The present invention relates to an image forming apparatus, using an electrophotographic system, such as a copying machine, a printer or a facsimile machine.
In the image forming apparatus of a tandem type using an intermediary transfer belt, photosensitive drums are provided along a substantially rectilinear line relative to the intermediary transfer belt. A primary transfer roller is provided adjacently to a contact position between the intermediary transfer belt and each of the photosensitive drums. Before start of image formation, the primary transfer roller contacts the intermediary transfer belt toward the associated photosensitive drum.
In the conventional image forming apparatus, a length of a contact portion between the intermediary transfer belt and the photosensitive drum and a length of a contact portion between the intermediary transfer belt and the primary transfer roller are substantially equal to each other. However, in this case, there is a liability that at a gap between the intermediary transfer belt and the upstream-side photosensitive drum, electric discharge generates, and thus toner scattering generates.
Therefore, in some cases, an auxiliary roller for pressing the intermediary transfer belt toward the photosensitive drum is provided to prolong the contact portion between the intermediary transfer belt and the photosensitive drum. However, there is a liability that speed non-uniformity is generated at every one of a plurality of rollers including the auxiliary roller, and thus toners of respective colors are transferred onto the intermediary transfer belt in a misregistration manner.
Therefore, in Japanese Laid-Open Patent Application (JP-A) 2003-91133, it is proposed that a length of an outer circumference of the primary transfer roller and a length of an outer circumference of the photosensitive drum are made so as to provide an integral multiple and then a color misregistration period is measured, and a color misregistration is corrected by adjusting timing of image formation by light exposure.
However, a conventional intermediary transfer unit was inserted into an image forming apparatus main assembly, and the intermediary transfer belt was contacted to the photosensitive drums while being stretched by a tension roller and a driving roller, and a mechanism for urging the intermediary transfer belt against the photosensitive drums was merely provided. For that reason, when the intermediary transfer unit is inserted into the image forming apparatus main assembly and is urged toward the photosensitive drums, a resistance due to friction is generated between the intermediary transfer belt and each of the photosensitive drums by the urging. By this resistance, there was a problem that the intermediary transfer belt rubs against the photosensitive drums while contacting the photosensitive drums.
With respect to the intermediary transfer belt, particularly in the image forming apparatus in which switching between operations in a full-color mode and a monochromatic mode is made, in a constitution in which contact and separation between the photosensitive drums for color image formation and the intermediary transfer belt are repeated, short lifetimes of the intermediary transfer belt and the photosensitive drums are problematic due to the friction (rubbing).
Objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.
The image forming apparatus 100 includes image forming stations SY, SM, SC and SK for yellow (Y), magenta (M), cyan (C) and black (K), respectively. The image forming stations SY, SM, SC and SK for the respective colors have many common constitutions and operations except for the colors of the toners. Accordingly, in the following, in the case where particular distinction is not needed, description will be made by omitting suffixes Y, M, C and K for representing the colors of constituent elements of the image forming apparatus.
Each of the image forming stations S includes a photosensitive drum 1, and at a periphery of the photosensitive drum 1, includes a charging roller 2, a developing means 3 and a photosensitive drum cleaner 4. The image forming apparatus 100 includes an intermediary transfer belt 5 having an endless belt shape. A plurality of the image forming stations S are disposed at contact positions of the photosensitive drums 1 with the intermediary transfer belt 5 along a substantially rectilinear line relative to the intermediary transfer belt 5. Below the image forming stations S in a side opposite from a side where the photosensitive drums 1 contact the intermediary transfer belt 5, an exposure means 6 is provided. The intermediary transfer belt 5 is stretched around a tension roller 7 and a driving roller 8, and a belt cleaner 9 is provided opposed to the tension roller 7 via the intermediary transfer belt 5. At a position opposing the driving roller 8 via the intermediary transfer belt 5, a secondary transfer roller 10 is provided. At a position opposing the associated one of the photosensitive drums 1 at a back surface of the intermediary transfer belt 5, a primary transfer roller 11 as a primary transfer means is provided. Further, at the back surface of the intermediary transfer belt, i.e., in the side where the primary transfer rollers 11 are provided, an auxiliary roller 12 is provided. At an inside lower portion of the image forming apparatus 100, a sheet feeding cassette 13 in which a transfer(-receiving) material P is accommodated is provided. With respect to a feeding and movement direction of the transfer material P accommodated in the sheet feeding cassette 13, a feeding roller pair 15, a registration roller pair 16, the secondary transfer roller 10, a fixing means 17 and a discharging portion 18 are provided. Further, as an accommodating portion for the transfer material P, in addition to the sheet feeding cassette 13, a manual feeding portion 14 is provided.
