JP2008091477A - Device for adjusting quantity of light and device for forming image - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To simply set a control target in a light-quantity adjusting device which receives an outgoing light from a light-emitting section and controls the light-emitting section so that the quantity of the light received reaches a target value. <P>SOLUTION: In a laser diode (LD) 72 used for forming an electrostatic latent image to a photosensitive-body drum in a laser printer, a monitor voltage VM obtained from a photodiode 74 receiving the laser beams is controlled at a reference voltage VT. An outgoing intensity from the LD 72 controlled by the control system is set by adjusting the resistance value of a variable resistor 76 used for detecting the monitor voltage VM so that when the irradiation intensity of laser beams on the surface of the photosensitive-body drum is measured by an optical-power meter, the irradiation intensity reaches a proper one. The variable resistor 76 having a changing characteristic of resistance values such that the outgoing intensity of laser beams from the LD 72 linearly changes in response to the operation amount of an operating section is used to simplify the setting work. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a light amount adjusting device that receives light emitted from a light emitting unit and controls the light emission intensity from the light emitting unit so that the amount of received light becomes a target value, and image formation including the light amount adjusting device. Relates to the device.

2. Description of the Related Art Conventionally, an image forming apparatus that forms an image by an electrophotographic method such as a laser printer or the like is provided with a light emitting unit composed of a semiconductor laser or the like in order to form an electrostatic latent image on a photosensitive member.
Further, in this type of image forming apparatus, when the light emission intensity from the light emitting portion varies, the density of the formed image changes, so that the light emission intensity from the light emitting portion is automatically adjusted before image formation. Has been.

  That is, before the image formation, the light emitting section is actually caused to emit light, and the emitted light is received by the light receiving sensor, and the amount of current flowing through the light receiving sensor at that time is converted into a voltage value, and the voltage value becomes the reference value. The light emitting unit is feedback controlled so as to be equal. Then, at the time of image formation, the voltage value finally obtained by this control is fixed, so that the control result is held and the light emission intensity from the light emitting portion is stabilized.

  By the way, since the feedback control is control for stabilizing the density of an image formed by the image forming apparatus, the reference value serving as a control target is the surface of the photosensitive member irradiated with light from the light emitting unit. It is necessary to correspond to the target light amount.

  Therefore, conventionally, a variable resistor for adjusting the detection voltage is provided on the current path for converting the amount of current flowing through the light receiving sensor into a voltage value, and the light emission intensity from the light emitting unit at the time of factory shipment or the like. The detection voltage value with respect to can be manually adjusted (see, for example, Patent Document 1).

According to this apparatus, the amount of light on the surface of the photosensitive member is monitored with an optical power meter or the like while the feedback control system is in operation at the time of factory shipment or the like so that the amount of light becomes the target amount of light. By adjusting the variable resistance, it is possible to make the emission intensity of the light from the light emitting unit automatically adjusted by the above control correspond to the target light amount on the surface of the photoreceptor.
JP 11-330599 A

  By the way, at the time of the manual adjustment described above, if the variable resistor is rotated, the detection voltage in the feedback control system changes according to the operation amount, and the light from the light emitting unit is adjusted so that the detection voltage becomes the target value. Is adjusted.

However, since the emission intensity of light from the light emitting portion does not change linearly with respect to the amount of operation of the variable resistor, there is a problem that adjustment work is difficult and adjustment requires skill.
That is, the variable resistor is normally configured such that the resistance value linearly changes with respect to the rotation amount (rotation ratio) of the manual adjustment knob, as shown in FIG. On the other hand, as illustrated in FIG. 9B, the emission intensity of light from the light emitting unit does not change linearly with respect to the rotation amount (rotation ratio) of the variable resistor, and depends on the rotation position of the variable resistor. The emission intensity may change greatly with a slight change in resistance value. For this reason, in order to manually adjust the emission intensity of light from the light emitting unit, skill is required.

  In FIG. 9B, the light emission intensity from the light emitting unit is represented by a current flowing through the light receiving sensor (monitor current). This is a proportional relationship between the amount of light received by the light receiving sensor and the monitor current. Because it is in.

  The present invention has been made in view of these problems, and is a control target in a light amount adjustment device that receives light emitted from a light emitting unit and controls the light emitting unit so that the amount of received light becomes a target value. It is an object to make it possible to easily set the emission intensity of light from a light emitting unit.

  The light amount adjusting device according to claim 1, which has been made to achieve such an object, includes a light receiving sensor that receives light emitted from the light emitting unit and flows a current corresponding to the amount of received light, and a variable resistor, A voltage output unit that converts the current flowing through the light receiving sensor into a voltage value based on the value and outputs the voltage value, a comparator that compares the voltage value output from the voltage output unit with a reference value, and an output of the comparator And a control means for controlling the emission intensity of the light from the light emitting unit.

