JPH10111588A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device capable of resolving the mutual displacement of a detected mark on an intermediate transfer body (timing of detection) and a drive means and inconsistency in the drive means each time a process for a separate color is carried out, and eliminating displacement resulting from them. SOLUTION: This device has the intermediate transfer body 415 which is disposed opposite a photoreceptor 414 and rotated in contact with the photoreceptor at the same peripheral speed as the photoreceptor 414, the mark provided on a part of the intermediate transfer body 415, and a sensor for mark detection provided in the area where the mark passes. It also has a primary transfer means in a primary transfer part formed in the part where the photoreceptor 414 and the intermediate transfer body 415 are in contact with each other, and an electrifying means in an electrifying position which is further upstream in the direction of the rotation of the photoreceptor than the position where the primary transfer means is disposed. The device is provided with a primary-transfer nip contact/separation mechanism which allows release from the contact of the photoreceptor and intermediate transfer body in the primary transfer part, that is, a primary transfer nip.

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. A primary transfer unit and a charging unit are provided at a charging position on the upstream side in the rotation direction of the photoconductor relative to the position where the primary transfer unit is disposed. In 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 photosensitive member and the intermediate transfer member, and the charged photosensitive member passed through the charging position is charged. Forming a toner image of an arbitrary color by light writing and development in the area, and then transferring the toner image of the arbitrary color to an intermediate transfer body by a primary transfer unit in the primary transfer unit for each of different colors. By repeatedly forming a color superimposed toner image on the intermediate transfer body, the color image is obtained by collectively transferring the superimposed toner image onto transfer paper. 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, a multi-color image forming apparatus disclosed in Japanese Patent Application Laid-Open No. 61-83557 discloses a method in which the peripheral length of the transfer means is set to an integral multiple of that of the photoreceptor so that one point on the photoreceptor is transferred. A technique is disclosed in which correspondence with a plurality of points of the circumferential length is ensured so that developed images of a plurality of colors do not shift on a transfer unit. Also, Japanese Patent Application Laid-Open No. 1-30
In the "color image forming apparatus" disclosed in Japanese Patent No. 7774, good image quality can be obtained by setting all reduction ratios of teeth engaged by a reduction gear connecting the photosensitive member driving means and the photosensitive member to integers. Is disclosed. In the primary transfer portion, the photosensitive member and the intermediate transfer member are in close contact to form a nip portion, and when both are charged, the contact force 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 always a certain range of dimensional variation, and the circumference ratio of each part often does not become 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 of the rotating means, and the reaction of the smaller peripheral speed causes the driven side to be faster than the drive side in the slower one of the photoconductor and the intermediate transfer body. As a result, when the backlash of the meshing portion of the gears constituting the driving means is eroded (at the time of relative rotation by the amount of the backlash), the driving force and the adhesion force of the primary transfer portion are increased. As a result, load fluctuation and local slip at the primary transfer nip portion occur, and the transferred image at that time is disturbed, resulting in displacement. 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]

In order to solve the above-mentioned problems,
The invention according to claim 1 is a photosensitive member comprising a rotating member driven to rotate, an intermediate transfer member arranged to face 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 body, 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 body. A primary transfer unit, a charging unit at a charging position on the upstream side in the rotation direction of the photoconductor relative to a position where the primary transfer unit is disposed,
During image formation, the image forming process is started after a certain timing from the detection of the mark by the sensor during the rotation of the photosensitive member and the intermediate transfer member, and the photosensitive member charged by the charging unit is started. Forming a toner image of an arbitrary color on the charged area by optical writing and development, and then transferring the toner image of the arbitrary color to the intermediate transfer body by a primary transfer unit in the primary transfer unit. The image forming apparatus obtains a color superimposed toner image on the intermediate transfer body, and collectively transfers the superimposed toner image onto transfer paper in a secondary transfer unit to obtain a color image. Wherein a primary transfer nip contact / separation mechanism is provided to enable release of the state of contact between the photoreceptor and the intermediate transfer member, ie, the primary transfer nip state. The invention according to claim 2 is characterized in that 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 according to the first aspect and a mark detecting sensor provided in a pass area of the mark. Before the position of the intermediate transfer member is detected, and
The OFF timing of the primary transfer nip contact / separation mechanism is after the end of the primary transfer. According to a fourth aspect 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 smaller than that of the intermediate transfer member. The play length of the surface of the intermediate transfer member due to backlash of the driving means is set to be large. The invention of claim 5 is
In the image forming apparatus according to the second aspect, the primary transfer nip contact / separation mechanism according to the second aspect is in an OFF state while the image forming apparatus main body is in an operation standby state or stopped.

