JP4982071B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an improvement in a driving mechanism of an intermediate transfer belt provided in an electrophotographic image forming apparatus such as a copying machine, a printer, and a facsimile machine.

A conventional electrophotographic image forming apparatus, particularly a full-color image forming apparatus adopting an image forming process by a tandem method, includes an image carrier composed of a photosensitive drum, and a charging unit that charges the image carrier to a predetermined potential. , An exposure unit for exposing the charged image carrier surface to form an electrostatic latent image, a developer for supplying toner to the electrostatic latent image on the image carrier to form a toner image, and a toner on each image carrier A plurality of sets of image forming units including a primary transfer unit that sequentially transfers an image on an intermediate transfer belt to form a superimposed toner image, a primary transfer roller, a cleaning unit that removes residue on the image carrier, and the like. The forming unit is arranged in series along the running surface of the intermediate transfer belt. Each image forming unit is a unit dedicated to each color toner using, for example, yellow, cyan, magenta, and black toner, respectively. The superimposed toner image formed on the intermediate transfer belt is transferred onto the sheet that has been conveyed to the secondary transfer means, and is then fixed and discharged outside the apparatus.
The intermediate transfer belt is driven in a state of being stretched by an inscribed driving roller, a driven roller, and a tension roller, and the driving roller travels by receiving a rotational driving force from a driving source via a driving force transmitting means.
Generally, in order to prevent both functional deterioration due to contact between the intermediate transfer belt and the photoreceptor image carrier, wear of a rubbing member such as a developing roller in the developing unit, change in charging characteristics of stored toner, etc. The intermediate transfer belt and the photosensitive member are separated from each other, and the driving of the developing unit including the photosensitive member is stopped, except when image formation on the photosensitive member or primary transfer operation by the primary transfer roller is necessary. (Patent Document 1).
In order to maximize the above effect by keeping the intermediate transfer belt and the photoconductor separated, the primary transfer rollers facing each other through the plurality of photoconductors and the intermediate transfer belt are set immediately after the primary transfer is completed. The developer is depressurized and separated from the photosensitive member, and the driving of the developing unit including the photosensitive member is stopped. At this time, the intermediate transfer belt stretched by the driving roller and the driven roller is loosened, and the conveyance path is changed, but the tension roller provided for adjusting the tension of the intermediate transfer belt moves to the outside. The slack is absorbed and adjusted, and the tension of the intermediate transfer belt is kept constant. However, since the tension roller is installed between the position where the print pattern is primarily transferred and the position where the print pattern is secondarily transferred onto the sheet, the tension roller moves outward from the primary transfer position. The moving distance of the superimposed toner image carried on the intermediate transfer belt portion to the transfer position becomes longer, the timing of the secondary transfer is delayed with respect to the sheet fed and conveyed to the secondary transfer position, and the sheet is overlapped with the sheet. Deviation occurs in the position of the toner image in the conveyance direction. For this reason, when images are continuously formed, the position in the conveyance direction of the superimposed toner image formed on the sheet of the last page and the position in the conveyance direction of the superimposed toner image formed on the other preceding sheet This is a cause of variation.
Patent Document 2 discloses a technique in which the alignment source of the image is improved by using the same motor for the drive source of the photosensitive belt and the drive source of the intermediate transfer belt. Cannot solve the problem of image misregistration on the sheet caused by separating the intermediate transfer belt from the photosensitive member.
JP 2003-216011 A JP-A-8-95339

As described above, in the conventional tandem-type full-color image forming apparatus, the final page, which is a problem caused by performing the operation of bringing the intermediate transfer belt into contact with or separating from the photoreceptor using the primary transfer roller, is performed. The problem of occurrence of misalignment of the toner image secondarily transferred onto the sheet could not be solved.
The object of the present invention is that even when the operation of bringing the intermediate transfer belt into contact with or separating from the photoreceptor using the primary transfer roller is performed, the secondary transfer position changes or varies with respect to the sheet conveyance direction. An object of the present invention is to provide an image forming apparatus capable of preventing the above-described problem.