Next, an image forming operation of the image forming apparatus 100 in this embodiment will be described.
The image forming apparatus 100 receives an image formation start signal from an unshown host computer or image reader or the like, and then starts the image forming operation. The four photosensitive drums 1Y, 1M, 1C and 1K are electrically charged to have uniform electric charges by the charging rollers 2Y, 2M, 2C and 2K, respectively. Into a laser scanner 6 as the exposure means, image signals for yellow (Y), magenta (M), cyan (C) and black (K) are inputted. Depending on the image signal, the surface of the associated photosensitive drum 1 is irradiated with laser light by the laser scanner 6, so that the electric charges are neutralized to form a latent image. The latent images formed on the photosensitive drums (image bearing members) 1 are developed with toners of yellow, magenta, cyan and black by the developing means 3Y, 3M, 3C and 3K. The toners used for developing the latent images on the photosensitive drums 1 are successively transferred onto the intermediary transfer belt 5 which is an endless belt-shaped intermediary transfer member, so that a full-color toner image consisting of superposed toners is formed on the intermediary transfer belt 5. A transfer residual toner remaining on each of the photosensitive drums 1 without being transferred is collected by the photosensitive drum cleaner 4.
On the other hand, a sheet P which is the transfer material such as recording paper which is fed from either one of the sheet feeding cassette 13 or the manual feeding portion 14 is fed toward the registration roller pair 16 by the feeding roller pair 15. A leading end of the sheet P abuts against the registration roller pair 16 placed in a rest state, and after oblique movement of the sheet P is corrected, rotation of the registration roller pair 16 is started in synchronism with the toner image on the intermediary transfer belt 5.
The toner image on the intermediary transfer belt 5 is transferred onto the sheet P at a secondary transfer portion N2 by the secondary transfer roller 10, and then is heated and pressed by the fixing means 17 to be fixed on the sheet P. Thereafter, the sheet P is discharged to an outside of an image forming apparatus main assembly 100M through the discharging portion 18. Further, a secondary transfer residual toner remaining on the intermediary transfer belt 5 without being transferred at the secondary transfer portion N2 is collected by an intermediary transfer belt cleaner 9.
In the image forming apparatus 100 in this embodiment, the intermediary transfer belt 5 is a part of a structure of an intermediary transfer unit 50, and the intermediary transfer unit 50 is constituted so as to be freely inserted into and dismounted from the image forming apparatus main assembly 100M of the image forming apparatus 100. The intermediary transfer unit 50 will be described.
The intermediary transfer belt 5, the tension roller 7, the driving roller 8, the auxiliary roller 12, the primary transfer roller 11 and the intermediary transfer belt cleaner 9 which are described above constitute the intermediary transfer unit 50 which integrally hold these members. The intermediary transfer unit 50 can be inserted and pulled in an arrow A1 direction along an intermediary transfer unit inserting and pulling rail (not shown) provided in the image forming apparatus main assembly 100M. Further, the intermediary transfer unit 50 includes an unshown intermediary transfer frame for rotatably supporting the tension roller 7, the driving roller 8 and the auxiliary roller 12. The tension roller 7 is movable relative to the intermediary transfer frame and is urged by a tension spring 71 in a direction of maintaining tension of the intermediary transfer belt 5. The driving roller 8 supplies a driving force to the intermediary transfer belt 5. At a surface opposing the tension roller 7 via the intermediary transfer belt 5, the intermediary transfer belt cleaner 9 is provided.
A phantom plane which is a common contact plane (surface) of the photosensitive drums 1 at the side where the photosensitive drums 1 contact the intermediary transfer belt 5 is F. After the intermediary transfer unit 50 is mounted in the image forming apparatus main assembly 100M, the respective stretching rollers 7, 8 and 12 enter the phantom plane toward the photosensitive drum 1 side. As a result, a contact region where the intermediary transfer belt 5 contacts the photosensitive drum is longer than a contact region where the intermediary transfer belt 5 contacts the primary transfer roller 11.
