JP4225202B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus such as a printer, a copying machine, and a facsimile.

  Conventionally, a yellow, magenta, cyan, or black toner formed on a photosensitive drum every rotation of the intermediate transfer belt, with the photosensitive drum and an intermediate transfer belt that is rotatably supported by a plurality of support rollers facing each other. A so-called four-cycle color image forming apparatus is known in which an image is transferred to an intermediate transfer belt and a full-color image is formed by rotating the intermediate transfer belt four times.

  On the other hand, as rollers used in image forming apparatuses, inexpensive and simple metal rollers (for example, aluminum rollers) including an outer tube, an inner tube into which a core shaft is inserted, and a rib connecting the outer tube and the inner tube are widely used. (See, for example, Patent Document 1).

However, in recent years, there has been a demand for using a cheaper resin roller instead of a metal roller. Since it is difficult to produce a resin roller having a sufficient width by resin molding, a resin roller is produced by resin-molding a plurality of rollers having relatively small widths and passing through the core shaft and aligning the end surfaces. In the mold configuration that pulls out in the circumferential direction of the roller, when the resin-molded roller is released from the mold, a joint seam (burr, etc.) is generated on the outer peripheral surface of the roller. It is necessary to prepare.
JP 2002-91158 A

  However, when the mold is pulled out in the axial direction, the outer peripheral surface of the roller has a slight taper. Therefore, when resin rollers are inserted into the core shaft, a step appears at the joint between the rollers. As a result, when the resin roller is used as a support roller for stretching the intermediate transfer belt, the resin roller locally contacts the belt, and the surface of the resin roller is scraped or the belt is easily damaged. Furthermore, if the joint positions in the belt width direction are the same among the plurality of support rollers, resin scraping and belt damage become remarkable, and image noise may occur.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus capable of minimizing damage to an endless belt such as an intermediate transfer belt and stably obtaining a good image.

In order to achieve the above object, one aspect of an image forming apparatus according to the present invention is:
An endless belt that rotatably supports an endless belt and an image bearing member that carries a toner image and an endless belt on which the toner image on the image bearing member is transferred or transferred onto a sheet that is conveyed on the belt A plurality of support rollers,
Each support roller includes a core shaft and a plurality of resin rollers that are supported by the core shaft and have a truncated cone shape having a large-diameter end surface and a small-diameter end surface. Adjacent resin rollers have a core shaft in a state in which the end surfaces are aligned. Is supported by
The joint of the resin rollers adjacent to each support roller is different in the position in the belt width direction from the joint of the resin rollers adjacent to each other of the support rollers.

  According to the present invention, since the joint positions of the resin rollers that may damage the endless belt are dispersed in the belt width direction, damage to the inner surface of the belt can be minimized, and as a result, stable A good image can be formed.

  Hereinafter, an embodiment of an image forming apparatus according to the present invention will be described with reference to the accompanying drawings. Hereinafter, an example in which the present invention is applied to a four-cycle color laser printer (hereinafter referred to as a printer) will be described, but the present invention can be applied to a tandem type color printer. The present invention can also be applied to an image forming apparatus other than a printer.

  In FIG. 1, the printer denoted by reference numeral 2 as a whole is provided with a photosensitive drum 6 as an image carrier that is driven to rotate in the direction of arrow A by a motor (not shown) at substantially the center of the inside. Around the photosensitive drum 6, a charging device (corona charger in the illustrated example) 8 that uniformly charges the surface of the photosensitive drum 6 along the rotation direction A, and a static for each color on the photosensitive drum 6. An exposure unit 10 for sequentially forming an electrostatic latent image, a developing unit 12 that sequentially supplies toner of each color to the photosensitive drum 6, and thereby developing an electrostatic latent image, a primary transfer roller 14, and a cleaner 16 are sequentially arranged.

  The primary transfer roller 14 is for transferring the toner adhering to the photosensitive drum 6 to the endless intermediate transfer belt 18, and a predetermined bias voltage is appropriately applied from a bias power source (not shown).

