JP2005070586A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To eliminate image irregularity due to the speed irregularity of a photoreceptor caused by frictional sliding with a cleaning member. <P>SOLUTION: The image forming apparatus is equipped with a photoreceptor 3, an exposure device 5, a developing means 8 having a developing roller, rotating and moving in a state where a plurality of different toner color developing cartridges are mounted in a rotary frame, performing development switching operation, and developing a formed latent image while abutting on the photoreceptor 3, a primary transfer roller 13 transferring a developed toner image on the photoreceptor 3 to an intermediate transfer belt 12 by applying transfer bias, in a state where it abuts on the photoreceptor 3, a photoreceptor cleaner 7 and a transfer belt cleaner 14. The toner image being a measure image in a 1st color is formed on the belt 12 opposed to the photoreceptor 3, from which the developing roller is separated by the development switching operation before forming an image, and the blade of the belt cleaner 14 is separated at the position of the toner image which is the measure image. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention provides an image carrier on which a latent image is formed, a latent image forming means for forming a latent image on the image carrier, a developing roller, and the latent image formed in contact with the image carrier. A developing means for developing the toner, a transfer means for applying a transfer bias in contact with the image carrier and transferring the developed toner image on the image carrier onto an intermediate transfer medium, and on the image carrier A first cleaning unit that constantly contacts the toner and removes residual toner after transfer; and a second cleaning unit that selectively removes the toner on the intermediate transfer medium by controlling the separation and contact of the blade by a separation and contact switching mechanism. And an image forming apparatus in which a developing roller is separated from the image carrier by the developing unit and performs a development switching operation.

  In the image forming apparatus, a charging device for uniformly charging the photoconductor along the rotation direction on the outer periphery of the photoconductor as an image carrier, an exposure device for forming an electrostatic latent image on the photoconductor, A developing device for developing the electrostatic latent image, a transfer device for transferring the toner image on the photosensitive member to the transfer member, a cleaner for cleaning the surface of the photosensitive member after the transfer, and the like are provided. The electrostatic latent image formed on the photosensitive member by the exposure device is developed by the developing device to form a toner image, the formed toner image is transferred to the transfer member, and transferred from the photosensitive member by the cleaner. The residual toner is removed.

In the case of a rotary-type full-color image forming apparatus that forms a full-color image, a color toner image formed on a photosensitive member by a developing device of yellow Y, magenta M, cyan C, and black K is placed on an intermediate transfer medium. Sequential transfer and color overlay. Therefore, each toner developing cartridge is detachably mounted on the developing rotary unit, and each time an electrostatic latent image for each color is formed on the photoreceptor, the developing rotary unit is driven by a developing color switching operation to The developing cartridge is rotated to the developing position to perform the developing operation (see, for example, Patent Documents 1 and 2).
JP 2002-82532 A JP 2003-66801 A

  In the image forming apparatus, the electrostatic latent image on the photoconductor is formed by repeatedly exposing an exposure beam modulated by an image forming signal in the direction of the rotation axis (main scanning direction) of the photoconductor from the exposure apparatus. Since the exposure beam is scanned and exposed to form a latent image while the photoconductor is rotating, if the photoconductor rotates unstable and there are vibrations or unevenness, streaks appear in the sub-scanning direction, resulting in banding. This causes the problem of deterioration.

  Factors that cause unstable rotation of the photosensitive member and cause vibration and unevenness are due to the structure of the train wheel of the drive system, but there are members that contact the outer periphery of the photosensitive member, cleaning members, and rotary type. In such a color image forming apparatus, there is a developing rotary unit for performing a developing color switching operation.

  When the toner image formed on the photosensitive member is transferred to the transfer member, the cleaning member cleans the residual toner on the photosensitive member after the transfer. In order to enhance the cleaning effect, an appropriate member is used. In addition, the residual toner is removed from the photosensitive member by contacting the outer peripheral surface of the photosensitive member with a constant pressure by a spring or the like. If the contact pressure is weak, the cleaning effect is naturally reduced. However, if the contact pressure is increased, irregular vibration associated with frictional sliding between the outer peripheral surface of the photosensitive member and the cleaning member is caused. Further, the angle at which the blade contacts the outer peripheral surface of the photosensitive member, the position of the fulcrum that supports the cleaning member with respect to the tangent to the contact surface, and the like also have an effect.

  Further, in the image forming apparatus in which the developing roller is retracted away from the developing position of the photosensitive member or the development is switched compared to the image forming device in which the developing roller is always in contact with the photosensitive member, the speed unevenness of the photosensitive member is reduced. It is observed that is prone to occur. For example, in a rotary type color image forming apparatus provided with a developing rotary unit, the developing rotary unit is rotated and moved by a developing color switching operation, and the mounted developing cartridge is repeatedly contacted and separated from the photosensitive member each time. There is a problem that the state of the outer peripheral surface of the photoconductor is not uniformly maintained in the contact state and the separated state, the frictional sliding of the cleaning member is not smoothly performed, and the speed of the photoconductor becomes unstable. is there.

  SUMMARY OF THE INVENTION The present invention solves the above-described problems, and is an image forming apparatus that performs a developing switching operation in which the developing roller comes into contact with and separates from the image unevenness due to the speed unevenness of the image carrier due to frictional sliding with the cleaning member. It is intended to eliminate image unevenness that occurs when forming an electrostatic latent image.

