Belt unit and image forming apparatus having the belt unit

A belt unit used for an image forming apparatus is provided. The belt unit includes a rotatable endless belt, a plurality of stretching members configured to stretch the belt, an urging member, and a contact and separation unit configured to be able to switch a position of the stretching member urged by the urging member. In moving the stretching member urged by the urging member from the separation position to the contact position, the contact and separation unit makes one end side of the stretching member urged by the urging member in a longitudinal direction coming into contact with the inner surface of the belt faster than the other end side, and temporarily decreases the movement speeds of the both ends of the stretching member in the longitudinal direction respectively before arriving at the contact position.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an image forming apparatus having a belt unit.

2. Description of the Related Art

Conventionally, configurations of stretching the inner surface of an endless belt using a plurality of stretching members have been known. Japanese Patent Application Laid-Open No. 2007-057953 discusses an image forming apparatus having a mechanism for moving at least one of a plurality of stretching members to a position where tension of a belt goes slack, and using the mechanism to cause the tension of the belt to be released.

In some cases, the image forming apparatus may not be used by users for a long time after the production of the image forming apparatus. For the above reason, configurations in which the tension of the belt is loosened at the time of manufacture, and the tension is applied to the belt at initial installation by a user have been known. For example, Japanese Patent Application Laid-Open No. 2007-286606 discusses an image forming apparatus having a mechanism for applying tension to a belt using power of a user when the user pulls a paper feed cassette of the image forming apparatus out of the apparatus body at initial installation.

However, in the known configurations, problems may occur in making the stretching member come in contact with the belt to set the tension of the belt at high level. In the configuration in Japanese Patent Application Laid-Open No. 2007-057953, one of the plurality of stretching members is moved while the relation with the other stretching members is kept in parallel, and the stretching members come in contact with the belt at the same time at the entire area in the axis direction. Accordingly, the impact in stretching the belt is large. Further, in controlling the positions of the stretching members using the cam discussed in Japanese Patent Application Laid-Open No. 2007-057953, due to a large impact generated when the stretching members come in contact with the belt, the cam may move. Then, the positions of the stretching members may not be kept at the regular positions.

As discussed in Japanese Patent Application Laid-Open No. 2007-286606, in the configuration the tension is applied to the belt using the user's power, depending on the power of the user, the impact due to the contact of the stretching members with the belt increases.

As described above, the large impact in stretching the belt may not only cause damage to the belt, but also cause an impact sound unpleasant to the users.

SUMMARY OF THE INVENTION

The present invention is directed to reducing damage and impact sound generated when stretching members come in contact with a belt by reducing impact in stretching the belt.

According to an aspect of the present invention, a belt unit used for an image forming apparatus is provided. The belt unit includes a rotatable endless belt, a plurality of stretching members configured to stretch the belt, an urging member configured to urge at least one of the stretching members from an inner surface side to an outer surface side of the belt, and a contact and separation unit configured to switch a position of the stretching member urged by the urging member to a contact position to come into contact with the inner surface of the belt or a separation portion for separating from the inner surface of the belt. In moving the stretching member urged by the urging member from the separation position to the contact position, the contact and separation unit makes one end side of the stretching member urged by the urging member in a longitudinal direction contact with the inner surface of the belt faster than the other end side, and temporarily decreases a movement speed of each of the both ends of the stretching member in the longitudinal direction respectively before arriving at the contact position.

DESCRIPTION OF THE EMBODIMENTS

FIG. 1is a cross sectional view illustrating an electrophotographic image forming apparatus according to the exemplary embodiment. As illustrated inFIG. 1, as the electrophotographic image forming apparatus according to the exemplary embodiment, an example of a four-cycle type full-color laser printer of a rotary type is described.

The image forming apparatus illustrated inFIG. 1includes, in the body, at least an image carrier1, an exposure unit5, a plurality of developing devices4Y,4M,4C, and4Bk, a rotary developing device unit4for holding each development device, an intermediate transfer belt unit19, and a fixing device10. In the exemplary embodiment, the image carrier is the photosensitive drum1for carrying a toner image. In each of the developing devices4Y,4M,4C, and4Bk, toner of yellow, magenta, cyan, and black is filled respectively. The photosensitive drum1, a charging device2, and a cleaning blade3for the photosensitive drum1are integrated to form a photosensitive unit26. Further, the image forming apparatus includes a controller28that serves as a control unit.

