JP2016071105A - Image forming apparatus, control method of the same, and computer program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress an unnecessary exposure part caused by lighting of a light source for receiving a laser beam from being developed by a developing part.SOLUTION: A control part of an image forming apparatus executes image forming control of forming, on a photoreceptor, an electrostatic latent image of an image to be transferred to a transfer target body by lighting a light source on the basis of image data, and laser beam receiving control of causing a light sensor to receive a laser beam by lighting the light source during a period different from an execution period of the image forming control. When executing the image forming control, the control part causes a charging part to adjust a charging potential on the surface of the photoreceptor to be an image forming potential, and when executing the laser light receiving control, causes the charging part to adjust a charging potential of the surface of the photoreceptor to be a laser light receiving potential having a larger absolute value than that of the image forming potential.SELECTED DRAWING: Figure 5

Description

  The technology disclosed in this specification relates to an image forming apparatus.

  There is known an image forming apparatus including a light source, a polygon mirror, a photoconductor, a charging unit, and a developing unit. In these image forming apparatuses, a charging unit is charged with a photosensitive member, and the photosensitive member is exposed by laser light emitted from a light source and reflected by a polygon mirror to form an electrostatic latent image. There is an image forming apparatus for developing the toner. Such an image forming apparatus is provided with a configuration for determining a so-called write-out timing at which the light source is turned on based on image data and the electrostatic latent image is formed on the photosensitive member. Specifically, in the image forming apparatus, an optical sensor is disposed at a position where the laser beam emitted from the light source and reflected by the polygon mirror is irradiated, and the light source is turned on before the light source is turned on based on the image data. The writing start timing is determined based on the timing at which the optical sensor detects that the laser beam emitted from the light source has been received.

  In the image forming apparatus having the above configuration, when the light source is turned on so that the optical sensor receives the laser light, the image data is obtained by irradiating the photoconductor with the laser light emitted from the light source and reflected by the polygon mirror. Apart from the electrostatic latent image based on the above, the photosensitive member may be unnecessarily exposed to form an electrostatic latent image. In this case, for example, an electrostatic latent image due to unnecessary exposure may be developed by the developing unit, and for example, a problem that the sheet or the transfer roller is soiled by the developer image occurs.

  Therefore, in the image forming apparatus having the above configuration, when the light source is turned on so that the optical sensor receives the laser beam in order to suppress unnecessary exposure, the intensity of the laser beam emitted from the light source is determined based on the image data. A technique for making the light source lower than when the light source is turned on has been proposed (for example, Patent Document 1).

JP 10-319331 A

  In the above conventional technique, the intensity of the laser beam from the light source is lowered, and the amount of received laser beam received by the optical sensor is reduced accordingly, so that the detection accuracy of the laser beam is lowered and the writing timing is accurate. There is a risk that it cannot be determined well. In addition, even if the above-described conventional technique is adopted, it may not be possible to prevent the photosensitive member from being unnecessarily exposed and the sheet or the like from being stained by the developer attached to the exposed portion, and further improvement is desired. Yes.

  It is not limited to the case where the writing start timing is determined. For example, when the operation of a reflector such as a polygon mirror is controlled based on the fact that the optical sensor receives laser light, or based on the amount of laser light received by the optical sensor. Even when the amount of laser light emitted from the light source is adjusted, the photoconductor may be exposed unnecessarily. In short, when the light source is turned on at a time different from the time when the light source is turned on based on the image data, and the laser light from the light source is received by the photosensor, the photoconductor is exposed unnecessarily, and the exposed portion The sheet or the like may be soiled by the developer adhering to the toner.

  The present specification discloses a technique capable of solving at least a part of the problems described above.

(1) An image forming apparatus disclosed in the present specification irradiates a light source that emits laser light, a deflection unit that deflects laser light emitted from the light source, and the laser light deflected by the deflection unit. A photosensitive member that is irradiated with the laser beam emitted from the light source, a charging unit that charges the photosensitive member, and an electrostatic latent image formed on the photosensitive member by the laser beam. A developing unit that develops using a developer, and a control unit, wherein the control unit turns on the light source based on image data, thereby generating an electrostatic latent image of an image to be transferred to the transfer target. Performing image formation control to be formed on the photoconductor and laser light reception control for causing the optical sensor to receive the laser light by turning on the light source at a time different from the execution time of the image formation control, and Execute image formation control When the laser charging control is performed, the charging unit sets the charging potential on the surface of the photoconductor to the image forming potential. A laser light receiving potential having an absolute value larger than the formation potential is set. According to this image forming apparatus, when the laser light receiving control is executed, the charging potential of the surface of the photosensitive member by the charging unit is set to a potential whose absolute value is larger than that at the time of executing the image forming control. As a result, even when the photosensitive member is exposed when performing laser light reception control, the potential of the exposed portion of the photosensitive member is larger than when the charging potential of the surface of the photosensitive member by the charging unit is the same as the execution timing of image formation control. However, since it is suppressed that it becomes the potential which can be developed, it can suppress that an exposed part is developed by the image development part.

