JP2004348064A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To eliminate the speed irregularity of an image carrier caused by frictional sliding on a cleaning member, particularly at the time of forming an electrostatic latent image by an image forming apparatus in which a developing rotary unit is mounted and where developing switching operation is performed. <P>SOLUTION: The image forming apparatus 1 is equipped with a developing means 8 having a developing roller abutting on the image carrier 3 on which the electrostatic latent image is formed and developing the image, a transfer means transferring a toner image from the image carrier 3 to an intermediate transfer medium 12 and a cleaning means 7 abutting on the image carrier 3 and removing residual toner after transfer, and the developing roller 6a is separated from the image carrier 3 so as to perform the developing switching operation. Then, the toner image being a corrective action image is formed on the image carrier 3 passing through a developing position in the midst of the developing switching operation that the roller 6a is separated from the image carrier 3 and on the medium 12 opposed to the image carrier 3 so as to prevent a situation that lubricant is not supplied to the image carrier 3 in the midst of the developing switching operation. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention is directed to an image carrier on which an electrostatic latent image is formed, a developing unit having a developing roller for abutting against the image carrier to perform development, and an intermediate transfer of the developed toner image on the image carrier. A transfer unit that transfers the image onto a medium; and a cleaning unit that abuts on the image carrier to remove residual toner after the transfer. The developing roller is separated from the image carrier to perform a development switching operation. The image forming apparatus according to
[0002]
[Prior art]
In the image forming apparatus, a charging device for uniformly charging the photoconductor along the rotation direction on an 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 photoconductor to the transfer member, a cleaner for cleaning the surface of the photoconductor after transfer, and the like are provided. Then, the electrostatic latent image formed on the photosensitive member by the exposure device is developed by a developing device to form a toner image, and the formed toner image is transferred to a transfer member, and the residual image on the photosensitive member after transfer is formed. The toner is removed from the photoreceptor by a cleaner.
[0003]
In the case of a rotary full-color image forming apparatus that forms a full-color image, a color toner image formed on a photoconductor by a developing device for each of yellow Y, magenta M, cyan C, and black K is transferred onto an intermediate transfer medium. Transfer and color superimpose sequentially. Therefore, the developing cartridge for each toner 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 drive the developing toner. The developing operation is performed by rotating the developing cartridge to the developing position (for example, see Patent Documents 1 and 2).
[0004]
[Patent Document 1]
JP-A-2002-82532
[Patent Document 2]
JP-A-2003-66801
[Problems to be solved by the invention]
2. Description of the Related Art In an image forming apparatus, an electrostatic latent image on a photoreceptor is repeatedly exposed in a rotation axis direction (main scanning direction) of a photoreceptor by an exposure beam of an exposure apparatus in which an outer peripheral surface uniformly rotating is modulated by an image forming signal. It is formed by doing. Since the latent image is formed by scanning with the exposure beam while the photoconductor is rotating, if the rotation of the photoconductor is unstable and there is vibration or unevenness, banding appears in the sub-scanning direction. Is degraded.
[0007]
Factors that cause the rotation of the photoconductor to be unstable and cause vibration and unevenness may be due to the configuration of the drive train, but a member that contacts along the outer periphery of the photoconductor, a cleaning member, and a rotary type In such a color image forming apparatus, there is a developing rotary unit for performing a developing color switching operation.
[0008]
When the toner image formed on the photoconductor is transferred to the transfer member, the cleaning member cleans the residual toner on the photoconductor after the transfer, and in order to enhance the cleaning effect, an appropriate member is required. At the same time, the residual toner is removed from the photoreceptor by being brought into contact with the outer peripheral surface of the photoreceptor at a constant pressure by a spring or the like. If the contact pressure is weak, the cleaning effect naturally decreases, but if the contact pressure is increased, irregular vibrations due to frictional sliding between the outer peripheral surface of the photoconductor and the cleaning member may be caused. In addition, the angle at which the blade contacts the outer peripheral surface of the photoreceptor, the position of a fulcrum supporting the cleaning member with respect to the tangent of the contact surface, and the like also influence.
[0009]
Further, in an image forming apparatus in which the developing roller separates from the developing position of the photoconductor and retreats or switches the development with respect to the image forming apparatus in which the developing roller is always in contact with the photoconductor, the speed variation of the photoconductor is Is easily observed. For example, in a rotary type color image forming apparatus having a developing rotary unit, the developing rotary unit is rotated by a developing color switching operation, and the mounted developing cartridge contacts and separates from the photoreceptor each time. The state of the outer peripheral surface of the photoconductor is not uniformly maintained between the contact state and the separated state, and the frictional sliding of the cleaning member is not performed smoothly, and the speed of the photoconductor becomes unstable. is there.
