JP2006001670A - Belt device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a belt device capable of preventing meandering of a belt with a simple structure. <P>SOLUTION: In this belt device, pulleys 29a and 29b formed separately from a driven roller 28 are provided on both ends of the driven roller 28, and ribs 24a and 24b fitted on the axial direction outer side of the pulleys 29a and 29b are provided on both side edge parts of a transfer belt 24 along the width direction. When deviation to the left occurs in traveling of the transfer belt 24, the rib 24a on the right side end of the transfer belt 24 is regulated by the axial direction outer side of the pulley 29a provided on the right side end of the driven roller 28, and meandering to the left is corrected in a position of the driven roller 28. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a belt device, and more particularly to a meandering prevention device for a transfer belt of an image forming apparatus.

  In image forming apparatuses, particularly color image forming apparatuses such as color copiers and color printers, a multi-stage drum type (tandem type) capable of high-speed processing is becoming more popular than a single drum type. In this tandem type color image forming apparatus, for example, image forming units are arranged side by side for each color of magenta, yellow, cyan, and black in the paper conveyance direction, and color toner images are sequentially formed by the image forming units of these colors. Is done.

  The image forming portions for each color are arranged to face the transfer belt, which is an image carrier, and the toner images sequentially formed by the image forming portions for each color are transferred to the transfer belt by the primary transfer means. The transfer belt is wound endlessly on a plurality of rollers, and a toner image on the transfer belt is transferred to a transfer material by a secondary transfer unit. On the other hand, the transfer material is conveyed from the paper feed unit to the transfer position via the registration roller pair.

  In such an image forming process, undulation or meandering may occur in the running direction of the transfer belt wound endlessly on a plurality of rollers. When meandering occurs on the transfer belt, image distortion, transfer deviation of each color, and the like occur, such as an essentially perpendicular image becoming a parallelogram image. Further, when the transfer belt is wavy, image deformation, transfer omission, and the like occur.

In order to accurately superimpose the images of the respective colors and obtain a high-quality image without image distortion, it is necessary that the transfer belt does not generate meandering or waviness and is stably driven and conveyed. Therefore, a method has been proposed in which ribs are provided on the back side of both sides of the belt, and the ribs hit against the holding roll side to prevent meandering. In addition, a method has been proposed in which both ends of the drive roller are crowned to prevent meandering. Further, a technique for correcting the meandering by tilting the steering roll in conjunction with the meandering of the belt has been proposed, and a technique for correcting the meandering by changing the meandering correction roll according to the meandering direction of the belt.
JP-A-3-21138 Japanese Patent Laid-Open No. 9-60693

  However, the method of providing the ribs on both sides of the belt described in JP-A-3-21138 is effective in preventing meandering, but the belt is affected by some factor such as the difference in the circumferential length of both sides of the belt and the parallelism between the rolls. If a large meander occurs in the belt, the ribs on both sides of the belt may run on the roll. Further, in the structure described in Japanese Patent Laid-Open No. 9-60693, it is necessary to add a meandering correction roll, which not only complicates the mechanical structure but also leads to an increase in the cost of the entire apparatus.

  Therefore, an object of the present invention is to provide a belt device that can prevent the meandering of the belt with a simple structure.

  The belt device according to claim 1 includes a driving roller, a driven roller, a pulley, and a belt, and ribs are formed on both side edges of the belt. Here, the drive row is driven by the drive unit to drive the belt. The driven roller is disposed to face the driving roller and is used to stretch the belt together with the driving roller. The pulleys are provided at both ends of the driven roller, and are arranged coaxially and relatively rotatably with respect to the driven roller, and are for preventing the meandering of the belt. The ribs are provided at both side edge portions of the belt, and are for preventing meandering that can be locked to the outside in the pulley axial direction.