(2) In the image forming apparatus, the photosensitive member is a photosensitive drum that is rotationally driven, and the control unit performs the laser light reception control using the laser light among the surface of the photosensitive drum. An area including an exposure area in which an exposure line is formed and the length of the photosensitive drum in the rotation direction is shorter than the entire circumference of the photosensitive drum may be the laser light receiving potential. According to this image forming apparatus, it is possible to suppress deterioration of the photosensitive drum over the entire circumference of the photosensitive drum as compared with the case where the charging potential of the surface of the photosensitive member by the charging unit is set to the laser light receiving potential.

(3) In the image forming apparatus, the control unit is adjacent to the exposure area and an upstream side and a downstream side in the rotation direction with respect to the exposure area, and the length in the rotation direction is the exposure line. It is good also as a structure which makes the area | region containing a pair of adjacent area more than the thickness of one line into the said laser receiving potential. According to this image forming apparatus, compared with the case where the charging potential is set to the laser light receiving potential only in the exposure region, the developing portion develops the exposed portion by turning on the light source for receiving the laser light of the optical sensor. It can be surely suppressed.

(4) In the image forming apparatus, the charging unit includes a charging wire and a grid, and the control unit adjusts the grid potential to change the charging potential, the image forming potential, and the laser. A configuration in which the light receiving potential is used may be employed. According to this image forming apparatus, by adjusting the grid potential, the charging potential on the surface of the photosensitive member by the charging unit can be set to the image forming potential and the laser light receiving potential.

(5) In the image forming apparatus, the charging unit includes a charging roller in contact with the photosensitive member, and the control unit adjusts the potential of the charging roller to adjust the charging potential to the image forming unit. A configuration may be used in which the potential and the laser light receiving potential are used. According to this image forming apparatus, the charging potential can be set to the image forming potential and the laser light receiving potential by adjusting the potential of the charging roller. In addition, since the charging roller and the photosensitive member are in contact with each other, it is possible to accurately set the region for the laser light receiving potential in the photosensitive member as compared with the configuration in which the charging unit and the photosensitive member are separated from each other. .

(6) In the image forming apparatus, the photosensitive member is a photosensitive drum that is rotationally driven, and the controller controls the rotational speed of the photosensitive drum to a first speed when executing the image forming control. By setting the charging potential to the image forming potential and performing the laser light reception control, the rotational speed of the photosensitive drum is set to a second speed that is lower than the first speed. The charging potential may be the laser light receiving potential. According to this image forming apparatus, the charging potential can be set to the image forming potential and the laser light receiving potential by adjusting the rotation speed of the photosensitive drum.

(7) In the image forming apparatus, the control unit may perform the development when a portion of the surface of the photoreceptor exposed by execution of the laser light reception control reaches a position facing the developing unit. The development potential of the part may be set to a potential having a smaller absolute value than when the image formation control is executed. According to this image forming apparatus, compared with the case where the development potential when the portion exposed by the execution of the laser light reception control reaches the position facing the developing portion is the same as that at the time of execution of the image formation control, It can suppress more reliably that an exposed part is developed by the image development part.

(8) In the image forming apparatus, the optical sensor is disposed at a position where the laser light emitted from the light source and reflected by the reflector is irradiated, and the control unit executes the image forming control. In this case, the light source may be turned on based on the image data based on the timing at which the optical sensor receives the laser light. In this image forming apparatus, the light source is turned on based on the image data based on the timing at which the optical sensor detects that the laser beam is received. In such a configuration, the photoconductor may be exposed before the light source is turned on based on the image data. However, according to this image forming apparatus, even if the photosensitive member is exposed and an electrostatic latent image is formed, the electrostatic latent image can be prevented from being developed by the developing unit.

(9) In the image forming apparatus, the optical sensor is disposed at a position where the laser light emitted from the light source and reflected by the reflector is irradiated, and the control unit executes the laser light reception control. In addition, the optical sensor may detect that the laser beam has been received, and the drive of the deflection unit may be controlled based on the detection timing. According to this image forming apparatus, the drive of the deflection unit is controlled based on the timing at which the optical sensor detects that the laser beam has been received. In such a configuration, the photosensitive member may be exposed during the control of the deflection unit drive. However, according to this image forming apparatus, even if the photosensitive member is exposed and an electrostatic latent image is formed, the electrostatic latent image can be prevented from being developed by the developing unit.

  The technology disclosed by this specification can be implemented in various forms. For example, the present invention can be realized in the form of an image forming apparatus, a process apparatus control method, an image forming apparatus, a process apparatus, a computer program for realizing the functions of the method or apparatus, a recording medium on which the computer program is recorded, and the like. Is possible.

1 is a schematic diagram illustrating a configuration of a printer 10 according to an embodiment. Schematic showing the configuration of the exposure unit 300 Block diagram showing the configuration of the printer 10 The flowchart which shows the control processing which CPU811 performs Timing chart showing ON / OFF of each motor, ON / OFF of LD310, BD signal, and each voltage The flowchart which shows the control processing which the exposure control part 380 performs Schematic showing the configuration of the process unit 400 Schematic which shows the structure of the printer 10 of another embodiment.

