JP2012242404A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device that prevents a change in speed of an intermediate transfer body during image formation and prevents image defects to be caused by transfer position displacement, without reducing the lifetime of a cartridge.SOLUTION: The image forming device includes discharge means 108 for discharging toner removed from an intermediate transfer body 11 by cleaning means, again to the intermediate transfer body 11. When developing means 7y in the most upstream image forming part 4y for forming an image for a moving direction of the intermediate transfer body 11 is moved from a separation state to a contact state with respect to a photoreceptor 5y, until a toner image developed by the developing means 7y reaches a primary transfer part T1y, the discharge means 108 discharges the toner to the intermediate transfer body 11 when the toner removed by the cleaning means is located in the primary transfer part T1y.

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention generally relates to an image forming apparatus such as a copying machine, a printer, a facsimile machine, and a multi-function machine that performs image formation by, for example, electrophotography. In particular, an image provided with a cleaning means used for removing and cleaning the toner remaining on the intermediate transfer member after the toner image formed on the photosensitive member as the image carrier is transferred to the transfer material via the intermediate transfer member. The present invention relates to a forming apparatus.

  For example, in an electrophotographic color image forming apparatus, a color image composed of a plurality of colors is formed using toners of different colors respectively supplied from a plurality of developing devices onto a photoreceptor as an image carrier. In such an image forming apparatus, the toner image formed on the photosensitive member is not directly transferred onto the transfer material, but all the toner images are transferred onto the intermediate transfer member and transferred (primary transfer). The toner images are collectively transferred (secondary transfer) onto the transfer material. As a means for transferring the toner image on the intermediate transfer member onto the transfer material, a transfer roller that contacts the surface of the intermediate transfer member while rolling is used. When the transfer material is passed between the transfer roller and the intermediate transfer member, the transfer roller applies a bias having a polarity opposite to the polarity of the toner from the transfer roller, thereby transferring the toner on the intermediate transfer member to the transfer material. It is transcribed above. In the transfer process to the transfer material, not all the toner on the intermediate transfer member is transferred to the transfer material, and the toner remains on the intermediate transfer member (hereinafter referred to as “transfer residual toner”). In order to prevent the transfer residual toner from remaining on the intermediate transfer member and moving to the primary transfer portion, the transfer residual toner is placed downstream of the secondary transfer portion and upstream of the primary transfer portion with mechanical force or static electricity. A cleaning means for removing by using a natural force is provided. Various configurations have been devised as the cleaning means.

  As a cleaning means using mechanical force, the toner on the intermediate transfer member is scraped off by a cleaning blade which is a cleaning member pressed against the intermediate transfer member, and then the waste toner container provided inside the image forming apparatus is used. There is a configuration to collect. As a cleaning means using electrostatic force, a bias voltage having a polarity opposite to that of the transfer residual toner on the intermediate transfer member is applied to a cleaning roller having a conductive rubber layer so that the polarity of the transfer residual toner on the intermediate transfer member is adjusted. Change. Accordingly, there is a configuration in which the transfer residual toner is moved to the photosensitive member and collected in the cartridge.

  In addition, there is a configuration in which both the cleaning blade and the cleaning roller are provided, the transfer residual toner is discharged from the cleaning roller to the intermediate transfer member, and the lubricant on the intermediate transfer member is simultaneously removed by the cleaning blade together with the discharged transfer residual toner. In this configuration, the surface energy of the intermediate transfer belt is increased to prevent image dropout (see Patent Document 1).

  Further, in Patent Document 2, a cleaning unit that removes toner remaining on the surface of the photoconductor has a cleaning blade that is in contact with the photoconductor, a function of removing and holding the residual toner, and a function of discharging the residual toner to the photoconductor. Has a brush. When a toner image is formed only on a part of the photoconductors, out of a plurality of photoconductors where the toner image is not formed, the residual toner is discharged from a brush corresponding to the photoconductor located relatively upstream, The cartridge is collected in a cartridge positioned relatively downstream. The collection into the cartridge is performed by scraping off the toner remaining on the surface of the photosensitive member with a cleaning blade in contact with the photosensitive member.

  Specifically, when a black and white image is formed on the black image cartridge located on the most downstream side, the photosensitive member of the cartridge located on the relatively downstream side among the color image cartridges that are not used for black and white image formation is driven. Let me. Next, preparation is made so as not to cause a delay when forming a color image. Among color image cartridges that are not used for black-and-white image formation, residual toner generated in a cartridge positioned relatively upstream is discharged toward a cartridge positioned relatively downstream. By doing so, it plays the role of a lubricant that reduces the friction between the photosensitive member of the cartridge located relatively downstream and the cleaning blade in contact with the photosensitive member, thereby improving the life of the cleaning blade and the photosensitive member. The effect is gained.

  By moving the primary transfer roller to the photosensitive member side, the intermediate transfer member obtains tension and contacts the photosensitive member, and then the developing device, that is, the developing roller contacts the photosensitive member and is formed on the photosensitive member formed by the laser. The toner is attached to the electrostatic latent image and developed. In the primary transfer, the toner is transferred to the intermediate transfer member by applying a bias having a polarity opposite to the polarity of the toner to the primary transfer roller. In general, there is a speed difference between the moving speed of the intermediate transfer member and the peripheral speed of the photosensitive member in order to increase the toner transfer efficiency, and the speed of the intermediate transfer member is slightly higher. Therefore, the intermediate transfer member is relatively braked by the frictional resistance between the intermediate transfer member and the photosensitive member. From the contact of the intermediate transfer member to the photosensitive member to the contact of the developing roller, no toner is present in the contact portion between the intermediate transfer member and the photosensitive member. When the developing roller comes into contact with the photosensitive member, a minute amount of toner is interposed in the contact portion between the intermediate transfer member and the photosensitive member, and the frictional resistance is lowered because it plays the role of a lubricant. Therefore, torque fluctuation occurs in the drive roller that moves the intermediate transfer member before and after the toner is interposed between the contact portion of the intermediate transfer member and the photosensitive member, thereby causing speed change of the intermediate transfer member.