  In this apparatus, the belt stretched between the driving roller and the driven roller is driven and driven by the driving roller. At that time, the ribs provided on both side edges of the belt are locked to the outside in the axial direction of the pulleys provided at both ends of the driven roller, so that the occurrence of meandering of the belt can be suppressed. Conventionally, there are ribs on both sides of the belt, but if the circumferential speed difference in the width direction of the belt is large due to the difference in the circumferential length of both ends of the belt, a large meandering occurs in the belt, and the rib is on the roller. There is a case to get on. However, since pulleys are provided at both ends of the driven roller so as to be coaxial and relatively rotatable with respect to the driven roller, the engaging surfaces of the ribs provided on the belt come into contact with each other and rotate integrally. Therefore, the meandering of the belt can be suppressed. In addition, wear of the locking surface of the rib can be reduced.

  In addition, if the driven roller side is free, the distance between the driving roller and the driven roller is large, and the belt length is long, the belt may meander due to reasons such as deviation in belt processing accuracy or roller cylindricity. Since there is no meandering restricting means on the driven roller side, the meandering of the belt gradually develops. However, in the present invention, since the pulley is provided on the driven roller side, the belt travel can be restricted from the driven roller side, and the effect of preventing meandering is remarkable as compared with the case where the pulley is provided on the drive roller side. It is.

  According to a second aspect of the present invention, in the belt device according to the first aspect, the diameter of the driven roller is such that the diameter of the central portion is larger than the diameter of both ends in the axial direction of the roller.

  In this apparatus, the driven roller has a so-called crown shape. In general, the belt has a property of being biased in the direction in which the belt tension is large, that is, in the direction in which the pressure contact force by the roller is large. Therefore, if belt meandering occurs while the belt is running and the belt is biased to the left or right end, if the driven roller has a crown shape, the pressure contact force at the center of the roller is large. The meandering can be prevented.

  In the present invention, meandering of the belt can be prevented with a simple structure by providing pulleys at both ends of the driven roller of the belt and engaging with ribs provided at both side edges of the belt.

  FIG. 1 is a diagram illustrating a configuration of a main part of a main body of a tandem type color printer in which an embodiment of the present invention is employed. The color printer 1 includes an image forming unit 2 for forming a color image, a transfer unit 3 that transfers a toner image formed by the image forming unit 2 to a transfer material, a paper feeding unit 4 that supplies the transfer material, A registration roller unit 5 for synchronizing transfer material conveyance and image formation, a transfer material conveyance guide mechanism 6 for guiding the transfer material reaching the registration roller unit 5 to a transfer position, and a toner image transferred to the transfer material A fixing unit 7 for fixing and a paper discharge unit 8 for discharging the transfer material are provided.

  The image forming unit 2 is located almost at the center of the color printer, and is provided with four process units 21a, 21b, 21c, and 21d corresponding to four colors of black, yellow, cyan, and magenta. Primary drums that transfer the toner images formed on the surfaces of the photosensitive drums 22a, 22b, 22c, and 22d on which the electrostatic latent images are formed, and the photosensitive drums 22a, 22b, 22c, and 22d. It includes transfer rollers 23a, 23b, 23c, and 23d, and a transfer belt 24 as an image carrier.

  Here, since the internal configurations of the four process units corresponding to the four colors of black, yellow, cyan, and magenta are the same, the configuration will be described using the black process unit 21a as an example. As shown in FIG. 2, a charging device 101a, an exposure device 102a, a developing device 103a, a cleaning device 104a, and a charge eliminating device 105a are arranged around the photosensitive drum 22a of the black process unit 21a.

  The paper feed unit 4 is provided below the image forming unit 2, and includes a cassette 41 for storing a transfer material, pickup rollers 42 and 43 for taking out the stored paper, and a conveyance path for the paper one by one. A pair of paper feed rollers 44 and 45 are provided for feeding to the printer. The transfer material conveyed from the paper supply unit 4 is conveyed to the transfer position through the vertical conveyance path 46. Registration roller pairs 5a and 5b are provided on the downstream side of the vertical conveyance path 46 in the conveyance direction. The registration roller pairs 5a and 5b wait for the transfer material conveyed from the sheet feeding unit 4 and transfer belt 24. Is sent to the transfer position A in synchronization with image formation.