  A configuration of the printer 10 according to the embodiment will be described with reference to FIGS. 1 to 3. The printer 10 is an electrophotographic image forming apparatus. As shown in FIG. 1, the printer 10 includes a paper feeding unit 100 and an image forming unit 200.

  The paper feed unit 100 includes a tray 110, a pickup roller 120, a transport roller 130, and a registration roller 140. The sheets W stored in the tray 110 are taken out one by one by the pickup roller 120, conveyed by the conveying roller 130, corrected in posture by the registration roller 140, and sent to the image forming unit 200 at a predetermined timing.

  The image forming unit 200 includes an exposure unit 300, a process unit 400, a fixing unit 500, a charging application unit 610, a development application unit 620, and a transfer application unit 630. The exposure unit 300 irradiates a laser beam L toward a photosensitive drum 410 described later. The configuration of the exposure unit 300 will be described in detail later.

  The process unit 400 includes a photosensitive drum 410, a charging unit 420, a developing unit 430, and a transfer roller 440. The charging unit 420 is a scorotron charging unit having a charging wire 421 and a grid 422, and uniformly charges the surface of the photosensitive drum 410. When the surface of the photosensitive drum 410 uniformly charged by the charging unit 420 is irradiated with the laser light L from the exposure unit 300 described above, an electrostatic latent image is formed on the surface of the photosensitive drum 410. The developing unit 430 develops the electrostatic latent image formed on the surface of the photosensitive drum 410 by supplying a developer. As a result, a developer image is formed on the surface of the photosensitive drum 410. The transfer roller 440 is disposed so as to face the photosensitive drum 410, and transfers the developer image formed on the surface of the photosensitive drum 410 onto the conveyed sheet W. The photosensitive drum 410 is an example of a photoconductor, the transfer roller 440 is an example of a transfer unit, and the sheet W is an example of a transfer target.

  The fixing unit 500 is disposed downstream of the photosensitive drum 410 in the conveyance direction of the sheet W, and fixes the developer image on the sheet W by heat. Thereafter, the sheet W is discharged through a discharge roller 710 to a discharge tray 720 formed on the upper surface of the printer 10.

  The charging application unit 610 performs a charging application operation in which a voltage VC having the same polarity as the developer of the developing unit 430 is applied to the charging wire 421 in accordance with an instruction from the CPU 811 described later. In this charging application operation, the charging application unit 610 detects the grid voltage VG of the grid 422, and the value of the current and voltage VC passed from the charging application unit 610 to the charging wire 421 so that the grid voltage VG becomes a target value. Adjust at least one of The target value of the grid voltage VG is changed to the first grid target value VG1 and the second grid target value VG2 in accordance with an instruction from the CPU 811. The first grid target value VG1 is a value of the grid voltage VG when the electrostatic latent image of the image to be transferred to the sheet W is formed on the photosensitive drum 410, and is, for example, +800 V. The first grid target value VG1 The charged potential on the surface of the photosensitive drum 410 charged with the grid voltage VG is an example of the image forming potential. The second grid target value VG2 is a value of the grid voltage VG having the same polarity as the first grid target value VG1 and an absolute value larger than the first grid target value VG1, for example, + 1200V. The charged potential on the surface of the photosensitive drum 410 charged with the grid voltage VG of the 2-grid target value VG2 is an example of the laser light receiving potential.

  In response to an instruction from the CPU 811, the development application unit 620 applies a development voltage VD having the same polarity as the developer to the development roller 431 of the development unit 430 and performs a development application operation for maintaining the development voltage VD at the development target value. Do. The development target value is changed to a first development target value VD1 and a second development target value VD2 in accordance with an instruction from the CPU 811. The first development target value VD1 is a value of the development voltage VD sufficient to develop the electrostatic latent image formed on the photosensitive drum 410, and is + 400V, for example. The second development target value VD2 is a value of the development voltage VD whose absolute value is smaller than the first development target value VD1, and is, for example, +100 to + 300V. Note that when the developing voltage VD is set to 0 V, for example, the developer on the photosensitive drum 410 may be attached to the developing roller 431, so the developing voltage VD is set to +100 V or more.

  The transfer application unit 630 can perform a forward transfer application operation in accordance with an instruction from the CPU 811. In the forward transfer application operation, the transfer application unit 630 applies a forward transfer voltage VTM having a polarity opposite to that of the developer to the transfer roller 440 and maintains the forward transfer voltage VTM at a forward transfer target value (for example, −1200 V). Note that the transfer application unit 630 may perform current control for maintaining the transfer current amount flowing through the transfer roller 440 at the target current amount instead of voltage control in the forward transfer application operation.

  As shown in FIG. 2, the exposure unit 300 includes a laser diode (hereinafter referred to as “LD”) 310 that emits a laser beam L, a first lens unit 320, a polygon mirror 330, a polygon motor 340, and a second lens unit. 350, a beam detector (hereinafter referred to as “BD”) 360, a monitor element 370, and an exposure control unit 380. The LD 310 is an example of a light source, and the laser beam L is an example of a laser beam. The polygon mirror 330 is an example of a deflection unit, and the BD 360 is an example of an optical sensor.

