JPH10111589A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate the relative positional deviation between a mark position on an intermediate transfer body and a driving means, etc., by providing a joint means having an arbitrary backlash in a rotational direction, in the connecting parts of a photoreceptor and the intermediate transfer body to each driving means. SOLUTION: The joint means is arranged between the driving means and a photoreceptor drum or an intermediate transfer belt. Assembling is attained so that the projection 440A-1 of a first joint part 440A is inserted into the recess 440B-4 of a second joint part 440B. At this time, play at an angle of α deg.is provided in the rotational direction, between the projection 440A-1 and a projection 440B-2, so that a backlash Aα in a moving direction corresponding to the play at an angle of α deg. is provided on the surface of the photoreceptor drum or the intermediate transfer belt. Since the backlash Aα is set larger than the travel deviation between the photoreceptor drum and the intermediate transfer belt, a floating state can be kept within the range of the backlash Aα, during one rotation of the intermediate transfer belt.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a copying machine, a printer,
With respect to improvements in image forming apparatuses such as facsimile machines, in particular, having a photoreceptor and an intermediate transfer member, a color toner image formed on the photoreceptor is sequentially transferred to the intermediate transfer member to form a superimposed transfer image. The present invention relates to an image forming apparatus of a type that transfers a superimposed transfer image onto transfer paper at a time.

[0002]

2. Description of the Related Art As a conventional image forming apparatus, an image forming apparatus having an intermediate transfer member disposed opposite to a photoreceptor constituted by a rotatable rotary member and rotated at the same peripheral speed as the photoreceptor in a contact state is provided. In this type of image forming apparatus, a sensor for detecting the mark is provided in a pass area of the mark provided on a part of the intermediate transfer body, and the primary transfer unit which is in a state of being in contact with the photoreceptor is provided. The primary transfer unit has a charging unit at a charging position upstream of the photoconductor in the rotation direction of the primary transfer unit. When forming an image, an image forming process is started after a certain timing from the detection of the mark by the sensor during rotation of the photoconductor and the intermediate transfer body, and the photoconductor charged through the charging position is started. Forming a toner image of an arbitrary color by optical writing and development on the charged area of the toner, and then transferring the toner image of the arbitrary color to an intermediate transfer body by a primary transfer unit in a primary transfer unit. Each time, a color superimposed toner image is formed on the intermediate transfer member, and the superimposed toner image is collectively transferred onto a transfer sheet to obtain a color image. By the way, in such an image forming apparatus, the circumference ratio of the photosensitive member, the intermediate transfer body, and the rotation means of the intermediate transfer body is set to an integer, and the reduction ratio of the gears and the timing belt constituting the drive means is set to an integer for each color. The speed fluctuations are made equal to enable accurate positioning. As such a conventional example, for example, Japanese Patent Application Laid-Open No. 61-83557 discloses a “multicolor image forming apparatus”.
By making the circumference of the transfer means an integral multiple of the photoreceptor, one point on the photoreceptor corresponds to multiple points of the transfer means circumference,
There is disclosed a technique for preventing a developed image of a plurality of colors from shifting on a transfer unit. Further, in the "color image forming apparatus" disclosed in Japanese Patent Application Laid-Open No. Hei 1-307774, the reduction ratio between all the teeth engaged with the reduction gear connecting the photosensitive member driving means and the photosensitive member is set to be an integer. There is disclosed a technique for obtaining high image quality. In the primary transfer section, the photoconductor and the intermediate transfer body are in close contact to form a nip,
When both are charged, the adhesion is increased by an electric force (Coulomb force). Even in such a state, if the circumferential length ratio between the photosensitive member and the intermediate transfer member is an integer, the two rotate completely in synchronization, and accurate toner image alignment is possible.