  The variable resistor has a resistance value with respect to the operation amount of the operation unit so that the relationship between the operation position of the operation unit for adjusting the resistance value and the light emission intensity from the light emitting unit controlled by the control unit is linear. Change characteristics are set.

  Therefore, according to the light amount adjusting device, when the resistance value of the variable resistor is changed via the operation unit, the light emission intensity from the light emitting unit controlled by the control unit is set to the operation amount of the variable resistor. The light intensity always changes at a constant rate, and the light emission intensity from the light emitting part does not change greatly even if the operation part is operated a little as in the conventional case. For this reason, when the apparatus is shipped, setting work for initial setting of the light emission intensity (that is, light emission amount) from the light emitting unit controlled by the control means can be easily performed using a variable resistor. become able to.

  Next, the light quantity adjusting device according to claim 2 is provided with a light receiving sensor, a voltage output unit, and a control means, as in the case of claim 1, and a variable resistor provided in the voltage output unit is provided. , Different from that described in claim 1.

  In other words, the variable resistor has a relationship between the operation position of the operation unit for adjusting the resistance value and the light emission intensity from the light emitting unit controlled by the control means, from the start point with the smallest resistance value to the end point with the largest resistance value. Among all the operation areas, in the operation start area including the start point and the operation end area including the end point, the change rate of the emission intensity with respect to the operation amount is large, and in the operation intermediate area which is wider than the operation start area and the operation end area, The change characteristic of the resistance value with respect to the operation amount of the operation unit is set so that the change rate of the emission intensity with respect to the operation amount becomes small.

  For this reason, according to this light quantity adjusting device, the operation area that is most frequently used when the variable resistor is operated to set the light emission intensity from the light emitting unit is substantially the center of the entire operation area of the variable resistor. Thus, if the resistance variable range of the variable resistor is set, the light emission amount setting operation can be performed in the operation intermediate region where the change rate of the emission intensity with respect to the operation amount is small. As in the case of the apparatus, the setting operation can be easily performed.

  In particular, according to the present invention, due to variations in the optical system that emits light from the light emitting unit, variations in the characteristics of the light emitting unit, and the like, the emission intensity of the light from the light emitting unit is reduced in the operation intermediate region of the variable resistor. Even if it cannot be set, since the light emission intensity from the light emitting unit can be set using the operation start area or the operation end area of the variable resistor, the adjustable range can be secured.

  Next, the light amount adjusting device according to a third aspect includes a light receiving sensor, a voltage output unit, and a control unit, as in the first and second aspects. The difference from the first and second aspects is that the variable resistor provided in the voltage output unit is configured by a digital variable resistor whose resistance value can be numerically controlled.

  According to this light amount adjusting device, when setting the intensity of light emitted from the light emitting unit, the numerical value for setting the resistance value of the digital variable resistor may be changed. Since there is no need for manual operation, it is possible to easily set the intensity of light from the light emitting unit.

  Next, a light amount adjusting device according to a fourth aspect of the present invention is the light amount adjusting device according to the third aspect, in which storage means storing characteristic information representing the relationship between the emission intensity of light from the light emitting portion and the resistance value of the variable resistor is stored. When the target intensity representing the light emission intensity from the light emitting unit is commanded from the outside, the control amount of the variable resistance is obtained based on the target intensity and the characteristic information stored in the storage means, and the resistance value of the variable resistance And target intensity changing means for changing.

  According to this light quantity adjusting device, the light emission intensity from the light emitting unit can be switched to an arbitrary target intensity by changing the resistance value of the variable resistor. For this reason, in order to switch the target intensity of the light emitting unit, it is not necessary to change the reference value used for control by the control unit as in the conventional case, and the control accuracy of the light emission amount by the control unit can be ensured.

  That is, for example, when the reference value is changed to 1/2 of the normal value (in other words, the appropriate value) in order to reduce the target intensity of the light emitting unit, the output voltage from the voltage output unit also becomes 1/2. The sensitivity of the entire control system is reduced, and a control delay occurs (decrease in accuracy). However, if the resistance value of the variable resistor is changed as in the present invention, only the target intensity of the light emitting unit can be changed while maintaining the sensitivity and responsiveness of the control system at appropriate values.

  Next, in the light amount adjusting apparatus according to claim 5, the control means includes a current source, a comparator that compares the voltage value output from the voltage output unit with a reference value, and an output of the comparator. Current control means for controlling the current flowing through the current source. In the energization path to the light emitting part, a switch for switching between energization / non-energization to the light emitting part, a current source, and a mirror circuit are configured, and a current source and a mirror circuit are configured. Current supply means for supplying the same current as the current flowing to the light-emitting portion is provided.

