JP2015045739A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress a rear surface of a recording sheet from being stained in an image forming apparatus which is a type for using both a charging roller and a transfer roller in one conductive roller as compared with conventional ones.SOLUTION: An image forming apparatus includes: application means of a bias composed of a photoreceptor drum 11, a charging transfer roller 12 using both a charging roller and a transfer roller, a charging power source 51, a transfer power source 52 and a change-over switch 61; and a control section which controls the change-over switch 61, applies a charging bias V1 to the charging transfer roller 12 (charging), applies a transfer bias V2 instead of the charging bias V1 to the charging transfer roller 12 after a developer image is formed on the photoreceptor drum 11 by exposure and development, and transfers the developer image on the photoreceptor drum 11 on a front surface Sa of a recording sheet S. A second cleaning roller 16 for removing toner (developer) contacting with a rear surface Sb of the recording sheet S and adhering to the rear surface is provided closer to a position at a conveyance direction downstream side of the recording sheet S than a transfer position 19.

Description

  The present invention relates to an image forming apparatus, and more particularly, to an image forming apparatus of a type in which a charging roller and a transfer roller are used as a single conductive roller, and to an improvement in technology for suppressing backside contamination of a recording sheet in such an apparatus.

As an electrophotographic image forming apparatus, there is known an image forming apparatus of a type in which a charging roller and a transfer roller are combined with one conductive roller (hereinafter referred to as a “charging transfer roller”) (for example, Patent Documents). 1).
Such an image forming apparatus has the advantage that the number of rollers can be reduced as compared with an image forming apparatus having an individual charging roller and transfer roller, and the apparatus can be reduced in size and cost. ing.

  The image forming apparatus described in Patent Document 1 applies the charging bias to the charging transfer roller at the first rotation of the photosensitive drum to uniformly charge the surface of the photosensitive drum, and performs exposure and development based on the image data. After the toner image is formed on the photosensitive drum, a transfer bias is applied to the charging transfer roller during the second rotation of the photosensitive drum so that the toner image on the photosensitive drum is transferred to the first surface of the recording sheet. It is configured to form an image by transferring the image to the image. Hereinafter, this image forming method is referred to as “two-rotation one-image forming method”.

  The toner remaining on the surface of the photosensitive drum after the toner image is transferred to the recording sheet is removed by a cleaning blade.

Japanese Patent Laid-Open No. 5-100582 JP 47-11539 A JP 55-37755 A Japanese Patent Laid-Open No. 3-123377

However, in some cases, the residual toner on the photosensitive drum cannot be sufficiently removed by the cleaning blade. When the charging transfer roller functions as a charging roller and is in contact with the surface of the photosensitive drum, the residual toner is charged for charging transfer. Adheres to the roller surface.
Recently, in order to further reduce the size and cost, a configuration in which the cleaning blade is omitted and the charging transfer roller is also used for cleaning the photosensitive drum has been proposed. As a result, residual toner adheres to the charging transfer roller.

The toner adhering to the charging transfer roller adheres to the back surface of the recording sheet when the charging transfer roller functions as a transfer roller in the next transfer process, and the backside of the recording sheet is generated.
The present invention has been made in view of the above-described problems, and in the image forming apparatus of the type in which the charging roller and the transfer roller are combined with one conductive roller, the back contamination of the recording sheet is suppressed more than before. The purpose is to do.

  In order to achieve the above object, an image forming apparatus according to the present invention uniformly charges the surface of a rotationally driven photosensitive rotator, exposes and develops it based on image data, and develops a developer image on the photosensitive rotator. An image forming apparatus for transferring the developer image onto a recording sheet after executing the image forming process for forming the photosensitive rotating member, and is disposed so as to be in contact with at least an image forming range in the rotation axis direction of the photosensitive rotating body. A conductive member, an application unit that selectively applies a charging bias and a transfer bias to the conductive member, and a charging bias that is applied to the conductive member by controlling the application unit in the image forming process. After forming the developer image on the photosensitive rotator by executing the image forming process, the application unit is controlled to apply a transfer bias to the conductive member in place of the charging bias, so that the photosensitive circuit is rotated. Recording that is conveyed at a position downstream of the contact position between the control member for transferring the developer image on the body to the first surface of the recording sheet and the photosensitive rotator of the conductive member in the conveyance direction of the recording sheet. And a cleaning member that contacts the second surface of the sheet and removes the developer attached to the second surface.

Here, the cleaning member is a cleaning roller that rotates and contacts the second surface of the recording sheet, and the cleaning roller is preferably configured to rotate in the forward direction along the recording sheet conveyance direction. .
Further, the conductive member is a conductive roller that rotates in a forward direction with respect to the photosensitive rotator, and the cleaning roller also contacts a peripheral surface of the conductive roller, so that It is desirable that the surface be cleaned.

Furthermore, a configuration in which a blade for scraping off the developer attached to the peripheral surface of the cleaning roller may be provided.
The cleaning member may be formed of a conductive member, and the cleaning member may be provided with a cleaning bias applying unit that applies a cleaning bias having the same polarity as the transfer bias.

Here, the absolute value of the cleaning bias is preferably larger than the absolute value of the transfer bias.
The cleaning member may be formed of a foam member.
The cleaning member may have a brush shape.
Further, the cleaning member has a brush-shaped portion, and in the brush-shaped portion, the amount of biting of the portion in contact with the conductive member is α, and the amount of biting of the portion in contact with the conveyed recording sheet is β. In this case, it is desirable that the biting amount α is larger than the biting amount β.

  According to the image forming apparatus having the above configuration, the developer is removed by the cleaning unit when it adheres to the second surface (surface on the conductive member side) of the recording sheet that has passed through the contact position of the conductive member with the photosensitive rotator. Since it is configured, it is possible to suppress the backside contamination of the recording sheet.

