JP2011033739A - Color image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a color image forming apparatus capable of enhancing quality of a monochromatic image by preventing deflection of an intermediate transfer belt in a monochromatic mode. <P>SOLUTION: The color image forming apparatus includes: the endless intermediate transfer belt 7; a plurality of photosensitive drums (image carrier) 2a to 2d; and a plurality of primary transfer rollers 5a to 5d, wherein a color mode to primarily transfer respective color toner images formed on the plurality of photosensitive drums 2a to 2d to the intermediate transfer belt 7, and a monochromatic mode to primarily transfer a monochromatic toner image formed on the photosensitive drum 2d to the intermediate transfer belt 7 are selectable, and in the monochromatic mode, the photosensitive drums 2a to 2c other than the monochromatic photosensitive drum are separated from the intermediate transfer belt 7. The image forming apparatus is provided with a primary pre-transfer roller 13 coming into contact with the intermediate transfer belt 7 on the upstream side of the photosensitive drum 2d, and is provided with a means for preventing the occurrence of the deflection of the intermediate transfer belt 7 between the primary pre-transfer roller 13 and the photosensitive drum 2d. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a color image forming apparatus capable of forming a monochrome monochrome image or a plurality of color images.

  In recent years, there has been a strong demand for colorization of image forming apparatuses such as copiers and printers that form images on paper by electrophotography, and color image forming apparatuses have been developed in response to this demand and are already in practical use. Since this color image forming apparatus is required to have a monochrome output speed, a tandem type color image forming apparatus has attracted attention.

  The tandem color image forming apparatus includes an endless intermediate transfer belt, a monochrome black image carrier, and three color image carriers of yellow, magenta, and cyan, and each color formed on each image carrier. The toner image is primarily transferred onto the intermediate transfer belt.

  By the way, in such a color image forming apparatus, it is possible to select a color mode for outputting a color image and a monochrome mode for outputting a black monochrome image, and when the monochrome mode is selected and the monochrome image is output. When yellow, magenta, and cyan color image carriers that are not used for image formation are operated, these color image carriers come into contact with the intermediate transfer belt, and the color image carrier and the intermediate transfer belt are worn out. There is a problem that the service life is reduced.

  Therefore, a color image forming apparatus has been proposed in which three color image carriers other than the black image carrier are separated from the intermediate transfer belt in the monochrome mode (see, for example, Patent Document 1).

  Further, in a color image forming apparatus, proposals have been made to prevent meandering and speed fluctuations of the intermediate transfer belt (see, for example, Patent Documents 2 and 3).

JP 2008-122601 A Japanese Patent No. 3473148 JP 2008-139749 A

  By the way, in a color image forming apparatus in which a monochrome mode and a color mode can be selected, and when the monochrome mode is selected, three color image carriers other than the black image carrier are separated from the intermediate transfer belt. In the monochrome mode, since there are few places in contact with the intermediate transfer belt, the tension of the intermediate transfer belt upstream of the black image carrier and the primary transfer roller portion facing the black image carrier is lower than that in the color mode. There is a problem that the primary transfer portion is bent and jitter (vertical line) or the like is generated in the monochrome image to deteriorate the image quality. In the color mode, all the image carriers are in contact with the intermediate transfer belt and sufficient tension is applied to the intermediate transfer belt, so that the above problem does not occur.

  The present invention has been made in view of the above problems, and an object thereof is to provide a color image forming apparatus capable of preventing the intermediate transfer belt from being bent in the monochrome mode and improving the quality of the monochrome image. It is in.

  In order to achieve the above object, an invention according to claim 1 is directed to an endless intermediate transfer belt, a plurality of monochrome image-bearing members, and a plurality of image carriers that are in contact with the image carrier via the intermediate transfer belt. A color mode that includes a primary transfer roller and primarily transfers toner images of each color formed on a plurality of image carriers onto the intermediate transfer belt; and a monochrome toner image formed on a monochrome image carrier on the intermediate transfer belt. In a color image forming apparatus in which a monochrome mode for primary transfer can be selected and a plurality of color image carriers other than those for monochrome are separated from the intermediate transfer belt in the monochrome mode, the monochrome image carrier A pre-primary transfer roller that contacts the intermediate transfer belt is provided on the upstream side.

