JP2018200451A - Image forming apparatus - Google Patents

Abstract

To reduce an error caused by return light from a polygon mirror in initialization APC processing to correctly set a driving current of a laser diode.SOLUTION: A polygon mirror 23 scans laser light in a main scanning direction. A PD sensor 24 receives the laser light being scanned and generates a synchronous signal in the main scanning direction. A photodetector PD detects part of the laser light. A driver circuit 31 executes initialization APC processing of adjusting the quantity of laser light during initialization of a light source on the basis of the detected voltage of the photodetector. When the polygon mirror 23 rotates at a speed lower than a normal rotation speed for image formation, the driver circuit 31 starts the initialization APC processing on the basis of the synchronous signal generated by the PD sensor 24 at a timing at which return light from the polygon mirror 23 to the photodetector PD does not occur.SELECTED DRAWING: Figure 2

Description

  The present invention relates to an image forming apparatus.

  Some electrophotographic image forming apparatuses such as printers and multifunction machines use a laser diode as a light source of an exposure apparatus. In such an image forming apparatus, automatic light control (APC: Automatic Power Control) is performed so that the light amount of the laser diode becomes appropriate.

  Such APC includes an initialization APC that is performed when the laser diode is initialized and a line APC that is performed for each line. The initialization APC is performed at the start of use of the laser diode, and thereafter each line. Line APC is performed at the same time (see, for example, Patent Document 1).

JP 2009-119736 A

Usually, the laser diode does not emit light when driving current I _OP does not exceed the threshold current I _th, exceeds the threshold current I _th, the light emission amount of the laser diode is increased in proportion to the increase of the driving current I _OP To go.

  For example, the laser light source unit is provided with a photo detector (PD: Photodetector) for detecting a part of laser light from the laser diode in addition to the laser diode.

In the initialization APC processing, while monitoring the detection voltage _{V PD} of the photodetector, gradually increasing the driving current _{I OP,} based on the value of the detected voltage _{V PD,} firstly, the threshold current _{I th} (i.e., laser Current value at which the diode starts to emit light), and then, based on the value of the drive current I _OP when the value of the detection voltage V _PD corresponding to the target light amount is reached, the drive current I from the threshold current I _th An increase in _OP (hereinafter referred to as light emission current I _sw ) is specified. Thus, the identified and inclination (slope efficiency) is the ratio of the increase in the threshold current I _th and the light emission current Isw and the light-emitting amount, the amount of characteristics of the laser diode with respect to the drive current I _OP is identified.

Figure 8 is a diagram for explaining the characteristics of the light emission amount with respect to the driving current I _OP of the laser diode. As shown in FIG. 8, when the drive current I _OP becomes equal to or higher than the threshold current I _th , the laser diode starts to emit light, and the light emission amount increases substantially in proportion to the increase in the drive current I _OP from the threshold current I _th. I will do it.

Further, in the line APC process, the drive current I _OP is changed from the threshold current I _{th in} a period other than the light emission period of the laser diode (a period during which light emission is possible for drawing an electrostatic latent image on the photosensitive drum). The light emission current I _sw is specified based on the value of the drive current I _OP when the value gradually increases and _reaches the value of the detection voltage V _PD corresponding to the target light amount, and based on the specified light emission current I _sw , The above characteristics are corrected.

  The laser light emitted from the above laser diode is scanned in the main scanning direction by the polygon mirror. Depending on the position of the polygon mirror on which the laser light is incident, return light from the polygon mirror to the laser light source unit side is generated. It may be detected by a photodetector of the laser light source unit.

When such return light is generated in the initialization APC process, an error due to the return light may occur in the threshold current I _th (or in the threshold current I _th and the light emission current I _sw ). The time required for the initialization APC process is longer than that for the line APC process. For example, when return light is generated at the boundary of the mirror surface of the polygon mirror, when the time required for the initialization APC process is longer than the time from when the laser beam enters the boundary of the mirror surface until it enters the next boundary Return light is generated in the initialization APC process.

Figure 9 is a diagram for explaining error due to the return light occurs threshold current I _th.

As shown in FIG. 9, in the initialization APC process, if return light is generated before the drive current I _OP reaches the threshold current I _th , the threshold current I is lower than the original threshold current I _th (I _{th_error} ). _th is detected. Thereafter, when the light emission current I _sw corresponding to the target light amount is detected after the return light is lost, the characteristic is erroneously measured as shown in FIG.