1 is a schematic diagram illustrating a configuration of a printer according to a first embodiment of the present invention. It is a figure for demonstrating the detailed structure of the image process part which the said printer has. It is a block diagram which shows the relationship between the structure of a control part, and the main component used as the control object by a control part. It is a time chart which shows an image formation process and a cleaning process. It is a figure which shows the structure of the image process part which the printer concerning 2nd Embodiment has. It is a figure which shows the structure of the image process part which the printer which concerns on 3rd Embodiment has. It is a figure which compares and shows a mode that the brush of the fur brush roller was bitten. It is a figure which shows the structure of the image process part which the printer which concerns on a modification has. It is a figure which shows the structure of the brush of the fur brush roller which concerns on a modification. It is a figure which compares and shows a mode that the brush of the fur brush roller of the modification was bitten. FIG. 3 is an enlarged schematic view showing a contact portion between a charge transfer roller having a rough surface and a photosensitive drum. FIG. 4 is a diagram illustrating a state where toner attached to a charge transfer roller having a rough surface is scraped off.

Hereinafter, a first embodiment of an image forming apparatus according to the present invention will be described with reference to the drawings taking a two-rotation / one-image forming type monochrome printer (hereinafter simply referred to as “printer”) as an example.
(1) Overall Configuration of Printer FIG. 1 is a schematic diagram showing the configuration of the printer 1 according to the present embodiment.

The printer 1 shown in FIG. 1 includes an image processing unit 10, a paper feeding unit 20, a fixing unit 30, and a control unit 40. The printer 1 is connected to a network (for example, a LAN) and receives print jobs from an external terminal device (not shown). When the execution instruction is received, a monochrome toner image is formed based on the instruction and printed on the recording sheet S.
The image processing unit 10 includes a photosensitive drum 11, a charging transfer roller 12 disposed around the photosensitive drum 11, an exposure unit 13, a developing device 14, and the like. During the two rotations of the photosensitive drum 11, charging, exposure, development, This is a two-rotation one-image forming system that executes a series of image forming processes for transfer.

The charging transfer roller 12 is selectively applied with a charging bias and a transfer bias. When the charging bias is applied, the charging transfer roller 12 functions as a charging unit that charges the photosensitive drum 11, and when the transfer bias is applied, It is configured to function as a transfer unit that generates a transfer electric field with respect to the photosensitive drum 11.
A charging bias is applied to the charging transfer roller 12 in the first rotation of the photosensitive drum 11 that is driven to rotate, and the peripheral surface of the photosensitive drum 11 is uniformly charged. The peripheral surface of the charged photosensitive drum 11 is exposed and scanned based on image data to be printed by the exposure unit 13 to form an electrostatic latent image, and the electrostatic latent image is developed by the developing unit 14 and is toner. An image is formed.

At the second rotation of the photosensitive drum 11, a transfer bias is applied to the charging transfer roller 12, and a transfer electric field is formed between the charging transfer roller 12 and the photosensitive drum 11. The detailed configuration of the image processing unit 10 will be described later.
The recording sheets S are fed one by one from the paper feeding unit 20 in accordance with the toner image formation timing.

  The paper feed unit 20 includes a paper feed cassette 21, a feed roller 22 that feeds and feeds the recording sheets S stored in the paper feed cassette 21 one by one, a paper feed roller pair 23, a timing roller pair 24, and the like. Prepare. The timing roller pair 24 moves the recording sheet S to the transfer position in accordance with the timing at which the toner image formed on the photoconductor drum 11 is conveyed to the transfer position 19 between the photoconductor drum 11 and the charging transfer roller 12. Transport toward 19. While the recording sheet S passes through the transfer position 19, a transfer bias is applied to the charging transfer roller 12, and the toner image on the photosensitive drum 11 is transferred to the recording sheet S by the action of the transfer electric field.

The recording sheet S to which the toner image is transferred is peeled from the photosensitive drum 11 by a peeling claw (not shown) and conveyed to the fixing unit 30.
The fixing unit 30 includes a heating roller 31 and a pressure roller 32. The recording sheet S on which the toner image is transferred is inserted into a fixing nip 33 formed between the two rollers, and heated in a pressurized state to record the recording sheet. The toner image is thermally fixed to S. The heating roller 31 includes a heating element such as a halogen heater. When the controller 40 performs on / off control of the heating element, the surface temperature of the heating roller 31 is controlled to be the fixing temperature. The heating method of the fixing unit 30 is not limited to the heater heating method as described above, and may be, for example, an electromagnetic induction heating method or a heating method using a resistance heating element.

The image-formed recording sheet S on which the toner image is fixed is conveyed to the discharge roller pair 27 by the conveyance roller pair 26a and 26b, and is discharged from the discharge roller pair 27 onto the discharge tray 28.
A sheet conveyance sensor 25 that detects the recording sheet S to be conveyed is provided at a position upstream of the timing roller pair 24 in the sheet conveyance direction.

The sheet conveyance sensor 25 is composed of, for example, a reflective photoelectric sensor, and an on (Hi level) signal is detected when the recording sheet S is detected, and an off (Low level) signal is detected when the recording sheet S is not detected. Output.
The control unit 40 determines that the leading edge and the trailing edge of the recording sheet S are from the rising edge (change point from Low to Hi level) and the falling edge (change point from Hi to Low level) of the output of the sheet conveyance sensor 25. It can be detected that the position of the transport sensor 25 has passed. Based on the detection result, the rotational driving of the timing roller pair 24 is controlled so that the recording sheet S is conveyed to the transfer position 19 at the above timing.