[0010]
[Means for Solving the Problems]
SUMMARY OF THE INVENTION The present invention solves the above-described problems, and eliminates unevenness in the speed of an image carrier due to frictional sliding with a cleaning member. In particular, an electrostatic latent image of an image forming apparatus equipped with a development rotary unit and performing a development switching operation. This is to eliminate unevenness in the speed of the image carrier during image formation.
[0011]
For this purpose, the present invention provides an image bearing member on which an electrostatic latent image is formed, a developing unit having a developing roller that contacts the image bearing member to perform development, and develops the toner image on the image bearing member. A transfer unit that transfers the image onto the intermediate transfer medium; and a cleaning unit that abuts on the image carrier to remove residual toner after the transfer. The developing roller is separated from the image carrier to perform a development switching operation. In the image forming apparatus, the toner image of the countermeasure image is formed on the intermediate transfer medium facing the image carrier passing the developing position during the development switching operation in which the developing roller is separated from the image carrier. It is characterized by forming.
[0012]
The formation of the toner image of the countermeasure image is performed in a certain period or a certain number of times of forming the image, and the toner image of the countermeasure image is formed by a line image at a certain interval or a dot pattern image at a certain interval. A reverse transfer from the intermediate transfer medium onto the image carrier passing the development position during the development switching operation, wherein the transfer unit performs primary transfer from the image carrier to the intermediate transfer medium; A transfer unit, a secondary transfer unit for performing a secondary transfer from the intermediate transfer medium to the recording medium, and a secondary cleaning unit for removing residual toner after the secondary transfer on the intermediate transfer medium; Is characterized in that the secondary cleaning means is separated so as not to be removed from the intermediate transfer medium.
[0013]
The developing unit includes a developing rotary unit that carries out a development switching operation by mounting a developing cartridge on a rotary rotating frame, and the developing rotary unit is equipped with a plurality of developing cartridges having different toner colors. The cleaning means may cause the blade to contact the image carrier at a predetermined pressure with a fulcrum as a rotation center, and the fulcrum may be provided outside the image carrier with respect to a tangent to the abutment. .
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a view 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 exposing device, 6 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, 15 is a secondary transfer roller, 16 is a power supply device, and 17 is paper feed. A tray, 20 is a fixing unit, 21 is a paper discharge tray, and 22 is a paper transport unit.
[0015]
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 part of a main body case 2 and a front cover 2a that is openably and closably mounted on a front surface. In the main body case 2, a developing rotary unit 8 having a plurality of developing cartridges mounted thereon, 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 unit 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 provided. A paper transport unit 22 that transports the recording medium from the paper feed tray 17 to the fixing unit 20 through the secondary transfer roller 15 is provided in the front cover 2a. Each unit is configured to be detachable from the main body, and is configured to be integrally detachable for repair or replacement during maintenance or the like.
[0016]
The photoreceptor 3 serving as an image carrier has a thin cylindrical conductive substrate and a photosensitive layer formed on the surface thereof. A charging device 4 for uniformly charging the photoconductor 3 along the rotation direction and an exposure device (or a writing device) for forming an electrostatic latent image on the photoconductor 3 are provided on the outer periphery of the photoconductor 3. 5.) a developing rotary unit 8 for developing the electrostatic latent image, an intermediate transfer belt 12 on which the toner image on the photoconductor 3 is transferred, and an intermediate transfer unit for primary 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 provided.
[0017]
The intermediate transfer unit is composed of a drive 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 indicated by the arrow 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, for primary transfer of the toner image on the photoconductor 3 to the intermediate transfer belt 12, And a transfer belt cleaner 14 for removing the residual toner from the intermediate transfer belt 12, and a four-color full-color toner image formed on the intermediate transfer belt 12 is secondarily transferred onto a recording medium (paper or the like). And a secondary transfer roller 15 for performing the transfer.
[0018]
A power supply device 16 is provided below the exposure device 5, and a paper feed cassette 17 is provided at the bottom of the main body case 2. The recording medium in the paper feed cassette 17 is provided with a pickup roller 18, a sheet material conveyance path, and the like. 19, the secondary transfer roller 15, and the fixing device 20 are configured to be conveyed to a paper discharge tray 21. The paper feed cassette 17 is mounted so as to be able to be pulled out to the front of the apparatus by a handle 17b, and an auxiliary cassette 17a is mounted so as to be able to be drawn out so as to protrude to the rear of the apparatus so as to cope with a case where the paper size is large. I have.