[0003]

However, since the photoreceptor, the intermediate transfer member, and the rotating means of the intermediate transfer member are industrial products, it is actually impossible that there is no dimensional error. There is a certain range of dimensional variation, and the peripheral length ratio of each part is often not an integer. Due to this dimensional variation, the peripheral speeds of the photosensitive member and the intermediate transfer member are slightly different, and this difference is absorbed by a small slip in the primary transfer portion, and the alignment by the mark detection is always performed under the same relative condition. It must be made. However, as described above, the cohesive force between the photoconductor and the intermediate transfer member in the primary transfer portion increases the adhesion between the photoreceptor and the intermediate transfer member. And try to rotate. As a result, a deviation occurs between the detected position of the mark and the relative position between the rotating means, and a reaction of the minute peripheral speed difference causes the driven side of the photosensitive member or the intermediate transfer body to be driven earlier than the driven side, whichever is slower. Will be rotated. on the other hand,
When a timing belt or the like is used as a driving means of the photoconductor and the intermediate transfer body, backlash in the gear portion can hardly be expected, and the photosensitive member is exposed to the adhesive force at the nip portion between the photoconductor and the intermediate transfer body. In order to drive the body and the intermediate transfer body at a constant rotation speed, the adhesion force and the driving force repel each other. This difference in peripheral speed is slightly absorbed by deformation of each member, etc., but if this absorption exceeds the limit,
The state of close contact at the primary transfer nip portion is peeled off, causing a slip, resulting in a displacement of the transferred image at that time and a worst case image blurring. SUMMARY OF THE INVENTION The present invention has been made in view of the above, and an object of the present invention is to detect a difference between a detected mark position (detection timing) on an intermediate transfer member, a relative position of a driving unit, and a contradiction of a driving unit in a process of each color. It is an object of the present invention to provide an image forming apparatus capable of solving the problem each time and eliminating a positional shift caused by the problem.

[0004]

According to a first aspect of the present invention, there is provided an image forming apparatus comprising: a photoreceptor comprising a rotating member which is driven to rotate; and a photoreceptor which is opposed to the photoreceptor and is in contact with the photoreceptor. An intermediate transfer member rotated at the same peripheral speed as the photosensitive member, a mark provided on a part of the intermediate transfer member, and a mark detection sensor provided in a pass area of the mark; A primary transfer unit at a primary transfer unit formed at a contact portion between the first transfer unit and the intermediate transfer body, and a charging unit at a charging position on the rotation direction upstream side of the photoconductor relative to a position where the primary transfer unit is provided, respectively. At the time of image formation, an image forming process is started after a certain timing from the detection of the mark by the sensor during rotation of the photoconductor and the intermediate transfer body, and light is applied to a charged area of the photoconductor charged by the charging unit. By writing and developing Forming a toner image of a desired color, and then transferring the toner image of an arbitrary color to the intermediate transfer body by a primary transfer unit in a primary transfer unit for each of the different colors. In an image forming apparatus which obtains a color superimposed toner image thereon and collectively transfers the superimposed toner image onto transfer paper in a secondary transfer section to obtain a color image, a contact between a photosensitive member and the intermediate transfer body in a primary transfer section is obtained. A primary transfer nip contact / separation mechanism that can release the primary transfer nip state, and a joint having an arbitrary play in the rotation direction with respect to the connecting portion between the photosensitive member and the intermediate transfer member and each drive unit. Means are provided. According to a second aspect of the present invention, the primary transfer nip contact / separation mechanism has a contact / separation mechanism driving unit, and can be turned on and off at an arbitrary timing. According to a third aspect of the present invention, the ON timing of the primary transfer nip contact / separation mechanism is determined by a mark provided on a part of the intermediate transfer member of the first aspect,
Before the time of detecting the position of the intermediate transfer member by the mark detecting sensor provided in the mark passage area, and the OFF timing of the primary transfer nip contact / separation mechanism is after the end of the primary transfer. Features. The invention of claim 4 is
2. The image forming apparatus according to claim 1, wherein a relative position error between the photosensitive member and the photosensitive member generated during one rotation of the intermediate transfer member due to a peripheral speed difference caused by component accuracy of the intermediate transfer member. The play in the rotation direction of the photosensitive member or the intermediate transfer member is set large.

