JP2010098168A - Laser drive, image forming device, and control program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laser drive, an image forming device, and a control program which improve reliability by shortening the time for applying reverse bias to a photodetector, as compared with a case of dispensing with this configuration. <P>SOLUTION: A reverse bias applied to light control of an LD70 and a PD72, based on a S/H signal output from a laser control section 52, is stopped. When light control (S/H signal is at a Low level) is performed, the current output from the PD72 is kept from flowing into a current potential conversion resistance 78 by a SW60, or makes the potential of the side of cathode and the anode of the PD72 equal. Furthermore, when performing light control (S/H signal is at a High level), the path between the anode side of the PD72 and a current potential conversion resistance 78 is connected by the SW60. Alternativeley, a reverse bias is applied, by making the potential by the side of the cathode of the PD72 so that the potential is higher than that of the anode side to the PD72. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a laser driving device, an image forming apparatus, and a control program.

  Japanese Patent Application Laid-Open No. 2003-228561 provides a technique for setting an appropriate sample hold time by providing two sample hold capacitors for controlling the light quantity of a semiconductor laser at the time of printing and switching between using them alone or using them in parallel. Is described. In this technique, the photodiode is in a state where a reverse bias is applied regardless of whether the semiconductor laser is on or off.

Patent Document 2 describes a technique for driving a laser with an appropriate amount of light by supplying a desired drive current to the laser using a plurality of ports of an image processing LSI. Also in this technique, the photodiode is in a state where a reverse bias is applied regardless of whether the semiconductor laser is on or off.
JP 2002-2021 A JP 2006-110801 A

  The present invention provides a laser driving device, an image forming apparatus, and a control program that have improved reliability by reducing the time for applying a reverse bias to a light receiving element as compared with the case without this configuration. With the goal.

  In order to achieve the above object, a laser driving device according to claim 1, a light emitting element that emits light according to image data, light that is emitted from the light emitting element, and a photocurrent that corresponds to the amount of light received. A light receiving element for outputting, a photocurrent voltage converting means for converting a photocurrent output from the light receiving element into a voltage, and a light current from the light receiving element to the light current voltage converting means. A photocurrent stop means for stopping the photocurrent flowing through the current-voltage conversion means; and a photocurrent stop control means for controlling the photocurrent stop means so as to stop the photocurrent according to the light emission operation of the light emitting element. Prepare.

  The laser drive device according to claim 2 is the laser drive device according to claim 1, wherein the photocurrent stop control means stops the photocurrent during a non-emission period of the light emitting element. Control the current stopping means.

  According to a third aspect of the present invention, in the laser driving device according to the first or second aspect, the photocurrent stop control means is in an image forming period for forming an image according to the image data. Controls the photocurrent stopping means to stop the photocurrent.

  A laser driving device according to a fourth aspect is the laser driving device according to any one of the first to third aspects, wherein light is emitted from the light emitting element in accordance with a photocurrent output from the light receiving element. A light amount adjustment unit that adjusts the light amount based on a light amount adjustment instruction signal input at a predetermined timing so that the light amount becomes a predetermined light amount; and the photocurrent stop control unit includes the light amount adjustment instruction. Based on the signal, during the light amount adjustment period of the light amount adjustment unit, the photocurrent stop unit is controlled to prohibit the stop of the photocurrent.

  The laser drive device according to claim 5, further comprising delay means for delaying a timing at which the light amount adjustment instruction signal is input to the light amount adjustment unit in the laser drive device according to claim 4, The light amount adjustment unit adjusts the light amount based on a light amount adjustment instruction signal input at a timing delayed by the delay unit.

  The laser drive device according to claim 6 is the laser drive device according to claim 5, wherein the predetermined time is a current of a photocurrent output from the light receiving element after the light amount adjustment period starts. This is the output stabilization time until the amount stabilizes.

  The laser drive device according to claim 7 is the laser drive device according to any one of claims 1 to 6, further comprising detection means for detecting an abnormality of the light receiving element, and the photocurrent stop control. The means controls the photocurrent stop means so as to stop the photocurrent when an abnormality is detected by the detection means.

  The laser drive device according to claim 8 is the laser drive device according to claim 7, wherein the abnormality detection means has a voltage converted by the photocurrent voltage conversion means exceeding a predetermined reference voltage. Is detected as an abnormality of the light receiving element.