  The fixing device 7 is provided above the transfer unit 3 and melts and fixes the toner transferred onto the transfer material. The fixing device 7 includes a heating roller 7a having a built-in heater and a pressure roller 7b that is in pressure contact with the heating roller 7a. The toner image is heat-fixed. Discharge rollers 81a and 81b are provided above the fixing device 7, and the transfer material on which the toner image is formed is disposed on the top of the color printer via the discharge rollers 81a and 81b. To be discharged.

  As shown in FIG. 1, the transfer belt 24 is disposed above each of the photosensitive drums 22a, 22b, 22c, and 22d, and is driven by a driving roller 25a that is rotated by driving means such as a motor (not shown). It is stretched between a driven roller 28 arranged away from 25a and is driven to circulate. A tension roller 25b is provided between 25a and the driven roller 28. The tension roller 25b maintains the tension of the transfer belt 24 by a tension adjusting mechanism (not shown). The primary transfer rollers 23a, 23b, 23c, and 23d are urged so as to be in pressure contact with the photosensitive drums 22a, 22b, 22c, and 22d via the transfer belt 24, respectively. 22a, 22b, 22c and 22d are in pressure contact. Further, an intermediate transfer cleaning device 26 for cleaning the toner and the like attached to the transfer belt 24 is provided at a position facing the driven roller 28.

  Here, as shown in FIGS. 2 and 3, a rib 24 a is provided on the right edge of the transfer belt 24 in the width direction. A similar rib 24 b is provided on the left edge of the transfer belt 24. The driven roller 28 has a so-called crown shape in which the diameter of the central portion of the roller is about 0.2 mm larger than the diameter of both end portions of the roller. At both ends of the driven roller 28, pulleys 29a and 29b formed separately from the driven roller are provided. The rib 24a at the right edge of the transfer belt 24 is engaged with the outside in the axial direction of a pulley 29a provided on the right side of the driven roller 28, and the rib 24b at the left edge of the transfer belt 24 is engaged with the driven roller 28. Is engaged on the outside in the axial direction of a pulley 29b provided on the left side.

  Next, an image forming operation will be described. First, when the color printer is turned on, various parameters are initialized, and initial settings such as setting the temperature of the fixing unit are performed. Image data is received from a personal computer or the like connected via a network or the like by an image data input unit (not shown). The image data received here is sent to the image forming unit 2.

  In each process unit 21a, 21b, 21c, 21d of the image forming unit 2, a toner image is formed based on the received image data. Here, the image forming operation will be described by taking the black process unit 21a as an example. First, the photosensitive drum 22a is charged by the charging device 101a, the exposure device 102a performs exposure corresponding to the black image data, and an electrostatic latent image corresponding to the black image data is formed on the surface of the photosensitive drum 22a. Is done. The electrostatic latent image is converted into a toner image by the black developing device 103a and transferred onto the transfer belt 24 by a transfer bias applied to the primary transfer roller 23a. The residual developer remaining on the photosensitive drum 22a is cleaned by the cleaning device 104a and discarded in a waste toner container (not shown). Further, the static elimination device 105a neutralizes the photosensitive drum 22a. Such an operation is also performed for the other colors, the magenta process unit 21b, the cyan process unit 21c, and the yellow process unit 21d, and a full-color toner image is formed on the transfer belt 24.

  At the same time, in the paper feed unit 4, the transfer material is taken out from the paper feed cassette 41 by the pickup rollers 42 and 43, and sent out to the vertical conveyance path 46 through the paper feed roller pair 44 and 45. Thereafter, the transfer material conveyed from the pair of registration rollers 5 a and 5 b in time with the image formation on the transfer belt 24 is guided to the transfer unit 3 by the transfer material conveyance guide mechanism 6. In the transfer unit 3, the secondary transfer roller 31 contacts the transfer belt 24, and the full-color toner image formed on the transfer belt 24 is transferred to the transfer material by the secondary transfer bias applied to the secondary transfer roller 31. Is done. Further, the full color toner image transferred to the transfer material is fixed to the transfer material by heating and pressurization by the fixing unit 7, and the transfer material on which the full color toner image is formed is discharged to the paper discharge unit 8. Further, the toner remaining on the transfer belt 24 is cleaned by the intermediate transfer cleaning device 26 and discarded in a waste toner container (not shown).

