JP5316934B2 - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus, restraining speed variation of a toner image support belt generated caused when a record medium enters a record medium transfer nip while restraining deterioration of durability of the toner image support belt. <P>SOLUTION: This image forming apparatus includes a belt displacement control mechanism 200. A plurality of stretching surfaces are formed by stretching an intermediate transfer belt 8 between a plurality of stretching rollers. In the mechanism, inward displacement of a second stretching surface 8b among the plurality of stretching surface where the downstream end in the moving direction of the intermediate transfer belt 8 is a transfer nip upstream stretching surface, which is a stretching surface serving as a secondary transfer nip N, is measured by a displacement sensor 22, and according to the measurement result, a third stretching surface 8c, which is not a second stretching surface 8b among the plurality of stretching surfaces of the intermediate transfer belt 8, is pressed by a pressure roller 25 to be displaced inward. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

The present invention is an electrophotographic method of recording to the sheet-like recording medium of a single leaf, an electrostatic recording method, ionographic, copier employing an image forming method such as a magnetic recording system, a printer, it relates to an image forming apparatus such as a facsimile The present invention relates to an image forming apparatus that obtains a final image by transferring a toner image on a toner image carrying belt such as an intermediate transfer belt to a recording medium.

Conventionally, as an image forming apparatus of this type, a toner image formed on a photosensitive member is primarily transferred onto an intermediate transfer belt that is stretched by a plurality of stretching rollers and moves endlessly, and two toner images on the intermediate transfer belt are transferred. There is an intermediate transfer belt type image forming apparatus that performs secondary transfer onto a sheet-like recording medium at the next transfer nip.
In the intermediate transfer belt type image forming apparatus, when the recording medium enters the secondary transfer nip, a speed fluctuation occurs in the moving speed of the endless movement of the intermediate transfer belt. In some cases, a difference in speed occurred, resulting in a transfer position shift.
Hereinafter, a mechanism in which the speed fluctuation of the intermediate transfer belt occurs when the recording medium that causes the transfer position deviation enters the secondary transfer nip will be described.

As an intermediate transfer belt type image forming apparatus, an intermediate transfer belt in which a contact position with a stretching roller (hereinafter referred to as a secondary transfer counter roller) forming a secondary transfer nip is a downstream end in the moving direction of the intermediate transfer belt. An intermediate transfer belt and a recording medium conveying member are arranged so that the recording medium enters the secondary transfer nip after the recording medium comes into contact with the tension surface (hereinafter referred to as the transfer nip upstream tension surface). There is. Specifically, the recording medium transported toward the secondary transfer nip has a layout in which the transport direction of the recording medium and the stretched surface on the upstream side of the transfer nip are not parallel, and the leading end of the transported recording medium is transferred. It is configured to contact the nip upstream tension surface and be guided to the secondary transfer nip by the surface movement of the intermediate transfer belt. In this way, by guiding the recording medium to the secondary transfer nip by bringing the leading end of the recording medium into contact with the upstream tension surface, the recording medium can stably enter the secondary transfer nip.
However, since the conveyance direction of the recording medium and the transfer nip upstream stretch surface are at an angle, when the leading end of the recording medium contacts the transfer nip upstream stretch surface, the transfer nip upstream stretch surface is It is pushed by the recording medium and is displaced to the inside of the endless intermediate transfer belt. When a part of the tension surface on the upstream side of the transfer nip is displaced inward, the secondary transfer counter roller is decelerated by a force that is pulled toward the upstream side in the moving direction of the intermediate transfer belt. On the other hand, the tension roller at the upstream end of the transfer nip upstream tension surface (hereinafter referred to as the transfer nip upstream tension roller) is intermediate when a part of the transfer nip upstream tension surface is displaced inward. A force that is pulled to the downstream side of the transfer belt in the moving direction is applied to accelerate.
Then, in the intermediate transfer belt at a position facing the photoconductor on the upstream side in the moving direction of the intermediate transfer belt with respect to the transfer nip upstream stretch roller, the transfer nip upstream stretch roller accelerates, so that the recording medium becomes secondary. A speed fluctuation occurs that accelerates faster than the moving speed before entering the transfer nip.
As a result, a speed difference is generated between the surface of the intermediate transfer belt and the surface of the photoreceptor, and a transfer position shift occurs.

As a configuration capable of suppressing the occurrence of a speed fluctuation of the intermediate transfer belt when the recording medium enters the secondary transfer nip, Patent Document 1 discloses a conveyance direction of the recording medium conveyed toward the secondary transfer nip. And a configuration in which the angle between the transfer nip upstream-side stretch surface is shallow. Thereby, when the recording medium enters the secondary transfer nip, it is suppressed that a part of the tension surface on the upstream side of the transfer nip is displaced inside the endless intermediate transfer belt by pressing the recording medium, Variation in the speed of the intermediate transfer belt due to this displacement can be suppressed. However, if the angle is shallow, the action of guiding the recording medium to the secondary transfer nip by bringing the leading end of the recording medium into contact with the upstream tension surface is reduced, and the conveyance of the recording medium to enter the secondary transfer nip is not effective. May become stable.
In Patent Document 2, a tension roller is provided on both the upstream side and the downstream side in the movement direction of the intermediate transfer belt in the secondary transfer nip so as to bend the belt inward so as to bend the belt inward. An image forming apparatus is described in which the tension of a belt is adjusted by a roller.

JP 2006-189667 A JP-A-2005-338884

However, in the image forming apparatus disclosed in Patent Document 2, the intermediate transfer belt is bent inward with a tension that is sufficient to suppress the occurrence of fluctuations in the speed of the intermediate transfer belt when the recording medium enters the secondary transfer nip. Therefore, local stress is generated at that location. This may cause a problem in durability of the intermediate transfer belt.
The speed fluctuation of the toner image carrying belt when the recording medium enters the transfer position for transferring the toner image from the toner image carrying belt to the recording medium is not limited to the case where the toner image carrying belt is an intermediate transfer belt. It can also be a body belt. When the speed fluctuation occurs in the photosensitive belt, a deviation occurs between the exposure light irradiation timing for forming the latent image and the timing when the surface of the photosensitive belt passes the exposure position, and the latent image formed on the photosensitive belt is shifted. Misalignment occurs.

The present invention has been made in view of the above problems, and an object, the toner image while suppressing deterioration of durability of the toner image bearing belt, the recording medium records medium transfer nip occur upon entering An object of the present invention is to provide an image forming apparatus capable of suppressing the speed fluctuation of the carrying belt.

In order to achieve the above object, a first aspect of the present invention provides a toner image carrying belt which is stretched by a plurality of stretching rollers and carries a toner image on its surface and moves endlessly, and among the plurality of stretching rollers. And a recording medium transfer member that forms a recording medium transfer nip that faces one of the toner image carrier belt and sandwiches the toner image carrier belt to transfer the toner image on the toner image carrier belt to a recording medium. Of the plurality of stretching surfaces formed by the supporting belt being stretched by the plurality of stretching rollers, the stretching surface in which the downstream end portion in the moving direction of the toner image carrying belt becomes the recording medium transfer nip In the image forming apparatus in which the toner image carrying belt and the recording medium conveying member are arranged so that the recording medium enters the recording medium transfer nip after the recording medium comes into contact with the transfer nip upstream stretch surface. Transcription Nik A belt displacement that displaces two of the plurality of tension surfaces of the toner image carrying belt that are not the upstream tension surfaces of the transfer nip inward according to the displacement of the upstream tension surface to the inside. It has a control mechanism.
According to a second aspect of the present invention, there is provided the image forming apparatus according to the first aspect, wherein the belt displacement control mechanism has one of the two tension surfaces according to the displacement inward of the tension surface on the upstream side of the transfer nip. In addition, the upstream end portion in the moving direction of the toner image carrying belt displaces the transfer nip downstream stretch surface, which is the stretch surface serving as the recording medium transfer nip, inward.
According to a third aspect of the present invention, in the image forming apparatus of the first or second aspect, the toner image carrying belt is stretched by three or more stretching rollers, and the belt displacement control mechanism is located upstream of the transfer nip. Depending on the inward displacement of the tensioning surface, one of the two tensioning surfaces is the upstream side of the transfer nip upstream side in the moving direction of the toner image carrier belt on the upstream side of the transfer nip. The stretched surface adjacent to the frame surface is displaced inward.
According to a fourth aspect of the present invention, in the image forming apparatus according to the first, second, or third aspect, the belt displacement control mechanism includes a measuring unit that measures a displacement amount of the stretching surface on the upstream side of the transfer nip, and an inward side. It has two pressing rollers that come into contact with each of the two tension surfaces to be displaced from the outside and press the tension surfaces inward, and a pressing amount control means for controlling the pressing amount of the pressing roller. It is characterized by.
According to a fifth aspect of the present invention, in the image forming apparatus according to the fourth aspect, the pressing amount control means controls the pressing amount of the two pressing rollers by independent pressing mechanisms. .
The invention of claim 6 is the image forming apparatus according to claim 4, the pressing amount control means is characterized in that to control the pressing amount in a single pressing mechanism two the pressing roller.
According to a seventh aspect of the present invention, in the image forming apparatus of the sixth aspect, the pressing mechanism includes a link mechanism that holds the two pressing rollers, and a link mechanism drive control unit that controls the driving of the link mechanism. It is characterized by having.
According to an eighth aspect of the present invention, in the image forming apparatus according to the fourth, fifth, sixth, or seventh aspect, the measuring unit is disposed inside the toner image carrying belt, and the inner side of the transfer nip upstream stretch surface. A distance sensor that measures the distance to the surface of the transfer nip, and the pressing amount control means displaces inward only when the distance between the distance sensor and the transfer nip upstream tension surface falls below a predetermined threshold. It is characterized by performing control to press the mounting surface with a pressing roller.
According to a ninth aspect of the present invention, in the image forming apparatus of the first, second, third, fourth, fifth, sixth, seventh or eighth aspect, the toner image carrying belt is carried on another toner image carrying body. It is an intermediate transfer belt that transfers a toner image and transfers the transferred toner image to a recording medium at a recording medium transfer nip.

