JP2010137481A - Optical scanner and image forming device with the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical scanner and an image forming device capable of stabilizing the light quantity of a semiconductor laser even in the case where fluctuational voltage is generated in a voltage source connected to the semiconductor laser or a semiconductor laser driving circuit. <P>SOLUTION: The optical scanner 10 has a comparing section 72, a set value adjusting section 77, a current value adjusting section 95, and a driving current adjusting section 70. The comparing section 72 compares a voltage value of the voltage source connected to a laser diode 74 and the set voltage value of the voltage source. The set value adjusting section 77 adjusts the set value of the driving current to be supplied to the laser diode 74 according to the light quantity detected by a photodiode 76 for detecting the light quantity of the laser diode 74. The current value adjusting section 95 adjusts the current value supplied to the laser diode 74. The driving current adjusting section 70 controls the current value adjusting section 95 from the comparing result of the comparing section 72 and the set value adjusted by the set value adjusting section 77. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an optical scanning device configured to expose an object using laser light emitted from a semiconductor laser, and an image forming apparatus including the optical scanning device.

  Various devices have been conventionally devised for controlling the amount of laser light emitted from a semiconductor laser.

  For example, a semiconductor laser of an optical scanning device is known to vary in amount of light depending on temperature, and a semiconductor housed in a laser light emitting package due to a temperature rise in the laser light emitting package accompanying light emission of the semiconductor laser. It is known that temperature changes of lasers and photodiodes occur.

For this reason, in order to correct the light amount of the semiconductor laser in response to the occurrence of a temperature change, the drive current value is corrected so that the light amount of the semiconductor laser becomes stable based on the detection value of the light amount sensor that detects the light emission amount of the semiconductor laser. There exists a technique to perform (for example, refer to Patent Document 1).
JP 2008-072068 A

  However, in order to properly use the technique according to Patent Document 1 described above, it is necessary that the voltage value of the voltage source connected to the semiconductor laser or the semiconductor laser driving circuit be kept constant. In the case where a fluctuating voltage is generated, it is difficult to stabilize the light quantity of the semiconductor laser even using the technique according to Patent Document 1 described above.

  An object of the present invention is to provide an optical scanning device and an image forming apparatus capable of stabilizing the amount of light of a semiconductor laser even when a fluctuating voltage is generated in a voltage source connected to the semiconductor laser or the semiconductor laser driving circuit. Is to provide.

  The optical scanning device according to the present invention is configured to expose an object using laser light emitted from a semiconductor laser. The optical scanning device includes a comparison unit, a set value adjustment unit, a current value adjustment unit, and a drive current control unit.

  The comparison unit compares the voltage value of the voltage source connected to the semiconductor laser with a reference voltage value indicating the set voltage value of the voltage source. The set value adjustment unit has a light amount detection unit that detects the light amount of the laser light emitted from the semiconductor laser, and adjusts the set value of the drive current to be supplied to the semiconductor laser according to the light amount detected by the light amount detection unit. .

  The current value adjustment unit adjusts the value of the current supplied to the semiconductor laser. As a configuration example of the current value adjustment unit, a configuration including a main current source connected in series to the semiconductor laser and an auxiliary current source connected in parallel to the main current source can be given. Another example of the configuration of the current value adjusting unit is a configuration including means for controlling the duty ratio of the drive current supplied to the semiconductor laser. Any one of these configurations may be used alternatively, or both configurations may be combined and used.

  The drive current control unit controls the current value adjustment unit based on the comparison result of the comparison unit and the set value adjusted by the set value adjustment unit.

  In this configuration, the drive current control unit can detect the fluctuation voltage in the voltage source of the semiconductor laser based on the comparison result of the comparison unit. For this reason, the drive current control unit can control the current value adjusting unit so as to cancel the fluctuation voltage in the voltage source of the semiconductor laser.

  As a result, even if a fluctuating voltage of the semiconductor laser voltage source occurs, the drive current supplied to the semiconductor laser can be stabilized, and the fluctuating voltage of the semiconductor laser voltage source adversely affects the image quality. Can be prevented.

  In the above-described configuration, it is preferable that the drive current control unit always controls the current value adjustment unit during light emission of the semiconductor laser. The reason is that the drive current supplied to the semiconductor laser is stabilized even during the exposure of the object (eg, photoconductor drum) using the laser light emitted from the semiconductor laser.