The belt unit according to the exemplary embodiment is the intermediate transfer belt unit19. The intermediate transfer belt unit19includes at least a rotatable endless intermediate transfer belt6and a plurality of stretching members for stretching the intermediate transfer belt6. The stretching members include a drive roller15for driving the intermediate transfer belt6, a first driven roller (tension roller)16, and a second driven roller17. The intermediate transfer belt unit19includes a primary transfer member14that is provided on the inner surface of the intermediate transfer belt6, and the member is opposed to the photosensitive drum1across the intermediate transfer belt6, and forms a primary transfer nip portion.

At a position opposed to the drive roller15across the intermediate transfer belt6, a secondary transfer member9is provided.

In transferring a toner image to a transfer material, the photosensitive drum1is rotated in the arrow direction (counterclockwise direction) inFIG. 1, then, in synchronization with the rotation, the intermediate transfer belt6is rotated in the same direction by the drive roller15. The surface of the photosensitive drum1is uniformly charged by the charging device2. Then, the photosensitive drum is exposed by the exposure unit5. More specifically, first, an exposure for forming a yellow image is performed on the photosensitive drum1, and the yellow electrostatic latent image is formed on the photosensitive drum1. Simultaneously with the electrostatic latent image formation, the rotary developing device4is driven to position the developing device4Y for yellow at a development position (the state illustrated inFIG. 1). Then, electric voltage of the same polarity as the charging polarity on the photosensitive drum1and substantially the same potential is applied to the developing device4Y such that a yellow toner adheres to the electrostatic latent image on the photosensitive drum1. The yellow tonner adheres to the electrostatic latent image, and the image is developed. Then, electric voltage of the reverse polarity of the toner is applied to the primary transfer roller14that is a primary transfer member in the intermediate transfer belt unit19, and primary transfer of the yellow toner image on the photosensitive drum1to the intermediate transfer belt6is performed.

In response to the completion of the primary transfer of the yellow toner image described above, the rotary developing device4rotates and positions such that the developing device4M is opposed to the photosensitive drum1, a magenta toner image is developed on the photosensitive drum1, and the primary transfer of the image to the intermediate transfer belt is performed similarly to the case of yellow. With respect to each color of cyan and black, similarly, the formation of an electrostatic latent image, the development, and the primary transfer is sequentially performed, and the toner images of four colors are overlapped on the intermediate transfer belt6.

While the toner images of four colors are overlapped on the intermediate transfer belt6, the secondary transfer roller9that serves as a secondary transfer member is in non-contact state with the intermediate transfer belt6. At the time, a cleaning unit18for collecting the toner remaining on the intermediate transfer belt6is positioned in a state the unit is in non-contact with the intermediate transfer belt6. The position regulation of the secondary transfer roller9, the cleaning unit18, and the intermediate transfer belt6is described below.

After the primary transfer of the toner image of the fourth color from the photosensitive drum1onto the intermediate transfer belt6is started, the secondary transfer roller9comes in contact with the intermediate transfer belt6. Further, in synchronization with the rotation of the intermediate transfer belt6, from a stacking unit13that stacks a plurality of transfer materials, the transfer material is separated and fed one by one by a pickup roller7. The fed transfer material is stopped at a predetermined position by a pair of conveyance rollers8, and then, conveyed toward the nip portion of the intermediate transfer belt6and the secondary transfer roller9at predetermined timing. To the secondary transfer roller9, an electric voltage of the reverse polarity of the toner is applied, and secondary-transfer of the toner image on the intermediate transfer belt6to the surface of the conveyed transfer material is performed collectively.

The transfer material on which the secondary-transfer is performed as described above is conveyed to the fixing device10, and the toner image is fixed onto the transfer material. Then, the transfer material is discharged to a discharge tray12in an upper part of the image forming apparatus by a discharge roller pair11, and the image formation ends. Generally, on the intermediate transfer belt, residual toner that has not been transferred to the transfer material and still remaining exists. The residual toner is charged with the reverse polarity to the polarity during the transfer by the cleaning unit18that comes in contact with the intermediate transfer belt6after the secondary transfer.