  In the image forming apparatus according to any one of the first to ninth aspects, the stretching surface other than the stretching surface on the upstream side of the transfer nip is displaced inward so that the stretching roller on the downstream side in the moving direction of the stretching surface on the upstream side of the transfer nip can be moved. In this case, a force that is pulled toward the downstream side in the moving direction of the toner image carrying belt is applied, and deceleration caused by the inward displacement of the tension surface on the upstream side of the transfer nip is suppressed. Further, by displacing the tensioning surface other than the tensioning surface on the upstream side of the transfer nip inward, the tensioning roller on the upstream side in the movement direction of the tensioning surface on the upstream side of the transfer nip is moved upstream in the movement direction of the toner image carrying belt. A pulling force is applied, and the acceleration caused by the inward displacement of the transfer nip upstream tension surface is suppressed. Furthermore, the tension surface other than the tension surface on the upstream side of the transfer nip is displaced inward according to the displacement of the tension surface on the upstream side of the transfer nip, so that the fluctuation in the speed of the toner image carrying belt can be suppressed. As compared with a configuration in which the tension is always applied, it is possible to suppress a decrease in durability of the toner image carrying belt.

According to the first to ninth aspects of the present invention, acceleration of the tension roller on the upstream side in the movement direction of the tension surface on the upstream side of the transfer nip due to the inward displacement of the tension surface on the upstream side of the transfer nip, and downstream in the movement direction. it is possible to suppress the reduction of the side of the tension roller, while suppressing the speed fluctuation of the toner image bearing belt which occurs when the recording medium to record medium transfer nip enters, the durability of the toner image bearing belt There is an excellent effect that the decrease can be suppressed.

Hereinafter, an electrophotographic printer (hereinafter simply referred to as a printer 100) will be described as an example of an embodiment of an image forming apparatus to which the present invention is applied. The image forming unit will be described as a process cartridge.
First, a basic configuration of the printer 100 that is an image forming apparatus will be described. FIG. 2 is a schematic configuration diagram of the printer 100. In FIG. 2, the printer 100 includes four process cartridges 6Y, M, C, and K for generating toner images of yellow, magenta, cyan, and black (hereinafter referred to as Y, M, C, and K). Yes. These use Y, M, C, and K toners of different colors as the image forming material, but the other configurations are the same and are replaced when the lifetime is reached.
Taking a process cartridge 6Y for generating a Y toner image as an example, as shown in FIG. 3, a drum-shaped photoreceptor 1Y, a drum cleaning device 2Y, a charge eliminating device (not shown), a charging device 4Y, a developing device 5Y, etc. I have. The process cartridge 6Y can be attached to and detached from the main body of the printer 100 so that consumable parts can be replaced at a time.

  The charging device 4Y uniformly charges the surface of the photoreceptor 1Y that is rotated clockwise in the drawing by a driving unit (not shown). The uniformly charged surface of the photoreceptor 1 </ b> Y is exposed and scanned by the laser beam L to carry an electrostatic latent image for Y. This Y electrostatic latent image is developed into a Y toner image by the developing device 5Y using Y toner. The Y toner image formed on the photoreceptor 1Y is intermediately transferred onto the intermediate transfer belt 8 at the primary transfer nip. The drum cleaning device 2Y removes the toner remaining on the surface of the photoreceptor 1Y after the primary transfer process. A static elimination device (not shown) neutralizes residual charges on the photoreceptor 1Y after cleaning. By this charge removal, the surface of the photoreceptor 1Y is initialized and prepared for the next image formation. In the other process cartridges 6M, C, and K, M, C, and K toner images are similarly formed on the photoreceptors 1M, C, and K, and are intermediately transferred onto the intermediate transfer belt 8.

In FIG. 2, the exposure device 7 is disposed below the process cartridges 6Y, 6M, 6C, and 6K.
The exposure device 7 serving as a latent image forming unit irradiates each of the photosensitive members 1Y, 1M, 1C, and 1K in the process cartridges 6Y, 6M, 6C, and 6K with a laser beam L emitted based on the image information. By this exposure, electrostatic latent images for Y, M, C, and K are formed on the photoreceptors 1Y, 1M, 1C, and 1K, respectively. The exposure device 7 irradiates the photoreceptors 1Y, 1M, 1C, and 1K with a laser beam L emitted from a light source via a plurality of optical lenses and mirrors while scanning with a polygon mirror that is rotationally driven by a motor. Is.

On the lower side of the exposure apparatus 7 in the figure, paper supply means including a paper storage cassette 26, a paper supply roller 27 incorporated therein, a pair of registration rollers 28, and the like are disposed. The paper storage cassette 26 stores a plurality of transfer papers P as recording media, and a paper feed roller 27 is in contact with the uppermost transfer paper P. When the paper feeding roller 27 is rotated counterclockwise in the drawing by a driving means (not shown), the uppermost transfer paper P is fed toward the rollers of the registration roller pair 28.
The registration roller pair 28 rotationally drives the pair of rollers so as to sandwich the transfer paper P, but once the transfer paper P is sandwiched, the rotation is temporarily stopped. Then, the transfer paper P is sent out toward a secondary transfer nip described later at an appropriate timing.
In the sheet feeding unit having such a configuration, a conveying unit is configured by a combination of the sheet feeding roller 27 and the registration roller pair 28 corresponding to the timing roller. This transport means transports the transfer paper P from a paper storage cassette 26 serving as a storage means to a secondary transfer nip described later.

Above the process cartridges 6Y, 6M, 6C, and 6K, an intermediate transfer unit 15 that moves the intermediate transfer belt 8 serving as an intermediate transfer member endlessly while stretching is disposed. In addition to the intermediate transfer belt 8, the intermediate transfer unit 15 includes four primary transfer bias rollers 9Y, M, C, and K, a cleaning device 10, and the like. Further, a driving roller 12 that is a secondary transfer counter roller, a tension roller 13 that applies tension to the intermediate transfer belt 8 by being biased toward the outside of the intermediate transfer belt 8 by a biasing member such as a spring, and secondary transfer. An entrance roller 14 that is a stretching roller on the entrance side of the nip N is also provided. The intermediate transfer belt 8 is endlessly moved counterclockwise in the figure by the rotational driving of the driving roller 12 while being stretched around these three rollers.
The tension roller 13 also has a function as a cleaning counter roller facing the cleaning device 10 with the intermediate transfer belt 8 interposed therebetween.

The primary transfer bias rollers 9Y, M, C, and K form the primary transfer nip by sandwiching the intermediate transfer belt 8 that is moved endlessly in this manner with the photoreceptors 1Y, M, C, and K, respectively. In these methods, a transfer bias having a polarity opposite to that of toner (for example, plus) is applied to the back surface (loop inner peripheral surface) of the intermediate transfer belt 8. All the rollers other than the primary transfer bias rollers 9Y, 9M, 9C, and 9K disposed on the back surface (loop inner peripheral surface) of the intermediate transfer belt 8 are electrically grounded.
The intermediate transfer belt 8 sequentially passes through the primary transfer nips for Y, M, C, and K along with the endless movement thereof, and Y, M, C, K toner images are superimposed and primarily transferred. As a result, a four-color superimposed toner image (hereinafter referred to as a four-color toner image) is formed on the intermediate transfer belt 8.