  The laser driving device according to claim 9 is the laser driving device according to any one of claims 1 to 8, wherein the light emitting element, the light receiving element, the photocurrent voltage converting means, and the photocurrent. Stop means is formed integrally on the semiconductor integrated circuit substrate.

  A laser driving device according to a tenth aspect is the laser driving device according to any one of the first to ninth aspects, wherein the photocurrent stop means includes a field effect transistor or a bipolar transistor.

  An image forming apparatus according to an eleventh aspect of the present invention includes: controlling the laser driving device according to any one of the first to tenth aspects and the light emitting element of the laser driving device according to the image data. And image forming means for forming an image on a recording medium.

  A control program according to a twelfth aspect causes a computer to function as the photocurrent stop control unit according to any one of the first to eleventh aspects.

  According to the first aspect of the present invention, compared to the case where the present configuration is not provided, the reliability can be improved by reducing the time for applying the reverse bias to the light receiving element. It is done.

  According to the second aspect of the present invention, there is an effect that a reverse bias is not applied to the light receiving element during the non-light emitting period of the light emitting element.

  According to the third aspect of the present invention, it is possible to obtain an effect that no reverse bias is applied to the light receiving element during the image forming period.

  According to the fourth aspect of the present invention, when the light amount control is performed, an effect that a reverse bias is applied to the light receiving element is obtained.

  According to the present invention described in claim 5, it is possible to obtain an effect that appropriate light amount adjustment can be performed as compared with the case where the present configuration is not provided.

  According to the sixth aspect of the present invention, it is possible to obtain an effect that appropriate light amount adjustment can be performed in accordance with the characteristics of the light receiving element.

  According to the seventh aspect of the present invention, it is possible to prevent the reverse bias from being applied to the light receiving element when an abnormality occurs in the light receiving element.

  According to the eighth aspect of the present invention, it is possible to prevent the reverse bias from being applied to the light receiving element when a leak current is generated.

  According to the ninth aspect of the present invention, an effect that an integrated circuit can be obtained is obtained.

  According to the tenth aspect of the present invention, it is possible to obtain an effect that the configuration can be appropriately configured as compared with the case where the present configuration is not provided.

  According to the present invention described in claim 11, compared to the case where the present configuration is not provided, there is an effect that the reliability can be improved by shortening the time for applying the reverse bias to the light receiving element. It is done.

  According to the twelfth aspect of the present invention, there is an effect that the reliability can be improved by shortening the time for applying the reverse bias to the light receiving element as compared with the case without the present configuration. It is done.

[First Embodiment]
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  In this embodiment, a reverse bias is applied to the photodiode only when the light emission amount of the laser diode for forming an image is controlled.

  FIG. 1 is a schematic diagram illustrating an example of a schematic configuration of an image forming apparatus according to the present embodiment. The image forming apparatus 10 of the present embodiment forms an image on a recording medium such as paper 18 based on image data.

  The image forming apparatus 10 includes an image forming unit 11 for forming an image on a paper 18 based on image data, a laser driving device 40, and a paper tray 32 for loading the paper 18.

  A manual feed tray 34 for manually inserting the paper 18 is provided on the side surface of the image forming apparatus 10. Further, a discharge tray 38 for discharging the paper 18 on which an image is formed is provided on the side surface opposite to the side surface on which the manual feed tray 34 is provided.

  The image forming unit 11 is a cylindrical photosensitive member 12 that rotates at a constant speed in the direction of arrow A in FIG. 1 and light that irradiates the photosensitive member 12 with a laser (light beam, see arrow B in FIG. 1) corresponding to image data. A scanning device 26 (described later in detail) and a fixing device 24 for fixing an image corresponding to the image data on the paper 18 are configured.

  A charger 14 for charging the photoconductor 12 is disposed on the circumferential surface of the photoconductor 12. The photosensitive member 12 charged by the charger 14 rotates in the direction of arrow A in FIG. 1 and is irradiated with a laser from the optical scanning device 26, whereby an electrostatic latent image corresponding to image data is formed on the photosensitive member 12. It is formed.