  The primary transfer is performed by superimposing toner images with a plurality of color cartridges. From the viewpoint of the life of the developing roller, the developing roller and the photosensitive drum are brought into contact immediately before the image writing position. Therefore, the contact of the developing roller is sequentially performed from the upstream side. The upstream primary transfer portion to be transferred first is affected by the speed fluctuation of the intermediate transfer member due to the toner in the downstream primary transfer portion to be transferred later, and the transfer position of the toner image is shifted. As a result, there is an image problem that a transfer position shift occurs between the colors.

  To solve this problem, there is a method in which toner is always discharged from the upstream cartridge to the intermediate transfer member (see Patent Document 3). By always discharging the toner from the upstream side, the intermediate transfer member and the photosensitive member at the primary transfer portion of all colors, from the beginning of the movement of the intermediate transfer member to the image writing position, and even between images in continuous paper passing. Since the toner intervenes between them, the speed fluctuation does not occur and the occurrence of the image problem is prevented.

  However, when the above-described means described in Patent Document 3 is used, the toner in the cartridge located upstream is used for other than image formation, so that the toner consumption is large, the life of the cartridge is shortened, and the user is stressed. There was a problem that gave.

JP 2006-30358 A JP 2007-192987 A JP 2004-117601 A

  An object of the present invention is to provide an image forming apparatus in which the speed of an intermediate transfer member does not change during image formation and an image problem due to a transfer position shift can be prevented.

  Another object of the present invention is to provide an image forming apparatus capable of preventing an image problem due to a transfer position shift without shortening the life of a cartridge, without causing a speed fluctuation of an intermediate transfer body during image formation. .

The above object is achieved by the image forming apparatus according to the present invention. In summary, the present invention
A plurality of image forming units each including a photosensitive member on which an electrostatic latent image is formed, and a developing unit that develops the electrostatic latent image formed on the photosensitive member into a toner image;
Contacting / separating means for bringing the developing means into contact with and away from the photoreceptor;
An intermediate transfer member that moves along the plurality of image forming units and onto which a toner image of the photosensitive member is transferred;
Primary transfer means for transferring the toner image on the photosensitive member to the moving intermediate transfer member at a primary transfer portion;
Secondary transfer means for transferring the toner image of the intermediate transfer member to a transfer material at a secondary transfer portion;
A cleaning unit that is disposed upstream of the primary transfer unit and downstream of the secondary transfer unit with respect to a moving direction of the intermediate transfer member, and removes transfer residual toner of the intermediate transfer member;
In an image forming apparatus having
The cleaning means has discharge means for discharging the toner removed from the intermediate transfer body to the intermediate transfer body again,
The toner image developed by the developing unit is moved by moving the developing unit in the most upstream image forming unit that forms an image with respect to the moving direction of the intermediate transfer body from the separated state to the contact state with respect to the photoconductor. The discharge unit discharges the toner to the intermediate transfer member at a timing when the toner removed by the cleaning unit is interposed in the primary transfer unit until reaching the primary transfer unit, and / or
The toner image developed by the developing unit is moved by moving the developing unit in the most upstream image forming unit that forms an image with respect to the moving direction of the intermediate transfer body from a contact state to a separated state with respect to the photoconductor. The discharging unit discharges the toner to the intermediate transfer member at a timing when the toner removed by the cleaning unit is interposed in the primary transfer unit after being removed from the primary transfer unit.
An image forming apparatus characterized by the above.

  According to the present invention, the toner discharged from the discharging unit is interposed between the intermediate transfer member and the photosensitive member after the intermediate transfer member and the photosensitive member are in contact until the developing unit and the photosensitive member are in contact with each other. Then, after the developing means comes into contact, the toner on the developing means is slightly interposed between the intermediate transfer member and the photosensitive member. Therefore, according to the present invention, fluctuations in the speed of the intermediate transfer member can be prevented. Further, it is possible to prevent the influence on the image due to the downstream primary transfer in which the developing unit comes into contact with the photosensitive member after the upstream primary transfer in which the developing unit comes into contact with the photosensitive member in advance.

1 is a schematic cross-sectional view of an embodiment of an image forming apparatus according to the present invention. FIG. 4 is a diagram for explaining a configuration of contact and separation of a developing device constituting a cartridge with respect to a photosensitive drum. FIG. 2 is an overall configuration diagram illustrating the configuration and operation of an intermediate transfer belt cleaning device. FIG. 4 is a perspective view illustrating a configuration around a charging roller in an intermediate transfer belt cleaning device. FIG. 6 is a perspective view illustrating a configuration of contact and separation of a charging roller in an intermediate transfer belt cleaning device. FIG. 10 is a diagram for explaining a start operation of discharging residual toner to the leading edge of the first image during printing. FIG. 10 is a diagram for explaining an end operation of discharging the transfer residual toner to the leading edge of the first image during printing. It is a figure explaining the operation | movement of the secondary transfer during printing. FIG. 10 is a diagram for explaining a start operation of discharging residual toner to the rear end of the last image during printing. FIG. 10 is a diagram for explaining an end operation of discharging residual toner to the rear end of the last image during printing. FIG. 6 is a flowchart illustrating a sequence of a transfer residual toner discharging operation. It is a figure explaining the transfer residual toner collection | recovery operation | movement of the charging roller in 2nd Example. It is a figure explaining the transfer residual toner holding | maintenance operation | movement of the holding roller in 2nd Example. FIG. 10 is a diagram illustrating a bias when transfer residual toner moves from a charging roller to a holding roller in a second embodiment. It is a figure explaining the discharge operation | movement to the intermediate transfer belt from the holding roller in 2nd Example. FIG. 10 is a diagram illustrating a bias when transfer residual toner moves from a holding roller to a charging roller in a second embodiment. FIG. 10 is a diagram illustrating an operation of starting the transfer residual toner discharge to the leading edge of the first image during printing in the second embodiment. FIG. 10 is a diagram illustrating an end operation of discharging residual toner to the leading edge of the first image during printing in the second embodiment. It is a figure explaining the operation | movement of the secondary transfer during printing in 2nd Example. FIG. 10 is a diagram illustrating a start operation of discharging residual toner to the rear end of the last image during printing in the second embodiment. FIG. 10 is a diagram illustrating an end operation of discharging residual toner to the rear end of the last image during printing in the second embodiment.