  The polygon mirror 330 is a rotating polygon mirror having six reflecting surfaces 331 arranged so as to constitute the side surface of a regular hexagonal prism. The polygon mirror 330 is rotationally driven by a polygon motor 340.

  The first lens unit 320 is formed of, for example, a collimator lens, converts the laser light L emitted from the LD 310 into a light beam, and irradiates the polygon mirror 330 with it. The second lens unit 350 is configured by, for example, an fθ lens, and irradiates the surface of the photosensitive drum 410 with the laser light L emitted from the first lens unit 320 and reflected by the reflection surface 331 of the polygon mirror 330.

  When the polygon mirror 330 rotates with the rotation of the polygon motor 340, the angle of the reflection surface 331 with respect to the irradiation direction of the laser light L from the first lens unit 320 changes periodically, so that the laser light L is periodically generated by the reflection surface 331. Biased. As a result, a linear electrostatic latent image (hereinafter referred to as an exposure line) is formed on the surface of the photosensitive drum 410 by the laser light L.

  The BD 360 is disposed at a position where the laser beam L reflected by the reflecting surface 331 is incident in a state where the angle of the reflecting surface 331 with respect to the irradiation direction of the laser beam L is a specific angle. The BD 360 outputs a BD signal (see FIG. 5) that is at a low level when the laser beam L is not incident and is at a high level when the laser beam L is incident. The monitor element 370 is disposed in the vicinity of the LD 310 and outputs a monitor signal corresponding to the amount of laser light L emitted from the L310. This monitor signal is used for light amount adjustment for adjusting the amount of laser light L emitted from the LD 310, for example.

  As will be described later, the exposure control unit 380 performs rotation control of the polygon motor 340 and light emission control of the LD 310 in accordance with an instruction from the CPU 811. The exposure control unit 380 is composed of one or a plurality of ASICs (Application Specific Integrated Circuits). A combination of the exposure control unit 380 and a CPU 811 described later is an example of a control unit.

  As shown in FIG. 3, the printer 10 receives a controller 810 that controls the printer 10, a communication interface (IF) 820 for connecting to an external device, and user operations in addition to the image forming unit 200 and the like described above. And an operation unit 830.

  The operation unit 830 includes various buttons and a touch panel (none of which are shown) that accept user operations. The touch panel also functions as a display unit that displays various types of information. The communication interface 820 is hardware that enables communication with an external device. Specifically, the communication interface 820 is, for example, a network interface, a serial communication interface, a parallel communication interface, or the like. The printer 10 acquires image data to be printed from an external device via the communication interface 820.

  The controller 810 includes a CPU 811, a ROM 812, a RAM 813, a nonvolatile memory 814, and an ASIC 815. The ROM 812 stores a control program for controlling the printer 10, various settings, initial values, and the like. The RAM 813 is used as a work area when the CPU 811 executes various programs and as a temporary storage area for data. The nonvolatile memory 814 is a rewritable memory such as NVRAM, flash memory, HDD, or EEPROM. The ASIC 815 is a hardware circuit dedicated to image processing, for example. The CPU 811 controls each component of the printer 10 according to a control program read from the ROM 812 and signals sent from various sensors.

  Control processing executed by the CPU 811 and the exposure control unit 380 will be described with reference to FIGS. When the CPU 811 receives a print command from the user via the operation unit 830, the CPU 811 executes the control process illustrated in FIG. Specifically, the CPU 811 activates a main motor (not shown) (S110, T1 in FIG. 5), and when the rotation speed of the main motor is stabilized at a predetermined target speed, the driving force of the main motor is changed to the sheet feeding unit 100 or the process. By being transmitted to the unit 400, the sheet W is taken out from the tray 110 and conveyed toward the image forming unit 200, and the photosensitive drum 410 and the like are driven to rotate. Further, the CPU 811 sets the grid target value to the first grid target value VG1, and causes the charging application unit 610 to start the above-described charging application operation (S110, T1 in FIG. 5). As a result, a portion of the surface of the photosensitive drum 410 that passes through the charging position X1 (see FIG. 7) facing the charging unit 420 is charged to approximately the same potential as the first grid target value VG1.

  The CPU 811 has a developing position where a portion of the surface of the photosensitive drum 410 that is charged by the charging application operation of the charging unit 420 (hereinafter also referred to as a charging portion) faces the developing roller 431 by the rotation of the photosensitive drum 410. It is determined whether or not X3 (see FIG. 7) has been reached (S120). Specifically, the CPU 811 determines whether or not the first waiting time ΔT1 has elapsed since the start of the charging application operation. The first standby time ΔT1 is a time required for the charged portion to reach the developing position X3 (see FIG. 7) facing the developing roller 431 from the charging position X1 due to the rotation of the photosensitive drum 410.

  When the CPU 811 determines that the charged portion has not reached the development position X3 (S120: NO), the CPU 811 stands by, and when it is determined that the charged portion has reached the development position X3 (S120: YES), the development target value is set to the first value. One development target value VD1 is set, and the development application unit 620 starts the development application operation (S130, T2 in FIG. 5). Accordingly, when the electrostatic latent image is formed on the surface of the photosensitive drum 410 by exposing the charged portion with the laser light L from the exposure unit 300, the electrostatic latent image is developed by the developing unit 430. Ready to develop.