  A developing device 16 for supplying toner to the photoconductor 12 is disposed downstream of the laser irradiation position of the optical scanning device 26 in the rotation direction of the photoconductor 12. The toner supplied from the developing device 16 adheres to the electrostatic latent image on the photoconductor 12, thereby forming a toner image on the photoconductor 12. A transfer charging member 20 for transferring the toner image formed on the photosensitive member 12 to the paper 18 is provided on the downstream side in the rotation direction of the photosensitive member 12 with respect to the arrangement position of the developing device 16. A cleaner 22 for removing the toner remaining on the surface of the photoconductor 12 after transfer is provided on the downstream side in the rotation direction of the photoconductor 12 from the arrangement position of the transfer charging member 20.

  The paper 18 sent out from the paper tray 32 is transported between the photosensitive member 12 and the transfer charging member 20 to transfer the toner image. The sheet 18 on which the toner image has been transferred is conveyed in the direction of arrow C in FIG. 1, and is subjected to toner fixing processing by being pressurized and heated by the pressure roller 36 and the heating roller 37 of the fixing device 24. After an image is formed on 18, the image is discharged to a discharge tray 38.

  The laser driving device 42 is for driving the laser 30 included in the optical scanning device 26 (details will be described later).

  FIG. 2 shows a block diagram of an example of the optical scanning device 26 and the laser driving device 40 of the present embodiment.

  The optical scanning device 26 of the present embodiment includes a laser light source 30 for emitting a laser, a collimator lens 42 for converting the laser emitted from the laser light source from a diffused light beam into a parallel light beam, a cylinder lens 43, and the photoconductor 12. Rotating polygon mirror (polygon mirror) 28 which is a scanning means for irradiating a laser beam, an fθ lens 45 for controlling the scanning speed of the laser, a reflecting mirror 46 for reflecting the laser in the direction of the photosensitive member 12, a mirror 47, and a photodetector 48. It is configured with.

  The laser emitted from the laser light source 30 is converted from a diffused light into a parallel light by the collimator lens 42 and is incident on the rotary polygon mirror 28 through the cylinder lens 43. The rotating polygonal mirror 28 is formed in a regular polygonal shape (for example, a hexagonal shape in the present embodiment) having a plurality of reflecting surfaces 28A on its side surface, so that the incident laser converges on the reflecting surface 28A. It has become. Further, the rotary polygon mirror 28 rotates in the direction of arrow D around the rotation shaft 44. That is, the incident angle of the laser on each reflecting surface 28A is continuously changed and deflected. As a result, the photoconductor 12 is irradiated with a laser beam by scanning in the axial direction of the photoconductor 12.

  An fθ lens 45 including a first lens 45A and a second lens 45B is disposed in the traveling direction of the laser beam reflected by the rotary polygon mirror 28. The fθ lens 45 controls the scanning speed when irradiating the photoconductor 12 with a laser, and forms an image point on the peripheral surface of the photoconductor 12. The laser beam that has passed through the fθ lens 45 is bent by the reflection mirror 46 and applied to the photosensitive member 12.

  The laser traveling in the left end direction of the photoconductor 12 is reflected by the mirror 47 and is incident on the photodetector 48. Each time the photoconductor 12 is scanned in the axial direction of the photoconductor 12, a laser traveling in the left end direction of the photoconductor 12 is incident, so that the photodetector 48 is a laser for each line applied to the photoconductor 12 by the optical scanning device 26. The irradiation start timing can be detected.

  The laser driving device 40 controls a light amount control unit 50 (details will be described later) for controlling the light amount of a laser diode (LD) included in the laser light source 30, an OR circuit 51, timing for emitting laser from the laser light source 30, and the like. And a laser control unit 52 (details will be described later).

  The laser control unit 52 includes a CPU (Central Processing Unit, not shown), and is included in the laser light source 30 based on the image data generated by the image data generation unit 54 and the detection signal from the photodetector 48. The laser diode is controlled to emit light.

  The light quantity control unit 50 causes the laser diode included in the laser light source 30 to emit light based on a signal based on the image data generated by the image data generation unit 54 and a control signal from the laser control unit 52. Further, the amount of emitted light is adjusted.

  In FIG. 3, an example of schematic structure of the light quantity control part 50 of this Embodiment is shown.