The residual toner that has been charged with the reverse polarity is electrostatically transferred to the photosensitive drum1at the primary transfer nip portion. Then, the residual toner is collected in a photosensitive unit26by a cleaning blade3for photosensitive drum1.

The drive roller15is wider than the secondary transfer roller9in the width direction, and wider than the contact portion of the cleaning unit18to the intermediate transfer belt6. The surface of the drive roller15is coated with a rubber having low electric resistance. The drive roller15serves as an opposite electrode of the secondary transfer roller9and the cleaning unit18.

The intermediate transfer belt unit19is described in detail with reference toFIG. 2andFIG. 3.FIG. 2is a perspective view illustrating a state in which the belt is removed from the intermediate transfer belt unit19.FIG. 3is a cross sectional view illustrating the state in which the belt is removed from the intermediate transfer belt unit19.FIGS. 2 and 3illustrate the internal mechanism, and the intermediate transfer belt6and the second driven roller17are not illustrated.

The drive roller15is rotatably held to an intermediate transfer belt frame20by a right side bearing201and a left side bearing202at the both ends. Through a drive gear21(at the left side inFIG. 2), predetermined rotary drive can be transmitted from the apparatus body.

A bearing203and a bearing204are provided to both ends of the primary driven roller16that is one of the plurality of stretching members. The bearings203and204are urged by springs205and206that serve as urging members. With the configuration, the first driven roller is urged from the inner surface side to the outer surface side of the belt by the urging members, and predetermined tension is applied to the intermediate transfer belt6.

In the vicinity of the both ends on the shaft of the drive roller15, phase cams207and208are rotatably held to the drive roller15. The phase cam207includes a gear portion207a, a secondary transfer roller position regulating cam portion207b, and a cleaning unit position regulating cam portion207c. The phase cam208has the symmetrical shape.

By the phase cams207and208, the secondary transfer roller9and the cleaning unit18come in contact with the intermediate transfer belt6or separate from the intermediate transfer belt6.

A cam drive shaft22is rotatably held to the intermediate transfer belt frame20at the both ends. Through a camshaft drive gear23and an idler gear24of the right side, predetermined rotary drive is transmitted from the apparatus body. In the vicinity of the both ends of the cam drive shaft22, gears209and210are integrated with the cam drive shaft22in the same phase and in the symmetrical shape. The gear209transmits the rotary drive to the gear portion207aof the phase cam207, and the gear210transmits the rotary drive to the gear portion208aof the phase cam208. Gear connection portions of the each gear are phase-controlled and assembled. By the configuration, the phase cams207and208rotate in the same phase with rotation of the cam drive shaft22. In the drive transmission gears209and210, belt stretching cams217and218are integrated with the cam drive shaft22. The belt stretching cams217and218are described in detail below. In the exemplary embodiment, the cam drive shaft22, the camshaft drive gear23, the idler gear24, and the like configure a drive transmission unit for driving the phase cams207and208. The drive transmission unit for driving the phase cams207and208may omit the cam drive shaft22. Specifically, the drive force can be directly transmitted from a drive source to the phase cams207and208respectively using gears, or the like.

As illustrated inFIG. 1, the secondary transfer roller9is rotatably held to the apparatus body at the both ends by a bearing301. By a secondary transfer roller spring302, the secondary transfer roller9is urged in a direction coming in contact with the drive roller15. In the vicinity of the both ends on the shaft of the secondary transfer roller9, a roller303is rotatably held to the secondary transfer roller9, and slides with secondary transfer roller position regulating cam portions207band208b. The secondary transfer roller9can move to a position coming in contact with the drive roller15or a position separating from the drive roller15depending on a phase of the secondary transfer roller position regulating cam portions207band208b.

The cleaning unit18is rotatably held to the intermediate transfer belt frame20at the both ends. The cleaning unit18is urged in a direction coming in contact with the drive roller15by a cleaning unit spring304. Protrusions305provided at the both ends of the cleaning unit18slide with cleaning unit position regulating cam portions207cand208c. The cleaning unit18can move to a position coming in contact with the drive roller15or a position separating from the drive roller15depending on a phase of the cleaning unit position regulating cam portions207cand208c.

