JP3835552B2 - Image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image bearing member on which an electrostatic latent image is formed, a latent image forming unit that forms a latent image on the image bearing member, and a developing unit that has a developing roller that contacts and develops the image bearing member. Transfer means for transferring the developed toner image on the image carrier onto the transfer body, and cleaning means for contacting the image carrier to remove residual toner after transfer. The image forming apparatus in which the developing roller is separated from the image carrier to perform the development switching operation.
[0002]
[Prior art]
In the image forming apparatus, a charging device for uniformly charging the photoconductor along the rotation direction on the outer periphery of the photoconductor as an image carrier, an exposure device for forming an electrostatic latent image on the photoconductor, A developing device for developing the electrostatic latent image, a transfer device for transferring the toner image on the photosensitive member to the transfer member, a cleaner for cleaning the surface of the photosensitive member after the transfer, and the like are provided. Then, the electrostatic latent image formed on the photosensitive member by the exposure device is developed by the developing device to form a toner image, the formed toner image is transferred to the transfer member, and the residual image on the photosensitive member after the transfer is transferred. The toner is removed from the photoreceptor by a cleaner.
[0003]
In the case of a rotary-type full-color image forming apparatus that forms a full-color image, a color toner image formed on a photosensitive member by a developing device of yellow Y, magenta M, cyan C, and black K is placed on an intermediate transfer medium. Sequential transfer and color overlay. Therefore, each toner developing cartridge is detachably mounted on the developing rotary unit, and each time an electrostatic latent image for each color is formed on the photoreceptor, the developing rotary unit is driven by a developing color switching operation to The developing cartridge is rotated to the developing position to perform the developing operation (see, for example, Patent Documents 1 and 2).
[0004]
[Patent Document 1]
JP 2002-82532 A
[Patent Document 2]
Japanese Patent Laid-Open No. 2003-66801
[Problems to be solved by the invention]
In the image forming apparatus, the electrostatic latent image on the photosensitive member is repeatedly exposed in the rotation axis direction (main scanning direction) of the photosensitive member by the exposure beam of the exposure device whose outer peripheral surface that is uniformly rotated is modulated by the image forming signal. Is formed. Since the exposure beam is scanned and exposed to form a latent image while the photoconductor is rotating, if the photoconductor rotates unstable and there are vibrations or unevenness, streaks appear in the sub-scanning direction, resulting in banding. This causes the problem of deterioration.
[0007]
Factors that cause unstable rotation of the photosensitive member and cause vibration and unevenness are due to the structure of the train wheel of the drive system, but there are members that contact the outer periphery of the photosensitive member, cleaning members, and rotary type. In such a color image forming apparatus, there is a developing rotary unit for performing a developing color switching operation.
[0008]
When the toner image formed on the photosensitive member is transferred to the transfer member, the cleaning member cleans the residual toner on the photosensitive member after the transfer. In order to enhance the cleaning effect, an appropriate member is used. In addition, the residual toner is removed from the photosensitive member by contacting the outer peripheral surface of the photosensitive member with a constant pressure by a spring or the like. If the contact pressure is weak, the cleaning effect is naturally reduced. However, if the contact pressure is increased, irregular vibration associated with frictional sliding between the outer peripheral surface of the photosensitive member and the cleaning member is caused. Further, the angle at which the blade contacts the outer peripheral surface of the photosensitive member, the position of the fulcrum that supports the cleaning member with respect to the tangent to the contact surface, and the like also have an effect.
[0009]
Further, in an image forming apparatus in which the developing roller is retracted away from the developing position of the photosensitive member or the development is switched with respect to the image forming device in which the developing roller is always in contact with the photosensitive member, the speed variation of the photosensitive member is reduced. It is observed that is prone to occur. For example, in a rotary type color image forming apparatus provided with a developing rotary unit, the developing rotary unit is rotated and moved by a developing color switching operation, and the mounted developing cartridge is repeatedly contacted and separated from the photosensitive member each time. There is a problem that the state of the outer peripheral surface of the photoconductor is not uniformly maintained in the contact state and the separated state, the frictional sliding of the cleaning member is not smoothly performed, and the speed of the photoconductor becomes unstable. is there.