  To this end, the present invention provides an image carrier on which a latent image is formed, a latent image forming unit for forming a latent image on the image carrier, and a plurality of developing cartridges each having a developing roller and having different toner colors. A developing means that rotates and moves to perform development switching operation to contact the image carrier to develop the latent image formed, and a transfer bias is applied to the image carrier to apply the transfer bias. A transfer unit that transfers the toner image on the image carrier onto the intermediate transfer medium; a first cleaning unit that steadily abuts on the image carrier to remove residual toner after transfer; And a second cleaning means for selectively removing the toner on the intermediate transfer medium by controlling the separation and contact of the blade by a contact switching mechanism, and the developing roller is separated from the image carrier by the developing means for development. Switching An image forming apparatus configured to perform an operation, wherein the intermediate transfer is opposed to the image carrier on which the developing roller is separated by a first toner color by the development switching operation prior to the formation of an output image. A toner image of the countermeasure image is formed on the medium, and the blade of the second cleaning unit is separated at the position of the toner image of the countermeasure image.

  The second cleaning unit abuts the blade at the position of the toner image of the countermeasure image every time the output image is formed a predetermined number of times, and immediately after the blade is abutted, the countermeasure image The toner image is formed again on the intermediate transfer medium, and the transfer unit is less than or equal to a normal transfer bias applied when forming the output image (zero, reverse polarity to the normal transfer bias, The latent image forming means is characterized in that the toner image of the countermeasure image is reversely transferred onto the image carrier by a transfer bias of not more than the normal transfer bias corresponding to the toner amount of the countermeasure image on an intermediate transfer medium. The image bearing member facing the intermediate transfer medium on which the toner image of the countermeasure image is formed is exposed.

  The toner image of the countermeasure image is at least on the intermediate transfer medium facing the image carrier on which the developing roller is separated, and passes through the first cleaning unit when a latent image is formed by the latent image unit. A region formed on the intermediate transfer medium facing the image carrier and forming the toner image of the countermeasure image is a two-color color switching region. .

  According to the present invention, an image carrier on which a latent image is formed, a latent image forming unit for forming a latent image on the image carrier, and a plurality of developing cartridges having different developing toner colors are arranged on a rotary rotating frame. And developing means for developing the latent image formed in contact with the image carrier by rotating and moving to change the development, and applying the transfer bias in contact with the image carrier and developing the image A transfer means for transferring the toner image on the body onto the intermediate transfer medium, a first cleaning means for removing the residual toner after the transfer by steadily contacting the image carrier, and a blade by a separation contact switching mechanism. And a second cleaning means for selectively removing the toner on the intermediate transfer medium by controlling the separation and contact of the toner, and the developing roller is separated from the image carrier by the developing means to perform the development switching operation. Forming equipment Then, prior to the formation of the output image, a toner image of the countermeasure image is formed on the intermediate transfer medium facing the image carrier on which the developing roller is separated by the first toner color by the development switching operation. Since the blade of the second cleaning unit is separated at the position of the toner image, the state in which no toner is supplied to the image carrier facing the blade of the first cleaning unit at the start of latent image formation is eliminated. The cleaning means that contacts the upper surface can be smoothly slid by friction, and the speed unevenness of the image carrier can be reduced. Therefore, the speed unevenness of the image carrier due to the frictional sliding with the cleaning member is eliminated. And the printing start time can be shortened.

  The second cleaning unit abuts the blade at the position of the toner image of the countermeasure image every time the output image is formed a predetermined number of times, and immediately intermediates the toner image of the countermeasure image immediately after the blade is abutted. Since it is formed on the transfer medium, the toner consumption can be reduced, and the minimum toner amount can be used to reduce the speed unevenness of the image carrier. The transfer means is applied when forming the output image. The toner image of the countermeasure image is reversely transferred onto the image carrier with a transfer bias of less than the normal transfer bias (zero, reverse polarity to the normal transfer bias, less than the normal transfer bias according to the toner amount of the countermeasure image on the intermediate transfer medium). The latent image forming means exposes the image carrier opposite to the intermediate transfer medium on which the toner image of the countermeasure image is formed, so that the toner image of the countermeasure image is reversed on the image carrier in the secondary transfer unit. Necessary for copying A moderate potential difference can be given, it is possible to reverse transcribe proper amount of toner in the required on an image bearing member in accordance with the toner amount of countermeasures images.

  The toner image of the countermeasure image is at least on the intermediate transfer medium facing the image carrier separated from the developing roller and facing the image carrier passing through the first cleaning unit when the latent image is formed by the latent image unit. The area on the intermediate transfer medium that forms the toner image of the countermeasure image that is formed in the area on the intermediate transfer medium that is to be used is a two-color color switching area. It is possible to eliminate the waste of forming a toner image of the image and reversely transferring it.

  According to the present invention, it is possible to perform exposure in a state where toner as a lubricant is supplied without running on the image carrier facing the blade of the cleaning unit at the start of latent image formation. Image formation is not performed in the state where toner as a lubricant is not supplied onto the carrier, and the cleaning means that is always in contact with the image carrier is smoothly rubbed to reduce the speed unevenness of the image carrier. Image formation in a state can be performed.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing an embodiment of an image forming apparatus according to the present invention. In the figure, 1 is an image forming apparatus, 2 is a main body case, 3 is a photoreceptor, 4 is a charging device, 5 is an exposure device, Is a developing cartridge, 7 is a photoreceptor cleaner, 8 is a developing rotary unit, 9 is a rotary frame, 12 is an intermediate transfer belt, 13 is a primary transfer roller, 14 is a transfer belt cleaner, 15 is a secondary transfer roller, and 16 is a power supply. 17, a paper feed tray, 20 a fixing unit, 21 a paper discharge tray, and 22 a paper transport unit.