  According to a second aspect of the present invention, in the first aspect of the present invention, a torque limiter is provided on the pre-primary transfer roller, and the pre-primary transfer roller is reverse to the moving direction of the intermediate transfer belt via the torque limiter. It is characterized by being configured to be rotationally driven.

  According to a third aspect of the present invention, in the first aspect of the invention, a sensor that detects a bend between the pre-primary transfer roller of the intermediate transfer belt and the monochrome carrier, and a bend detected by the sensor. Control means for changing the rotation state of the pre-primary transfer roller is provided.

  According to the first aspect of the present invention, even when the tension of the intermediate transfer belt is lower than that in the color mode in the monochrome mode in which the color image carrier is separated from the intermediate transfer belt, the primary transfer of the intermediate transfer belt is performed. The occurrence of bending between the front roller and the monochrome carrier is prevented by the pre-primary transfer roller, so image quality such as jitter due to bending of the intermediate transfer belt does not occur, and high-quality monochrome images Can be obtained.

  According to the second aspect of the present invention, when the intermediate transfer belt is bent between the pre-primary transfer roller and the monochrome carrier, a driving load is applied to the pre-primary transfer roller by the torque limiter. Even if the belt tension is lower than that in the color mode, the occurrence of bending between the pre-primary transfer roller of the intermediate transfer belt and the monochrome carrier can be prevented, and a high-quality monochrome image can be obtained. it can.

  According to the third aspect of the invention, when the sensor detects the deflection of the intermediate transfer belt, the state of the roller before the primary transfer is changed, so that the deflection of the intermediate transfer belt is surely removed, and the high quality in the monochrome mode. Monochrome image can be obtained.

1 is a side sectional view of a color image forming apparatus (color laser printer) according to the present invention. FIG. 2 is a side sectional view of the periphery of an intermediate transfer belt of the color image forming apparatus (color laser printer) in FIG. 1. 1 is a perspective view of a roller before primary transfer of a color image forming apparatus (color laser printer) according to Embodiment 1 of the present invention. It is a fragmentary sectional view of the color image forming apparatus (color laser printer) which concerns on Embodiment 2 of this invention.

  Embodiments of the present invention will be described below with reference to the accompanying drawings.

  FIG. 1 is a side cross-sectional view of a color laser printer as an embodiment of a color image forming apparatus according to the present invention. The illustrated color laser printer is a tandem type, and a magenta image is formed in the central portion of the main body 100. The forming unit 1M, the cyan image forming unit 1C, the yellow image forming unit 1Y, and the black image forming unit 1K are arranged in tandem at regular intervals.

  Each of the image forming units 1M, 1C, 1Y, and 1K is provided with photosensitive drums 2a, 2b, 2c, and 2d, which are image carriers, and a charger 3a is disposed around each of the photosensitive drums 2a to 2d. 3b, 3c, 3d, developing devices 4a, 4b, 4c, 4d, primary transfer rollers 5a, 5b, 5c, 5d and drum cleaning devices 6a, 6b, 6c, 6d, respectively.

  Here, the photosensitive drums 2a to 2d are drum-shaped photosensitive members, and are rotationally driven at a predetermined process speed in a direction indicated by an arrow (counterclockwise) by a drive motor (not shown). The chargers 3a to 3d uniformly charge the surfaces of the photosensitive drums 2a to 2d to a predetermined potential by a charging bias applied from a charging bias power source (not shown).

  Further, the developing devices 4a to 4d contain magenta (M) toner, cyan (C) toner, yellow (Y) toner, and black (K) toner, respectively, and are formed on the photosensitive drums 2a to 2d. In addition, the toner of each color is attached to each electrostatic latent image to visualize each electrostatic latent image as a toner image of each color.

  2 is a side sectional view of the periphery of the intermediate transfer belt of the color image forming apparatus (color laser printer) shown in FIG. 1, (a) shows the state of the transfer belt in the color mode, and (b) is in the monochrome mode. The state of the transfer belt is shown. The primary transfer rollers 5a to 5d are disposed so as to be in contact with the photosensitive drums 2a to 2d via an endless intermediate transfer belt 7 at each primary transfer portion. Here, the intermediate transfer belt 7 is stretched between a secondary transfer counter roller 8 that is rotationally driven by a drive motor (not shown), a plurality of driven rollers 9a to 9d, and a tension roller 10, and each photosensitive drum 2a to 2d. The secondary transfer counter roller 8 can contact the secondary transfer roller 11 via the intermediate transfer belt 7 in the secondary transfer portion. Is arranged. A belt cleaning device 12 is provided in the vicinity of the driven roller 9.