The control unit 40 controls the image processing unit 10, the paper feeding unit 20, and the fixing unit 30 in a unified manner. Details will be described later.
(2) Detailed Configuration of Image Processing Unit (2-1) Configuration of Charging, Exposure, Development, and Transfer FIG. 2 is a diagram for explaining the detailed configuration of the image processing unit 10.

As shown in the figure, the photosensitive drum 11 is rotationally driven in the direction of arrow A by a drive motor M1. The outer diameter of the photoconductive drum 11 is set so that a print image can be formed on the peripheral surface of a recording sheet having a maximum size (for example, A4 horizontal size) that can be used in the printer 1, and is about 70 mm.
The charge transfer roller 12 includes, for example, a cored bar and a conductive rubber layer formed around the cored bar, is parallel to the photosensitive drum 11, and is directed toward the photosensitive drum 11 by a biasing member (not shown). And is arranged so as to be in contact with at least an image forming range in which the toner image is formed on the circumferential surface of the photosensitive drum 11 in the rotation axis direction. The charging transfer roller 12 is connected to a driving motor M2 via a driving force transmission mechanism (gear or the like) (not shown), and is sensitive to the rotation of the photosensitive drum 11 (arrow C direction). The body drum 11 is driven to rotate at the same speed as the peripheral speed.

Further, the charging transfer roller 12 is selectively connected to the output terminal of the charging power source 51 and the output terminal of the transfer power source 52 via the changeover switch 61.
When the charging transfer roller 12 functions as a charging roller, a charging bias V1 of −700 V, for example, is applied from the charging power supply 51, and when the charging transfer roller 12 functions as a transfer roller, a transfer bias of +1000 V, for example, is applied. V2 is applied.

The control unit 40 controls the selector switch 61 to selectively switch the charging / transfer roller 12 between applying the charging bias V <b> 1, applying the transfer bias V <b> 2, or neither.
The exposure unit 13 includes a light emitting element such as a laser diode, for example, and is configured to receive the drive signal generated by the control unit 40 based on image data to be printed, emit laser light L, and perform exposure scanning. The potential of the electrostatic latent image by exposure is, for example, −50V.

The developing device 14 includes a developing roller 141, a supply roller 142, and a stirring roller 143 in a housing 140, and is filled with nonmagnetic one-component toner (not shown) as a developer. The toner has a negative charging characteristic.
The developing roller 141, the supply roller 142, and the agitation roller 143 are rotationally driven by a driving motor M3 via a driving force transmission mechanism (gear, etc.) (not shown), respectively, and toner supplied from a toner cartridge (not shown) is photoreceptord. It is conveyed to the drum 11 side.

Further, the developing roller 141 is connected to the output terminal of the developing power source 53 via the switch 62, and a developing bias V 3 of −350 V, for example, is applied from the developing power source 53.
Due to the action of the developing roller 141 to which the developing bias V3 is applied, in other words, the electrostatic force due to the potential difference between the electrostatic latent image portions on the peripheral surfaces of the developing roller 141 and the photosensitive drum 11, the toner flies and the photosensitive drum 11 The electrostatic latent image on the peripheral surface is developed to form a toner image.

The control unit 40 switches the connection destination of the changeover switch 61 in accordance with the timing when the leading end of the formed toner image reaches the transfer position 19 and applies the transfer bias V <b> 2 to the charging transfer roller 12. As a result, the toner image is transferred to the first surface (hereinafter referred to as “surface”) Sa on the photosensitive drum 11 side of the recording sheet S passing through the transfer position 19.
Each of the drive motors M1 to M3 is constituted by, for example, a DC brushless motor.

(2-2) Configuration of Cleaning The developing device 14 also functions as a cleaning device that collects toner remaining on the peripheral surface of the photosensitive drum 11 after transfer.
That is, of the residual toner on the peripheral surface of the photosensitive drum 11 after the transfer, the residual toner of the portion exposed for the next image formation is used as it is as a toner image, and thus does not need to be collected. When the remaining residual toner (residual toner on the peripheral surface of the photosensitive drum 11 which has not been exposed) whose potential is −700 V due to charging before exposure reaches the position of the developing roller 141, the potential is high. The toner is drawn by the developing roller 141 (−350 V) and collected in the developing device 14.

  Note that when the peripheral surface of the photosensitive drum 11 is charged, the charging transfer roller 12 directly contacts the peripheral surface of the photosensitive drum 11, so that one of the residual toner on the photosensitive drum 11 that could not be collected by the developing unit 14. The portion adheres to the charging transfer roller 12. In this sense, the charging transfer roller 12 also functions as a cleaner, and the first cleaning roller 15 further cleans the peripheral surface of the charging transfer roller 12.

  The first cleaning roller 15 is composed of, for example, a long cored bar and conductive foamed urethane formed around the cored bar, and is biased toward the charging transfer roller 12 by a biasing member (not shown). ing. The first cleaning roller 15 is rotationally driven by the drive motor M2 in a counter direction with respect to the rotational direction C of the charge transfer roller 12 via a drive force transmission mechanism (gear or the like) (not shown), and the charge transfer roller. 12 is configured to rotate and come into contact with the peripheral surface of 12 and wipe off the residual toner adhered (mechanical cleaning).

  The first cleaning roller 15 is connected to the output terminal of the cleaning power supply 54 via the switch 63, and has a polarity opposite to that of the toner from the cleaning power supply 54 and higher than the transfer bias V2, for example, + 1500V cleaning bias. V4 is applied to the first cleaning roller 15. Accordingly, the toner can be adsorbed and removed by the electrostatic force due to the potential difference between the charge transfer roller 12 and the first cleaning roller 15 (electrical cleaning).