[0010]
[Means for Solving the Problems]
The present invention solves the above-described problems, eliminates unevenness of the speed of the image carrier due to frictional sliding with the cleaning member, and in particular, provides an electrostatic latent image of an image forming apparatus that is equipped with a developing rotary unit and performs a developing switching operation. It is intended to eliminate unevenness in the speed of the image carrier during image formation.
[0011]
Therefore, the present invention includes an image carrier on which an electrostatic latent image is formed, a latent image forming unit that forms a latent image on the image carrier, and a developing roller that performs development in contact with the image carrier. A developing means; a first transfer means for transferring the toner image developed on the image carrier onto an intermediate transfer medium; and a second for transferring the toner image transferred onto the intermediate transfer medium onto a recording medium. Transfer means, a first cleaning means that contacts the image carrier to remove residual toner after transfer, and the intermediate transfer medium by contacting or separating and contacting the intermediate transfer medium. A second cleaning unit for removing toner on the medium , wherein the developing unit separates the developing roller from the image carrier and performs a development switching operation. Means breaker And the toner transferred on the intermediate transfer medium is transported without being removed, and the toner transported by the first transfer means is reversely transferred onto the image carrier, and at least the latent image is transferred. And a toner replenishing unit that replenishes the toner so that the toner is present on the image bearing member facing the blade of the first cleaning unit at the start of latent image formation by the forming unit.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing an embodiment of an image forming apparatus according to the present invention. In the figure, 1 is an image forming apparatus, 2 is a main body case, 3 is a photoreceptor, 4 is a charging device, 5 is an exposure device, Is a developing cartridge, 7 is a photoconductor 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 portion of a main body case 2 and a front cover 2 a that is openably and detachably inserted on the front surface. In the main body case 2, a developing rotary unit 8 equipped with a plurality of developing cartridges, a photosensitive member 3 on which an electrostatic latent image is formed and developed to form a toner image, and a toner image on the photosensitive member 3 are transferred. An intermediate transfer unit, a control unit for controlling each drive motor and bias, a power supply device 16, a paper feed tray 17 for storing a recording medium, a fixing unit 20 for fixing a toner image on the recording medium, and the like are arranged. A paper transport unit 22 for transporting a recording medium from the paper feed tray 17 to the fixing unit 20 through the secondary transfer roller 15 is disposed in the front cover 2a. Each unit is configured to be detachable from the main body, and can be removed and repaired or replaced integrally during maintenance or the like.
[0016]
The photoreceptor 3 as an image carrier has a thin cylindrical conductive substrate and a photosensitive layer formed on the surface thereof. On the outer periphery of the photosensitive member 3, a charging device 4 for charging the photosensitive member 3 uniformly along the rotation direction, and an exposure device (or writing device) for forming an electrostatic latent image on the photosensitive member 3 5) a developing rotary unit 8 for developing the electrostatic latent image, an intermediate transfer belt 12 to which the toner image on the photoreceptor 3 is transferred, and an intermediate transfer unit for primarily transferring the toner image to the intermediate transfer belt 12. A photoreceptor cleaner 7 for cleaning the surface of the photoreceptor 3 after the primary transfer is disposed.
[0017]
The intermediate transfer unit is made up of a driving roller 10 and a driven roller 11 and an endless belt. The intermediate transfer belt is wound around the rollers 10 and 11 and driven in the direction of the arrow in the drawing to transfer the toner image on the photoreceptor 3. 12, a primary transfer roller 13 disposed on the back surface of the intermediate transfer belt 12 so as to face the photoconductor 3 and primarily transferring a toner image on the photoconductor 3 to the intermediate transfer belt 12, and the intermediate transfer belt 12 A transfer belt cleaner 14 that removes residual toner and a four-color full-color toner image formed on the intermediate transfer belt 12 that is disposed opposite to the driving roller 10 are secondarily transferred onto a recording medium (such as paper). And a secondary transfer roller 15 for this purpose.
[0018]
A power supply device 16 is disposed below the exposure device 5, and a paper feed cassette 17 is disposed at the bottom of the main body case 2. A recording medium in the paper feed cassette 17 is a pickup roller 18, a sheet material conveyance path. 19, the secondary transfer roller 15, and the fixing device 20 are conveyed to the paper discharge tray 21. The paper feed cassette 17 is attached to the front of the apparatus by a handle 17b so that it can be pulled out, and an auxiliary cassette 17a is attached so that it can be pulled out so as to protrude toward the rear of the apparatus so as to cope with a large paper size. Yes.