[0019]
In the image forming apparatus 1 having the above configuration, when an image forming signal is input to the exposure device 5, the photosensitive member 3, the developing roller 6a of the developing rotary unit 8, the intermediate transfer belt First, the outer peripheral surface of the photoconductor 3 is uniformly charged by the charging device 4. Thereafter, the exposure device 5 performs selective exposure on the surface of the photoconductor 3 according to 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 comes into contact with the photoconductor 3. As a result, a toner image of an electrostatic latent image is formed on the photoconductor 3. The toner image formed on the photoconductor 3 is transferred onto the intermediate transfer belt 12 by a primary transfer roller 13 to which a primary transfer voltage having a polarity opposite to the charging polarity of the toner is applied, and remains on the photoconductor 3. The remaining toner is removed by the photoconductor cleaner 7.
[0020]
In the full-color image forming apparatus, developing cartridges 6Y, 6M, 6C, and 6K for yellow Y, magenta M, cyan C, and black K are detachably mounted on the developing rotary unit 8. In the image forming operation, the exposure device 5 performs selective exposure on the surface of the photoconductor 3 in accordance with the first color, for example, yellow Y image information, and forms 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 comes into contact with the photoreceptor 3, and a toner image of a yellow Y electrostatic latent 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 charged polarity of the toner is applied.
[0021]
During this time, the transfer belt cleaner 14 and the secondary transfer roller 15 are separated from the intermediate transfer belt 12. The four-color full-color image is obtained by repeating this series of processing in correspondence with the second, third, and fourth colors of the image forming signal, so that yellow Y, The magenta M, cyan C, and black K toner images are sequentially superimposed and transferred on the intermediate transfer belt 12 from the photoconductor 3 to be formed.
[0022]
Then, at the timing when the image on which the toner images of the respective colors are superimposed reaches the secondary transfer roller 15, the recording medium in 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. When the secondary transfer roller 15 is pressed against the intermediate transfer belt 12 and a secondary transfer voltage is applied, 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 onto which the toner image has been transferred in this way is conveyed to the fixing unit 20 by the paper conveying unit 22, the fixing unit 20 heats and pressurizes the toner image on the recording medium and fixes it. The toner remaining on the intermediate transfer belt 12 is removed by the transfer belt cleaner 14.
[0023]
In the case of double-sided printing, the recording medium that has exited the fixing unit 20 is switched back so that the rear end thereof is at the front end, passes through the conveyance path for double-sided printing of the paper conveyance unit 22, and is again returned to the secondary transfer roller 15. The full-color toner image on the intermediate transfer belt 12 is transferred onto a recording medium, heated and pressed again by the fixing unit 20 to be fixed, and is discharged onto a discharge tray 21.
[0024]
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, and a four-color full-color image forming apparatus is provided. As an apparatus, only the developing cartridge 6K of black K toner is mounted and mounted, the developing cartridge 6K stands by at a standby position (home position), and the black K developing cartridge 6K rotates and moves from the standby position during image formation. At the development position, the electrostatic latent image on the photoconductor 3 may be developed into a toner image. As a result, the developing rotary unit 8 having the same design specification can be used for the full color and the mono color, and the maintenance and management can be performed as compared with the case of designing the image forming apparatus dedicated to the full color and the mono color by sharing the full color and the mono color. Design and manufacturing costs can be significantly reduced.
[0025]
Next, a mechanism relating to the speed unevenness of the photoconductor and a countermeasure thereof will be described. FIG. 2 is a diagram showing measurement data for observing the speed unevenness of the photoconductor, and FIG. 3 is a diagram for explaining an area where the speed unevenness of the photoconductor occurs according to an operation sequence.
[0026]
In the color image forming apparatus of the present embodiment, when the developing rotary unit 8 is at the home position in the standby state, none of the developing cartridges 6Y, 6M, 6C, and 6K is at the developing position facing the photosensitive member 3. That is, the developing roller 6a is not in contact with the photoconductor 3. Normally, when the developing roller 6a is in contact with the photoreceptor 3, even if there is no image writing from the exposure device 5, a little fog toner is placed on the photoreceptor 3, and the fog toner contacts the photoreceptor cleaner 7. By acting as a kind of lubricant on the contact surface, the photosensitive member 3 smoothly frictionally slides against the photosensitive member cleaner 7, and the speed unevenness of the photosensitive member 3 is slight.