In one rotation, the phase cams207and208move the secondary transfer roller9and the cleaning unit18to the position separating from the drive roller15, and only the secondary transfer roller9to the position coming in contact with the drive roller15. Further, the phase cams207and208move the secondary transfer roller9and the cleaning unit18to the position coming in contact with the drive roller15. The secondary transfer roller9and the cleaning unit18shift these three states in this order. The positions of the secondary transfer roller9and the cleaning unit18are switched to one of the three states in each one rotation of the idler gear24. Rotation of an apparatus body driveline (not shown) for transmitting drive force to the idler gear24is controlled by a solenoid. The drive force is transmitted to the idler gear24only when the positions of the secondary transfer roller9and the cleaning unit18are switched.

A contact and separation unit for switching the stretched state of the intermediate transfer belt6is described with reference toFIGS. 1 to 4. The contact and separation unit can switch the position of the driven roller16to a position the driven roller16comes in contact with the inner surface of the belt and a position the driven roller16separates from the inner surface of the belt. The contact and separation unit includes a holding member for holding an end of the driven roller16, a regulating member for regulating the position of the holding member, and a pressing member for pressing the regulating member. Further, the contact and separation unit includes at least a drive transmission member for coming in contact with an end of the regulating member and moving the regulating member in a direction opposite to the pressing direction of the pressing member, and a shock-absorbing member for reducing moving force of the regulating member that is moved by the drive transmission member. The contact and separation unit according to the exemplary embodiment includes the holding member, the regulating member, the pressing member, the drive transmission member, and the shock-absorbing member at each side of the both ends in the longitudinal direction of the driven roller16respectively.

FIGS. 2 and 3illustrate states where the driven roller is separated from the intermediate transfer belt6and the stretched state of the intermediate transfer belt6is released.FIG. 4illustrates a state where the driven roller comes in contact with the intermediate transfer belt6and the intermediate transfer belt6is being stretched. Tension release levers211and212serve as the holding member. The tension release levers211and212are connected to the bearings203and204that are provided at both ends of the driven roller16respectively.

Tension release links213and214serve as the control member. Long hole portions213aand214aare held in a state slidably fit to boss portions20aof the intermediate transfer belt frame20. The tension release links213and214receive urging force from the intermediate transfer belt frame20by compression springs215and extension springs216. Specifically, the tension release links213and214are pressed by force in directions from the central part of the intermediate transfer belt frame20toward each end part side by the compression springs215that serve as the pressing member.

Cam sliding portions213band214bof the tension release links213and214slide with the belt stretching cams217and218respectively that serve as the drive transmission member. By rotation of the cam drive shaft22, the orientation of the tension release links213and214changes. The orientation of the tension release links213and214can be changed within the plane of the cross sectional view illustrated inFIGS. 3 and 4. The action of the belt stretching cams is described below.

To begin with, release of the stretched state of the intermediate transfer belt6by moving the driven roller from the intermediate transfer belt6to the separation position by the contact and separation unit is described. First, the tension release levers211and212are moved toward the arrow B direction inFIG. 4. As illustrated inFIG. 4, the tension release links213and214are pressed in the arrow A directions by the compression springs215respectively. Accordingly, if the tension release levers211and212are moved the length C or more in the arrow B direction, engaging portions213cand214cof the tension release links213and214are set into hole portions211aand212aof the tension release levers211and212.

As a result, the tension release links213and214are pressed in the direction opposite to the arrow B by the power of the compression springs205and206through the tension release levers211and212.

Then, at positions latching portions213dand214dof the tension release links213and214hit against protrusions20bof the intermediate transfer belt frame20, the force applied to the tension release links213and214balances with each other. The positions illustrated inFIG. 3are the positions where the force applied to the tension release links213and214balances with each other, and the state the positions of the tension release links213and214are surely regulated. By regulating the positions of the tension release links213and214with the protrusion portions, even if some load changes act on the intermediate transfer belt6in the releasing operation, change in the positions of the tension release links213and214can be prevented.

Protrusions213eand214erotate belt holding members27(belt regulating members27) in the arrow D direction illustrated inFIG. 2by the rotation of the tension release links213and214to the A directions. The belt holding members27are rotatably held to the intermediate transfer belt frame20outside the both ends of the intermediate transfer belt6in the longitudinal direction. In the state the intermediate transfer belt6is stretched, the belt holding members27do not apply any regulation to the tension release links213and214. In the exemplary embodiment, as illustrated inFIG. 5A, in the state the intermediate transfer belt6is stretched, the belt holding members27keep the positions separated from the intermediate transfer belt6under its own weight.

