JP5268587B2 - Color image forming apparatus - Google Patents

Description

  The present invention relates to a color image forming apparatus that forms a color image by superimposing and transferring toner images formed on a plurality of image carriers arranged in tandem onto an intermediate transfer member.

  A color image forming apparatus such as a color copying machine or a color printer that forms a color image on a sheet by electrophotography uses a plurality of image carriers and a plurality of primary transfers that face each other with an intermediate transfer member interposed therebetween. Means for forming a color image by juxtaposing the color toner images formed on the image bearing members on the intermediate transfer member in a superimposed manner along the intermediate transfer member. The upper color image is batch-transferred onto a recording sheet.

  In such a color image forming apparatus, a plurality of drive sources for rotationally driving each image carrier are provided, and a configuration in which a drive force is transmitted from each drive source to each image carrier via a gear is employed. .

  By the way, in the color image forming apparatus, the misregistration of each color toner image on the intermediate transfer member causes the color misregistration of the final color image and causes the image quality to deteriorate.

  Therefore, in Patent Document 1, in order to improve image quality by attenuating a shock or vibration caused by a drive system other than a drum (image carrier) by a timing belt unit, a motor as a drive source and an image carrier are provided. An angle formed by a driving pulley, a rotating unit driving belt other than the image carrier, a motor holding plate for holding the motor, a pulley center of the image carrier, a driving pulley center of the motor, and other rotating unit driving pulley centers There has been proposed an image forming apparatus comprising a motor holding plate position regulating means provided on the bisector and a motor tension load means provided on the bisector.

  In Patent Document 2, in a steel belt driving device in which an endless steel belt is stretched between a driving pulley and a driven pulley so as to be freely circulated, the steel belt is allowed to travel stably, and resonance and resonance noise during belt driving are described. For the purpose of solving the problem, a covering portion in which both end portions in the width direction of the steel belt are covered with an elastic material such as rubber is provided, and a hook-like protrusion that guides the covering portion to both end portions in the axial direction of the driving pulley and the driven pulley. The structure which provides a part is proposed.

  In Patent Document 3, in a color image forming apparatus using a photoconductor and an intermediate transfer body, a toothed pulley is connected to a photoconductor of each color and connected to a motor in order to reduce registration shift and banding of each color image. The driving force is transmitted from each toothed pulley to each photoconductor via a toothed belt, a plurality of gears are connected to the intermediate transfer member, and each color toner image formed on each photoconductor is applied to the intermediate transfer member in two colors. A configuration for superimposing and transferring each one has been proposed.

  In Patent Document 4, for the purpose of preventing color misregistration of a color image forming apparatus, transfer unevenness caused by eccentricity of a photoreceptor drive system gear of a transfer image by each process unit onto a transfer sheet conveyed on a transfer belt is disclosed. A configuration has been proposed in which the maximum eccentric direction of the drive system gear is set so as to synchronize with each other, and the distance between the photosensitive drums and the circumference of the photosensitive drums are matched.

In Patent Document 5, in order to suppress color misregistration and image deterioration, a color image forming apparatus provided with two or more drive input means for driving a photosensitive member and other process means such as a developing means is disclosed. Proposals have been made to use an involute spline system for driving the body and an Older coupling system to drive other process means.
JP 2006-072206 A JP 2004-1000085 A JP 2000-267373 A JP-A-8-194361 JP 2000-214654 A

  However, in a color image forming apparatus, if a system in which a plurality of image carriers are individually driven by the same number of drive sources as these is employed, the number of drive sources such as motors increases, resulting in an increase in cost and color image formation. In order to prevent the occurrence of color misregistration, there is a problem that the control of each drive source for synchronizing the rotation of each image carrier is complicated.

In addition, if a system in which the driving force from the driving source is transmitted to each image carrier by a gear or a toothed belt is adopted, each image carrier is caused by gear eccentricity, backlash, toothed belt elongation, etc. There is a problem in that rotation unevenness occurs in the body, and it is difficult to synchronize the rotation of these image carriers, and color misregistration is likely to occur in the color image.