[0027]
However, while the developing roller 6a is separated from the photoreceptor 3, the surface of the photoreceptor 3 cleaned by the photoreceptor cleaner 7 rotationally moves and comes into contact with the photoreceptor cleaner 7 again to frictionally slide. Since there is no toner at all, the frictional resistance of the photoconductor 3 is increased at the contact surface with the photoconductor cleaner 7 without the so-called lubricant, and the rotation speed of the photoconductor 3 becomes unstable. In other words, it is considered that the frictional resistance of the surface of the photoreceptor 3 is increased, so that the photoreceptor 3 repeats minute locking and sliding phenomena with respect to the photoreceptor cleaner 7, and the speed unevenness and vibration of the photoreceptor 3 appear.
[0028]
This can be recognized from FIG. In FIG. 2, the vertical axis represents speed unevenness, and the horizontal axis represents time. First, periodic large speed unevenness appears here at the joint between encoders that performs rotation detection, and signal disturbance. , Which is not directly indicative of rotational disturbances and is therefore ignored. This measurement data indicates that a developing color switching operation of switching the developing cartridge 6 and bringing the developing roller 6a into contact with the photosensitive member 3 is performed in accordance with the timing of performing exposure by an image signal for each of the colors Y, M, C, and K. A time period t (between 0 and 6) in which the speed unevenness is large is observed immediately after the start of the exposure. Then, the speed unevenness has been resolved after the developing roller 6a has been in contact with the photoreceptor 3 for a period of time from when the developing roller 6a contacts the photoreceptor cleaner 7, and thereafter.
[0029]
Further, a region where the speed unevenness of the photosensitive member occurs will be described with reference to an operation sequence. FIG. 3 shows an outline of an operation sequence of the color image forming apparatus according to the present embodiment, and includes a vsync signal, a transfer belt motor, a scanner motor, an image signal, a rotary operation, a developing operation, a primary transfer bias, and a 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 indicates the developing operation start point, that is, the position on the photosensitive member 3 where the developing color switching operation is completed and the developing roller 6a is in contact. Similarly, the oblique dotted line n indicates a developing operation end point, that is, a position on the photoconductor 3 where the developing roller 6a is separated by the start of the developing color switching operation.
[0030]
As shown in FIG. 3, the photosensitive drum 3, the developing roller 6a of the developing rotary unit 8, the medium drive motor and the scanner motor of the exposure device 5 start to be driven to rotate the intermediate transfer belt 12, the scanner and the photosensitive drum 3. After the start, the developing color switching operation by the developing rotary unit 8 is started, the outer peripheral surface of the photoconductor 3 is uniformly charged by the charging device 4, and the image signal is turned on in synchronization with the vsync signal to expose the image. And image formation is sequentially performed. Then, by turning on the primary transfer bias in synchronization with the start of image formation, the toner image on the photoconductor is primarily transferred onto the intermediate transfer belt 12.
[0031]
As shown in FIG. 1, the exposure point on the photoreceptor 3 is on the rotation upstream side of the developing position, and when the exposure is started and the image signal is turned on as shown in FIG. 3, the exposure position is rotationally moved to the developing position. By this time, the developing roller 6a may be in contact with the photoconductor 3, and the time when the developing roller 6a comes into contact with the photoconductor 3 and the development is started is slightly delayed from the time when the image signal is turned on. The position on the photoconductor 3 where the developing roller 6a is in contact with is rotationally moved to the photoconductor cleaner position when the dotted line m in the drawing crosses the photoconductor cleaner position.
[0032]
Therefore, during the time t 'from the time when the image signal is turned on to the time when the dotted line m crosses the photosensitive member cleaner position, the developing roller 6a is not in contact, that is, the toner serving as the lubricant exists on the photosensitive member 3. In this state, the peripheral surface of the photoconductor 3 frictionally slides with the photoconductor cleaner 7, thereby forming a region where the speed unevenness of the photoconductor 3 occurs. In the second to fourth colors as well, similar regions where the speed unevenness of the photosensitive member 3 occurs appear from the development operation end point (n) to the development operation start point (m).
[0033]
In the color image forming apparatus of the present embodiment, toner and other lubricant are supplied onto the photoconductor 3 during the switching operation of the developing device in which the developing roller 6a is not in contact with the photoconductor 3. During the switching operation, the operation is performed on the surface of the photoconductor 3 which is originally in contact with the developing roller 6a, facing the developing position. However, as described above, before the image signal is turned on and the exposure is started, the image is not directly affected and the image unevenness due to the speed unevenness does not occur. Therefore, at least at the time when the image signal is turned on, that is, the latent image is formed on the photoconductor 3. It is sufficient that toner or other lubricant is supplied to the photoconductor 3 facing the blade of the photoconductor cleaner 7 at the start of the exposure, and toner or other lubricant is supplied to the photoconductor 3 facing the blade of the photoconductor cleaner 7. The exposure may not be performed when the lubricant is not supplied.
