JP2017052206A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device that controls laser beam quantities with simpler configuration than before.SOLUTION: The image forming device comprises: a semiconductor laser 12 that emits laser beams which are irradiated to a photosensitive drum; a BD 20 that senses laser beams before the beams are irradiated to the photosensitive drum; and a laser circuit board 11. The laser circuit board 11 comprises a capacitor 38a accumulating a first electric charge corresponding to a first driving current and a capacitor 38b accumulating a second electric charge corresponding to a second driving current. The laser circuit board 11 supplies currents to the semiconductor laser 12 using the capacitor 38a when making the BD 20 to sense the laser beams, and supplies currents to the semiconductor laser 12 using the capacitor 38b when the beams are irradiated to the photosensitive drum.SELECTED DRAWING: Figure 3

Description

  The present invention relates to an electrophotographic image forming apparatus, and more particularly to a technique for controlling the amount of laser light used for image formation.

  An electrophotographic image forming apparatus forms an electrostatic latent image by irradiating a photoreceptor with laser light, and forms an image by attaching a developer to the electrostatic latent image. The laser light is output from an optical scanning device having an exposure device including a semiconductor laser, a rotating polygon mirror, an f-θ lens, and the like. The semiconductor laser outputs laser light. Laser light output from the semiconductor laser is periodically deflected by a rotating polygon mirror, and irradiates the photoconductor via an f-θ lens. The laser beam scans on the photosensitive member by continuously changing the reflection direction by the rotation of the rotary polygon mirror.

  The optical scanning device includes a detection sensor for detecting laser light (hereinafter referred to as “BD (Beam Detector)”). The BD receives the laser beam before or after the laser beam scans on the photosensitive member. The BD generates a BD signal by receiving laser light. The BD signal is used to control the emission timing of laser light based on image data in one scanning cycle. The BD signal is used to define the timing for switching the control mode of the laser driver. Patent Document 1 discloses an image forming apparatus in which a laser beam incident on a BD to generate a BD signal and a laser beam that scans a photoconductor have the same light amount.

JP 2005-280070 A

  However, the image forming apparatus disclosed in Patent Document 1 has the following problems. FIG. 10 is a timing chart of light emission control of a semiconductor laser used in a conventional optical scanning device. In order to cope with a change in the state of the main body of the image forming apparatus and a rapid environmental change around the image forming apparatus when continuously forming images, the amount of laser light that scans the photoconductor is controlled as shown in FIG. It is assumed that this must be done. At this time, as shown in FIG. 10, the amount of the laser beam scanned on the photosensitive member is controlled by changing the value of the reference voltage Vref. At this time, if the amount of laser light incident on the BD and the amount of laser light scanned on the photosensitive member are set to be the same as in a conventional image forming apparatus, the waveform of the BD signal fluctuates before and after the light amount control. Resulting in. Therefore, there arises a problem that the image writing position is different before and after the light amount control. In order to solve such problems, there is a demand for an image forming apparatus capable of controlling the light amount of laser light for generating a BD signal and the light amount of laser light that scans the photosensitive member.

  The image forming apparatus of the present invention includes a photoconductor, a semiconductor laser including a light emitting element that emits laser light for exposing the photoconductor, and the light emitted from the light emitting element to control the amount of the laser light. A first light receiving element that receives laser light and generates a light reception signal having a voltage corresponding to the amount of received light, and deflects the laser light so that the laser light emitted from the light emitting element scans the photosensitive member. Based on the deflection means, the second light receiving element that receives the laser light deflected by the deflection means to generate the synchronization signal, and the image data in one scanning period of the laser light based on the generation timing of the synchronization signal Timing control means for controlling the emission timing of the laser beam based on the above, output means for outputting the first reference voltage or the second reference voltage, a first capacitor, and a second capacitor Sensor, the light reception signal and a reference voltage output from the output means are input, and the voltage of the light reception signal is compared with the first reference voltage or the second reference voltage, and based on the comparison result, Voltage control means for controlling the voltage of the first capacitor or the voltage of the second capacitor, and a current having a value corresponding to one of the voltage of the first capacitor and the voltage of the second capacitor is supplied to the light emitting element. A current supply means; and a switching means for switching a capacitor whose voltage is controlled by the voltage control means between the first capacitor and the second capacitor, and the output means is incident on the second light receiving element. Outputting the first reference voltage to control the amount of laser light to be output, and outputting the second reference voltage to control the amount of laser light to scan on the photoconductor, The switching means is configured to control the voltage of the first capacitor based on a comparison result between the light reception signal and the first reference voltage, and based on a comparison result between the light reception signal and the second reference voltage. The voltage control means switches the capacitor for controlling the voltage between the first capacitor and the second capacitor so that the voltage of the second capacitor is controlled.

  According to the present invention, the amount of laser light can be controlled with a simpler configuration than in the past.

1 is a configuration diagram of an image forming apparatus. The block diagram of an exposure device. The block diagram of a laser circuit board. The timing chart which shows the selection method of a hold capacitor. (A), (b) is explanatory drawing of a reference voltage production | generation part. (A), (b) is a timing chart at the time of performing light emission control. Explanatory drawing of the relationship between received light quantity and output delay time. The other block diagram of a laser circuit board. (A), (b) is a timing chart at the time of performing light emission control of a semiconductor laser. 6 is a timing chart of conventional semiconductor laser light emission control.

  Hereinafter, embodiments will be described in detail with reference to the drawings.

Example 1
FIG. 1 is a configuration diagram of an electrophotographic image forming apparatus. The image forming apparatus 1 is, for example, a copying machine or a multifunction machine. The image forming apparatus 1 includes a plurality of optical scanning devices 2a, 2b, 2c, and 2d, a control unit 5, a scanner 500, an image forming unit 503, a fixing device 504, a paper feeding / conveying unit 505, and a manual feed tray 509. The image forming unit 503 includes a plurality of photosensitive drums 25 that are photosensitive members corresponding to the plurality of optical scanning devices 2a, 2b, 2c, and 2d, a developing unit 512 that is provided corresponding to each photosensitive drum 25, and an intermediate unit. A transfer body 511 is provided.

  The scanner 500 irradiates a document placed on a document table, receives the reflected light, and optically reads a document image. The scanner 500 converts the received reflected light into an electrical signal and outputs it. The control unit 5 processes the electrical signal output from the scanner 500 and generates image data corresponding to the document image. The control unit 5 controls the light emission of the optical scanning devices 2a, 2b, 2c, and 2d based on the generated image data.