The driving roller 12, which is a secondary transfer counter roller, sandwiches the intermediate transfer belt 8 with the secondary transfer roller 19 to form a secondary transfer nip. The four-color toner image formed on the intermediate transfer belt 8 is transferred onto the transfer paper P at the secondary transfer nip.
Transfer residual toner that has not been transferred to the transfer paper P adheres to the intermediate transfer belt 8 after passing through the secondary transfer nip. This is cleaned by the cleaning device 10.

At the secondary transfer nip, the transfer paper P is sandwiched between the intermediate transfer belt 8 and the secondary transfer roller 19 whose surfaces move endlessly in the forward direction, and conveyed in the direction opposite to the registration roller pair 28 side. Is done.
When the transfer paper P sent out from the secondary transfer nip passes between rollers of the fixing device 20, the four-color toner image transferred to the surface is fixed by heat and pressure. Thereafter, the transfer paper P is discharged out of the apparatus through a pair of paper discharge rollers 29.
A stack unit 30 is formed on the upper surface of the main body of the printer 100, and the transfer paper P discharged to the outside by the discharge roller pair 29 is sequentially stacked on the stack unit 30.

  A bottle container 31 is disposed between the stack unit 30 located above the intermediate transfer unit 15 and the intermediate transfer unit 15. The bottle container 31 stores toner bottles 32Y, 32M, 32C, and 32K as replenishing toner storage units that store Y, M, C, and K toners. The toner bottles 32Y, 32M, 32C, and 32K are installed on the bottle container 31 so as to be placed from above for each toner color. The Y, M, C, and K toners in the toner bottles 32Y, 32M, 32C, and 32K are supplied from developing devices 5Y, M, C and K are replenished appropriately. These toner bottles 32Y, 32M, 32C, and 32K are detachable from the main body of the printer 100 independently of the process cartridges 6Y, 6M, C, and K.

Next, the configuration of the developing device 5Y provided in the process cartridge 6Y will be described. FIG. 3 is a schematic cross-sectional view of the process cartridge 6Y as viewed from the axial direction of the rotation shaft of the photosensitive member.
The developing device 5Y includes a developing unit 51Y as a developer carrying member having a magnetic field generating means therein and carrying a two-component developer containing magnetic particles and toner on the surface, and carried on the developing sleeve 51Y. And a developing doctor 52Y as a developer regulating member that regulates the layer thickness of the conveyed developer.
Below the developing sleeve 51Y, there is a developer accommodating portion surrounded by the casing 55Y. The first developer accommodating portion 53Y that supplies the developer to the developing sleeve 51 by the partition wall 59Y, and the toner from the toner replenishing portion 58Y. The second developer containing portion 54Y that receives the replenishment is partitioned. A first conveying screw 61Y for agitating and conveying the toner is provided in the first developer accommodating portion 53Y, and a second conveying screw 62Y is provided in the second developer accommodating portion 54Y. The 1st conveyance screw 61Y and the 2nd conveyance screw 62Y have the structure which fixed the helical wing | blade part to the axial part. Further, the developer in the first developer accommodating portion 53Y is conveyed from the near side to the far side in FIG. 3 by the rotation of the first conveying screw 61Y, and the developer in the second developer accommodating portion 54Y is the second one. By the rotation of the transport screw 62Y, the transport screw 62Y is transported from the back side to the near side in FIG. Then, both end portions of the partition wall 59Y in the axial direction of the conveying screw (front-back direction in FIG. 3) are openings, and the developer is a first developer accommodating portion 53Y and a second developer accommodating portion. It circulates between 54Y.

The developing device 5Y includes a toner concentration sensor 56Y that detects the toner concentration of the developer in the second developer accommodating portion 54Y on the lower outer wall surface of the portion of the casing 55Y that forms the second developer accommodating portion 54Y. Yes.
The toner density sensor 56Y is a non-contact type toner density sensor that can detect the toner density without providing a part of the sensor at a position in contact with the developer. The toner concentration sensor is not limited to a non-contact sensor, and for example, a sensor attached in such a manner that the sensor surface protrudes inward from the outside of the casing 55Y may be used. Further, it may be arranged on the inner wall surface of the casing 55Y.

Next, the operation of the developing device 5Y will be described. In the developing device 5Y, the developer in the developer accommodating portion (53Y, 54Y) includes a carrier and toner, and the toner is taken in such that the developer falls within a predetermined toner density range. The toner passes from the toner bottle 32Y through the toner transport pipe 43Y of the toner transport device (not shown), and is replenished from the toner replenishing portion 58Y to the second developer accommodating portion 54Y. Thereafter, it is agitated by the second conveying screw 62Y and the first conveying screw 61Y, taken into the developer, and charged by frictional charging with the carrier. The developer containing charged toner in the first developer accommodating portion 53Y is supplied to the surface of the developing sleeve 51Y having a magnetic pole inside, forms a developer layer by magnetic force, and is carried on the surface of the developing sleeve 51Y. . The developer layer carried on the developing sleeve 51Y is conveyed in the direction of the arrow as the developing sleeve 51Y rotates. In the middle, after the developer doctor 52Y regulates the layer thickness of the developer layer, the developer is transported to the developing area facing the photoreceptor 1Y.
In the development area, toner is supplied to the latent image formed on the photoreceptor 1Y for development. The developer layer remaining on the surface of the developing sleeve 51Y that has passed through the developing region is conveyed to the upstream portion in the developer conveying direction of the first developer accommodating portion 53Y as the developing sleeve 51Y rotates.

  When the toner is consumed by the development and the toner concentration in the developing device 5Y decreases, the toner concentration sensor 56Y below the second developer containing portion 54Y and a toner concentration control unit (not shown) detect the decrease in toner concentration. Based on the detection result, a toner concentration control unit (not shown) drives a toner supply device (not shown), and the toner is supplied from the toner transport pipe 43Y.

Next, the problem of the intermediate transfer belt of the conventional image forming apparatus will be described.
FIG. 4 is a schematic diagram showing an intermediate transfer unit 15, a secondary transfer roller 19, four photoreceptors 1, and a registration roller pair 28 provided in a conventional image forming apparatus. The registration roller pair 28 includes a registration roller 28a that is rotated by being driven, and a registration pressure roller 28b that is in pressure contact with the registration roller 28a and rotates around the registration roller 28a.
As shown in FIG. 4, the intermediate transfer belt 8 is stretched by a driving roller 12, a tension roller 13, and an entrance roller 14. The intermediate transfer belt 8 is endlessly moved in the counterclockwise direction in the drawing when the driving roller 12 is driven to rotate in the direction of the arrow in FIG.

  As described above, the transfer paper P fed from the paper storage cassette 26 stands by once at the registration roller pair 28. When toner images are transferred from the four photoconductors 1 to the intermediate transfer belt 8, the registration roller pair 28 is driven by a registration drive motor (not shown) and transferred in synchronization with the leading end of the toner image on the intermediate transfer belt 8. The paper P is conveyed to the secondary transfer nip N, which is a pressure contact portion between the drive roller 12 and the secondary transfer roller 19, and is carried on the intermediate transfer belt 8 by the applied pressure and a transfer bias formed by bias applying means (not shown). The transferred toner image is transferred to the transfer paper P.

Here, as shown in FIG. 4, the tension surface between the tension roller 13 and the inlet roller 14 is the first tension surface 8 a, and the tension surface between the inlet roller 14 and the drive roller 12 is the second tension surface. It is set as the mounting surface 8b. A tension surface between the driving roller 12 and the tension roller 13 is a third tension surface 8c.
Since the intermediate transfer belt 8 primarily transfers the toner image from the photoconductor 1 on the first tension surface 8a, the surface movement speed of the intermediate transfer belt 8 and the surface movement speed of the photoconductor 1 are controlled to be the same. Has been.
When the transfer paper P enters the secondary transfer nip N, the moving speed of the intermediate transfer belt 8 on the first stretching surface 8a, which is the primary transfer surface facing the photoreceptor 1 and forming four one transfer nips, is illustrated in FIG. A speed fluctuation as shown by 5 occurs. T _{1 in} FIG. 5 is a time point when the transfer paper P enters the secondary transfer nip N. As shown in FIG. 5, T ₁ is a previous point in time is the surface moving speed of the intermediate transfer belt 8 in the first stretched surface 8a is constant, the transfer sheet P is the secondary transfer nip T ₁ after having entered the N time Then, the surface moving speed of the intermediate transfer belt 8 varies.
Note that the speed fluctuation of the intermediate transfer belt 8 on the first stretched surface 8a has substantially the same behavior as the speed fluctuation of the surface moving speed of the entrance roller 14, and therefore the speed fluctuation of the entrance roller 14 will be used instead.