  However, even if such a first cleaning roller 15 is provided, it is difficult to remove 100% of the toner adhering to the charge transfer roller 12, and therefore, the residual toner adhering to the charge transfer roller 12 is not transferred to the next recording sheet. In the transfer process, the recording sheet S passing through the transfer position 19 is further adhered to the second surface (hereinafter referred to as “back surface”) Sb opposite to the photoconductive drum 11, and the recording sheet S May cause dirt on the back.

Therefore, in the present embodiment, the second cleaning roller 16 for directly cleaning the back surface Sb of the recording sheet S is provided downstream of the transfer position 19 in the conveyance direction B of the recording sheet S, and the back surface of the recording sheet S is provided. After cleaning Sb, it is configured to be conveyed to the fixing unit 30.
The second cleaning roller 16 has substantially the same configuration as the first cleaning roller 15 and is composed of a long cored bar and conductive foamed urethane formed around the cored bar.

  The second cleaning roller 16 is disposed between the transfer position 19 and the fixing unit 30 on the opposite side of the photosensitive drum 11 with a conveyance path (indicated by a broken line in the figure) being conveyed. . The guide member 29 constituting the conveyance path between the transfer position 19 and the fixing unit 30 includes an upstream member 29a and a downstream member 29b. The second cleaning roller 16 is not shown so that the top portion 16a protrudes slightly from the gap provided between the upstream member 29a and the downstream member 29b and comes into contact with the back surface Sb of the recording sheet S being conveyed. Is held by the frame.

  Specifically, the protrusion amount of the top portion 16a of the second cleaning roller 16 is, for example, about 0.1 to 2.0 mm when the guide surface that guides the recording sheet S of the guide member 29 is used as the reference surface. If it is less than 0.1 mm, the top portion 16a may be instantaneously separated from the back surface Sb of the recording sheet S, and if it exceeds 2.0 mm, the leading end of the recording sheet S being conveyed reaches the top portion 16a. This is because the toner image before heat fixing may be disturbed due to the collision.

The second cleaning roller 16 is driven in a forward direction (in the direction of arrow D) along the conveyance direction B of the recording sheet S by a drive motor M4 (for example, a DC brushless motor) and at a circumferential speed substantially the same as the conveyance speed of the recording sheet S. Driven by rotation. This is because if the second cleaning roller 16 is rotated in the reverse direction, sheet jam may occur due to the rotation of the second cleaning roller 16.
Even if the toner adhered to the charging transfer roller 12 during the transfer further adheres to the back surface Sb of the recording sheet S, the second cleaning roller 16 is applied to the back surface Sb before the recording sheet S is conveyed to the fixing unit 30. Since the rotating toner is directly contacted to wipe off the adhering toner, it is possible to effectively suppress the backside contamination of the recording sheet.

  Further, by applying a cleaning bias (for example, +1500 V) similar to that of the first cleaning roller 15 to the second cleaning roller 16 from the cleaning power source 54 via the switch 64, the toner is adsorbed and removed by electrostatic force. Therefore, it is possible to more effectively suppress the backside contamination of the recording sheet as compared with a configuration in which physical wiping is performed. Hereinafter, in order to distinguish from the cleaning bias V4 applied to the first cleaning roller 15, the cleaning bias applied to the second cleaning roller 16 is set to V5.

  The toner wiped off by the first and second cleaning rollers 15 and 16 adheres to and is held on the peripheral surfaces of the rollers. For this reason, if the toner adhesion amount increases, the cleaning ability of the first and second cleaning rollers 15 and 16 decreases, so that replacement is required at a predetermined timing. For this replacement timing, for example, a relationship between the toner adhesion amount and the cleaning ability and a relationship between the number of printed sheets and the toner adhesion amount are obtained in advance through experiments, and the first and second cleaning rollers 15 and 16 are obtained based on the results. This can be determined by setting the print limit number of sheets to use. Here, the set print limit number is not significantly different from, for example, the print limit number (life) of the photosensitive drum 11.

In the present embodiment, the image processing unit 10 is configured as a cartridge that can be attached to and detached from the housing of the printer 1, and the first and second cleaning rollers 15 and 16 are replaced by replacement of the cartridge.
(3) Configuration of Control Unit FIG. 3 is a diagram illustrating a relationship between the configuration of the control unit 40 and main components that are controlled by the control unit 40.

As shown in the figure, the control unit 40 includes a CPU (Central Processing Unit) 401, a ROM (Read Only Memory) 402, a RAM (Random Access Memory) 403, a communication interface (I / F) unit 404, an image data storage unit. 405, a timer 406, and the like.
The CPU 401 executes a program for controlling the image processing unit 10, the paper feeding unit 20, the fixing unit 30, the operation panel 50, and the like. The ROM 402 is a storage that stores various programs executed by the CPU 401. A RAM 403 is a work area when the CPU 401 executes a program. The communication I / F unit 404 is an interface for connecting to a LAN such as a LAN card or a LAN board.

The image data storage unit 405 stores image data for printing from the external terminal received via the communication I / F unit 404.
When the CPU 401 receives an instruction to execute a print job from an external terminal device (not shown) via the communication I / F unit 404, the CPU 401 forms a toner image on the surface of the photosensitive drum 11, and records the recording sheet. A printing process for printing on S is executed.

During this printing process, the CPU 401 controls the drive motors M <b> 1 to M <b> 4 to control the rotation of the photosensitive drum 11, the charge transfer roller 12, the developing roller 141, the first cleaning roller 15, and the second cleaning roller 16.
Further, the CPU 401 uses the timer 406 to measure the time after the rotation of the photoconductor drum 11 is started, calculates the rotation angle of the photoconductor drum 11 based on the measurement time, and thereby the charging bias V1 at the time of image formation. The application timing of the transfer bias V2, the developing bias V3, the cleaning bias V4 and V5, and the irradiation timing of the laser beam L by the exposure unit 13 are acquired. Then, the charging power source 51, the transfer power source 52, the developing power source 53, and the cleaning power source 54 are controlled via the switches 61 to 64, and the charging bias V1, the transfer bias V2, the developing bias V3, and the cleaning bias V4 are adjusted in accordance with the acquired timing. , V5 are applied, and the laser beam L is irradiated from the exposure unit 13.