  The optical scanning devices 2a, 2b, 2c, and 2d irradiate the corresponding photosensitive drums 25 with laser beams (laser beams). The image forming unit 503 rotationally drives each photosensitive drum 25 and charges its surface with a charger. An electrostatic latent image is formed on the surface of the photosensitive drum 25 whose surface is charged by laser light irradiation. The developing unit 512 stores toner as a developer, and develops the toner by attaching the toner to the electrostatic latent image. As a result, a toner image is formed on the photosensitive drum 25. Different color toner images are formed on the photosensitive drum 25. For example, yellow, magenta, cyan, and black toner images are formed on the photosensitive drum 25. The toner images formed on the respective photosensitive drums 25 are transferred onto the intermediate transfer member 511 so as to be superimposed. As a result, a full-color toner image is formed on the intermediate transfer member 511.

  A sheet feeding / conveying unit 505 conveys a sheet placed on a sheet feeding cassette or a manual feed tray 509 to a position where the sheet contacts with the intermediate transfer member 511. The toner image formed on the intermediate transfer member 511 is transferred to the sheet. The sheet on which the toner image is transferred is conveyed to the fixing device 504. The fixing device 504 thermally press-bonds the toner image to the sheet. As a result, the image is fixed on the sheet. The sheet on which the image is fixed is discharged to the outside of the image forming apparatus 1. As described above, the image forming apparatus 1 performs the image forming process.

  FIG. 2 is a configuration diagram of the optical scanning device 2a. Since the optical scanning devices 2a, 2b, 2c, and 2d have the same configuration, the optical scanning device 2a will be described here, and the description of the other optical scanning devices 2b, 2c, and 2d will be omitted.

  The optical scanning device 2a includes a laser circuit board 11, a semiconductor laser 12 that emits laser light, a collimating lens 13, a cylindrical lens 14, a polygon mirror 15a that is a rotating polygon mirror, an f-θ lens 17, a reflection mirror 18, and a condenser lens. 19 and BD20.

  A reference voltage generation circuit 33, a laser driver 30, and a semiconductor laser 12 to be described later are mounted on the laser circuit board 11. Laser light emitted from an LD 12a (described later) of the semiconductor laser 12 passes through the collimating lens 13 and the cylindrical lens 14 and enters the reflecting surface of the polygon mirror 15a. The polygon mirror 15a is driven to rotate clockwise in the figure by the drive motor 15. The laser beam is deflected by the polygon mirror 15a so as to scan the photosensitive drum 25 in the direction of the arrow. The laser beam deflected by the polygon mirror 15 a passes through the f-θ lens 17 and is reflected by the reflection mirror 18 to be guided onto the photosensitive drum 25.

  The BD 20 is arranged to receive laser light that scans the non-image area. The BD 20 receives the laser beam L1 deflected by the polygon mirror 15a through the f-θ lens 17 and the condenser lens 19. The BD 20 is a photoelectric conversion element, and outputs a BD signal 21 (or a synchronization signal) that is a light reception signal having a voltage corresponding to the amount of received light. The BD signal 21 is input to the control unit 5. The control unit 5 converts the BD signal 21 into a pulse signal using a threshold of a predetermined voltage, and performs laser beam emission timing control based on image data in each scanning period based on the generation timing of the pulse signal. . Since the BD signal 21 is generated by the laser light deflected on each of the plurality of reflecting surfaces of the polygon mirror 15a, the BD signal 21 is output at a constant period when the rotation speed of the polygon mirror 15a is stable.

  FIG. 3 is a control block diagram for driving the semiconductor laser 12. On the laser circuit board 11, a laser driver 30, a reference voltage generation circuit 33, a resistor 37, a capacitor 38a (first hold capacitor), a capacitor 38b (second hold capacitor), a switch 44, a resistor 40, and the semiconductor laser 12 are mounted. ing. The laser circuit board 11 is connected to the control unit 5 by a cable.

  The semiconductor laser 12 includes a laser diode (hereinafter referred to as “LD”) 12 a that is a light emitting element that emits laser light, and a photodiode (hereinafter referred to as “PD”) that is a light receiving element that receives the laser light emitted from the LD 12 a. .) 12b. The LD 12a emits a laser beam having a light amount corresponding to the value of the current ILD supplied from the laser driver 30. The PD 12 b inputs a current Ipd having a value corresponding to the amount of received light to the laser driver 30. The semiconductor laser 12 of this embodiment is an edge-emitting semiconductor laser that emits laser light in both directions. Laser light emitted from one side of the semiconductor laser 12 enters the collimating lens 13, and laser light emitted from the other side enters the PD 12b.

  The laser driver 30 includes an APC circuit 35 (voltage control circuit), a switch 36, a comparator 39, a transistor 41, and a transistor 43, and supplies current to the LD 12a. A video signal 42 which is a PWM signal is input from the control unit 5 to the laser driver 30. The video signal 42 is a signal for turning on / off the transistor 41. For example, when the video signal 42 is at a high level, the current ILD flows through the LD 12a. The LD 12a emits a laser beam having a light amount corresponding to the value of the current ILD. On the other hand, when the video signal 42 is at the low level, the current ILD does not flow through the LD 12a. The transistor 41 is a switch for turning on / off the LD 12a, and does not substantially have a current amplification function.

  The capacitor 38a is provided in order to emit laser light that enters the BD 20 from the LD 12a. On the other hand, the condenser 38b is provided to emit laser light for scanning the photosensitive drum 25 from the LD 12a.

  The switch 44 operates in response to the capacity switching signal 45 shown in FIG. When the capacitance switching signal 45 is Low, the switch 44 connects the terminal a and the terminal b. When the terminals a and b are connected, the voltage Vch_a of the capacitor 38a is applied to the non-inverting terminal of the comparator 39. On the other hand, when the capacitance switching signal 45 is High, the switch 44 connects the terminal a and the terminal c. When the terminal a and the terminal c are connected, the voltage Vch_b of the capacitor 38b is applied to the non-inverting terminal of the comparator 39. The inverting terminal of the comparator 39 is connected to the emitter terminal of the transistor 43 and the anode terminal of the resistor 40. Therefore, the voltage V− at the inverting terminal of the comparator 39 is equal to the voltage at the anode terminal of the resistor 40.

  The value of the current ILD is defined by the voltage of the capacitor connected to the non-inverting terminal of the comparator 39 of the capacitors 38 a and 38 b and the resistance value of the resistor 40. The anode terminal of the resistor 40 is connected to the emitter terminal of the transistor 41. The cathode terminal of the resistor 40 is grounded. The collector terminal of the transistor 41 is connected to the emitter terminal of the transistor 43. The base terminal of the transistor 43 is connected to the output terminal of the comparator 39.

