JP2010091889A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus preventing the occurrence of image shift by accurately synchronously rotating an image carrier and a transfer belt. <P>SOLUTION: The image forming apparatus (color laser printer) moves an intermediate transfer belt 7 interposed between photoreceptors (image carriers) 2a to 2d rotationally driven by a driving source and transfer rollers 5a to 5d, and transfers toner images formed on the photoreceptor drums 2a to 2d onto the intermediate transfer belt 7 by the transfer rollers 5a to 5d. In the image forming apparatus, the intermediate transfer belt 7 is driven by the photoreceptor drums 2a to 2d. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus that employs a method of transferring a toner image on an image carrier onto a transfer belt.

  A color image forming apparatus for forming a color image on a sheet by electrophotography has four photosensitive drums and four transfer rollers opposed to each other with an intermediate transfer belt interposed therebetween in tandem, and is formed on each photosensitive drum. The magenta, cyan, yellow, and black toner images are primarily transferred onto the intermediate transfer belt and superimposed to form a full-color toner image. The toner image is then transferred onto the recording material sheet as a secondary transfer. A system that forms full-color images is adopted.

  In such a color image forming apparatus, each of the photosensitive drums and the intermediate transfer belt is configured to rotate synchronously by a power transmission mechanism such as an independent motor and a speed reduction mechanism. However, in such a configuration, the number of motors increases. In addition, the transfer between the photosensitive drum and the intermediate transfer due to uneven rotation of each motor, assembly error of the power transmission mechanism, elongation of the intermediate transfer belt, changes in dynamic friction and static friction due to the amount of toner interposed between the photosensitive drum and the intermediate transfer belt, etc. There is a difference in the linear velocity of the belt, and there is a possibility that the two do not rotate accurately in synchronization. As described above, when the photosensitive drum and the intermediate transfer belt are not accurately rotated synchronously, there is a problem that color misregistration occurs in a color image.

  In view of this, Japanese Patent Application Laid-Open No. H10-228561 proposes an image forming apparatus in which a plurality of photosensitive members that are rotatably supported are driven to rotate by an intermediate transfer belt.

In Patent Document 2, the distance along the outer peripheral surface of the belt at the upstream end in the belt moving direction in each of adjacent transfer sections is set to an integral multiple of the distance that the belt moves when the drive roller makes one rotation. Thus, there has been proposed an image forming apparatus that suppresses the occurrence of color misregistration of developer images transferred and superimposed from the photosensitive drum.
JP 2001-134108 A JP 2007-093682 A

  However, in the configuration described in Patent Document 1, a plurality of photoconductors are driven and rotated by the intermediate transfer belt, so that a large-capacity driving source such as a motor for driving the intermediate transfer belt is required and the intermediate transfer belt is used. Since a large load acts on the belt, the intermediate transfer belt is stretched, and there is a possibility that the photoconductor and the intermediate transfer belt do not rotate accurately in synchronization.

  In the configuration described in Patent Document 2, since the photosensitive drum and the belt are driven by an independent driving source and a power transmission mechanism, respectively, the photosensitive drum and the belt are accurately synchronously rotated as described above. There is a possibility that the problem that it cannot be made to occur.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide an image forming apparatus capable of preventing image misalignment by accurately synchronously rotating an image carrier and a transfer belt. is there.

  In order to achieve the above object, the invention described in claim 1 is a toner formed on the image carrier by running a transfer belt interposed between an image carrier and a transfer roller which are rotationally driven by a drive source. In the image forming apparatus for transferring an image onto the transfer belt by the transfer roller, the transfer belt is driven by the image carrier.

  According to a second aspect of the present invention, in the first aspect of the present invention, a plurality of motors that independently rotate and drive each of the plurality of image carriers, a rotation detection sensor that detects a rotation variation of each motor, or the transfer belt. An ID sensor for detecting a speed fluctuation is provided, and the motors are feedback-controlled based on a rotation fluctuation of each motor detected by the rotation sensor or a speed fluctuation of the transfer belt detected by the ID sensor. And

  According to a third aspect of the present invention, in the first aspect of the invention, the plurality of image carriers are rotationally driven by a single motor via the speed increasing / decreasing mechanism, and the speed increasing / decreasing ratio of the speed increasing / decreasing mechanism is set to an integer ratio. It is characterized by setting.