  By the way, in the present embodiment, the primary transfer abutting on the inner surface of the intermediate transfer belt 7 is located upstream of the transfer nip between the black photosensitive drum 2d and the primary transfer roller 5d (upstream in the seven running directions of the intermediate transfer belt). The front roller 13 is rotatably arranged. Here, the primary transfer rollers 5a to 5c and the driven roller 9b are movable in conjunction with the upper retracted position shown in FIG. When the primary transfer rollers 5a to 5c and the driven roller 9b move, the intermediate transfer belt 7 moves to a position indicated by a broken line and moves away from the surfaces of the photosensitive drums 2a to 2c other than the black photosensitive drum 2d. At this time, only the pre-primary transfer roller 13 is in contact with the intermediate transfer belt 7 between the black photosensitive drum 2d on the downstream side from the driven roller 9a.

  Further, a laser scanner unit (LSU) 14 is disposed below the image forming units 1M, 1C, 1Y, and 1K in the apparatus main body 100, and a paper feed cassette 15 is detachably attached to the bottom of the main body 100 below the image forming units. is set up. A plurality of sheets (not shown) are stacked and accommodated in the paper feed cassette 15, and a pickup roller 17 that picks up paper from the paper feed cassette 15 and a picked up paper are placed near the paper feed cassette 15. A feed roller 18 and a retard roller 19 are provided that are separated and fed one by one to the transport path L1. Further, a manual feed tray 16 is mounted on the right side surface of the main body 100, and sheets can be directly set on the manual feed tray 16 from above.

  Incidentally, a paper discharge tray 20 is provided on the upper surface of the apparatus main body 100, and the transport path L <b> 1 extends to the paper discharge tray 20 at the side of the apparatus main body 100. In the middle of the transport path L1, a pair of transport rollers 21 for transporting the paper and a contact portion between the secondary transfer counter roller 8 and the secondary transfer roller 11 at a predetermined timing after the paper is temporarily put on standby. A pair of registration rollers 22 to be supplied to a certain secondary transfer unit, a fixing device 23 for fixing a toner image on a sheet, a pair of conveying rollers 24 for conveying the fixed sheet, and a sheet to the discharge tray 20 A paper discharge roller pair 25 for discharging is provided.

  On the other hand, a transport path L2 extending substantially horizontally from the manual feed tray 16 to the transport path L1 is provided below the laser scanner unit (LSU) 14 in the apparatus main body 100, and in the vicinity of the manual feed tray 16, A pick-up roller 26 that picks up paper from the manual feed tray 16, a feed roller 27 that separates the picked-up paper and sends it one by one to the transport path L2, and a retard roller 28 are provided. The transport path L2 is provided with a plurality of transport roller pairs 29 for feeding paper to the upstream side of the registration roller pair 22 in the transport path L1.

  A double-sided path L3 is branched from the downstream side of the conveying roller pair 24 on the upper side of the conveying path L1 on the side in the apparatus main body 100, and a switching flapper 30 for switching the sheet conveying direction is provided at the branched portion. Is provided. The double-sided path L2 curves in an inverted shape from the branching portion and extends vertically downward, then curves in a U-shape and joins the upstream side of the registration roller pair 22 in the conveyance path L1. Are provided with a pair of reversing rollers 31, 32, 33.

  Next, an image forming operation by the color laser printer having the above configuration will be described.

  The color laser printer according to the present embodiment can select a color mode for outputting a color image and a monochrome mode for outputting a monochrome image. Hereinafter, image forming operations in the color mode and the monochrome mode will be described.