[0019]
In the image forming apparatus 1 having the above-described configuration, when an image forming signal is input to the exposure device 5, the photoconductor 3, the developing roller 6 a of the developing rotary unit 8, and the intermediate transfer belt are controlled according to the drive motor and bias control by the control unit. First, the outer peripheral surface of the photosensitive member 3 is uniformly charged by the charging device 4. Thereafter, the exposure device 5 selectively exposes the surface of the photoreceptor 3 in accordance with the image information to form an electrostatic latent image. At this time, the developing rotary unit 8 rotates so that the developing roller 6 a of the developing cartridge 6 contacts the photosensitive member 3. As a result, a toner image of an electrostatic latent image is formed on the photoreceptor 3. The toner image formed on the photoreceptor 3 is transferred onto the intermediate transfer belt 12 by the primary transfer roller 13 to which a primary transfer voltage having a polarity opposite to the toner charging polarity is applied, and remains on the photoreceptor 3. The remaining toner is removed by the photoreceptor cleaner 7.
[0020]
In the full-color image forming apparatus, development cartridges 6Y, 6M, 6C, and 6K for yellow Y, magenta M, cyan C, and black K are detachably mounted on the development rotary unit 8. In the image forming operation, the exposure device 5 selectively exposes the surface of the photoreceptor 3 in accordance with image information of the first color, for example, yellow Y, to form a yellow Y electrostatic latent image. At this time, the developing rotary unit 8 rotates so that the developing roller 6a of the yellow Y developing cartridge 6Y contacts the photoreceptor 3, and a yellow Y electrostatic latent image toner image is formed on the photoreceptor 3. Subsequently, the toner image is transferred onto the intermediate transfer belt 12 by the primary transfer roller 13 to which a primary transfer voltage having a polarity opposite to the charging polarity of the toner is applied.
[0021]
During this time, the transfer belt cleaner 14 and the secondary transfer roller 15 are separated from the intermediate transfer belt 12. A four-color full-color image is obtained by repeating this series of processes corresponding to the second color, the third color, and the fourth color of the image formation signal, thereby obtaining yellow Y, Magenta M, cyan C, and black K toner images are sequentially superimposed and transferred from the photoreceptor 3 onto the intermediate transfer belt 12.
[0022]
The recording medium on the paper feed tray 17 is conveyed from the pickup roller 18 to the secondary transfer roller 15 through the registration roller and the sheet material conveyance path 19 at the timing when the superimposed image of each color toner image reaches the secondary transfer roller 15. The secondary transfer roller 15 is pressed against the intermediate transfer belt 12 and a secondary transfer voltage is applied, and the toner image on the intermediate transfer belt 12 is transferred onto the recording medium by the secondary transfer roller 15. When the recording medium having the toner image transferred thereon is conveyed to the fixing unit 20 by the paper conveying unit 22, the toner image on the recording medium is heated and pressed by the fixing unit 20 and fixed. The toner remaining on the intermediate transfer belt 12 is removed by the transfer belt cleaner 14.
[0023]
In the case of double-sided printing, the recording medium that has exited the fixing unit 20 is switched back so that the trailing edge is the leading edge, passes through the double-sided printing conveyance path of the paper conveyance unit 22, and is again transferred to the secondary transfer roller 15. The full-color toner image on the intermediate transfer belt 12 is transferred onto the recording medium, heated and pressed again by the fixing unit 20, and discharged onto the paper 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 to form a four-color full-color image forming apparatus. As a device, only the black K developing cartridge 6K is mounted and mounted, and the developing cartridge 6K stands by at the standby position (home position). During image formation, the black K developing cartridge 6K rotates from the standby position. The electrostatic latent image on the photoreceptor 3 may be developed into a toner image at the development position. This makes it possible to use the development rotary unit 8 having the same design specifications for full color and mono color, and maintenance management compared to designing an image forming apparatus dedicated to full color and mono color by sharing full color and mono color. Design and manufacturing costs can be greatly reduced.
[0025]
Next, a mechanism related to the speed unevenness of the photoreceptor and countermeasures will be described. FIG. 2 is a diagram illustrating measurement data in which unevenness in speed of the photosensitive member is observed, and FIG. 3 is a diagram for explaining a region where unevenness in speed of the photosensitive member is generated according to an operation sequence.