When the transfer sheet P enters the secondary transfer nip, the speed of the intermediate transfer belt 8 on the first stretched surface 8a fluctuates, whereas the photoreceptor 1 also transfers the transfer sheet P when the transfer sheet P enters the secondary transfer nip. P is rotationally driven at substantially the same surface movement speed as before P enters the secondary transfer nip N. Therefore, when the transfer paper P enters the secondary transfer nip N, a speed difference occurs between the surface of the photoreceptor 1 and the first stretched surface 8a of the intermediate transfer belt 8.
When such a speed difference occurs, a transfer position shift occurs in the primary transfer nip.

FIG. 6 is an explanatory diagram schematically showing the transfer paper P on which a toner image having a misalignment is transferred as a final image when a single color image is formed.
The toner image including the transfer position deviation in the primary transfer nip generated when the transfer paper P is transferred to the transfer nip N is transferred at a position L from the front end of the paper, where L is the distance from the primary transfer nip to the secondary transfer nip N. Transferred and fixed on paper P. For this reason, as shown in FIG. 6, the final image on the transfer paper P to be discharged is a portion I _{2 that} is lighter in color than the portion I ₁ of a normal image or a portion I that is darker in color from the leading end of the paper to L. _The image has local density unevenness of ₃ .
In addition, when a multi-color image is formed, the distance from the primary transfer nip to the secondary transfer nip N is different for each color, so that an image having a different distance L from the front end of the paper to the density unevenness is output for each color. The
As described above, in order to prevent the transfer position shift in the primary transfer nip that occurs when the transfer paper P enters the secondary transfer nip, it is necessary to suppress the speed fluctuation of the entrance roller 14 when the transfer paper P enters the secondary transfer nip. is there. The mechanism by which the speed fluctuation of the inlet roller 14 occurs will be described below.

Here, the secondary transfer nip N is divided into a pre-nip and a main nip defined as follows.
Pre-nip: Before the transfer paper P enters the secondary transfer nip N, the inner peripheral surface of the intermediate transfer belt 8 does not contact the drive roller 12, but the outer peripheral surface of the intermediate transfer belt 8 is in contact with the secondary transfer roller 19. The part that comes into contact.
Main nip: Before the transfer paper P enters the secondary transfer nip N, the inner peripheral surface of the intermediate transfer belt 8 contacts the driving roller 12, and the outer peripheral surface of the intermediate transfer belt 8 contacts the secondary transfer roller 19. The part that comes into contact. That is, a portion where the intermediate transfer belt 8 is held between the drive roller 12 and the secondary transfer roller 19.

  The speed fluctuation of the inlet roller 14 is roughly divided into the following three fluctuations (1) to (3).

(1) Speed Fluctuation due to Prep Nipping of Transfer Paper P FIG. 7 is an explanatory diagram of speed fluctuations that occur when the transfer paper P enters the prenip. FIG. 7A is an enlarged explanatory view in the vicinity of the secondary transfer nip N when the transfer paper P enters the prenip, and FIG. 7B is a graph for explaining speed fluctuation due to the transfer paper P entering the prenip. It is. The thick line portion of the graph in FIG. 7B is a portion where the speed fluctuation occurs due to the pre-nip entry. Also, the alternate long and short dash line in FIG. 7A indicates the second stretched surface 8b of the intermediate transfer belt 8 before the transfer paper P enters the secondary transfer nip N.
When the transfer paper P enters the prenip, the speed fluctuation due to the transfer paper P entering the prenip is caused by the leading edge of the transfer paper P being pushed inward by the intermediate transfer belt 8 in the prenip. 14 is a phenomenon of acceleration.

(2) Speed Fluctuation Due to Transfer Paper P Entering the Main Nip FIG. 8 is an explanatory diagram of speed fluctuations that occur when the transfer paper P enters the main nip. FIG. 8A is an enlarged explanatory view of the vicinity of the secondary transfer nip N when the transfer paper P enters the main nip, and FIG. 8B illustrates speed fluctuation due to the transfer paper P entering the main nip. It is a graph to do. The thick line portion of the graph in FIG. 8B is a portion where the speed variation occurs due to the entrance to the nip. Also, the alternate long and short dash line in FIG. 8A indicates the second stretched surface 8b of the intermediate transfer belt 8 before the transfer paper P enters the secondary transfer nip N.
The speed fluctuation due to the transfer paper P entering the main nip is a phenomenon in which when the transfer paper P enters the main nip, the leading edge of the transfer paper P bites into the main nip and the drive roller 12 and the entrance roller 14 are both decelerated. is there.
Here, a mechanism in which the driving roller 12 and the entrance roller 14 are both decelerated by the transfer paper P entering the main nip will be described with reference to FIG.
As shown in FIG. 9, the secondary transfer roller 19 is pressed toward the drive roller 12 by a secondary transfer roller pressing spring 19a. In addition, each arrow in FIG. 9 is an arrow A is a pressing force by the secondary transfer roller pressing spring 19a, an arrow B is a force by which the transfer paper P pushes down the secondary transfer roller 19, and an arrow C is the transfer paper P The torque required to push down the secondary transfer roller 19 is shown. In a state where the leading edge of the transfer paper P is caught between the intermediate transfer belt 8 and the secondary transfer roller 19, if the secondary transfer roller 19 is not pushed down by an amount corresponding to the thickness of the transfer paper P, the transfer paper P is no more. Can't go forward.
The secondary transfer roller 19 is pressed against the driving roller 12 via the intermediate transfer belt 8 by a pressing force (arrow A in FIG. 9) by the secondary transfer roller pressing spring 19a. Therefore, in order to push down the secondary transfer roller 19, the rotational torque of the drive roller 12 (arrow C in FIG. 9) pushes down the secondary transfer roller 19 through the transfer paper P (arrow B in FIG. 9). Therefore, it is necessary to exceed the pressing force (arrow A in FIG. 9) by the secondary transfer roller pressing spring 19a.
In other words, the driving roller 12 at the time of the sheet biting needs a rotational torque for pushing down the secondary transfer roller 19 separately from the conveyance of the normal intermediate transfer belt 8. This becomes a rotational load of the drive roller 12, and the drive roller 12 decelerates.
As for the entrance roller 14, if the transfer paper P does not move forward, a frictional force between the intermediate transfer belt 8 and the transfer paper P causes a running load of the intermediate transfer belt 8. To do.

(3) Speed Fluctuation Due to Return of Intermediate Transfer Belt 8 FIG. 10 is an explanatory diagram of speed fluctuation caused by the return of the intermediate transfer belt 8 that has been displaced inward after the leading edge of the transfer paper P enters the main nip. It is. FIG. 10A is an enlarged explanatory view in the vicinity of the secondary transfer nip N when the intermediate transfer belt 8 is returned, and FIG. 10B is a graph for explaining a speed variation due to the return of the intermediate transfer belt 8. FIG. is there. The thick line part of the graph in FIG. 10B is a part where the speed fluctuation occurs due to the entrance to the nip. Further, the alternate long and short dash line in FIG. 10A indicates the second stretched surface 8b of the intermediate transfer belt 8 before the transfer paper P enters the secondary transfer nip N.
The speed fluctuation due to the return of the intermediate transfer belt 8 is a speed fluctuation generated when the leading edge of the transfer paper P passes through the main nip and the secondary transfer roller 19 is pushed down as shown in FIG. When the leading edge of the transfer paper P passes through the main nip, the intermediate transfer belt 8 that has been pushed inward returns to the original state. Occur. That is, the drive roller 12 is accelerated and the entrance roller 14 is decelerated.

