JP2013037361A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of securely preventing density unevenness caused by a load difference between a pressure spring and a power feeding spring to a transfer roller.SOLUTION: An image forming apparatus comprises: a photoreceptor drum; an image forming unit that forms a toner image on the photoreceptor drum; an endless transfer belt stretched over a plurality of rollers including a driving roller; a transfer roller that pressure-contacts the photoreceptor drum with the transfer belt sandwiched therebetween; a power feeding spring that contacts the transfer roller and provides the transfer roller with an electric charge for transferring the toner image on the photoreceptor drum to a surface of the transfer belt; a power feeding spring supporting part that supports the power feeding spring and holds the transfer roller; and a power feeding spring locking part that is provided integrally with the power feeding spring supporting part and locks the power feeding spring with the supported portion of the power feeding spring sandwiched between the power feeding spring locking part and the transfer roller.

Description

  Embodiments described herein relate generally to an image forming apparatus that transfers a toner image formed on a photosensitive drum to a recording medium.

  In an image forming apparatus, a transfer medium having a polarity opposite to that of a toner image on a transfer belt is applied to a transfer roller, and a current having the same polarity as that of the toner image is applied to a roller opposite to the transfer roller. A transfer electric field is formed in such a direction as to be attracted to the side, and the toner image is secondarily transferred from the transfer belt to the recording medium by the transfer electric field.

  The transfer roller is provided with pressure springs at both ends and is rotatably supported by a conductive bearing. To supply power to the transfer roller, a voltage is applied by a voltage generator provided in the image forming apparatus, and the transfer belt is charged to a predetermined potential by the transfer roller. One end or both ends of the transfer roller are urged in the vertical direction by a torsion coil spring (feed spring).

  When the pressure spring and the power supply spring are urged to one end, a load difference is generated between both ends of the transfer roller. Even when the power supply spring is urged to both ends, the power supply spring has a large load variation, so that a load difference is generated at both ends and a difference in transfer efficiency is caused by this load difference. For this reason, there is a possibility that density unevenness may occur during transfer to a recording medium.

JP-A-11-334925

  SUMMARY An advantage of some aspects of the invention is that it provides an image forming apparatus that can reliably prevent density unevenness due to a load difference between a pressure spring to a transfer roller and a power supply spring.

  In order to achieve the above object, an image forming apparatus according to an embodiment includes a photosensitive drum, an image forming unit that forms a toner image on the photosensitive drum, and an endless shape spanned by a plurality of rollers including a driving roller. The transfer belt, a transfer roller pressed against the photoconductive drum across the transfer belt, and a charge for contacting the transfer roller and transferring the toner image on the photoconductive drum onto the transfer belt surface. A power supply spring to be applied to the transfer roller, a power supply spring support portion that supports the power supply spring and holds the transfer roller, and the power supply spring support portion are provided integrally, and the transfer roller and a support portion of the power supply spring are provided. A power supply spring locking portion that holds the power supply spring sandwiched therebetween is provided.

1 is a partial cross-sectional front view showing a configuration of an image forming apparatus in the present embodiment. FIG. 2 is a perspective view of a belt conveyance unit of the image forming apparatus illustrated in FIG. 1. FIG. 3 is an enlarged perspective view of a part of the belt conveyance unit shown in FIG. 2.

  The color image forming apparatus according to this embodiment will be described in detail below.

  An image forming apparatus 1 according to the present embodiment shown in FIG. 1 includes a box-shaped apparatus main body 2, and a document placement section 3 is disposed on the upper surface of the apparatus main body 2. The document placement section 3 is provided with a transparent document table (glass plate) 4 for document placement, and a cover 5 is provided on the document table 4 so as to be freely opened and closed. In addition, instead of the cover 5, a known automatic document feeder (ADF) may be disposed on the document placing unit 3. A carriage 6 is provided on the lower surface side of the document table 4, and an exposure lamp 7 is provided on the carriage 6. The carriage 6 reciprocates along the lower surface of the document table 4. The exposure lamp 7 is turned on while the carriage 6 moves forward, so that the document on the document table 4 is exposed. By this exposure, a reflected light image of the document placed on the document table 4 is obtained and projected onto a CCD (Charge Coupled Device) 12 by the reflection mirrors 8, 9 and 10 and the zoom lens 11. The CCD 12 outputs an image signal corresponding to the reflected light image of the document.