  According to the present invention, even when a fluctuating voltage is generated in a voltage source connected to a semiconductor laser or a semiconductor laser driving circuit, the light quantity of the semiconductor laser can be stabilized.

  FIG. 1 is a diagram schematically illustrating an image forming apparatus 100 according to an embodiment of the present invention. The image forming apparatus 100 forms a multicolor image and a single color image on a predetermined sheet (recording paper) in accordance with image data transmitted from the outside, and includes an image forming unit 110 and a document reading unit 120. ing.

  The image forming unit 110 includes an optical scanning device 10, a developing device 102, a photosensitive drum 103, a cleaner unit 104, a charger 105, an intermediate transfer belt unit 106, a fixing unit 107, a paper feed cassette 181, a paper discharge tray 191, and the like. Configured.

  A document placing table 192 made of transparent glass on which a document is placed is provided above the image forming unit 110, and an automatic document processing device 125 is attached to the upper side of the document placing table 192. The automatic document processor 125 automatically conveys the document on the document table 192. The document processing device 125 is configured to be rotatable in the direction of the arrow 300, and the document can be placed manually by opening the document table 192.

  The image data handled in this image forming apparatus corresponds to a color image using each color of black (K), cyan (C), magenta (M), and yellow (Y). Accordingly, four developing units 102, photosensitive drums 103, charging units 105, and cleaner units 104 are provided to form four types of latent images corresponding to the respective colors. Black, cyan, magenta, and yellow are respectively provided. These are set to form four image stations.

  The charger 105 is a charging means for uniformly charging the surface of the photosensitive drum 103 to a predetermined potential. In addition to a charger type as shown in FIG. 1, a contact type roller type or brush type charger is used. Sometimes used.

  The optical scanning device 10 is configured to form an electrostatic latent image on the surface of the photosensitive drum 103 based on input image data. Details of the optical scanning device 10 will be described later.

  The developing device 102 visualizes the electrostatic latent images formed on the respective photosensitive drums 103 with toner of four colors (YMCK). The cleaner unit 104 removes and collects toner remaining on the surface of the photosensitive drum 103 after development and image transfer.

  The intermediate transfer belt unit 106 disposed above the photosensitive drum 103 includes an intermediate transfer belt 161, an intermediate transfer belt driving roller 162, an intermediate transfer belt driven roller 163, an intermediate transfer roller 164, and an intermediate transfer belt cleaning unit 165. I have. Four intermediate transfer rollers 164 are provided corresponding to each color for YMCK.

  The intermediate transfer belt driving roller 162, the intermediate transfer belt driven roller 163, and the intermediate transfer roller 164 stretch and drive the intermediate transfer belt 161. Each intermediate transfer roller 164 provides a transfer bias for transferring the toner image on the photosensitive drum 103 onto the intermediate transfer belt 161.

  The intermediate transfer belt 161 is provided so as to be in contact with each photoconductor drum 103, and the toner images of the respective colors formed on the photoconductor drum 103 are sequentially superimposed on the intermediate transfer belt 161 and transferred. Also, it has a function of forming a color toner image (multicolor toner image) on the intermediate transfer belt 161. The intermediate transfer belt 161 is formed in an endless shape using, for example, a film having a thickness of about 100 μm to 150 μm.

  Transfer of the toner image from the photosensitive drum 103 to the intermediate transfer belt 161 is performed by an intermediate transfer roller 164 that is in contact with the back side of the intermediate transfer belt 161. A high-voltage transfer bias (a high voltage having a polarity (+) opposite to the toner charging polarity (−)) is applied to the intermediate transfer roller 164 in order to transfer the toner image. The intermediate transfer roller 164 is a roller whose base is a metal (for example, stainless steel) shaft having a diameter of 8 to 10 mm and whose surface is covered with a conductive elastic material (for example, EPDM, urethane foam, or the like). With this conductive elastic material, a high voltage can be uniformly applied to the intermediate transfer belt 161. In this embodiment, a roller shape is used as the transfer electrode, but a brush or the like can also be used.