In order to achieve the above object, the invention of claim 1 is formed by sequentially transferring a plurality of image carriers each carrying a toner image of a different color and each color toner image from each image carrier. An intermediate transfer belt that carries and conveys a superimposed toner image, and the intermediate transfer belt is pressed against or released from the image carrier in order to sequentially transfer the toner image on each image carrier onto the intermediate transfer belt. Primary transfer means, and secondary transfer means for collectively transferring the superimposed toner images on the intermediate transfer belt onto the sheet. The intermediate transfer belt includes an inscribed drive roller, driven roller, and tension roller. In an image forming apparatus that is driven in a stretched state and is transmitted with rotational driving force from a driving source to a driving roller via a driving force transmitting means, a drive from the driving source to the driving roller is performed. A coupling is provided in the force transmission path, and the coupling includes a driving side member connected to the driving source, a driven side member connected to the driving roller, the driving side member, and the driven side member. and a resilient biasing member for transmitting the driving force of the rotational direction is disposed between the said tension rollers, the primary transfer of the toner image by the intermediate transfer belt conveyance direction downstream of the primary transfer means The elastic transfer member is disposed between the position and a secondary transfer position of the toner image onto the sheet by the secondary transfer unit. in the first case to be pressed against the, is stretched by the driving force, the rotated phase angles delayed in the rotational direction relative to the drive-side member to the driven-side member, the image formed on the plurality of sheets In the case of After the primary transfer for the image is terminated after the driving force required to drive the driven-side member by the primary transfer means for releasing the pressure contact of the respective image carriers of the intermediate transfer belt wherein the to relax when the second decreasing as compared to the case of 1, by rotating such that the phase angle advances the driven-side member than that of the first relative to the driving-side member, By canceling that the intermediate transfer belt is loosened between the driving roller and the driven roller and the tension roller moves outward to delay the traveling of the intermediate transfer belt, the first case and the second in the case of, it characterized that you adjusted to a constant transit time of the intermediate transfer belt between the secondary transfer position and the primary transfer position.
According to a second aspect of the present invention, in the first aspect of the present invention, the drive side member and the driven side member are each provided with a regulating member that regulates a relative rotational direction positional relationship between both of them in a constant manner. .
According to a third aspect of the present invention, in the first or second aspect, the coupling is configured as one intermediate transfer unit including the intermediate transfer belt.
According to a fourth aspect of the present invention, in any one of the first to third aspects, a locking means is provided for fixing or releasing the rotational positional relationship between the driving side member and the driven side member.

In the present invention, a coupling (driving side member, driven side member, elastic urging member) is provided in the driving transmission means from the driving source of the image forming apparatus main body to the driving roller of the intermediate transfer belt, and the driving force transmitted is large. By using the difference in size and expanding and contracting the elastic urging member, it is possible to cancel image position shifts and variations caused by changes in the intermediate transfer belt position, and images on the sheets of the last page and other pages. The position shift can be eliminated.
Further, since the stopper for engaging the driving side member and the driven side member is provided, when the driving force of a certain level or more is applied and the elastic biasing member extends to a predetermined length, the driving side member and the driven side member Since the driving force can be transmitted by contacting each other, the driving force can be transmitted stably.
In addition, since the part including the coupling is integrally formed as an intermediate transfer unit, not in the main body of the apparatus, maintenance such as replacement of parts can be easily performed when the coupling or other parts are damaged. it can.
In addition, when high accuracy is required for the printing position deviation with respect to the sheet feeding direction, the coupling comprising the driving side member, the driven side member, and the elastic biasing member is operated. By configuring the side member and the driven side member so as not to operate, it is possible to increase the margin of reliability, durability, etc. of the apparatus while maintaining the printing position accuracy equivalent to the conventional apparatus. . Therefore, any mode can be appropriately selected and used in accordance with the required print position accuracy with respect to the print position deviation.