[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 photoconductor 414 is applied to the surface of the intermediate transfer belt 415, which is driven at a constant speed in contact with the photoconductor, by a belt transfer corona discharger (hereinafter, referred to as a belt transfer unit) 416. Transcribed. Hereinafter, the transfer of the toner image from the photosensitive drum 414 to the intermediate transfer belt 415 is referred to as belt transfer.

A small amount of 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. The intermediate transfer belt 41
5 includes BK, C, and BK sequentially formed on the photosensitive drum 414.
The M and Y toner images are sequentially aligned on the same
A color transfer belt transfer image is formed, and thereafter, batch transfer is performed on transfer paper by a corona discharge transfer device. By the way, on the photoconductor drum 414 side, after the BK image forming process, C
The process proceeds to an 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 a laser beam using the image data. The C developing device 420C has a
After the trailing end of the BK latent image has passed and before the leading end of the C latent image has arrived, the rotating operation of the revolver developing device is performed to develop the C latent image with C toner. Thereafter, the development of the C latent image area is continued, but when the rear end 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 420C is sent out. The next M developing device 420M is positioned at the developing position. This operation, too,
This is performed before the leading end of the next M latent image reaches the developing section. In the process of each image of M and Y, the operation of reading, latent image formation, and development of each image data is performed in the above-described B mode.
The description is omitted because it follows the steps of the K image and the C image.

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.
Then, 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 to 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 passage area of the belt cleaning device 415U, and it may be difficult to arrange depending on the model or the like. . 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 centering on a photoconductor, and FIGS. 3A and 3B are specific configurations 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 an explanatory diagram of backlash. The primary transfer nip contacting / separating mechanism shown in detail in FIG. 3 rotatably supports the pressure roller 415F by a shaft 433b at the other end of the swing bracket 433 rotatably supported in the direction of the arrow by a fulcrum 433a. ,
The swing bracket 433 is urged to a retracted position shown in FIG. 3A by elastic means (not shown) or its own weight. 431
Is an eccentric cam which is driven to rotate about a shaft 431a. When the cam 431 is in the non-pressing position shown in FIG.
33c is retracted to a position where it is not pressed. Conversely, when the cam 431 is in the pressed position shown in FIG.
The pressed surface 433c of the bracket 433 is pressed by 31b. As a result, in the retracted state (a), the intermediate transfer belt 415 is not in contact with the photoconductor 414, and conversely (b)
At the pressing position, the belt is pressed toward the photoconductor, so that a part of the belt nips with the photoconductor 414 over 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 was set such that the backlash of the surface of the intermediate transfer member due to backlash of the driving means (the meshing portion of the gears) of the intermediate transfer member was increased. For this reason, even if the photosensitive member and the intermediate transfer member are rotated synchronously by the adhesion force due to the Coulomb force in the primary transfer nip, the peripheral speed difference can be absorbed by backlash. 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.

More specifically, in FIG. 2, the average peripheral speed of the photosensitive drum 414 is Va, and the intermediate transfer belt 415 is shown in FIG.
Assuming that the average peripheral speed is Vb, the time t required for one rotation of the intermediate transfer belt 415 having the circumferential length Lb is t = Lb / Vb, and the moving distance La of the surface of the photosensitive drum 414 during the time t is 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, the photosensitive drum 414 and the belt driving roller 415D
The driving means, for example, in the case of the gear drive system, always backlash △ x _i of the gear is present between the drive gear and the driven gear, as shown in FIG. If the gear train is composed of n gears, the total backlash is

[0018]