  As described above, the electrostatic images visualized on the respective photosensitive drums 103 according to the respective hues are stacked on the intermediate transfer belt 161. As described above, the stacked image information is transferred onto the sheet by the rotation of the intermediate transfer belt 161 by the transfer roller 110 disposed at a contact position between the sheet and the intermediate transfer belt 161 described later.

  At this time, the intermediate transfer belt 161 and the transfer roller 110 are pressed against each other at a predetermined nip, and a voltage for transferring the toner to the sheet is applied to the transfer roller 110 (the polarity opposite to the toner charging polarity (−)). (+) High voltage). Further, in order to obtain the nip constantly, the transfer roller 110 uses either the transfer roller 110 or the intermediate transfer belt driving roller 162 as a hard material (metal or the like) and the other as a soft material (elasticity such as an elastic roller). A rubber roller, a foaming resin roller, or the like) is used.

  Further, as described above, the toner attached to the intermediate transfer belt 161 by contacting the photosensitive drum 103 or the toner remaining on the intermediate transfer belt 161 without being transferred onto the sheet by the transfer roller 110 is used in the next step. Therefore, the intermediate transfer belt cleaning unit 165 is configured to remove and collect the toner. The intermediate transfer belt cleaning unit 165 includes a cleaning blade as a cleaning member that contacts the intermediate transfer belt 161, for example, and the intermediate transfer belt 161 that contacts the cleaning blade is supported by an intermediate transfer belt driven roller 163 from the back side. ing.

  The paper feed cassette 181 is a tray for storing sheets (recording paper) used for image formation, and is provided below the optical scanning device 10 of the image forming unit 110. A sheet used for image formation can also be placed in the manual paper feed cassette 182. A paper discharge tray 191 provided above the image forming unit 110 is a tray for stacking printed sheets face down.

  Further, the image forming unit 110 has a substantially vertical sheet conveyance path 200 for sending the sheets of the sheet feeding cassette 181 and the manual sheet feeding cassette 182 to the sheet discharge tray 191 via the transfer roller 110 and the fixing unit 107. Is provided. Pickup rollers 111A and 111B, a plurality of transport rollers 112A to 112D, a registration roller 113, a transfer roller 110, and a fixing unit are disposed in the vicinity of the paper transport path 200 from the paper feed cassette 181 or the manual paper feed cassette 182 to the paper discharge tray 191. 107 etc. are arranged.

  The conveyance rollers 112 </ b> A to 112 </ b> D are small rollers for promoting / assisting sheet conveyance, and a plurality of conveyance rollers 112 </ b> A to 112 </ b> D are provided along the sheet conveyance path 200. The pickup roller 111 </ b> A is provided near the end of the paper feed cassette 181, picks up sheets one by one from the paper feed cassette 181, and supplies them to the paper transport path 200. Similarly, the pickup roller 111 </ b> B is provided near the end of the manual paper feed cassette 182, picks up one sheet at a time from the manual paper feed cassette 182, and supplies it to the paper transport path 200.

  The registration roller 113 temporarily holds the sheet being conveyed through the sheet conveyance path 200. The sheet has a function of conveying the sheet to the transfer roller 110 at the timing when the leading edge of the toner image on the photosensitive drum 103 is aligned with the leading edge of the sheet.

  The fixing unit 107 includes a heat roller 171 and a pressure roller 172, and the heat roller 171 and the pressure roller 172 rotate with the sheet interposed therebetween. The heat roller 171 is set to have a predetermined fixing temperature by a control unit based on a signal from a temperature detector (not shown), and the toner is thermocompression bonded to the sheet together with the pressure roller 172. It has the function of fusing, mixing, and pressing the transferred multicolor toner image and thermally fixing the sheet. An external heating belt 173 for heating the heat roller 171 from the outside is provided.

    Next, the sheet conveyance path will be described in detail. As described above, the image forming apparatus is provided with the sheet feeding cassette 181 for storing sheets and the manual sheet feeding cassette 182 in advance. Pickup rollers 111A and 111B are disposed to feed sheets from the sheet feeding cassettes 181 and 182 so as to guide the sheets one by one to the conveyance path 200.