  The cleaner 16 includes a blade 20 that comes into contact with the surface of the photosensitive drum 6, and scrapes off toner remaining on the photosensitive drum 6 after transfer.

  The exposure unit 10 is for selectively irradiating the photosensitive drum 6 with laser light. Specifically, when an image signal is input from an external device (for example, a personal computer) to the image signal processing unit (not shown) of the printer 2, the image signal is color-converted into yellow, cyan, magenta, and black by the image signal processing unit. A digital image signal is generated and this signal is transmitted to a drive circuit (not shown). The drive circuit controls the exposure unit 10 based on the input digital signal to expose the photosensitive drum 6.

  The developing unit 12 includes four developing units 21 (21Y, 21M, 21C, and 21K) containing yellow (Y), magenta (M), cyan (C), and black (K) toners in a counterclockwise direction in FIG. Are sequentially attached to the developing rack 22 by 90 degrees, and can be rotated counterclockwise about the shaft 24. Each time an electrostatic latent image of each color is formed on the photosensitive drum 6, the developing unit 12 moves the developing roller 26 of the corresponding developing device 21 to a developing position that is close to or in contact with the photosensitive drum 6. Rotate. A predetermined bias voltage is appropriately applied to the developing roller 26 from a bias power source (not shown).

  The intermediate transfer belt 18 is supported by the outer peripheral portions of the primary transfer roller 14 and the other three rollers 28, 30, and 32 and is driven to rotate in the direction of arrow B. The roller 28 is a tension roller that applies tension to the intermediate transfer belt 18. The roller 32 is connected to a drive motor (not shown), and the rollers 14, 28, and 30 are driven to rotate as the roller 32 rotates. In the present embodiment, the primary transfer roller 14 is positioned immediately downstream of the photosensitive drum 6 with respect to the rotation direction B of the intermediate transfer belt 18, thereby pressing the intermediate transfer belt 18 toward the photosensitive drum 6, It is ensured that the transfer belt 18 is conveyed between the photosensitive drum 6 and the primary transfer roller 14 in a state of being in close contact with the photosensitive drum 6.

  In this embodiment, the rollers 14, 28, 30, and 32 are resin rollers having substantially the same axial length. Among these, as shown in FIG. 2, the roller 30 includes a core shaft 36 made of stainless steel, for example, and a plurality of (in the example shown, five) resins rotatably supported on the core shaft 36 so that the end surfaces thereof are aligned with each other. The roller 38a and a pair of E-rings 40 attached to both ends of the core shaft 36 in order to fix the axial positions of the plurality of resin rollers 38a. The core shaft 36 is fixed to the main body of the printer 2. Instead, the resin roller 38a may be fixed to the core shaft 36, and the core shaft 36 may be rotatably supported by a bearing provided in the printer 2 body. Each resin roller 38a is manufactured by pulling out a mold in the roller axis direction after resin molding, and has a truncated cone shape having a large-diameter end surface 38L and a small-diameter end surface 38S. Although the taper angle is about 3 ° at the maximum, the taper angle is shown to be larger than the actual one in the drawing (note that the hole into which the core shaft 36 is inserted also has a taper angle, but the illustration is omitted). .) These resin rollers 38a are formed using the same mold, and as a result, the taper angles are substantially the same. As shown in the figure, one large-diameter end surface 38L and the other small-diameter end surface 38S of adjacent resin rollers 38a may be adjacent to each other. As a result, a steep step 41 appears on the outer peripheral surface of the resin roller. As a result, a concentrated load acts on the inner surface of the intermediate transfer belt 18.