In this way, a series of image formation processing and cleaning processing of charging, exposure, development, and transfer is executed.
(4) Image Forming Process and Cleaning Process FIG. 4 is a time chart showing the image forming process and the cleaning process.
FIG. 4 shows the drive timings of the drive motors M1 to M4, the application timings of the charging bias V1, the transfer bias V2, the developing bias V3, the cleaning biases V4 and V5, and the exposure timing.

Here, an example is shown in which an image is formed on a recording sheet S of A4 horizontal size (the maximum size that can be used by the printer 1). The A4 horizontal size conveyance direction length and the circumferential length of the photosensitive drum 11 are shown. It is assumed that the length of the print image in the conveyance direction is substantially equal.
As shown in the figure, the control unit 40 first starts (On) driving of the drive motors M1 to M3, and moves the photosensitive drum 11, the charge transfer roller 12, the developing roller 141, and the first cleaning roller 15 respectively. Rotate (time T1). At the same time, a charging bias V1 is applied to the charging transfer roller 12 to start charging the peripheral surface of the photosensitive drum 11. At this time, the cleaning bias V4 is applied to the first cleaning roller 15, and the cleaning operation (mechanical and electrical cleaning) for the charging transfer roller 12 is started.

  Thereafter, when the tip of the charged region on the peripheral surface of the photosensitive drum 11 reaches the exposure position P1 (see FIG. 2) of the exposure unit 13 by the laser light L, the control unit 40 converts the image data to be printed. Based on this, exposure is started (On) (time T2). Further, the developing bias V3 is applied in accordance with the timing when the leading end reaches the developing position P2 (see FIG. 2) facing the developing roller 141, and development of the peripheral surface of the photosensitive drum 11 is started (time T3). .

Then, the control unit 40 switches the bias voltage applied to the charging / transfer roller 12 from the charging bias V1 to the transfer bias V2 at the timing when the photosensitive drum 11 rotates once (time T4), and is conveyed to the transfer position 19. The developed image is transferred to the coming recording sheet S.
In parallel with this, driving of the drive motor M4 is started (On) to rotate the second cleaning roller 16, and a cleaning bias V5 is applied to the second cleaning roller 16. As a result, a cleaning operation (mechanical and electrical cleaning) is started in which the second cleaning roller 16 is brought into rotational contact with the back surface Sb of the recording sheet S that passes through the transfer position 19 and is conveyed to the fixing unit 30 to remove the toner. To do.

The cleaning operation of the second cleaning roller 16 is continued until the trailing edge of the conveyed recording sheet S passes the position of the second cleaning roller 16 (time T8).
Here, the time T8 is, for example, when the time when the trailing edge of the recording sheet S passes the position of the sheet conveyance sensor 25 is T0 (not shown), the time T0, the position of the sheet conveyance sensor 25, and the second time. It can be obtained from the transport distance k of the recording sheet S between the top portions 16a of the cleaning roller 16 and the transport time t obtained from the transport speed v of the recording sheet S (T8 = T0 + t).

In FIG. 4, the time point when the exposure based on the image data is completed is indicated as time T5, the time point when the development is completed is indicated as time T6, and the time point when the transfer is completed is indicated as time T7.
The above is the flow of the image forming process and the cleaning process in the present embodiment.
In the present embodiment, the charging power source 51, the transfer power source 52, and the changeover switch 61 function as an application unit that selectively applies the charging bias V1 and the transfer bias V2 to the charging transfer roller 12 (conductive member). Yes.
<Second Embodiment>
In the second embodiment, the cleaning roller dedicated to the charge transfer roller is not provided, and the second cleaning roller 16 that cleans the back surface of the recording sheet is also used for cleaning the charge transfer roller 12. This is different from the embodiment.

Since other configurations are basically the same as those of the printer 1 of the first embodiment, the same configurations are denoted by the same reference numerals, and description thereof is omitted.
FIG. 5 is a diagram illustrating a configuration of an image processing unit included in the printer according to the present embodiment.
As shown in the figure, the second cleaning roller 16 included in the image processing unit 110 is in contact with the back surface Sb of the recording sheet S conveyed through the transfer position 19 and also in contact with the peripheral surface of the charging transfer roller 12. Are arranged as follows.

The rotation direction D of the second cleaning roller 16 is the same as the first cleaning roller 15 in the first embodiment and is a counter direction with respect to the rotation direction C of the charge transfer roller 12 (and the conveyance direction of the recording sheet S). Therefore, it is possible to wipe off the toner adhering to the charging transfer roller 12 when it is in rotational contact.
Since the second cleaning roller 16 is also used for cleaning the charging transfer roller 12, the number of parts can be reduced. Therefore, the apparatus can be reduced in size and cost compared with the first embodiment. be able to.

Also in this embodiment, since the back surface Sb of the recording sheet S is directly cleaned by the second cleaning roller 16, the same effect as that of the first embodiment can be obtained.
<Third Embodiment>
In the third embodiment, a fur brush is used as a second cleaning roller that cleans both the back surface of the recording sheet and the charge transfer roller, and a cleaning blade that scrapes and removes toner adhering to the fur brush is provided. This is different from the second embodiment.

Since other configurations are basically the same as those of the printer of the second embodiment, the same configurations are denoted by the same reference numerals, and description thereof is omitted.
FIG. 6 is a diagram illustrating a configuration of an image processing unit included in the printer according to the present embodiment.
As shown in the drawing, the second cleaning roller 216 included in the image processing unit 210 has a brush-like peripheral surface, and is provided with a cleaning blade 217 that removes toner attached to the brush. Hereinafter, the second cleaning roller 216 is referred to as “fur brush roller 216”.