  The present invention has been made in view of the above problems, and its object is to reduce the cost by reducing the number of drive sources and to synchronize the rotation of a plurality of image carriers so that there is no color misregistration. An object of the present invention is to provide a color image forming apparatus capable of stably obtaining a quality color image.

In order to achieve the above object, the invention according to claim 1 is characterized in that a plurality of image carriers and a plurality of primary transfer means facing these image carriers with an intermediate transfer member interposed therebetween are arranged along the intermediate transfer member. A color image forming apparatus for forming a color image by superimposing and transferring a toner image formed on each image carrier onto the intermediate transfer member or a sheet conveyed on the intermediate transfer member;
Two image carriers adjacent to both sides of one drive shaft are arranged symmetrically, and an endless metal belt having the same diameter is wound between the drive shaft and each image carrier,
A tension pulley for applying a predetermined tension to each metal belt is provided symmetrically on the slack side of each metal belt and on both sides of the drive shaft,
The driving force from one driving source is transmitted to two adjacent image carriers by the metal belt, and the image carriers are rotationally driven.

According to a second aspect of the present invention, in the first aspect of the present invention, a rotation sensor for detecting a rotation speed of the image carrier is provided only on one side of two adjacent image carriers .

According to the first aspect of the present invention, since the driving force is transmitted from one drive shaft to two adjacent image carriers by the metal belt with little elongation, the rotation of all the image carriers is synchronized. Therefore, it is possible to stably obtain a high-quality color image without color misregistration by preventing registration misregistration of each color toner image on the intermediate transfer member or paper.

In addition, since two adjacent image carriers are rotationally driven by a driving force transmitted from one driving source through a metal belt, the number of driving sources can be halved to reduce the size and cost of the apparatus. Can do.

Further, since two image carriers are arranged symmetrically on both sides of one drive shaft, and a metal belt of the same diameter is wound between the drive shaft and each image carrier, the drive shaft of the drive source from each metal belt. A radial load of the same magnitude acts in the opposite direction. For this reason, the radial loads acting on the drive shaft of the drive source cancel each other, the bending deformation of the drive shaft of the drive source is suppressed, the impossibility of bearings supporting the drive shaft is reduced, and vibration and noise are reduced. Occurrence is prevented. Since tension pulleys for applying a predetermined tension to each metal belt are provided symmetrically on the slack side of each metal belt and on both sides of the drive shaft, a predetermined tension is applied to each metal belt by the tension pulley . As a result, the slack of each metal belt is prevented, and all the image carriers are driven to rotate stably synchronously.

According to the second aspect of the invention, since the rotation sensor for detecting the rotation speed of the image carrier is provided only on one side of the two adjacent image carriers, the number of rotation sensors can be halved.

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

  FIG. 1 is a 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 at the center of the main body 100. The 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, respectively, and around each of the photosensitive drums 2a to 2d, chargers 3a, 3b, 3c, 3d, developing devices 4a, 4b, 4c, 4d, transfer rollers 5a, 5b, 5c, 5d and drum cleaning devices 6a, 6b, 6c, 6d are arranged, respectively.

  Here, the photosensitive drums 2a to 2d are drum-shaped photosensitive members, and are driven to rotate at a predetermined process speed in a direction indicated by an arrow (clockwise) by a driving 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.

  Further, the transfer rollers 5a to 5d are arranged so as to be able to contact the photosensitive drums 2a to 2d with the intermediate transfer belt 7 interposed therebetween in each primary transfer portion, and along the intermediate transfer belt 7, the photosensitive drums 2a to 2d. It is juxtaposed in tandem with 2d. Here, the intermediate transfer belt 7 is stretched between the secondary transfer counter roller 8, the tension roller 9, and the driving roller 10, and is disposed on the lower surface side of each of the photosensitive drums 2 a to 2 d. The secondary transfer counter roller 8 is disposed so as to be in contact with the secondary transfer roller 11 via the intermediate transfer belt 7 in the secondary transfer portion. A belt cleaning device 12 is provided in the vicinity of the tension roller 9.