[0026]
In the color image forming apparatus of the present embodiment, none of the developing cartridges 6Y, 6M, 6C, and 6K is in the developing position facing the photoreceptor 3 in the standby state in which the developing rotary unit 8 is at the home position. That is, the developing roller 6 a is not in contact with the photosensitive member 3. Normally, when the developing roller 6 a is in contact with the photosensitive member 3, even if no image is written from the exposure device 5, some fog toner is placed on the photosensitive member 3, and the fog toner is in contact with the photosensitive member cleaner 7. By acting as a kind of lubricant on the contact surface, the photoconductor 3 smoothly frictionally slides with respect to the photoconductor cleaner 7, so that the speed unevenness of the photoconductor 3 is slight.
[0027]
However, when the developing roller 6a is separated from the photoconductor 3, the surface of the photoconductor 3 cleaned by the photoconductor cleaner 7 rotates and contacts the photoconductor cleaner 7 again and frictionally slides. Since there is no toner at all, there is no so-called lubricant, and the frictional resistance of the photosensitive member 3 increases at the contact surface with the photosensitive member cleaner 7, and the rotational speed of the photosensitive member 3 becomes unstable. That is, it is considered that when the frictional resistance of the surface of the photoconductor 3 is increased, the photoconductor 3 repeats a minute lock and slip phenomenon with respect to the photoconductor cleaner 7, thereby causing speed irregularities and vibrations of the photoconductor 3.
[0028]
This can be recognized by FIG. In FIG. 2, the vertical axis represents speed unevenness and the horizontal axis represents time. First, the large speed unevenness appears periodically at the joint of the encoder that performs rotation detection. It is ignored because it does not directly indicate rotational disturbance. This measurement data is used for each color Y, M, C, and K to perform a development color switching operation in which the development cartridge 6 is switched in accordance with the timing of exposure based on the image signal and the development roller 6a is brought into contact with the photosensitive member 3. A time zone t (between 0 and 6) with a large speed unevenness is observed immediately after the start of exposure. The speed unevenness is eliminated after a lapse of time from the time when the developing roller 6 a contacts the photoconductor 3 until the contact surface reaches the photoconductor cleaner 7.
[0029]
Further, the speed unevenness occurrence region of the photoconductor will be described based on the operation sequence. FIG. 3 shows an outline of the operation sequence of the color image forming apparatus according to the present embodiment. The vsync signal, the transfer belt motor, the scanner motor, the image signal, the rotary operation, the developing operation, the primary transfer bias, and the photoconductor. The position of the cleaner, the secondary transfer bias, and the position of the transfer belt cleaner are shown. The oblique dotted line m is the developing operation start point, that is, the position on the photosensitive member 3 where the developing roller 6a abuts after the developing color switching operation is completed. Similarly, a diagonal position n indicates a developing operation end point, that is, a position on the photosensitive member 3 where the developing roller 6a is separated by the start of the developing color switching operation.
[0030]
As shown in FIG. 3, the photosensitive member 3, the developing roller 6a of the developing rotary unit 8, the medium drive motor, and the scanner motor of the exposure device 5 are started to rotate the intermediate transfer belt 12, the scanner, and the photosensitive member 3. After the start, the developing color switching operation by the developing rotary unit 8 is started, the outer peripheral surface of the photoreceptor 3 is uniformly charged by the charging device 4, and the exposure is performed by turning on the image signal in synchronization based on the vsync signal. The image formation is performed sequentially. Then, by turning on the primary transfer bias in synchronization with the start of image formation, the toner image on the photoreceptor is primarily transferred onto the intermediate transfer belt 12.
[0031]
As shown in FIG. 1, the exposure point on the photosensitive member 3 is on the upstream side of the development position. When exposure is started and the image signal is turned on as shown in FIG. 3, the exposure position rotates to the development position. Since the developing roller 6a has only to be in contact with the photosensitive member 3 until the development roller 6a is in contact with the photosensitive member 3, the development start time is slightly delayed from the time when the image signal is turned on. The position on the photosensitive member 3 with which the developing roller 6a abuts is rotationally moved to the photosensitive member cleaner position when the dotted line m intersects the photosensitive member cleaner position.