  The voltage V− at the inverting terminal of the comparator 39 is defined by the value of the current ILD and the resistor 40. The comparator 39 controls the base voltage of the transistor 43 based on the comparison result between the voltage V + at the non-inverting terminal and V− at the inverting terminal. That is, the base voltage of the transistor 43 is controlled to be a voltage corresponding to the voltage of the capacitor 38a or the capacitor 38b. By controlling the base voltage of the transistor 43 in this way, the voltage of the anode terminal of the resistor 40 is controlled, and as a result, the value of the current ILD is controlled.

  Next, APC (Automatic Power Control) will be described. APC is executed to control the amount of laser light emitted from the LD 12a to a target amount of light. That is, APC in the image forming apparatus 1 of this embodiment is to control the voltage of the capacitor 38a or the capacitor 38b to a voltage corresponding to the target light amount of the laser beam. In the image forming apparatus 1 of the present embodiment, a plurality of target light amounts are set. One target light amount among the plurality of target light amounts is a target light amount (first target light amount) of laser light incident on the BD 20. Further, the other target light amount among the plurality of target light amounts is a target light amount (second target light amount) of the laser light that scans on the photosensitive drum 25. The APC of this embodiment is a sequence that is executed during one scanning period of the laser light in order to control the light amount of the laser light to the first target light amount and the second target light amount. The image forming apparatus 1 according to the present exemplary embodiment includes an APC for controlling laser light to a first target light amount (first light amount control mode described later) and an APC for controlling laser light to a second target light amount (described later). The second light quantity control mode) is executed once during each scanning period of the laser light.

  The control unit 5 connects the switch 36 by a sample hold signal when executing APC. The controller 5 outputs a voltage setting signal 31 corresponding to the target light amount of the laser light emitted from the LD 12a. In this embodiment, the voltage setting signal 31 is a PWM (Pulse Width Modulation) signal. The control unit 5 outputs a PWM signal having a pulse width corresponding to the target light amount of the laser light.

  FIG. 5A is a circuit configuration example diagram of the reference voltage generation circuit 33. The reference voltage generation circuit 33 includes a field effect transistor (FET) 52. The drain terminal of the FET 52 is connected to a voltage source 51 that outputs a fixed voltage (for example, 5 [V]). The gate terminal of the FET 52 is connected to the control unit 5. The voltage setting signal 31 is input from the control unit 5 to the gate terminal of the FET 52. The source terminal of the FET 52 is connected to one terminal of the resistor 53 and one terminal of the resistor 55. The other terminal of the resistor 55 is grounded. The other terminal of the resistor 53 is connected to the capacitor 54.

  The FET 52 executes a switching operation for connecting or releasing the drain terminal and the source terminal by a PWM signal input to the gate terminal. When the FET 52 is turned on, the voltage at the source terminal of the FET 52 becomes the voltage 5 [V] output from the voltage source 51. On the other hand, when the FET 52 is turned OFF, the voltage at the source terminal of the FET 52 becomes 0 [V]. Therefore, the voltage of the source terminal of the FET 52 takes a value between two values of 5 [V] and 0 [V] according to the duty ratio of the PWM signal.

  The resistor 53 and the capacitor 54 are electronic components that constitute a smoothing circuit. The smoothing circuit outputs, as the Vref signal 34, a voltage Vref obtained by smoothing the voltage at the source terminal that varies depending on the switching operation of the FET 52. For example, as shown in FIG. 5B, when the duty ratio of the PWM signal input to the gate terminal of the FET 52 is 100 [%], Vref is 5 [V]. When the duty ratio of the PWM signal input to the gate terminal of the FET 52 is 50 [%], Vref is 2.5 [V]. When the duty ratio of the PWM signal input to the gate terminal of the FET 52 is 25 [%], Vref is 1.25 [V]. Thus, the reference voltage Vref can be controlled to the target value by controlling the pulse width of the PWM signal. The Vref signal 34 generated by the reference voltage generation circuit 33 is input to an APC circuit 35 built in the laser driver 30.

  The control unit 5 sets the video signal 42 to a high level when executing APC. As a result, a current ILD having a value corresponding to the voltage Vch_b of the capacitor 38b flows through the LD 12a. The LD 12a emits a laser beam having a light amount corresponding to the value of the current ILD. The PD 12b receives the laser light and outputs a current Ipd (light reception signal) having a value corresponding to the amount of light. The PD 12 b is connected to the resistor 37 and the APC circuit 35. The current Ipd flows through the resistor 37 to the ground. The voltage Vpd at the anode of the resistor 37 is defined by the current Ipd and the resistance value of the resistor 37. The voltage Vpd is input to the APC circuit 35. That is, the voltage Vpd is generated when the PD 12b outputs the current Ipd.

  The APC circuit 35 includes a comparator (not shown) that compares the reference voltage Vref and the voltage Vpd. The APC circuit 35 controls the voltage of the capacitor 38a or the capacitor 38b based on the comparison result between the reference voltage Vref and the voltage Vpd. That is, when the reference voltage Vref> the voltage Vpd, the APC circuit 35 charges the capacitor 38a or the capacitor 38b so that the voltage of the capacitor 38a or the capacitor 38b increases. On the other hand, when the reference voltage Vref <voltage Vpd, the APC circuit 35 discharges the electric charge from the capacitor 38a or the capacitor 38b so that the voltage of the capacitor 38a or the capacitor 38b decreases. The APC circuit 35 maintains the voltage of the capacitor 38a or the capacitor 38b when the reference voltage Vref = the voltage Vpd.

  When the APC is completed, the control unit 5 releases the connection of the switch 36 by the sample hold signal. When the switch 36 is released, the voltage of the capacitor 38a or the capacitor 38b is held.

  Thus, when the laser driver 30 executes APC, the amount of laser light emitted from the LD 12a can be controlled to the target amount of light. Normally, regardless of the video signal 42, the LD 12a is supplied with a bias current as a standby current during image formation. However, in this embodiment, the description of the bias current is omitted for the sake of simplicity. Yes.

  The reference voltage generation circuit 33 may be provided in the control unit 5. In addition, when the voltage setting signal 31 is a serial or parallel n-bit (n is an integer of 2 or more) digital signal, the reference voltage generation circuit 33 converts the voltage setting signal 31 from digital to analog and generates a Vref signal 34. It may be generated.