  The image forming apparatus according to the present invention will be described below in more detail with reference to the drawings.

Example 1
An image forming apparatus 1 according to the present invention will be described using an electrophotographic four-drum color image forming apparatus. FIG. 1 is a longitudinal sectional view showing the overall configuration of a full-color laser beam printer (hereinafter simply referred to as “printer”) which is a color image forming apparatus of this embodiment.

  In this embodiment, a cassette 2 is housed in the lower part of the printer 1 so as to be drawable. A manual feed unit 3 is disposed on the right side of the printer 1. The transfer material S is stacked and accommodated in the cassette 2 and the manual feed unit 3, respectively, and the transfer material S is separated and fed one by one. In the present embodiment, the printer 1 has a plurality of four cartridges 4 (4y, 4m) corresponding to each color of yellow, magenta, cyan, and black as image forming means (image forming units) arranged in a horizontal row. 4c, 4k). The cartridge 4 has a drum-shaped electrophotographic photosensitive member (hereinafter referred to as “photosensitive drum”) 5 (5y, 5m, 5c, 5k) as an image carrier. Around the photosensitive drum 5, a charging device 6 (6y, 6m, 6c, 6k) for uniformly negatively charging the surface of the photosensitive drum 5, and image information is exposed to the uniformly charged photosensitive drum 5. An exposure device 9 serving as a scanner unit for forming an electrostatic latent image is disposed. Around the photosensitive drum 5, developing rollers 7 (7y, 7m, 7c, 7c, 7c, 7c, 7c, 7c, and 7c) that constitute a developing unit that develops a toner image by attaching toner to an electrostatic latent image on the photosensitive drum. 7k) is arranged. Further, around the photosensitive drum 5, a cleaning blade 8 (8y, 8m, 8c, 8k) is provided as a photosensitive member cleaning means for removing residual toner remaining on the photosensitive drum 5.

  With reference to FIG. 2, the contact / separation means with respect to the photosensitive drum 5 of the developing device will be described with reference to the cartridge 4y as a representative. In this embodiment, the developing roller 7y provided in the developing device can move to a contact state and a separation state with respect to the photosensitive drum 5y by the contact / separation means, that is, can be contacted and separated. ing. As the contact / separation means, various configurations can be adopted. For example, as shown in FIG. 2, a cam mechanism 42 including a drive shaft 42a and a cam 42b can be used. That is, in this embodiment, the cartridge 4y has a developing frame 40 that rotatably supports the developing roller 7y, and the developing frame 40 is a cartridge frame (not shown) that integrally constitutes the cartridge 4y. ) With a support shaft 41 so as to be swingable. Then, the developing frame 40 is controlled by driving a drive shaft 42a of the cam mechanism 42 by a driving motor (not shown) or the like, so that the cam 42b is swung, whereby the developing frame 40 and the developing roller 7y are exposed to light. The body drum 5 can be contacted and separated. The other cartridges 4m, 4c, and 4k have the same configuration.

  The contact / separation means 42 contacts and separates the developing roller 7 from the photosensitive drum 5 in accordance with the electrostatic latent image, thereby improving the life of the developing roller 7. That is, as will be described in detail later, the life of the developing roller 7 can be extended by a configuration in which the plurality of developing rollers 7 are brought into contact with or separated from the photosensitive drum 5 at different timings. In this embodiment, the developing roller 7 contacts the developing rollers 7y, 7m, 7c, and 7k in this order.

  Further, as described above, the scanner unit 9 that forms an electrostatic latent image on the photosensitive drum 5 by irradiating the laser beam based on the image information, and the intermediate transfer unit 10A are provided in the vicinity of the toner cartridge 4. Yes.

  In FIG. 1, the intermediate transfer unit 10 </ b> A is a cleaning that removes transfer residual toner from the primary transfer roller 10 (10 y, 10 m, 10 c, 10 k), the intermediate transfer belt 11, the driving roller 12, the driven roller 13, and the intermediate transfer belt 11. The apparatus 100 is integrally formed. Further, since the intermediate transfer belt 11 as an intermediate transfer member is a consumable item, the intermediate transfer unit 10A can be attached to and detached from the image forming apparatus main body.

  The intermediate transfer belt 11 is an endless cylindrical belt and is stretched around a driving roller 12 and a driven roller 13. The driven roller 13 is grounded and is urged by an urging means (not shown) in the direction of arrow A in FIG. 1 to apply a predetermined tension to the intermediate transfer belt 11. The drive roller 12 is driven to rotate by a motor (not shown) or the like, so that the intermediate transfer belt 11 rotates at a predetermined speed in the direction of arrow B in FIG.

  In the primary transfer, a positive bias voltage is applied to primary transfer rollers 10y, 10m, 10c, and 10k as primary transfer means, and a potential difference from the negatively charged photosensitive drums 5y, 5m, 5c, and 5k is used. Is going on. Intermediate transfer belt primarily transferred from the photosensitive drum 5 at a nip portion (primary transfer portion) T1 (T1y, T1m, T1c, T1k) formed by the primary transfer rollers 10y, 10m, 10c, and 10k and the photosensitive drum 5. 11 is transferred to the transfer material S at the secondary transfer portion T2. In the secondary transfer portion T2, a secondary transfer roller 14 as a secondary transfer unit is disposed facing the driving roller 12 as a secondary transfer counter roller.