[0032]
Therefore, the developing roller 6a is not in contact with the time t ′ from when the image signal is turned on until the dotted line m intersects the photoreceptor cleaner position, that is, toner serving as a lubricant is present on the photoreceptor 3. In this state, the peripheral surface of the photoconductor 3 frictionally slides with the photoconductor cleaner 7, and this causes a region of occurrence of speed unevenness of the photoconductor 3. In the second to fourth colors, the same speed unevenness generation region of the photosensitive member 3 appears in the same manner from the development operation end point (n) to the development operation start point (m).
[0033]
The color image forming apparatus of this embodiment is opposed to the blades of the photoreceptor cleaner 7 when the developing rotary unit 8 performs a developing color switching operation and starts forming a latent image by the exposure beam B of the exposure device 5 and thereafter. The toner is replenished so that the toner exists on the photoreceptor 3. Therefore, during the switching operation of the developing device, the photosensitive member 3 that moves to the position facing the blade of the photosensitive member cleaner 7 at the start of latent image formation with respect to the developing position facing surface of the photosensitive member 3 that is originally in contact with the developing roller 6a. Replenish toner on top. The toner is replenished by reversely transferring the toner image of the countermeasure image from the intermediate transfer belt 12 onto the photoreceptor 3 at the primary transfer point where the toner image on the photoreceptor 3 is primarily transferred to the intermediate transfer belt 12. Do. Alternatively, it can be performed by arranging a lubricant application means around the photosensitive member 3.
[0034]
Thus, before the image signal is turned on and exposure is started, there is no direct influence on the image and image unevenness due to speed unevenness does not occur. Therefore, at least when the image signal is turned on, that is, exposure for starting latent image formation on the photoreceptor 3. It is sufficient that toner is replenished on the photosensitive member 3 facing the blade of the photosensitive member cleaner 7 at the start. On the contrary, on the other hand, exposure is not performed when toner or other lubricant is not replenished on the photoreceptor 3 facing the blade of the photoreceptor cleaner 7, or image unevenness is prevented from occurring. It is effective in.
[0035]
FIG. 4 is a diagram showing an operation sequence of an embodiment for forming a countermeasure image. FIG. 5 is a diagram showing an embodiment in which a lubricant application device is used as a lubricant application means disposed around the photosensitive member. 6 is a view showing an embodiment in which a rotating brush is used as a lubricant application means disposed around the photosensitive member.
[0036]
In order to reversely transfer the toner image from the intermediate transfer belt 12 onto the photosensitive member 3, the transfer belt cleaner 14 is separated so that the toner on the intermediate transfer belt 12 is conveyed to the primary transfer point without being removed. The toner image on the intermediate transfer belt 12 is obtained by transferring the toner image or the fog toner from the photosensitive member 3 at the primary transfer point.
[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 photoreceptor 3. In this case, as shown in FIG. 4, prior to the formation of the print image, first, a countermeasure image is formed and the primary transfer bias is controlled to transfer the countermeasure image toner image onto the intermediate transfer belt 12 in advance. From (1), the first color image formation is started. As a result, since residual toner of the toner image of the countermeasure image is present on the photosensitive member 3, the photosensitive member 3 and the photosensitive member cleaner 7 are smoothly slid by friction and no speed unevenness occurs. 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 6 a does not contact the photosensitive member 3, and the countermeasure image is transferred from the intermediate transfer belt 12. The toner image is reversely transferred to replenish the toner ((2) to (4)). As a result, at least during the formation of the latent image by the exposure beam B, the time during which no lubricant is present at the contact portion between the photosensitive member 3 and the photosensitive member cleaner 7 can be eliminated.
[0038]
Considering the state in which the developing roller 6a is in contact with the photosensitive member 3 at the developing position, when the toner image is not formed on the photosensitive member 3, the developing roller 6a contacts the photosensitive member cleaner 7 with the fog toner from the developing roller 6a to the photosensitive member 3. The role of the lubricant at the contact portion is sufficient. Further, when a toner image is formed on the photoreceptor 3, the toner image at the contact portion with the photoreceptor cleaner 7 due to residual toner after the toner image is primarily transferred to the intermediate transfer belt 12 at the primary transfer point. The role as a lubricant is sufficient.