The configuration and operation of the image forming apparatus of the present invention will be described below based on the embodiments shown in the drawings.
FIG. 1 is a schematic view showing the overall configuration of an image forming apparatus having an intermediate transfer belt conveyance speed adjusting mechanism according to the present invention, FIGS. 2 and 3 are front views showing the configuration of an intermediate transfer unit, and FIG. It is a top view.
This image forming apparatus is a tandem full color image forming apparatus, and includes an image forming unit A, an exposure device writing device B, a paper feeding unit C, a transport system D, and the like.
The image forming unit A includes four image forming units A-1, an intermediate transfer unit A-2 disposed across the image forming units A-1, and a fixing device A-3.
Each image forming unit A-2 includes an image carrier 1 composed of a photosensitive drum, a charging unit that charges the image carrier 1 to a predetermined potential, and an exposure that exposes the charged image carrier surface to form an electrostatic latent image. Part 2, a developing device that supplies toner to the electrostatic latent image on the image carrier to form a toner image, and sequentially transfers the toner images on each image carrier onto the intermediate transfer belt 21 to form a superimposed toner image The primary transfer means includes a primary transfer roller 26, a cleaning unit for removing the residue on the image carrier, and the like. The image forming units A-1 are arranged in series along the traveling surface of the intermediate transfer belt 21. Each image forming unit A-1 is a unit dedicated to each color toner using, for example, yellow, cyan, magenta, and black toner, respectively. The superimposed toner image formed on the intermediate transfer belt 21 is transferred onto the sheet conveyed from the paper feeding unit C to the secondary transfer unit 41, and then the toner image is fixed on the sheet by the fixing device A-3. It is discharged outside the machine.
The intermediate transfer belt unit A-2 includes an intermediate transfer belt 21, a driven roller 22, a driving roller 23, a tension roller 24, a secondary transfer roller 41, and the like that are inscribed in the intermediate transfer belt 21 and endlessly stretched. .
The image pattern written as an electrostatic latent image on each photoconductor 1 by the exposure device B is visualized as a toner image by the developing device, and the primary transfer roller 26 is pressed against the photoconductor 1 via the intermediate transfer belt 21. In this state, the image is transferred onto the intermediate transfer belt 21, transferred onto the sheet by the secondary transfer roller 41 in synchronization with the sheet fed and conveyed by the sheet feeding unit C, and fixed onto the sheet by the fixing device A-3. The

As shown in the plan view of FIG. 4 and the enlarged views of the couplings of FIGS. 5 and 6, a coupling 30 is disposed at the input side end of the drive shaft 23 a of the drive roller 23. By the action, the conveyance speed of the intermediate transfer belt is adjusted.
5A and 5B are an enlarged view showing a configuration of the coupling in a state where the elastic urging member is extended, and an AA cross-sectional view, and FIGS. 6A and 6B are elastically attached. It is an enlarged view which shows the structure of the coupling in the state which the biasing member relaxed, and BB sectional drawing.
The coupling 30 includes a driven side member 31 whose shaft center is integrally fixed to a drive shaft 23a of the drive roller, a drive side member 32 whose shaft center is rotatably supported by the drive shaft 23a, and a driven member. An elastic biasing member 33 made of a tension spring such as a coil spring having both ends fixed to pins 31 a and 32 a formed on the opposing surfaces of the driving side member 31 and the driving side member 32 is provided.
That is, the coupling 30 includes a driving side member 32 connected to the driving source on the apparatus main body side, a driven side member 31 connected to the driving roller 23, and between the driving side member 32 and the driven side member 31. And an elastic urging member 33 that transmits the driving force in the rotational direction. The elastic urging member 33 is deformed by a change in the magnitude of the driving force necessary to drive the driven member 31. Thus, the conveyance speed of the intermediate transfer belt is adjusted.
Contrary to the above configuration, the shaft center portion of the driven side member 31 is supported by the drive shaft 23a of the drive roller so as to be relatively rotatable, while the shaft center portion of the drive side member 32 is fixed to the drive shaft 23a. May be.