  That is, according to this light quantity adjusting device, in order to control the emission intensity of light from the light emitting section, the control means does not directly control the current flowing through the light emitting section, but the current source of the control means and the light emitting section are energized. The control means indirectly controls the current flowing through the light emitting unit through a mirror circuit including a current supply means provided in the path.

  For this reason, for example, even if the contact resistance of the switch contact changes after the light emission amount of the light emitting unit is initially set and the drive voltage of the light emitting unit changes from the initial voltage, Is always controlled such that the voltage value output from the voltage output unit is equal to the reference value. Therefore, according to the present invention, it is possible to always optimally control the emission intensity of light from the light emitting unit.

On the other hand, the invention described in claim 6 relates to an image forming apparatus, and the light intensity adjusting device according to any one of claims 1 to 5 and the light emission intensity are controlled by the light amount adjusting apparatus. By modulating the light emitted from the light emitting unit according to image data and irradiating the photosensitive member, an electrostatic latent image is formed, and the electrostatic latent image is developed and transferred to a recording medium. And image forming means for forming an image.

  Therefore, according to the present invention, it is possible to provide an image forming apparatus having effects similar to those of the first to fifth aspects.

Embodiments of the present invention will be described below with reference to the drawings.
<Configuration of the entire laser printer>
FIG. 1 is a schematic side sectional view showing the overall configuration of a laser printer 1 as an image forming apparatus to which the present invention is applied.

  As shown in FIG. 1, the laser printer 1 includes a feeder unit 4 for feeding a sheet 3 as a recording medium and an image for forming an image on the fed sheet 3 in a main body case 2. The formation part 5 etc. are provided.

  The feeder unit 4 includes a paper feed tray 6 that is detachably attached to the bottom of the main body case 2, a paper pressing plate 7 provided in the paper feed tray 6, and an upper end of one end side of the paper feed tray 6. The paper feed roller 8 and the paper feed pad 9 provided in the paper, the paper dust removing roller 10 provided on the downstream side of the paper feed roller 8 in the direction of carrying the paper 3, the carry roller 11, and the paper feed roller 8. And a registration roller 12 provided on the downstream side in the transport direction.

  The sheet pressing plate 7 can stack the sheets 3 in a laminated form, and is supported so as to be swingable at the end far from the sheet feeding roller 8, so that the near end moves up and down. It is made possible, and is biased upward by a spring (not shown) from the back side.

  Therefore, as the amount of stacked sheets 3 increases, the sheet pressing plate 7 swings downward against the urging force of the spring with the end far from the sheet feeding roller 8 as a fulcrum. The paper feed roller 8 and the paper feed pad 9 are arranged to face each other, and the paper feed pad 9 is pressed toward the paper feed roller 8 by a spring 13 provided on the back side of the paper feed pad 9.

  The uppermost sheet 3 on the sheet pressing plate 7 is pressed toward the sheet feeding roller 8 by the spring from the back side of the sheet pressing plate 7, and the sheet feeding roller 8 and the sheet feeding pad are rotated by the rotation of the sheet feeding roller 8. After being sandwiched between 9, the sheets are fed one by one.

  The fed paper 3 is removed from the paper dust by the paper dust removing roller 10 and then sent to the registration roller 12 by the transport roller 11. The registration roller 12 is composed of a pair of rollers, and sends the sheet 3 to the image forming position after a predetermined registration. Note that the image forming position is a position at which the toner image is transferred to the paper 3 and is a contact position between the photosensitive drum 27 and the transfer roller 30 in this embodiment.

  The feeder unit 4 further includes a multipurpose tray 14, a multipurpose side feed roller 15 and a multipurpose side feed pad 25 for feeding the paper 3 stacked on the multipurpose tray 14. Yes.

  The multi-purpose sheet feed roller 15 and the multi-purpose sheet feed pad 25 are arranged to face each other, and the multi-purpose sheet feed pad 25 is provided by a spring disposed on the back side of the multi-purpose sheet feed pad 25. Is pressed toward the multi-purpose side paper feed roller 15.

The paper 3 stacked on the multi-purpose tray 14 is a multi-purpose side feed roller 15.
Is rotated between the multi-purpose side paper feed roller 15 and the multi-purpose side paper feed pad 25 and then fed one by one to the registration roller 12.

Next, the image forming unit 5 includes a scanner unit 16 as an optical control device, a process unit 17, a fixing unit 18, and the like.
The scanner unit 16 is disposed on the lower surface side of the paper discharge tray 46 in the upper part of the main body case 2, and includes a laser diode unit 19 (see FIG. 2), a polygon mirror 20 that is rotationally driven, lenses 21 and 23, and a reflecting mirror. 22 etc. are provided.