  Incidentally, toner containers 13a, 13b, 13c, and 13d for supplying toner to the developing devices 4a to 4d are arranged in a line above the image forming units 1M, 1C, 1Y, and 1K in the apparatus main body 100. A laser scanner unit (LSU) (not shown) is arranged in the vicinity of the toner containers 13a to 13d.

  A paper feed cassette 14 is detachably installed in the lower part of the apparatus main body 100, and a plurality of sheets (not shown) are stacked and accommodated in the paper feed cassette 14. In the vicinity of the paper feed cassette 14, there are a pick roller 15 for taking out the paper from the paper feed cassette 14, a feed roller 16 and a retard roller 17 for separating the taken paper one by one and feeding them to the transport path L. Is provided.

  The conveyance path L is curved in a horizontal U shape at one side (right side in FIG. 1) in the apparatus main body 100 and extends substantially horizontally to the other side (left side in FIG. 1). Is vertically extended upward to a paper discharge tray 18 formed on the upper surface of the paper. In addition, conveyance rollers 19 and 20 having large and small diameters are arranged in a curved portion having a substantially U shape of the conveyance path L, and a registration roller pair 21, the secondary transfer roller 11 and the fixing device 22 are arranged in a horizontal portion. In the vertical portion, a pair of conveying rollers 23 and 24 and a pair of paper discharge rollers 25 are arranged.

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

  When an image formation start signal is issued, the photosensitive drums 2a to 2d are driven to rotate at a predetermined process speed in the direction of the arrow (clockwise) in the image forming units 1M, 1C, 1Y, and 1K, and these photosensitive drums 2a. ˜2d are uniformly charged by the chargers 3a to 3d. A laser scanner unit (not shown) emits a laser beam modulated by a color image signal for each color, and irradiates the surface of each photosensitive drum 2a to 2d with the laser beam on each photosensitive drum 2a to 2d. An electrostatic latent image corresponding to each 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 moved in the direction of the arrow in the figure by the action of the transfer roller 5a to which a primary transfer bias having a polarity opposite to that of the toner is applied in the primary transfer portion (transfer nip portion) between the photosensitive drum 2a and the transfer roller 5a. Primary transfer is performed on the intermediate transfer belt 7 that is rotationally driven.

  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.

  Then, the full color toner image on the intermediate transfer belt 7 is picked from the paper feed cassette 14 in accordance with the timing at which the leading end of the full color toner image reaches the secondary transfer portion (transfer nip portion) between the secondary transfer counter roller 8 and the secondary transfer roller 11. The sheet fed to the conveyance path L by the roller 15, the feed roller 16 and the retard roller 17 is conveyed to the secondary transfer unit by the registration roller pair 21. 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. .

  Thus, the sheet on which the full-color toner image has been transferred is conveyed to the fixing device 22, and the sheet on which the full-color toner image has been fixed by being heated and pressurized and thermally fixed on the surface of the sheet. The pair of transport rollers 23 and 24 are transported upward in the vertical portion of the transport path L, and are discharged onto the paper discharge tray 18 by the pair of paper discharge rollers 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.

  Next, the configuration of the drive system of the photosensitive drums 2a to 2d will be described with reference to FIGS.

  2 is a front view of an image forming unit (photosensitive drum, transfer roller, and intermediate transfer belt portion) of a color laser printer, FIG. 3 is a perspective view of the image forming unit, and FIG. 4 is a perspective view showing a configuration of a drive system of the photosensitive drum. 5 is a perspective view showing the configuration of the drive system of two adjacent photosensitive drums, FIG. 6 is a front view showing a metal belt winding structure of the two adjacent photosensitive drums, and FIG. 7 is the perspective view. .