  The light amount control unit 50 according to the present embodiment includes a current-voltage conversion unit 56 for converting the photocurrent output from the photodiode (PD) 72 into a voltage, a light amount adjustment unit 58 for adjusting the light amount of the LD 70, and A switch (SW) 60 for stopping the reverse bias applied to the PD 72 is provided.

  The current-voltage conversion unit 56, the light amount adjustment unit 58, and the SW 60 are semiconductor integrated circuits formed on the same substrate 61.

  Note that the laser light source 30 of the present embodiment emits light based on the DATA signal input from the laser control unit 52, thereby emitting light from the LD 70 and the LD 70 for forming an image corresponding to the image data on the proton 8. It is comprised by PD72 for detecting a light quantity. The resistor 73 is a dummy resistor through which current flows when no current flows through the LD 70 (when the LD 70 is off).

  The light amount adjustment unit 58 includes a switching transistor 62, a switching transistor 63, an inverter 64, a transistor 65, an amplifier circuit 66, a sample hold circuit 67, a comparator 68, a reference power supply 69, a current detection resistor 74, and a sample hold capacitor 76. It is configured.

  When the DATA signal input from the laser controller 52 is at the LOW level, the switching transistor 63 is turned on and the switching transistor 62 is turned off. The switching transistor 62 and the switching transistor 63 are in conflict with each other by the inverter 64.

  The voltage of the sample hold capacitor 76 is applied to the positive input side of the amplifier circuit 66, and the current flowing through the LD 70 is controlled so that the voltage generated across the current detection resistor 74 becomes equal to the voltage of the sample hold capacitor 76.

  When the PD 72 receives the back beam generated by the light emission of the LD 70, the PD 72 outputs a light amount (photocurrent) corresponding to the received light amount, that is, the light emission amount of the LD 70. When the current output from the PD 72 flows through the current-voltage conversion resistor 78 of the current-voltage conversion unit 56, a voltage (monitor voltage) corresponding to the amount of light emitted by the LD 70 is generated.

  The light amount is adjusted based on an S / H (sample hold) signal input from the laser controller 52, and the light amount is adjusted when the S / H signal is at a high level.

  When adjusting the amount of light, the monitor voltage input from the current-voltage conversion resistor 78 is compared with the voltage of the reference power source 69 by the comparator 68. The comparison result is input to the sample hold circuit 67. The sample hold circuit 67 enters a sample state in response to an S / H signal (High level) input from the laser control unit 52. When the sample and hold circuit 67 is in the sample state, the output of the comparator 68 is applied to the sample and hold capacitor 76 and to the positive input side of the amplifier circuit 66. The output of the amplifier 66 is input to the base of the transistor 65 and controls the current of the LD 70.

  When the amount of light is not adjusted, the sample hold circuit 67 enters a hold state based on the S / H signal (Low level) input from the laser control unit 52. The voltage held in the sample hold capacitor 76 is applied to the positive input side of the comparator 68.

  In this embodiment, when the light amount is not adjusted, the application of the reverse bias to the PD 72 is stopped by the SW 60. That is, a reverse bias is applied to the PD 72 only when adjusting the amount of light.

  A specific example of the SW 60 of the present embodiment is shown in FIG. FIG. 4A shows the case where a field effect transistor (P-channel MOS transistor) is used. When the P-channel MOS transistor 60 is used, the source is connected to the PD 72 side and the drain is connected to the current-voltage conversion resistor 78 side. On / off is controlled by an S / H signal (control signal) input from the gate.

  FIG. 4B shows the case where a bipolar transistor (NPN junction transistor) is used. The NPN junction transistor 60 has a collector connected to the PD 72 side and an emitter connected to the current-voltage conversion resistor 78 side. On / off is controlled by an S / H signal (control signal) input from the base.

  The specific configuration of the SW 60 is not limited to this, and may be other switching elements.

  Further, a specific configuration for stopping application of the reverse bias of the PD 72 by the SW 60 will be described with reference to FIG. 5A to 5B show an example of a specific configuration.

  FIG. 5A shows a configuration in the case where the application of the reverse bias is stopped by preventing the current output from the PD 72 from flowing into the current-voltage conversion resistor 78. The SW 60 is disposed on the anode side of the PD 72. When stopping the application of the reverse bias, the SW 60 is turned off by the control signal. At this time, when turned off, the monitor voltage becomes 0V.