  The invention according to claim 4 is the invention according to any one of claims 1 to 3, wherein the intermediate transfer belt has a multilayer structure including a rubber layer.

  The invention according to claim 5 is the invention according to any one of claims 1 to 4, wherein an auxiliary roller for pressing the transfer belt toward the image carrier is provided in the vicinity of the transfer roller.

  According to a sixth aspect of the present invention, in the invention according to any one of the first to fifth aspects, pulleys are provided at both ends in the axial direction of the transfer roller so as to be freely rotatable, and the pulleys are used to carry the image through the transfer belt. It is characterized by pressing against the non-image areas at both ends in the axial direction of the body.

  According to the first aspect of the present invention, since the transfer belt is driven by the image carrier, the transfer belt is reliably driven without slipping due to static friction generated between the image carrier and the difference in linear velocity between the two. Can be kept small. For this reason, the transfer belt and the image carrier can be accurately and synchronously rotated, and image quality due to the linear velocity difference between them can be suppressed, and a high quality image can be stably obtained. Further, since a driving source for the transfer belt is not required, the structure can be simplified and the cost can be reduced.

  According to the second aspect of the present invention, since each motor is feedback-controlled based on the rotation fluctuation of each motor detected by the rotation sensor or the speed fluctuation of the transfer belt detected by the ID sensor, each motor or transfer The belt speed fluctuations are suppressed, and the linear velocity difference between the image carrier and the transfer belt due to these speed fluctuations becomes zero as much as possible, and both can be rotated accurately and synchronously.

  According to the third aspect of the present invention, the plurality of image carriers are rotationally driven by a single motor via the acceleration / deceleration mechanism, and the acceleration / deceleration ratio of the acceleration / deceleration mechanism is set to an integer ratio. The rotation fluctuations of the body are synchronized, and the transfer belt can be driven at a constant speed while suppressing the rotation fluctuation of each image carrier by controlling the rotation of a single motor. Further, the number of motors can be reduced to further simplify the structure and reduce the cost.

  According to the fourth aspect of the present invention, since the transfer belt has a multilayer structure including a rubber layer, the transfer belt is reliably driven by the image carrier without slipping by bringing the rubber layer having a large friction coefficient into contact with the image carrier. In addition, the transfer belt and the image carrier can be rotated accurately and synchronously, and the linear velocity difference between the two can be kept small.

  According to the fifth aspect of the present invention, the nip amount between the transfer belt and the image carrier can be increased by the auxiliary roller provided in the vicinity of the transfer roller, and the static friction force between the two is increased, and the transfer belt is moved by the image carrier. It can be driven more reliably. For this reason, the linear velocity difference between the image carrier and the transfer belt can be made as close to 0 as possible, and both can be rotated synchronously accurately, and image deviation due to the linear velocity difference between the transfer belt and the image carrier can be prevented. A high quality image can be stably obtained while suppressing.

  According to the sixth aspect of the present invention, the transfer belt can be pressed against the image carrier from the inside by pulleys provided so as to be freely rotatable at both ends in the axial direction of the transfer roller, so that the conveying force of the image carrier is increased. The image carrier can drive the transfer belt more reliably without slipping. In this case, since the pulley is pressed against the non-image areas at both ends in the axial direction of the image carrier, the life of the image carrier and the image quality are not affected. Further, since the pulley is supported coaxially with the transfer roller so as to be freely rotatable, the load on the transfer belt of the pulley is reduced and the transfer gap can be adjusted. Further, by setting the electric resistance of the pulley higher than that of the transfer belt, or by configuring the pulley with an insulator, it is possible to prevent leakage of excess current to the pulley.

  Further, by arranging the meandering prevention rib attached to the transfer belt on the inner side in the width direction of the pulley, the pulley can function as a guide for the meandering prevention rib.