[ Reference configuration example 1 ]
Next, a first reference configuration example (hereinafter referred to as reference configuration example 1 ) of the printer 100 of this embodiment that prevents the speed fluctuation of the entrance roller 14 will be described.
The printer 100 of the reference configuration example 1 is a belt displacement that suppresses the “speed fluctuation due to the pre-nip entering of the transfer paper P” in (1) and the “speed fluctuation due to the main nip entering of the transfer paper P” in (2). A control mechanism is provided.
FIG. 1 is a schematic diagram illustrating an intermediate transfer unit 15, a secondary transfer roller 19, four photosensitive members 1, a registration roller pair 28, and a belt displacement control mechanism 200 provided in the printer 100 of Reference Configuration Example 1 . FIG. 11 is a block diagram of a control circuit of the belt displacement control mechanism 200 provided in the printer 100 of the reference configuration example 1 .
As shown in FIG. 1, in the printer 100 of the reference configuration example 1 , the displacement sensor 22 is installed inside the intermediate transfer belt 8 in the pre-nip, and the pressing roller 25 is arranged outside the intermediate transfer belt 8 on the third stretching surface 8c. It is installed. As shown in FIG. 1, the pressing roller 25 is close to a region where the driving roller 12 contacts the inner peripheral surface of the intermediate transfer belt 8 on the third tension surface 8 c and the driving roller 12 supports the intermediate transfer belt 8. It is the structure which presses a part.
The belt displacement control mechanism 200 includes a pressing roller 25, an electromagnetic solenoid 24 that moves the pressing roller 25 toward the intermediate transfer belt 8 by supporting and driving both ends in the axial direction of the pressing roller 25, and the electromagnetic solenoid 24. It is comprised with the solenoid control apparatus 3 which controls a drive. As shown in FIG. 11, the solenoid control device 3 includes a microprocessor 16, a memory 17, and an electromagnetic solenoid drive circuit 18.

Next, the operation of the belt displacement control mechanism 200 will be described.
FIG. 12 is a graph schematically showing belt inner displacement and inlet roller speed fluctuation over time.
The upper graph in FIG. 12 is a graph showing the change with time of the distance from the displacement sensor 22 to the intermediate transfer belt 8 measured by the displacement sensor 22, and the lower graph in FIG. 12 is the surface movement of the entrance roller. It is a graph which shows a time-dependent change of speed.
As described in (1) above, when the speed of the transfer paper P fluctuates due to entering the prenip, the intermediate transfer belt 8 is pushed inward by the leading edge of the transfer paper P, so that the drive roller 12 decelerates as described above. The roller 14 accelerates. In order to suppress the acceleration of the entrance roller 14, a portion where the pressing roller 25 of the third stretching surface 8 c that is a stretching surface on the downstream side in the surface movement direction of the intermediate transfer belt 8 contacts the secondary transfer nip N. The intermediate transfer belt 8 may be displaced inward. As a result, a force acts in the direction of accelerating the intermediate transfer belt 8 in the secondary transfer nip N, so that deceleration of the drive roller 12 is suppressed and acceleration of the entrance roller 14 is suppressed.
In the belt displacement control mechanism 200 provided in the printer 100 of the reference configuration example 1 , as shown in FIG. 12, a threshold is set in advance for the distance between the displacement sensor 22 and the intermediate transfer belt 8, and the displacement sensor 22 and the intermediate When the distance to the transfer belt 8 falls below this threshold, the electromagnetic solenoid 24 is driven by a predetermined amount, and the intermediate transfer belt 8 is displaced inward via the pressing roller 25.

  As described in (2) above, when the speed of the transfer paper P changes due to the entry into the main nip, the leading edge of the transfer paper P bites into the main nip, so that both the drive roller 12 and the entrance roller 14 are decelerated. Therefore, the intermediate transfer belt 8 may be displaced inward at the portion where the pressing roller 25 of the third tension surface 8c continues to contact. By doing so, the force acts in the direction of accelerating the intermediate transfer belt 8 in the secondary transfer nip N, so that deceleration of the drive roller 12 and the entrance roller 14 is suppressed. At this time, in the belt displacement control mechanism 200, as shown in FIG. 12, since the distance between the displacement sensor 22 and the intermediate transfer belt 8 remains below the threshold value, the electromagnetic solenoid 24 is continuously driven and the pressure roller 25, the intermediate transfer belt 8 is displaced inward.

  Thereafter, when the secondary transfer roller 19 is pushed down by the leading edge of the transfer paper P, the intermediate transfer belt 8 on the second stretched surface 8b that has been pushed inward returns to its original position and is further displaced outward. At this time, in the belt displacement control mechanism 200, as shown in FIG. 12, since the distance between the displacement sensor 22 and the intermediate transfer belt 8 exceeds the threshold value, the driving of the electromagnetic solenoid 24 is released. Accordingly, the pressing roller 25 is pushed outward by the reaction that has pushed the intermediate transfer belt 8 inward on the third tension surface 8c, and returns to the original position.

FIG. 13 is a flowchart of the operation of the belt displacement control mechanism 200 of Reference Configuration Example 1 .
When an image is formed on a normal sheet as the transfer sheet P, the displacement amount of the intermediate transfer belt 8 when the transfer sheet P enters the secondary transfer nip N is small, and the influence on the transfer position deviation is small. On the other hand, when the transfer paper P is thicker than normal paper, the amount of displacement of the intermediate transfer belt 8 when the transfer paper P enters the secondary transfer nip N increases, and the transfer position shift is also affected. growing. For this reason, in the printer 100 of the reference configuration example 1 , when a thick paper is used as the transfer paper P, the belt displacement control mechanism 200 is operated, and the speed of the intermediate transfer belt 8 when the transfer paper P enters the secondary transfer nip N. Suppress fluctuations.

When the user presses a start button of an operation unit (not shown) of the printer 100, image formation is started (S1), and it is determined whether or not the mode is the thick paper mode (S2). Whether or not the card is in the thick paper mode may be determined by inputting that the paper is thick before the start button is pressed when the thick paper is used, or the transfer is performed upstream of the registration roller pair 28 in the transport direction. A paper thickness detection sensor for detecting the paper thickness of the paper P may be arranged, and it may be determined whether or not it is in the thick paper mode based on the detection result of the paper thickness detection sensor. If it is determined that the mode is not the thick paper mode (NO in S2), the control of the belt displacement control mechanism 200 ends (S8), the displacement of the intermediate transfer belt 8 is not measured by the displacement sensor 22, and the electromagnetic solenoid 24 is turned off. Normal image formation is performed with the drive stopped. On the other hand, when it is determined that the cardboard mode is selected (YES in S2), the control by the belt displacement control mechanism 200 is continued, and the distance between the intermediate transfer belt 8 and the displacement sensor 22 is determined based on the measurement result of the displacement sensor 22. It is determined whether or not it is below the threshold (S3). When the distance between the intermediate transfer belt 8 and the displacement sensor 22 exceeds the threshold value (NO in S3), the drive of the electromagnetic solenoid 24 is stopped and the intermediate transfer belt 8 based on the measurement result of the displacement sensor 22 is stopped. And the control for determining whether or not the distance between the displacement sensor 22 and the displacement sensor 22 is less than the threshold value is repeated. On the other hand, when the distance between the intermediate transfer belt 8 and the displacement sensor 22 is smaller than the threshold value (YES in S3), the drive circuit of the electromagnetic solenoid 24 is turned on (S4). As a result, the pressing roller 25 displaces the intermediate transfer belt 8 inward.
When the drive circuit of the electromagnetic solenoid 24 is turned on, it is determined whether or not the distance between the intermediate transfer belt 8 and the displacement sensor 22 exceeds the threshold based on the measurement result of the displacement sensor 22 (S5). If the distance between the intermediate transfer belt 8 and the displacement sensor 22 is less than the threshold value (NO in S5), the intermediate transfer belt 8 based on the measurement result of the displacement sensor 22 is maintained while the electromagnetic solenoid 24 is kept driven. And the control for determining whether the distance between the sensor and the displacement sensor 22 exceeds the threshold value is repeated. On the other hand, when the distance between the intermediate transfer belt 8 and the displacement sensor 22 is smaller than the threshold value (YES in S5), the drive circuit of the electromagnetic solenoid 24 is turned off (S6). As a result, there is no force that the pressing roller 25 presses the intermediate transfer belt 8, and the pressing roller 25 returns to the original position by the reaction force of the intermediate transfer belt 8. Thereby, the control by the belt displacement control mechanism 200 ends (S7).