(Equation 1) Becomes The photosensitive drum 414 due to the backlash
Alternatively, the play in the movement direction on the surface of the intermediate transfer belt 415 is a value obtained by multiplying the coefficient A in consideration of the speed reduction ratio and the radius ratio, that is, Ax. Here, the process error △ between the photosensitive drum 414 and the intermediate transfer belt 415 described above.
By setting the above-mentioned play Ax (the play length of the surface of the intermediate transfer member due to backlash of the driving means of the intermediate transfer member) to be larger than L (the relative position error with respect to the photosensitive member generated during one rotation of the intermediate transfer member). During one rotation of the intermediate transfer belt 415, reverse torque is not transmitted from the driven gear to the drive gear in the drive system of the device with the lower peripheral speed, and the floating state is maintained within the range of backlash. Dripping. In addition, by performing the primary transfer nip release operation every one rotation of the intermediate transfer belt 415, the external force due to the adhesion force of the nip is eliminated, and the backlash in the floating state returns to the initial state. In order to prevent the intermediate transfer belt 415 from slipping with the driving roller 415D and to form a sufficient primary transfer nip,
There is some necessary tension. Therefore, when the machine is not operating (during the primary transfer), the primary transfer nip contact / separation mechanism is set in the released state (the state shown in FIG. 3A) to store the intermediate transfer belt 415 with a weak tension. And fatigue can be reduced and durability can be increased.

[0019]

According to the first aspect of the present invention, since the primary transfer nip contact / separation mechanism is provided, the photosensitive member and the intermediate transfer belt are brought into close contact with each other by the Coulomb force in the primary transfer nip. Thus, it is possible to prevent 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. In the image forming apparatus of the present invention, the primary transfer nip contact / separation mechanism is provided with a contact / separation mechanism driving unit that can be turned on (pressed) and turned off (retracted) at an arbitrary timing. Can be released by the Coulomb force. 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 may be set to an intermediate time by a mark detection sensor provided in a pass area of a mark provided in a part of the intermediate transfer body. Set before the timing of detecting the position of the transfer body (mark detection),
By setting the OFF timing of the primary transfer nip contact / separation mechanism after the end of the primary transfer, the Coulomb force in the primary transfer nip can be used during the time when the primary transfer is not performed without losing the accuracy of the alignment by the mark detection. The adhesion can be released. In the image forming apparatus according to the fourth aspect, the 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 larger than that of the intermediate transfer member. Since the backlash of the surface of the intermediate transfer member is set to be large due to the backlash of the driving means, 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 is reduced. The toner image is initialized each time the toner image is overlapped by one operation by the operation of the primary transfer nip contact / separation mechanism for each rotation of the intermediate transfer member, as described in claim 3, so that the adhesion force of the primary transfer nip is obtained. And the drive system can be prevented from displacement due to tension. In the image forming apparatus according to the fifth aspect, when the primary transfer operation is not required, the nip is released by turning off the primary transfer contact / separation mechanism, and the tension of the intermediate transfer body is reduced, so that the mechanical force of the intermediate transfer body is reduced. Fatigue can be reduced.

[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.

FIG. 5 is a diagram illustrating backlash between a driving gear and a driven gear.

[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, 420YY 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,

Claims (5)

[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 An image forming apparatus provided with a primary transfer nip contact / separation mechanism that enables release of an image. 2. The method according to claim 1, wherein the primary transfer nip contact / separation mechanism has a contact / separation mechanism drive unit, and the contact / separation mechanism drive unit can control ON / OFF of the primary transfer nip contact / separation mechanism at an arbitrary timing. 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. A relative position error between the photoconductor and the photoconductor caused during one rotation of the intermediate transfer body due to a peripheral speed difference caused by component accuracy between the photoconductor and the intermediate transfer body. 4. The image forming apparatus according to claim 1, wherein a play length of the surface of the intermediate transfer member due to backlash of a driving unit is set to be large. 5. The image forming apparatus according to claim 2, wherein
3. The image forming apparatus according to claim 2, wherein the primary transfer nip contact / separation mechanism is in an OFF state while the image forming apparatus main body is in an operation standby state or stopped.