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

  FIG. 1 is a sectional view of a color laser printer as an embodiment of a color image forming apparatus according to the present invention. FIG. 2 is an enlarged sectional view of an image forming portion of the color laser printer. The illustrated color laser printer is a tandem type. In the central portion of the main body 100, a magenta image forming unit 1M, a cyan image forming unit 1C, a yellow image forming unit 1Y, and a black image forming unit 1K are arranged in tandem at regular intervals.

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

  Here, each of the photosensitive drums 2a to 2d is a drum-shaped photosensitive body, and these are predetermined processes in a direction indicated by an arrow (clockwise) by a driving force transmitted from a motor (not shown) via a power transmission mechanism. Driven by speed. The arrangement pitch of the photosensitive drums 2a to 2d is set to an integral multiple of the rotation period of the photosensitive drums 2a to 2d. In the present embodiment, a sensor (not shown) that detects the rotational position of each of the photosensitive drums 2a to 2d is provided.

  The charging rollers 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.

  The transfer rollers 5a to 5d are arranged so as to be in contact with the photosensitive drums 2a to 2d via an endless intermediate transfer belt 7 which is an intermediate transfer body at each primary transfer portion. Here, the intermediate transfer belt 7 is an endless belt configured as a multilayer structure including a rubber layer, and the outermost rubber layer is in contact with the photosensitive drums 2a to 2d. The intermediate transfer belt 7 is stretched between rollers 8 and 9 supported so as to be freely rotatable, and is disposed on the upper surface side of each of the photosensitive drums 2a to 2d. Here, the rollers 8 and 9 are both supported by a rolling bearing so as to be freely rotatable, and one of the rollers 8 can come into contact with the secondary transfer roller 10 via the intermediate transfer belt 7 in the secondary transfer portion. The belt cleaning device 11 is provided in the vicinity of the other roller 9.

  Incidentally, toner containers 12a, 12b, 12c, and 12d 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. It is installed.

  In addition, a laser scanner unit (LSU) 13 is disposed below the image forming units 1M, 1C, 1Y, and 1K in the apparatus main body 100, and a paper feed cassette 14 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 14, and a pickup roller 15 for taking out the paper one by one from the paper feed cassette 14 is taken out in the vicinity of the paper feed cassette 14. A feed roller 16 and a retard roller 17 are provided for feeding the fed paper to the transport path L.

  Further, the conveyance path L extending in the vertical direction on the side of the apparatus main body 100 includes a conveyance roller pair 18 that conveys the sheet, and the driving roller 8 and the secondary transfer roller at a predetermined timing after the sheet is temporarily held. A registration roller pair 19 is provided to be supplied to a secondary transfer portion which is a contact portion with the main body 10. Next to the transport path L, another transport path L ′ used for forming an image on both sides of the sheet is formed, and a plurality of transport roller pairs 20 are appropriately used in the transport path L ′. Are provided at regular intervals.

  By the way, the conveyance path L arranged in the vertical direction on one side in the apparatus main body 100 extends to the paper discharge tray 21 provided on the upper surface of the apparatus main body 100, and the fixing device 22 and the discharge path are in the middle. A paper roller pair 23 is provided.

  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 in the image forming units 1M, 1C, 1Y, and 1K are respectively rotated at a predetermined process speed in a direction indicated by an arrow (clockwise) in FIG. When driven, the photosensitive drums 2a to 2d are uniformly charged by the charging rollers 3a to 3d. The laser scanner unit 13 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. The magenta toner image is obtained by applying a primary transfer bias having a polarity opposite to that of the toner to the intermediate transfer belt 7 by the transfer roller 5a at the primary transfer portion (transfer nip portion) between the photosensitive drum 2a and the transfer roller 5a. 1 is primarily transferred onto the intermediate transfer belt 7 which is rotationally driven in the direction of the arrow in FIG.

  Here, in this embodiment, the intermediate transfer belt 7 is supported by rollers 8 and 9 so as to be freely rotatable, and the intermediate transfer belt 7 is driven by the photosensitive drums 2a to 2d. In this case, a rotation detection sensor (not shown) for detecting rotation fluctuations of four motors that independently rotate and drive each of the photosensitive drums 2a to 2d or an ID sensor (not shown) for detecting speed fluctuations of the intermediate transfer belt 7 are provided. Each motor is feedback-controlled based on the rotation fluctuation of each motor detected by the rotation sensor or the speed fluctuation of the intermediate transfer belt 7 detected by the ID sensor.