[0005]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a color image forming apparatus as a multicolor image forming apparatus according to one embodiment of the present invention will be described with reference to FIG. A color image reading device (hereinafter, referred to as a color scanner) 200 transmits an image of the document 180 on the contact glass 202 to a color sensor 207 via an illumination lamp 205, mirror groups 204A, 204B, 204C, and the like, and a lens 206. After forming an image, the color image information of the original is read for each color separation light of, for example, blue (hereinafter, referred to as B), green (hereinafter, referred to as G), and red (hereinafter, referred to as R). Convert to image signal. In this example, the color sensor 207 includes B, G, and R color separation means and a photoelectric conversion element such as a CCD (solid-state imaging device), and performs simultaneous reading of three colors. Based on the color separation image signal intensity levels of B, G, and R obtained by the color scanner 200,
A color conversion process is performed by an image processing unit (not shown), and black (hereinafter, referred to as BK), cyan (hereinafter, referred to as C), magenta (hereinafter, referred to as M), and yellow (hereinafter, referred to as Y). To obtain color image data including the color information. Using the color image data, a color image recording device (hereinafter, referred to as a color printer) 400 described below is used.
Accordingly, the operation method of the color scanner 200 for obtaining the image data of BK, C, M, and Y is such that the illumination lamp 205 and the mirror group 204 receive the scanner start signal synchronized with the operation of the color printer 400.
An illumination / mirror optical system including A, 204B, and 204C scans the document in the direction of the left arrow, and obtains one-color image data for each scan. By repeating this operation a total of four times, sequential four-color image data is obtained. And each time,
While the images are sequentially visualized by the color printer 400, they are superimposed to form a full-color image of four colors.

Next, an outline of the color printer 400 will be described. Writing optical unit 40 as exposure means
1 converts the color image data from the color scanner 200 into an optical signal, performs optical writing corresponding to the original image, and places the image on a photosensitive drum 414 which is a latent image carrier corresponding to a photosensitive member according to the present invention. An electrostatic latent image is formed. The optical writing optical unit 401 includes a laser light emitting unit 441, a light emission drive control unit (not shown) for driving the laser light emitting unit 441, a polygon mirror 443, a rotation motor 444 for driving the polygon mirror 443, an fθ lens 442, a reflection mirror 446, and the like. I have.
The photoconductor drum 414 rotates in a counterclockwise direction as indicated by an arrow. Around the photoconductor cleaning unit 421, a neutralization lamp 414M, a charger 419 as a charging unit, and a latent image on the photoconductor drum. A potential sensor 414D for detecting a potential, a selected developing device of the revolver developing device 420, a development density pattern detector 414P, an intermediate transfer belt 415 as an intermediate transfer member according to the present invention, and the like are arranged. The revolver developing device 420 has a BK
Developing unit 420K, C developing unit 420C, M developing unit 420
It comprises an M and Y developing unit 420Y, a revolver rotation drive unit (not shown) for rotating each developing unit in a counterclockwise direction as shown by an arrow, and the like. In order to develop the electrostatic latent image, each of these developing units is provided with a developing sleeve 420KS and a developing sleeve 420K which are rotated by bringing an ear of the developer into contact with the surface of the photosensitive drum 414.
20CS, 420MS, 420YS, and a developing paddle that rotates to pump and agitate the developer.

In the standby state, the revolver developing device 420 is set at a position where development is performed by the BK developing device 420. When the copying operation is started, the BK image data is read from the color scanner 200 at a predetermined timing. Starts, and based on this image data, optical writing / latent image formation by laser light starts (hereinafter, an electrostatic latent image based on BK image data is referred to as a BK latent image. C, M, Y).
The same applies to each image data.) In order to enable development from the leading end of the BK latent image, a developing sleeve 420KS is used before the leading end of the latent image reaches the developing position of the BK developing unit 420.
Is started, and the BK latent image is developed by the BK toner. Thereafter, the developing operation of the BK latent image area is continued, but when the rear end of the latent image has passed the BK latent image position, the BK
The revolver developing device 420 is driven to rotate from the developing position by the developing device 420K to the developing position by the next color developing device. This rotation operation is completed at least before the leading end of the latent image based on the next image data arrives. When the image forming cycle is started, the photosensitive drum 414 rotates counterclockwise as shown by an arrow, and the intermediate transfer belt (intermediate transfer body) 415 is rotated clockwise by a drive motor (not shown). To rotate. Intermediate transfer belt 415
BK toner image formation, C toner image formation, M toner image formation, and Y toner image formation are sequentially performed with the rotation of the intermediate transfer belt 415 in the order of BK, C, M, and Y.
A toner image is formed on top of the toner image.

