 Laser driver 121 Sequence controller LD100 Semiconductor laser LD1-LD8 Laser diode

Claims (12)

An optical scanning device that forms a latent image on the image carrier by scanning and exposing the image carrier with a light beam,
Based on image data for forming the latent image on the image carrier, it is configured to be capable of turning on and off, and a light source having a plurality of light emitting elements each emitting a light beam;
Control means for performing a control for delaying or advancing the light emission timing of at least one light emitting element among the plurality of light emitting elements that are simultaneously turned on in the light source, with respect to the light emission timing other than the at least one light emitting element;
An optical scanning device comprising: An optical scanning device that forms a latent image on the image carrier by scanning and exposing the image carrier with a laser beam,
A semiconductor laser having a plurality of light emitting elements each emitting a laser beam, which is configured to be capable of blinking control of turning on and off based on image data for forming the latent image on the image carrier,
Image processing means for converting the image data into a blinking signal for turning on and off each of the light emitting elements of the semiconductor laser;
Detecting means for detecting a rising edge of image data corresponding to a rising timing of lighting of each light emitting element of the semiconductor laser;
If the number of simultaneously rising edges of the image data detected by the detecting means is greater than or equal to a preset number, a control means for performing control to delay or accelerate the rising timing of the simultaneously rising edges of the image data;
An optical scanning device comprising: An optical scanning device that forms a latent image on the image carrier by scanning and exposing the image carrier with a laser beam,
A semiconductor laser having a plurality of light emitting elements each emitting a laser beam, which is configured to be capable of blinking control of turning on and off based on image data for forming the latent image on the image carrier,
Image processing means for converting the image data into a blinking signal for turning on and off each of the light emitting elements of the semiconductor laser;
Detecting means for detecting a falling edge of image data corresponding to a lighting falling timing of each of the light emitting elements of the semiconductor laser;
When the number of edges that fall simultaneously in the image data detected by the detection means is greater than or equal to a preset number, control that delays or accelerates the fall timing of the edges that fall simultaneously in the image data Means,
An optical scanning device comprising: An optical scanning device that forms a latent image on the image carrier by scanning and exposing the image carrier with a laser beam,
A semiconductor laser having a plurality of light emitting elements each emitting a laser beam, which is configured to be capable of blinking control of turning on and off based on image data for forming the latent image on the image carrier,
Image processing means for converting the image data into a blinking signal for turning on and off each of the light emitting elements of the semiconductor laser;
Detecting means for detecting a rising edge of image data corresponding to a rising timing of lighting of each light emitting element of the semiconductor laser, and a falling edge of image data corresponding to a falling timing of lighting of each of the light emitting elements; ,
When the difference between the number of simultaneously rising edges of the image data detected by the detecting means and the number of simultaneously falling edges of the image data is greater than or equal to a preset number, the rising timing of the simultaneously rising edges of the image data And a control means for performing a control for delaying or advancing the falling timing of the falling edge of the image data simultaneously falling edge,
An optical scanning device.   5. The optical scanning device according to claim 2, wherein an amount of pixel pieces constituting image data for performing the control for delaying the timing or the control for advancing the timing is 10 μm or less. 6. .   When the number of edges of the image data for delaying the timing or the number of edges of the image data for advancing the timing is a preset number, the control means is configured to detect the number of edges of the image data equal to or greater than the preset number. 5. The optical scanning device according to claim 2, wherein control for delaying the timing or control for advancing the timing is performed again.   An image forming apparatus comprising the optical scanning device according to claim 1. A light source having a plurality of light emitting elements each capable of turning on and off based on image data for forming a latent image on the image carrier and capable of emitting a light beam is provided, and the image carrier is scanned with the light beam. A method of controlling an optical scanning device for forming a latent image on the image carrier by exposing the image carrier,
A control step of performing a control for delaying or advancing the light emission timing of at least one light emitting element among the plurality of light emitting elements that are turned on simultaneously in the light source with respect to the light emission timing other than the at least one light emitting element. Characteristic control method. A semiconductor laser having a plurality of light-emitting elements each capable of turning on and off based on image data for forming a latent image on an image carrier and capable of emitting a laser beam, and scanning the image carrier with a laser beam And a method of controlling the optical scanning device that forms a latent image on the image carrier by exposing,
An image processing step of converting the image data into a flashing signal for turning on and off each of the light emitting elements of the semiconductor laser;
A detecting step of detecting a rising edge of image data corresponding to a rising timing of lighting of each light emitting element of the semiconductor laser;
If the number of simultaneously rising edges of the image data detected by the detection step is equal to or greater than a preset number, a control step of performing control to delay or accelerate the rising timing of the simultaneously rising edges of the image data;
A control method characterized by comprising: A semiconductor laser having a plurality of light-emitting elements each capable of turning on and off based on image data for forming a latent image on an image carrier and capable of emitting a laser beam, and scanning the image carrier with a laser beam And a method of controlling the optical scanning device that forms a latent image on the image carrier by exposing,
An image processing step of converting the image data into a flashing signal for turning on and off each of the light emitting elements of the semiconductor laser;
A detection step of detecting a falling edge of image data corresponding to a lighting falling timing of each of the light emitting elements of the semiconductor laser;
When the number of simultaneously falling edges of the image data detected by the detection step is equal to or greater than a preset number, control for delaying or advancing control of the falling timing of the simultaneously falling edges of the image data Process,
A control method characterized by comprising: A semiconductor laser having a plurality of light-emitting elements each capable of turning on and off based on image data for forming a latent image on an image carrier and capable of emitting a laser beam, and scanning the image carrier with a laser beam And a method of controlling the optical scanning device that forms a latent image on the image carrier by exposing,
An image processing step of converting the image data into a flashing signal for turning on and off each of the light emitting elements of the semiconductor laser;
A detection step of detecting a rising edge of image data corresponding to a rising timing of lighting of each light emitting element of the semiconductor laser, and a falling edge of image data corresponding to a falling timing of lighting of the light emitting element;
When the difference between the number of simultaneously rising edges of the image data detected by the detection step and the number of simultaneously falling edges of the image data is greater than or equal to a preset number, the rising timing of the simultaneously rising edges of the image data And a control step for performing a control for delaying or advancing the fall timing of the falling edges of the image data at the same time,
A control method characterized by comprising:   The program which has a computer-readable program code for making a computer perform the control method of the optical scanning device of any one of Claims 8 thru | or 11.