  Next, the transfer material S onto which the toner image has been transferred at the secondary transfer portion T2 passes through a fixing device 15 that fixes the transferred image. Thereafter, the conveyance path is switched by the double-sided flapper 16 and conveyed to either the discharge roller pair 17 or the switchback roller pair 18. The transfer material conveyed to the switchback roller pair 18 side is reversely conveyed by the switchback roller pair 18 portion, and again passes through the secondary transfer portion T2 and the fixing device 15, and is then conveyed to the discharge roller pair 17 side. The After passing through the discharge roller pair 17, the transfer material S is discharged to the transfer material stacking unit 19.

  Next, the overall configuration and operation of the transfer residual toner cleaning device for the intermediate transfer belt 11 in this embodiment will be described with reference to FIG.

  The cleaning device 100 is upstream of the primary transfer portion T1y formed by the photosensitive drum 5y and the primary transfer roller 10y with respect to the moving direction of the intermediate transfer belt 11 (the direction of arrow B in FIG. 3), and the secondary transfer portion. It arrange | positions downstream from T2. The cleaning blade 101 uses a deformable elastic rubber as a material, and is adhered to a holding member 102 formed of sheet metal. Then, it has a width equal to or larger than the LTR paper size in the longitudinal direction, and the transfer residual toner on the intermediate transfer belt 11 is removed by being pressed against the intermediate transfer belt 11. Further, the cleaning blade 101 is pressed against the driven roller 13 in order to obtain a desired linear pressure capable of removing the transfer residual toner. The transfer residual toner scraped off from the intermediate transfer belt 11 by the cleaning blade 101 moves on the toner conveyance path 104 by the toner conveyance member 103 and freely passes through the groove 106 formed by the holding member 102 and the frame 100F of the cleaning device 100. Fall. Then, it is stored in the temporary storage unit 105. That is, the primary storage unit 105 can store the toner removed by the cleaning blade 101 even if there is a large amount of residual toner remaining on the intermediate transfer belt 11 after the secondary transfer due to continuous printing or the like.

  The toner conveying member 103 has holes formed in a lattice shape and is held by a shaft 107 that rotates eccentrically. Since the shaft 107 rotates eccentrically, the toner conveying member 103 as a whole reciprocates substantially in the directions of arrows C1 and C2 in FIG. At the time of forward movement, the toner conveying member 103 moves substantially horizontally along the bottom surface of the toner conveying path 104 to convey the untransferred toner in the direction of arrow C1 in FIG. During the backward movement, the toner conveying member 103 is lifted obliquely upward from the bottom surface of the toner conveying path 104 so that the toner is not separated from the pushed transfer residual toner and returned to the cleaning blade 101 side.

  When the transfer residual toner is stored in the temporary storage unit 105 to some extent, the transfer residual toner starts to contact the charging roller 108. Thereafter, a bias voltage having the same polarity as the bias voltage applied to the primary transfer roller 10 at the time of primary transfer is applied to the charging roller 108 to discharge the residual toner. The transfer residual toner having the same polarity as the bias voltage applied to the primary transfer roller 10 is moved from the charging roller 108 to the intermediate transfer belt 11 and then the most upstream side photosensitive drum having the same polarity as that at the time of primary transfer. Move to 5y. Next, it is scraped off by the photosensitive member cleaning blade 8y that is in contact with the photosensitive drum 5y, and is collected in the cartridge 4y. In this embodiment, the charging roller 108 functions as a toner discharge unit that discharges the toner removed from the intermediate transfer belt 11 to the intermediate transfer belt 11 again.

  When the printer 1 is in the initial use, a small amount of toner is put in the temporary storage unit 105 in advance to discharge the toner from the charging roller 108 to the intermediate transfer belt 11 until the transfer residual toner is accumulated. In order to prevent a large amount of untransferred toner from being discharged to the intermediate transfer belt 11 at a time, a metal toner regulating member 109 fixed to the holding member 102 is in contact with the surface of the charging roller 108. Yes. Thereby, the transfer residual toner on the charging roller 108 is thinly and uniformly extended. Further, a sheet 110 is provided between the cleaning device 100 and the intermediate transfer belt 11, and the transfer residual toner from the temporary storage unit 105 is prevented from flowing out by lightly contacting the intermediate transfer belt 11.

  Next, detailed description of the periphery of the charging roller 108 will be given based on FIG. 4, and the configuration of contact and separation of the charging roller 108 will be described based on FIG.

  As shown in FIG. 4, the charging roller 108 includes a metal core bar 108a and a conductive rubber layer 108b, and both ends of the charging roller 108 are rotatably held by a resin bearing 111. A conductive resin is used for at least one of the bearings 111. The charging roller 108 and the intermediate transfer belt 11 are brought into contact with each other with a desired pressure by pressing the bearing 111 toward the driven roller 13 with the spring 112. Since both ends of the charging roller 108 are pressed, the charging roller 108 is pressed uniformly against the intermediate transfer belt 11 in the longitudinal direction. The spring 112 also has a function of an electrical contact, and a bias voltage can be applied to the spring 112 by bringing the contact portion 112a into contact with a contact (not shown) provided on the image forming apparatus main body side. It has become. When a bias voltage is applied to the spring 112, the bias voltage flows to the conductive rubber layer 108b of the charging roller 108 via the bearing 111 having conductivity.

  In this embodiment, the toner is negatively charged when an image is formed. Therefore, during primary transfer and secondary transfer, a positive voltage opposite to the charging polarity of the toner is applied to the primary transfer roller 10 and the secondary transfer roller 14. Therefore, although there is some toner that changes to a positive characteristic during primary transfer and secondary transfer, most of the transfer residual toner remaining on the intermediate transfer belt 11 after the secondary transfer remains negatively charged. It has become. When a positive voltage is applied to the charging roller 108, the transfer residual toner attached to the charging roller 108 from the temporary storage unit 105 is discharged, so that the transfer residual toner is positively charged. For example, if the secondary transfer voltage is increased to obtain the best transfer performance in a high humidity environment, the charge polarity of the transfer residual toner may become very unstable. Even in such a case, since a positive voltage is applied to the charging roller 108 and discharging is performed, the transfer residual toner adhered to the surface of the charging roller 108 may be positive or negative, regardless of whether the transfer residual toner is positive or negative. It can be positively charged without problems.