[0034]
In the present embodiment, the supply of the lubricant forms a toner image of a countermeasure image on the intermediate transfer belt 12 facing the photoconductor 3 passing the development position during the development switching operation in which the developing roller 6a is separated from the photoconductor 3. It is done by doing. As a result, at the primary transfer point where the intermediate transfer belt 12 abuts on the photoconductor 3, the primary transfer bias, speed, and pressure are controlled, or the intermediate transfer belt 12 can be controlled without any special control. Since the toner image of the countermeasure image is reverse-transferred onto the photoconductor 3, the toner reverse-transferred onto the photoconductor 3 acts as a lubricant between the photoconductor cleaner 7 and the speed of the photoconductor 3 is reduced. Maintains stable. Of course, it can also be performed by disposing a lubricant applying means around the photoreceptor 3.
[0035]
FIG. 4 is a diagram showing an operation sequence of an embodiment for forming a countermeasure image, and FIG. 5 is a diagram showing an embodiment using a lubricant applying device as a lubricant applying means disposed around a photoreceptor. FIG. 6 is a view showing an embodiment in which a rotary brush is used as a lubricant applying means disposed around the photoconductor.
[0036]
In order to reversely transfer the toner image from the intermediate transfer belt 12 onto the photoconductor 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 a toner image or fog toner transferred from the photoreceptor 3 at a primary transfer point.
[0037]
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 photoconductor 3. In this case, as shown in FIG. 4, prior to the formation of a print image, first, a countermeasure image is formed, a primary transfer bias is controlled, and a toner image of the countermeasure image is transferred onto the intermediate transfer belt 12 in advance. From (1), image formation for the first color is started. As a result, since the residual toner of the toner image of the countermeasure image exists on the photoconductor 3, the photoconductor 3 and the photoconductor cleaner 7 smoothly slide with each other, so that the speed unevenness does not occur. In the second to fourth colors, the primary transfer bias is controlled on the photosensitive member 3 during the developing color switching operation in which the developing roller 6a does not come into contact with the photosensitive member 3, and the countermeasure image is removed from the intermediate transfer belt 12. The toner image is reversely transferred to supply toner ((2) to (4)). As a result, it is possible to eliminate at least the time during which the lubricant does not exist at the contact portion between the photoconductor 3 and the photoconductor cleaner 7 during the formation of the latent image by the exposure beam B.
[0038]
Considering that the developing roller 6a is in contact with the photosensitive member 3 at the developing position, when a toner image is not formed on the photosensitive member 3, the developing roller 6a contacts the photosensitive member cleaner 7 by fogging toner from the developing roller 6a to the photosensitive member 3. The role of the lubricant in the contact area is sufficient. Further, when a toner image is formed on the photoconductor 3, the toner image is primarily transferred to the intermediate transfer belt 12 at the primary transfer point, and the residual toner is used at a contact portion with the photoconductor cleaner 7. Its role as a lubricant is sufficient.
[0039]
As described above, the amount of toner from the intermediate transfer belt 12 to be reverse-transferred as a lubricant onto the photoreceptor 3 is small, and therefore, by controlling the amount of toner to be reverse-transferred at the primary transfer point, a plurality of It is also possible to reversely transfer a part of the toner little by little by repeating the process. The number of repetitions can be controlled by, for example, the number of image formations, the toner amount of the countermeasure image, and the bias at the time of reverse transfer.
[0040]
The toner image (measured image) previously transferred from the photoreceptor 3 to the intermediate transfer belt 12 is, for example, a periodic line image in which exposure by the exposure beam B from the exposure device 5 is set to one line on and ten lines off. , An image with a regular dot pattern can be used. On the intermediate transfer belt 12, an image area and a non-image area are allocated, and when the exposure device 5 starts exposing with the exposure beam B according to the image signal from that point, the photoconductor 3 and the photoconductor cleaner 7 The contact point is determined, and the area to which the toner is to be transferred is determined in advance based on the calculation.
[0041]
In the above-described embodiment, the toner image of the countermeasure image is placed on the intermediate transfer belt 12 in advance, and the developing roller 6a is separated at the time of the developing color switching operation of the developing rotary unit 8 so that the intermediate transfer is performed in a region where the lubricant on the photoconductor 3 is used up. The countermeasure image formation, the primary transfer, and the control of the transfer belt cleaner 14 were performed so that the toner was replenished onto the photoconductor 3 by reverse transfer from the belt 12. For example, as shown in FIG. 5, a lubricant application device 31 is provided so as to supply a lubricant onto the body 3, and a lubricant such as zinc stearate is lubricated separately from the waste toner removed from the photoconductor 3 by cleaning. The lubricant may be applied to the peripheral surface of the photoconductor 3 by the agent application device 31 so that the lubricant is not always cut off from the peripheral surface of the photoconductor 3. Further, as shown in FIG. 6, a rotating brush 32, a brush, and a waste toner circulating mechanism such as a roller are provided in the vicinity of the photosensitive member cleaner 7, and the waste toner removed from the photosensitive member 3 by the photosensitive member cleaner 7 is removed by the rotating brush 32. The toner may be circulated and returned to the peripheral surface of the photoreceptor 3 by a waste toner circulating mechanism such as a brush, a roller, or the like.