  Next, the CPU 811 activates the polygon motor 340 by sending a rotation signal to the polygon motor 340 (S140, T3 in FIG. 5). Thus, after the polygon mirror 330 is rotationally driven and the rotational speed of the polygon mirror 330 is stabilized at a predetermined target speed, the CPU 811 switches the grid target value to the second grid target value VG2 (S150, T4 in FIG. 5). ). As a result, the surface of the photosensitive drum 410 is charged to a charging potential having the same polarity as the developer and a larger absolute value.

  Then, the CPU 811 determines whether or not the charged portion charged with the second grid target value VG2 has reached the exposure position X2 (S160). Specifically, the CPU 811 determines whether or not the second standby time ΔT2 has elapsed since the grid target value was switched to the second grid target value VG2. The second waiting time ΔT2 is a time slightly shorter than the time required for the charged portion to reach the exposure position X2 from the charging position X1 due to the rotation of the photosensitive drum 410. If the CPU 811 determines that the charged portion has not reached the exposure position X2 (S160: NO), the CPU 811 waits. If the CPU 811 determines that the charged portion has reached the exposure position X2 (S160: YES), the CPU 811 notifies the exposure control unit 380. Then, the control process shown in FIG. 6 is started (S170).

  In the control process shown in FIG. 6, the exposure control unit 380 causes the exposure unit 300 to start BD light reception control (S310, T5 in FIG. 5). The BD light reception control sends a light emission signal to the LD 310 in order to detect that the BD 360 has received the laser beam L before executing image formation control (S7 in FIG. 5) based on image data to be described later. This is an example of laser light reception control. As described above, when the grid target value is switched to the second grid target value VG2 and the second standby time ΔT2 has elapsed, the BD light reception control is performed, so that the laser L by the BD light reception control is The exposed portion charged to the potential of the 2-grid target value VG2 can be irradiated.

  After the start of the BD light reception control, the exposure control unit 380 determines whether or not the BD 360 has received the laser beam L based on the BD signal from the BD 360 (S320), and if the BD 360 has not received the laser beam L. If it is determined (S320: NO), it stands by with the LD 310 turned on, and if it is determined that the BD 360 has received the laser beam L (S320: YES), the LD 310 is turned off and the BD light reception control is stopped ( S330). The exposure control unit 380 can specify a period during which the laser beam L from the exposure unit 300 is not irradiated onto the photosensitive drum 410 and the BD 360 is irradiated based on the light reception timing of the laser beam L at S320. Hereinafter, this period is referred to as a BD lighting period.

  Next, the exposure control unit 380 determines the writing start timing (S340). The write-out timing is a timing at which the LD 310 is turned on based on the image data and each exposure line is started to be formed on the photosensitive drum 410. Specifically, the exposure control unit 380 turns on the LD 310 during the BD lighting period (T6 in FIG. 5), and determines the writing start timing based on the timing at which the BD 360 receives the laser beam L. Specifically, the exposure control unit 380 performs image formation control when a writing start timing has arrived after a predetermined time has elapsed since the BD 360 received the laser beam L (S350, T7 in FIG. 5). Specifically, the exposure control unit 380 turns on the LD 310 based on the image data, thereby forming an electrostatic latent image of the image to be transferred onto the sheet W, specifically, one exposure line on the photosensitive drum 410. To do. Thereafter, the exposure control unit 380 repeatedly executes the process of S350 and the process of S360 (S360: NO), and determines that the process for all image data has been completed (S360: YES), this control process is performed. finish.

  Here, as shown in FIG. 5, when the BD light receiving control is executed (T5), since the developing unit 430 is already in a developable state (see T2), the light is emitted from the exposure unit 300 by the BD light receiving control. When the photosensitive drum 410 is irradiated with the laser light L, the photosensitive drum 410 may be unnecessarily exposed to form an electrostatic latent image separately from the electrostatic latent image based on the image data. Then, for example, an electrostatic latent image due to unnecessary exposure is developed by the developing unit 430, the developer adheres to the transfer roller 440, and the sheet W is soiled by the adhered developer, so-called back dirt may occur. . Hereinafter, a portion of the surface of the photosensitive drum 410 that is exposed by executing the BD light reception control is referred to as an unnecessary exposure portion.

  In order to prevent the unnecessary exposure portion from being developed by the developing unit 430, the CPU 811 sets the charging potential of the surface of the photosensitive drum 410 to the first grid target by the charging unit 420 when executing image formation control. When the laser light reception control is executed with the potential of the value VG1 (T7 in FIG. 5), the charging unit 420 sets the charging potential of the surface of the photosensitive drum 410 to the potential of the second grid target value VG2 (S150 in FIG. 5). 5 T4). As described above, since the absolute value of the second grid target value VG2 is larger than the first grid target value VG1, the absolute value of the charged potential on the surface of the photosensitive drum 410 after being exposed by the exposure unit 300 becomes large. Therefore, the developer is less likely to adhere. That is, it is possible to suppress the unnecessary exposure portion from being developed by the developing unit 430.