The formation of a BK image is performed as follows. The charger 419 uniformly charges the photosensitive drum 414 with a negative charge to about -700 V in the dark by corona discharge. Subsequently, the laser diode 441 performs raster exposure based on the BK signal. When the raster image is exposed in this manner, in the initially exposed portion of the photosensitive drum 414 that is uniformly charged, the charge proportional to the amount of exposure light disappears, and an electrostatic latent image is formed. The toner in the revolver developing device 420 is negatively charged by stirring with the ferrite carrier, and the BK developing sleeve 420 KS of the present developing device is connected to the metal base layer of the photosensitive drum 414 by a power supply (not shown). , Are biased to a potential obtained by superimposing a negative DC potential and an AC. As a result, no toner adheres to the portion of the photosensitive drum 414 where the charge remains, and BK toner is adsorbed to the portion having no charge, that is, the exposed portion, and the BK toner similar to the latent image is absorbed.
A visible image is formed. The intermediate transfer belt 415 is stretched around a drive roller 415D, a transfer opposed roller 415T, a cleaning opposed roller 415C, and a driven roller group, and is driven and controlled by a drive motor (not shown).

The BK toner image formed on the photoreceptor 414 is placed on the surface of an intermediate transfer belt 415 which is driven at a constant speed in contact with the photoreceptor. ) 416. Hereinafter, the photosensitive drum 414 to the intermediate transfer belt 41
Transfer of the toner image to No. 5 is referred to as belt transfer. Some untransferred residual toner on the photoconductor drum 414 is cleaned by the photoconductor cleaning unit 421 in preparation for reuse of the photoconductor drum 414. The collected toner is stored in a waste toner tank (not shown) via a collection pipe. Note that, on the intermediate transfer belt 415, BK, C, M, and Y toner images sequentially formed on the photosensitive drum 414 are formed.
A four-color superimposed belt transfer image is formed by sequentially aligning the same on the same surface, and thereafter, collective transfer is performed on transfer paper by a corona discharge transfer device. By the way, on the photosensitive drum 414 side,
After the BK image forming process, the process proceeds to the C image forming process. At a predetermined timing, reading of C image data by a color scanner starts, and a C latent image is formed by writing laser light using the image data. C developing unit 42
0C indicates that the rotation of the revolver developing device is performed with respect to the developing position after the trailing edge of the previous BK latent image has passed and before the leading end of the C latent image has arrived. Develop with toner. Thereafter, the development of the C latent image area is continued. When the rear end portion of the latent image passes, the revolver developing device 420 is driven in the same manner as in the case of the BK developing device, and the C developing device 42 is driven.
0C is sent, and the next M developing device 420M is positioned at the developing position. This operation is also performed before the leading end of the next M latent image reaches the developing unit. Note that the steps of reading the respective image data, forming the latent image, and developing the M and Y images are the same as those of the above-described BK image and C image steps, and thus the description thereof is omitted.

The belt cleaning device 415U includes an inlet seal, a rubber blade, a discharge coil, and a mechanism for contacting and separating the inlet seal and the rubber blade. 1
After the BK image of the color is transferred to the belt, while the second, third, and fourth colors are being transferred to the belt, the blade seal mechanism separates the entrance seal, the rubber blade, and the like from the intermediate transfer belt surface. . A paper transfer corona discharger (hereinafter, referred to as a paper transfer device) 417 uses an AC + DC or DC component to transfer the superposed toner image on the intermediate transfer belt 415 to the transfer paper. This is applied to the transfer belt. Transfer papers of various sizes are stored in a transfer paper cassette 482 in the paper feed bank, and a registration roller pair 4 is fed from a storage cassette storing paper of a designated size by a paper feed roller 483.
Paper is fed and conveyed in the 18R direction. Note that reference numeral 412B2
Indicates a paper feed tray for manually feeding OHP paper or thick paper. At the time when the image formation is started, the transfer paper is fed from any one of the above-mentioned paper feed trays, and is waiting at the nip portion of the registration roller pair 418R. Then, when the leading end of the toner image on the intermediate transfer belt 415 approaches the paper transfer unit 417, the registration roller pair 418R is driven so that the leading end of the transfer paper coincides with the leading end of the image, and the paper and the image are transferred. A resist alignment is performed.