[0039]
As described above, since the amount of toner from the intermediate transfer belt 12 that is reversely transferred as a lubricant onto the photosensitive member 3 may be small, by controlling the amount of toner to be reversely transferred at the primary transfer point, a plurality of toners are transferred from the intermediate transfer belt 12. It is also possible to reversely transfer 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 (countermeasure image) previously transferred from the photosensitive member 3 to the intermediate transfer belt 12 is, for example, a periodic line image in which exposure with the exposure beam B from the exposure device 5 is 1 line on or 10 line off. Images with regular dot patterns 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 exposure with the exposure beam B in accordance with the image signal from the point, the photoreceptor 3 and the photoreceptor cleaner 7 A contact point is obtained, and based on the calculation, a region to which toner is transferred is determined in advance.
[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 intermediate transfer is performed in the region where the developing roller 6a is separated and the lubricant on the photosensitive member 3 runs out during the developing color switching operation of the developing rotary unit 8. Control image formation, primary transfer, and transfer belt cleaner 14 are controlled so that toner is replenished onto the photosensitive member 3 by reverse transfer from the belt 12. As shown in FIG. 5, for example, a lubricant application device 31 is provided so as to supply the lubricant onto the body 3, and zinc stearate containing a toner for lubrication separately from the waste toner removed from the photoreceptor 3 by cleaning, etc. The lubricant may be applied to the peripheral surface of the photoreceptor 3 by the lubricant application device 31 so that the lubricant is not always cut from the peripheral surface of the photoreceptor 3. Further, as shown in FIG. 6, a waste toner circulation mechanism such as a rotating brush 32, a brush, a roller, or the like is provided in the vicinity of the photoreceptor cleaner 7, and the waste toner removed from the photoreceptor 3 by the photoreceptor cleaner 7 is supplied to the rotating brush 32. Alternatively, the toner may be circulated back to the peripheral surface of the photoreceptor 3 by a waste toner circulation mechanism such as a brush or a roller.
[0042]
FIG. 7 is a view showing an embodiment of the positional relationship of the fulcrum with respect to the tangent of the blade of the photoconductor cleaner. As shown in FIG. 7A, the photoconductor cleaner 7 has a blade 7a as a spring around the fulcrum 7b. 7c is pressed against the photosensitive member 3 with a predetermined pressure, and the position of the fulcrum 7b is on the tangent line p where the blade 7a is in contact with the photosensitive member 3 or as shown in FIG. Provided outside the tangent line p (opposite to the photoreceptor 3). By setting the position of the fulcrum 7b as described above, the fulcrum 7b of the photoconductor cleaner 7 is more resistant to the rotation disorder of the photoconductor 3 than the tangent line p in contact with the photoconductor 3 (on the side of the photoconductor 3). However, the contact state of the photoconductor cleaner 7 with respect to the photoconductor 3 can be kept stable.
[0043]
Next, control for replenishing toner from the intermediate transfer belt 12 onto the photoreceptor 3 will be specifically described. FIG. 8 is a diagram for explaining how the countermeasure image is formed on the photosensitive member, and FIG. 9 is a diagram in which the countermeasure image is transferred from the photosensitive member to the intermediate transfer belt, and the print image is subsequently formed on the photosensitive member. FIG. 10 is a diagram for explaining the state in which the formation of the print image is completed and the image is transferred to the intermediate transfer belt. FIG. 11 is a diagram illustrating the development rotary unit starting the development color switching operation. FIG. 12 is a diagram for explaining how toner is reversely transferred from the intermediate transfer belt onto the photosensitive member, FIG. 12 is a diagram for explaining how image formation of the next toner color is started, and FIG. 13 is the final diagram. FIG. 14 is a diagram for explaining a state in which a color image is being formed, FIG. 14 is a diagram for explaining a state in which an image in which all colors are superimposed is secondarily transferred, and FIG. 15 is a state at the cleaning start timing of the transfer belt cleaner. To explain It is a diagram of.
[0044]
In the image forming apparatus 1 of the present embodiment, prior to the image forming operation, first, the photosensitive member 3, the developing roller 6a of the developing rotary unit 8, and the intermediate transfer belt 12 are rotationally driven in the directions of Ro, Rd, and Rb, respectively. The outer peripheral surface of the body 3 is uniformly charged by the charging device 4. Thereafter, as shown in FIG. 8, the exposure device 5 exposes the countermeasure image on the surface of the photoreceptor 3 to form an electrostatic latent image. At this time, the developing rotary unit 8 rotates so that the developing roller 6 a of the developing cartridge 6 contacts the photosensitive member 3. As a result, a toner image 35 of the countermeasure image is formed on the photoreceptor 3.