  The CPU 811 instructs the exposure control unit 380 to execute the control process of the exposure unit 300, and determines whether or not the third standby time ΔT3 has elapsed since the grid target value was switched to the second grid target value VG2. (S180). The third waiting time ΔT3 is longer than the second waiting time ΔT2. When the CPU 811 determines that the third waiting time ΔT3 has not elapsed since switching to the second grid target value VG2 (S180: NO), the CPU 811 waits, and when determining that the third waiting time ΔT3 has elapsed (S180). : YES), the grid target value is returned from the second grid target value VG2 to the first grid target value VG1 (S190).

  Here, as shown in FIG. 7, when executing the BD light reception control, the rotation area of the photosensitive drum 410 includes the exposure area E <b> 1 where the exposure line is formed by the laser beam L on the surface of the photosensitive drum 410. A region E2 having a length shorter than the entire circumferential length of the photosensitive drum 410 is set to the potential of the second grid target value VG2. Thereby, the deterioration of the photosensitive drum 410 can be suppressed as compared with the case where the charging potential is set to the potential of the second grid target value VG2 over the entire circumference of the photosensitive drum 410. Specifically, the charge potential of the photosensitive drum 410 becomes the potential of the second grid target value VG2 whose absolute value is larger than the first grid target value VG1, so that charge is accumulated and internal discharge or the like occurs. Thus, the deterioration of the photosensitive layer can be suppressed.

  The area E2 is adjacent to the exposure area E1 and the upstream and downstream sides in the rotation direction of the photosensitive drum 410 with respect to the exposure area E1, and the length in the rotation direction is the thickness of one exposure line. This is a region including the pair of adjacent regions E3. As a result, compared to the case where the charging potential is set to the potential of the second grid target value VG2 only in the exposure area E1, an unnecessary exposure portion due to lighting of the light source for receiving the laser light L of the BD 360 is developed by the developing unit 430. Can be more reliably suppressed.

  The CPU 811 determines whether or not the charged portion charged with the second grid target value VG2 has reached the development position X3 (S200). Specifically, the CPU 811 determines whether or not the fourth standby time ΔT4 has elapsed since the grid target value was switched to the second grid target value VG2. The fourth waiting time ΔT4 is a time slightly shorter than the time required for the charged portion to reach the developing position X3 from the charging position X1 due to the rotation of the photosensitive drum 410. When the CPU 811 determines that the charged portion has not reached the development position X3 (S200: NO), the CPU 811 stands by, and when it is determined that the charged portion has reached the development position X3 (S200: YES), the development target value is set as follows. The first development target value VD1 is switched to the second development target value VD2 for a predetermined time (S210, T8 in FIG. 5). Thereafter, the CPU 811 causes the transfer applying unit 630 to apply the forward transfer voltage VTM to the transfer roller 440 (S220, T9 in FIG. 5). Accordingly, the developer image based on the image data formed on the surface of the photosensitive drum 410 by the image formation control in S350 can be transferred to the sheet W at the transfer position X4. The CPU 811 ends the control process when the process is completed for all image data.

  For example, it is assumed that the charged potential of the surface of the photosensitive drum 410 is lowered by 700 V due to the exposure of the laser beam L. Then, when the image formation control is executed, the charging potential of the surface of the photosensitive drum 410 is set to a potential of +800 V (first grid voltage value) by the charging unit 420, and +100 V (== + 800V-700V). At this time, since the development target value of the developing unit 430 is +400 V (first development target value), a positive polarity developer can be sufficiently adhered to the exposed portion for development.

  On the other hand, when executing the BD light reception control, the charging potential on the surface of the photosensitive drum 410 is set to +1200 V (second grid voltage value) by the charging unit 420 and +500 V (= + 1200V-700V). At this time, since the development target value of the developing unit 430 is +100 to +300 V (second development target value), the positive polarity developer is repelled on the exposed portion and hardly adheres.

  As described above, according to this embodiment, when the unnecessary exposure portion exposed by the execution of the BD light reception control on the surface of the photosensitive drum 410 reaches the transfer position X4, the developer of the developing unit 430 A reverse transfer voltage VTP having the same polarity is applied to the transfer roller 440. As a result, even when the unnecessary exposure portion reaches the transfer position X4, the unnecessary exposure portion by turning on the light source for causing the BD 360 to receive the laser light L as compared with the case where the voltage having the same polarity as the developer is not applied to the transfer roller 440. It is possible to suppress the developer adhering to the transfer roller 440 from adhering to the transfer roller 440, and thus to prevent the back side of the sheet W from being stained. In addition, it is not necessary to change the emission intensity of the laser beam L of the LD 310. Furthermore, it is more reliable that the unnecessary exposure portion is developed by the developing unit 430 than when the development potential when the unnecessary exposure portion reaches the development position X3 is made the same as that at the time of execution of the image formation control. Can be suppressed.

  The technology disclosed in the present specification is not limited to the above-described embodiments, examples, and modifications, and can be realized with various configurations without departing from the spirit of the technology.

