JP6082611B2 - Transfer device and image forming apparatus - Google Patents

Description

  The present invention relates to a transfer apparatus and an image forming apparatus configured to perform transfer of a toner image from an image carrier to a transfer member and reverse transfer of toner from the transfer member to the image carrier.

  An electrophotographic image forming apparatus includes a transfer device that applies a transfer voltage for transferring a toner image of an image carrier to a transfer member disposed opposite to the image carrier. As a combination of the image carrier and the transfer member, there are a photosensitive member and an intermediate transfer member, an intermediate transfer member and a secondary transfer member, and a photosensitive member and a paper transport belt.

  The toner remaining on the surface of the image carrier after the toner image is transferred is cleaned by an image carrier cleaning member to cause deterioration of image quality in the next image forming process. May adhere to the surface. The toner adhering to the surface of the transfer member may cause contamination of paper or the like during subsequent image forming processing, and thus the surface of the transfer member needs to be cleaned. If the transfer member is provided with a dedicated cleaning member, the transfer device Increases in size.

  Therefore, the conventional transfer device includes a first power supply unit that outputs a transfer voltage with a constant current and a second power supply unit that outputs a cleaning voltage having a reverse characteristic to the transfer voltage. (For example, refer to Patent Document 1). When the toner is reversely transferred from the surface of the transfer body to the image carrier, a cleaning voltage having a polarity opposite to the transfer voltage applied when the toner image is transferred is applied to the transfer body. The toner reversely transferred to the image carrier is cleaned by the image carrier cleaning member.

  Here, the resistance value of the image carrier or the transfer body may change due to the influence of humidity change, thermal expansion, or the like. When the cleaning voltage is applied at a constant voltage, when the resistance value between the image carrier and the transfer member increases, the current flowing between the image carrier and the transfer member is insufficient, resulting in poor cleaning. In particular, when the image carrier or the transfer member is a belt, it is easily affected by changes in humidity, thermal expansion, etc., and the resistance value is likely to change. For this reason, it is conceivable that the cleaning voltage is applied at a constant current.

JP-A-10-32979

However, when the first power supply unit is activated at the start of application of the transfer voltage , a current may flow through the first power supply unit, even before the first power supply unit is activated. Although this current is in the same direction as the current that flows when the transfer voltage is applied, the current flow is hereinafter referred to as “reverse flow”, including the meaning that it flows before the first power supply unit is activated. The first power supply unit usually needs to be started in a state where no current flows at the start of applying the transfer voltage . However, when the first power supply unit is started in a state where a backflowing current is generated in the first power supply unit, a start failure may occur in the first power supply voltage, and the first power supply unit may be destroyed.

  An object of the present invention is to provide transfer and transfer of a toner image from an image carrier by providing two power supply units that output a transfer voltage and a cleaning voltage having different polarities without using a transfer member cleaning member. It is an object of the present invention to provide a transfer device and an image forming apparatus capable of reliably cleaning the surface of a body.

The transfer device according to the present invention is a transfer device that transfers a toner image carried on the image carrier to a transfer target that passes between the image carrier and the transfer member, the first power supply unit, comprising a second power supply unit, and a control unit. The first power supply unit outputs a transfer voltage for moving the toner from the image carrier side to the transfer body side by constant current control . The second power supply unit is connected in series to the first power supply unit, and outputs a cleaning voltage for moving the toner from the transfer body side to the image carrier side by either a switchable constant current control or a constant voltage control. . The control unit outputs the cleaning voltage to the second power supply unit by constant voltage control at the start of transfer of the toner image to the transfer target, and activates the first power supply unit in this state .

When starting the first power supply unit at the start transfer of the toner image to the transfer member, the control unit by outputting the cleaning voltage in the constant voltage control to the second power supply unit, a current reverse to the first power supply unit As a result, it is possible to prevent the first power supply unit from being destroyed . Further, when the cleaning of the transfer member, the control unit, by applying a cleaning voltage to the second power supply unit to the transfer member is output in the constant current control, resistance of the transfer member under the influence of such changes in humidity, thermal expansion Even if the value changes, a current can be passed through the transfer member without a shortage.