  The sheet conveyed from each of the sheet feeding cassettes 181 and 182 is conveyed to the registration roller 113 by the conveying roller 112A of the sheet conveying path 200, and the transfer roller is aligned with the leading edge of the sheet and the leading edge of the image information on the intermediate transfer belt 161. The image information is written on the sheet. Thereafter, the sheet passes through the fixing unit 107 so that the unfixed toner on the sheet is melted and fixed by heat, and is discharged onto the paper discharge tray 191 through the transport roller 112B disposed thereafter.

  The above-described conveyance path is for a single-sided printing request for a sheet. On the other hand, when a double-sided printing request is made, the trailing edge of the sheet that has finished single-sided printing and has passed through the fixing unit 107 as described above. When the sheet is held by the final conveyance roller 112B, the conveyance roller 112B rotates backward to guide the sheet to the conveyance rollers 112C and 112D. Then, after printing is performed on the back side of the sheet through the registration roller 113, the sheet is discharged to the discharge tray 191.

  FIG. 2 is a block diagram illustrating an electrical configuration of the image forming apparatus 100. The image forming apparatus 100 includes a main CPU 41. The main CPU 41 is connected to an image memory 44, an image processing unit 48, a hard disk drive (HDD) 54, a network interface card (NIC) 53, an operation panel 65, and sub CPUs 60 and 61. The main CPU 41 comprehensively controls each unit based on a program written in advance in the ROM 42 and temporarily stores input / output data in a predetermined memory area of the RAM 43. The image memory 44 stores the image data output from the image processing unit 48. The print data and password transmitted from the client PC 55 are recorded in the HDD 54.

  The NIC 53 has a communication function for communicating with the client PC 55 via a communication line. The image forming apparatus 100 performs printing based on print data transferred from the client PC 55. Further, the image forming apparatus 100 transfers the image data read by the document reading unit 120 to the client PC 55 via the NIC 53.

  The image forming unit 110 includes a fixing heater 21, a fixing temperature sensor 23, a driver 47, and an A / D converter 62, and these devices are controlled by the sub CPU 60. The fixing temperature sensor 23 detects the temperature of the heat roller 171 in the fixing unit 107 and outputs temperature data to the sub CPU 60. Upon receiving a predetermined warm-up command from the main CPU 41, the sub CPU 60 energizes the fixing heater 21 and determines the surface temperature of the heat roller 171 heated by the fixing heater 21 based on the temperature information obtained from the fixing temperature sensor 23. The energization of the fixing heater 21 is controlled so as to be constant at a desired temperature. When the surface of the heat roller 171 reaches a predetermined temperature, the sub CPU 60 determines that the processable state has been reached and supplies a signal to that effect to the main CPU 41. The process driving unit 56 includes various motors that drive the process mechanism and a driver that controls the driving of the solenoid and adjusts the speed of the motor that drives the photosensitive drum 103.

  The document reading unit 120 includes a light source lamp 121, a light amount sensor 123, a driver 45, and an A / D converter 63, and these devices are controlled by the sub CPU 61. The light amount sensor 123 detects the amount of light emitted from the light source lamp 121 and supplies light amount data to the sub CPU 61. When receiving a predetermined warm-up command from the main CPU 41, the sub CPU 61 energizes the light source lamp 121 so that the light amount of the light source lamp 121 is made constant at a desired light amount based on the light amount information obtained from the light amount sensor 123. The current supply to the light source lamp 121 is controlled. When the light amount of the light source lamp 121 reaches a predetermined light amount, the sub CPU 61 determines that the processable state has been reached and supplies a signal to that effect to the main CPU 41.

  In addition to the above-described configuration, the sub CPUs 60 and 61 are connected to a number of input / output devices such as motors, clutches, solenoids, and sensors in the image forming unit 110 and the image reading unit 120. The sub CPUs 60 and 61 read detection data into the sensor at a predetermined timing during the image reading process and the image forming process, and execute drive control of a motor, a clutch, a solenoid, and the like according to the read detection data.

  FIG. 3 schematically shows a configuration for driving the laser diode 74 included in the optical scanning device 10. The optical scanning device 10 has a function of forming an electrostatic latent image corresponding to image data on the surface thereof by exposing the charged photosensitive drum 103 according to input image data. In the optical scanning device 10, since a known technique can be applied to a configuration other than the configuration for driving the laser diode 74 (eg, a configuration for driving a polygon motor), the description thereof is omitted here.