  The scanner unit 16 then generates a laser beam generated by a laser diode 72 (see FIG. 3) as a semiconductor laser housed in the laser diode unit 19 as indicated by an alternate long and short dash line in FIG. The surface of the photosensitive drum 27 as the photosensitive member in the process unit 17 is scanned and exposed by passing or reflecting the lens 21, the reflecting mirror 22, and the lens 23 in this order.

  Next, the process unit 17 includes a photosensitive drum 27, a scorotron charger 29, a transfer roller 30 as a transfer means, a cleaning roller 51, a secondary roller 52, and the like in a drum cartridge 26 as a photosensitive unit. Yes.

The photosensitive drum 27 is disposed at a side position of the developing roller 31 so as to be able to rotate in an arrow direction (counterclockwise in FIG. 1) in a state of facing the developing roller 31.
The scorotron charger 29 is a positively charged scorotron charger that generates corona discharge from a charging wire such as tungsten, and uniformly charges the surface of the photosensitive drum 27 to a positive polarity.

  The surface of the photosensitive drum 27 is first uniformly charged positively by the scorotron charger 29 as the photosensitive drum 27 rotates, and then exposed by high-speed scanning of the laser beam from the scanner unit 16. Then, an electrostatic latent image based on the image data is formed.

  The transfer roller 30 is disposed below the photosensitive drum 27 so as to face the photosensitive drum 27, and is supported by the drum cartridge 26 so as to be rotatable in a predetermined direction (clockwise in FIG. 1).

  At the time of transfer, the transfer roller 30 is applied with a transfer bias (transfer forward bias) from a transfer bias application power source. Therefore, the visible image carried on the surface of the photosensitive drum 27 is transferred to the paper 3 while the paper 3 passes between the photosensitive drum 27 and the transfer roller 30.

  The developing cartridge 28 includes a developing roller 31, a layer thickness regulating blade 32, a supply roller 33, a toner box 34, and the like. In the toner box 34, a positively charged non-magnetic single component is used as a developer. Toner is filled.

  The toner in the toner box 34 is agitated by the rotation of the agitator 36 supported by the rotation shaft 35 provided at the center of the toner box 34 in the direction of the arrow (counterclockwise in FIG. 1). 34 is discharged to a toner supply port opened at a side portion of 34.

The supply roller 33 is disposed at a side position of the toner supply port so as to be rotatable in a direction opposite to the agitator 36 (clockwise in FIG. 1). The development roller 31 faces the supply roller 33. Is rotatably arranged.

  Next, the electrostatic charge formed on the surface of the photosensitive drum 27 when the positively charged toner carried on the developing roller 31 comes into contact with the photosensitive drum 27 by the rotation of the developing roller 31. A latent image, that is, a visible image formed by being selectively carried on an exposed portion of the surface of the photosensitive drum 27 that is uniformly positively charged and exposed to a laser beam and lowered in potential. Is done.

  Next, the fixing unit 18 is disposed on the downstream side of the process unit 17, and is provided on the downstream side of the heating roller 41, the pressing roller 42 that presses the heating roller 41, and the heating roller 41 and the pressing roller 42. A pair of transport rollers 43 is provided.

The heating roller 41 heat-fixes the toner transferred onto the paper 3 while the paper 3 passes between the heating roller 41 and the pressing roller 42.
<Configuration of scanner unit>
Next, the configuration of the scanner unit 16 will be described.

  As shown in FIG. 2, the polygon mirror 20 in the scanner unit 16 is rotationally driven by a polygon motor (not shown) around a rotation shaft 20A. The laser beam emitted from the laser diode unit 19 is scanned in the axial direction (main scanning direction) of the photosensitive drum 27 in accordance with the rotation of the polygon mirror 20, and is photosensitive as described above through the lens 21, the reflecting mirror 22, and the like. The surface of the body drum 27 is reached.

  In addition, a BD sensor 60 for detecting a scanning origin is provided at one corner (outside the image forming range) in the laser beam scanning range. The detection signal of the BD sensor 60 is input to the ASIC 62, and the laser diode unit 19 is controlled by the ASIC 62.

The ASIC 62 is connected to a microcomputer (hereinafter simply referred to as a microcomputer) 64 that controls the operation of the entire laser printer. In accordance with a command from the microcomputer 64, the operation mode of the laser diode unit 19 is switched, and a personal computer. The amount of light emission is controlled based on the image data input to the data input unit 68 from an external device. The microcomputer 64 is connected to an operation panel 66 provided with a switch for setting the operation of the laser printer 1 and a lamp for displaying the operation state.
<Laser diode unit drive circuit>
Next, FIG. 3 is a circuit diagram showing a drive circuit of the laser diode unit 19. This drive circuit corresponds to the light amount adjusting device of the present invention, and is incorporated in the scanner unit 16 or the ASIC 62.