  As shown in FIG. 1, the image forming apparatus 1 according to the present embodiment includes a paper discharge tray 21 formed on an upper portion of a main body case 2 and a front cover 2 a that is openably and detachably inserted on the front surface. In the main body case 2, a developing rotary unit 8 equipped with a plurality of developing cartridges, a photosensitive member 3 on which an electrostatic latent image is formed and developed to form a toner image, and a toner image on the photosensitive member 3 are transferred. An intermediate transfer unit, a control unit for controlling each drive motor and bias, a power supply device 16, a paper feed tray 17 for storing a recording medium, a fixing unit 20 for fixing a toner image on the recording medium, and the like are arranged. A paper transport unit 22 for transporting a recording medium from the paper feed tray 17 to the fixing unit 20 through the secondary transfer roller 15 is disposed in the front cover 2a. Each unit is configured to be detachable from the main body, and can be removed and repaired or replaced integrally during maintenance or the like.

  The photoreceptor 3 as an image carrier has a thin cylindrical conductive substrate and a photosensitive layer formed on the surface thereof. On the outer periphery of the photosensitive member 3, a charging device 4 for charging the photosensitive member 3 uniformly along the rotation direction, and an exposure device (or writing device) for forming an electrostatic latent image on the photosensitive member 3 5) a developing rotary unit 8 for developing the electrostatic latent image, an intermediate transfer belt 12 to which the toner image on the photoreceptor 3 is transferred, and an intermediate transfer unit for primarily transferring the toner image to the intermediate transfer belt 12. A photoreceptor cleaner 7 for cleaning the surface of the photoreceptor 3 after the primary transfer is disposed.

  The intermediate transfer unit is made up of a driving roller 10 and a driven roller 11 and an endless belt. The intermediate transfer belt is wound around the rollers 10 and 11 and driven in the direction of the arrow in the drawing to transfer the toner image on the photoreceptor 3. 12, a primary transfer roller 13 disposed on the back surface of the intermediate transfer belt 12 so as to face the photoconductor 3 and primarily transferring a toner image on the photoconductor 3 to the intermediate transfer belt 12, and the intermediate transfer belt 12 A transfer belt cleaner 14 that removes residual toner and a four-color full-color toner image formed on the intermediate transfer belt 12 that is disposed opposite to the driving roller 10 are secondarily transferred onto a recording medium (such as paper). And a secondary transfer roller 15 for this purpose.

  A power supply device 16 is disposed below the exposure device 5, and a paper feed cassette 17 is disposed at the bottom of the main body case 2. A recording medium in the paper feed cassette 17 is a pickup roller 18, a sheet material conveyance path. 19, the secondary transfer roller 15, and the fixing device 20 are conveyed to the paper discharge tray 21. The paper feed cassette 17 is attached to the front of the apparatus by a handle 17b so that it can be pulled out, and an auxiliary cassette 17a is attached so that it can be pulled out so as to protrude toward the rear of the apparatus so as to cope with a large paper size. Yes.

  In the image forming apparatus 1 having the above-described configuration, when an image forming signal is input to the exposure device 5, the photoconductor 3, the developing roller 6 a of the developing rotary unit 8, and the intermediate transfer belt are controlled according to the drive motor and bias control by the control unit. First, the outer peripheral surface of the photosensitive member 3 is uniformly charged by the charging device 4. Thereafter, the exposure device 5 selectively exposes the surface of the photoreceptor 3 in accordance with the image information to form an electrostatic latent image. At this time, the developing rotary unit 8 rotates so that the developing roller 6 a of the developing cartridge 6 contacts the photosensitive member 3. As a result, a toner image of an electrostatic latent image is formed on the photoreceptor 3. The toner image formed on the photoreceptor 3 is transferred onto the intermediate transfer belt 12 by the primary transfer roller 13 to which a primary transfer voltage having a polarity opposite to the toner charging polarity is applied, and remains on the photoreceptor 3. The remaining toner is removed by the photoreceptor cleaner 7.

  In the full-color image forming apparatus, development cartridges 6Y, 6M, 6C, and 6K for yellow Y, magenta M, cyan C, and black K are detachably mounted on the development rotary unit 8. In the image forming operation, the exposure device 5 selectively exposes the surface of the photoreceptor 3 in accordance with image information of the first color, for example, yellow Y, to form a yellow Y electrostatic latent image. At this time, the developing rotary unit 8 rotates so that the developing roller 6a of the yellow Y developing cartridge 6Y contacts the photoreceptor 3, and a yellow Y electrostatic latent image toner image is formed on the photoreceptor 3. Subsequently, the toner image is transferred onto the intermediate transfer belt 12 by the primary transfer roller 13 to which a primary transfer voltage having a polarity opposite to the charging polarity of the toner is applied.

  During this time, the transfer belt cleaner 14 and the secondary transfer roller 15 are separated from the intermediate transfer belt 12. A four-color full-color image is obtained by repeating this series of processes corresponding to the second color, the third color, and the fourth color of the image formation signal, thereby obtaining yellow Y, Magenta M, cyan C, and black K toner images are sequentially superimposed and transferred from the photoreceptor 3 onto the intermediate transfer belt 12.