As described above, the characteristic configuration of the present invention is such that the elastic coupling member 33 is interposed between the driving side member 32 and the driven side member 31 of the coupling supported so as to be relatively rotatable with each other by the driving shaft 23a. The elastic urging member 33 is deformed by the magnitude of the driving force required to engage and drive the driven side member 31, thereby enabling the conveyance speed of the intermediate transfer belt 21 to be adjusted. Furthermore, the structure which provided both the drive side member 32 and the to-be-driven side member 31 with the stopper (regulation member) 32b and 31b which restrict | limit the relative rotational direction positional relationship between both uniformly is also characteristic. Each stopper 32b, 31b is arranged on the opposite side to each pin 32a, 31a across the drive shaft 23a. The angle θ1 between the stopper 32b centered on the drive shaft 23a and the pin 32a and the angle θ2 between the stopper 31b centered on the drive shaft 23a and the pin 31a are both less than 180 degrees. It is preferable to set.
The driving side member 32 receives the rotational driving force from the driving source by driving force transmission means such as a gear on the apparatus main body side, and transmits the driving force to the driven side member 31 via the elastic biasing member 33. When the primary transfer roller 26 presses the intermediate transfer belt 21 against the photoreceptor 1 as shown in FIG. 2, a large driving force is required to drive the intermediate transfer belt by the resistance. That is, since the resistance of the driven side member 31 increases, the rotation of the driven side member 31 slows down, and the tension spring 33 is stretched as shown in FIG. 5, and the stopper 32b of the driving side member 32 catches up with the stopper 31b of the driven side member 31. Direct drive force is transmitted by contact.

When a plurality of pages are continuously printed by the image forming apparatus, the intermediate transfer belt 21 repeats the printing in the state shown in FIG. 2, but when the last page is printed, the intermediate transfer belt 21 is placed on the intermediate transfer belt 21 from the most downstream photoconductor 1d. Immediately after the print pattern (toner image) is transferred, the primary transfer roller 26 is depressurized and lowered as shown in FIG. At this time, since the primary transfer roller 26 that follows the movement of the intermediate transfer belt 21 is released, the resistance applied to the drive roller 23 decreases, and the tension spring 33 returns to the initial state shown in FIG. On the other hand, the driven member 31 advances relatively in the rotation direction. That is, since both the stoppers 31 b and 32 b are separated from each other, the driving force from the driving side member 32 is transmitted to the driven side member 31 exclusively through the elastic biasing member 33.
Therefore, immediately after the primary transfer of the toner image from the most downstream photoconductor 1d to the intermediate transfer belt 21, each primary transfer roller 26 is depressurized and separated from the intermediate transfer belt, and the drive roller 23 and the driven roller 22 are separated. Thus, the intermediate transfer belt 21 stretched by the rise and press of each primary transfer roller 26 is loosened, and the tension roller 24 moves outward to delay the intermediate transfer belt. The deviation in the transport direction from the image is equivalent to the other preceding pages.

As described above, in the present invention, the coupling 30 is provided in the driving force transmission mechanism (driving force transmission path) from the driving source of the apparatus main body to the driving roller 23 of the intermediate transfer belt 21 and is supported so as to be relatively rotatable with respect to each other. By connecting the driving side member 32 and the driven side member 31 with an elastic biasing member 33 such as a spring, the primary transfer roller 26 is pressed against the photoreceptor 1 via the intermediate transfer belt 21, that is, the driving roller. When the driving force applied to 23 is large, the elastic biasing member 33 extends to accumulate torque, and the driven side member 31 rotates with respect to the driving side member 32 at an angular phase delayed in the rotational direction.
On the other hand, when the primary transfer roller 26 is separated from the intermediate transfer belt 21, that is, when the driving force applied to the driving roller 23 is reduced, the elastic biasing member 33 is loosened as shown in FIG. The intermediate transfer belt 21 rotates quickly while the phase of the driven side member 31 being delayed with respect to the driving side member 32 and the elastic biasing member 33 is loosened, and the time to the secondary transfer position is shortened. As a result, the distance between the front end of the sheet and the front end of the toner image is reduced. At the same time, a phenomenon occurs in which the transport distance from the primary transfer position to the secondary transfer position becomes longer due to the relaxation of the intermediate transfer belt 21 in which the primary transfer roller 26 is pressed and stretched by the photosensitive member 1, and the leading edge of the sheet And acts to increase the distance between the image tips.