In this configuration, it is preferable that the control unit outputs the transfer voltage to the first power supply unit by constant current control after starting the first power supply unit. The control unit, when the outputting the cleaning voltage in the constant voltage control to the second power supply unit, so that the absolute value of the cleaning voltage is greater than the absolute value of the transfer voltage, by controlling the second power supply unit Is preferred. This according to the transfer voltage so as to control the voltage value of the cleaning voltage, the current to the first power supply unit is reversely flow can be prevented reliably, thereby preventing the destruction of the first power supply unit.

  An image forming apparatus according to the present invention includes the above-described transfer device. The transfer body has a secondary transfer belt, an intermediate transfer belt as an image carrier, and a transfer roller disposed opposite to the other, with one of the secondary transfer belt sandwiched between the intermediate transfer belt and the secondary transfer belt. The toner image carried by the intermediate transfer belt is transferred to a transfer medium that passes between them. The power supply unit applies to the transfer roller.

  Even if the resistance value of the intermediate transfer belt or the secondary transfer belt changes due to humidity, thermal expansion, or the like, the image forming apparatus applies the cleaning voltage at a constant current to apply the toner adhering to the secondary transfer belt to the middle. Transfer to the transfer belt can be ensured, and the paper can be prevented from being soiled in the next image forming process.

  An image forming apparatus according to the present invention includes the above-described transfer device. The transfer body is a transfer roller, and transfers a toner image carried by a photosensitive drum as an image carrier onto an intermediate transfer belt or paper as a transfer body.

  Even if the resistance value of the intermediate transfer belt or the conveyance belt that conveys the paper changes due to humidity or thermal expansion, the image forming apparatus conveys the intermediate transfer belt or the paper by applying a constant cleaning voltage. The toner adhering to the conveyance belt can be reliably transferred to the photosensitive drum, and deterioration of image quality in the next image forming process can be prevented.

  According to the present invention, the transfer of the toner image from the image carrier can be performed by providing the two power supply units that output the transfer voltage and the cleaning voltage having different polarities even without the cleaning member for the transfer body. The surface of the transfer body can be reliably cleaned.

1 is a schematic diagram of a part of an image forming apparatus according to an embodiment of the present invention. 2 is a block diagram of a control unit of the image forming apparatus. FIG. 2 is a circuit diagram of a power supply unit of the image forming apparatus. FIG. It is a flowchart which shows the transfer process in the control part.

  An image forming apparatus including a secondary transfer unit which is a transfer apparatus according to the present invention will be described with reference to the drawings. As shown in FIG. 1, the image forming apparatus 100 includes, as an example, a process unit 1, an intermediate transfer unit 2, a secondary transfer unit 3, a power supply unit 5, and a control unit 200, based on instructions from the control unit 200. Then, image formation processing by electrophotography is performed on a sheet using image data input from an external device (not shown).

  The process unit 1 includes an exposure unit 11 and photosensitive drums 12A to 12D. The process unit 1 irradiates image light based on the image data from the exposure unit 11 to form electrostatic latent images on the surfaces of the photosensitive drums 12A to 12D, and supplies toner to visualize the electrostatic latent images as toner images. To do.

  The intermediate transfer unit 2 includes an intermediate transfer belt (corresponding to an image carrier of the present invention) 21, a driving roller (corresponding to a transfer member of the present invention) 22, a driven roller 23, primary transfer rollers 24A to 24D, and And a cleaning unit 25. The intermediate transfer belt 21 is stretched around the driving roller 22 and the driven roller 23, and moves along a circulation path that passes through the photosensitive drums 12D, 12C, 12B, and 12A in this order. The primary transfer rollers 24A to 24D are disposed so as to face the photosensitive drums 12A to 12D with the intermediate transfer belt 21 interposed therebetween. The primary transfer rollers 24 </ b> A to 24 </ b> D primarily transfer the toner images formed on the surfaces of the photosensitive drums 12 </ b> A to 12 </ b> D to the surface of the intermediate transfer belt 21 in order by applying a primary transfer voltage.

  The secondary transfer unit 3 includes a secondary transfer belt (corresponding to a transfer body of the present invention) 31 and a secondary transfer roller 32. The secondary transfer roller 32 is grounded.

  The driving roller 22 is connected to the power supply unit 5 and passes a secondary transfer position between the intermediate transfer belt 21 and the secondary transfer belt 31 by application of a secondary transfer voltage (the transfer target of the present invention). The toner image is secondarily transferred from the intermediate transfer belt 21. The cleaning unit 25 removes the toner remaining on the surface of the intermediate transfer belt 21 after the secondary transfer of the toner image to the paper.