  As shown in FIG. 3, the laser diode unit 19 receives a laser diode (hereinafter also simply referred to as LD) 72 as a light emitting unit and a laser beam generated by the LD 72, and supplies a current corresponding to the amount of received light. A photodiode (hereinafter also simply referred to as PD) 74 as a sensor is accommodated.

  The anode of the PD 74 is grounded to the ground line, and the cathode is connected to the power supply line via the variable resistor 76. The connection point between the cathode of the PD 74 and the variable resistor 76 is connected to the differential amplifier 82 via the inverting circuit 78 and the hold circuit 80.

That is, since the PD 74 receives the laser beam emitted from the LD 72, when the LD 72 emits light, the PD 74 causes the current IM (monitor) corresponding to the intensity of the laser beam emitted from the LD 72 via the variable resistor 76. Current) flows. Therefore, a voltage obtained by subtracting the voltage “VR × IM” determined by the resistance value VR of the variable resistor 76 and the monitor current IM from the power supply voltage VC is generated at the connection point between the PD 74 and the variable resistor 76.

  Therefore, in the present embodiment, the connection point voltage is inverted by the inverting circuit 78 to generate the monitor voltage VM that changes in proportion to the monitor current IM, and the monitor voltage VM is passed through the hold circuit 80. The signal is input to the differential amplifier 82. In the present embodiment, the variable resistor 76 and the inverting circuit 78 correspond to the voltage output unit of the present invention.

  Next, the differential amplifier 82 generates a control voltage according to the difference between the monitor voltage VM and the reference value (voltage) VT. The generated control voltage is a current that controls the current flowing through the LD 72. It is input to the control unit 84.

  The current control unit 84 includes a constant current circuit 85 that can control the amount of current with a control voltage from the differential amplifier 82, and a PNP transistor TR1 that supplies current to the constant current circuit 85 from the power supply line. . The PNP transistor TR1 has an emitter connected to the power supply line via the resistor R1, a collector connected to the constant current circuit 85, and a collector-base connected directly.

  Then, the constant current circuit 85 causes the constant current when the emission intensity of the laser beam from the LD 72 becomes larger than the target intensity and the monitor voltage VM becomes higher than the reference voltage VT due to the control voltage output from the differential amplifier 82. When the current flowing through the circuit 85 decreases and, conversely, when the emission intensity of the laser beam from the LD 72 becomes smaller than the target intensity and the monitor voltage VM becomes lower than the reference voltage VT, the current flowing through the constant current circuit 85 increases. To be controlled.

  On the other hand, the cathode of the LD 72 is grounded to the ground line, and the anode is connected to the power supply line via the current supply unit 86, the resistor R2 having the same resistance value as the resistor R1, and the mechanical switch 88. The current supply unit 86 includes a PNP transistor TR2 that forms a current mirror circuit together with the PNP transistor TR1 in the current control unit 84.

  That is, the PNP transistor TR2 has a base connected to the base of the PNP transistor TR1 in the current control unit 84, an emitter connected to the power supply line via the resistor R2, and a collector connected to the anode of the LD 72. The same current as the current flowing through the constant current circuit 85 of the control unit 84 is supplied to the LD 72.

  Accordingly, the current flowing through the LD 72 is controlled so that the monitor voltage VM becomes the reference voltage VT by the operations of the differential amplifier 82, the current control unit 84, and the current supply unit 86. By this control, the current from the LD 72 is controlled. The emission intensity of the laser beam is controlled to the target intensity.

  In this embodiment, the differential amplifier 82, the current control unit 84, and the current supply unit 86 correspond to the control unit of the present invention, and among these, the differential amplifier 82 particularly corresponds to the current control unit of the present invention. The current control unit 84 corresponds to the current source of the present invention, and the current supply unit 86 corresponds to the current supply means of the present invention.

  Next, the mechanical switch 88 forcibly cuts off the power supply path to the LD 72 so that the laser beam is not emitted from the LD 72 when the case cover of the laser printer 1 is opened for maintenance or the like. An interlock device that is turned on / off in conjunction with opening and closing of the case lid. In other words, the mechanical switch 88 is turned on when the case lid is closed, permits power supply to the LD 72, and is turned off when the case cover is open, and prohibits power supply to the LD 72. .

  Further, the hold circuit 80 monitors the monitor voltage output from the inverting circuit 78 when adjusting the emission intensity of the laser beam from the LD 72 by the operations of the differential amplifier 82, the current control unit 84, and the current supply unit 86 described above. Is output to the differential amplifier 82, and when this adjustment is completed, the monitor voltage VM is sampled and held, and the emission intensity of the laser beam from the LD 72 is fixed to the target intensity. The operation is switched by the mode switching signal. It is done.