In this way, the transfer paper P is superimposed on the color superimposed image on the intermediate transfer belt and passes over the paper transfer unit 417 connected to a positive potential. At this time, the transfer paper is charged with a positive charge by the corona discharge current, and most of the toner image is transferred onto the transfer paper. Subsequently, when the transfer paper passes through a separation neutralizer with a neutralization brush (not shown) disposed on the left side of the paper transfer unit 417, the transfer paper is neutralized, and the intermediate transfer belt 415 is removed.
From the paper transport belt 422. The transfer paper on which the four-color superimposed toner image has been collectively transferred from the intermediate transfer belt surface is conveyed to a fixing device 423 by a paper conveyance belt 422, and the fixing roller 423A is controlled to a predetermined temperature.
The toner image is fused and fixed at the nip portion of the pressure roller 423B, sent out of the main body by the discharge roll pair 424, and stacked face up on a copy tray (not shown) to obtain a full color copy. The photosensitive drum 4 after the belt transfer
The surface of the cleaning member 14 is cleaned by a photoconductor cleaning unit 421 including a brush roller, a rubber blade, and the like, and is uniformly discharged by a discharge lamp 414M. Further, the intermediate transfer belt 4 after transferring the toner image onto the transfer paper
The surface 15 is again cleaned by pressing the blade with the blade contact / separation mechanism of the cleaning unit 415U.

In the case of the repeat copy, the operation of the color scanner and the image formation on the photosensitive member follow the first-color image process of the first sheet and proceed to the first-color image process of the second sheet at a predetermined timing. In the case of the intermediate transfer belt 415, the second BK toner image is transferred to a region where the surface of the intermediate transfer belt 415 is cleaned by the belt cleaning device, following the batch transfer process of the first four-color superimposed image onto the transfer paper. Be transferred. After that, the operation is the same as that of the first sheet. The above is the description of the copy mode for obtaining the four-color full-color copy. However, in the case of the three-color copy mode and the two-color copy mode, the same operation as described above is performed for the designated color and the number of times. Become. Further, in the case of the single-color copy mode, until the predetermined number of sheets is completed, only the developing device of the revolver developing device 420 of the predetermined color is located at the developing position of the predetermined color, the developing operation is performed, and the belt cleaning device 415U The copying operation is continuously performed while the blade is pressed against the belt. In such an image forming apparatus, a mark for position detection is provided on the outer peripheral surface or the inner peripheral surface of the belt 415. However, on the outer peripheral surface side, it is necessary to devise a way to avoid the passing area of the belt cleaning device 415U, and it may be difficult to dispose it depending on the model or the like. In that case, it is provided on the inner peripheral surface side. . Although the optical sensor is not shown in FIG. 1,
It is provided at a position between a driving roller 415D that supports the belt 415 and a support roller 415F.

Next, an embodiment of the present invention will be described in detail with reference to FIGS. FIG. 2 is a schematic view of an image forming section centered on a photoconductor, and FIGS. 3A and 3B are specific diagrams of a primary transfer nip contact / separation mechanism for bringing an intermediate transfer member into and out of the photoconductor. FIG. 4 is a timing chart showing the relationship between the rotation of the cam and the contact / separation operation, and FIG. 5 is a diagram for explaining the play in the rotation direction of the joint means. The primary transfer nip contact / separation mechanism shown in detail in FIG. 3 includes a swing bracket 43 supported rotatably in a direction indicated by an arrow by a fulcrum 433a.
The pressure roller 415F is rotatably supported by a shaft 433b at the other end of the shaft 3, and the swing bracket 433 is urged to a retracted position shown in FIG. 3A by elastic means (not shown) or its own weight. Reference numeral 431 denotes an eccentric cam which is driven to rotate about a shaft 431a. When the cam 431 is at the non-pressing position shown in (a), its pressing surface 431b is retracted to a position where it does not press the pressed surface 433c of the bracket 433. Conversely, when the cam 431 is at the pressing position shown in FIG. 4B, the pressing surface 431c of the cam 431 presses the pressed surface 433c of the bracket 433. As a result, in the retracted state (a), the intermediate transfer belt 415 is not in contact with the photoconductor 414, and conversely, in the pressing position (b), the belt is pressed toward the photoconductor. Part of the photoconductor 41
Nip over 4 and a predetermined width w.