  A sensor 41 is disposed on the upstream side of the secondary transfer position in the paper transport direction. The sensor 41 detects the passage of paper.

  As illustrated in FIG. 2, the control unit 200 includes a CPU 201, a ROM 202, a RAM 203, and a motor driver 204, and is connected to the sensor 41, the motor 42, the power supply unit 5, and the operation unit 40.

  The CPU 201 reads out a control program recorded in the ROM 202, and executes the control program using the RAM 203 as a working area. The CPU 201 outputs drive data to the motor driver 204 at a predetermined timing in the image forming process. The motor driver 204 selectively supplies power to the rotatable motor 42 based on the drive data. The CPU 201 controls the power supply unit 5 to selectively apply the secondary transfer voltage and the cleaning voltage to the drive roller 22.

  The operation unit 40 receives an instruction to start an image forming process. The motor 42 is connected to a drive roller 22 that stretches the intermediate transfer belt 21, a roller that stretches the secondary transfer belt 31, and the like, and rotates these rollers when power is supplied.

  As shown in FIG. 3, the power supply unit 5 includes a first power supply unit 51 that outputs a transfer voltage and a second power supply unit 52 that outputs a cleaning voltage, and is connected to the driving roller 22. The first power supply unit 51 includes a positive drive circuit 511, a first transformer 512, diodes 513 and 514, and a capacitor 515. In the first transformer 512, the positive side drive circuit 511 is connected to the primary side, and the first rectifier circuit including the diodes 513 and 514 is connected to the secondary side. The first power supply unit 51 selectively operates based on an instruction from the CPU 201.

  The positive-by drive circuit 511 is an oscillation circuit and determines the voltage VA at the point A through the first transformer 512 so that the current flowing through the point A on the output side of the first rectifier circuit becomes a predetermined set value SA. Control with current. Further, the voltage VA is controlled to have the same polarity (minus) as the charging polarity (for example, minus) of the toner. As the predetermined set value SA, a current value necessary for transferring the toner image is set. A capacitor 515 is connected to the output side of the first rectifier circuit.

  The second power supply unit 52 includes a cleaning drive circuit 521, a second transformer 522, diodes 523 and 524, a capacitor 525, and feedback circuits 526 and 527. The second transformer 522 has a cleaning drive circuit 521 connected to the primary side, and a second rectifier circuit composed of diodes 523 and 524 connected to the secondary side. The second power supply unit 52 selectively operates based on an instruction from the CPU 201.

  The cleaning drive circuit 521 is an oscillation circuit, and selectively receives feedback from the feedback circuits 526 and 527 via the second transformer 522 based on an instruction from the CPU 201, and switches the voltage VB at the point B to be determined. Control with current or constant current. The cleaning drive circuit 521 controls the voltage VB at the point B so that the voltage VB at the point B becomes a predetermined set value SB1 when the voltage is constant, and outputs the second rectifier circuit when the current is constant. The voltage VB at the point B is controlled so that the current flowing through the point B on the side becomes a predetermined set value SB2. The voltage VB is controlled so as to have a polarity (plus) opposite to the charging polarity of the toner. As the set value SB1 when making the voltage VB constant, a voltage value having an absolute value larger than the voltage VA is set. As the set value SB2 for making the voltage VB constant, a current value necessary for cleaning the secondary transfer belt 31 is set. A capacitor 525 is connected to the output side of the second rectifier circuit. One end of the capacitor 525 is connected to the capacitor 515 in series, and the other end is grounded.

  The feedback circuits 526 and 527 are connected at a connection point C between the capacitor 525 and the ground. The feedback circuit 526 feeds back the current value at the connection point C to the cleaning drive circuit 521. The feedback circuit 527 feeds back the voltage value at the connection point C to the cleaning drive circuit 521. Note that the feedback circuits 526 and 527 may feed back the amount of charge stored in the capacitor 525. The amount of charge can be acquired by detecting the current value and voltage value at the connection point C. The capacitor 515 is connected in parallel with the drive roller 22.