  The image signal output from the CCD 12 is appropriately processed and then supplied to the exposure unit 13. The exposure unit 13 includes a laser beam B1 corresponding to a yellow color image signal, a laser beam B2 corresponding to a magenta color image signal, a laser beam B3 corresponding to a cyan color image signal, and a laser corresponding to a black color image signal. The beam B4 is emitted toward the photosensitive drum 20 for yellow color, the photosensitive drum 21 for magenta color, the photosensitive drum 22 for cyan color, and the photosensitive drum 23 for black color.

  The photosensitive drums 20, 21, 22, and 23 are arranged in a substantially horizontal direction at regular intervals. A transfer belt 24 is provided above the photosensitive drums 20, 21, 22 and 23. The transfer belt 24 is stretched around the drive roller 25, guide rollers 26, 27, and 28 and the driven roller 29, receives power from the drive roller 25, and rotates in the counterclockwise direction.

  Around the photosensitive drum, a well-known image forming unit (not shown) including a charger, a developing device, a static eliminator, and a cleaner is arranged.

  Primary transfer rollers 30, 31, 32, and 33 are provided at positions facing the photosensitive drums 20, 21, 22, and 23 with the transfer belt 24 interposed therebetween. The primary transfer rollers 30, 31, 32, and 33 are in contact with the transfer belt 24 and transfer the visible images on the photosensitive drums 20, 21, 22, and 23 to the transfer belt 24.

  A plurality of paper feed cassettes 40 are provided below the exposure unit 13. In these paper feed cassettes 40, paper is stored as recording media of different sizes. Sheets are taken out one by one from any one of these sheet cassettes 40. A pick-up roller 41 is provided in each paper feed cassette 40 for this take-out. The taken paper is separated by the separation roller 42 so that a plurality of sheets are not supplied together, and is supplied to the conveyance path 43.

  The conveyance path 43 extends to the upper discharge port 44 via the driven roller 29. The paper discharge port 44 faces a paper discharge tray 45 connected to the outer peripheral surface of the apparatus main body 2.

  On the start end side of the transport path 43, paper feed rollers 46 are provided in the vicinity of the separation rollers 42, respectively. Further, a secondary transfer roller 47 is provided at a position facing the driven roller 29 in a substantially midway portion of the transport path 43 with the transfer belt 24 interposed therebetween. A registration roller 48 is provided at a position before the driven roller 29 and the secondary transfer roller 47 (upstream side in the sheet conveyance direction). The registration roller 48 feeds the paper between the transfer belt 24 and the secondary transfer roller 47 in synchronization with the secondary transfer timing of the toner image on the transfer belt 24. The secondary transfer roller 47 transfers the toner image (visible image) transferred to the transfer belt 24 onto the paper while sandwiching the paper fed from the registration roller 48 between the transfer belt 24 on the driven roller 29. Let

  In the conveyance path 43, a heat roller 49 for heat fixing and a pressure roller 50 in contact with the heat roller 49 are provided at a position downstream of the secondary transfer roller 47 in the sheet conveyance direction. A paper discharge roller 51 is provided at the end of the conveyance path 43.

  A conveyance path 52 for inverting the front and back of the sheet is provided from the end of the conveyance path 43 to the upstream position of the registration roller 48. In the conveyance path 52, paper feed rollers 53.54.55 are provided. The sheet that has reached the end of the conveyance path 43 is returned to the conveyance path 43 through the conveyance path 52 by switching the rotation direction of the paper discharge roller 51, so that the visible image on the transfer belt 24 is also formed on the back surface of the sheet. Transcribed.

  On the other hand, a cleaner 56 is provided at a position facing the drive roller 25 with the transfer belt 24 interposed therebetween. The cleaner 56 has a cleaning blade 57 in contact with the transfer belt 24, and scrapes off the toner (developer) remaining on the transfer belt 24 through the secondary transfer process by the cleaning blade 57.