More specifically, referring to FIGS. 2 and 3, the pressure roller 4 supported by the swing bracket 433 will be described.
3F, the photosensitive drum 414 and the intermediate transfer belt 415 are separated from each other at the retracted position lowered in FIG.
In FIG. 3B, the photosensitive drum 414 and the intermediate transfer belt 415 are in close contact with each other at an increased pressing position, and have an arbitrary width w.
Nip is formed. The up-and-down operation is performed by rotating the cam 431 connected to the half-turn clutch 430, which stops by rotating by 180 degrees at an arbitrary timing when an electric signal is input.
, And the half-rotation clutch 430 is rotationally driven by the drive train 432. That is, the primary transfer nip contact / separation mechanism is turned on at an arbitrary timing by the contact / separation mechanism driving unit 430 or the like that operates under the control of the control unit.
(Press) and OFF (Retreat) are controlled. Then, for example, the ON timing of the primary transfer nip contact / separation mechanism is determined by the timing at which the position of the intermediate transfer body is detected by a mark provided on a part of the intermediate transfer body and the mark detection sensor provided in a pass area of the mark. It is preferable to control the OFF timing of the primary transfer nip contact / separation mechanism before the end of the primary transfer.

This point will be described with reference to FIG. 4 which shows the vertical timing of the pressure roller 415F by the operation of the cam 431. The cam 431 is more predetermined than the timing when the mark detection sensor, which is the timing reference for color registration, is turned on. 3, that is, a time t1 to t2 that is sufficient to stop the vibration of the machine due to the cam operation,
The upper position (pressing position) shown in (b) is reached, and the nip w is formed. Then, after the rear end of the image to be primarily transferred is transferred from the photosensitive drum 414 to the intermediate transfer belt 415 (t4), the lower position (retreat position) in FIG. 3A is reached, and the nip is released (t5). ). According to this embodiment, it is possible to release the cohesive force due to the Coulomb force in the primary transfer nip portion during the time when the primary transfer is not performed without deteriorating the accuracy of the alignment by the mark detection, thereby maintaining the image quality. It is possible to do.

Next, in another embodiment of the present invention, a relative position error between the photosensitive member and the photosensitive member caused during one rotation of the intermediate transfer member due to a peripheral speed difference caused by component accuracy between the photosensitive member and the intermediate transfer member is reduced. The play is set so that the play in the moving direction in the joint means described later becomes large. For this reason, even if the photosensitive member and the intermediate transfer member rotate synchronously due to the adhesion force due to the Coulomb force in the primary transfer nip, the peripheral speed difference can be absorbed by the play. Further, as described later, the nip is released and initialized each time the toner image is overlapped by one color by the operation of the primary transfer nip contact / separation mechanism for each rotation of the intermediate transfer member, so that the primary transfer nip adhesion and drive It is possible to prevent displacement due to tension of the system.
This will be described in detail with reference to FIG.
Assuming that the average peripheral speed of the intermediate transfer belt 415 is Va and the average peripheral speed of the intermediate transfer belt 415 is Vb, the time t required for one rotation of the intermediate transfer belt 415 having the circumferential length Lb is t = Lb / Vb. The moving distance La on the surface of the body drum 414 is as follows: La = Va · t Here, the driving means of the belt driving roller 415D for driving the photosensitive drum 414 and the intermediate transfer belt 415 is set to be equal to the theoretical setting ratio of the circumference of the photosensitive drum 414 and the intermediate transfer belt 415. If the circumferential lengths of the drum 414 and the belt driving roller 415D are equal, La = Lb. However, in practice, there is a limit in the accuracy of the parts, and an error always occurs. Therefore, an error ΔL occurs between La and Lb. . ΔL = La−Lb On the other hand, a joint means 440 shown in FIGS. 5A and 5B is arranged between the drive means and the photosensitive drum 414 or the intermediate transfer belt 415. As shown in FIG.
The joint means 440 is connected to the first joint 44
OA and a second joint portion 440B, one of which is connected to the drive side shaft and the other is connected to the driven side. The first joint portion 440A has two engagement protrusions 440A-1 protruding at an interval of 180 as shown in the figure, and the central portion thereof is supported by a shaft 440A-2 to rotate. The other second joint part 440B
Has two projections 440B-2 at 180-degree intervals on the surface of a disk-shaped base 440B-1, and rotates about a shaft 440B-3 integrated at the center thereof. Each shaft 440A
, 440B-3 are coaxially arranged, and the protrusion 440A-1 of the first joint 440A is
Are assembled so as to enter into the recesses 440B-4 between the protrusions 440B-2 of the joint 440B. By providing a play at an angle α ° in the rotation direction between the projections 440A-1 and 440B-2 at this time, the play at the angle α ° is provided on the surface of the photosensitive drum 414 or the intermediate transfer belt 415. In the moving direction.