  FIG. 5B shows a configuration in the case where the application of the reverse bias is stopped by equalizing the potential of the cathode side and the anode side of the PD 72. One end of the SW 60 is connected to a 5V power source, and the other end is connected to the anode side of the PD 72. In order to stop the application of the reverse bias, the SW 60 is turned on by a control signal. At this time, the monitor voltage is 5 V which is the power supply voltage.

  In FIG. 5C, by preventing the current output from the PD 72 from flowing into the current-voltage conversion resistor 78, application of the reverse bias is stopped, and a predetermined voltage (Vref.) Is determined from the monitor voltage. The configuration when output is shown. SW60A is arranged on the anode side of PD72. One end of the SW 60B is connected to a 5V power source, and the other end is connected to the opposite side to the PD 72 of the SW 60A. When stopping the application of the reverse bias, SW60A is turned off and SW60B is turned on by the control signal. At this time, the monitor voltage becomes a voltage (Vref.) Based on the resistor 79 and the 5V power supply.

  The present invention is not limited to this, as long as the current output from the PD 72 does not flow to the current-voltage conversion resistor 78 or the cathode 72 and the anode side of the PD 72 have the same potential. It may be. If the power supply of the PD 72 (5V power supply in FIG. 5) is cut off, the power supply to the LD 70 is also cut off, so that the application of the reverse bias cannot be stopped during the light emission period of the LD 70, particularly during image writing. By adopting any of the above configurations, only the reverse bias application of the PD 72 is stopped without disturbing the light emission of the LD 70.

  Note that in the structure example illustrated in FIG. 5A, a field-effect transistor is preferably used like the P-channel MOS transistor illustrated in FIG. This is preferable because the gate current is small and does not affect the photocurrent of the PD 72. In particular, it may be applied when the light quantity control unit 50 is formed as a CMOS integrated circuit.

  In the configuration example shown in FIG. 5A, when a bipolar transistor is used like the NPN junction transistor shown in FIG. 4B, the base current of the bipolar transistor is superimposed on the photocurrent of the PD 72. It is not preferable. Therefore, when a bipolar transistor is used as SW60, it is preferable to configure as in the configuration example shown in FIG. In this case, a saturation voltage between the collector and the emitter of the bipolar transistor (specifically, 0.6 V to 0.7 V) remains between the cathode terminal and the anode terminal of the PD 72, but when the SW 60 is off (normally) For example, the occurrence of ion migration can be suppressed because the voltage is lower than the reverse bias of 5V.

  In this embodiment, the SW 60 is operated so that the reverse bias application is stopped when the S / H signal is at the LOW level so that the current output from the PD 72 does not flow into the current-voltage conversion resistor 78. Or the potential of the cathode side and the anode side of the PD 72 is made equal, but the SW60 is turned on or off depending on the configuration or the like, so the level of the S / H signal is changed by an inverter as necessary. A signal obtained by inverting is used as a control signal for operating the SW 60.

  The combination of the types of the SW 60 shown in FIG. 4 and the configuration shown in the specific example in FIG. 5 is not limited to these, and is required for the integrated circuit of the light quantity control unit 50 and the light quantity control unit 50. These may be combined as appropriate in consideration of the characteristics to be performed.

  As described above, in the present embodiment, the light amount control of the LD 70 and the reverse bias applied to the PD 72 are stopped based on the S / H signal output from the laser control unit 52. When light amount control is not performed (S / H signal is low level), the current output from the PD 72 is prevented from flowing into the current-voltage conversion resistor 78 by the SW 60, or the potential between the cathode side and the anode side of the PD 72 Are equal. When the light amount control is performed (S / H signal is high level), the SW 60 connects the path between the anode side of the PD 72 and the current-voltage conversion resistor 78, or the cathode side potential of the PD 72 is connected from the anode side. Also, a reverse bias is applied to the PD 72. Thereby, for example, the energization time of the PD 72 is reduced, and deterioration and failure are suppressed.