In order to operate according to the flowchart described with reference to FIG. 13, in the solenoid control device 3, the electromagnetic solenoid 24 is energized when the distance between the displacement sensor 22 and the intermediate transfer belt 8 falls below a threshold value. It is necessary to incorporate a microprocessor 16 having a built-in program that stops energization of the electromagnetic solenoid 24 when the threshold is exceeded again from a state below the threshold. Further, since the threshold value of the distance between the displacement sensor 22 and the intermediate transfer belt 8 and the drive displacement amount of the electromagnetic solenoid 24, the speed fluctuation amount of the entrance roller 14 varies depending on the layout and physical property values of the intermediate transfer unit 15. Decide while looking at the suppression effect.
Here, in consideration of the time constant of the pressing roller 25, etc., the electromagnetic solenoid 24 is set to be driven according to a preset driving amount at the same time as the electromagnetic solenoid 24 is turned on. However, an actuator that operates at a higher speed and a large-capacity memory are provided. If there is, a profile of the driving amount of the pressing roller 25 with respect to time may be stored in a memory in advance, and the actuator may be driven according to the profile.

[ Reference configuration example 2 ]
Next, a second reference configuration example (hereinafter referred to as reference configuration example 2 ) of the printer 100 of this embodiment that prevents the speed fluctuation of the entrance roller 14 will be described.
The printer 100 of the reference configuration example 2 is a belt displacement that suppresses the “speed fluctuation due to the pre-nip entering of the transfer sheet P” in (1) and the “speed fluctuation caused by the return of the intermediate transfer belt 8” in (3). A control mechanism is provided.

FIG. 14 is a schematic diagram illustrating the intermediate transfer unit 15, the secondary transfer roller 19, the four photosensitive members 1, the registration roller pair 28, and the belt displacement control mechanism 200 provided in the printer 100 of the reference configuration example 2 .
The belt displacement control mechanism 200 provided in the printer 100 of the reference configuration example 2 is located outside the intermediate transfer belt 8 on the first tension surface 8a and upstream of the primary transfer unit where the intermediate transfer belt 8 faces the four photosensitive members 1. The pressing roller 25 is installed at the side position.
As described in (1) above, when the speed of the transfer paper P changes due to the pre-nip, the intermediate transfer belt 8 is pushed inward by the leading edge of the transfer P, so that the drive roller 12 is decelerated and the entrance roller as described above. 14 accelerates. In order to suppress the acceleration of the entrance roller 14, the intermediate transfer belt 8 on the upstream side of the primary transfer portion may be displaced inward. As a result, a force acts in the direction of decelerating the intermediate transfer belt 8 on the first stretched surface 8a serving as the primary transfer portion, so that the acceleration of the entrance roller 14 is suppressed.
In the belt displacement control mechanism 200 provided in the printer 100 of the reference configuration example 2 , as in the reference configuration example 1 , the electromagnetic solenoid 24 is energized when the value falls below the threshold value, and the intermediate transfer belt 8 is moved inward via the pressing roller 25. Displace. In the printer 100 of the reference configuration example 2 , in order to keep the intermediate transfer belt 8 in contact with the photosensitive member 1 even when the upstream side of the primary transfer portion on the first stretching surface 8a is displaced inward, A pre-primary transfer roller 39 is provided.
As described in (3) above, when the speed is changed due to the return of the intermediate transfer belt 8, the intermediate transfer belt 8 on the second stretched surface 8b that has been pushed inward returns to its original position and is displaced outward. . Therefore, the driving roller 12 is accelerated and the entrance roller 14 is decelerated. In order to suppress the deceleration of the entrance roller 14, the intermediate transfer belt 8 on the upstream side of the primary transfer portion of the first tension surface 8a that has been displaced inward may be returned to its original position. Since the force acts in the direction of accelerating the intermediate transfer belt 8 in the primary transfer portion and the entrance roller 14, the deceleration of the entrance roller 14 can be suppressed.

In the belt displacement control mechanism 200 of the reference configuration example 2 , similarly to the reference configuration example 1 , the driving of the electromagnetic solenoid 24 is released when the threshold value is exceeded again after falling below the threshold value. If it does so, the pressure roller 25 will be pushed outside by the reaction which pushed the intermediate transfer belt 8 inside, and comes to return to the original position.
A series of operation flows is the same as in Reference Configuration Example 1 . By merely changing the position of the pressing roller 25 from the vicinity of the secondary transfer nip N of the third stretching surface 8c to the upstream side of the first stretching surface 8a near the primary transfer portion, the intermediate transfer belt 8 of (3) described above can be obtained. Although it becomes possible to cope with the speed fluctuation due to the return, the effect of suppressing the speed fluctuation due to the entry of the transfer paper P (2) into the main nip cannot be obtained. Therefore, the (2) when you want to suppress the speed fluctuation according to the nip enters the reference configuration example 1 of the transfer paper P, when it is desired to suppress the speed fluctuation caused by the intermediate transfer belt 8 described above (3) returns the reference configuration Example 2 may be adopted. Which of the above (2) and (3) is dominant depends on the layout and physical property values constituting the secondary transfer nip. As a tendency, the transfer direction of the transfer sheet P and the transfer direction of the transfer sheet P in the secondary transfer nip N are parallel, and when the nip pressure in the secondary transfer nip N is large, the fluctuation of (2) is dominant. become.

[ Example 1 ]
Then, one eye embodiment of the printer 100 of the present embodiment to prevent the velocity fluctuation of the inlet roller 14 (hereinafter, referred to as Example 1) will be described.
The printer 100 according to the first exemplary embodiment suppresses each of the “speed fluctuation due to the transfer sheet P entering the main nip” in (2) and the “speed fluctuation due to the return of the intermediate transfer belt 8” in (3). While observing the effect, the amount of displacement of the first tension surface 8a and the third tension surface 8c to the inside of the intermediate transfer belt 8 can be controlled independently.
FIG. 15 is a schematic diagram illustrating the intermediate transfer unit 15, the secondary transfer roller 19, the four photosensitive members 1, the registration roller pair 28, and the belt displacement control mechanism 200 included in the printer 100 of the first embodiment .
In the belt displacement control mechanism 200 provided in the printer 100 according to the first embodiment , the first pressing roller 25a is installed at a position close to the driving roller 12 outside the intermediate transfer belt 8 on the third tension surface 8c. Further, the belt displacement control mechanism 200 according to the first exemplary embodiment is positioned outside the intermediate transfer belt 8 on the first tension surface 8a and on the upstream side of the primary transfer portion where the intermediate transfer belt 8 faces the four photosensitive members 1. The second pressing roller 25b is installed. The first electromagnetic solenoid 24a and the first solenoid control device 3a for controlling the pressing amount of the first pressing roller 25a against the third stretching surface 8c, and the pressing amount of the second pressing roller 25b against the first stretching surface 8a are set. A second electromagnetic solenoid 24b to be controlled and a second solenoid control device 3b are provided. Accordingly, while ascertaining the suppression effect in each of the “speed fluctuation due to the transfer paper P entering the main nip” in (2) and the “speed fluctuation due to the return of the intermediate transfer belt 8” in (3) above, The pressing amount of the first pressing roller 25a and the second pressing roller 25b can be controlled independently.

[ Example 2 ]
Next, two eyes embodiment of the printer 100 of the present embodiment to prevent the velocity fluctuation of the inlet roller 14 (hereinafter, referred to as Example 2) will be described.
The printer 100 according to the second embodiment can control the amount of displacement of the first tension surface 8a and the third tension surface 8c inward of the intermediate transfer belt 8 with a single solenoid control device.
FIG. 16 is a schematic diagram illustrating the intermediate transfer unit 15, the secondary transfer roller 19, the four photosensitive members 1, the registration roller pair 28, and the belt displacement control mechanism 200 provided in the printer 100 according to the second embodiment . In the belt displacement control mechanism 200 provided in the printer 100 according to the second embodiment , the first pressing roller 25a is installed at a position close to the driving roller 12 outside the intermediate transfer belt 8 on the third tension surface 8c. Further, the belt displacement control mechanism 200 according to the second exemplary embodiment is located outside the intermediate transfer belt 8 on the first stretching surface 8a and on the upstream side of the primary transfer portion where the intermediate transfer belt 8 faces the four photosensitive members 1. The second pressing roller 25b is installed. Further, the first pressing roller 25a and the second pressing roller 25b are supported by the link member 40 fixed to the apparatus main body at the rotation center 40a, and the link member 40 is constituted by one electromagnetic solenoid 24 and one solenoid control device 3. Drive control is performed.
As shown in FIG. 16, when the transfer sheet P is in a steady state before entering the secondary transfer nip N, the link member 40 is installed so as to be pressed from above in the vertical direction at the root of the stroke of the electromagnetic solenoid 24. When the electromagnetic solenoid 24 is turned on, the iron core of the electromagnetic solenoid 24 is pushed out, the link member 40 rotates around the rotation center 40a, and the first pressing roller 25a and the second pressing roller 25b move from the outside of the intermediate transfer belt 8 to the inside. Will be displaced in the direction. Unlike the printer 100 of the first embodiment , the amount of pressure applied to the inside of the intermediate transfer belt 8 by the pressure roller 25 cannot be set independently, and the ratio of the amount of pressure is determined by the position of the rotation center 40a of the link member 40. However, since only one electromagnetic solenoid 24 and one solenoid control device 3 are required, this is advantageous in terms of cost.