The stretching rollers 7, 8 and 12 constituting the intermediary transfer unit 50 are disposed in the following manner. The intermediary transfer belt 5 is stretched by the stretching rollers 7 and 8 when the intermediary transfer unit 50 is mounted in the image forming apparatus main assembly 100M and the intermediary transfer belt 5 does not contact the photosensitive drums 1. With respect to the movement direction of the intermediary transfer belt 5, each of the photosensitive drums 1 has the contact region positioned downstream of the tension roller 7 and upstream of the driving roller 8. The contact regions are regions where the intermediary transfer belt 5 contacts the photosensitive drums 1Y, 1M, 1C and 1K, respectively, in the listed order from an upstream side of the movement direction of the intermediary transfer belt 5. At positions, inside the intermediary transfer belt 5, corresponding to the respective contact regions, the primary transfer rollers are disposed.
The stretching rollers which enter the photosensitive drum side of phantom plane F described above are the tension roller 7 positioned upstream of the photosensitive drums 1 with respect to the movement direction of the intermediary transfer belt 5, the driving roller 8 positioned downstream of the photosensitive drums 1 with respect to the movement direction of the intermediary transfer belt 5, and the auxiliary roller 12 positioned between the photosensitive drums 1M and 1C. A constitution in which these stretching rollers 7, 8 and 12 enter the phantom plane F and thus the intermediary transfer belt 5 winds about the photosensitive drums 1 is employed.
Next, an operation of the intermediary transfer unit 50 in the case where the intermediary transfer unit 50 is gradually inserted into the image forming apparatus main assembly 100M will be described with reference to
As shown in
As shown in
Thereafter, as shown in
Then, the gear 81 rotating integrally with the driving roller 8 is separated from the rack 82, so that the driving roller 8 is rotatable in an opposite direction, i.e., in an image forming direction. The bearing member 72 of the tension roller 7 is disengaged from the releasing means 73, so that the intermediary transfer unit 50 is mounted in the image forming apparatus main assembly 100M, i.e., disposed at the image forming position.
Substantially simultaneous therewith, fixing of the tension roller 7 by an unshown rotation-locking means is also released. This fixing is made for slacking the intermediary transfer belt 5 by sending, toward the photosensitive drums 1, the slackness of the intermediary transfer belt 5 generated by rotation of the driving roller 8 based on the engagement between the rack 82 and the gear 81 as described above. When the tension roller 7 is rotated, the intermediary transfer belt 5 sent toward the photosensitive drums 1 is moved as it is, so that the slackness cannot be left in the photosensitive drum 1 side. Therefore, when the intermediary transfer unit 50 is inserted in the image forming apparatus main assembly 100M, the tension roller 7 is fixed to be prevented from rotating.
A feature portion, of this embodiment, including the releasing means 73, the gear 81 and the rack 82 will be specifically described.
In the image forming apparatus main assembly 100M in which the intermediary transfer unit 50 is inserted and mounted, as described above, the releasing means 73 engageable with the bearing member 72 of the tension roller 7 of the intermediary transfer unit 50 is disposed in the image forming apparatus main assembly side.
The releasing means 73 is provided at a position where the releasing means 74 contacts a rotational axis direction end portion of the bearing member 72 of the tension roller 7 at a rearmost portion of the unshown intermediary transfer unit inserting and pulling (dismounting) rail. The releasing means 73 is a substantially doglegged member having two surfaces substantially perpendicular to the arrow A3 direction, of
Substantially simultaneously with the contact of the bearing member 72 with the releasing means 73, the gear 81 provided on the driving roller 8 of the intermediary transfer unit 50 engages with the rack 82 disposed in the neighborhood of an end portion of the inserting and pulling rail in the image forming apparatus main assembly 100M in an entrance port side where the intermediary transfer unit 50 is inserted into the image forming apparatus main assembly 100M. The position of this rack 82 is a position where the rack 82 contacts the gear 81 in a state in which the tension of the intermediary transfer belt 5 is not loosened when the bearing member 72 of the tension roller 7 of the intermediary transfer unit 50 contacts the releasing means 73.