1) In color mode:
When the color mode is selected, all the image forming units 1M, 1C, 1Y, and 1K operate, and as shown in FIG. 1, all the photosensitive drums 2a to 2d are moved to the intermediate transfer belt as shown in FIG. 7. When an image formation start signal is issued in this state, the photosensitive drums 2a to 2d in each of the image forming units 1M, 1C, 1Y, and 1K are subjected to a predetermined process in the illustrated arrow direction (counterclockwise direction). The photosensitive drums 2a to 2d are driven to rotate at a speed, and are uniformly charged by the chargers 3a to 3d. The laser scanner unit 14 emits a laser beam modulated by a color image signal for each color, irradiates the surface of each photosensitive drum 2a to 2d with the laser beam, and each color is applied to each photosensitive drum 2a to 2d. An electrostatic latent image corresponding to the color image signal is formed.

  First, magenta toner is attached to the electrostatic latent image formed on the photosensitive drum 2a of the magenta image forming unit 1M by the developing device 4a to which a developing bias having the same polarity as the charged polarity of the photosensitive drum 2a is applied. The electrostatic latent image is visualized as a magenta toner image. This magenta toner image is shown in the figure by the action of the primary transfer roller 5a to which a primary transfer bias having a polarity opposite to that of the toner is applied in a primary transfer portion (transfer nip portion) between the photosensitive drum 2a and the primary transfer roller 5a. Primary transfer is performed on the intermediate transfer belt 7 which is rotationally driven in the direction.

  The intermediate transfer belt 7 on which the magenta toner image has been primarily transferred as described above moves to the next cyan image forming unit 1C. In the cyan image forming unit 1C as well, the cyan toner image formed on the photosensitive drum 2b is transferred to the magenta toner image on the intermediate transfer belt 7 in the primary transfer portion in the same manner as described above.

  Similarly, yellow and black toners respectively formed on the photosensitive drums 2c and 2d of the yellow and black image forming units 1Y and 1K on the magenta and cyan toner images superimposed and transferred on the intermediate transfer belt 7, respectively. The images are sequentially superimposed at each primary transfer portion, and a full-color toner image is formed on the intermediate transfer belt 7. The transfer residual toner which is not transferred onto the intermediate transfer belt 7 and remains on the photosensitive drums 2a to 2d is removed by the drum cleaning devices 6a to 6d, and the photosensitive drums 2a to 2d are prepared for the next image formation. It is done.

  When cassette feeding is performed, the timing of the leading edge of the full-color toner image on the intermediate transfer belt 7 reaches the secondary transfer portion (transfer nip portion) between the secondary transfer counter roller 8 and the secondary transfer roller 11 is matched. The sheet fed from the sheet feeding cassette 15 to the conveyance path L1 by the pickup roller 17, the feed roller 18, and the retard roller 19 is conveyed to the registration roller pair 22 by the conveyance roller pair 21, and then the registration roller at an appropriate timing. The pair 22 is conveyed to the secondary transfer unit. Then, a full color toner image is secondarily transferred collectively from the intermediate transfer belt 7 to the sheet conveyed to the secondary transfer unit by the secondary transfer roller 11 to which a secondary transfer bias having a polarity opposite to that of the toner is applied. . When manual feeding is performed, the sheet fed from the manual feed tray 16 to the transport path L2 by the pickup roller 26, the feed roller 27, and the retard roller 29 is transported along the transport path L2 by the transport roller pair 29. It is transported to pass L1 and reaches the registration roller pair 22, and thereafter undergoes secondary transfer of a full-color toner image through the same process as described above.

  Thus, the sheet on which the full-color toner image has been transferred is conveyed to the fixing device 23, where the full-color toner image is heated and pressurized and thermally fixed on the surface of the sheet, and the sheet on which the toner image is fixed Then, the paper is transported to the paper discharge roller pair 25 by the transport roller 24 and is discharged onto the paper discharge tray 20 by the paper discharge roller pair 25 to complete a series of image forming operations. The transfer residual toner that is not transferred onto the sheet and remains on the intermediate transfer belt 7 is removed by the belt cleaning device 12, and the intermediate transfer belt 7 is prepared for the next image formation.