  Next, the control mode of the laser driver 30 after the activation of the optical scanning device 2a will be described. The control unit 5 switches the control mode of the optical scanning device 2a at the timing starting from the falling edge of the BD signal 21. The control mode of the laser driver 30 of the present embodiment includes a stop (DISCHARGE) mode, a first light quantity control mode (APC (1)), a second light quantity control mode (APC (2)), an OFF mode, and a VIDEO mode. The control unit 5 outputs a 3-bit control signal (not shown) corresponding to each of the five modes to the laser driver 30 in order to switch the control mode. The laser driver 30 switches the control mode by receiving the control signal.

  The stop mode is a standby mode in a state where a job for image formation is not input. The first light amount control mode is a mode that is executed to control the light amount of the laser light incident on the BD 20 to the target light amount. The second light quantity control mode is a mode that is executed to control the light quantity of the laser light that scans the photosensitive drum 25 to the target light quantity. The OFF mode is a mode in which the transistor 41 is controlled to be OFF so that laser light is not emitted from the LD 12a. The VIDEO mode is a mode in which scanning on the photosensitive drum 25 by laser light based on image data is executed. The amount of laser light that scans the photosensitive drum 25 in the VIDEO mode is set in the second light amount control mode. Hereinafter, each mode will be described.

  FIG. 6 is a timing chart showing the control state of the laser circuit board 11. FIG. 6A shows a timing chart when the optical scanning device 2a is activated, and FIG. 6B shows a timing chart of one scanning cycle of laser light during image formation. Subsequent to FIG. 6A, processing corresponding to the timing chart of FIG. 6B is performed. The control state of the laser driver 30 is switched by the control unit 5 starting from the falling edge of the BD signal 21.

  Prior to activation of the optical scanning device 2a, the control unit 5 sets the control mode of the laser driver 30 to the stop (DISCHARGE) mode. In the stop mode, no charge is accumulated in the capacitor 38a and the capacitor 38b. When the image data is input to the image forming apparatus 1, the control unit 5 transmits an acceleration signal to the motor driver 16 in order to start the rotation of the polygon mirror 15a of the optical scanning device 2a. The controller 5 sets the control mode of the laser driver 30 to the first control mode (APC (1)) when starting the optical scanning device 2a. The image forming apparatus 1 of the present embodiment rotates the polygon mirror 15a at the target rotation speed using the BD signal 21. The BD signal 21 is not generated unless the voltage of the received light signal output from the BD 20 exceeds the threshold value. Therefore, the control unit 5 sets the laser driver 30 to the first light quantity control mode so that the BD signal 21 is generated.

  A first light amount control mode executed by the laser driver 30 when the optical scanning device 2a is activated will be described with reference to FIG. First, it is necessary to generate a BD signal in order to stabilize the rotation speed of the polygon mirror 15a. Therefore, the control unit 5 controls the laser drive circuit to the first light quantity control mode, thereby shifting the optical scanning device 2a to a state where a BD signal can be generated.

  The controller 5 outputs a voltage setting signal 31 having a duty ratio of 100 [%] in the first light quantity control mode. In addition, the control unit 5 outputs a low level sample hold signal in the first light quantity control mode. The switch 36 is connected by the low level sample hold signal. In addition, the control unit 5 outputs a high-level video signal 42 in the first light quantity control mode. Furthermore, the control unit 5 outputs a low-level capacitance switching signal 45 in the first light quantity control mode. The switch 44 connects the terminal a and the terminal b by the low-level capacitance switching signal 45.

  In FIG. 6A, immediately after the first light quantity control mode is started, no electric potential difference is generated between both ends of the resistor 40 because the capacitor 38a is not charged. Therefore, no current flows through the LD 12a immediately after the first control mode is started. Accordingly, the PD 12b does not output a current Ipd corresponding to the amount of laser light.

  The APC circuit 35 is supplied with the Vref signal 34 generated by the voltage setting signal 31 having a duty ratio of 100 [%]. The APC circuit 35 charges the capacitor 38a based on the comparison result between the voltage Vref and the voltage Vpd of the Vref signal 34 by the internal comparator. The voltage Vch_a of the capacitor 38a is increased by charging by the APC circuit 35. As the voltage Vch_a of the capacitor 38a increases, the potential difference across the resistor 40 increases. When a potential difference is generated between both ends of the resistor 40, the current ILD flows through the LD 12a. As shown in FIG. 6A, the amount of laser light emitted from the LD 12 (laser output) increases as the voltage Vch_a of the capacitor 38a increases as the APC circuit 35 is charged.

  While the first light quantity control mode is set, the voltage Vch_a of the capacitor 38a gradually increases. As the voltage Vch_a of the capacitor 38a increases, the amount of laser light emitted from the LD 12a also increases. Since the light reception signal output from the BD 20 exceeds the threshold when the amount of laser light increases to some extent, the BD signal 21 is generated. Thereafter, the laser driver 30 controls the voltage Vch_a of the capacitor 38a until the voltage Vref and the voltage Vpd of the Vref signal 34 become equal. When the BD 20 detects the laser beam L1 a predetermined number of times and outputs the BD signal 21 a predetermined number of times, the laser control mode becomes the second light quantity control mode (APC (2)), and the optical scanning device 2a performs an image of one line. Light emission control at the time of formation is performed (FIG. 6B).

  The control unit 5 starts image formation in response to the BD signal 21 being generated at the target period. Hereinafter, a control mode set in the laser driver 30 during image formation will be described with reference to FIG. FIG. 6B is a timing chart for one cycle of the BD signal. During image formation, the laser driver 30 repeats the control mode shown in FIG. 6B every one scanning cycle.

  As shown in FIG. 6B, the control unit 5 changes the control mode of the laser driver 30 within the first scanning cycle to the first light amount control mode, the OFF mode, the second light amount control mode, the OFF mode, the VDO mode, and OFF. The mode and the first light quantity control mode are switched in this order.

  The control unit 5 sets the laser driver 30 to the first light quantity control mode in order to generate the BD signal 21. The first light quantity control mode is as described above. The controller 5 sets the laser driver 30 to the first light quantity control mode slightly before the next laser beam scans the BD 20 with the latest BD signal 21 as a reference. Before the laser beam scans the BD 20, the light amount of the laser beam reaches a light amount corresponding to the voltage setting signal 31 with a duty ratio of 100 [%], and the BD signal 21 is generated by the laser beam of that light amount.