  The transfer residual toner reversed from the negative polarity to the positive polarity moves to the intermediate transfer belt 11 due to the potential difference between the charging roller 108 and the driven roller 13 that is in contact with the ground. At this time, as described above, in order to prevent a large amount of untransferred toner from being discharged to the intermediate transfer belt 11 at one time, a metal toner regulating member 109 is in contact with the charging roller 108, and the charging roller 108. The upper transfer residual toner is thinly and uniformly extended. In addition to the untransferred toner, foreign matters such as paper dust, dust, and dust marks remaining on the intermediate transfer belt 11 remain. The foreign matter is mixed with the transfer residual toner, and the foreign matter is also transported to the temporary storage unit 105. However, when the toner control member 109 extends the transfer residual toner on the charging roller 108 thinly and uniformly, the foreign matter separation described above is also performed. Can be done simultaneously. Further, in order to stably discharge the untransferred toner thinly and uniformly extended to the intermediate transfer belt 11, it is ideal that the charging roller 108 is rotated at a constant speed with respect to the intermediate transfer belt 11. In order to obtain a constant speed, the driven roller 13 and the charging roller 108 are connected by a gear (not shown), and the charging roller 108 is rotated by using the driven roller 13 as a drive source.

  As described above, the untransferred toner moved from the charging roller 108 to the intermediate transfer belt 11 is normally negatively charged by the most upstream primary transfer roller 10y to which a positive bias is applied and the charging device 6y. By using the potential difference from the surface of the photosensitive drum 5y, the photosensitive drum 5y moves. Thereafter, the photoconductor drum 5y is cleaned by the photoconductor cleaning blade 8y and collected in the cartridge 4y.

  As shown in FIG. 5, a separation member 113 is provided in the vicinity of the bearing 111 holding the charging roller 108, and the cam 113a for contacting and separating the charging roller 108 and the intermediate transfer belt 11 and the rotational drive are transmitted. The gear 113b is integrally formed. Gears 114a are provided at both ends of the drive shaft 114 located above the charging roller 108, and the drive shaft 114 and the gear 114a are rotated by a motor (not shown) provided in the image forming apparatus main body. . When the rotational drive from the gear 114a is transmitted to the gear 113b, the cam 113a rotates, and the bearing 111 slides in the directions of arrows D1 and D2 in FIG. The charging roller 108 and the intermediate transfer belt 11 can be separated from each other when slid in the direction D1, and can be brought into contact with each other when slid in the direction D2. In this embodiment, the charging roller 108 is separated from the intermediate transfer belt 11 by an amount that does not cause plastic deformation of the toner regulating member 109, and the separation amount is 0.5 to 1 mm. Cleaning of the transfer residual toner on the intermediate transfer belt 11 is performed by the cleaning blade 101. Therefore, when the charging roller 108 can be brought into contact with and separated from the intermediate transfer belt 11, it is possible to selectively discharge the transfer residual toner to the intermediate transfer belt 11 at any timing.

  Next, with respect to the area for discharging the transfer residual toner carried out according to the present invention, the front end area in the first image at the time of printing will be described based on FIGS. 6 to 8, and the rear end area in the last image at the time of printing Will be described with reference to FIGS. When the number of printed sheets is only one, untransferred toner is discharged at the leading edge and trailing edge of the image. In order to make it easy to determine the type of toner, the toner from the cartridge 4 is represented by a circle, and the untransferred toner is represented by a square.

  As described above, the surface of the photosensitive drum 5 is uniformly negatively charged by the charging device 6 and then an exposure device 9 irradiates a laser beam based on the image information to form an electrostatic latent image on the photosensitive drum 5. ing. Thereafter, the developing roller 7 attaches toner to the electrostatic latent image to develop it as a toner image, and the toner image on the photosensitive drum 5 is transferred to the intermediate transfer belt 11 at the primary transfer nip T1 (T1y, T1m, T1c, T1k). The primary transfer. During continuous printing, charging, latent image, development, primary transfer, and cleaning processes are repeated.

  FIG. 6 shows the transfer residual toner discharge operation immediately after the printer 1 receives the print signal. Upon receiving the print signal, the printer 1 starts conveying the transfer material S by the paper feeding unit 2 based on the image information, and starts an image forming operation by the image forming unit 4. In the image forming unit 4, as described above, images are formed in order from the upstream side. The charging roller 108 is applied to the intermediate transfer belt 11 before the developing roller 7y contacts the uppermost photosensitive drum 5y. The toner remaining after transfer is discharged by contacting and positively charging. In the primary transfer portions T1y to T1c, the photosensitive drums 5y to 5c are controlled to be positive, and the primary transfer rollers 10y to 10c are controlled to be negative, and the positively charged transfer residual toner is transferred to the primary transfer nip portions T1y to T1c. Then, it moves downstream while being carried on the intermediate transfer belt 11 (see FIG. 7).

  As shown in FIG. 7, the untransferred toner that has reached the most downstream photosensitive drum 5k is a positive bias applied to the primary transfer roller 10k, and the surface of the photosensitive drum 5k negatively charged by the charging device 6k. Is moved to the photosensitive drum 5k. Then, it is scraped off by the photosensitive member cleaning blade 8k and collected in the cartridge 4k. Thereafter, when development on the photosensitive drum 5y begins to be performed in the most upstream image forming portion (cartridge) 4y, the developing roller 7y develops the toner image on the electrostatic latent image portion on the photosensitive drum 5y. Contact a little earlier than the area. At the stage where the developing roller 7y comes into contact, a small amount of toner moves to the photosensitive drum 5y, and thereafter, development is performed on the electrostatic latent image portion.