Here, Aα is calculated from the stroke error ΔL between the photosensitive drum 414 and the intermediate transfer belt 415 (the relative positional error between the photosensitive drum and the photosensitive member during one rotation of the intermediate transfer member). By setting a large value, during one rotation of the intermediate transfer belt 415, the drive system of the device having the lower peripheral speed does not transmit reverse torque from the driven gear to the drive gear, and the floating state is maintained within the range of the play Aα. Will be kept. Also,
Since the primary transfer nip releasing operation is performed every one rotation of the intermediate transfer belt 415, the external force due to the nip adhesion force is eliminated, and only the driving means is driven.
The zero play Aα returns to the initial state.

[0018]

As described above, in the image forming apparatus of the first aspect, since the primary transfer nip contact / separation mechanism is provided, the photosensitive member and the intermediate transfer belt are excessively large due to Coulomb force in the primary transfer nip. The close contact by force prevents the occurrence of a situation in which only the surface is rotated synchronously without causing a slip. As a result, there is no deviation between the detected mark position and the relative position between the rotating means, and as a result, a small difference in peripheral speed causes a reaction by the driving means of the photosensitive element or the intermediate transfer body, whichever is slower. Load fluctuation and local slippage of the primary transfer nip due to the rotation of the driven side faster than the driven side can be prevented, and it is possible to prevent the transfer image from being disturbed or displaced.
Also, since the joint means is arranged between the driving means and the photoreceptor or the intermediate transfer body to provide play in the rotational direction, the photoreceptor and the intermediate transfer body are synchronized by the cohesive force of the primary transfer nip due to Coulomb force. Even if it rotates, the peripheral speed difference can be absorbed by the play length at the joint. In the image forming apparatus according to the second aspect, the primary transfer nip contact / separation mechanism is turned on (pressed) at an arbitrary timing,
Since the FF (retractable) contact / separation mechanism driving unit is provided, it is possible to cancel the cohesive force due to the Coulomb force in the primary transfer nip at an arbitrary timing. As a result, similarly to the case of the first aspect, the occurrence of load fluctuation and local slippage of the primary transfer nip can be prevented, and the occurrence of disturbance and displacement in a transferred image can be prevented. In the image forming apparatus according to the third aspect, the ON timing of the primary transfer nip contact / separation mechanism is determined by the intermediate transfer by a mark detection sensor provided in a pass area of a mark provided in a part of the intermediate transfer body according to the first aspect. By setting the timing before the position detection of the body (mark detection) and the OFF timing of the primary transfer nip contact / separation mechanism after the end of the primary transfer, the positioning accuracy by the mark detection is not impaired. During the time when the primary transfer is not performed, the adhesion force due to the Coulomb force in the primary transfer nip can be released. In the image forming apparatus according to the fourth aspect, the drive unit and the photosensitive member are more sensitive to a relative position error between the photosensitive member and the photosensitive member caused during one rotation of the intermediate transfer member due to a peripheral speed difference caused by component accuracy of the intermediate transfer member. Even if the photoreceptor and the intermediate transfer member are rotated synchronously by the cohesive force due to the Coulomb force in the primary transfer nip, the rotational play in the joint provided between the body and the intermediate transfer member is set to be large. The difference in peripheral speed is absorbed by the play length in the joint, and further, the operation is performed by the primary transfer nip contacting / separating mechanism for each rotation of the intermediate transfer member, and the toner image is initialized each time one color is overlapped. Therefore, it is possible to prevent the displacement due to the adhesion force of the primary transfer nip and the pulling of the drive system.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of an image forming apparatus according to an embodiment of the present invention.