In the present invention, the above-described two effects cancel each other, so that the positional deviation amount in the conveyance direction of the sheet and the image pattern can be made equal to the positional deviation amount in the other preceding pages even in the final page.
Further, since the coupling 30 is configured as one intermediate transfer unit A-2 including the intermediate transfer belt 21, maintenance such as component replacement is easily performed when the coupling or other components are damaged. be able to.
Further, as a modification, it is preferable to provide a lock unit that fixes or releases the rotational position 32 of the driving side member 32 and the driven side member 31. That is, a lock means for fixing the relative angle between the driving side member and the driven side member 31 is provided, and either the case of changing or fixing the relative angle between the driving side member and the driven side member is selected. Make it possible.
By configuring in this way, when the locking means is operated, the positional relationship between the driving side member 32 and the driven side member 31 is fixed, so that the above function of the coupling is not exhibited, When the locking means is not operated, the original function by the above coupling is exhibited.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. Sectional drawing which shows the state of an intermediate transfer belt and peripheral components. Sectional drawing which shows the state of an intermediate transfer belt and peripheral components. The top view of an intermediate transfer belt and peripheral parts. The block diagram of the coupling and peripheral component of this invention. The block diagram of the coupling and peripheral component of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Image carrier (photosensitive body), 2 ... Exposure part, 21 ... Intermediate transfer belt, 22 ... Driven roller, 23 ... Drive roller, 23a ... Drive shaft, 24 ... Tension roller, 26 ... Primary transfer roller, 30 ... Cup Ring, 31 ... driven side member, 31a ... pin, 31b ... stopper, 32 ... drive side member, 32a ... pin, 32b ... stopper, 33 ... elastic biasing member, 41 ... secondary transfer roller.

Claims (4)

A plurality of image carriers that respectively carry toner images of different colors; an intermediate transfer belt that carries and conveys a superimposed toner image formed by sequentially transferring the toner images of each color from each image carrier; A primary transfer means for pressing the intermediate transfer belt against each image carrier and releasing the pressure contact in order to sequentially transfer the toner images on each image carrier onto the intermediate transfer belt; and a superimposed toner image on the intermediate transfer belt Secondary transfer means for transferring the images onto the sheet all at once,
The intermediate transfer belt is driven in a state in which the intermediate transfer belt is stretched by an inscribed driving roller, a driven roller, and a tension roller, and a rotational driving force is transmitted to the driving roller from a driving source via a driving force transmitting unit. In the forming device,
A coupling is provided in a driving force transmission path from the driving source to the driving roller,
The coupling is disposed between the driving side member connected to the driving source, the driven side member connected to the driving roller, and the driving side member and the driven side member in the rotation direction. An elastic biasing member that transmits the driving force of
The tension roller is disposed between a primary transfer position of the toner image by the primary transfer unit at the most downstream side in the conveyance direction of the intermediate transfer belt and a secondary transfer position of the toner image onto the sheet by the secondary transfer unit. Place and
The elastic biasing member is
If the primary transfer means of the first to press the intermediate transfer belt to each of the image bearing member is stretched by the driving force, the rotational direction of the driven-side member relative to the driving-side member Rotate with delayed phase angle,
After the primary transfer is completed for the last image in the case of forming an image on a plurality of sheets, the primary transfer unit releases the pressure contact of the intermediate transfer belt to each of the image bearing members, whereby the driven side member is removed. In the second case where the driving force necessary for driving is reduced compared to the first case, the driving side member is relaxed relative to the driving side member as compared to the first case. By rotating so that the phase angle advances, the intermediate transfer belt is loosened between the driving roller and the driven roller, and the tension roller moves outward to delay the running of the intermediate transfer belt. By
Wherein in the first case and the second case, the image forming apparatus characterized that you adjusted to a constant transit time of the intermediate transfer belt between the secondary transfer position and the primary transfer position.   The image forming apparatus according to claim 1, wherein a regulation member that regulates a relative rotational direction positional relationship between both the driving side member and the driven side member to be constant is provided.   The image forming apparatus according to claim 1, wherein the coupling is configured as one intermediate transfer unit including the intermediate transfer belt.   4. The image forming apparatus according to claim 1, further comprising: a lock unit that fixes or releases a positional relationship in a rotational direction between the driving side member and the driven side member. 5. .

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