  The area where the residual toner is discharged is such that at least the discharged toner front end is interposed in the primary transfer nip T1k of the most downstream cartridge 4k when the discharged rear end of the toner passes through the primary transfer nip T1y of the uppermost stream cartridge 4y. It is supposed to be. Further, in all of the downstream cartridges 4m, 4c, and 4k, the developing roller 7y contacts the photosensitive drum 5y, and the discharged toner is primarily transferred before the minute toner begins to intervene in the primary transfer nip T1y. The nip portions T1m, T1c, and T1k are reached. At the rear end of the discharged toner, in the most upstream cartridge 4y, the minute toner is interposed in the primary transfer nip portion T1y so that the discharged toner and the minute toner overlap each other. Further, the charging roller 108 is controlled to be separated to stop the discharge at the beginning of the minute toner.

  Further, in the image forming units 4m to 4k disposed downstream from the most upstream image forming unit 4y, the developing rollers 7m to 7k perform the primary transfer of the toner image in the relatively upstream image forming unit 4. When in contact with the photosensitive drum, it moves to a contact state.

  When the primary transfer of the toner image is performed up to the most downstream cartridge 4k, as shown in FIG. 8, the toner image on the intermediate transfer belt 11 is transferred so that the leading end is aligned with the toner image. Secondary transferred to S.

  This completes the description of the transfer residual toner discharge region at the leading end region in the first image. During continuous printing of the second and subsequent sheets, the developing roller 7 is always in contact with the photosensitive drum 5, and the toner in the cartridge 4 is interposed in the primary transfer nip T1 (T1y to T1k). In the rear end region of the last image at the time of printing, the developing roller 7 and the photosensitive drum 5 are sequentially separated from the upstream cartridge 4y where the image formation is completed to the downstream cartridge 4k. That is, the developing roller 7 of each image forming unit moves from the contact state to the separated state when primary transfer of the toner image is performed in the relatively downstream image forming unit.

  As shown in FIG. 9, the charging roller 108 abuts and discharges the toner so that the transfer residual toner starts to intervene immediately upstream where the toner is not supplied from the most upstream cartridge 4y to the primary transfer nip T1y. As shown in FIG. 10, the transfer residual toner is discharged so that the transfer residual toner is interposed in the primary transfer nip T1y of the most upstream cartridge 4y until the primary transfer of the toner image is completed in the most downstream cartridge 4k. The charging roller 108 is separated and controlled to stop discharging.

  The above is the description of the discharge residual toner discharge region at the leading end region in the last image.

  As shown in FIG. 11, when receiving a print signal (S1), the printer 1 first determines whether or not continuous printing is performed (S2). In the case of continuous printing (Yes in S2), it is determined whether it is the first image or the last image (S3), and as described above, control is performed so that the transfer residual toner is discharged to the leading edge or trailing edge of the image. That is, in the case of the first image (Yes in S3), control is performed so that the transfer residual toner is discharged to the leading edge of the image (S4). If it is not the first image (No in S3), it is determined whether or not it is the last image (S5). If it is the last image (Yes in S5), the transfer residual toner is discharged to the rear end of the image. Control is performed (S6). If it is not the last image (No in S5), control is performed so that the untransferred toner is not discharged (S7).

  If the printing is not continuous printing (No in S2), control is performed so that the transfer residual toner is discharged to the leading edge and the trailing edge of the image (S8).

  The effects of this embodiment will be described below. When the toner starts to be interposed from the state where the toner does not intervene in the primary transfer portion T1, the toner acts as a lubricant and the frictional resistance between the intermediate transfer belt 11 and the photosensitive drum 5 becomes low. It gets faster for a moment. On the other hand, when the toner is not present from the state where it is present in the primary transfer portion T1, the frictional resistance is increased, so that the moving speed of the intermediate transfer belt 11 is momentarily decreased.

  As described above, the contact of the developing roller 7 when developing an image is performed in order from the upstream cartridge 4 in order to extend the life of the developing roller 7. For this reason, when the toner in the cartridge 4 begins to intervene in the downstream primary transfer nip portion T1 while the primary transfer is being performed on the upstream side, the speed of the intermediate transfer belt 11 increases momentarily. Therefore, the toner interval on the intermediate transfer belt 11 changes in all the nip portions where the primary transfer is performed on the upstream side, and the position is shifted from the image superimposed on the downstream primary transfer portion. Occurs. Similarly, the separation of the developing roller 7 is performed in order from the cartridge 4 on the upstream side. Therefore, when the primary transfer is performed on the downstream side and the toner of the cartridge 4 does not intervene in the upstream primary transfer nip portion, the speed of the intermediate transfer belt 11 decreases momentarily. For this reason, the toner interval on the intermediate transfer belt 11 changes in all the nip portions where the primary transfer is performed on the downstream side, and the position is shifted from the image superimposed on the upstream primary transfer portion.

  Therefore, as in this embodiment, the untransferred toner is interposed in all the primary transfer nips before the upstream developing roller 7 contacts the leading edge of the first image. Thereby, even if the downstream developing roller 7 comes into contact with the toner of the cartridge 4 in the primary transfer nip portion, the speed of the intermediate transfer belt 11 does not change. Similarly, at the rear end of the last image, the untransferred toner is interposed in all the primary transfer nips on the upstream side before the developing roller 7 on the downstream side is separated. As a result, the speed of the intermediate transfer belt 11 does not change even when the developing roller 7 on the downstream side is separated and the toner of the cartridge 4 does not intervene in the primary transfer nip portion. Therefore, an image problem as an uneven transfer image can be prevented.