The fur brush roller 216 includes, for example, a long cored bar and a brush 216a formed around the cored bar by weaving conductive rayon with a hair. As the cleaning blade 217, for example, a blade made of a PET (PolyEthylene Terephthalate) recording sheet is used.
The length of the bristles of the brush 216a is, for example, about 500 μm, the biting amount α of the portion in contact with the charging transfer roller 12 is about 300 μm, and the biting amount β of the portion in contact with the recording sheet S is about 100 μm. The fur brush roller 216 is arranged at the position. The cleaning blade 217 is attached so that the tip thereof faces the rotation direction D of the fur brush roller 216 and bites into the brush 216a.

In (ii) to (iv) of FIG. 7, a state in which the brush 216 a is encroached in a portion surrounded by broken lines E <b> 1 to E <b> 3 of FIG. 6 is shown in comparison. FIG. 7I shows a state where the brush 216a is not tilted for further comparison.
First, as shown in (ii) and (iii), the biting amount α of the portion in contact with the charging transfer roller 12 is made larger than the biting amount β of the portion in contact with the recording sheet S (α> β). Since the toner Ta scraped from the charging transfer roller 12 is held at a position deeper than the biting amount β, the toner Ta can be prevented from adhering to the recording sheet S.

  Then, as shown in (iv), by setting the biting amount γ of the cleaning blade 217 to be larger than the biting amounts α and β (γ> α> β), the charging transfer roller 12 and the recording sheet S are scraped from the back surface. Both the removed toner Ta and Tb can be scraped and removed by the cleaning blade 217. The toner removed from the fur brush roller 216 is collected in a waste toner box (not shown).

  If the toner enters a position deeper than the biting amount γ of the brush 216a, it cannot be removed by the cleaning blade 217, but the toner at a position deeper than the biting amount γ does not contact the recording sheet S. There is no worry of causing the recording sheet S to become dirty. When the toner rises to a shallow position, it is removed by the cleaning blade 217.

Thus, in the present embodiment, since the toner attached to the fur brush roller 216 is removed by the cleaning blade 217, the cleaning ability of the fur brush roller 216 can be maintained over a long period of time, thereby Long life can be achieved.
Also in the present embodiment, by applying the cleaning bias V5 to the fur brush roller 216, the toner can be adsorbed by electrostatic force, and the toner can be efficiently transferred from the charging transfer roller 12 and the back surface Sb of the recording sheet S. Can be removed.

  The configuration of the material, the length of the bristle, the thickness, the density of hair, etc. of the brush 216a of the fur brush roller 216 is not particularly limited and is appropriately selected according to the specifications of the image processing unit 10. . Further, the configuration of the cleaning blade 217 such as the material and shape is not particularly limited, and is appropriately selected according to the specifications of the image processing unit 10 such as the fur brush roller 216. The sizes of the biting amounts α, β, and γ are not particularly limited, and are set to appropriate sizes so that the backside contamination of the recording sheet S can be suppressed.

<Modification>
The present invention is not limited to the above-described embodiment, and the following modifications can be considered.
(1) In the above-described embodiment, the peripheral speed of the second cleaning roller that cleans the back surface of the recording sheet S is substantially the same as the conveyance speed of the recording sheet S. However, the present invention is not limited to this. .

For example, it is preferable that the peripheral speed be made faster or slower than the conveyance speed of the recording sheet S so that a speed difference is provided. This is because the ability to scrape off the toner can be enhanced by providing the speed difference.
Of these, the configuration is such that the peripheral speed of the second cleaning roller is faster than the conveyance speed of the recording sheet S. Compared with a case where the recording sheet S is slower than the conveyance speed, the conveyance resistance to the recording sheet S can be suppressed, and therefore, the conveyance resistance becomes too large to prevent the recording sheet S from vibrating and distorting the toner image. Because it can be done.

(2) In the above embodiment, the configuration in which not only mechanical cleaning is performed by the first and second cleaning rollers but also electrical cleaning by applying a cleaning bias is shown. However, the present invention is not limited to this. Absent.
For example, a configuration in which only mechanical cleaning is performed may be employed. Also in this case, since the back surface of the recording sheet is directly cleaned, it is possible to prevent the back of the sheet from being soiled more than before. In this case, the first and second cleaning rollers can be configured using an insulating member.

(3) In the first embodiment, the configuration in which the cleaning bias V5 different from the transfer bias V2 is applied to the second cleaning roller 16 is shown, but the present invention is not limited to this.
For example, the same bias (+ 1000V) as the transfer bias V2 may be applied to the second cleaning roller 16.

In this case, if the cleaning bias V4 is not applied to the first cleaning roller 15, the cleaning power source 54 becomes unnecessary, and accordingly, the apparatus can be reduced in size and cost can be reduced.
(4) In the first embodiment, the configuration in which the first cleaning roller 15 is used to clean the charging transfer roller 12 is shown, but the present invention is not limited to this. Alternatively, a cleaning blade can be used.

(5) In the above-described embodiment, the configuration in which the roller that rotates and contacts the recording sheet S is used as the cleaning member that directly cleans the back surface Sb of the recording sheet S. However, the present invention is not limited to this.
For example, as illustrated in FIG. 8, a configuration using a cleaning brush 316 that is in sliding contact with the back surface Sb of the recording sheet S may be used. Further, instead of the cleaning brush 316, for example, a cleaning pad (not shown) made of foamed urethane or the like may be used.