  The printer 100 according to the above-described embodiment is configured to transfer the toner image on the intermediate transfer belt 8 onto the transfer paper P. However, the configuration similar to the belt displacement control mechanism 200 according to the present embodiment is a belt-like photosensitive. The present invention is also applicable to a configuration for controlling the amount of displacement of a photosensitive belt configured to transfer a toner image on a photosensitive belt, which is a body, to a recording medium.

  As described above, the printer 100 according to the present embodiment includes the intermediate transfer belt 8 that is a toner image carrying belt that is stretched by a plurality of stretching rollers and carries a toner image on the surface and moves endlessly, and the plurality of stretching rollers. In a recording medium transfer nip that is opposed to a driving roller 12 as a secondary transfer counter roller, which is one of the above, with the intermediate transfer belt 8 interposed therebetween, and that transfers a toner image on the intermediate transfer belt 8 onto a transfer sheet P that is a recording medium. A secondary transfer roller 19 that is a recording medium transfer member that forms a secondary transfer nip N; Of the plurality of stretching surfaces formed by the intermediate transfer belt 8 being stretched by a plurality of stretching rollers, the end portion on the downstream side in the moving direction of the intermediate transfer belt 8 becomes the secondary transfer nip N. A tension that is not the second tension surface 8b among the plurality of tension surfaces of the intermediate transfer belt 8 according to the inward displacement of the second tension surface 8b that is the tension surface upstream of the transfer nip that is the tension surface. A belt displacement control mechanism 200 is provided that displaces at least one of the first and third tension surfaces 8a and 8c, which are the tension surfaces, inward. As a result, a force is applied to the drive roller 12 which is a tension roller on the downstream side in the movement direction of the second tension surface 8b, so that the driving roller 12 is pulled downstream in the movement direction of the intermediate transfer belt 8. Deceleration caused by inward displacement is suppressed. Further, by displacing the tensioning surface other than the second tensioning surface 8b inward, the moving direction of the intermediate transfer belt 8 is applied to the inlet roller 14 which is a tensioning roller on the upstream side in the movement direction of the second tensioning surface 8b. A force that is pulled to the upstream side is applied, and acceleration due to the inward displacement of the second tension surface 8b is suppressed. Further, since at least one of the first tension surface 8a and the third tension surface 8c is displaced inward according to the inward displacement of the second tension surface 8b, the speed variation of the toner image carrying belt is reduced. Compared with a configuration in which tension is applied to such an extent that generation can be suppressed, a decrease in durability of the intermediate transfer belt 8 can be suppressed. Therefore, since the acceleration of the entrance roller 14 and the deceleration of the drive roller 12 caused by the inward displacement of the second tension surface 8b can be suppressed, the transfer paper P enters the secondary transfer nip N. It is possible to suppress a decrease in the durability of the intermediate transfer belt 8 while suppressing fluctuations in the speed of the intermediate transfer belt 8 that occur in the above.

Further, in particular, the belt displacement control mechanism 200 of the printer 100 of the reference configuration example 1 is a tension surface on the downstream side of the second tension surface 8b according to the displacement inward of the second tension surface 8b. The configuration is such that the third stretched surface 8c, which is the stretched surface on the downstream side of the transfer nip where the end on the upstream side in the moving direction of the intermediate transfer belt 8 becomes the secondary transfer nip N, is displaced inward. As a result, when the transfer paper P enters the secondary transfer nip N, two types of speed fluctuations are suppressed: speed fluctuation due to the pre-nip entering the transfer paper P and speed fluctuation due to the transfer paper P entering the main nip. It becomes possible.

In the printer 100 of this embodiment, the intermediate transfer belt 8 is stretched by three stretching rollers.
In particular, the belt displacement control mechanism 200 of the printer 100 of the reference configuration example 2 is upstream of the second stretching surface 8b among the plurality of stretching surfaces in response to the inward displacement of the second stretching surface 8b. The first tension surface 8a adjacent to the second tension surface 8b is displaced inwardly on the upstream side of the second tension surface 8b in the moving direction of the intermediate transfer belt 8. As a result, when the transfer paper P enters the secondary transfer nip N, there are two types of speed fluctuation due to the pre-nip entering of the transfer paper P and speed fluctuation due to the return of the intermediate transfer belt 8 that has been pushed inward. It is possible to suppress the speed fluctuation.

In particular, the belt displacement control mechanism 200 according to the first embodiment is a tension surface on the downstream side of the second tension surface 8b according to the inward displacement of the second tension surface 8b. The upstream end in the moving direction of the second transfer nip N is a transfer surface on the downstream side of the transfer nip Nc, a third extension surface 8c, and a tension surface on the upstream side of the second extension surface 8b. In this configuration, the second stretching surface 8b and the adjacent first stretching surface 8a are displaced inward on the upstream side of the second stretching surface 8b in the moving direction of the intermediate transfer belt 8. As a result, when the transfer paper P enters the secondary transfer nip N, the speed fluctuation due to the pre-nip entering of the transfer paper P, the speed fluctuation due to the transfer paper P entering the main nip, and the intermediate transfer belt that has been pushed inward. It is possible to suppress three types of speed fluctuations, that is, speed fluctuation caused by the return of 8.

  In addition, the belt displacement control mechanism 200 provided in the printer 100 of the present embodiment includes a displacement sensor 22 that is a measuring unit that measures the amount of displacement of the second stretching surface 8b, and an outer surface that is displaced inward. A pressing roller 25 that touches the tensioning surface inward, and an electromagnetic solenoid 24 and a solenoid control device 3 that are pressing amount control means for controlling the pressing amount of the pressing roller 25. Since the belt displacement control mechanism 200 can freely adjust the amount of displacement of the tensioning surface to be displaced inward according to the amount of displacement of the second tensioning surface 8b, the speed of the intermediate transfer belt 8 can be adjusted. The effect of suppressing fluctuation can be controlled.

In particular, the belt displacement control mechanism 200 provided in the printer 100 according to the first embodiment includes the two pressing rollers 25, and the tension surfaces to be displaced inward by the belt displacement control mechanism 200 are the first tension surface 8a and the third tension surface. The tension surface 8c is a two and the pressing amount control means for controlling the pressing amount of the two pressing rollers 25 is an independent pressing mechanism for the first pressing roller 25a and the second pressing roller 25b. The pressing amount is controlled by the solenoid 24a and the first solenoid control device 3a and the second electromagnetic solenoid 24b and the second solenoid control device 3b. By such a belt displacement control mechanism 200, the displacement amount of the first tension surface 8a and the displacement amount of the third tension surface 8c can be freely set according to the displacement amount of the intermediate transfer belt 8 on the second tension surface 8b. Can be adjusted to. Therefore, there are three types of speed fluctuations: speed fluctuation due to the pre-nip entering of the transfer paper P, speed fluctuation due to the main paper nip entering the transfer paper P, and speed fluctuation due to the return of the intermediate transfer belt 8 that has been pushed inward. The speed change suppression effect can be controlled independently.

In particular, the belt displacement control mechanism 200 included in the printer 100 according to the second embodiment includes the two pressing rollers 25, and the tension surfaces to be displaced inward by the belt displacement control mechanism 200 are the first tension surface 8a and the third tension surface. The tension amount control means for controlling the pressing amount of the two pressing rollers 25 includes the first pressing roller 25a and the second pressing roller 25b. The pressing amount is controlled by the control device 3). By such a belt displacement control mechanism 200, the displacement amount between the first stretching surface 8a and the third stretching surface 8c can be adjusted according to the displacement amount of the intermediate transfer belt 8 on the second stretching surface 8b. it can. Therefore, there are three types of speed fluctuations: speed fluctuation due to the pre-nip entering of the transfer paper P, speed fluctuation due to the main paper nip entering the transfer paper P, and speed fluctuation due to the return of the intermediate transfer belt 8 that has been pushed inward. The effect of suppressing the speed change can be controlled. Moreover, since the pressing amount of the two pressing rollers 25 is controlled by one pressing mechanism, the cost is lower than that in the first embodiment .