  The recording medium on the paper feed tray 17 is conveyed from the pickup roller 18 to the secondary transfer roller 15 through the registration roller and the sheet material conveyance path 19 at the timing when the superimposed image of each color toner image reaches the secondary transfer roller 15. The secondary transfer roller 15 is pressed against the intermediate transfer belt 12 and a secondary transfer voltage is applied, and the toner image on the intermediate transfer belt 12 is transferred onto the recording medium by the secondary transfer roller 15. When the recording medium having the toner image transferred thereon is conveyed to the fixing unit 20 by the paper conveying unit 22, the toner image on the recording medium is heated and pressed by the fixing unit 20 and fixed. The toner remaining on the intermediate transfer belt 12 is removed by the transfer belt cleaner 14.

  In the case of double-sided printing that prints on both sides of the recording medium, the recording medium that has exited the fixing unit 20 is switched back so that its trailing edge is the leading edge, and passes through the duplex printing conveyance path of the paper conveyance unit 22. Then, it is supplied again to the secondary transfer roller 15. Here, when the full-color toner image on the intermediate transfer belt 12 is transferred onto the recording medium, it is heated and pressurized again by the fixing unit 20, and is discharged onto the discharge tray 21.

  In the developing rotary unit 8 of the present embodiment, the four developing cartridges 6Y, 6M, 6C, and 6K are detachably mounted as described above to form a four-color full-color image forming apparatus. As a device, only the black K developing cartridge 6K is mounted and mounted, and the developing cartridge 6K stands by at the standby position (home position). During image formation, the black K developing cartridge 6K rotates from the standby position. The electrostatic latent image on the photoreceptor 3 may be developed into a toner image at the development position. This makes it possible to use the development rotary unit 8 having the same design specifications for full color and mono color, and maintenance management compared to designing an image forming apparatus dedicated to full color and mono color by sharing full color and mono color. Design and manufacturing costs can be greatly reduced.

  Next, a mechanism related to the speed unevenness of the photoreceptor and countermeasures will be described. FIG. 2 is a diagram illustrating measurement data in which unevenness in speed of the photosensitive member is observed, and FIG. 3 is a diagram for explaining a region where unevenness in speed of the photosensitive member is generated according to an operation sequence.

  In the color image forming apparatus of the present embodiment, none of the developing cartridges 6Y, 6M, 6C, and 6K is in the developing position facing the photoreceptor 3 in the standby state in which the developing rotary unit 8 is at the home position. That is, the developing roller 6 a is not in contact with the photosensitive member 3. Normally, when the developing roller 6 a is in contact with the photosensitive member 3, even if no image is written from the exposure device 5, some fog toner is placed on the photosensitive member 3, and the fog toner is in contact with the photosensitive member cleaner 7. By acting as a kind of lubricant on the contact surface, the photoconductor 3 smoothly frictionally slides with respect to the photoconductor cleaner 7, so that the speed unevenness of the photoconductor 3 is slight.

  However, when the developing roller 6a is separated from the photoconductor 3, the surface of the photoconductor 3 cleaned by the photoconductor cleaner 7 rotates and contacts the photoconductor cleaner 7 again and frictionally slides. Since there is no toner at all, there is no so-called lubricant, and the frictional resistance of the photoconductor 3 is increased at the contact surface with the photoconductor cleaner 7, so that the rotational speed of the photoconductor 3 becomes unstable. That is, it is considered that when the frictional resistance of the surface of the photoconductor 3 is increased, the photoconductor 3 repeats a minute lock / slide phenomenon with respect to the photoconductor cleaner 7, and the speed unevenness and vibration of the photoconductor 3 appear.

  This can be recognized by FIG. In FIG. 2, the vertical axis represents speed unevenness and the horizontal axis represents time. First, the large speed unevenness appears periodically at the joint of the encoder that performs rotation detection. It is ignored because it does not directly indicate rotational disturbance. This measurement data is used for each color Y, M, C, and K to perform a development color switching operation in which the development cartridge 6 is switched in accordance with the timing of exposure based on the image signal and the development roller 6a is brought into contact with the photosensitive member 3. A time zone t (between 0 and 6) with a large speed unevenness is observed immediately after the start of exposure. The speed unevenness is eliminated after a lapse of time from the time when the developing roller 6 a contacts the photoconductor 3 until the contact surface reaches the photoconductor cleaner 7.

  Further, the speed unevenness occurrence region of the photoconductor will be described based on the operation sequence. FIG. 3 shows an outline of the operation sequence of the color image forming apparatus according to the present embodiment. The vsync signal, the transfer belt motor, the scanner motor, the image signal, the rotary operation, the developing operation, the primary transfer bias, and the photoconductor. The position of the cleaner, the secondary transfer bias, and the position of the transfer belt cleaner are shown. The oblique dotted line m is the developing operation start point, that is, the position on the photosensitive member 3 where the developing roller 6a abuts after the developing color switching operation is completed. Similarly, a diagonal position n indicates a developing operation end point, that is, a position on the photosensitive member 3 where the developing roller 6a is separated by the start of the developing color switching operation.

  As shown in FIG. 3, the photosensitive member 3, the developing roller 6a of the developing rotary unit 8, the medium drive motor, and the scanner motor of the exposure device 5 are started to rotate the intermediate transfer belt 12, the scanner, and the photosensitive member 3. After the start, the developing color switching operation by the developing rotary unit 8 is started, the outer peripheral surface of the photoreceptor 3 is uniformly charged by the charging device 4, and the exposure is performed by turning on the image signal in synchronization based on the vsync signal. The image formation is performed sequentially. Then, by turning on the primary transfer bias in synchronization with the start of image formation, the toner image on the photoreceptor is primarily transferred onto the intermediate transfer belt 12.