[0042]
FIG. 7 is a view showing an embodiment of the positional relationship of the fulcrum with respect to the tangent line of the blade of the photosensitive member cleaner. As shown in FIG. 7C, the fulcrum 7b is pressed at a predetermined pressure on the tangent p at which the blade 7a is in contact with the photoconductor 3, or as shown in FIG. It is provided outside the tangent line p (on the side opposite to the photoconductor 3). By setting the fulcrum 7b at such a position, the fulcrum 7b of the photoreceptor cleaner 7 is more susceptible to the disturbance of the rotation of the photoreceptor 3, However, the contact state of the photoconductor cleaner 7 with respect to the photoconductor 3 can be stably maintained.
[0043]
Next, control for replenishing toner from the intermediate transfer belt 12 onto the photoconductor 3 will be specifically described. FIG. 8 is a diagram for explaining how the countermeasure image is formed on the photoconductor, and FIG. 9 is a diagram in which the countermeasure image is transferred from the photoconductor to the intermediate transfer belt, and subsequently, a print image is formed on the photoconductor. FIG. 10 is a diagram for explaining a state in which the formation of a print image has been completed and the image has been transferred to an intermediate transfer belt. FIG. 11 is a diagram illustrating a state in which the developing rotary unit starts a developing color switching operation. FIG. 12 is a diagram for explaining a state in which the toner is reversely transferred from the intermediate transfer belt to the photoconductor, FIG. 12 is a diagram for explaining a state in which image formation of the next toner color is started, and FIG. FIG. 14 is a diagram for explaining a state during color image formation, FIG. 14 is a diagram for explaining a state of secondary transfer of an image in which all colors are superimposed, and FIG. 15 is a state at a cleaning start timing of a transfer belt cleaner. To explain It is a diagram of.
[0044]
In the image forming apparatus 1 of the present embodiment, first, before the image forming operation, the photoconductor 3, the developing roller 6a of the developing rotary unit 8, and the intermediate transfer belt 12 are driven to rotate 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. Then, as shown in FIG. 8, the surface of the photoconductor 3 is exposed to the countermeasure image by the exposure device 5, and an electrostatic latent image is formed. At this time, the developing rotary unit 8 rotates so that the developing roller 6 a of the developing cartridge 6 comes into contact with the photoconductor 3. As a result, a toner image 35 of the countermeasure image is formed on the photoconductor 3.
[0045]
When the toner image 35 of the countermeasure image is formed on the photoconductor 3, as shown in FIG. 9, the primary transfer roller 13 to which a primary transfer voltage having a polarity opposite to the charging polarity of the toner is applied, from above the photoconductor 3. The toner image is transferred onto the intermediate transfer belt 12 as a toner image 35 '. Then, exposure and development of the print image are started to form a toner image 36, and primary transfer is started.
[0046]
As described above, since the transfer belt cleaner 14 and the secondary transfer roller 15 are separated from the intermediate transfer belt 12, when the formation of the first color print image on the photoconductor 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 a developing color switching operation for forming an image of the second color, and as shown in FIG. 11, the developing rotary unit 8 is rotated in the direction of Rr and the developing roller 6a is moved to the photosensitive member. 3, the toner image 35 'of the countermeasure image previously transferred on the intermediate transfer belt 12 reaches the primary transfer point and is reverse-transferred onto the photoconductor 3 as a toner image 35 ". Even when the developing roller 6a is separated from the photoconductor 3, the toner is replenished on the photoconductor 3 at the primary transfer point, and is supplied as a lubricant to a contact portion with the photoconductor cleaner 7.
[0047]
Similarly, when the image formation of the second color is started, as shown in FIG. 12, when the exposure device 5 exposes the photoconductor 3 with the exposure beam B, the contact portion with the photoconductor cleaner 7 is formed. Is supplied with the toner 35 ″, which has been reversely transferred from the intermediate transfer belt 12 and replenished onto the photoconductor 3, as a lubricant, so that stable rotation of the photoconductor 3 can be maintained. An image forming operation is also performed.