Thereafter, for example, when it is desired to emit laser light with a target light amount, the value of the drive current I _OP is set to (I _{th_error} + I _sw ), so that the laser light is emitted with the target light amount. When it is desired to emit laser light with a% light quantity (50% light quantity of the target light quantity), the value of the drive current I _OP is set to (I _{th_error} + I _sw / 2). Laser light is emitted with an incorrect light amount lower than 50% light amount.

  In the main scanning correction, even when the light emission amount is the same, the irradiation light amount varies depending on the position in the main scanning direction when the irradiation light amount is different between the region where the line APC processing is performed (non-drawing region) and the drawing region. The light emission amount is corrected so as to be substantially constant.

FIG. 10 is a diagram illustrating an error that occurs in the threshold current I _th and the light emission current I _sw due to the return light.

As shown in FIG. 10, in the initialization APC process, when return light is generated when the drive current I _OP reaches the threshold current I _th and when the light emission current I _sw is measured, a value lower than the original threshold current I _th ( with the threshold current _{I th} at _I th_error) is detected, the light emission current _{I sw} is detected at the original emission current _{I sw} lower values _{(I sw_error).} Therefore, the characteristic is erroneously measured as shown in FIG.

After that, for example, when it is desired to emit laser light with a target light amount, the value of the drive current I _OP is set to (I _{th_error} + I _{sw_error} ), so that the laser light is emitted with an incorrect light amount lower than the original target light amount. . For example, when it is desired to emit laser light with 50% light quantity (50% light quantity of the target light quantity) for main scanning correction, the value of the drive current I _OP is set to (I _{th_error} + I _{sw_error} / 2). As shown in FIG. 10, laser light is emitted with an incorrect light amount lower than the original 50% light amount.

  The present invention has been made in view of the above problems, and obtains an image forming apparatus that suppresses an error caused by return light from a polygon mirror in initialization APC processing and correctly sets a driving current of a laser diode. For the purpose.

  An image forming apparatus according to the present invention generates a synchronization signal in a main scanning direction by receiving a light source that emits laser light, a polygon mirror that scans the laser light in a main scanning direction, and the laser light that is being scanned. Initialization APC that drives the light source and adjusts the light amount of the laser light upon initialization of the light source based on the detection voltage of the photodetector. And a driver circuit for executing processing. Then, the driver circuit, based on the synchronization signal generated by the sensor when the polygon mirror has a rotation speed lower than the normal rotation speed at the time of drawing, returns light from the polygon mirror to the photodetector. The initialization APC process is started at a timing that does not occur.

  According to the present invention, it is possible to obtain an image forming apparatus that suppresses errors caused by return light from the polygon mirror in the initialization APC process and correctly sets the drive current of the laser diode.

  These and other objects, features and advantages of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.

FIG. 1 is a side view showing a part of a mechanical internal configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a view showing an example of the configuration of the exposure apparatuses 2a to 2d in FIG. 1 and the configuration of the peripheral electronic circuit. FIG. 3 is a diagram showing a detailed configuration of the light source 21 and the driver circuit 31 in FIG. FIG. 4 is a flowchart for explaining the operation of the driver circuit 31 when the initial APC process is started during the acceleration period of the polygon mirror 23 in the first embodiment. FIG. 5 is a flowchart for explaining the operation of the driver circuit 31 when the initial APC process is started during the inertial rotation period of the polygon mirror 23 in the first embodiment. FIG. 6 is a flowchart for explaining the operation of the driver circuit 31 in the second embodiment (1/2). FIG. 7 is a flowchart for explaining the operation of the driver circuit 31 in the second embodiment (2/2). Figure 8 is a diagram for explaining the characteristics of the light emission amount with respect to the driving current I _OP of the laser diode. Figure 9 is a diagram for explaining error due to the return light occurs threshold current I _th. FIG. 10 is a diagram illustrating an error that occurs in the threshold current I _th and the light emission current I _sw due to the return light.

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

Embodiment 1 FIG.

  FIG. 1 is a side view showing a part of a mechanical internal configuration of an image forming apparatus according to an embodiment of the present invention. The image forming apparatus shown in FIG. 1 is an apparatus having an electrophotographic printing function, such as a printer, a facsimile machine, a copying machine, or a multifunction machine.