  As shown in FIG. 3, the optical scanning device 10 includes a drive current control unit 70 configured to control the drive current supplied to the laser diode 74 based on input image data and the like. The drive current control unit 70 is connected to the main current source 88, the auxiliary current source 90, the correction PWM-DUTY control unit 84, and the main control unit 41, respectively.

  The main current source 88 is connected in series to the laser diode 74 via a semiconductor switch 86 composed of a MOS-FET or the like, and has a function of setting a current value supplied to the laser diode 74. The auxiliary current source 90 is connected in parallel with the main current source 88 and has a function of finely adjusting the current value supplied to the laser diode 74. The correction PWM-DUTY control unit 84 has a function of adjusting the duty ratio of the drive current supplied to the laser diode 74 by performing on / off switching control of the semiconductor switch 86. In this embodiment, the main current source 88, the auxiliary current source 90, the semiconductor switch 86, and the correction PWM-DUTY control unit 84 constitute a current value adjustment unit 95.

  The optical scanning device 10 further includes a photodiode 76, a current-voltage conversion unit 78, an APC comparison unit 80, and an APC control unit 85 for performing APC control. A part of the laser generated from the laser diode 74 is detected by the photodiode 76, and a current (photocurrent) proportional to the light emission amount flows through the photodiode 76.

  The current-voltage converter 78 converts the current value of the photocurrent into a voltage V. Specifically, as shown in FIG. 4, the current-voltage converter 78 includes an operational amplifier 782 and the like, and a value obtained by multiplying the photocurrent and the resistance value of the resistor 784 is output as the output V of the operational amplifier. The drive current control unit 70 can control the amount of laser light generated from the laser diode 74 by changing the resistance value of the resistor 784.

  The APC comparison unit 80 compares the output V of the operational amplifier with the light amount control voltage V0 as a reference voltage, and outputs the comparison result to the APC control unit 85. When the light emission amount is small, that is, when the output V is lower than the reference voltage V0, the APC control unit 85 calculates a value obtained by increasing the LD current set value and sets it in the register. On the other hand, when the light emission amount is large, that is, when the output V is higher than the reference voltage V0, the APC control unit 85 calculates a value obtained by lowering the LD current set value and sets it in the register. The value stored in the register can be read by the drive current control unit 70. In controlling the laser light quantity, the resistance value of the resistor 784 may be changed, or the value of the light quantity control voltage V0 may be changed. In this embodiment, the set value adjustment unit 77 is configured by the photodiode 76, the current-voltage converter 78, the APC comparison unit 80, and the APC control unit 85.

  Subsequently, the operation of the drive current control unit 70 will be described with reference to FIGS. 3 and 5. FIG. 5A shows the target light emission timing in one line. The drive current control unit 70 performs control as described below in order to keep the drive current (Iop) supplied to the laser diode 74 stable.

  First, the reference voltage value (Vref) and the LD power supply voltage (LD_Vcc) are input to the comparison unit 72 in the drive current control unit 70. The comparison unit 72 compares these values and extracts a fluctuation voltage value. In FIG. 5B, the ripple fluctuation voltage (Vd) is extracted as the fluctuation voltage value.

  The drive current control unit 70 determines a correction voltage value (Vref_comp) based on the comparison result of the comparison unit 72. As shown in FIG. 5C, the drive current control unit 70 sets the correction voltage value (Vref_comp) to a positive value when the LD power supply voltage (LD_Vcc) is lower than the reference voltage (Vref), and is higher than the reference voltage (Vref). If the LD power supply voltage (LD_Vcc) is high, the correction voltage value (Vref_comp) is negative. Here, the correction voltage value (Vref_comp) is an antiphase voltage of ripple fluctuation.

  Subsequently, the drive current control unit 70 determines the current value based on the extracted correction voltage value (Vref_comp) so that the LD drive current Iop is finally constant regardless of the occurrence of the ripple fluctuation voltage (Vd). The adjustment unit 95 is controlled.

  When the LD drive current Iop is fixed, the drive current control unit 70 supplies the current from the auxiliary current source 90 to the laser diode 74 by the correction PWM-DUTY control unit 84, which superimposes the current from the auxiliary current source 90 on the current from the main current source 88. Either the second method of adjusting the duty ratio of the driving current to be performed, or the third method using both the first method and the second method is used.