Further, on the power supply system path from the current supply unit 86 to the LD 72, after adjusting the light amount of the LD 72, the laser beam is scanned to form an electrostatic latent image on the photosensitive drum 27 (that is, at the time of image formation). A modulation circuit 90 is connected for modulating the current flowing through the LD 72 (that is, the emission intensity of the laser beam from the LD 72) in accordance with the image data.
<Characteristics of Variable Resistance and Effects of Embodiment>
As described above, in the laser diode unit 19, the emission intensity of the laser beam from the LD 72 is automatically adjusted before image formation by the operations of the differential amplifier 82, the current control unit 84, and the current supply unit 86. The target intensity needs to be set so that the light intensity of the irradiation intensity of the laser beam on the surface of the photosensitive drum 27 becomes an optimum intensity for forming an electrostatic latent image.

  The variable resistor 76 is used for this setting. When the general variable resistor shown in FIG. 9A is used as the variable resistor 76, the laser from the LD 72 is used for the operation amount of the variable resistor. Since the beam emission intensity does not change linearly, the target intensity setting operation by the variable resistor 76 becomes extremely troublesome.

  Therefore, in the present embodiment, as shown in FIG. 4, the monitor voltage VM output from the inverting circuit 78 is input to the differential amplifier 82 and the current flowing through the LD 72 is controlled. When the knob (operation unit) is rotated, the monitor current IM (the laser beam emission intensity from the LD 72) changes linearly corresponding to the rotation ratio (operation position) of the knob (FIG. 4B). (See FIG. 4 (a)). A change characteristic of the resistance value with respect to the rotation ratio of the knob of the variable resistor 76 is set.

  That is, in the present embodiment, as the variable resistor 76, by appropriately setting the width and thickness of the resistor pattern in which the contact is slid by the operation of the operation unit according to the characteristics of the drive system of the laser diode unit 19, A variable resistor set so that the change characteristic of the resistance value with respect to the rotation ratio becomes the characteristic shown in FIG. 4B is used.

  Therefore, according to this embodiment, an optical power meter is arranged on the surface of the photosensitive drum 27, and the resistance value of the variable resistor 76 is manually adjusted so that the measured intensity of the laser beam by the optical power meter becomes the target intensity. At this time, the intensity measured by the optical power meter changes substantially in proportion to the operation amount of the variable resistor 76.

  Therefore, when the laser printer 1 is shipped from the factory, setting work for initial setting of the emission intensity of the laser beam from the LD 72 controlled by the operations of the differential amplifier 82, the current control unit 84, and the current supply unit 86 is performed. It becomes very easy to do.

  In this embodiment, the current flowing through the LD 72 is not directly controlled by the control voltage output from the differential amplifier 82, but the current flowing through the current control unit 84 is controlled by the control voltage. The same current as the current flowing through the current control unit 84 is supplied to the LD 72 via the.

For this reason, even if carbon or the like adheres to the contact of the mechanical switch 88 and the drive voltage of the LD 72 is lower than the normal drive voltage, the current flowing through the LD 72 (and thus the emission intensity of the laser beam from the LD 72) is The monitor voltage VM is always controlled to be the reference voltage VT. Therefore, according to the present invention, the emission intensity of the laser beam from the LD 72 can always be optimally controlled.
<Modification 1>
As mentioned above, although one Embodiment of this invention was described, this invention is not limited to the said embodiment, A various aspect can be taken in the range which does not deviate from the summary of this invention.

  For example, as shown in FIG. 5, the characteristic of the variable resistor 76 (see FIG. 5A) is that the resistance value of the variable resistor 76 is the smallest starting point (rotation ratio 100%) to the largest resistance value (rotation ratio). 0%), in the operation start area including the start point and the operation end area including the end point, the change rate of the monitor current IM with respect to the operation amount (change in the rotation ratio) is large, and the operation start area and operation end In the operation intermediate range that is wider than the range, the change rate of the monitor current IM with respect to the operation amount (change in the rotation ratio) may be set to be small (see FIG. 5B).

  In other words, the change characteristic of the resistance value with respect to the rotation ratio of the knob of the variable resistor 76 is set as shown in FIG. 5A, and the operation range that is most often used when setting the emission intensity of the laser beam from the LD 72 is set. If the resistance variable range of the variable resistor 76 is set so as to be approximately the center of the entire operation region of the variable resistor 76, the setting operation of the intensity of the laser beam emitted from the LD 72 is performed with respect to the rotation ratio of the variable resistor 76. The operation can be performed in the operation intermediate range where the intensity change rate is small, and the setting operation can be easily performed as in the above embodiment.