  The image forming apparatus shown in FIG. 1 has a tandem color developing device. The color developing device includes photosensitive drums 1a to 1d, exposure devices 2a to 2d, and developing devices 3a to 3d. The photoconductor drums 1a to 1d are four-color photoconductors of cyan, magenta, yellow, and black.

  The exposure devices 2a to 2d set an exposure pulse width for each pixel and irradiate the photosensitive drums 1a to 1d with light rays to form electrostatic latent images. The exposure apparatuses 2a to 2d include a laser diode that is a light source of laser light and optical elements (lenses, mirrors, polygon mirrors, etc.) that guide the laser light to the photosensitive drums 1a to 1d.

  Further, around the photosensitive drums 1a to 1d, a charger such as a scorotron, a cleaning device, a static eliminator and the like are arranged. The cleaning device removes residual toner on the photosensitive drums 1a to 1d after the primary transfer, and the static eliminator neutralizes the photosensitive drums 1a to 1d after the primary transfer.

  Each of the developing devices 3a to 3d is mounted with a toner cartridge filled with toners of four colors of cyan, magenta, yellow and black, and the toner is supplied from the toner cartridge and constitutes a developer together with the carrier. The developing devices 3a to 3d attach the toner to the electrostatic latent images on the photosensitive drums 1a to 1d to form a toner pattern.

  The photosensitive drum 1a, the exposure device 2a, and the developing device 3a develop magenta, and the photosensitive drum 1b, the exposure device 2b, and the developing device 3b develop cyan, the photosensitive drum 1c, and the exposure device. Yellow development is performed by the device 2c and the developing device 3c, and black development is performed by the photosensitive drum 1d, the exposure device 2d, and the developing device 3d.

  The intermediate transfer belt 4 is an annular image carrier that contacts the photosensitive drums 1a to 1d and primarily transfers the toner images on the photosensitive drums 1a to 1d. The intermediate transfer belt 4 is stretched around the driving roller 5 and circulates in the direction from the contact position with the photosensitive drum 1d to the contact position with the photosensitive drum 1a by the driving force from the driving roller 5.

  The transfer roller 6 brings the conveyed paper into contact with the intermediate transfer belt 4 and secondarily transfers the toner image on the intermediate transfer belt 4 to the paper. The sheet on which the toner image has been transferred is conveyed to the fixing device 9 and the toner image is fixed on the sheet.

  The roller 7 has a cleaning brush, and the cleaning brush is brought into contact with the intermediate transfer belt 4 to remove the toner remaining on the intermediate transfer belt 4 after the transfer of the toner image onto the paper.

  The density sensor 8 is an optical sensor used for measuring the density of the toner pattern, and irradiates the intermediate transfer belt 4 with a light beam and detects the reflected light. For example, when adjusting the toner density, the density sensor 8 irradiates a predetermined area of the intermediate transfer belt 4 with a light beam, detects the reflected light, and outputs an electrical signal corresponding to the light quantity.

  FIG. 2 is a view showing an example of the configuration of the exposure apparatuses 2a to 2d in FIG. 1 and the configuration of the peripheral electronic circuit. Note that the exposure apparatus shown in FIG. 2 is an exposure apparatus 2a for the photosensitive drum 1a, and the exposure apparatuses 2b to 2d for the photosensitive drums 1b to 1d have the same configuration.

  In FIG. 2, a light source 21 is a light source unit that emits laser light with a laser diode. The optical system 22 is various lens groups arranged between the light source 21 and the polygon mirror 23 and / or between the polygon mirror 23 and the photosensitive drum 1a and the PD sensor 24. For the optical system 22, an fθ lens or the like is used.

  The polygon mirror 23 is an element having an axis perpendicular to the axis of the photosensitive drum 1a, a cross section perpendicular to the axis being a polygon, and a side surface being a mirror. The polygon mirror 23 rotates about its axis by the driving force of the motor, and scans the laser light emitted from the light source 21 along the axial direction (main scanning direction) of the photosensitive drum 1a.