  In such an image forming process, when the driving roller 25a is driven and rotated by a driving device (not shown), the transfer belt 24 starts to run. Following the running of the transfer belt 24, the tension roller 25b and the driven roller 28 that stretch the transfer belt 24 are also rotated. At this time, for example, when a deviation to the left side of the transfer belt 24 occurs between the driving roller 25a and the driven roller 28 due to a difference in circumferential length between both sides of the belt, the rib 24a at the right end of the transfer belt 24 is generated. However, it is regulated by the edge of the pulley 29a provided at the right end of the driven roller 28, and the meandering to the left side is corrected at the position of the driven roller 28. Further, the pulley 29a is configured separately from the driven roller 28, and there is an interval of 0 to 1 mm between the axially outer side of the pulley 29a and the right end rib 24a of the transfer belt 24. The meandering of the transfer belt 24 can be corrected while 29a moves left and right, and wear on the rib 24a at the right end of the transfer belt 24 can be reduced.

  In the present invention, the driven roller 28 has a so-called crown shape in which the diameter of the central portion of the roller is approximately 0.2 mm larger than the diameter of both end portions of the roller. The belt has a property of being biased in the direction in which the belt tension is large, that is, in the direction in which the pressure contact force by the roller is large. Therefore, if the belt meanders while the transfer belt 24 is running and the transfer belt 24 is biased to the left side, the driven roller 28 has a crown shape, so the pressure contact force on the left side of the roller is small, and the roller The pressure contact force at the center is large. Accordingly, the transfer belt 24 naturally returns to the central portion, and the meandering can be prevented.

[Effect of this embodiment]
In the present embodiment, pulleys 29 a and 29 b formed separately from the driven roller 28 at both ends of the driven roller 28 are provided, and shafts of the pulleys 29 a and 29 b are provided at both side edges in the width direction of the transfer belt 24. Ribs 24a and 24b that are locked outward in the direction are provided. When a deviation to the left side occurs while the transfer belt 24 is running, the rib 24a at the right end of the transfer belt 24 is restricted by the outside in the axial direction of the pulley 29a provided at the right end of the driven roller 28. The meandering to the left side is corrected at the position of the driven roller 28. If meandering to the right occurs, meandering can be corrected in a similar manner. Therefore, even when the length of the transfer belt 24 is long, the belt meandering can be corrected with a simple structure by the restriction of the driven roller 28.

[Other Embodiments]
In this embodiment, a case where a tandem type color printer is used as the image forming apparatus and the belt is a transfer belt is illustrated. However, a monochrome printer is used as the image forming apparatus, and the belt is a photosensitive belt. Needless to say, the present invention can be applied to belts of this type. The present invention can also be applied to image forming apparatuses such as copying machines, printers, and facsimiles.

The block diagram of the principal part of a color printer. Enlarged view of the black process unit. The perspective view of the belt in a driven roller part. The enlarged view of a driven roller axial direction outer side.

Explanation of symbols

24 transfer belt 24a, 24b rib 25a driving roller 28 driven roller 29a, 29b pulley

Claims (2)

A driving roller driven by a driving unit;
A driven roller disposed opposite the drive roller;
Pulleys disposed coaxially and relative to the driven roller at both ends of the driven roller;
A belt stretched between the drive roller and the driven roller;
Ribs for preventing meandering that can be locked to the outside in the pulley axial direction are formed on both side edges of the belt,
Belt device.   2. The belt device according to claim 1, wherein at least the diameter of the driven roller is such that a diameter of a central portion is larger than a diameter of both end portions in the axial direction of the roller.

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