  The image forming apparatus may be a printer capable of forming a color image. The image forming apparatus is not limited to a single printer, but may be a copier, a facsimile machine, or a multifunction machine. The present invention can also be applied to these copying machines and the like. In addition, the image forming apparatus is not limited to a configuration in which development is performed using a positive polarity developer, but may be configured to perform development using a negative polarity developer. In the case of the latter configuration, the polarities of the voltages VC, VG, VD, VTM, and VTP are opposite to those in the above embodiment.

  In the above-described embodiment, a scorotron type is described as an example of the charging unit. However, the charging unit is not limited to this, and the charging unit may be a corotron type without a grid or may rotate while being in contact with the photosensitive drum 410. A contact type having a charging roller may be used. Specifically, the printer 10A illustrated in FIG. 8 includes a charging unit 420A having a charging roller 421A that rotates while contacting the photosensitive drum 410, and a charging application unit 610A that applies a voltage VC to the charging roller 421A. With such a configuration, by adjusting the potential of the charging roller 421A, the charging potential can be set to the image forming potential and the laser light receiving potential. In addition, since the charging roller 421A and the photosensitive drum 410 are in contact with each other, compared with the configuration in which the charging unit and the photosensitive drum 410 are separated from each other, the region of the photosensitive drum 410 where the laser light receiving potential is set is set with high accuracy. can do.

  The photoreceptor is not limited to a drum but may be a photosensitive belt. The transfer unit is not limited to a roller body, and may be a belt body. In the case of an image forming apparatus including a conveyance belt to which a mark for detecting the density and position of an image is transferred, the transfer medium may be the conveyance belt.

  The deflecting unit has a plurality of reflecting surfaces and includes a rotating polygon mirror that is driven to rotate, and reflects the laser light from the light source in a direction according to the rotation angle of the rotating polygon mirror, in other words, the displacement of the reflecting surface. By doing so, it is not limited to the polygon scanning system that deflects the laser beam. The deflecting unit includes, for example, a reflection mirror that tilts within a predetermined angle range, and reflects the laser light from the light source in a direction corresponding to the tilt angle of the reflection mirror, thereby deflecting the laser light. Or a reciprocating oscillating mirror system that deflects the laser light by reflecting the laser light from the light source in a direction corresponding to the vibration angle of the oscillating mirror. .

  4 and 6 executed by the CPU 811 and the exposure control unit 380 may be executed by one or a plurality of CPUs, or only by a dedicated hardware circuit such as an ASIC. Alternatively, it may be executed by both the CPU and the hardware circuit. In this case, one or more CPUs are examples of the “control unit”. "

  In 150 of FIG. 4, the charging potential may be set to the potential of the second grid target value VG2 only in the exposure region E1.

  The laser light reception control is not limited to the BD light reception control. For example, before starting the image formation control, the LD 310 is turned on, and the rotational operation and rotational speed of the polygon mirror 330 are controlled based on the BD signal periodically output from the BD 360. Control may be performed, or the light amount of the LD 310 may be adjusted based on the monitor signal of the monitor element 370. Even in such a case, the photosensitive drum 410 may be unnecessarily exposed during the rotation control of the polygon mirror 330.

  However, by applying the present invention, even if the photosensitive drum 410 is unnecessarily exposed and an electrostatic latent image is formed, the developer attached to the electrostatic latent image is prevented from adhering to the transfer roller 440. can do. In short, when the light source is turned on at a time different from the time when the light source is turned on based on the image data and the BD 360 receives the laser light from the light source, the photosensitive drum 410 may be unnecessarily exposed. . In such a case, by applying the present invention, it is possible to suppress the developer attached to the unnecessary exposure portion from attaching to the transfer roller 440. The monitor element 370 is an example of an optical sensor.

  When executing the image formation control, the CPU 811 sets the charging speed of the surface of the photosensitive drum 410 to the image formation potential by setting the rotation speed of the photosensitive drum 410 to the first speed, and when executing the BD light reception control. The charging potential on the surface of the photosensitive drum 410 may be changed to the laser light receiving potential by setting the rotational speed of the photosensitive drum 410 to a second speed that is lower than the first speed. According to this configuration, the charging potential can be set to the image forming potential and the laser light receiving potential by adjusting the rotation speed of the photosensitive drum 410.

  DESCRIPTION OF SYMBOLS 10: Printer 10A: Printer 200: Image forming part 300: Exposure part 310: Laser diode 330: Polygon mirror 360: Beam detector 370: Monitor element 380: Exposure control part 400: Process part 410: Photosensitive drum 420: Charging part 420A: Charging unit 421: Charging wire 421A: Charging roller 422: Grid 430: Development unit 440: Transfer roller 810: Controller E1: Exposure region E2: Region E3: Adjacent region VD1: First development target value VD2: Second development target value VG1 : First grid target value VG2: Second grid target value VTM: Forward transfer voltage VTP: Reverse transfer voltage W: Sheet X1: Charging position X2: Exposure position X3: Development position

Claims (11)