  In the present embodiment, the application of the reverse bias of the PD 72 is stopped during the light amount control period in which the light amount control of the LD 70 is performed based on the S / H signal for the light amount control output from the laser control unit 52. However, it is not limited to this. Further, a signal other than the S / H signal may be used. For example, in an image forming apparatus that forms an image at a higher speed, the control time for stabilizing the output of the PD 72 is shortened, and the PD 72 may become inaccurate by stopping the reverse bias voltage. In such a case, the reverse bias is applied only during the image formation period based on the light emission instruction signal of the LD 70 and the rotation instruction signal of the polygon mirror (FIG. 2, polygon mirror 28), and the reverse bias is applied outside the image formation period. May be stopped.

  In the present embodiment, the integrated circuit is formed on the substrate 61. However, the present invention is not limited to this, and the integrated circuit may be omitted. However, the integrated circuit may be formed for ease of formation. preferable.

  In the present embodiment, the case where the image forming apparatus 10 is a monochrome printer has been described in detail. However, the present invention is not limited to this, and the same can be applied to a color printer.

[Second Embodiment]
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  In the present embodiment, a reverse bias is applied to the photodiode only when the light emission amount of the laser diode is controlled, and the light amount control is performed after the output of the photodiode is stabilized. Note that the image forming apparatus and the optical scanning apparatus of the present embodiment are substantially the same as those of the first embodiment, and only the light amount control unit is different. Therefore, only the light amount control unit will be described in detail here. Also, the same parts as those in the first embodiment of the light quantity control unit 50 are denoted by the same reference numerals, detailed description thereof is omitted, and only different parts will be described in detail.

  In FIG. 6, an example of schematic structure of the light quantity control part 80 of this Embodiment is shown.

  The light quantity control unit 80 of this embodiment includes a delay circuit 82 for delaying the timing at which the S / H signal is input to the sample hold circuit 67. Further, the SW 60 uses an NPN junction transistor 86 (see FIG. 4B) and has the configuration shown in FIG. In the case of this configuration, the signal level of the S / H signal is inverted by the inverter 84 in order to turn off the NPN junction transistor 86 when the application of the reverse bias is stopped (S / H signal is at the low level). The SW 60 is operated by the control signal.

  The operation of the light quantity control unit 80 of the present embodiment will be described in detail with reference to FIG. In the present embodiment, the LD 70 is driven at a constant current during the image formation period, and emits light outside the image formation period (outside the image area), for example, between the sheets 18 and 18. Perform light control. Therefore, the reverse bias is applied to the PD 72 only when the LD 70 emits light outside the image area, and the reverse bias application is stopped during the other periods regardless of whether the LD 70 emits light.

  As shown in FIG. 5, under the control of the laser controller 52, the laser lighting signal is turned on or off in accordance with the image data (DATA signal) during the image formation period (image region). Further, after that, outside the image forming area, the light is turned on again for a light amount control and lighted by the LD 70 before a predetermined time before the next synchronization detection signal generation expected timing. At this time, it waits for the next synchronization detection signal to rise. This operation is repeated for each scan.

  Further, the S / H signal output from the laser control unit 52 is set from the rising edge of the synchronization detection signal outside the image formation period (outside the image area) with reference to the synchronization detection signal, for example, by counting the pixel clock. It turns on (High level) after time x, and turns off (Low level) after the light amount control period y.

  When the S / H signal is at a high level, the PNP junction transistor 86 is turned off, and a reverse bias is applied to the PD 72. The output of the PD 72 gradually increases as shown in FIG. 5, and after a while, the output becomes stable (almost constant). For this reason, it is preferable to operate the light amount adjustment unit 58 (sample hold circuit 67) after the output of the PD 72 is stabilized.

  In order to set the sample hold circuit 67 to the sample state after the output of the PD 72 is stabilized, the delay circuit 82 inputs a high level signal of the S / H signal after the delay time z. As a specific example, the delay time z is preferably obtained in advance based on a time constant based on the matching capacitance of the PD 72 and the resistance value of the current-voltage conversion resistor 78.

  As described above, in this embodiment, after the PD 72 operates (the S / H signal is at the high level), after the delay time z by the delay circuit 82, the S / H signal is input to the sample hold circuit 67, and the sample hold circuit 67 67 becomes a sample state, and the light quantity control is performed. That is, since the light amount control is performed after the output of the PD 72 is stabilized, the light amount control is performed based on the voltage value obtained by converting an appropriate current amount.