[0045]
When the toner image 35 of the countermeasure image is formed on the photoreceptor 3, as shown in FIG. 9, the primary transfer roller 13 to which a primary transfer voltage having a polarity opposite to the charged polarity of the toner is applied is applied from above the photoreceptor 3. The toner image 35 ′ is transferred onto the intermediate transfer belt 12. Subsequently, exposure and development of the printed image are started to form a toner image 36, and primary transfer is started.
[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 photoreceptor 3 is completed, FIG. As shown, the toner image 35 ′ of the countermeasure image on the intermediate transfer belt 12 moves to near the primary transfer point. Then, the developing rotary unit 8 starts the developing color switching operation in order to form the second color image. As shown in FIG. 11, the developing rotary unit 8 rotates and moves in the direction of Rr, and the developing roller 6a is moved to the photosensitive member. When the toner image 35 ′ is separated from the toner image 35, the countermeasure image toner image 35 ′ previously transferred onto the intermediate transfer belt 12 reaches the primary transfer point and is reversely transferred onto the photoreceptor 3 as a toner image 35 ″. Even if the developing roller 6a is separated from the photosensitive member 3 by copying, toner is supplied to the photosensitive member 3 at the primary transfer point and supplied as a lubricant to a contact portion with the photosensitive member cleaner 7.
[0047]
Similarly, when the image formation of the second color is started, the contact portion with the photoconductor cleaner 7 at the time when the photoconductor 3 is exposed by the exposure beam B from the exposure device 5 as shown in FIG. Is supplied with toner 35 ″ reversely transferred from the intermediate transfer belt 12 as a lubricant and replenished onto the photoreceptor 3, so that stable rotation of the photoreceptor 3 can be maintained. An image forming operation is also executed.
[0048]
When image formation of the fourth color is started, the images of all colors are overlaid on the intermediate transfer belt 12 as shown in FIG. 13, and the secondary transfer roller 15 is in the middle as shown in FIG. The full-color toner image 37 ′ is brought into contact with the transfer belt 12 and secondary transfer is started from the intermediate transfer belt 12 to the recording medium to form a transfer image 37 ″. During this time, the transfer belt cleaner 14 is shown in FIGS. As shown in FIG. 15, the toner image 35 ′ of the countermeasure image on the intermediate transfer belt 12 passes and comes into contact with the intermediate transfer belt 12 as shown in FIG. 15. Cleaning of residual toner corresponding to the print image area is started, and residual toner after secondary transfer of the print image on the intermediate transfer belt 12 is removed.
[0049]
In addition, this invention is not limited to the said embodiment, A various deformation | transformation is possible. For example, in the above embodiment, it has been described as solving the problem during the development color switching operation of the rotary type four-color full-color image forming apparatus. However, during standby, the developing roller is held away from the photoconductor to form an image. As long as the developing roller is brought into contact with the photosensitive member in accordance with the execution of the job, whether the developing rotary unit is installed or not, whether the developing rotary unit is installed or not. Needless to say, the present invention can be applied to the mono black image forming apparatus in the same manner and can solve the same problems. Further, when the countermeasure image is reversely transferred from the intermediate transfer belt onto the photoconductor, not only a reverse bias is applied, but also the primary transfer bias is lowered to reduce the potential difference or to turn it 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. The countermeasure image is not only formed with the first color or black K toner image, but may be formed with, for example, a low-visibility yellow Y toner image, or only immediately before the first color image formation. First, it is performed when setting the position to the standby state when replacing the cartridge or unit, or when starting the image forming operation from the standby state, and after that, it is formed on the intermediate transfer belt on a constant basis according to the number of job executions. You may make it leave.