  Subsequently, as illustrated in FIG. 6B, the control unit 5 switches the laser driver 30 from the first light amount control mode to the OFF mode at a timing based on the BD signal 21. In the OFF mode, the control unit 5 outputs a high level sample hold signal. The laser driver 30 releases the connection of the switch 36 by receiving the high level sample hold signal. Therefore, the voltage Vch_a of the capacitor 38a is a voltage set in the first light quantity control mode immediately before switching to the OFF mode. Since the switch 36 is released, the capacitor 38a is not charged / discharged by the APC circuit 35.

  In the OFF mode, the control unit 5 does not output the video signal 42. Therefore, in the OFF mode, the transistor 41 is turned OFF and the current ILD does not flow through the LD 12a. Further, in the OFF mode, the control unit 5 outputs a voltage setting signal 31 having a duty ratio of 100 [%] or less to the laser driver 30. FIG. 6B shows a state in which the control unit 5 outputs a voltage setting signal 31 having a duty ratio of 25 [%].

  Further, the control unit 5 switches the capacitance switching signal 45 from Low to High during the OFF mode. The switch 44 connects the terminal a and the terminal c by the high level capacitance switching signal 45.

  As shown in FIG. 6B, the control unit 5 switches the laser driver 30 from the OFF mode to the second light amount control mode at a timing with the BD signal 21 as a reference. In the second light quantity control mode, the control unit 5 outputs a low level sample hold signal. The laser driver 30 connects the switch 36 by receiving a low level sample hold signal. In the second light quantity control mode, the control unit 5 outputs a high level video signal 42. Therefore, in the second light quantity control mode, the transistor 41 is turned on, a current ILD flows through the LD 12a, and the LD 12a emits a laser beam having a light quantity corresponding to the value of the current ILD. Furthermore, in the second light quantity control mode, the voltage setting signal 31 having the duty ratio output in the OFF mode immediately before switching is continuously output.

  In the second light quantity control mode, the laser light emitted from the LD 12a enters the PD 12b. The PD 12b outputs a current Ipd having a value corresponding to the amount of received light. A voltage at one end of the resistor 37 is input to the APC circuit 35. The APC circuit 35 receives the Vref signal 34 generated by the voltage setting signal 31 having a duty ratio of 25 [%]. The APC circuit 35 controls the voltage Vch_b of the capacitor 38b based on the comparison result between the voltage Vref of the Vref signal 34 and the voltage Vpd by an internal comparator.

  As illustrated in FIG. 6B, the control unit 5 switches the laser driver 30 from the second light amount control mode to the OFF mode at a timing based on the BD signal 21. In the OFF mode between the second light quantity control mode and the VDO mode, the control unit 5 continues to output the high level capacity switching signal 45.

  Subsequently, as illustrated in FIG. 6B, the control unit 5 switches the laser driver 30 from the OFF mode to the VDO mode at a timing based on the BD signal 21. In the VDO mode, the control unit 5 continues to output the high level sample hold signal and the high level capacitance switching signal 45 from the immediately preceding OFF mode. Therefore, the connection of the switch 36 of the laser driver 30 is released. Since the switch 36 is disconnected, the voltage ch_b of the capacitor 38b is maintained at the voltage set in the immediately preceding second light quantity control mode. Since the switch 36 is released, the capacitor 38b is not charged / discharged by the APC circuit 35. Further, since the terminals a and c are connected by the capacitance switching signal 45, the voltage of the capacitor 38b is input to the non-inverting terminal of the comparator 39.

  In the VDO mode, the control unit 5 outputs a video signal (PWM signal) generated based on the image data. Therefore, in the VDO mode, the transistor 41 is ON / OFF controlled based on the pulse of the VDO signal. When the transistor 41 is turned on, the current ILD flows through the LD 12a. At this time, the value of the current ILD flowing through the LD 12a is based on the voltage ch_b of the capacitor 38b set in the second light quantity control mode. That is, the current ILD flowing through the LD 12 a is defined by the potential difference between both terminals of the resistor 40 and the resistance value of the resistor 40. The voltage at one end of the resistor 40 is based on the voltage ch_b of the capacitor 38b.

  Subsequently, as illustrated in FIG. 6B, the control unit 5 switches the laser driver 30 from the VDO mode to the OFF mode at a timing based on the BD signal 21. In the OFF mode at this time, the control unit 5 switches the capacitance switching signal 45 from the high level to the low level. Thereby, the switch 44 connects the terminal a and the terminal b.

  Subsequently, as illustrated in FIG. 6B, the control unit 5 switches the laser driver 30 from the OFF mode to the first light amount control mode at a timing based on the BD signal 21. As described above, the control unit 5 outputs the voltage setting signal 31 having a duty ratio of 100 [%] in the first light quantity control mode. In addition, the control unit 5 outputs a low level sample hold signal in the first light quantity control mode. The switch 36 is connected by the low level sample hold signal. Further, the control unit 5 outputs a high-level video signal in the first light quantity control mode. The voltage ch_a of the capacitor 38a immediately before switching to the first light quantity control mode is the voltage set in the previous first light quantity control mode. In the first light quantity control mode, the APC circuit 35 controls the voltage ch_a of the capacitor 38a based on the comparison result between the voltages Vref and Vpd of the Vref signal 34 corresponding to the voltage setting signal having a duty ratio of 100 [%].

  Here, the second light quantity control mode will be described. The electrophotographic image forming apparatus 1 needs to control the laser light that exposes the photosensitive drum 25 in accordance with the state of the image forming apparatus 1. That is, the sensitivity of the photosensitive drum 25 to the laser light varies depending on the deterioration of the photosensitive drum 25 with time and the environmental condition (temperature, humidity) in which the image forming apparatus 1 is placed. Further, the charge amount of the toner stored in the developing unit 512 varies depending on the environmental state. Such a change causes a difference between the image density output from the image forming apparatus 1 and the image density required by the user. In order to solve such a problem, the electrophotographic image forming apparatus 1 controls the light quantity of the LD 12a immediately after the apparatus is turned on in response to satisfying a predetermined condition such as forming an image on a predetermined number of sheets. To do. For example, the image forming apparatus 1 forms a density detection pattern for each color formed on the intermediate transfer member 511, and controls the light quantity of the LD 12a corresponding to each color based on the detection result.

  As described above, the control unit 5 performs the above-described switching of the control mode within one scanning cycle, so that the light amount control of the laser light incident on the BD 20 and the light amount control of the laser light scanning on the photosensitive drum 25 are individually performed. Can be done. As a result, both the amount of laser light incident on the BD 20 and the amount of laser light exposed on the photosensitive drum 25 can be accurately controlled. Since the amount of laser light incident on the BD 20 is controlled to be substantially constant regardless of the amount of laser light that exposes the photosensitive drum 25, the image in the main scanning direction is controlled regardless of the amount of laser light that exposes the photosensitive drum 25. The writing position can be made substantially constant. The amount of laser light that exposes the photosensitive drum 25 is less than the amount of laser light that enters the BD 20. For this reason, the voltage Vref of the Vref signal 34 is such that the reference voltage when the laser light incident on the BD 20 is emitted is equal to or higher than the reference voltage when the laser light that exposes the photosensitive drum 25 is emitted.