[Third Embodiment]
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  In the present embodiment, when an abnormality occurs in the photodiode during operation of the photodiode (during application of the reverse bias), application of the reverse bias is stopped.

  Since the present embodiment has substantially the same configuration and operation as the first embodiment, only an operation for detecting an abnormality of the photodiode and stopping the application of the reverse bias will be described in detail here.

  First, an example of abnormality of PD72 is demonstrated. For example, when dew condensation occurs between the terminals of the PD 72, a leak current is generated due to the applied reverse bias voltage. If the leakage current is generated, the silver ions of the silver paste that fixes the cathode of the PD 72 to the pedestal move due to the leakage current, and ion migration occurs. Since a reverse bias is applied and current limitation is applied by the current-voltage conversion resistor 78, when ion migration grows between the terminals of the PD 72, the current short-circuit path formed thereby is maintained as it is even if dew condensation disappears, for example. It may be done. Therefore, the laser driving device 40 does not operate normally. Therefore, in the present embodiment, the abnormality of the PD 72 is detected by the occurrence of a leak current. It is determined that the leak current is generated when the monitor voltage exceeds a predetermined reference value.

  In the present embodiment, as an example, a case where the laser controller 52 detects an abnormality of the PD 72 and outputs a signal so as to stop the application of the reverse bias will be described in detail.

  FIG. 8 is a processing flow for detecting abnormality of the PD 72 and stopping the application of the reverse bias by the CPU included in the laser control unit 52. A program for executing this processing flow may be stored in an HDD (not shown) such as the laser control unit 52.

  First, in step 100, a printing (image forming) operation is started. When the printing operation is started, a main motor (not shown) of the image forming apparatus 10 is activated, and the polygon mirror 28 starts to rotate. Further, the LD 70 is in a light emission ready state and emits light according to the image data (DATA signal).

  In the next step 102, a reverse bias is applied to the PD 72. In this embodiment, the SW 60 is controlled by the S / H signal so that the current output from the PD 72 does not flow into the current-voltage conversion resistor 78, or the potentials on the cathode side and the anode side of the PD 72 are made equal. To do.

  In the next step 104, the synchronization detection signal (see FIG. 7) is confirmed. In the present embodiment, when a leak current is generated in the PD 72, the monitor voltage exceeds the reference value regardless of the amount of light emitted from the LD 70, and the light amount adjustment unit 58 stops the light emission of the LD 70 in order to reduce the laser drive current. . When the light emission of the LD 70 is stopped, the synchronization detection signal is not generated. Here, if the synchronization detection signal is not confirmed even after a predetermined time has elapsed, it is regarded as an abnormality of the PD 72, the result is negative, and the process proceeds to step 110. On the other hand, if it is confirmed, the determination is affirmative and the routine proceeds to step 106.

  In the next step 106, it is determined whether printing has been completed. If the result is negative, the process returns to step 104 to repeat the process of confirming the synchronization detection signal. On the other hand, if an image corresponding to the image data is formed, the determination is affirmative and the routine proceeds to step 108. In step 108, after the printing operation is completed, the process proceeds to step 110. When the printing operation is finished, the main motor stops and the rotation of the polygon mirror 28 stops. Also, the light emission of the LD 70 stops.

  If the synchronization detection signal is not confirmed, or in step 110 after the printing operation is finished, the reverse bias applied to the PD 72 is stopped, and then this processing is finished. In the present embodiment, the SW 60 is controlled by the S / H signal so that the current output from the PD 72 flows to the current-voltage conversion resistor 78, or the potential on the cathode side of the PD 72 is made higher than the potential on the anode side. Increase it.

  Thus, in the present embodiment, during printing, it is determined whether or not a leak current is generated in the PD 72 based on whether or not the laser control unit 52 can confirm the synchronization detection signal. If the synchronization detection signal cannot be confirmed, a leak current is generated and detected as abnormal, an S / H signal is output, and the reverse bias applied to the PD 72 is stopped by the SW 60. Therefore, the application of reverse bias is stopped when a leak current occurs, so that the growth of ion migration is suppressed.

  In the present embodiment, an abnormality is detected depending on whether or not the synchronization detection signal can be confirmed, but the present invention is not limited to this. For example, a monitor voltage detection unit that detects the output value of the monitor voltage itself may be provided, thereby detecting an abnormality.