[0048]
When the image formation for the fourth color is started, the images of all colors are superimposed on the intermediate transfer belt 12 as shown in FIG. 13, and the secondary transfer roller 15 is moved to the intermediate position as shown in FIG. Secondary transfer of the full-color toner image 37 ′ from the intermediate transfer belt 12 to the recording medium is started by contacting the transfer belt 12 to form a transfer image 37 ″. During this time, the transfer belt cleaner 14 is shown in FIGS. As shown in FIG. 15, the toner image 35 'of the countermeasure image on the intermediate transfer belt 12 passes through the intermediate transfer belt 12 as shown in FIG. The cleaning of the residual toner corresponding to the print image area is started, and the residual toner after the secondary transfer of the print image on the intermediate transfer belt 12 is removed.
[0049]
Note that the present invention is not limited to the above embodiment, and various modifications are possible. For example, in the above-described embodiment, the problem during the developing color switching operation of the rotary four-color full-color image forming apparatus has been described. However, during standby, the developing roller is held in a state of being separated from the photoreceptor, and image forming is performed. If the developing roller is brought into contact with the photoreceptor in accordance with the execution of the job, the image forming apparatus is not necessarily a rotary image forming apparatus equipped with a developing rotary unit, and whether or not the developing rotary unit is installed. Regardless, it goes without saying that the present invention can be similarly applied to a mono-black image forming apparatus and the same problem can be solved. Further, when the countermeasure image is reverse-transferred from the intermediate transfer belt onto the photoreceptor, not only a reverse bias is applied but also the primary transfer bias is lowered so that the potential difference is reduced or turned off. The secondary transfer bias may be controlled, the primary transfer speed may be changed, or the pressure of the primary transfer roller may be changed. Further, the countermeasure image may be formed not only with the first color or the black K toner image but also with, for example, a low-visibility yellow Y toner image, or may be formed immediately before the first color image formation. This is done at the time of position setting operation to the standby state at the time of replacing the cartridge or unit, or when starting the image forming operation from the standby state, and thereafter forming the intermediate transfer belt on the intermediate transfer belt on a fixed basis according to the number of job executions. You may keep it.
[0050]
【The invention's effect】
As is apparent from the above description, according to the present invention, an image bearing member on which an electrostatic latent image is formed, a developing unit having a developing roller that contacts the image bearing member to perform development, A transfer unit that transfers the toner image on the image carrier onto the intermediate transfer medium; and a cleaning unit that abuts on the image carrier and removes residual toner after transfer. The developing roller is separated from the image carrier. In the image forming apparatus, the developing roller is separated from the image bearing member during the developing switching operation, and the toner of the countermeasure image is formed on the intermediate transfer medium facing the image bearing member passing the developing position during the developing switching operation. Since an image is formed, it is possible to prevent the toner as a lubricant from being supplied to the image carrier during the development switching operation, and to smoothly frictionally slide the cleaning unit that contacts the image carrier. Carrier It is possible to reduce the speed variation. Therefore, the speed unevenness of the image carrier due to frictional sliding with the cleaning member is eliminated, and particularly, the speed unevenness of the image carrier at the time of forming an electrostatic latent image of the image forming apparatus mounted with the developing rotary unit and performing the development switching operation is reduced. Can be eliminated.
[0051]
The formation of the toner image of the countermeasure image is performed with a certain period or a certain number of image formation cycles, and the toner image of the countermeasure image is formed by a line image at a certain interval or a dot pattern image at a certain interval. During the switching operation, reverse transfer is performed from the intermediate transfer medium onto the image carrier passing through the developing position, and the transfer unit performs primary transfer from the image carrier to the intermediate transfer medium and records from the intermediate transfer medium with the primary transfer unit A secondary transfer unit for performing secondary transfer on the medium; and a secondary cleaning unit for removing residual toner after the secondary transfer on the intermediate transfer medium, so that the toner image of the countermeasure image is not removed from the intermediate transfer medium. Since the secondary cleaning means is separated from the image carrier, it is possible to prevent the toner as a lubricant from being supplied to the image carrier with a simple structure, and to smoothly slide the cleaning means which always contacts the image carrier. Rukoto can, it is possible to reduce the speed variation of the image carrier.
[0052]
The developing means includes a developing rotary unit that carries out a development switching operation by mounting a developing cartridge on a rotary rotating frame, and the developing rotary unit includes a plurality of developing cartridges having different toner colors. It is possible to prevent the lubricant from being supplied to the image carrier due to the unit-specific development switching operation, and the cleaning means causes the blade to contact the image carrier at a predetermined pressure with the fulcrum as the rotation center. At the same time, the fulcrum is provided outside the image carrier from the tangent line where it comes into contact, so that the blade can be brought into contact with the image carrier in a stable state, and the cleaning means that always abuts on the image carrier smoothly frictionally slides. And unevenness in the speed of the image carrier can be reduced.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating an embodiment of an image forming apparatus according to the present invention.