  As shown in FIG. 1, the exposure point on the photosensitive member 3 is on the upstream side of the development position. When exposure is started and the image signal is turned on as shown in FIG. 3, the exposure position rotates to the development position. Since the developing roller 6a has only to be in contact with the photosensitive member 3 until the development roller 6a is in contact with the photosensitive member 3, the development start time is slightly delayed from the time when the image signal is turned on. The position on the photosensitive member 3 with which the developing roller 6a abuts is rotationally moved to the photosensitive member cleaner position when the dotted line m intersects the photosensitive member cleaner position.

  Accordingly, the developing roller 6a does not come into contact with the time t ′ from when the image signal is turned on until the dotted line m intersects the photoreceptor cleaner position, that is, no toner serving as a lubricant exists on the photoreceptor 3. . In this state, while the peripheral surface of the photoconductor 3 frictionally slides with the photoconductor cleaner 7, an area where the speed unevenness of the photoconductor 3 occurs is generated. In the second to fourth colors, the same speed unevenness generation region of the photosensitive member 3 appears in the same manner from the development operation end point (n) to the development operation start point (m).

  The color image forming apparatus according to the present embodiment replenishes toner onto the photosensitive member 3 where the developing device is separated by a switching operation. The toner is replenished by forming a toner image of the countermeasure image on the intermediate transfer belt 12 so that the toner is present on the photoreceptor 3 facing the blade of the photoreceptor cleaner 7 at least after the start of latent image formation. Then, the toner image of the countermeasure image and the residual toner are transferred by reverse transfer from the intermediate transfer belt 12 onto the photoreceptor 3. The toner image of the countermeasure image on the intermediate transfer belt 12 depends on the amount of toner (the density of the toner image), the contact pressure, etc. due to the mechanical peeling action because the intermediate transfer belt 12 and the photosensitive member 3 are in contact. Then, the image is reversely transferred onto the photoreceptor 3 by controlling the transfer bias.

  Before the image signal is turned on and exposure is started, the image is not directly affected and image unevenness due to speed unevenness does not occur. At least when the image signal is turned on, that is, at the start of exposure for starting the formation of a latent image on the photoconductor 3, it is sufficient that the toner is supplied to the photoconductor 3 facing the blade of the photoconductor cleaner 7. Therefore, even when the developing roller 6a is in contact with the photosensitive member 3 facing the blade of the photosensitive member cleaner 7, that is, when the developing roller 6a is in contact with the photosensitive member 3 early, the photosensitive member 3 is also in contact. The above condition is satisfied because the fog toner is placed on the developing roller 6a.

  FIG. 4 is a diagram showing an operation sequence of the embodiment for forming the countermeasure image. In order to reversely transfer the toner image from the intermediate transfer belt 12 onto the photosensitive member 3, the transfer belt cleaner 14 is separated so that the toner on the intermediate transfer belt 12 is conveyed to the primary transfer point without being removed. The toner image on the intermediate transfer belt 12 is obtained by transferring the toner image or the fog toner from the photosensitive member 3 at the primary transfer point.

  FIG. 4 shows an operation sequence of an embodiment in which a toner image of a countermeasure image is formed and held on the intermediate transfer belt 12 and reversely transferred onto the photoreceptor 3. In this embodiment, before the output image is formed, first, when the development cartridge 6 of the first color is rotated and moved to the development position by the development switching operation of the development rotary unit 8, the development switching operation is performed according to the first color of toner. An image signal is turned on to form a latent image of the countermeasure image on the photosensitive member 3 in which the developing roller 6a is spaced, and a latent image of the countermeasure image is formed and developed, and a primary transfer bias is applied to the toner image of the countermeasure image at the primary transfer point. Then, the image is transferred onto the intermediate transfer belt 12 (1).

  As apparent from the operation sequence of FIG. 4, the leading edge of the countermeasure image reaches the position of the photoreceptor cleaner of the photoreceptor 3 before and after the countermeasure image of the first color is transferred and formed on the intermediate transfer belt 12. Therefore, even if the latent image of the output image of the first color is immediately formed, the residual toner of the toner image of the countermeasure image exists on the photosensitive member 3, so that the photosensitive member cleaner 7 smoothly smoothes the peripheral surface of the photosensitive member 3. Thus, the frictional sliding state is maintained, and the speed variation does not occur. In addition, when the countermeasure image is formed in the first color before the output image is formed and the output image is continuously formed, the output image formation start timing (print start time) is shortened while preventing banding. be able to.

  For the second to fourth colors, the toner image of the countermeasure image is reversely transferred from the intermediate transfer belt 12 onto the photosensitive member 3 during the developing color switching operation in which the developing roller 6 a does not contact the photosensitive member 3. (2) to (4). As a result, at least during the formation of the latent image by the exposure beam B, there is no time when no lubricant is present at the contact portion between the photoconductor 3 and the photoconductor cleaner 7, and the photoconductor cleaner 7 smoothly moves the peripheral surface of the photoconductor 3. Thus, the frictional sliding state is maintained, and the speed variation does not occur.

  Considering the state in which the developing roller 6a is in contact with the photosensitive member 3 at the developing position, when no toner image is formed on the photosensitive member 3, there is fog toner from the developing roller 6a to the photosensitive member 3, and this fog toner is It plays the role of a lubricant at the contact portion with the photoreceptor cleaner 7. Further, when a toner image is formed on the photoreceptor 3, residual toner after the toner image is primarily transferred to the intermediate transfer belt 12 at the primary transfer point is also in contact with the photoreceptor cleaner 7. It plays a sufficient role as a lubricant.