Such a cleaning brush 316 and a cleaning pad may be formed of a conductive member, and a cleaning bias may be applied so that toner is adsorbed and removed by electrostatic force.
(6) In the third embodiment, the configuration in which the brush 216a of the fur brush roller 216 is formed of hair having the same length (about 500 μm) is shown. More preferably, for example, as shown in FIG. In addition, the long hair k1 and the short hair k2 are combined.

In this case, the tip of the short hair k2 is slidably contacted with the charging transfer roller 12 having the large bite amount α so that the tip of the long hair k1 is slidably contacted with the recording sheet S having the small bite amount β. Each length can be set (for example, the length of the long hair k1 is about 500 μm and the length of the short hair k2 is about 300 μm).
Thus, as shown in FIG. 10 (ii), the long hair k1 is tilted by the charge transfer roller 12 and tilted greatly at the contact portion with the charge transfer roller 12, whereas the short hair k2 is The inclination is suppressed, and the ability to scrape off the toner Ta is increased accordingly, and therefore the toner cleaning ability can be improved as compared with the case of only the long hair k1. Further, as shown in FIG. 10 (iii), the adhering toner Tb can be scraped off and removed by the long hair k1 in the portion in contact with the recording sheet S. At this time, since the short hair k2 does not come into contact with the recording sheet S, the back surface of the recording sheet S due to the toner Ta scraped off by the short hair k2 does not occur.

Thus, the toners Ta and Tb scraped off by the long hair k1 and the short hair k2 are scraped off and removed by the cleaning blade 217 ((iv) in FIG. 10), as in the third embodiment.
(7) Although not specifically mentioned in the above embodiment, the surface roughness Rmax of the charging transfer roller 12 is made larger than the normal surface roughness (for example, 5 to 10 μm), whereby the charging transfer roller 12 You may comprise so that the residual toner of the surrounding surface of the photoconductive drum 11 may be actively scraped off by the unevenness | corrugation of the surface.

The advantages of this configuration will be described.
The charging performance of the toner deteriorates due to, for example, deterioration with time or reuse (recovered residual toner is used by the developing device 14). For this reason, when the toner whose charging performance has deteriorated remains on the peripheral surface of the photosensitive drum 11, the residual toner cannot be collected by the developing device 14, and the image may be fogged. Therefore, by actively removing the residual toner by the charge transfer roller 12, such image fog can be suppressed.

FIG. 11 is an enlarged schematic view showing a contact portion between the charging transfer roller 12 having a rough surface and the photosensitive drum 11, and the surface of the charging transfer roller 12 is exaggerated for easy understanding. It is drawn.
The charge transfer roller 12 shown in the figure has a surface roughness Rmax of 20 μm, for example, and the residual toner T is removed from the peripheral surface 11a of the photosensitive drum 11 by the concave portion 12a formed on the surface. Can do.

Since the charge transfer roller 12 is elastically pressed against the photosensitive drum 11, if the surface unevenness is small, the unevenness is crushed at the pressure contact portion with the photosensitive drum 11, and the effect of scraping off the toner is diminished. By increasing the surface roughness Rmax, it is possible to secure surface irregularities at the pressure contact portion with the photosensitive drum 11 and enhance the effect of scraping off the toner.
Here, the reason why the surface roughness Rmax of the charging transfer roller 12 is set to 20 μm is that when it exceeds 20 μm, uneven charging on the surface may cause uneven charging. Further, the surface roughness Rmax may be 20 μm or less, and even when the surface roughness is normal (5 to 10 μm), the effect of scraping off the toner can be obtained. If the surface roughness Rmax is less than 5 μm, the unevenness at the pressure contact portion with the photosensitive drum 11 is almost eliminated, so that the effect of scraping off the toner is greatly reduced as compared with the case where there is an unevenness. . Therefore, the surface roughness Rmax of the charge transfer roller 12 is desirably in the range of 5 μm to 20 μm.

In this case, it is desirable to use the fur brush roller 216 that combines the deformable (7) long hair k1 and short hair k2 as a cleaning member for removing the toner adhering to the charge transfer roller 12 (FIG. 9). See also).
Then, as shown in FIG. 12, if the hair is long, the tip of the hair passes over the toner Ta in the recess 12a and cannot be scraped off. This is because the toner Ta can be removed by scraping the tip into the recess 12a.

  Note that, even when the hair k1 is long, it is possible to adsorb and remove the toner Ta by electrostatic force by applying a cleaning bias. Therefore, the structure as a cleaning member for cleaning the charging transfer roller 12 having a rough surface is used. Is not limited to the configuration of a fur brush roller in which long hairs and short hairs are combined. For example, a roller made of conductive foamed urethane may be used.

(8) In the first embodiment, a configuration is shown in which a drive motor M2 is provided to rotate the charge transfer roller 12 and the first cleaning roller 15, and a drive motor M4 is provided to rotate the second cleaning roller 16. However, the present invention is not limited to this.
For example, the drive motor M1 that rotates the photosensitive drum 11 is used as a drive source, and the charge transfer roller 12 and the first and second cleaning rollers 15 and 16 are rotationally driven through a power transmission mechanism such as a gear or belt. It can also be. In this case, the peripheral speed of the charge transfer roller 12 can be matched with the peripheral speed of the photosensitive drum 11 by adjusting the gear ratio or the diameter ratio of the pulley that rotates the belt. Further, the peripheral speed of the second cleaning roller 16 can be made to coincide with the conveyance speed of the recording sheet S or can be made faster than the conveyance speed of the recording sheet S.

In addition, an electromagnetic clutch is arranged in the middle of the power transmission path between the drive motor M1 and the second cleaning roller 16, and the electromagnetic clutch is on / off controlled to drive the second cleaning roller 16 at a desired timing. Can be stopped.
In this way, the number of drive motors can be reduced as compared with the case of the first embodiment, and there is an advantage that the apparatus can be reduced in size and cost.