1 is a schematic configuration diagram illustrating an example of a schematic configuration of an image forming apparatus according to a first embodiment of the present invention. It is a block diagram which shows an example of schematic structure of the light quantity control part which concerns on the 1st Embodiment of this invention. It is a schematic block diagram which shows an example of schematic structure of the light quantity control part which concerns on the 1st Embodiment of this invention. It is explanatory drawing for demonstrating the specific example of the switch which concerns on the 1st Embodiment of this invention. It is explanatory drawing for demonstrating the specific example of the structure for stopping a reverse bias with the switch which concerns on the 1st Embodiment of this invention. It is a schematic block diagram which shows an example of schematic structure of the light quantity control part provided with the delay circuit which concerns on the 2nd Embodiment of this invention. It is a timing chart for demonstrating the delay by the delay circuit based on the 2nd Embodiment of this invention. It is a flowchart which shows an example of the process which stops the application of a reverse bias at the time of abnormality of PD performed by the laser control part which concerns on embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Image forming apparatus 26 Optical scanning device 30 Laser light source 40 Laser drive device 50, 80 Light quantity control part 52 Laser control part 56 Current voltage conversion part 58 Light quantity adjustment part 60 Switch (SW)
61 Substrate 67 Sample hold circuit 70 Laser diode (LD)
72 Photodiode (PD)
78 Current-voltage conversion resistor 82 Delay circuit

Claims (12)

A light emitting element that emits light according to image data;
A light receiving element that receives light emitted from the light emitting element and outputs a photocurrent according to the amount of light received;
Photocurrent-voltage conversion means for converting the photocurrent output from the light receiving element into a voltage;
A photocurrent stopping means provided between the light receiving element and the photocurrent voltage converting means, and for stopping a photocurrent flowing from the light receiving element to the photocurrent voltage converting means;
A photocurrent stop control means for controlling the photocurrent stop means so as to stop the photocurrent according to the light emission operation of the light emitting element;
A laser drive device comprising: The photocurrent stop control means controls the photocurrent stop means so as to stop the photocurrent during a non-emission period of the light emitting element.
The laser driving device according to claim 1. The photocurrent stop control means controls the photocurrent stop means so as to stop the photocurrent during an image forming period for forming an image according to the image data.
The laser drive device according to claim 1 or 2. The amount of light is adjusted based on a light amount adjustment instruction signal input at a predetermined timing so that the amount of light emitted from the light emitting element becomes a predetermined amount of light according to the photocurrent output from the light receiving element. A light amount adjustment unit is further provided,
The photocurrent stop control means controls to prohibit the photocurrent stop means from stopping the photocurrent during the light quantity adjustment period of the light quantity adjustment unit based on the light quantity adjustment instruction signal.
The laser driving device according to any one of claims 1 to 3. A delay unit for delaying a timing at which the light amount adjustment instruction signal is input to the light amount adjustment unit;
The light amount adjustment unit adjusts the light amount based on a light amount adjustment instruction signal input at a timing delayed by the delay unit,
The laser driving device according to claim 4. The predetermined time is an output stabilization time from the start of the light amount adjustment period to the stabilization of the amount of photocurrent output from the light receiving element.
The laser driving device according to claim 5. Further comprising detecting means for detecting an abnormality of the light receiving element,
The photocurrent stop control means controls the photocurrent stop means so as to stop the photocurrent when an abnormality is detected by the detection means.
The laser driving device according to any one of claims 1 to 6. The abnormality detection means detects a case where the voltage converted by the photocurrent voltage conversion means exceeds a predetermined reference voltage as an abnormality of the light receiving element;
The laser driving device according to claim 7. The light emitting element, the light receiving element, the photocurrent voltage conversion means, and the photocurrent stop means are formed integrally on a semiconductor integrated circuit substrate.
The laser driving device according to any one of claims 1 to 8. The photocurrent stopping means includes a field effect transistor or a bipolar transistor,
The laser drive device according to any one of claims 1 to 9. The laser driving device according to any one of claims 1 to 10,
Image forming means for forming an image on a recording medium by controlling the light emitting element of the laser driving device according to the image data;
An image forming apparatus.   A control program for causing a computer to function as the photocurrent stop control means according to any one of claims 1 to 11.

Images