  The PD sensor 24 is a sensor that receives laser light scanned by the polygon mirror 23 to generate a main scanning synchronization signal and generates a synchronization signal in the main scanning direction. When the laser beam is incident, the PD sensor 24 induces an output voltage corresponding to the amount of light. The PD sensor 24 is arranged at a predetermined position on the line where light is scanned, detects the timing when the light spot passes through the position, and generates a pulse-like synchronization signal.

  The driver circuit 31 is a circuit that drives the light source 21. The driver circuit 31 controls the light source 21 to emit laser light based on a drive signal for image formation. The controller 32 outputs a drive signal to the driver circuit 31 based on the image data supplied from the image processing unit 33, and forms an electrostatic latent image based on the image data on the photosensitive drum 1a.

  FIG. 3 is a diagram showing a detailed configuration of the light source 21 and the driver circuit 31 in FIG.

  The light source 21 includes a laser diode LD that emits the above-described laser light, and a photodetector PD such as a photodiode that receives a part of the laser light.

The driver circuit 31 includes a driver IC 31a and a current detection resistor R. Current detection resistor R is a resistor for detecting the value of the monitor current I _PD which conducts the photodetector PD in accordance with the amount of the laser beam emitted from the laser diode LD.

Drivers IC31a is caused to conduct the drive current _{I OP} to the laser diode LD, as a light amount of the laser light corresponding to the driving current _{I OP,} the voltage across _{V PD} of the current detection resistor R corresponding to the monitor current _{I PD,} a photodetector It is an IC chip that measures the detection voltage of PD.

  Then, the driver IC 31a executes an initialization APC process for adjusting the amount of laser light when the light source 21 is initialized based on the detection voltage of the photodetector PD. The driver IC 31a also executes line APC processing.

As described above, in the initialization APC process, drivers IC31a, while monitoring the detection voltage _{V PD} of the photodetector PD, the driving current _{I OP} of the laser diode LD, from well below a predetermined value than zero or the threshold current _{I th} gradually increased, based on the value of the detected voltage V _PD, firstly, identify the threshold current I _th, then the driving current I _OP when a value of the detected voltage V _PD corresponding to the target light quantity Based on the value, an increase (light emission current I _sw ) of the drive current I _OP from the threshold current I _th is specified. Thereby, the characteristic of the light quantity of the laser diode LD with respect to the drive current _IOP is specified.

Further, the line APC process, drivers IC31a in a period other than the light emission period of the laser diode LD, the driving current _{I OP} is gradually increased from the threshold current _{I th,} the value of the output voltage _{V PD} corresponding to the target light quantity The light emission current I _sw is specified based on the value of the drive current I _OP at the time, and the above-described characteristics are corrected based on the specified light emission current I _sw .

  In particular, the driver IC 31a of the driver circuit 31 is lower than the normal rotation speed when the polygon mirror 23 draws images (that is, the rotation speed when the electrostatic latent images are formed on the photosensitive drums 1a to 1d by laser light). Based on the synchronization signal generated by the PD sensor 24 at the rotation speed, the initialization APC process is started at a timing at which return light from the polygon mirror to the photodetector PD does not occur.

  For example, the driver IC 31a of the driver circuit 31 includes (a) an acceleration period from the start of driving of the polygon mirror 23 to a normal rotation speed, or (b) an inertia rotation period of the polygon mirror 23 (that is, the polygon mirror in the normal rotation speed state). In the deceleration period in which power supply to the motor that drives the motor 23 is stopped and the polygon mirror 23 rotates due to inertia and the rotational speed gradually decreases due to frictional resistance), the polygon is based on the synchronization signal generated by the PD sensor 24. Initialization APC processing is started at a timing when no return light is generated from the mirror 23 to the photodetector PD.

  When the initialization APC process is started during the acceleration period, the driver IC 31a of the driver circuit 31 stops the initialization APC process when the elapsed time of the initialization APC process becomes longer than the period of the synchronization signal. Note that the period of the synchronization signal is measured immediately before the initialization APC process.

  When the initialization APC process is started during the inertia rotation period, the driver IC 31a of the driver circuit 31 stops the initialization APC process when the elapsed time of the initialization APC process becomes longer than the period of the synchronization signal. Then, the initialization APC process is restarted at a timing when no return light is generated from the polygon mirror 23 to the photo detector PD.