The CPU 201 controls the second power supply unit 52 to operate the first power supply unit 51 so that the cleaning voltage is output at a constant voltage when the transfer of the toner image onto the paper is started . Further, the CPU 201 controls the second power supply unit so that when the secondary transfer belt 31 is cleaned, the first power supply unit 51 is stopped and the cleaning voltage is output at a constant current.

As described above, when starting the first power supply portion 51 at the time of initiation of transcription of the toner image to the sheet, by Rukoto is set higher than the voltage value of the voltage value is the voltage VA of the voltage VB by the power supply unit 5, a first it is prevented that the power supply unit 51 current reverse flow, as a result, it is possible to prevent the breakage of the positive by the drive circuit 511.

  Further, when the secondary transfer belt 31 is cleaned, since the first drive circuit 51 is stopped, the power supply unit 5 applies a cleaning voltage having a polarity opposite to the charging polarity of the toner to a constant current and applies it to the drive roller 22. be able to.

  Further, when the operation unit 40 receives an instruction to start the image forming process, the CPU 201 starts the image forming process. The image forming process includes an image forming process for forming a toner image on the surface of the photoconductive drums 12A to 12D, a transfer process for transferring the toner image from the photoconductive drums 12A to 12D to a sheet via the intermediate transfer belt 21, and A fixing process for fixing the toner image transferred to the paper is included. Hereinafter, the transfer process in the CPU 201 will be described with reference to FIG. Note that the sheet is conveyed at a predetermined timing.

  As shown in FIG. 4, the CPU 201 waits until the transfer processing start timing comes (S11). The CPU 201 rotates the motor 42 at the start timing (S12). As the motor 42 rotates, the intermediate transfer belt 21 and the secondary transfer belt 31 move along the circulation path.

  The CPU 201 applies a primary transfer voltage to the primary transfer rollers 24A to 24D (S13). As a result, the toner images carried on the photosensitive drums 12 </ b> A to 12 </ b> D are transferred to the surface of the intermediate transfer belt 21.

  The CPU 201 controls the second power supply unit 52 to output the cleaning voltage at a constant voltage (S14), and controls the first power supply unit 51 to output the secondary transfer voltage at a constant current (S15). ). As a result, a secondary transfer voltage under constant current control is applied to the drive roller 22, and the toner image carried by the intermediate transfer belt 21 is transferred onto the paper.

  The CPU 201 waits until the sensor 41 detects the trailing edge of the sheet (S16). When the sensor 41 detects the trailing edge of the paper, the CPU 201 determines whether there is next image data (S17). If there is image data, the CPU 201 returns to the process of S13.

  If there is no image data, the CPU 201 stops applying the primary transfer voltage (S18). The CPU 201 controls the first power supply unit 51 to stop the output of the secondary transfer voltage (S19), and controls the second power supply unit 52 to output the cleaning voltage with a constant current (S20). As a result, a cleaning voltage under constant current control is applied to the drive roller 22, and the toner adhering to the secondary transfer belt 31 is transferred to the intermediate transfer belt 21. The toner attached to the surface of the intermediate transfer belt 21 is removed by the cleaning unit 25.

  The CPU 201 waits for a predetermined time to elapse after the cleaning voltage is output at a constant current (S21). The predetermined time is the time required for the secondary transfer belt 31 to make one revolution.

  When the predetermined time has elapsed, the CPU 201 controls the second power supply unit 52 to stop the output of the cleaning voltage (S22), and stops the rotation of the motor 42 (S23).

As described above, the CPU 201 controls the first power supply unit 51 and the second power supply unit 52 to make the secondary transfer voltage constant and output in a state where the cleaning voltage is made constant, and outputs the secondary transfer voltage. The cleaning voltage is made constant after the output is stopped. That is, the cleaning voltage having a constant voltage is always output before the output of the secondary transfer voltage by the first power supply unit 51 is started . Thus, CPU 201 is prevented from current to the first power supply portion 51 is reversely flow, since the drive roller 22 a secondary transfer voltage can be surely applied, it can be prevented poor transfer.

  Further, the CPU 201 applies the cleaning voltage at a constant current when cleaning the secondary transfer belt 31. As a result, even when the resistance value of the intermediate transfer belt 21 and the secondary transfer belt 31 changes due to humidity, thermal expansion, or the like, the CPU 201 allows a current to flow between the intermediate transfer belt 21 and the secondary transfer belt 31 without a shortage. Therefore, the toner adhering to the secondary transfer belt 31 can be reliably transferred to the intermediate transfer belt 21, and the cleaning failure of the surface of the secondary transfer belt 31 can be prevented.