A light source that emits laser light;
A deflecting unit for deflecting the laser light emitted from the light source;
A photoreceptor to which the laser beam deflected by the deflection unit is irradiated;
An optical sensor to which the laser light emitted from the light source is irradiated;
A charging unit for charging the photoreceptor;
A developing unit that develops the electrostatic latent image formed on the photosensitive member by the laser beam using a developer;
A control unit,
The controller is
Image formation control for forming an electrostatic latent image of an image to be transferred to a transfer body on the photoreceptor by turning on the light source based on image data;
Laser light reception control for causing the optical sensor to receive the laser light by turning on the light source at a time different from the execution time of the image formation control, and
When the image forming control is executed, the charging unit sets the charging potential of the surface of the photoconductor to an image forming potential, and when the laser light receiving control is executed, the charging unit controls the surface of the photoconductor. An image forming apparatus, wherein a charging potential is a laser light receiving potential having an absolute value larger than the image forming potential. The image forming apparatus according to claim 1,
The photoreceptor is a photosensitive drum that is driven to rotate,
The controller is
When executing the laser light reception control, the photosensitive drum includes an exposure area in which an exposure line is formed by the laser light on the surface of the photosensitive drum, and the length of the photosensitive drum in the rotation direction is the entire circumference of the photosensitive drum. An image forming apparatus in which a region shorter than a length is set to the laser light receiving potential. The image forming apparatus according to claim 2,
The controller is
A pair of adjacent regions adjacent to the exposure region and upstream and downstream in the rotation direction with respect to the exposure region, the length in the rotation direction being equal to or greater than the thickness of the one exposure line; An image forming apparatus in which the region including the laser light receiving potential is set to the laser receiving potential. The image forming apparatus according to claim 1, wherein the image forming apparatus comprises:
The charging unit has a charging wire and a grid,
The controller is
An image forming apparatus in which the charging potential is set to the image forming potential and the laser light receiving potential by adjusting a potential of the grid. The image forming apparatus according to claim 1, wherein the image forming apparatus comprises:
The charging unit has a charging roller in contact with the photoconductor,
The controller is
An image forming apparatus that adjusts the potential of the charging roller to change the charging potential to the image forming potential and the laser light receiving potential. An image forming apparatus according to any one of claims 1 to 5, wherein
The photoreceptor is a photosensitive drum that is driven to rotate,
The controller is
When executing the image forming control, the rotational speed of the photosensitive drum is set to the first speed so that the charging potential is set to the image forming potential, and when performing the laser light receiving control, the photosensitive drum is used. An image forming apparatus in which the charging potential is set to the laser light receiving potential by setting the rotation speed of the second rotation speed to a second speed lower than the first speed. An image forming apparatus according to any one of claims 1 to 6,
The controller is
When the exposed portion of the surface of the photoconductor by execution of the laser light receiving control reaches a position facing the developing section, the developing potential of the developing section is set from the time of execution of the image forming control. An image forming apparatus that uses a potential having a small absolute value. An image forming apparatus according to any one of claims 1 to 7,
The optical sensor is disposed at a position where the laser light emitted from the light source and reflected by the reflector is irradiated,
The controller is
An image forming apparatus that, when executing the image forming control, turns on the light source based on the image data based on a timing at which the optical sensor receives the laser light. An image forming apparatus according to any one of claims 1 to 8,
The optical sensor is disposed at a position where the laser light emitted from the light source and reflected by the reflector is irradiated,
The controller is
An image forming apparatus that detects that the optical sensor has received the laser beam at the execution time of the laser light reception control, and controls driving of the deflection unit based on the detection timing. A light source;
A deflecting unit for deflecting the laser light emitted from the light source;
A photoreceptor to which the laser beam deflected by the deflection unit is irradiated;
An optical sensor to which the laser light emitted from the light source is irradiated;
A charging unit for charging the photoreceptor;
A developing unit that develops, using a developer, an electrostatic latent image formed on the photoconductor by the laser beam, and a control method for an image forming apparatus,
Executing image formation control for forming an electrostatic latent image of an image to be transferred to a transfer body on the photoreceptor by turning on the light source based on image data;
Executing laser light reception control for causing the optical sensor to receive the laser light by turning on the light source at a time different from the execution time of the image formation control;
When the image forming control is executed, the charging unit sets the charging potential of the surface of the photoconductor to an image forming potential, and when the laser light receiving control is executed, the charging unit controls the surface of the photoconductor. A step of changing the charging potential to a laser light receiving potential having an absolute value larger than the image forming potential;
A control method comprising: A light source;
A deflecting unit for deflecting the laser light emitted from the light source;
A photoreceptor to which the laser beam deflected by the deflection unit is irradiated;
An optical sensor to which the laser light emitted from the light source is irradiated;
A charging unit for charging the photoreceptor;
A computer program for controlling an image forming apparatus comprising: a developing unit that develops an electrostatic latent image formed on the photoconductor by the laser beam using a developer;
A process of performing image formation control to form an electrostatic latent image of an image to be transferred to a transfer body on the photoreceptor by turning on the light source based on image data;
A process of performing laser light reception control for causing the optical sensor to receive the laser light by turning on the light source at a time different from the execution time of the image formation control;
When the image forming control is executed, the charging unit sets the charging potential of the surface of the photoconductor to an image forming potential, and when the laser light receiving control is executed, the charging unit controls the surface of the photoconductor. A process of changing the charging potential to a laser light receiving potential having an absolute value larger than the image forming potential;
A computer program for causing the image forming apparatus to execute.

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