  Thus, 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.

  On the other hand, the pickup roller 15 and the feed roller 15 are fed from the paper feed cassette 14 in accordance with the timing at which the leading end of the full color toner image on the intermediate transfer belt 7 reaches the secondary transfer portion (transfer nip portion) between the roller 8 and the secondary transfer roller 10. The sheet sent to the conveyance path L by the roller 16 and the retard roller 17 is conveyed to the secondary transfer unit by the registration roller pair 19. Then, a full-color toner image is collectively transferred from the intermediate transfer belt 7 to the sheet conveyed to the secondary transfer unit by the secondary transfer roller 10 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. Then, the paper is discharged onto the paper discharge tray 21 by the paper discharge roller pair 23 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 11, and the intermediate transfer belt 7 is prepared for the next image formation.

  As described above, in the present embodiment, since the intermediate transfer belt 7 is driven by the photosensitive drums 2a to 2d as described above, the intermediate transfer belt 7 slides due to static friction generated between the photosensitive drums 7a to 7d. It is reliably driven without any difference between the linear speeds. For this reason, the intermediate transfer belt 7 and the photosensitive drums 2a to 2d can be accurately rotated synchronously, and a high-quality image can be stably obtained by suppressing the occurrence of color misregistration of the full-color image due to the difference in linear velocity between them. Can do. Further, in this embodiment, since the drive source for the intermediate transfer belt 7 is not required, the structure can be simplified and the cost can be reduced.

  In particular, in this embodiment, since the intermediate transfer belt 7 has a multilayer structure including a rubber layer, the intermediate transfer belt 7 is moved by the photosensitive drums 2a to 2d by bringing a rubber layer having a large friction coefficient into contact with the photosensitive drums 2a to 2d. The intermediate transfer belt 7 and the photosensitive drums 2a to 2d can be accurately and synchronously rotated to suppress the difference in linear velocity between them.

  In the present embodiment, each motor or intermediate is controlled by feedback control of each motor based on the rotation fluctuation of each motor detected by the rotation sensor or the speed fluctuation of the intermediate transfer belt 7 detected by the ID sensor. Variations in the speed of the transfer belt 7 are suppressed, and the difference in linear velocity between the photosensitive drums 2a to 2d and the intermediate transfer belt 7 due to these speed variations becomes zero and the two can be accurately rotated synchronously.

  By the way, in the present embodiment, a configuration is adopted in which the four photosensitive drums 2a to 2d are rotationally driven by four independent motors, respectively. However, the four photosensitive drums 2a to 2d are driven by a single motor via an acceleration / deceleration mechanism. If the configuration in which the acceleration / deceleration ratio of the acceleration / deceleration mechanism is set to an integer ratio is adopted, the rotational fluctuations of the photosensitive drums 2a to 2d are synchronized, and the rotation of a single motor is controlled. The intermediate transfer belt 7 can be driven at a constant speed while suppressing rotational fluctuations of the photosensitive drums 2a to 2d. Further, the number of motors can be reduced to further simplify the structure and reduce the cost.

  As shown in FIG. 3, auxiliary rollers 24 and 25 are provided on both sides of the transfer rollers 5a to 5d, respectively, and the intermediate transfer belt 7 is pressed toward the photosensitive drums 2a to 2d by the auxiliary rollers 24 and 25. If the configuration is adopted, the nip amount between the intermediate transfer belt 7 and each of the photosensitive drums 2a to 2d can be increased by the auxiliary rollers 24 and 25, and the static friction force between the two can be increased and the intermediate transfer belt 7 can be increased by the photosensitive drums 2a to 2d. Can be driven more reliably. For this reason, the linear velocity difference between the photosensitive drums 2a to 2d and the intermediate transfer belt 7 can be brought close to 0 as much as possible, and the two can be accurately rotated synchronously, and the linear velocity between the intermediate transfer belt 7 and the photosensitive drums 2a to 2d can be obtained. It is possible to stably obtain a high-quality image while suppressing the occurrence of image shift due to the difference. Even if only one auxiliary roller 24, 25 (especially the auxiliary roller 24 on the upstream side) is provided, the above effect can be obtained.