When the gear 81 engages with the rack 82, the driving roller 8 rotating integrally with the gear 81 by being inserted in the arrow A2 direction rotates in the arrow RA2 direction (clockwise direction) shown in
By the above-described contact with the releasing means 73 and the urging by the insertion in the arrow A2 direction, the bearing member 72 of the tension roller 7 of the intermediary transfer unit 50 is urged in the arrow A3 direction in the figures. As a result, the stretching of the intermediary transfer belt 5 by the tension roller 7 and the driving roller 8 and the tension by the tension spring 71 which urges the tension roller 7 are weakened. For that reason, the tension of the intermediary transfer belt 5 is loosened as a whole. By the rotation of the driving roller 8 in the arrow RA2 direction based on the above-described rotation of the gear 81 by the rack 82, the loosening of the intermediary transfer belt 5 is sent toward the side where the intermediary transfer belt 5 contacts the photosensitive drums 1. Further, the tension roller 7 including the bearing member 72 contacting the releasing means 73 is constituted so as not to rotate, during the insertion of the intermediary transfer unit 50 into the image forming apparatus main assembly 100M and the dismounting of the intermediary transfer unit 50 from the image forming apparatus main assembly 100M, by the unshown rotation-locking means. For this reason, the slackness (loosening) sent toward the contact side of the intermediary transfer belt 5 with the photosensitive drums 1 is accumulated in the contact side with the photosensitive drums 1 since the tension roller 7 does not rotate.
As a result, as shown in
In the state in which the slackness of the intermediary transfer belt 5 is provided, as shown in
As described above, according to this embodiment, in the case where the intermediary transfer unit 50 is mounted in the image forming apparatus main assembly 100M, when the intermediary transfer belt 5 contacts the photosensitive drums 1, the tension is loosened, so that the surface, of the intermediary transfer belt 5, where the intermediary transfer belt 5 contacts the photosensitive drums 1 flexes. For this reason, a contact pressure of the intermediary transfer belt 5 to the photosensitive drums 1 is decreased, so that damages on the drums and the belt due to the rubbing between the intermediary transfer belt 5 and each of the photosensitive drums 1 can be suppressed to the minimum.
In addition to the case where the intermediary transfer unit 50 is mounted in the image forming apparatus main assembly 100M, also when the mounted intermediary transfer unit 50 is dismounted from the image forming apparatus main assembly 100M, an effect can be obtained. When the intermediary transfer unit 50 is dismounted from the image forming apparatus main assembly 100M, first, the intermediary transfer unit 50 is moved in a direction in which the intermediary transfer unit 50 is spaced from the photosensitive drums 1, i.e., a direction opposite to the arrow A4 direction. At this time, the bearing member 72 of the tension roller 7 of the intermediary transfer unit 50 contacts the first surface 73b of the releasing means 73 to move in a tension-slacking direction, i.e., the arrow A3 direction. At the same time, the gear 81 engages with the rack 82. At this time, the driving roller 8 itself is rotation-limited by the gear 81 engaging with the rack 82. Further, also the tension roller 7 is rotation-stopped by the rotation-locking means with start of a dismounting operation of the intermediary transfer unit 50. As a result, the intermediary transfer belt 5 is spaced and dismounted from the photosensitive drums 1 while maintaining the loosening of the intermediary transfer belt 5 which has been shifted toward the photosensitive drums 1 during the mounting, so that the operation can be performed in a state in which the contact pressure to the photosensitive drums 1 is suppressed to a low level. As a result, the damages on the drums and the belt due to the rubbing between the intermediary transfer belt 5 and each of the photosensitive drums 1 can be suppressed to the minimum.
As described above, according to this embodiment, by causing the rollers for stretching the intermediary transfer belt 5 to enter the photosensitive drum 1 side, it is possible to obtain a long lifetime of each of the intermediary transfer belt 5 and the photosensitive drums 1.
The image forming apparatus 100 in this embodiment is not provided with the primary transfer rollers 11. Further, a primary transfer electric field is generated at a primary transfer portion, which is a contact portion between the intermediary transfer belt 5 and each of the photosensitive drums 1, from the secondary transfer roller 10 via an inner peripheral surface of the intermediary transfer belt 5 having a low resistance at the inner peripheral surface, so that the toner image is transferred from each of the photosensitive drums 1 onto the intermediary transfer belt 5. Other constituent elements and operations are substantially the same as those in Embodiment 1. Therefore, members having constitutions and functions similar to those of the image forming apparatus 100 in Embodiment 1 are represented by the same reference numerals or symbols and will be omitted from detailed description. Only a difference from Embodiment 1 will be described below.