  Note that the duty ratio of the voltage setting signal 31 for generating the BD signal 21 may not be 100 [%]. For example, it is desirable that the duty ratio of the voltage setting signal 31 for generating the BD signal 21 is adjusted individually for each device at the time of assembly by the gain of the photoelectric conversion element of the BD 20.

  Next, a specification example of the semiconductor laser 12 and an example of a control target value are shown.

(specification)
The emission start current Ith of the semiconductor laser 12 is 5 [mA], and the emission efficiency η is 0.5 [mW / mA].
The charge / discharge current Id of the laser driver 30 is 1 [μA], the leakage current I_leak of the terminal to which the switch 44 is connected is 0.1 [μA], the current amplification factor α is 100 times, and the resistance 40 is 10 [kΩ]. is there.
The scanning time of the optical scanning device 2a is 25 [μS] in the first light emission control mode, and 500 [μS] in the image forming mode.

(Control target value)
The control target value in each laser control mode when the light amount Po = 5 [mW] is as follows.
In the first light quantity control mode, the rise time Tr of the light quantity waveform is set to 5 [μS] or less (first target value).
In the image forming mode, the light amount fluctuation rate ΔPo is set to 0.5 [%] or less (second target value).

The capacitance of the capacitor 38a needs to converge within the time T1 of the first light quantity control mode with respect to the fluctuation amount ΔVcha of the voltage across the terminals of the capacitor 38a generated during the scanning in the first light quantity control mode. For that purpose, it is necessary to satisfy the first target value. The fluctuation amount ΔILD of the driving current with respect to the light quantity fluctuation rate ΔPo of the semiconductor laser 12 is expressed by Expression 1, and ΔILD is determined by the fluctuation amount ΔVch_a of the voltage across the capacitor 38a shown in Expression 2.
ΔILD = ΔPo / η
= 5 [mW] x 0.5% / 0.5 [mW / mA]
= 0.05 [mA] (Formula 1)
ΔVch_a = ΔILD × Rs / α
= 0.05 [mA] × 10 [kΩ] / 100
= 0.005 [V] (Formula 2)

From the above, the smaller the capacitance of the capacitor 38a, the more it can reach ΔVch_a, which can be derived from Equation 3 from the light amount control / rise time Tr and the charge / discharge current Id.
Capacitor 38a capacity = Tr × Id / ΔVch_a
= 5 [μS] × 1 [μA] /0.005 [V] ≦ 1000 [pF] (Formula 3)

  The capacitor 38b holds the voltage Vch_b controlled by the second light quantity control mode. The drive current of the semiconductor laser 12 is determined by the voltage across the capacitor 38b. In order to satisfy the second target value, it is necessary to make the fluctuation amount ΔVch_b of the voltage across the terminals of the capacitor 38b equal to or less than the value obtained by Equation 2.

The fluctuation amount ΔVch_b is generated by the leakage current I_leak of the laser driver 30 and the time T2 of the image forming mode in which the capacitor 38b accumulates electric charges. The capacitor 38b can suppress ΔVch_b as the capacitance increases, and can be derived from Expression 4 based on the image forming mode time T2 and the leakage current I_leak.
Capacitor 38b capacity = T2 × I_leak / ΔVch_b
= 500 [μS] × 0.1 [μA] /0.005 [V] ≧ 0.01 [μF] (4)

  Thus, the capacity of the capacitor 38a selected in the first light quantity control mode needs to be smaller than the capacity of the capacitor 38b selected in the second light quantity control mode. By setting the capacities of the capacitors 38a and 38b as described above, the rise time Tr is set to 5 [μS] or less in the first light quantity control mode, and the light quantity variation rate ΔPo is set to 0.5% or less in the image forming mode. be able to.

  FIG. 7 is an explanatory diagram of the relationship between the received light amount Pd of the BD 20 and the output delay time τd. The BD 20 cannot detect the laser beam L1 when the received light quantity Pd is 10 [μW] or less, and does not output the BD signal 21. In the BD 20, when the light quantity fluctuation rate ΔPo is 0.5%, the output delay time τd of the BD signal 21 fluctuates by about 25 [ns] when the received light quantity Pd is 20 [μW]. When the received light quantity Pd is 100 [μW], the output delay time τd of the BD signal is about 5 [ns], and the output delay time is reduced to about 1/5 when the received light quantity Pd is 20 [μW]. Can do.

  In this manner, the control unit 5 switches between the condenser 38a and the condenser 38b within one scanning period, thereby individually controlling the light quantity control of the laser light incident on the BD 20 and the light quantity control of the laser light scanned on the photosensitive drum 25. It can be carried out. As a result, both the amount of laser light incident on the BD 20 and the amount of laser light exposed on the photosensitive drum 25 can be accurately controlled.

  Further, by controlling the amount of laser light incident on the BD 20 and the amount of laser light scanned on the photosensitive drum 25 with different capacitors, an increase in voltage control time of each capacitor can be suppressed. When the amount of laser light incident on the BD 20 and the amount of laser light scanned on the photosensitive drum 25 are controlled by one capacitor, the capacitor voltage is controlled by the second light amount control mode based on the voltage of the capacitor controlled by the first light amount control mode. The voltage must be changed. Further, the capacitor voltage must be changed in the first light amount control mode with reference to the capacitor voltage controlled in the second light amount control mode. If the difference between the target light amount of the laser light incident on the BD 20 and the target light amount of the laser light that scans the photosensitive drum 25 is large, the voltage fluctuation amount of the capacitor increases, and the time for reaching the target voltage increases. Each light control time must be secured for a long time.

  In contrast, the image forming apparatus according to the present embodiment switches the two capacitors as described above. Therefore, when executing each light quantity control mode, the voltage controlled in the same light quantity control mode in the previous scanning cycle is used as a reference. The voltage of each capacitor can be controlled. Therefore, an increase in the light amount control time is suppressed.