If the tension release links213and214rotate to release the stretched state of the intermediate transfer belt6, the belt holding members27rotate in the arrow D direction. As illustrated inFIG. 5B, the belt holding member27supports the intermediate transfer belt6, that is loosened, between the first driven roller16and the second driven roller17. With the operation, the loosened intermediate transfer belt6can be prevented from coming in contact with the other components in the image forming apparatus. In the exemplary embodiment, the intermediate transfer belt6is prevented from coming in contact with a mechanical section (for example, the pickup roller7) that is located below the intermediate transfer belt unit19.

Next, change of the state of the intermediate transfer belt6from the state the stretched state is released to the stretched state is described with reference toFIGS. 6A to 6F.

If electric power is supplied to a power source unit (not shown), a solenoid is set by a controller28, and the cam drive shaft22rotates. The operation of the belt stretching cam217and the tension release link213at the time is described with reference toFIGS. 6A to 6F. The operation of the belt stretching cam218and the tension release link214is similar to that of the operation of the belt stretching cam217and the tension release link213, and accordingly, the description of the operation is omitted. The belt stretching cams217and218have symmetrical shapes, and are held in a state their phases with respect to the cam drive shaft22are shifted by 180 degrees with each other. Accordingly, the timing a cam face217aof the belt stretching cam217comes in contact with a cam sliding portion213bof the tension release link213differs from the timing a cam face218aof the belt stretching cam218comes in contact with a cam sliding portion214bof the tension release link214.

FIGS. 6A to 6Fillustrate the process the cam face217aof the belt stretching cam217comes in contact with the cam sliding portion213bof the tension release link213and the tension release link213is moved. In the state inFIG. 6A, the cam face217astarts to push the tension release link213toward the left side in the drawing. In response to the cam sliding portion213bof the tension release link213being pushed by the cam face and moved to the left side in the drawing, a portion213cmoves on a tapered portion of the tension release lever211, and moves in the direction separating from the tension release lever211(from the end part to the central part).

When the tension release link213is pushed to the position illustrated inFIG. 6B, by the stretching force of the spring205, the tension release link213separates from the cam face217a, and rotates fast. At the time, to prevent the tension release link213from separating at once from the tension release lever211, a shock-absorbing member29is provided to the intermediate transfer belt frame20.

As illustrated inFIG. 6C, the moving speed of the tension release link213temporarily decreases due to the resistance force of the shock-absorbing member29. In the exemplary embodiment, the tension release link213is stopped moving temporarily by the resistance force of the shock-absorbing member29. With the configuration, the driven roller16can be restrained from moving instantaneously from the separation position to the contact position movement of.

The frictional sliding face of the shock-absorbing member29with the tension release link213is covered with a frictional sliding portion30composed of a rigid body of low coefficient of friction. The material and shape of the shock-absorbing member29are selected such that when the tension release link213temporarily stops at the position illustrated inFIG. 6C, the bearing203of the primary driven roller16is arranged in a substantially intermediate position between the contact position (FIG. 6E) and the separation position (FIG. 6A) of the intermediate transfer belt6. A position more contact position side than the position substantially intermediate position can be selected.

When the cam drive shaft22rotates further, the cam face217apushes the resistance force of the shock-absorbing member29, and then, the tension release link213is moved again in the direction separating from the tension release lever211. When the tension release link213moves to the position illustrated inFIG. 6D, the engaging portion213cof the tension release link213comes off the hole portion211aof the tension release lever211. As a result, the tension release lever211and the bearing203of the primary driven roller16move to the contact position on the intermediate transfer belt6by the spring205(the bearing203moves in the downward direction inFIG. 6D).

The tension release link213rotates to a sufficiently separated position from the tension release lever211by the stretching cam217as illustrated inFIG. 6F. Then, as illustrated inFIG. 6E, by the compression spring215, the tension release link213returns to a position the tension release link213comes in contact with the side surface of the tension release lever211.