  Further, although not shown, pulleys are provided at both ends in the axial direction of the respective transfer rollers 5a to 5d so as to be freely rotatable, and the pulleys are provided in non-image areas at both ends in the axial direction of the respective photosensitive drums 2a to 2d via the intermediate transfer belt 7. You may employ | adopt the structure to press.

  If the said structure is employ | adopted, since the intermediate transfer belt 7 can be pressed to the photosensitive drums 2a-2d from the inside with the pulley provided in the axial direction both ends of the transfer rollers 5a-5d so that free rotation was possible, it is the photosensitive drums 2a-2d. The intermediate transfer belt 7 can be driven more reliably without slipping by the photosensitive drums 2a to 2d. In this case, since the pulley is pressed against the non-image areas at both ends in the axial direction of the photosensitive drums 2a to 2d, the life of the photosensitive drums 2a to 2d and the image quality are not affected. Further, since the pulley is supported coaxially with the transfer rollers 5a to 5d so as to be freely rotatable, the load on the intermediate transfer belt 7 by the pulley is reduced and the transfer gap can be adjusted.

  Furthermore, by setting the electric resistance of the pulley higher than that of the intermediate transfer belt 7, or by configuring the pulley with an insulator, it is possible to prevent leakage of excess current to the pulley. Further, by arranging a meandering prevention rib (not shown) attached to the intermediate transfer belt 7 on the inner side in the width direction of the pulley, the pulley can function as a guide for the meandering prevention rib.

  Although the present invention has been described with respect to an embodiment in which the present invention is applied to a color laser printer, the present invention is not limited to a printer, but can be applied to any other image forming apparatus such as a copying machine, a facsimile, or a multifunction machine using a transfer belt. Of course, the same applies.

1 is a cross-sectional view of a color laser printer according to the present invention. It is an expanded sectional view of the image forming part of the color laser printer according to the present invention. It is sectional drawing of the color laser printer principal part which shows another form of this 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 Charging roller 4a to 4d Developing device 5a to 5d Transfer roller 6a to 6d Drum cleaning device 7 Intermediate transfer belt (transfer belt)
8,9 Roller 10 Secondary transfer roller 11 Belt cleaning device 12a to 12d Toner container 13 Laser scanner unit (LSU)
DESCRIPTION OF SYMBOLS 14 Paper feed cassette 15 Pickup roller 16 Feed roller 17 Retard roller 18 Transport roller pair 19 Registration roller pair 20 Transport roller pair 21 Paper discharge tray 22 Fixing device 23 Paper discharge roller pair 24, 25 Auxiliary roller 100 Image forming apparatus main body L, L '' Transport path

Claims (6)

Image formation in which a transfer belt interposed between an image carrier that is rotationally driven by a drive source and a transfer roller is run, and a toner image formed on the image carrier is transferred onto the transfer belt by the transfer roller In the device
An image forming apparatus, wherein the transfer belt is driven by the image carrier.   A plurality of motors that independently rotate and drive each of the plurality of image carriers, and a rotation detection sensor that detects a rotation fluctuation of each motor or an ID sensor that detects a speed fluctuation of the transfer belt, are detected by the rotation sensor. 2. The image forming apparatus according to claim 1, wherein the motors are feedback-controlled based on rotation fluctuations of the motors or speed fluctuations of the transfer belt detected by the ID sensor.   2. The image forming apparatus according to claim 1, wherein a plurality of image carriers are rotationally driven by a single motor via an acceleration / deceleration mechanism, and the acceleration / deceleration ratio of the acceleration / deceleration mechanism is set to an integer ratio.   The image forming apparatus according to claim 1, wherein the intermediate transfer belt has a multilayer structure including a rubber layer.   The image forming apparatus according to claim 1, wherein an auxiliary roller that presses the transfer belt toward the image carrier is provided in the vicinity of the transfer roller.   6. A pulley is provided at both ends in the axial direction of the transfer roller so as to be freely rotatable, and the pulley is pressed against a non-image area at both ends in the axial direction of the image carrier via the transfer belt. The image forming apparatus according to any one of the above.

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