(Example 2)

  FIG. 8 is another configuration diagram of the laser circuit board 11. The laser circuit board 11 of Example 2 performs light emission control of the LDs 12a and 12c, which are a plurality of light emitting elements that emit light. The laser circuit board 11 includes a plurality of laser drivers 60a and 60b having the same configuration as the laser driver 30 of FIG. The laser driver 60a and the laser driver 60b may be one IC or separate ICs. Since the configuration of each of the laser drivers 60a and 60b is the same as that of the laser driver 30 of the first embodiment, description thereof is omitted. The control unit 5 inputs the sample hold signals 62a and 62b and the video signals 72a and 72b to the two laser drivers 60a and 60b, respectively.

  The laser circuit board 11 includes a reference voltage generation circuit 33 and a PD switch 80 in addition to the two laser drivers 60a and 60b. The reference voltage generation circuit 33 has the same configuration and function as those shown in FIG. 3, and generates the Vref signal 34 according to the voltage setting signal 31 input from the control unit 5. The PD switch 80 inputs the current Ipd output from the PD 12b in response to the PD switching signal 81 input from the control unit 5 to one of the laser driver 60a and the laser driver 60b.

  FIG. 9 is a timing chart showing the control state of the laser circuit board 11 of FIG. FIG. 9A shows a timing chart when the optical scanning device 2a is activated, and FIG. 9B shows a timing chart of one scanning cycle of laser light during image formation of one line. Subsequent to FIG. 9A, processing corresponding to the timing chart of FIG. 9B is performed. The laser circuit board 11 performs light emission control of the semiconductor laser 12 based on the falling edge of the BD signal 21 in accordance with the sample hold signals 62a and 62b and the video signals 72a and 72b input from the control unit 5. The image forming apparatus 1 according to the present embodiment generates the BD signal 21 by causing the laser light L1 emitted from the LD 12a to enter the BD 20. The laser beam L2 emitted from the LD 12c does not contribute to the generation of the BD signal 21. FIG. 9 is a time chart based on the BD signal 21 output when the BD 20 receives the laser beam L1 output from the LD 12a. The laser drivers 60a and 60b are controlled in their control states starting from the falling edge of the BD signal 21.

  Prior to activation of the optical scanning device 2a, the control unit 5 sets the control mode of the laser drivers 60a and 60b to a stop (DISCHARGE) mode. In the stop mode, no charge is accumulated in the capacitor 68a, the capacitor 68b, the capacitor 69a, and the capacitor 69b.

  When the image data is input to the image forming apparatus 1, the control unit 5 transmits an acceleration signal to the motor driver 16 in order to start the rotation of the polygon mirror 15a of the optical scanning device 2a. The controller 5 sets the control mode of the laser driver 60a to the first light quantity control mode (LD1-APC (1)) when the optical scanning device 2a is activated. Note that the laser driver 60b is in the OFF mode while the first light quantity control mode is being executed. Also, the OFF mode shown in FIGS. 9A and 9B indicates that both the laser drivers 60a and 60b are in the OFF mode. In the OFF mode, the controller 5 outputs low level video signals 72a and 72b. As a result, the transistors 71a and 71b are turned off, the current ILD1 does not flow through the LD 12a, and the current ILD2 does not flow through the LD 12c.

  In the first light quantity control mode (LD1-APC (1)), the control unit 5 sets the video signal 72a to the high level and sets the video signal 72b to the low level. As a result, the transistor 71a is turned on and the transistor 71b is turned off. In the first light quantity control mode, the control unit 5 outputs a voltage setting signal 31 having a duty ratio of 100 [%]. Further, in the first light quantity control mode, the control unit 5 outputs the High level PD switching signal 81 to connect the PD 12b and the resistor 67a, and outputs the Low level sample hold signal 62a to thereby switch the switch 66a. Connect (sample state). At this time, the sample hold signal 62b is at a high level, and the switch 66b is in a disconnected state (hold state).

  In the first light quantity control mode, the laser driver 60a has a difference between the value of the Vref signal 34 obtained by smoothing the voltage setting signal 31 having a duty ratio of 100 [%] and the terminal voltage Vpd1 on the non-grounded side of the resistor 67a. The capacitor 68a is gradually charged so as to decrease. As the voltage of the capacitor 68a increases, the amount of laser light L1 emitted from the LD 12a also increases. Since the light reception signal output from the BD 20 exceeds the threshold when the light amount of the laser light L1 emitted from the LD 12a increases to some extent, the BD signal 21 is generated. Thereafter, the laser driver 30 controls the voltage of the capacitor 68a until the voltage Vref of the Vref signal 34 becomes equal to the terminal voltage Vpd1. When the BD 20 detects the laser beam L1 a predetermined number of times and outputs the BD signal 21 a predetermined number of times, the laser control mode becomes the second light amount control mode (LD1-APC (2)). The optical scanning device 2a performs light emission control when forming a one-line image (FIG. 9B).

The control unit 5 starts image formation in response to the BD signal 21 being generated at the target period. Hereinafter, a control mode set in the laser driver 60a during image formation will be described with reference to FIG. The control mode is similarly set for the laser driver 60b.
After the first light quantity control mode shown in FIG. 9A, the control unit 5 switches the laser driver 60a from the first light quantity control mode to the OFF mode at a timing based on the BD signal 21 (see FIG. 9B). ). Thereafter, the control unit 5 switches the control mode of the laser driver 60a from the OFF mode to the second light amount control mode (LD1-APC (2)) at a timing based on the BD signal 21. Note that the laser driver 60b is in the OFF mode while the second light quantity control mode is set.

  In the second light quantity control mode (LD1-APC (2)), the control unit 5 sets the video signal 72a to the high level and sets the video signal 72b to the low level. As a result, the transistor 71a is turned on and the transistor 71b is turned off. In the second light quantity control mode, the control unit 5 outputs a voltage setting signal 31 with a duty ratio of 25 [%] to the laser circuit board 11. As a result, the value of the Vref signal 34 is also ¼ that when the duty ratio of the voltage setting signal 31 is 100 [%]. The amount of laser light emitted from the semiconductor laser 12 is also ¼ that when the duty ratio of the voltage setting signal 31 is 100 [%].

  In the second light quantity control mode, the control unit 5 outputs the High level PD switching signal 81 to connect the PD 12b and the resistor 67a, and also connects the switch 66a by outputting the Low level sample hold signal 62a. (Sample state). At this time, the sample hold signal 62b is at a high level, and the switch 66b is in a disconnected state (hold state).

  In the second light quantity control mode, the laser driver 60a compares the Vref signal 34 obtained by smoothing the voltage setting signal 31 having a duty ratio of 25 [%] with the terminal voltage Vpd1 on the non-grounded side of the resistor 67a. The laser driver 60a controls the voltage of the capacitor 68a so that both voltages are equal. The current ILD1 having a value based on the voltage controlled here is supplied to the LD 12a during a period in which the photosensitive drum 25 is scanned.