  As described above, since the amount of toner from the intermediate transfer belt 12 that is reversely transferred as a lubricant onto the photosensitive member 3 may be small, by controlling the amount of toner to be reversely transferred at the primary transfer point, a plurality of toners are transferred from the intermediate transfer belt 12. By repeating the rotation, a part of the toner can be reversely transferred little by little. The number of repetitions can be controlled by, for example, the number of image formations, the toner amount of the countermeasure image (toner image density), and the bias at the time of reverse transfer.

  The toner image (countermeasure image) previously transferred from the photoreceptor 3 to the intermediate transfer belt 12 is periodically turned on / off such that the exposure by the exposure beam B from the exposure device 5 is 1 line on and 10 line off, for example. It is possible to use a line image such as a pattern, a diagonal line pattern at regular intervals, a lattice pattern, a regular dot pattern, a halftone pattern, or the like. On the intermediate transfer belt 12, an image area and a non-image area are allocated. When the exposure device 5 starts exposure with the exposure beam B in accordance with the image signal, the photoreceptor 3 and the photoreceptor cleaner 7 are assigned. A region where a toner image as a countermeasure image is to be transferred is calculated and determined in advance from the point where the toner contacts.

  When the formation of the output image is completed, the transfer belt cleaner is brought into contact with the intermediate transfer belt 12 up to the transfer belt cleaner position [b] shown in FIG. The toner image of the countermeasure image formed on the belt 12 is cleaned. In the case where the output image is continuously formed, the transfer belt cleaner is brought into contact with the intermediate transfer belt 12 up to the transfer belt cleaner position [A] shown in FIG. Only the residual toner is cleaned, and the toner is repeatedly reversely transferred from the intermediate transfer belt 12 onto the photoreceptor 3 until an output image is formed a predetermined number of times (for example, 10 sheets or 20 sheets). If the output image formation is completed before the predetermined number of times, the countermeasure image toner image formed on the intermediate transfer belt 12 may be immediately cleaned as shown in FIG. After completion, the timer may be operated so that the toner image of the countermeasure image is cleaned by bringing the transfer belt cleaner into contact with the intermediate transfer belt 12 after a predetermined time has elapsed.

  Next, control for replenishing toner from the intermediate transfer belt 12 onto the photoreceptor 3 will be specifically described. FIG. 5 is a diagram for explaining a state in which the countermeasure image is formed on the photosensitive member. FIG. 6 is a diagram in which the countermeasure image is transferred from the photosensitive member to the intermediate transfer belt, and the print image is subsequently formed on the photosensitive member. FIG. 7 is a diagram for explaining a state in which the formation of the print image is completed and transferred to the intermediate transfer belt, and FIG. 8 is a diagram at the same time when the developing rotary unit starts the developing color switching operation. FIG. 9 is a diagram for explaining a state in which toner is reversely transferred from the intermediate transfer belt onto the photosensitive member, FIG. 9 is a diagram for explaining a state in which image formation of the next toner color is started, and FIG. 10 is a final diagram. FIG. 11 is a diagram for explaining a state in which a color image is being formed, FIG. 11 is a diagram for explaining a state in which an image in which all colors are overlaid is subjected to secondary transfer, and FIG. Illustration for explaining A.

  In the image forming apparatus 1 of the present embodiment, prior to the image forming operation, first, the photosensitive member 3, the developing roller 6a of the developing rotary unit 8, and the intermediate transfer belt 12 are rotationally driven in the directions of Ro, Rd, and Rb, respectively. The outer peripheral surface of the body 3 is uniformly charged by the charging device 4. Thereafter, as shown in FIG. 5, the exposure device 5 exposes the countermeasure image on the surface of the photoreceptor 3 to form an electrostatic latent image. At this time, the developing rotary unit 8 rotates so that the developing roller 6 a of the developing cartridge 6 contacts the photosensitive member 3. As a result, a toner image 35 of the countermeasure image is formed on the photoreceptor 3.

  When the toner image 35 of the countermeasure image is formed on the photoconductor 3, the primary transfer roller 13 to which a primary transfer voltage having a polarity opposite to the toner charging polarity is applied is applied from the photoconductor 3 as shown in FIG. 6. The toner image 35 ′ is transferred onto the intermediate transfer belt 12. Subsequently, exposure and development of the printed image are started to form a toner image 36, and primary transfer is started.

  Since the transfer belt cleaner 14 and the secondary transfer roller 15 are separated from the intermediate transfer belt 12 as described above, when the formation of the first color print image on the photosensitive member 3 is completed, FIG. As shown, the toner image 35 ′ of the countermeasure image on the intermediate transfer belt 12 moves to near the primary transfer point. Then, the developing rotary unit 8 starts the developing color switching operation to form the second color image. As shown in FIG. 8, the developing rotary unit 8 rotates and moves in the direction of Rr, and the developing roller 6a moves to the photosensitive member. When the toner image 35 ′ is separated from the toner image 35, the countermeasure image toner image 35 ′ previously transferred onto the intermediate transfer belt 12 reaches the primary transfer point and is reversely transferred onto the photoreceptor 3 as a toner image 35 ″. Even if the developing roller 6a is separated from the photosensitive member 3 by copying, toner is supplied to the photosensitive member 3 at the primary transfer point and supplied as a lubricant to a contact portion with the photosensitive member cleaner 7.