During the operation, the cam face218aof the belt stretching cam218does not come in contact with the cam sliding portion214bof the tension release link214. Accordingly, the tension release link214keeps the state in which the stretching force of the intermediate transfer belt6is released. When the cam drive shaft22rotates further, the cam face218aof the belt stretching cam218comes in contact with the cam sliding portion214bof the tension release link214and the tension release link214is moved. The process is similar to the above-described process of the tension release link213. Specifically, by the contact and separation unit, the one end side of the driven roller16in the longitudinal direction is made to come in contact with the inner face of the belt faster than the other end side, and the movement speeds of the both ends are temporarily decreased before arriving at the contact positions respectively.

FIGS. 7A to 7Eillustrate states from the state in which the stretched state of the intermediate transfer belt is released to the state in which the released state is changed to the stretched state. As illustrated inFIGS. 7B and 7D, the primary driven roller16stops once at the both end portions while the driven roller16moves from the separation position to the contact position.

In the exemplary embodiment, the belt stretching cams217and218are disposed such that the phases with respect to the cam drive shaft22are shifted by 180 degrees with each other, however, it is not limited to the example. For example, after the tension release link213is temporarily stopped at the position inFIG. 6Cby the belt stretching cam217, the tension release link214is moved to the same position (the temporary stop position) by the belt stretching cam218. Then, the tension release link213can be moved again to the stretch position of the intermediate transfer belt6by the belt stretching cam217, and finally, the tension release link214can be moved to the stretch position of the intermediate transfer belt6by the belt stretching cam218.

Only in the initial installation in which the above-described operation is performed, a drive motor (not shown) connected to the cam drive shaft22is operated at a low speed to restrain the movement speed of the tension release links213and214. Once the tension release links213and214move to the positions for stretching the intermediate transfer belt6, the state in which the tension release links213and214urged to the back of the apparatus body is maintained by the extension spring216(FIGS. 6E and 6F).

Then, the tension release levers211and212maintain the state in which the tension release levers211and212are urged to the front of the apparatus body by the springs205and206. In other word, the tension release links213and214are prevented from automatically returning to the positions for releasing the stretching force of the intermediate transfer belt6by the rotation of the belt stretching cams217and218once the intermediate transfer belt6is stretched. For example, in the state inFIG. 6E, the positions of the tension release links213and214are to be regulated such that the cam sliding portions213band214bof the tension release links213and214do not come in contact with the belt stretching cams217and218respectively. Further, in a case where the tension release links213and214are slightly rotated by the belt stretching cams217and218, the engaging portions213cand214care to be regulated not to be set into the hole portions211aand212aof the tension release levers211and212.

In a case where the apparatus body is packed in a state in which the intermediate transfer belt unit19is mounted on the apparatus body, and the apparatus body is shipped, the stretched state of the intermediate transfer belt6may be released. In the configuration according to the exemplary embodiment, by simply moving the tension release levers211and212by an operator, the stretched state of the intermediate transfer belt6can be released, and the released state can be maintained with the simple configuration.

Further, even if a large vibration occurs during shipment of the apparatus body, the tension release links213and214are being pressed by the compression spring215. With the configuration, even if the large vibration occurs, the engagement state between the hole portions211aand212aof the tension release levers and the portions213cand214cof the tension release links can be maintained.

With the above-described configurations, the stretching force of the belt is applied in the width direction of the belt through multiple steps. Accordingly, the impact sound in the stretching operation can be reduced. Further, the regulating members for regulating the stretching roller positions of the belt are moved through multiple steps, and the drive force necessary in the stretching operation can be reduced.

Further, it is not necessary to newly provide a drive unit for driving the contact and separation unit. Accordingly, the costs and the size of the product are not increased. Further, only at the initial installation, the drive unit is operated at a low speed. Accordingly, the impact sound in stretching the belt can be further decreased.

In the exemplary embodiment, the color image forming apparatus of the rotary type in which the development devices rotate, the apparatus having one image carrier (photosensitive drum) and using the intermediate transfer belt has been described. However, the present invention is not limited to the above, the invention can also be applied to a belt unit used for color image formation of a tandem type having a plurality of image carriers and uses the intermediate transfer belt as illustrated inFIG. 8. Further, the present invention can be applied to an image forming apparatus using a belt unit that employs a conveyance belt for bearing and conveying a transfer material.

This application claims priority from Japanese Patent Application No. 2010-185293 filed Aug. 20, 2010, which is hereby incorporated by reference herein in its entirety.