FIG. 2 is a configuration diagram of a main part of FIG. 1;

FIGS. 3A and 3B are diagrams showing a configuration example and operation of a contact / separation mechanism driving unit of a primary transfer nip contact / separation mechanism.

FIG. 4 is a diagram showing vertical timing of a pressure roller by operation of a cam.

FIGS. 5 (a) and (b) are diagrams showing a configuration of a Jonting means.

[Explanation of symbols]

200 color image reading device (color scanner), 202 contact glass, 204A, 204
B, 204C mirror, 205 illumination lamp, 206 lens, 207 color sensor, 400 color image recording device (color printer), 401 writing optical unit, 414 photosensitive drum, 415 intermediate transfer belt, 415D drive roller, 415T transfer opposed roller 415C cleaning opposing roller, 419 charger, 420 revolver developing device, 420K BK developing device, 420CC developing device, 421 photoconductor cleaning unit, 420MM developing device, 420Y Y developing device, 441 laser light emitting means, 442 fθ lens,
443 polygon mirror, 444 rotation motor 44
4, 446 Reflection mirror, 431 Eccentric cam, 431a
Shaft, 431b pressing surface, 433 swing bracket, 43
3a fulcrum, 433b axis, 433c pressed surface, 44
0 joint means, 440A first joint part,
440A-1 Engagement protrusion, 440A-2 Shaft, 440B
Second joint section, 440B-1 Base section, 440B
-2 engagement protrusion, 440B-3 shaft, 440B-4 recess,

Claims (4)

[Claims] A photosensitive member comprising a rotating member driven to rotate, an intermediate transfer member disposed opposite to the photosensitive member and rotated at the same peripheral speed as the photosensitive member in contact with the photosensitive member; A mark provided on a part of the intermediate transfer member, and a mark detection sensor provided in a pass area of the mark; and a primary transfer portion formed at a contact portion between the photoconductor and the intermediate transfer member. A primary transfer unit having a charging unit at a charging position upstream of the position of the primary transfer unit in the rotation direction of the photoconductor, and a charging unit that rotates the photoconductor and the intermediate transfer member during image formation. An image forming process is started after a certain timing from the detection of the mark by the sensor, and a toner image of an arbitrary color is formed by light writing and development on a charged area of the photoconductor charged by the charging unit. , This arbitrary color toner image is transferred to the intermediate transfer body by the primary transfer means in the primary transfer unit for each different color, to obtain a color superimposed toner image on the intermediate transfer body, In an image forming apparatus for obtaining a color image by collectively transferring the superimposed toner image onto transfer paper in a secondary transfer section, a state in which the photoconductor and the intermediate transfer body are in contact with each other in the primary transfer section, that is, a primary transfer nip state A primary transfer nip contact / separation mechanism that enables release of the toner, and a joint unit having an arbitrary play in the rotation direction is provided for a connection portion between the photosensitive member and the intermediate transfer member and each drive unit. Image forming apparatus. 2. The method according to claim 1, wherein the primary transfer nip contact / separation mechanism has a contact / separation mechanism driving unit, and the primary transfer nip contact / separation mechanism can be controlled to be ON / OFF at an arbitrary timing by the contact / separation mechanism driving unit. The image forming apparatus according to claim 1, wherein: 3. The intermediate transfer by means of a mark provided on a part of the intermediate transfer body of claim 1 and a sensor for detecting the mark provided in a passing area of the mark, the ON timing of the primary transfer nip contact / separation mechanism. 3. The image forming apparatus according to claim 2, wherein the timing of turning off the primary transfer nip contacting / separating mechanism is later than the end of the primary transfer before the body position is detected. 4. The image forming apparatus according to claim 1, wherein
The relative position error between the photosensitive member and the intermediate transfer member caused by one rotation of the intermediate transfer member due to a peripheral speed difference caused by the component accuracy of the intermediate transfer member indicates that the photosensitive member or the intermediate transfer by the joint means is performed. An image forming apparatus, wherein play in the body rotation direction is set large.