  As shown in FIGS. 2 and 3, four transfer rollers 5 a to 5 d are arranged opposite to each other with the intermediate transfer belt 7 interposed between the four photosensitive drums 2 a to 2 d arranged side by side in tandem. The photosensitive drums, that is, the magenta photosensitive drum 2a and the cyan photosensitive drum 2b, the yellow photosensitive drum 2c, and the black photosensitive drum 2d are respectively rotated by a single motor 26 as a driving source. The driving force is transmitted to the photosensitive drum 2a, cyan photosensitive drum 2b, yellow photosensitive drum 2c, and black photosensitive drum 2d by an endless metal belt (SUS belt in this embodiment) (FIG. 2). To FIG. 4).

  Here, the details of the configuration of the drive system of the magenta photosensitive drum 2a and the cyan photosensitive drum 2b will be described with reference to FIGS. The configuration of the drive system for the yellow photosensitive drum 2c and the black photosensitive drum 2d is the same as that of the drive system for the magenta photosensitive drum 2a and the cyan photosensitive drum 2b.

  The motor 26 is supported horizontally on a vertically supported motor support plate 28, and a motor shaft 26a, which is an output shaft of the motor 26, passes through the motor support plate 28 and is exposed to the photosensitive drums 2a and 2b. It protrudes horizontally on the side (front side in the figure). The photosensitive drums 2a and 2b are symmetrically arranged on both sides of the motor shaft 26a.

  Incidentally, a pulley 29 having the same diameter larger than the motor shaft 26a is attached to one end in the axial direction of each photosensitive drum 2a, 2b on the side where the motor 26 is provided. The metal belts 27 having the same diameter are wound around the belt. The slack side of each metal belt 27 is in contact with a tension pulley 30 that is rotatably supported by the motor support plate 28. The tension pulley 30 applies a predetermined tension to each metal belt 27. Has been.

  Thus, when the motor 26 is started, the rotation of the motor shaft 26a, which is its output shaft, is decelerated at a predetermined ratio through each metal belt 27 and each pulley 29 and transmitted to each photosensitive drum 2a, 2b. The photosensitive drums 2a and 2b are rotationally driven at a predetermined process speed in the direction of the arrow (clockwise) in FIG. At this time, since the diameter of the pulley 29 is the same as described above, both the photosensitive drums 2a and 2b are rotationally driven at the same speed. Similarly, the other photosensitive drums 2c and 2d are also rotationally driven, and all of the four photosensitive drums 2a to 2d are rotationally driven at the same speed.

  As described above, in the present embodiment, since the driving force is transmitted from the motor 26 to each of the photosensitive drums 2a to 2d by the metal belt 27 with little elongation, the rotation of all the photosensitive drums 2a to 2d is synchronized. Therefore, it is possible to prevent a registration shift of each color toner image on the intermediate transfer belt 7 and to stably obtain a high-quality color image having no color shift. In particular, in the present embodiment, since the metal belt 27 is specially rolled over the entire circumference, the physical properties thereof are uniform over the entire circumference, there is no unevenness, and the durability is enhanced.

  In the present embodiment, the two adjacent photosensitive drums 2a and 2b and the photosensitive drums 2c and 2d are each driven to rotate by a driving force transmitted from one motor 26 through the metal belt 27. The number of devices can be halved from four to two to reduce the size and cost of the device. Since the two adjacent photosensitive drums 2a and 2b and the photosensitive drums 2c and 2d are driven to rotate at the same speed by one motor 26, the rotational speed of these photosensitive drums 2a to 2d is stabilized. When a rotation sensor is provided, a rotation sensor may be provided on each of the two adjacent photosensitive drums 2a, 2b and photosensitive drums 2c, 2d, and the number of rotation sensors can be halved. In the present embodiment, since the metal belt 27 is formed to be ultra-thin, a compact drive system can be designed.