[0050]
【The invention's effect】
As is apparent from the above description, according to the present invention, an image carrier on which an electrostatic latent image is formed, a latent image forming unit for forming a latent image on the image carrier, and a contact with the image carrier. A developing means having a developing roller for developing; a first transfer means for transferring a toner image developed on the image carrier onto the intermediate transfer medium; and a toner image transferred on the intermediate transfer medium on the recording medium. A second transfer means for transferring the toner onto the image carrier, a first cleaning means for contacting the image carrier to remove residual toner after transfer, and abutting or separating on the intermediate transfer medium. And a second cleaning unit that removes toner on the intermediate transfer medium, and a developing roller is separated from the image carrier by the developing unit to perform a development switching operation . Remove the cleaning blade. The toner transferred onto the intermediate transfer medium is transported without being removed, and the toner transported by the first transfer means is reversely transferred onto the image carrier, and at least the latent image forming means is started by the latent image forming means. The toner carrying means for replenishing the toner so that the toner is present on the image carrying body facing the blade of the first cleaning means at the time, the image carrying body facing the blade of the cleaning means at the start of latent image formation It is possible to eliminate the state where the toner is not supplied on the upper surface, and to smoothly slide the cleaning means in contact with the image carrier, thereby reducing the speed unevenness of the image carrier. Therefore, the speed unevenness of the image carrier due to frictional sliding with the cleaning member is eliminated, and in particular, the speed unevenness of the image carrier during the formation of the electrostatic latent image of the image forming apparatus equipped with the developing rotary unit and performing the development switching operation. Can be eliminated.
[Brief description of the drawings]
FIG. 1 is a diagram showing an embodiment of an image forming apparatus according to the present invention.
FIG. 2 is a diagram showing measurement data in which speed irregularities of a photoreceptor are observed.
FIG. 3 is a diagram for explaining a speed unevenness generation region of a photoconductor by an operation sequence.
FIG. 4 is a diagram illustrating an operation sequence of an embodiment for forming a countermeasure image.
FIG. 5 is a diagram showing an embodiment in which a lubricant applying device is used as a lubricant applying means disposed around a photoreceptor.
FIG. 6 is a diagram showing an embodiment in which a rotating brush is used as a lubricant application unit disposed around a photoconductor.
FIG. 7 is a diagram showing an embodiment of a positional relationship of a fulcrum with respect to a tangent of a blade of a photoconductor cleaner.
FIG. 8 is a diagram for explaining how a countermeasure image is formed on a photoconductor.
FIG. 9 is a diagram for explaining a state in which a countermeasure image is transferred from the photosensitive member to an intermediate transfer belt, and a print image is continuously formed on the photosensitive member.
FIG. 10 is a diagram for explaining a state in which the formation of a print image is completed and transferred to an intermediate transfer belt.
FIG. 11 is a diagram for explaining a state where toner is reversely transferred from the intermediate transfer belt to the photosensitive member at the same time when the developing rotary unit starts the developing color switching operation;
FIG. 12 is a diagram for explaining a state in which image formation of the next toner color is started.
FIG. 13 is a diagram for 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 the timing of starting the cleaning of the transfer belt cleaner.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 2 ... Main body case, 3 ... Photoconductor, 4 ... Charging apparatus, 5 ... Exposure apparatus, 6 ... Developing cartridge, 7 ... Photoconductor cleaner, 8 ... Development rotary unit, 9 ... Rotary frame, 12 ... Intermediate transfer belt, 13 ... primary transfer roller, 15 ... secondary transfer roller, 16 ... power supply, 17 ... paper feed tray, 20 ... fixing unit, 21 ... paper discharge tray, 22 ... paper transport unit

Claims (1)

An image carrier on which an electrostatic latent image is formed, a latent image forming unit that forms a latent image on the image carrier, a developing unit that includes a developing roller that contacts and develops the image carrier, and the image A first transfer means for transferring the toner image developed on the carrier onto the intermediate transfer medium; a second transfer means for transferring the toner image transferred onto the intermediate transfer medium onto the recording medium; A first cleaning unit that abuts on the image carrier to remove residual toner after transfer, and abuts on or away from the intermediate transfer medium, thereby removing toner on the intermediate transfer medium. In the image forming apparatus in which the developing roller is separated from the image carrier by the developing means to perform the development switching operation, the blade of the second cleaning means is separated. Middle The toner transferred onto the transfer medium is transported without being removed, and the toner transported by the first transfer means is reversely transferred onto the image carrier, and at least a latent image formed by the latent image forming means. An image forming apparatus comprising: a toner replenishing unit that replenishes toner so that the toner exists on the image carrier facing the blade of the first cleaning unit at the start of formation.

Images