  In other words, according to the present invention, the discharge means (between the intermediate transfer belt 11 and the photosensitive drum 5) from when the intermediate transfer belt 11 and the photosensitive drum 5 come into contact until the developing roller 7 and the photosensitive drum come into contact with each other. The toner discharged from the charging roller 108) is interposed. Further, since the toner on the developing roller 7 is slightly interposed between the intermediate transfer belt 11 and the photosensitive drum 5 after the developing roller 7 contacts, fluctuations in the speed of the intermediate transfer belt 11 can be prevented. Further, the upstream primary transfer in which the developing roller 7 comes into contact with the photosensitive drum 5 first prevents the downstream primary transfer in which the developing roller 7 comes into contact with the photosensitive drum 5 later from affecting the image. Is possible.

  In addition, by providing the temporary storage unit 105, it is possible to remove even when printing an image with a large amount of residual toner, and even when the cleaning device 100 is new, it is possible to store toner for discharging in advance. Is possible.

  Further, by applying a bias voltage having a polarity opposite to that of the transfer residual toner removed from the intermediate transfer belt 11 to the charging roller 108, the potential difference between the bias voltage applied to the primary transfer roller 10k and the surface of the photosensitive member is utilized. It is possible to reliably collect the transfer residual toner in the cartridge 4k.

  Furthermore, according to the present invention, the toner in the upstream cartridge is not used for image formation, but the amount of toner consumption is increased with respect to the upstream cartridge, and the life of the cartridge is shortened. Is also resolved.

Example 2
The printer 1 according to the second embodiment of the present invention is the same as that of the first embodiment except for the cleaning device 100 for the transfer residual toner and the discharging method. Therefore, the description of the entire configuration is omitted, and the description of the first embodiment is cited. To do. Characteristic portions different from the first embodiment regarding the cleaning device 100 and the discharging method for the transfer residual toner will be described with reference to FIGS. 12, 13, and 15 are explanatory diagrams of the configuration and operation of the cleaning device 100 according to the second embodiment. 14 and 16 are diagrams illustrating an example of the potential relationship between the charging roller 108 and the holding roller 117 in the second embodiment.

  As shown in FIG. 12, the cleaning device 100 is always in contact with the intermediate transfer belt 11 and uses a charging roller 108 that can apply a bias, and a conductive rubber that is in contact with the charging roller 108 and can apply a bias. A holding roller 117. The driven roller 13 is grounded. The intermediate transfer belt 11 is provided with a bias roller 118 that is positioned upstream of the cleaning device 100 and downstream of the secondary transfer portion T2 in the moving direction of the intermediate transfer belt 11 and for uniformizing the polarity of the transfer residual toner. It is in contact. The transfer residual toner on the intermediate transfer belt 11 is negatively charged by applying a negative bias to the bias roller 118. When the charging roller 108 is positively charged, the transfer residual toner on the intermediate transfer belt 11 that is negatively charged is moved from the intermediate transfer belt 11 to the charging roller 108.

  Thereafter, the holding roller 117 is charged more positively than the charging roller 108 as shown in FIG. 13, thereby giving a relative potential difference and holding the transfer residual toner from the charging roller 108, for example, as shown in FIG. 14. The transfer residual toner is removed from the intermediate transfer belt 11 by being moved to the roller 117.

  When discharging the untransferred toner collected by the cleaning device 100, as shown in FIG. 15, the holding roller 117 and the charging roller 108 are negatively charged to give a relative potential difference as shown in FIG. 16, for example. The collected transfer residual toner moves from the holding roller 117 to the charging roller 108. Since the driven roller 13 is grounded, a potential difference is generated between the charging roller 108 and the transfer residual toner is discharged to the intermediate transfer belt 11. The area discharged from the charging roller 108 to the intermediate transfer belt 11 is the same as in the first embodiment. However, in this embodiment, the untransferred toner discharged by the charging roller 108 is negatively charged unlike the case of the first embodiment. Therefore, the polarity of the voltage applied to each photosensitive drum 5 and the primary transfer roller 10 is different from that in the first embodiment.

  17 to 21 correspond to FIGS. 6 to 10 described in the first embodiment. That is, FIG. 17 to FIG. 19 explain the leading end region in the first image during printing for the region where the residual toner is discharged, and FIGS. 20 and 21 show the rear region in the last image during printing. Explains the edge area. As in the first embodiment, when the number of printed sheets is only one, the transfer residual toner is discharged to the leading edge and the trailing edge of the image. Further, in order to make it easy to determine the type of toner, the toner from the cartridge 4 is represented by a circle, and the transfer residual toner is represented by a square.

  FIG. 17 shows a transfer residual toner discharge operation immediately after the printer 1 receives a print signal. Similar to the first embodiment, when receiving the print signal, the printer 1 starts to convey the transfer material S by the paper feeding unit 2 based on the image information, and starts the image forming operation by the image forming unit 4. In the image forming unit 4, as described above, images are formed in order from the upstream side, but before the developing roller 7y contacts the most upstream photosensitive drum 5y, the charging roller 108 and the holding roller 117 are negatively charged. By applying a bias, the transfer residual toner charged negative is discharged. At the primary transfer portions T1y to T1c, the photosensitive drums 5y to 5c are controlled to be negative, and the primary transfer rollers 10y to 10c are controlled to be positive, and negative transfer residual toner is transferred to the primary transfer nip portions T1y to T1c. Then, it moves downstream while being carried on the intermediate transfer belt 11 (see FIG. 18).

  As shown in FIG. 18, the untransferred toner that has reached the most downstream photosensitive drum 5k is a negative bias applied to the primary transfer roller 10k, and the surface of the photosensitive drum 5k positively charged by the charging device 6k. Is moved to the photosensitive drum 5k. Then, it is scraped off by the photosensitive member cleaning blade 8k and collected in the cartridge 4k. Thereafter, when development on the photosensitive drum 5y begins to be performed in the most upstream image forming portion (cartridge) 4y, the developing roller 7y develops the toner image on the electrostatic latent image portion on the photosensitive drum 5y. Contact a little earlier than the area. At the stage where the developing roller 7y comes into contact, a small amount of toner moves to the photosensitive drum 5y, and thereafter, development is performed on the electrostatic latent image portion.