  Similarly, when the image formation of the second color is started, the contact portion with the photoconductor cleaner 7 at the time when the photoconductor 3 is exposed by the exposure beam B from the exposure device 5 as shown in FIG. Is supplied with toner 35 ″ reversely transferred from the intermediate transfer belt 12 as a lubricant and replenished onto the photoreceptor 3, so that stable rotation of the photoreceptor 3 can be maintained. An image forming operation is also executed.

  When image formation of the fourth color is started, the images of all colors are superimposed on the intermediate transfer belt 12 as shown in FIG. 10, and the secondary transfer roller 15 is intermediated as shown in FIG. The full-color toner image 37 ′ is brought into contact with the transfer belt 12 and the secondary transfer is started from the intermediate transfer belt 12 to the recording medium to form a transfer image 37 ″. During this time, the transfer belt cleaner 14 is shown in FIGS. As shown in FIG. 12, the toner image 35 ′ of the countermeasure image on the intermediate transfer belt 12 passes and comes into contact with the intermediate transfer belt 12 as shown in FIG. 12. Cleaning of residual toner corresponding to the print image area is started, and residual toner after secondary transfer of the print image on the intermediate transfer belt 12 is removed.

  FIG. 13 is a diagram showing another embodiment in which the transfer bias is controlled to be lower than the normal transfer bias in the region where the toner image of the countermeasure image is reversely transferred, and FIG. 14 is the transfer bias in the region where the toner image of the countermeasure image is reversely transferred. FIG. 15 is a diagram showing another embodiment for controlling off, FIG. 15 is a diagram showing another embodiment for controlling the transfer bias to the normal transfer bias reverse polarity in the region where the toner image of the countermeasure image is reversely transferred, and FIG. It is a figure which shows other embodiment which exposes a photoreceptor in the area | region which reversely transfers the toner image of a countermeasure image.

  In the embodiment shown in FIG. 4, the toner image of the countermeasure image is reversely transferred from the intermediate transfer belt 12 onto the photoreceptor 3 in a state where the normal transfer bias applied when forming the output image is applied. In this case, in the primary transfer portion, for example, if the photosensitive member 3 is uniformly charged to −600 V and a normal transfer bias of 200 to 300 V is applied, it has a potential difference of 800 to 900 V. . When this potential difference is reduced, reverse transfer can be promoted. Therefore, the toner of the countermeasure image can be selected according to the toner amount (toner image density) of the countermeasure image, the pattern, the pressing force between the intermediate transfer belt 12 and the photosensitive member 3, and the like. In the area where the image is reversely transferred, the transfer bias may be lowered from the normal transfer bias and further applied with the reverse polarity.

  In the embodiment shown in FIG. 13, a countermeasure image is formed on the photoreceptor 3 prior to the first color image shaping, and the toner image is applied to the intermediate transfer belt 12 by applying a primary transfer bias at the primary transfer portion. In the second to fourth colors, the primary transfer bias of the primary transfer portion is lowered in accordance with the reverse transfer timing of the countermeasure image toner image from the intermediate transfer belt 12 to the photosensitive member 3. As a result, the toner image of the countermeasure image is reversely transferred onto the photoreceptor 3 with an appropriate toner amount (density). Further, FIG. 14 shows an embodiment in which the primary transfer bias is turned off (zero) as a means for lowering the primary transfer bias of the primary transfer portion, and an embodiment in which a bias of reverse polarity is applied. This is shown in FIG.

  According to the example in which the charging of the photosensitive member 3 and the normal transfer bias at the primary transfer portion are the above numerical values, in the embodiment shown in FIG. 13, the potential difference is shown in FIG. In the embodiment, up to 600 V, and in the embodiment shown in FIG. 15, the potential difference can be compressed to 400 V by setting the transfer bias to −200 V having a reverse polarity, so that reverse transfer can be further promoted.

  As shown in the above embodiments, the primary transfer bias of the primary transfer unit is controlled to a normal value or less in accordance with the reverse transfer timing of the toner image of the countermeasure image from the intermediate transfer belt 12 to the photoreceptor 3. As a result, the amount of toner to be reversely transferred is controlled and changed by changing the potential difference with the photosensitive member 3 at the primary transfer portion. Therefore, as shown in the embodiment of FIG. Instead of changing the primary transfer bias of the transfer portion, the potential on the photoreceptor 3 may be changed by exposure. Since the potential of the photosensitive member 3 uniformly charged to −600 V is lowered to about −50 V by exposure, the effect of promoting reverse transfer equivalent to the case where the primary transfer bias is controlled to a normal value or less is realized. can do.

  In addition, this invention is not limited to the said embodiment, A various deformation | transformation is possible. For example, in the above embodiment, it has been described as solving the problem during the development color switching operation of the rotary type four-color full-color image forming apparatus. However, during standby, the developing roller is held away from the photoconductor to form an image. As long as the developing roller is brought into contact with the photosensitive member in accordance with the execution of the job, whether the developing rotary unit is installed or not, whether the developing rotary unit is installed or not. Needless to say, the present invention can be similarly applied to a single-color image forming apparatus and can solve the same problems. Further, when the countermeasure image is reversely transferred from the intermediate transfer belt onto the photosensitive member, the primary transfer is performed so that a reverse bias is applied or the primary transfer bias is lowered to reduce the potential difference or to turn it off. In addition to controlling the bias, the primary transfer speed or the pressure of the primary transfer roller may be changed. Further, the countermeasure image may not be formed with the first color or black K toner image, but may be formed with, for example, a low-visibility yellow Y toner image, or only immediately before the first color image formation. First, it is performed when setting the position to the standby state when replacing the cartridge or unit, or when starting the image forming operation from the standby state, and after that, it is formed on the intermediate transfer belt on a constant basis according to the number of job executions. You may make it leave.