FIG. 2 is a diagram showing measurement data for observing unevenness in speed of a photoconductor.
FIG. 3 is a diagram for explaining a speed unevenness generation region of a photoconductor by an operation sequence.
FIG. 4 is a diagram showing an operation sequence of an embodiment for forming a countermeasure image.
FIG. 5 is a diagram illustrating an embodiment in which a lubricant applying device is used as a lubricant applying unit disposed around a photosensitive member.
FIG. 6 is a diagram showing an embodiment in which a rotary brush is used as a lubricant applying unit disposed around a photosensitive member.
FIG. 7 is a diagram illustrating an embodiment of a positional relationship of a fulcrum with respect to a tangent line of a blade of the photoconductor cleaner.
FIG. 8 is a diagram illustrating a state in which a countermeasure image is formed on a photoconductor.
FIG. 9 is a view for explaining a state in which a countermeasure image is transferred from the photoconductor to the intermediate transfer belt and a print image is subsequently formed on the photoconductor.
FIG. 10 is a diagram for explaining a state in which formation of a print image is completed and the image is transferred to an intermediate transfer belt.
FIG. 11 is a diagram for explaining a state in which the developing rotary unit starts the developing color switching operation and simultaneously reversely transfers the toner from the intermediate transfer belt to the photosensitive member.
FIG. 12 is a diagram illustrating a state in which image formation of the next toner color is started.
FIG. 13 is a diagram illustrating a state during image formation of a final color.
FIG. 14 is a diagram for explaining a state in which an image in which all colors are superimposed is secondarily transferred.
FIG. 15 is a view for explaining a state at a cleaning start timing of the transfer belt cleaner.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 2 ... Body case, 3 ... Photoconductor, 4 ... Charging device, 5 ... Exposure device, 6 ... Developing cartridge, 7 ... Photoconductor cleaner, 8 ... Development rotary unit, 9 ... Rotary frame, 12 ... Intermediate transfer belt, 13: primary transfer roller, 15: secondary transfer roller, 16: power supply device, 17: paper feed tray, 20: fixing unit, 21: paper discharge tray, 22: paper transport unit

Claims (10)

An image carrier on which an electrostatic latent image is formed, a developing unit having a developing roller for abutting the image carrier to perform development, and transferring the developed toner image on the image carrier to an intermediate transfer medium An image transfer device, and a cleaning device that abuts on the image carrier to remove residual toner after transfer, wherein the developing roller is separated from the image carrier to perform a development switching operation. In the forming apparatus, a toner image of a countermeasure image is formed on an intermediate transfer medium facing a surface of the image carrier that passes through a development position during a development switching operation in which the developing roller is separated from the image carrier. Image forming apparatus. 2. The image forming apparatus according to claim 1, wherein the formation of the toner image of the countermeasure image is performed with a certain period as a cycle. The image forming apparatus according to claim 1, wherein the forming of the toner image of the countermeasure image is performed with a certain number of image forming cycles. The image forming apparatus according to claim 1, wherein the toner image of the countermeasure image is formed as a line image at a constant interval. The image forming apparatus according to claim 1, wherein the toner image of the countermeasure image is formed by a dot pattern image at regular intervals. 6. The image forming apparatus according to claim 1, wherein the toner image of the countermeasure image is reversely transferred from the intermediate transfer medium onto the image carrier passing a developing position during the development switching operation. Image forming apparatus. A transfer unit configured to perform primary transfer from the image carrier to the intermediate transfer medium; a secondary transfer unit configured to perform secondary transfer from the intermediate transfer medium to a recording medium; 2. A secondary cleaning device for removing residual toner after transfer, wherein the secondary cleaning device is separated so that the toner image of the countermeasure image is not removed from the intermediate transfer medium. An image forming apparatus according to any one of claims 1 to 6. 2. The image forming apparatus according to claim 1, wherein the developing unit includes a developing rotary unit that mounts a developing cartridge on a rotary rotating frame and rotates and performs a developing switching operation. 9. The image forming apparatus according to claim 8, wherein the developing rotary unit includes a plurality of developing cartridges having different toner colors. The cleaning means may cause the blade to contact the image carrier at a predetermined pressure with a fulcrum as a rotation center, and the fulcrum may be provided outside the image carrier with respect to a tangent line with which the contact is made. The image forming apparatus according to claim 1.

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