  The return light described above is generated, for example, when the incident position of the laser light passes through the boundary of the mirror surface of the polygon mirror 23 (the connection point between the mirror surface and the mirror surface adjacent to the mirror surface). Therefore, the driver IC 31 a of the driver circuit 31 starts the initialization APC process immediately after the incident position of the laser light from the light source 21 passes through the boundary of the mirror surface of the polygon mirror 23.

  The timing at which the incident position of the laser light passes the boundary of the mirror surface of the polygon mirror 23 is specified based on the above-described synchronization signal.

  Next, the operation of the image forming apparatus according to the first embodiment will be described.

(A) When initial APC processing is started during the acceleration period of the polygon mirror 23

  FIG. 4 is a flowchart for explaining the operation of the driver circuit 31 when the initial APC process is started during the acceleration period of the polygon mirror 23 in the first embodiment.

In this case, first, in a state where the polygon mirror 23 is stopped, the driver IC31a performs initialization APC processing, specifying the driving current _{I OP} with respect to the target light intensity (step S1). In this initialization APC process, there is a possibility that the specified drive current _IOP is affected by the return light. Therefore, the initialization APC process is performed again after step S7 described later.

  When the initialization APC process in step S1 is completed, the driver IC 31a controls a motor (not shown) to start driving the polygon mirror 23 (step S2). Thereby, the rotational speed of the polygon mirror 23 is gradually increased until it reaches the normal rotational speed.

  Then, the driver IC 31a starts lighting the laser diode LD with the drive current IOP based on the initialization APC process in step S1 (step S3).

  As a result, the laser beam being scanned is received by the PD sensor 24. The driver IC 31a acquires the synchronization signal (pulse signal) from the PD sensor 24 a plurality of times (step S4), and specifies the interval of the synchronization signals as the period of the synchronization signal (step S5).

  When the period of the synchronization signal is specified, the driver IC 31a immediately stops lighting the laser diode LD (step S6) and starts the initialization APC process (step S7).

  That is, immediately after the synchronization signal is detected, the incident position of the laser light passes through the boundary of the mirror surface of the polygon mirror 23, so the initialization APC process in step S7 is started at a timing at which no return light is generated.

  The driver IC 31a starts measuring the elapsed time from the start timing of the initialization APC process, whether the elapsed time is equal to or longer than the period of the synchronization signal (step S8), and whether the initialization APC process is completed. (Step S9) is monitored.

Incidentally, the driver IC31a is gradually increased drive current IOP, it identifies a threshold current _{I th} and the light emission current _{I sw} based on the detected voltage VPD. Once identified the threshold current _{I th} and the light emission current _{I sw,} drivers IC31a determines that initialization APC processing is completed.

  If the elapsed time is equal to or longer than the period of the synchronization signal before the initialization APC process is completed, the driver IC 31a stops the initialization APC process because there is a possibility of being influenced by the return light. (Step S10).

  On the other hand, if the initialization APC process is completed before the elapsed time becomes equal to or greater than the period of the synchronization signal, the driver IC 31a determines that the initialization APC process has been performed normally.

(B) When the initial APC process is started during the inertial rotation period of the polygon mirror 23

  FIG. 5 is a flowchart for explaining the operation of the driver circuit 31 when the initial APC process is started during the inertial rotation period of the polygon mirror 23 in the first embodiment.

In this case, first, in a state where the polygon mirror 23 is stopped, the driver IC31a performs initialization APC processing, specifying the driving current _{I OP} with respect to the target light intensity (step S21). In this initialization APC process, there is a possibility that the specified drive current _IOP is affected by the return light. Therefore, the initialization APC process is performed again after step S28 described later.

  When the initialization APC process in step S21 is completed, the driver IC 31a controls a motor (not shown) to start driving the polygon mirror 23 (step S22). Thereby, the rotational speed of the polygon mirror 23 increases gradually. Thereafter, when a predetermined rotation speed (for example, normal rotation speed) is reached, the driver IC 31a controls a motor (not shown) to stop driving the polygon mirror 23 (step S23). As a result, the polygon mirror 23 starts inertial rotation, and the rotation speed of the polygon mirror 23 gradually decreases.

  Then, the driver IC 31a starts lighting the laser diode LD with the drive current IOP based on the initialization APC process in step S21 (step S24).