Further, in the present embodiment, two photosensitive drums 2a and 2b and photosensitive drums 2c and 2d are arranged symmetrically on both sides of one motor 26, and the motor shaft 26a of the motor 26 and the photosensitive drums 2a to 2d are arranged. Since the metal belts 27 having the same diameter are wound between the pulleys 29, radial loads having the same magnitude act on the motor shaft 26a from the metal belts 27 in the opposite direction. For this reason, the radial loads acting on the motor shaft 26a cancel each other, the bending deformation of the motor shaft 26a is suppressed, the load on the bearing that supports the motor shaft 26a is reduced, and the generation of vibration and noise is prevented. It is possible to speed up. Moreover, as a result of reducing the load on the bearing that supports the motor shaft 26a, a sintered metal sliding bearing can be used as a bearing instead of a conventional rolling bearing such as a ball bearing.

Other, in the present embodiment, since the predetermined tension is applied to the metal belt 27 by the tension roller 30, slack of the metal belt 27 is prevented, stable and all the photosensitive drum 2a~2d synchronization Driven by rotation.

  In the above, the embodiment in which the present invention is applied to the color laser printer has been described. However, the present invention is similarly applied to any other color image forming apparatus such as a color copying machine or a color multifunction peripheral. Of course, it is possible. In the above, the embodiment in which the present invention is applied to a color image forming apparatus that employs a method of sequentially superimposing and transferring toner images formed on a plurality of image carriers onto an intermediate transfer member has been described. Is similarly applicable to a color image forming apparatus that employs a system in which toner images formed on a plurality of image carriers are sequentially superimposed and transferred onto a sheet conveyed on an intermediate transfer member.

1 is a cross-sectional view of a color laser printer according to the present invention. FIG. 3 is a front view of an image forming unit (photosensitive drum, transfer roller, and intermediate transfer belt portion) of the color laser printer according to the present invention. FIG. 3 is a perspective view of an image forming unit (photosensitive drum, transfer roller, and intermediate transfer belt portion) of the color laser printer according to the present invention. FIG. 2 is a perspective view showing a configuration of a photosensitive drum drive source of the color laser printer according to the present invention. FIG. 2 is a perspective view showing a configuration of a drive system of two adjacent photosensitive drums of the color laser printer according to the present invention. It is a front view which shows the winding structure of the metal belt of two adjacent photosensitive drums of the color laser printer which concerns on this invention. FIG. 3 is a perspective view showing a metal belt winding structure of two adjacent photosensitive drums of the color laser printer according to the present invention.

Explanation of symbols

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 transfer roller (primary transfer means)
6a to 6d Drum cleaning device 7 Intermediate transfer belt (intermediate transfer member)
8 Secondary Transfer Counter Roller 9 Tension Roller 10 Drive Roller 11 Secondary Transfer Roller 12 Belt Cleaning Device 13a-13d Toner Container 14 Paper Feed Cassette 15 Pick Roller 16 Feed Roller 17 Retard Roller 18 Paper Discharge Tray 19, 20 Transport Roller 21 Resist Roller pair 22 Fixing device 23, 24 Conveying roller pair 25 Discharge roller pair 26 Motor (drive source)
26a Motor shaft 27 Metal belt 28 Motor support plate 29 Photosensitive drum pulley 30 Tension pulley 100 Image forming apparatus main body L Conveyance path

Claims (2)

A plurality of image carriers and a plurality of primary transfer means facing each other with the intermediate transfer member sandwiched between these image carriers are arranged along the intermediate transfer member, and toner images formed on the respective image carriers are arranged. In the color image forming apparatus for forming a color image by superimposing and transferring the intermediate transfer body or a sheet conveyed on the intermediate transfer body,
Two image carriers adjacent to both sides of one drive shaft are arranged symmetrically, and an endless metal belt having the same diameter is wound between the drive shaft and each image carrier,
A tension pulley for applying a predetermined tension to each metal belt is provided symmetrically on the slack side of each metal belt and on both sides of the drive shaft,
A color image forming apparatus, wherein a driving force from one driving source is transmitted to two adjacent image carriers by the metal belt to rotationally drive the image carriers.
2. The color image forming apparatus according to claim 1, wherein a rotation sensor for detecting a rotation speed of the image carrier is provided only on one side of two adjacent image carriers .

Images