1 is a diagram showing an embodiment of an image forming apparatus according to the present invention. It is a figure which shows the measurement data by which the speed nonuniformity of a photoreceptor is observed. It is a figure for demonstrating the speed nonuniformity generation | occurrence | production area | region of a photoreceptor with an operation | movement sequence. It is a figure which shows the operation | movement sequence of embodiment which forms a countermeasure image. It is a figure for demonstrating a mode that the countermeasure image is formed on the photoreceptor. FIG. 6 is a diagram for explaining a state in which a countermeasure image is transferred from the photosensitive member to an intermediate transfer belt and a print image is subsequently formed on the photosensitive member. FIG. 6 is a diagram for explaining a state in which formation of a print image is completed and transferred to an intermediate transfer belt. FIG. 6 is a diagram for explaining a state in which toner is reversely transferred from an intermediate transfer belt to a photosensitive member at the same time when a developing rotary unit starts a developing color switching operation. FIG. 6 is a diagram for explaining a state in which image formation of the next toner color is started. FIG. 6 is a diagram for explaining a state during image formation of a final color. It is a figure for demonstrating a mode which carries out the secondary transfer of the image which overlapped all the color colors. It is a figure for demonstrating the mode at the time of the cleaning start timing of a transfer belt cleaner. FIG. 10 is a diagram illustrating another embodiment in which a transfer bias is controlled to be lower than a normal transfer bias in a region where a toner image of a countermeasure image is reversely transferred. FIG. 10 is a diagram illustrating another embodiment in which a transfer bias is controlled to be off in a region where a toner image of a countermeasure image is reversely transferred. FIG. 10 is a diagram showing another embodiment in which the transfer bias is controlled to the normal transfer bias reverse polarity in the area where the toner image of the countermeasure image is reversely transferred. It is a figure which shows other embodiment which exposes a photoreceptor in the area | region which reversely transfers the toner image of a countermeasure image.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 2 ... Main body case, 3 ... Photoconductor, 4 ... Charging apparatus, 5 ... Exposure apparatus, 6 ... Developing cartridge, 7 ... Photoconductor cleaner, 8 ... Developing rotary unit, 9 ... Rotary frame, 12 ... Intermediate transfer belt, 13 ... primary transfer roller, 14 ... transfer belt cleaner, 15 ... secondary transfer roller, 16 ... power supply, 17 ... paper feed tray, 20 ... fixing unit, 21 ... paper discharge tray, 22 ... paper transport unit

Claims (11)

An image carrier on which a latent image is formed;
Latent image forming means for forming a latent image on the image carrier;
Developing means for developing a latent image formed by mounting a plurality of developing cartridges having different developing colors on a rotary rotating frame, rotating the developing cartridge, performing a developing switching operation, and contacting the image carrier When,
A transfer means for applying a transfer bias in contact with the image carrier and transferring the developed toner image on the image carrier onto an intermediate transfer medium;
A first cleaning means for constantly contacting the image carrier to remove residual toner after transfer;
And a second cleaning means for selectively removing the toner on the intermediate transfer medium by controlling the separation / contact of the blade by a separation / contact switching mechanism, and the developing means separates the developing roller from the image carrier. An image forming apparatus configured to perform a development switching operation,
Prior to the formation of the output image, a toner image of a countermeasure image is formed on the intermediate transfer medium facing the image carrier on which the developing roller is separated by the first toner color by the development switching operation. An image forming apparatus, wherein the blade of the second cleaning unit is separated at a position of a toner image of an image. The second cleaning unit abuts the blade at the position of the toner image of the countermeasure image every time the output image is formed a predetermined number of times, and immediately after the blade is abutted, the countermeasure image The image forming apparatus according to claim 1, wherein the toner image is formed again on the intermediate transfer medium. 3. The transfer unit according to claim 1, wherein the toner image of the countermeasure image is reversely transferred onto the image carrier by a transfer bias that is equal to or lower than a normal transfer bias applied when the output image is formed. The image forming apparatus according to any one of the above. The image forming apparatus according to claim 3, wherein the transfer unit reversely transfers the toner image of the countermeasure image onto the image carrier with a transfer bias set to zero. The image forming apparatus according to claim 3, wherein the transfer unit reversely transfers the toner image of the countermeasure image onto the image carrier with a transfer bias having a reverse polarity to the normal transfer bias. The transfer means reversely transfers the toner image of the countermeasure image onto the image carrier with a transfer bias equal to or lower than the normal transfer bias corresponding to the toner amount of the countermeasure image on the intermediate transfer medium. Item 4. The image forming apparatus according to Item 3. The image forming apparatus according to claim 6, wherein a toner amount of the countermeasure image is determined based on a formation pattern of the countermeasure image. The image forming apparatus according to claim 6, wherein the toner amount of the countermeasure image is determined based on the number of times of the development switching operation. The image forming apparatus according to claim 1, wherein the latent image forming unit exposes the image bearing member facing the intermediate transfer medium on which the toner image of the countermeasure image is formed. apparatus. The toner image of the countermeasure image is at least on the intermediate transfer medium facing the image carrier on which the developing roller is separated, and passes through the first cleaning unit when a latent image is formed by the latent image unit. The image forming apparatus according to claim 1, wherein the image forming apparatus is formed in a region on the intermediate transfer medium facing the image carrier. The image forming apparatus according to claim 1, wherein an area on the intermediate transfer medium on which the toner image of the countermeasure image is formed is a two-sheet color switching area.

Images