  As a result, the laser beam being scanned is received by the PD sensor 24. The driver IC 31a acquires the synchronization signal (pulse signal) from the PD sensor 24 a plurality of times (step S25), and specifies the interval of the synchronization signals as the period of the synchronization signal (step S26).

  When the period of the synchronization signal is specified, the driver IC 31a immediately stops lighting the laser diode LD (step S27) and starts the initialization APC process (step S28).

  That is, immediately after the synchronization signal is detected, the incident position of the laser beam passes through the boundary of the mirror surface of the polygon mirror 23, so the initialization APC process in step S28 is started at a timing at which no return light is generated.

  The driver IC 31a starts measuring the elapsed time from the start timing of the initialization APC process, whether the elapsed time is equal to or longer than the period of the synchronization signal (step S29), and whether the initialization APC process is completed. (Step S30) is monitored.

Incidentally, the driver IC31a is gradually increased driving current _{I OP,} identifies a threshold current _{I th} and the light emission current _{I sw} based on the detection voltage _{V PD.} Once identified the threshold current _{I th} and the light emission current _{I sw,} drivers IC31a determines that initialization APC processing is completed.

  If the elapsed time is equal to or greater than the period of the synchronization signal before the initialization APC process is completed, the driver IC 31a may stop the initialization APC process because there is a possibility of being affected by the return light. Returning to step S24, the synchronization signal is detected again, the period of the synchronization signal is specified, and the initialization APC process is started again (steps S24 to S28).

  On the other hand, if the initialization APC process is completed before the elapsed time becomes equal to or greater than the period of the synchronization signal, the driver IC 31a determines that the initialization APC process has been performed normally and resumes driving of the polygon mirror 23 ( Step S31).

  As described above, according to the first embodiment, the polygon mirror 23 scans the laser beam in the main scanning direction. The PD sensor 24 receives the laser beam being scanned and generates a synchronization signal in the main scanning direction. The photodetector PD detects a part of the laser light. The driver circuit 31 executes an initialization APC process that adjusts the amount of the laser beam when the light source is initialized, based on the detection voltage of the photodetector. The driver circuit 31 does not generate return light from the polygon mirror 23 to the photodetector PD based on the synchronization signal generated by the PD sensor 24 when the polygon mirror 23 has a rotation speed lower than the normal rotation speed at the time of drawing. The initialization APC process is started at the timing.

Thereby, in the initialization APC process, an error caused by the return light from the polygon mirror is suppressed, and the laser diode drive current I _OP is set correctly.

Embodiment 2. FIG.

  In the second embodiment, when the initialization APC process is stopped in the acceleration period, the driver circuit 31 stops the driving of the polygon mirror 23 to rotate the polygon mirror 23 in an inertial direction, and is generated by the PD sensor 24 in the inertial rotation period. Based on the synchronization signal, the initialization APC process is started again at a timing when no return light is generated from the polygon mirror 23 to the photodetector PD.

  Also in the second embodiment, for example, the driver IC 31a of the driver circuit 31 starts the initialization APC process immediately after the incident position of the laser light from the light source 21 passes through the boundary of the mirror surface of the polygon mirror 23.

  6 and 7 are flowcharts for explaining the operation of the driver circuit 31 according to the second embodiment.

  In the second embodiment, first, during the acceleration period, as in the first embodiment (steps S1 to S7), the driver circuit 31 starts the initialization APC process after specifying the period of the synchronization signal (steps S41 to S41). S47). The driver IC 31a starts measuring the elapsed time from the start timing of the initialization APC process, whether the elapsed time is equal to or longer than the period of the synchronization signal (step S48), and whether the initialization APC process is completed. (Step S49) is monitored.

  When the initialization APC process is completed before the elapsed time becomes equal to or longer than the period of the synchronization signal, the driver IC 31a determines that the initialization APC process has been performed normally.

  On the other hand, if the elapsed time becomes equal to or longer than the period of the synchronization signal before the initialization APC process is completed, the driver IC 31a may perform the initialization APC process because there is a possibility of being influenced by the return light. Discontinue. Thereafter, in the second embodiment, the driver IC 31a controls a motor (not shown) to stop driving the polygon mirror 23 (step S50). As a result, the polygon mirror 23 starts inertial rotation, and the rotation speed of the polygon mirror 23 gradually decreases.