  The case where an image is formed on one side of the paper has been described above. However, when an image is formed on both sides of the paper, the paper discharge roller pair 25 reverses the paper on which the image is formed on one side through the above process. At the same time, the conveyance direction is switched by the switching flapper 30 to switch back to the double-sided path L3 with the rear end first, and after the double-sided path L3 is conveyed downward by the reverse roller pairs 31 to 33, the conveyance path. It reaches the registration roller pair 22 provided at L1, and is conveyed again to the secondary transfer portion by the registration roller pair 22 at an appropriate timing. Then, a full color toner image is secondarily transferred from the intermediate transfer belt 7 onto the opposite surface of the sheet at the secondary transfer portion, and then the toner image is fixed by the fixing device 23 as described above. Thereafter, the paper is discharged to the paper discharge tray 20 by the paper discharge roller pair 25.

2) In monochrome mode:
When the monochrome mode is selected, only the black image forming unit 1K operates, and the other magenta, cyan, and yellow image forming units 1M, 1C, and 1Y are suspended. Therefore, in the black image forming unit 1K similar to the above, The black toner image formed on the photosensitive drum 2d is primarily transferred onto the intermediate transfer belt 7 in a primary transfer portion that is a contact portion between the photosensitive drum 2d and the primary transfer roller 5d. The black toner image primarily transferred onto the intermediate transfer belt 7 is transferred from the paper feed cassette 15 or the manual feed tray 16 to the secondary transfer portion (the contact portion between the secondary transfer counter roller 8 and the secondary transfer roller 11). After being secondarily transferred to a sheet supplied at an appropriate timing, the black toner image is fixed in the fixing device. Then, the paper on which the black monochrome image is formed is discharged to the paper discharge tray 20 by the paper discharge roller pair 25.

  Even in the monochrome mode, a monochrome image can be formed on both sides of the sheet by passing the secondary transfer portion and the fixing device 23 twice while inverting the sheet in the same manner as in the color mode.

  Incidentally, since the three color photosensitive drums 2a to 2c are separated from the intermediate transfer belt 7 in the monochrome mode, the tension of the intermediate transfer belt 7 on the upstream side of the black image forming unit 1K is lower than that in the color mode. As described above, there is a problem that the primary transfer portion of the intermediate transfer belt 7 is bent and jitter (vertical line) or the like is generated in the monochrome image, thereby degrading the image quality.

  Therefore, in the present invention, the intermediate portion of the black image forming unit 1K on the upstream side (the upstream side in the running direction of the intermediate transfer belt 7) of the primary transfer portion (the contact portion between the photosensitive drum 2d and the primary transfer roller 5d in contact therewith). A pre-primary transfer roller 13 in contact with the transfer belt 7 is provided, and means for preventing the intermediate transfer belt 7 from being bent between the pre-primary transfer roller 23 and the photosensitive drum 2d is provided. Hereinafter, specific embodiments thereof will be described.

<Embodiment 1>
In the present embodiment, as shown in the perspective view of FIG. 3, a torque limiter 34 is coaxially provided on the pre-primary transfer roller 13 and is bent by the intermediate transfer belt 7 between the pre-primary transfer roller 13 and the photosensitive drum 2d. A torque load is applied to the pre-primary transfer roller 13 by the torque limiter 34 so as not to occur. In this way, the intermediate transfer belt 7 is subjected to a rotational load on the pre-primary transfer roller 13 and a brake is applied to the intermediate transfer belt 7 between the pre-primary transfer roller 13 and the photosensitive drum 2d. It is pulled between the roller 13 and the photosensitive drum 2d. Alternatively, the torque limiter 34 may be rotationally driven so that the primary transfer roller 13 rotates in the direction opposite to the moving direction of the intermediate transfer belt 7. In this case, while the intermediate transfer belt 7 is not bent, the pre-primary transfer roller 13 is driven and rotated by the intermediate transfer belt 7, but the intermediate transfer belt 7 is interposed between the pre-primary transfer roller 13 and the photosensitive drum 2d. When the bending occurs, the pre-primary transfer roller 13 is reversely driven by the action of the torque limiter 34, and the intermediate transfer belt 7 is positively pulled upstream to absorb the bending quickly. As a result, even if the tension of the intermediate transfer belt 7 in the monochrome mode is lower than that in the color mode, the deflection between the pre-primary transfer roller 13 of the intermediate transfer belt 7 and the photosensitive drum 2d is removed, and the intermediate transfer is performed. Generation of image defects such as jitter due to the bending of the belt 7 is prevented, and a high-quality monochrome image is obtained.