Further, the pressing mechanism of the belt displacement control mechanism 200 provided in the printer 100 of the second embodiment includes a link member 40 that is a link mechanism that holds the first pressing roller 25a and the second pressing roller 25b. A set of electromagnetic solenoid 24 and solenoid control device 3 are provided as link mechanism drive control means for controlling drive. Thereby, the mechanism which adjusts the amount of pressing of the two pressing rollers 25 by one pressing mechanism is realizable.

  Further, in the belt displacement control mechanism 200 provided in the printer 100 of the present embodiment, the displacement sensor 22 is disposed inside the intermediate transfer belt 8 and measures a distance from the inner surface of the second stretching surface 8b. The solenoid control device 3 serving as the pressing amount control means presses the tensioning surface that is displaced inward only when the distance between the displacement sensor 22 and the second tensioning surface 8b falls below a predetermined threshold. Control to press with. By providing such a belt displacement control mechanism 200, desired belt displacement control can be performed only when the intermediate transfer belt 8 on the second tension surface 8b is pushed inward by the leading edge of the transfer paper P. Further, by not performing control to press when returning to the original state from the state of being pushed inward, the belt tries to return to the outside by the reaction of pushing the intermediate transfer belt 8 inward by belt displacement control. It is possible to suppress the belt speed fluctuation that occurs when the intermediate transfer belt 8 is returned to the original state.

  Further, the belt displacement control mechanism 200 provided in the printer 100 of the present embodiment controls the amount of displacement of at least one of the tension surfaces other than the second tension surface 8b of the intermediate transfer belt 8 to the inside of the transfer paper P. Can be prevented from occurring in the transfer position of the primary transfer to the photosensitive member 1 or the intermediate transfer belt 8, which may occur when the toner enters the secondary transfer nip N.

FIG. 3 is a schematic diagram showing the vicinity of an intermediate transfer unit and a belt displacement control mechanism of a printer of Reference Configuration Example 1 . 1 is a schematic configuration diagram of a printer according to an embodiment. FIG. 2 is a schematic configuration diagram of a process cartridge for Y of the printer. FIG. 10 is a schematic view of the vicinity of an intermediate transfer unit of a conventional image forming apparatus. FIG. 6 is an explanatory diagram of fluctuations in the transfer speed of the intermediate transfer belt. FIG. 3 is an explanatory diagram schematically showing a transfer paper on which a toner image in which positional deviation has occurred is transferred. Explanatory drawing of the speed fluctuation that occurs when the transfer paper enters the prenip, (a) is an enlarged explanatory view of the vicinity of the secondary transfer nip when the transfer paper enters the prenip, and (b) is the prenip entry of the transfer paper. The graph explaining the speed fluctuation by. (A) is an enlarged explanatory diagram of the vicinity of the secondary transfer nip when the transfer paper enters the main nip, and (b) is an explanatory diagram of the transfer paper when the transfer paper enters the main nip. The graph explaining the speed fluctuation | variation by this nip approach. Explanatory drawing of the mechanism in which both a drive roller and an entrance roller decelerate by the main nip approach of a transfer paper. Explanatory view of speed fluctuation caused by the return of the intermediate transfer belt that has been displaced inward, (a) is an enlarged explanatory view of the vicinity of the secondary transfer nip when the intermediate transfer belt returns, and (b) is an intermediate transfer belt. The graph explaining the speed fluctuation by returning. The block diagram of the control circuit of a belt displacement control mechanism. 6 is a graph schematically showing belt inner displacement and inlet roller speed fluctuation over time. The flowchart of operation | movement of a belt displacement control mechanism. FIG. 6 is a schematic diagram showing the vicinity of an intermediate transfer unit and a belt displacement control mechanism of a printer of Reference Configuration Example 2 . FIG. 3 is a schematic diagram illustrating the vicinity of an intermediate transfer unit and a belt displacement control mechanism of the printer according to the first exemplary embodiment . FIG. 6 is a schematic diagram illustrating the vicinity of an intermediate transfer unit and a belt displacement control mechanism of a printer of Embodiment 2 .

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photoconductor 2 Drum cleaning apparatus 3 Solenoid control apparatus 3a 1st solenoid control apparatus 3b 2nd solenoid control apparatus 4 Charging apparatus 5 Developing apparatus 6 Process cartridge 8 Intermediate transfer belt 8a First stretching surface 8b Second stretching surface 8c First Triaxial mounting surface 12 Driving roller 13 Tension roller 14 Entrance roller 15 Intermediate transfer unit 16 Microprocessor 17 Memory 18 Electromagnetic solenoid drive circuit 22 Displacement sensor 24 Electromagnetic solenoid 24a First electromagnetic solenoid 24b Second electromagnetic solenoid 25 Pressing roller 25a First pressing Roller 25b Second pressing roller 26 Paper storage cassette 27 Paper feed roller 28 Registration roller pair 28a Registration roller 28b Registration pressure roller 100 Printer 200 Belt displacement control mechanism

Claims (9)

A toner image carrying belt which is stretched by a plurality of stretching rollers and carries a toner image on the surface and moves endlessly;
A recording medium transfer member that faces one of the plurality of stretching rollers across the toner image carrier belt and forms a recording medium transfer nip that transfers the toner image on the toner image carrier belt to the recording medium And
Of the plurality of stretching surfaces formed by the toner image carrying belt being stretched by the plurality of stretching rollers, the downstream end of the toner image carrying belt in the moving direction becomes the recording medium transfer nip. An image forming apparatus in which the toner image carrying belt and the recording medium conveying member are arranged so that the recording medium enters the recording medium transfer nip after the recording medium comes into contact with the stretching surface on the upstream side of the transfer nip, which is a stretching surface In
In accordance with the inward displacement of the transfer nip upstream tension surface, two tension surfaces that are not the transfer nip upstream tension surface of the plurality of tension surfaces of the toner image carrying belt are displaced inward. An image forming apparatus having a belt displacement control mechanism. The image forming apparatus according to claim 1.
The belt displacement control mechanism is configured such that the upstream end portion in the moving direction of the toner image carrying belt serves as one of the two tension surfaces according to the displacement inward of the tension surface on the upstream side of the transfer nip. An image forming apparatus characterized in that a transfer nip downstream tension surface, which is a tension surface serving as a medium transfer nip, is displaced inward. The image forming apparatus according to claim 1 or 2,
The toner image carrying belt is stretched by three or more stretching rollers,
The belt displacement control mechanism is configured such that the toner image carrier belt on the upstream surface of the transfer nip serves as one of the two extended surfaces according to the inward displacement of the upstream surface of the transfer nip. An image forming apparatus characterized in that a tensioning surface adjacent to the tensioning surface upstream of the transfer nip is displaced inward on the upstream side in the moving direction. The image forming apparatus according to claim 1, 2 or 3.
The belt displacement control mechanism contacts from outside the measuring means for measuring the displacement amount of the tension surface on the upstream side of the transfer nip, and each of the two tension surfaces displaced inward. An image forming apparatus comprising two pressing rollers that press inward and a pressing amount control unit that controls a pressing amount of the pressing roller. The image forming apparatus according to claim 4.
The image forming apparatus according to claim 1, wherein the pressing amount control means controls the pressing amount of the two pressing rollers by independent pressing mechanisms. The image forming apparatus according to claim 4.
It is the pressing amount control means image forming apparatus characterized by controlling the pressing amount in a single pressing mechanism two upper Symbol pressing roller. The image forming apparatus according to claim 6.
The image forming apparatus, wherein the pressing mechanism includes a link mechanism that holds the two pressing rollers, and a link mechanism drive control unit that controls driving of the link mechanism. The image forming apparatus according to claim 4, 5, 6, or 7.
The measuring means includes a distance sensor that is disposed inside the toner image carrying belt and measures a distance from an inner surface of the transfer nip upstream stretch surface,
The pressing amount control means performs control to press the tensioning surface that is displaced inward only when the distance between the distance sensor and the tensioning surface on the upstream side of the transfer nip falls below a predetermined threshold with a pressing roller. An image forming apparatus. The image forming apparatus according to claim 1, 2, 3, 4, 5, 6, 7 or 8.
The toner image carrying belt is an intermediate transfer belt to which a toner image carried on another toner image carrying member is transferred, and the transferred toner image is transferred to a recording medium at a recording medium transfer nip. Image forming apparatus.

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