  Then, the driver IC 31a starts lighting the laser diode LD with the drive current IOP based on the initialization APC process in step S41 (step S51).

  As a result, the laser beam being scanned is received by the PD sensor 24. The driver IC 31a acquires the synchronization signal (pulse signal) from the PD sensor 24 a plurality of times (step S52), and specifies the interval of the synchronization signals as the period of the synchronization signal (step S53).

  When the period of the synchronization signal is specified, the driver IC 31a immediately stops lighting the laser diode LD (step S54) and starts the initialization APC process (step S55).

  That is, immediately after the synchronization signal is detected, the incident position of the laser beam passes through the boundary of the mirror surface of the polygon mirror 23, so the initialization APC process in step S55 is started at a timing at which no return light is generated.

  The driver IC 31a starts measuring the elapsed time from the start timing of the initialization APC process, whether or not the elapsed time is equal to or longer than the period of the synchronization signal (step S56), and whether or not the initialization APC process is completed. (Step S57) is monitored.

  If the elapsed time is equal to or greater than the period of the synchronization signal before the initialization APC process is completed, the driver IC 31a may stop the initialization APC process because there is a possibility of being affected by the return light. Returning to step S51, the synchronization signal is detected again, the period of the synchronization signal is specified, and the initialization APC process is started again (steps S51 to S55).

  On the other hand, if the initialization APC process is completed before the elapsed time becomes equal to or greater than the period of the synchronization signal, the driver IC 31a determines that the initialization APC process has been performed normally and resumes driving of the polygon mirror 23 ( Step S58).

  Since the other configuration and operation of the image forming apparatus according to the second embodiment are the same as those of the first embodiment, the description thereof is omitted.

  Various changes and modifications to the above-described embodiment will be apparent to those skilled in the art. Such changes and modifications may be made without departing from the spirit and scope of the subject matter and without diminishing its intended advantages. That is, such changes and modifications are intended to be included within the scope of the claims.

  The present invention can be applied to, for example, an image forming apparatus that performs exposure by scanning a laser beam with a polygon mirror.

21 Light source 23 Polygon mirror 24 PD sensor (an example of sensor)
31 Driver circuit

Claims (6)

A light source that emits laser light;
A polygon mirror that scans the laser beam in the main scanning direction;
A sensor that receives the laser beam being scanned and generates a synchronization signal in the main scanning direction;
A photodetector for detecting a part of the laser beam;
A driver circuit that drives the light source and executes an initialization APC process that adjusts the amount of the laser light when the light source is initialized based on a detection voltage of the photodetector;
The driver circuit does not generate return light from the polygon mirror to the photodetector based on the synchronization signal generated by the sensor when the polygon mirror has a rotation speed lower than a normal rotation speed at the time of drawing. Starting the initialization APC process at a timing;
An image forming apparatus.   In the acceleration period from the start of driving of the polygon mirror to the normal rotation speed or in the inertial rotation period of the polygon mirror, the driver circuit is configured to output the polygon mirror from the polygon mirror based on the synchronization signal generated by the sensor. The image forming apparatus according to claim 1, wherein the initialization APC process is started at a timing at which return light to the detector does not occur.   When the initialization APC process is started in the acceleration period, the driver circuit stops the initialization APC process when an elapsed time of the initialization APC process becomes longer than a period of the synchronization signal. The image forming apparatus according to claim 2.   When the initialization APC process is stopped, the driver circuit stops the driving of the polygon mirror to rotate the polygon mirror by inertia, and based on the synchronization signal generated by the sensor during the inertia rotation period 4. The image forming apparatus according to claim 3, wherein the initialization APC process is started again at a timing at which no return light is generated from the polygon mirror to the photodetector.   When the driver circuit starts the initialization APC process in the inertia rotation period, when the elapsed time of the initialization APC process becomes longer than the period of the synchronization signal, the driver circuit stops the initialization APC process, 5. The image forming apparatus according to claim 2, wherein the initialization APC process is restarted at a timing at which no return light is generated from a polygon mirror to the photodetector. The return light is generated when the incident position of the laser light passes the boundary of the mirror surface of the polygon mirror,
The driver circuit starts the initialization APC process immediately after the incident position of the laser beam passes the boundary of the mirror surface of the polygon mirror;
The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus.

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