  When the first method is used, the drive current control unit 70 corrects the current value to be positive when the correction voltage value (Vref_comp) is positive, as shown in FIG. 5D, and corrects the correction voltage value (Vref_comp). ) Is negative, the current value is corrected to negative.

  When the second method is used, the correction PWM-DUTY control unit 84 generates a PWM control signal according to the signal from the drive current control unit 70 and supplies the generated PWM control signal to the semiconductor switch 86. The correction PWM-DUTY control unit 84 corrects the light emission time of the laser diode 74 to be longer when the correction voltage value (Vref_comp) is positive, while the correction voltage value (Vref_comp) is negative when the correction voltage value (Vref_comp) is negative. Try to shorten the flash time. For example, as shown in FIG. 5E, the correction PWM-DUTY control unit 84 increases the light amount when the correction voltage value (Vref_comp) is positive because the light emission time becomes long (eg, t3 with respect to i3). On the other hand, when the correction voltage value (Vref_comp) is negative, the light emission time is shortened (eg, t8 with respect to i8), so that the amount of light is controlled to decrease.

  In the above-described embodiment, the drive current control unit 70 does not control the drive current only in the non-image area (the beginning or end of one line), but always drives during the light emission of the laser diode 74 including the non-image area. It is preferable to control the current. As a result, the drive current of the laser diode 74 can be made constant even during image writing in the main scanning direction on the photosensitive drum 103.

  The reference voltage (Vref) is preferably supplied from a power source different from the power source that supplies power to the laser diode 74 or a drive circuit that causes the laser diode 74 to emit light. The reason is that the reference voltage value (Vref) is not easily affected by the ripple fluctuation voltage generated in the LD power supply voltage (LD_Vcc).

  The above description of the embodiment is to be considered in all respects as illustrative and not restrictive. The scope of the present invention is shown not by the above embodiments but by the claims. Furthermore, the scope of the present invention is intended to include all modifications within the meaning and scope equivalent to the scope of the claims.

1 is a diagram schematically illustrating an image forming apparatus according to an embodiment of the present invention. 1 is a block diagram illustrating an outline of an image forming apparatus. It is a figure which shows the outline of the structure which drives the laser diode of an optical scanning device. It is a figure which shows the structural example of a current-voltage converter. It is a figure explaining the drive current control of a laser diode.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10- Optical scanning device 70- Drive current control part 72- Comparison part 74- Laser diode 84- Correction | amendment PWM-DUTY control part 86- Semiconductor switch 88- Main current source 90- Auxiliary current source 100- Image forming apparatus

Claims (5)

An optical scanning device configured to expose an object using laser light emitted from a semiconductor laser,
A comparison unit that compares a voltage value of a voltage source connected to the semiconductor laser and a reference voltage value indicating a set voltage value of the voltage source;
A setting value adjustment for adjusting a setting value of a drive current to be supplied to the semiconductor laser according to the light amount detected by the light amount detection unit, having a light amount detection unit that detects a light amount of laser light emitted from the semiconductor laser And
A current value adjusting unit for adjusting the value of the current supplied to the semiconductor laser;
A drive current control unit that controls the current value adjustment unit based on a comparison result of the comparison unit and a set value adjusted by the set value adjustment unit;
An optical scanning device comprising: The current value adjustment unit includes a main current source connected in series to the semiconductor laser, and an auxiliary current source connected in parallel to the main current source,
2. The optical scanning device according to claim 1, configured to cancel a fluctuation voltage of a voltage source connected to the semiconductor laser by superimposing a current from an auxiliary current source on a current from the main current source. The current value adjustment unit includes means for controlling a duty ratio of a drive current supplied to the semiconductor laser,
3. The optical scanning device according to claim 1, wherein the optical scanning device is configured to cancel a fluctuation voltage of a voltage source connected to the semiconductor laser by controlling a duty ratio of a driving current supplied to the semiconductor laser.   4. The optical scanning device according to claim 1, wherein the drive current control unit always controls the current value adjustment unit during light emission of the semiconductor laser. 5. The optical scanning device according to any one of claims 1 to 4, comprising:
An image forming apparatus for exposing an image carrier by the optical scanning device.

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