(9) Further, without using a power drive source such as a drive motor, the charging transfer roller 12 is driven to rotate by the rotation of the photosensitive drum 11, and the first cleaning roller 15 is driven to rotate by the rotation of the charging transfer roller 12. The second cleaning roller 16 may be configured to be driven and rotated by frictional contact with the recording sheet S being conveyed.
In this case, a motor, a power transmission mechanism, an electromagnetic clutch, and the like for rotationally driving the charging / transfer roller 12, the first and second cleaning rollers 15 and 16 are not required, and thus the apparatus is further improved than the above modification (8). It is possible to realize downsizing and cost reduction.

(10) The surface of the charging transfer roller 12 may be provided with a spiral scraping groove for scraping off the toner. In this case, the depth of the groove is set to a depth (for example, about 20 μm or less) that can suppress the occurrence of uneven charging and uneven transfer.
Further, the conveyance force of the recording sheet S can be increased by providing the scraping groove.
In this case, in order to prevent the conveyance force of the recording sheet S from fluctuating between the right and left in the conveyance direction, the scraping groove is formed so as to go from the center in the axial direction of the surface of the charging transfer roller 12 toward both ends. Is desirable.

(11) Although not particularly mentioned in the above embodiment, a cleaning blade that is in contact with the peripheral surface of the photosensitive drum 11 and removes remaining toner may be provided.
By mechanically removing the residual toner on the peripheral surface of the photoconductive drum 11 with the cleaning blade, the amount of residual toner adhering to the charging transfer roller 12 can be reduced, so that the residual toner adheres to the back surface of the recording sheet. Can be effectively suppressed. On the other hand, if the cleaning blade is kept in contact with the peripheral surface of the photosensitive drum 11 during charging, the charged potential may be disturbed. For this reason, it is necessary to separate the cleaning blade from the peripheral surface of the photosensitive drum 11, and providing the separation mechanism leads to an increase in the size of the apparatus. Therefore, it is desirable to select a configuration in which a cleaning blade for removing residual toner on the peripheral surface of the photosensitive drum 11 is selected according to the specifications of the printer 1 including the image processing unit 10.

(12) In the above-described embodiment, a configuration in which a one-component developer consisting only of toner is used as the developer is not limited to this, and a two-component developer using a carrier and toner may be used. I do not care.
(13) In the above embodiment, a monochrome printer is used as the image forming apparatus. However, the scope of application of the present invention is not limited to this. If it has an image process section including a transfer roller, it can be applied to a tandem color printer, a tandem color copier, a monochrome copier, a facsimile machine, and the like.

  Further, the contents of the above-described embodiment and modification examples may be combined as much as possible.

  The present invention can be used as a technique for suppressing backside contamination of a recording sheet.

DESCRIPTION OF SYMBOLS 1 Printer 10 Image process part 11 Photosensitive drum 12 Charging transfer roller 13 Exposure part 14 Developing device 15 1st cleaning roller 16 2nd cleaning roller 19 Transfer position (contact position with photosensitive drum of charging transfer roller)
20 Feeder 30 Fixing Unit 40 Control Unit 51 Charging Power Supply 52 Transfer Power Supply 53 Development Power Supply 54 Cleaning Power Supply 141 Development Roller 216 Fur Brush Roller 217 Cleaning Blade 316 Cleaning Brush V1 Charging Bias V2 Transfer Bias V3 Development Bias V4, V5 Cleaning Bias

Claims (9)

The surface of the rotationally driven photosensitive rotator is uniformly charged, exposed and developed based on image data, and after executing an image forming process to form a developer image on the photosensitive rotator, the developer image is recorded. An image forming apparatus for transferring onto a sheet,
A conductive member disposed so as to contact at least an image forming range in the rotation axis direction of the photosensitive rotating body;
Applying means for selectively applying a charging bias and a transfer bias to the conductive member;
In the image forming process, the application unit is controlled to apply a charging bias to the conductive member, and a developer image is formed on the photosensitive rotator by executing the image forming process, and then the application unit is controlled. Control means for applying a transfer bias to the conductive member instead of a charging bias to transfer the developer image on the photosensitive rotator to the first surface of the recording sheet;
At a position downstream of the contact position of the conductive member with the photosensitive rotator in the recording sheet conveyance direction, the developer that contacts the second surface of the recording sheet conveyed and adheres to the second surface is removed. An image forming apparatus comprising: a cleaning member to be removed.   The cleaning member is a cleaning roller that is in rotational contact with the second surface of the recording sheet, and the cleaning roller is configured to rotate in the forward direction along the conveyance direction of the recording sheet. Item 2. The image forming apparatus according to Item 1. The conductive member is a conductive roller that rotates in a forward direction with respect to the photosensitive rotator,
The image forming apparatus according to claim 2, wherein the cleaning roller is configured to contact the peripheral surface of the conductive roller to clean the peripheral surface of the conductive roller. The image forming apparatus according to claim 2, wherein a blade that scrapes off the developer attached to the peripheral surface of the cleaning roller is provided. The cleaning member is formed of a conductive member;
The image forming apparatus according to claim 1, wherein a cleaning bias applying unit that applies a cleaning bias having the same polarity as the transfer bias is provided on the cleaning member. The image forming apparatus according to claim 5, wherein an absolute value of the cleaning bias is larger than an absolute value of the transfer bias. The image forming apparatus according to claim 1, wherein the cleaning member is formed of a foam member. The image forming apparatus according to claim 1, wherein the cleaning member has a brush shape. When the cleaning member has a brush-like portion, the amount of biting of the portion in contact with the conductive member in the brush-like portion is α, and the amount of biting of the portion in contact with the conveyed recording sheet is β The image forming apparatus according to claim 3, wherein the biting amount α is larger than the biting amount β.

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