The secondary transfer roller 10 contacts the intermediary transfer belt 5, and by a bias power source V10 connected to the secondary transfer roller 10, the primary transfer bias is applied to the intermediary transfer belt 5 at predetermined timing, so that the primary transfer is made. The toner images primary-transferred on the intermediary transfer belt 5 are secondary-transferred onto the sheet P at the secondary transfer portion N2 by applying the secondary transfer bias to the secondary transfer roller 10.
The stretching rollers which enter the photosensitive drum side of phantom plane F described above are the tension roller 7 positioned upstream of the photosensitive drums 1 with respect to the movement direction of the intermediary transfer belt 5, the driving roller 8 positioned downstream of the photosensitive drums 1 with respect to the movement direction of the intermediary transfer belt 5, and the auxiliary roller 12 positioned between the photosensitive drums 1M and 1C. A constitution in which these stretching rollers 7, 8 and 12 enter the phantom plane F and thus the intermediary transfer belt 5 winds about the photosensitive drums 1 is employed.
Next, an operation of the intermediary transfer unit 50 in the case where the intermediary transfer unit 50 is gradually inserted into the image forming apparatus main assembly 100M will be described with reference to
As shown in
As shown in
Thereafter, as shown in
Then, the gear 81 rotating integrally with the driving roller 8 is separated from the rack 82, so that the driving roller 8 is rotatable in an opposite direction, i.e., in an image forming direction. The bearing member 72 of the tension roller 7 is disengaged from the releasing means 73, so that the mounting of the intermediary transfer unit 50 in the image forming apparatus main assembly 100M is completed. The structure and the operation of the releasing means 73 are similar to those in Embodiment 1.
Simultaneously therewith, fixing of the tension roller 7 by an unshown rotation-locking means is also released. This fixing is made for loosening the intermediary transfer belt 5 by sending, toward the photosensitive drums 1, the slackness of the intermediary transfer belt 5 generated by rotation of the driving roller 8 based on the engagement between the rack 82 and the gear 81 as described above. When the tension roller 7 is rotated, the intermediary transfer belt 5 sent toward the photosensitive drums 1 is moved as it is, so that the slackness cannot be left in the photosensitive drum 1 side and therefore, when the intermediary transfer unit 50 is inserted in the image forming apparatus main assembly 100M, the tension roller 7 is fixed to be prevented from rotating.
As described above, in this embodiment described with reference to
Similarly as in Embodiment 1, also in this embodiment, in the case where the intermediary transfer unit 50 is mounted in the image forming apparatus main assembly 100M, when the intermediary transfer belt 5 contacts the photosensitive drums 1, the tension is slacked, so that the surface, of the intermediary transfer belt 5, where the intermediary transfer belt 5 contacts the photosensitive drums 1 flexes. For this reason, a contact pressure of the intermediary transfer belt 5 to the photosensitive drums 1 is decreased, so that damages on the drums and the belt due to the rubbing between the intermediary transfer belt 5 and each of the photosensitive drums 1 can be suppressed to the minimum.
As described above, in this embodiment, although the case where the intermediary transfer unit 50 is mounted in the image forming apparatus main assembly 100M is described, similarly as in Embodiment 1 also when the mounted intermediary transfer unit 50 is dismounted from the image forming apparatus main assembly 100M, an effect can be obtained.
As described above, also in the image forming apparatus including no primary transfer roller, it is possible to obtain a long lifetime of each of the intermediary transfer belt 5 and the photosensitive drums 1.
While the invention has been described with reference to the structures disclosed herein, it is not confined to the details set forth and this application is intended to cover such modifications or changes as may come within the purpose of the improvements or the scope of the following claims.
This application claims priority from Japanese Patent Application No. 259431/2013 filed Dec. 16, 2013, which is hereby incorporated by reference.
Number | Date | Country | Kind |
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2013-259431 | Dec 2013 | JP | national |
Number | Name | Date | Kind |
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5517290 | Marumoto et al. | May 1996 | A |
6298212 | Kono et al. | Oct 2001 | B1 |
Number | Date | Country |
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2001-215809 | Aug 2001 | JP |
2003-091133 | Mar 2003 | JP |
2003-171030 | Jun 2003 | JP |
Number | Date | Country | |
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20150168879 A1 | Jun 2015 | US |