In this case, for example, the intensity of the laser beam emitted from the LD 72 cannot be set in the operation intermediate region of the variable resistor 76 due to variations in the optical system that emits the laser beam from the LD 72, degradation of the characteristics of the LD 72, or the like. Even so, since the emission intensity of the laser beam from the LD 72 can be set using the operation start area or the operation end area of the variable resistor 76, the adjustable range can be ensured.
<Modification 2>
On the other hand, as shown in FIG. 6, instead of the manual adjustment variable resistor 76 having a knob as an operation unit, a digital variable resistor 92 whose resistance value can be numerically controlled is configured. The value may be set according to control data set by the microcomputer 64.

  In this case, since the relationship between the resistance value of the digital variable resistor 92 and the control data is known, the inverting circuit 78 is temporarily set with the resistance value of the digital variable resistor 92 set by arbitrary control data. The monitor voltage VM output from the digital amplifier 82 is input to the differential amplifier 82, the current flowing through the LD 72 is controlled, and at that time, the irradiation intensity of the laser beam on the surface of the photosensitive drum 27 is measured with an optical power meter. The resistance value of the variable resistor 92 can be set to an optimum value.

  That is, if the irradiation intensity of the laser beam on the surface of the photosensitive drum 27 is measured with the optical power meter as described above, the monitor current IM flowing through the PD 74 is calculated from the measurement result and the resistance value of the digital variable resistor 92. can do.

  Since the monitor current IM is proportional to the irradiation intensity of the laser beam on the surface of the photosensitive drum 27, if the monitor current IM is calculated as described above, the monitor current IM and the irradiation intensity are calculated as shown in FIG. The characteristic (that is, the proportionality constant) that expresses the relationship with can be obtained.

If this characteristic is obtained, the monitor current IM (target value) when the irradiation intensity of the laser beam onto the surface of the photosensitive drum 27 is controlled to the target intensity can be obtained, and the monitor current IM (target value) is obtained. Therefore, if the resistance value of the digital variable resistor 92 is calculated backward, the resistance value of the digital variable resistor 92 necessary for controlling the irradiation intensity of the laser beam to the target intensity and the control data thereof can be obtained.

  As described above, if the digital variable resistor 92 is used, the control data of the digital variable resistor 92 necessary for setting the emission intensity of the laser beam from the LD 72 to the optimum value can be easily obtained. It will be easier to do.

  Furthermore, if the digital variable resistor 92 is used, the resistance value can be easily changed by the control data. Therefore, the digital variable resistor 92 can be used to switch the density of the image formed by the laser printer 1.

  Specifically, for example, the normal control data of the digital variable resistor 92 necessary for controlling the formed image to the normal density, and the density of the formed image is lower than the normal density in order to suppress toner consumption (toner saving). Also, the toner save control data of the digital variable resistor 92 necessary for reducing the thickness is registered in a memory (ROM or nonvolatile RAM shown in FIG. 2) as storage means built in the microcomputer 64, respectively. The microcomputer 64 executes the resistance value changing process shown in FIG.

  This resistance value changing process is a process for realizing the function as the target strength changing means of the present invention by the microcomputer 64, and it is determined whether or not a density switching command is input via the operation panel unit 66. When a density switching command is input (S110), control data corresponding to the density switching command is read from the memory (S120), and the read control data is output to the digital variable resistor 92 via the ASIC 62 (S110). (S130).

  In this way, in order to switch the emission intensity of the laser beam from the LD 72, there is no need to change the reference voltage VT as in the prior art, and the differential amplifier 82, the current control unit 84, and the current supply unit The control accuracy of the emission intensity by 86 can be improved.

  That is, if the reference voltage VT is changed, the monitor voltage VM also changes. Therefore, the sensitivity of the entire control system is lowered and a control delay occurs, or the sensitivity of the entire control system becomes too high, and the stability of the control is increased. However, if the resistance value of the digital variable resistor 92 is changed as described above, the emission intensity of the laser beam from the LD 72 can be switched while maintaining the control system characteristics at appropriate values. it can.

  As described above, when the emission intensity of the laser beam from the LD 72 is switched by the operation of the microcomputer 64, the memory (ROM or non-volatile RAM shown in FIG. 2) as a storage means built in the microcomputer 64 is used. Instead of registering the control data as the characteristic information, the characteristic information indicating the relationship between the monitor current IM and the irradiation intensity shown in FIG. 7 may be registered as it is.

  In this case, in S120 shown in FIG. 8, the monitor current IM necessary for realizing the target density (in other words, irradiation intensity) corresponding to the density switching command is read from the characteristic information in the memory, and in S130. Then, the resistance value (in other words, control data) of the digital resistor 92 may be obtained from the monitor current IM.