  The area where the residual toner is discharged is such that at least the discharged toner front end is interposed in the primary transfer nip T1k of the most downstream cartridge 4k when the discharged rear end of the toner passes through the primary transfer nip T1y of the uppermost stream cartridge 4y. It is supposed to be. Further, in all of the downstream cartridges 4m, 4c, and 4k, the developing roller 7y contacts the photosensitive drum 5y, and the discharged toner is primarily transferred before the minute toner begins to intervene in the primary transfer nip T1y. The nip portions T1m, T1c, and T1k are reached. At the rear end of the discharged toner, in the most upstream cartridge 4y, the minute toner is interposed in the primary transfer nip portion T1y so that the discharged toner and the minute toner overlap each other. In addition, a positive bias is applied to the charging roller 108 and the holding roller 117 in accordance with the beginning of the minute toner, and the discharge is stopped.

  When the primary transfer of the toner image is performed up to the most downstream cartridge 4k, as shown in FIG. 19, the toner image on the intermediate transfer belt 11 is transferred so that the leading edge is aligned with the toner image. Secondary transferred to S.

  This completes the description of the transfer residual toner discharge region at the leading end region in the first image. During continuous printing of the second and subsequent sheets, the developing roller 7 is always in contact with the photosensitive drum 5, and the toner in the cartridge 4 is interposed in the primary transfer nip T1. In the rear end region of the last image at the time of printing, the developing roller 7 and the photosensitive drum 5 are sequentially separated from the upstream cartridge 4y where the image formation is completed to the downstream cartridge 4k.

  As shown in FIG. 20, the charging roller 108 is negatively charged to the charging roller 108 and the holding roller 117 so that the untransferred toner starts to be immediately upstream from the time when the toner is not supplied to the primary transfer nip T1y from the most upstream cartridge 4y. Extinguishing is performed by applying a bias of. As shown in FIG. 21, the transfer residual toner is discharged so that the transfer residual toner is interposed in the primary transfer nip T1y of the most upstream cartridge 4y until the primary transfer of the toner image is completed in the most downstream cartridge 4k. Thereafter, the discharge is stopped by applying a positive bias to the charging roller 108 and the holding roller 117.

  Also in the present embodiment, the same effect as that of the first embodiment can be achieved.

1 Printer (image forming device)
4 (4y-4k) cartridge (image forming unit)
5 (5y-5k) Photosensitive drum (photosensitive member)
7 (7y-7k) Developing roller (developing means)
10A Intermediate transfer unit 10 (10y to 10k) Primary transfer roller (primary transfer means)
11 Intermediate transfer belt (intermediate transfer member)
14 Secondary transfer roller (secondary transfer means)
42 Contacting / separating means 100 Intermediate transfer belt cleaning device (cleaning means)
108 Charging roller (toner discharging means)
117 Holding roller 118 Bias roller

Claims (6)

A plurality of image forming units each including a photosensitive member on which an electrostatic latent image is formed, and a developing unit that develops the electrostatic latent image formed on the photosensitive member into a toner image;
Contacting / separating means for bringing the developing means into contact with and away from the photoreceptor;
An intermediate transfer member that moves along the plurality of image forming units and onto which a toner image of the photosensitive member is transferred;
Primary transfer means for transferring the toner image on the photosensitive member to the moving intermediate transfer member at a primary transfer portion;
Secondary transfer means for transferring the toner image of the intermediate transfer member to a transfer material at a secondary transfer portion;
A cleaning unit that is disposed upstream of the primary transfer unit and downstream of the secondary transfer unit with respect to a moving direction of the intermediate transfer member, and removes transfer residual toner of the intermediate transfer member;
In an image forming apparatus having
The cleaning means has discharge means for discharging the toner removed from the intermediate transfer body to the intermediate transfer body again,
The toner image developed by the developing unit is moved by moving the developing unit in the most upstream image forming unit that forms an image with respect to the moving direction of the intermediate transfer body from the separated state to the contact state with respect to the photoconductor. The discharge unit discharges the toner to the intermediate transfer member at a timing when the toner removed by the cleaning unit is interposed in the primary transfer unit until reaching the primary transfer unit, and / or
The toner image developed by the developing unit is moved by moving the developing unit in the most upstream image forming unit that forms an image with respect to the moving direction of the intermediate transfer body from a contact state to a separated state with respect to the photoconductor. The discharging unit discharges the toner to the intermediate transfer member at a timing when the toner removed by the cleaning unit is interposed in the primary transfer unit after being removed from the primary transfer unit.
An image forming apparatus.   In the image forming unit disposed downstream from the most upstream image forming unit, the developing unit of each of the image forming units is configured such that the primary transfer unit in the upstream image forming unit is transferred from the photoconductor to the intermediate transfer unit. The image forming apparatus according to claim 1, wherein the image forming apparatus moves from a separated state to a contact state with respect to the photosensitive member during primary transfer of a toner image to the body.   The developing unit of each image forming unit applies the toner image to the photosensitive member when the primary transfer unit in the downstream image forming unit performs primary transfer of the toner image from the photosensitive member to the intermediate transfer member. The image forming apparatus according to claim 1, wherein the image forming apparatus moves from a contact state to a separated state.   The image forming apparatus according to claim 1, wherein the cleaning unit includes a temporary storage unit that stores toner removed from the intermediate transfer member.   The discharging unit is a charging roller that discharges toner stored in the temporary storage unit to the intermediate transfer member, and applies a bias voltage to the charging roller to discharge toner to the intermediate transfer member. Item 5. The image forming apparatus according to any one of Items 1 to 4.   The image forming apparatus according to claim 1, wherein the charging roller is capable of contacting and separating from the intermediate transfer member.

Images