At the start of the transfer of the toner image onto the paper , the CPU 201 has made the voltage constant based on the voltage VA at the point A so that the absolute value of the voltage VB at the point B is larger than the absolute value of the voltage VA. The set value SB1 of the voltage VB may be changed. For example, CPU 201, the voltage VA is controlled when it is detected that exceeds a predetermined value (+ 300 V), a second power supply unit 52 so as to + 800 V from + 500V settings SB1 voltage VB. Note that the setting value SB1 of the voltage VB is associated with each of a plurality of predetermined values, and the CPU 201 may change the setting value SB1 of the voltage VB step by step.

  Further, for example, the CPU 201 stores a history of the voltage VA in a storage unit (not shown), predicts a change in the voltage VA based on the history of the voltage VA, and the absolute value of the voltage VA is the voltage VB. The second power supply unit 52 may be controlled so as not to exceed the absolute value.

From the above, it is predicted that the voltage value of the voltage VA at the point A may change greatly at the start of transfer of the toner image onto the paper, and the absolute value of the voltage VA does not exceed the absolute value of the voltage VB. to control the setting value SB1 voltage VB as it can reliably prevent the current to the first power supply portion 51 is reversely flow, the destruction of the positive by the drive circuit 511 can be reliably prevented.

  In the above-described embodiment, the power supply unit 5 is connected to the drive roller 22, but the power supply unit 5 may be connected to the secondary transfer roller 32. The secondary transfer voltage applied to the secondary transfer roller 32 and the charging polarity of the cleaning voltage are opposite in polarity to the secondary transfer voltage applied to the driving roller 22 and the charging polarity of the cleaning voltage.

  Further, a power supply unit having the same configuration as that of the power supply unit 5 may be connected to the primary transfer rollers (corresponding to the transfer body of the present invention) 24A to 24D. The toner images carried by the photosensitive drums (corresponding to the image carrier of the present invention) 12A to 12D can be transferred to the intermediate transfer belt (corresponding to the transferred material of the present invention) 21, and the primary transfer roller. The toner attached to the surface of the intermediate transfer belt 21 during the cleaning of 24A to 24D can be transferred to the photosensitive drums 12A to 12D.

  Further, a transfer roller (transfer body of the present invention) is provided on a sheet of paper (corresponding to a transfer body of the present invention) on which a toner image carried by a photosensitive drum (corresponding to the image carrier of the present invention) is transported by a transport belt. In the transfer device for transferring, a power supply unit similar to the power supply unit 5 may be connected to the transfer roller.

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

21: Intermediate transfer belt 22 ... Driving roller 22
3 ... secondary transfer unit 31 ... secondary transfer belt 5 ... power supply unit 51 ... first power supply unit 52 ... second power supply unit 200 ... control unit

Claims (4)

A transfer device for transferring a toner image carried on the image carrier to a transfer member passing between the image carrier and a transfer member,
A first power supply unit that outputs a transfer voltage for moving toner from the image carrier side to the transfer body side by constant current control ;
A second power supply connected in series to the first power supply unit and outputting a cleaning voltage for moving the toner from the transfer member side to the image carrier side by either a switchable constant current control or a constant voltage control. And
A control unit that selectively applies the transfer voltage or the cleaning voltage between the image carrier and the transfer body by controlling the first power supply unit and the second power supply unit;
With
The control unit causes the second power supply unit to output the cleaning voltage by constant voltage control at the start of transfer of a toner image to the transfer target, and activates the first power supply unit in this state . The transfer device according to claim 1, wherein the control unit causes the first power supply unit to output the transfer voltage by constant current control after starting the first power supply unit. The control unit controls the second power supply unit so that the absolute value of the cleaning is larger than the absolute value of the transfer voltage when the second power supply unit outputs the cleaning voltage by constant voltage control . The transfer device according to claim 2 . An intermediate transfer belt as an image carrier;
A transfer roller which is a transfer body and is disposed to face the intermediate transfer belt;
The transfer device according to claim 1, wherein the transfer device is applied to transfer of a toner image from the intermediate transfer belt to a transfer medium that passes between the intermediate transfer belt and the transfer roller;
An image forming apparatus.

Images