It is a schematic sectional drawing showing the structure of the laser printer of embodiment. It is explanatory drawing showing the structure of the scanner unit of a laser printer. It is a circuit diagram showing the structure of the drive circuit of the laser diode unit provided in a scanner unit. It is explanatory drawing explaining the characteristic of the variable resistance provided in the drive circuit. FIG. 11 is an explanatory diagram illustrating characteristics of a variable resistor according to Modification 1. FIG. 10 is a circuit diagram illustrating a configuration of a drive circuit of a laser diode unit according to Modification 2. It is explanatory drawing explaining the resistance value setting operation | movement of the digital variable resistance provided in the drive circuit. 10 is a flowchart illustrating a resistance value changing process according to a second modification. It is explanatory drawing showing the relationship between the rotation ratio of the conventional variable resistance, and monitor current.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Laser printer, 16 ... Scanner unit, 19 ... Laser diode unit, 20 ... Polygon mirror, 21 ... Lens, 22 ... Reflector, 23 ... Lens, 26 ... Drum cartridge, 27 ... Photosensitive drum, 62 ... ASIC, 64 DESCRIPTION OF SYMBOLS ... Microcomputer, 66 ... Operation panel part, 68 ... Data input part, 76 ... Variable resistance, 78 ... Inversion circuit, 80 ... Hold circuit, 82 ... Differential amplifier, 84 ... Current control part, 85 ... Constant current circuit, 86 ... Current supply unit, 86... Current supply unit, 88 .. mechanical switch, 90... Modulation circuit, 92 .. digital variable resistor, R1, R2 .. resistor, TR1, TR2.

Claims (6)

A light receiving sensor that receives light emitted from the light emitting unit and flows a current corresponding to the amount of light received;
A voltage output unit that includes a variable resistor and converts the current flowing through the light receiving sensor into a voltage value based on the resistance value;
A comparator that compares the voltage value output from the voltage output unit with a reference value;
Control means for controlling the emission intensity of the light from the light emitting unit according to the output of the comparator;
The variable resistor has an operation amount of the operation unit so that a relationship between an operation position of the operation unit for adjusting the resistance value and an emission intensity of light from the light emitting unit controlled by the control unit is linear. A light quantity adjusting device characterized in that a change characteristic of a resistance value with respect to is set. A light receiving sensor that receives light emitted from the light emitting unit and flows a current corresponding to the amount of light received;
A voltage output unit that includes a variable resistor and converts the current flowing through the light receiving sensor into a voltage value based on the resistance value;
A comparator that compares the voltage value output from the voltage output unit with a reference value;
Control means for controlling the emission intensity of the light from the light emitting unit according to the output of the comparator;
The variable resistor has the highest resistance value from the starting point where the resistance value is the smallest, the relationship between the operation position of the operation unit for adjusting the resistance value and the light emission intensity from the light emitting unit controlled by the control means. Of all the operation areas up to a large end point, in the operation start area including the start point and the operation end area including the end point, the change rate of the emission intensity with respect to the operation amount is large, and is wider than the operation start area and the operation end area. A light quantity adjusting device, wherein a change characteristic of a resistance value with respect to an operation amount of the operation unit is set so that a change rate of the emission intensity with respect to an operation amount becomes small in a certain operation intermediate region. A light receiving sensor that receives light emitted from the light emitting unit and flows a current corresponding to the amount of light received;
A voltage output unit that includes a variable resistor and converts the current flowing through the light receiving sensor into a voltage value based on the resistance value;
A comparator that compares the voltage value output from the voltage output unit with a reference value;
Control means for controlling the emission intensity of the light from the light emitting unit according to the output of the comparator;
And the variable resistor is a digital variable resistor whose resistance value can be numerically controlled. Storage means for storing characteristic information representing a relationship between an emission intensity of light from the light emitting unit and a resistance value of the variable resistor;
When a target intensity representing the light emission intensity from the light emitting unit is commanded from the outside, a control amount of the variable resistance is obtained based on the target intensity and characteristic information stored in the storage means, and the variable A target strength changing means for changing the resistance value of the resistor;
The light quantity adjusting device according to claim 3, comprising: The control means includes a current source, a comparator that compares a voltage value output from the voltage output unit with a reference value, and current control means that controls a current flowing through the current source in accordance with an output of the comparator. With
In the energization path to the light emitting unit,
A switch that switches between energization and de-energization of the light emitting unit by conducting and blocking the energization path;
2. A current supply means that constitutes a mirror circuit with the current source and supplies the same current as the current flowing through the current source to the light emitting unit when the switch is turned on is provided. The light quantity adjusting device according to claim 4. A light amount adjusting device according to any one of claims 1 to 5,
The light emitted from the light-emitting unit whose light emission intensity is controlled by the light amount adjusting device is modulated in accordance with the image data and irradiated onto the photosensitive member to form an electrostatic latent image. Image forming means for developing the image and transferring it to a recording medium,
An image forming apparatus comprising:

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