  In FIG. 2, the belt conveying device 60 includes a drive roller 25, a driven roller 29, and a transfer belt 24 (not shown) between them. Both ends of the drive roller 25 are supported by non-conductive bearings 61 so as to be rotatable between the front side plate 62 and the rear side plate 63 of the belt conveying device 60.

  In FIG. 2, the primary transfer rollers 30, 31, 32, 33 are provided with a conductive power supply spring support 64 on the rear plate 63 side. The power supply spring support portion 64 has a bearing 65 formed coaxially with the shaft (not shown) of the primary transfer rollers 30, 31, 32, 33 and a power supply spring support shaft provided on the downstream side of the transfer belt 24. 66.

  Power supply to each of the primary transfer rollers 30, 31, 32, 33 is transmitted from a CPU (not shown) provided in the apparatus main body 2 to a high voltage power source (not shown). This is done by applying a voltage via a high voltage power source.

  The primary transfer rollers 30, 31, 32, and 33 are urged vertically downward by a power supply spring 67 and charge is applied to the transfer belt 24. As shown in detail in FIG. 3, the coil portion of the power supply spring 67 is wound around the power supply spring support shaft 66. One end of the feeding spring 67 is held on the shaft of the primary transfer rollers 30, 31, 32, 33, and the other end is latched and held by a concave feeding spring latching portion 68 formed integrally with the feeding spring support portion 64. Has been.

  Further, the feeding spring locking portion 68 formed on the feeding spring support portion 64 biases the feeding spring 67 in the conveying direction upstream and the downstream side is also biased downward.

  As a voltage to be applied to the primary transfer rollers 30, 31, 32, 33, when the toner charge transferred to the paper P is charged, for example, negative (−), the paper P is charged positive (+). Thus, for example, it is necessary to apply a transfer voltage of about +2.0 to 2.3 kV and a drum direction current (20 to 30 μA).

  In the nip of the primary transfer rollers 30, 31, 32, 33 and the surrounding area, the recording medium that has received the toner image transferred from the surface of the photosensitive drums 20, 21, 22, 23 is the transfer rollers 30, 31. , 32, 33 are separated from the photoconductive drums 20, 21, 22, 23 in the static elimination regions formed by the. This static elimination voltage (current) is set so as to weaken the surface charge on the transfer side of the recording medium while maintaining the adsorption force between the recording medium and the transfer belt 24 to some extent. Further, the static elimination voltage is set to be considerably smaller than the transfer voltage so that the toner image transferred onto the recording medium is not retransferred to the photosensitive drums 20, 21, 22, and 23 side.

  According to the present embodiment, in such a configuration, one of the power supply springs 67 is pressed against the primary transfer rollers 30, 31, 32, 33, and the other is supplied to the power supply spring locking portion 68 of the power supply spring support shaft 66. Support with.

  In this way, even if the tension of the power supply spring 67 varies, the power supply spring support portion 64 cancels the load of the power supply spring 67. Further, since the power supply spring 65 is fixed by the power supply spring locking portion 68, density unevenness is prevented.

  The feeding spring support portion 64 is integrally formed with the bearing 65 and the feeding spring locking portion 68, but it goes without saying that it may be a separate body.

  Although the embodiments of the present invention have been described, these embodiments are presented as examples, and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 2 Main body 20, 21, 22, 23 Photosensitive drum 24 Transfer belt 30, 31, 32, 33 Primary transfer roller 64 Feed spring support part 65 Bearing 66 Feed spring support shaft 67 Feed spring 68 Feed spring lock Part

Claims (2)

A photosensitive drum;
An image forming unit for forming a toner image on the photosensitive drum;
An endless transfer belt stretched around a plurality of rollers including a driving roller;
A transfer roller in pressure contact with the photosensitive drum across the transfer belt;
A power supply spring that contacts the transfer roller and applies a charge to the transfer roller for transferring a toner image on the photosensitive drum to the surface of the transfer belt;
A power supply spring support that supports the power supply spring and holds the transfer roller;
Provided integrally with the power supply spring support part, the power supply spring locking part for locking the power supply spring with the transfer roller and the power supply spring support part interposed therebetween,
An image forming apparatus comprising: The image forming apparatus according to claim 1, wherein the power supply spring support portion is formed of a conductive material.

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