<Embodiment 2>
Next, a second embodiment of the present invention will be described with reference to FIG.

  FIG. 4 is a partial cross-sectional view showing another embodiment of a means for preventing the intermediate transfer belt from being bent. In this figure, the same elements as those shown in FIG. The re-explanation about them is omitted.

  In the present embodiment, a sensor 35 for detecting the deflection between the primary transfer roller 13 and the primary transfer roller 5d between the intermediate transfer belt 7 and the primary transfer roller 5d is disposed inside the intermediate transfer belt 7 and is selected as the primary transfer roller 13. A rotatable friction roller 36 that abuts against the intermediate transfer belt 7 when the sensor 35 detects the deflection of the intermediate transfer belt 7, and the friction roller 36 abuts on the pre-primary transfer roller 13 as shown in FIG. Features. In addition, in the configuration in which the torque limiter 34 is provided on the pre-primary transfer roller 13 of the first embodiment, the torque limiter 34 may be driven to rotate reversely upon detection of bending by the sensor 35. Furthermore, the reverse rotation speed of the torque limiter 34 may be increased when the sensor 35 detects the deflection of the intermediate transfer belt 7 using a motor capable of changing the rotation speed such as a stepping motor. .

  As described above, in the present embodiment, when the sensor 35 detects the deflection of the intermediate transfer belt 7, the friction roller 36 is brought into contact with the pre-primary transfer roller 13 to apply a load to the rotation of the pre-primary transfer roller 13. Therefore, the bend between the pre-primary transfer roller 13 of the intermediate transfer belt 7 and the photosensitive drum 2d is removed, and image defects such as jitter due to the bend of the intermediate transfer belt 7 are prevented, and high quality is prevented. A monochrome image is obtained.

  In the above embodiment, the embodiment in which the present invention is applied to a color laser printer has been described. However, the present invention can select a color mode and a monochrome mode, and in monochrome mode, a monochrome image carrier. Of course, the present invention can be similarly applied to any other color image forming apparatus that employs a configuration in which a color image carrier other than the above is separated from the intermediate transfer belt.

1M Magenta image forming unit 1C Cyan image forming unit 1Y Yellow image forming unit 1K Black image forming unit 2a to 2d Photosensitive drum (image carrier)
3a to 3d charger 4a to 4d developing device 5a to 5d primary transfer roller 6a to 6d drum cleaning device 7 intermediate transfer belt 8 secondary transfer counter roller 9a to 9d driven roller 10 tension roller 11 secondary transfer roller 12 belt cleaning device 13 Roller before primary transfer 14 Laser scanner unit (LSU)
15 paper feed cassette 16 manual feed tray 17 pickup roller 18 feed roller 19 retard roller 20 paper discharge tray 21 transport roller pair 22 registration roller pair 23 fixing device 24 transport roller pair 25 paper discharge roller pair 26 pickup roller)
27 Feed roller 28 Retarder roller 29 Conveying roller pair 30 Switching flapper 31-33 Reverse roller pair 34 Torque limiter 35 Sensor 36 Friction roller 100 Image forming apparatus main body L1, L2 Conveying path L3 Double-sided path

Claims (3)

An endless intermediate transfer belt, a plurality of image carriers including those for monochrome, and a plurality of primary transfer rollers that come into contact with the image carrier via the intermediate transfer belt are formed on a plurality of image carriers. A color mode for primary transfer of each color toner image to the intermediate transfer belt and a monochrome mode for primary transfer of a monochrome toner image formed on a monochrome image carrier to the intermediate transfer belt can be selected. In a color image forming apparatus in which a plurality of color image carriers other than those for monochrome and the intermediate transfer belt are separated from each other,
A color image forming apparatus comprising: a pre-primary transfer roller that contacts the intermediate transfer belt on an upstream side of the monochrome image carrier.   2. The first primary transfer roller is provided with a torque limiter, and the first primary transfer roller is reversely driven with respect to the moving direction of the intermediate transfer belt via the torque limiter. Color image forming apparatus. A sensor for detecting a bend between the pre-primary transfer roller of the intermediate transfer belt and the monochrome carrier, and a control unit for changing the rotation state of the pre-primary transfer roller by detecting the bend by the sensor are provided. The color image forming apparatus according to claim 1.

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