  Thereafter, the control unit 5 switches the laser driver 60a from the second light quantity control mode to the OFF mode at a timing based on the BD signal 21 (see FIG. 9B). Then, the control unit 5 switches the laser driver 60b from the OFF mode to the third light quantity control mode (LD2-APC (2)).

  In the third light quantity control mode (LD2-APC (2)), the control unit 5 sets the video signal 72a to the low level and sets the video signal 72b to the high level. Thus, the transistor 71a is turned off and the transistor 71b is turned on. In the third light quantity control mode, the control unit 5 outputs a voltage setting signal 31 having a duty ratio of 25 [%] to the laser circuit board 11. As a result, the value of the Vref signal 34 is also ¼ that when the duty ratio of the voltage setting signal 31 is 100 [%]. The amount of laser light emitted from the semiconductor laser 12 is also ¼ that when the duty ratio of the voltage setting signal 31 is 100 [%].

  In the third light quantity control mode, the control unit 5 outputs the Low level PD switching signal 81 to connect the PD 12b and the resistor 67b, and connects the switch 66b by outputting the High level sample hold signal 62b. (Sample state). At this time, the sample hold signal 62a is at the low level, and the switch 66a is in a disconnected state (hold state).

  In the third light quantity control mode, the laser driver 60a compares the Vref signal 34 obtained by smoothing the voltage setting signal 31 having a duty ratio of 25 [%] with the terminal voltage Vpd2 on the non-grounded side of the resistor 67a. The laser driver 60a controls the voltage of the capacitor 68b so that both voltages are equal. The current ILD2 having a value based on the voltage controlled here is supplied to the LD 12c during a period in which the photosensitive drum 25 is scanned.

  As shown in FIG. 9B, the image forming apparatus 1 according to the present embodiment performs the first light amount control mode, the second light amount control mode, and the third light amount control mode by 1 each in one scanning period of the laser light. Run once. The image forming apparatus 1 controls the laser light L1 to the first target light amount in the first light amount control mode. The image forming apparatus 1 controls the laser light L1 to the second target light amount in the second light amount control mode. The image forming apparatus 1 controls the laser light L2 to the second target light amount in the third light amount control mode.

  As described above, the control unit 5 executes the control mode switching described above within one scanning cycle, thereby controlling the light amount of the laser beam L1 incident on the BD 20 and the laser beam L1 and the laser beam L2 that scan the photosensitive drum 25. The light quantity control can be performed individually. Thereby, it is possible to accurately control both the light quantity of the laser light L1 incident on the BD 20 and the light quantities of the laser lights L1 and L2 exposing the photosensitive drum 25. Since the amount of laser light L1 incident on the BD 20 is controlled to be substantially constant regardless of the amount of laser light L1 and L2 that exposes the photosensitive drum 25, it is related to the amount of laser light L1 and L2 that exposes the photosensitive drum 25. First, the image writing position in the main scanning direction can be made substantially constant.

  DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 2a, 2b, 2c, 2d ... Optical scanning device, 5 ... Control part, 11 ... Laser circuit board, 12 ... Semiconductor laser, 13 ... Collimate lens, 14 ... Cylindrical lens, 15 ... Polygon motor, 15a ... polygon mirror, 17 ... f-theta lens, 20 ... BD, 21 ... BD signal, 25 ... photosensitive drum, 30, 60a, 60b ... laser driver

Claims (7)

A photoreceptor,
A semiconductor laser comprising a light emitting element that emits laser light for exposing the photoreceptor;
A first light receiving element that receives the laser light emitted from the light emitting element in order to control the light quantity of the laser light, and generates a light receiving signal having a voltage corresponding to the received light quantity;
Deflecting means for deflecting the laser beam so that the laser beam emitted from the light emitting element scans the photosensitive member;
A second light receiving element for receiving the laser light deflected by the deflecting means to generate a synchronization signal;
Timing control means for controlling the emission timing of the laser beam based on image data in one scanning period of the laser beam based on the generation timing of the synchronization signal;
Output means for outputting a first reference voltage or a second reference voltage;
A first capacitor;
A second capacitor;
The light reception signal and a reference voltage output from the output means are input, the voltage of the light reception signal is compared with the first reference voltage or the second reference voltage, and the first capacitor is based on the comparison result. Or voltage control means for controlling the voltage of the second capacitor;
Current supply means for supplying current to the light emitting element with a value corresponding to one of the voltage of the first capacitor and the voltage of the second capacitor;
Switching means for switching between the first capacitor and the second capacitor, a capacitor whose voltage is controlled by the voltage control means,
The output means outputs the first reference voltage to control the amount of laser light incident on the second light receiving element, and controls the amount of laser light scanned on the photosensitive member. Output a second reference voltage,
The switching means controls a voltage of the first capacitor based on a comparison result between the light reception signal and the first reference voltage, and based on a comparison result between the light reception signal and the second reference voltage. The voltage control means switches the capacitor for controlling the voltage between the first capacitor and the second capacitor so that the voltage of the second capacitor is controlled,
Image forming apparatus. The capacity of the first capacitor is smaller than the capacity of the second capacitor,
The image forming apparatus according to claim 1. The voltage control means includes a comparison means for comparing the first reference voltage or the second reference voltage with the voltage of the light reception signal,
The first capacitor is charged and discharged according to a comparison result between the first reference voltage and the voltage of the light reception signal,
The second capacitor is charged and discharged according to a comparison result between the second reference voltage and the voltage of the light reception signal.
The image forming apparatus according to claim 1. The output means outputs the first reference voltage or the second reference voltage in accordance with a pulse width of a signal for setting a target light amount of the laser light.
The image forming apparatus according to claim 1. The output means adjusts a reference voltage according to the pulse width,
The current supply means adjusts the current according to the adjusted reference voltage, and shortens the output delay time of the laser light emitted from the light emitting element,
The image forming apparatus according to claim 4. The semiconductor laser has a plurality of light emitting elements,
The second light receiving element receives any one of the laser beams emitted from the plurality of light emitting elements and generates the synchronization signal;
The current supply means supplies current to the plurality of light emitting elements,
The image forming apparatus according to claim 1. The current supply means supplies the current of a value corresponding to the voltage of the first capacitor to the light emitting element until the synchronization signal is output a predetermined number of times, and when the synchronization signal is output a predetermined number of times, Supplying the current having a value corresponding to a second capacitor to the light emitting element;
The image forming apparatus according to claim 1.

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