  Referring to FIG. 3, tension roller 28 has the same configuration as roller 30 except that the number of resin rollers 38 b is different (seven in the illustrated example). In FIG. 3, the taper of the resin roller is not shown. The primary transfer roller 14 also has the same configuration as the roller 30 except that the number of resin rollers 38c is different (eight in the example in the figure). However, since the primary transfer roller 14 needs to have conductivity, a resin roller is formed by mixing a resin material with a conductive material such as carbon black. It is preferable that the resin rollers of each of the driven rollers 14, 28, 30 are relatively rotatable.

  The drive roller 32 has a different number of resin rollers 38d (six in the example in the figure), and an outer peripheral layer (not shown) made of a material such as rubber having a high coefficient of static friction around the resin roller 38d as a base. It has the same configuration as the roller 30 except that it is provided and the resin roller 38d is fixed to the core shaft. In order to transmit the driving force from the driving motor to the intermediate transfer belt 18 with high efficiency, it is preferable that the plurality of resin rollers 38d constituting the driving roller 32 can rotate integrally.

  As described above, the positions of the joints of the resin rollers adjacent to the rollers 14, 28, 30, and 32 (end face alignment position) are different in the roller axial direction (width direction of the intermediate transfer belt 14) as shown in FIG. 3. ing.

  Returning to FIG. 1, the secondary transfer roller 44 is pressed against the portion of the intermediate transfer belt 18 supported by the roller 32. A predetermined bias voltage is applied to the secondary transfer roller 44 from a bias power source (not shown), and a nip portion between the secondary transfer roller 44 and the intermediate transfer belt 18 is a secondary transfer region 46. .

  A blade 47 for scraping off residual toner on the intermediate transfer belt 18 is pressed against a portion of the intermediate transfer belt 18 supported by the roller 30. The blade 47 and the secondary transfer roller 44 are configured to be able to contact and separate from the intermediate transfer belt 18.

  A paper feed cassette 48 is detachably disposed below the printer 2. The sheets S stacked and stored in the sheet cassette 48 are one sheet at a time from the uppermost one by the rotation of the sheet supply roller 50 disposed at a position facing the vicinity of the front end of the sheet S stacked in the sheet cassette 48. It is sent out to the conveyance path 52.

  The conveyance path 52 includes a nip portion of the conveyance roller pair 54, a nip portion of the timing roller pair 56, a secondary transfer region 46, a nip portion of the fixing roller pair 57, and a nip portion of the discharge roller pair 58 from the paper feed cassette 48. It extends to the paper discharge unit 60 provided on the upper surface of the printer 2.

  In the present embodiment, the photosensitive drum 6, the charging device 8, the exposure unit 10, the developing unit 12, the primary transfer roller 14, the intermediate transfer belt 18, and the secondary transfer roller 44 constitute an image forming unit. Further, the paper feed roller 50, the transport roller 54, the timing roller 56, and the paper discharge roller 58 constitute a transport system.

  Next, the printing operation (image forming operation) of the printer 2 will be described.

  At the start of the printing operation, the secondary transfer roller 44 and the cleaning blade 47 are separated from the intermediate transfer belt 18. When the printing operation is started, the photosensitive drum 6 is rotationally driven in the arrow A direction and the intermediate transfer belt 18 in the arrow B direction at the same peripheral speed, and the surface of the photosensitive drum 6 is uniformly charged by the charging device 8. .

  Subsequently, after the developing unit 12 is rotated and the developing unit 21Y is moved to the developing position, exposure is performed by the exposure device 10, and an electrostatic latent image of a yellow toner image is formed on the photosensitive drum 6. The electrostatic latent image is developed by the developing device 21Y, and the developed yellow toner image is primarily transferred onto the intermediate transfer belt 18 by the action of the primary transfer roller 14. Next, the developing device 21M moves to the developing position, and exposure, development, and primary transfer relating to the magenta toner image are performed. Subsequently, the developing unit 21C moves to the development position, and exposure, development, and primary transfer for the cyan toner image are performed. Thereafter, the developing device 21K moves to the developing position, and exposure, development, and primary transfer for the black toner image are performed. In this way, the toner images of the respective colors are primarily transferred in a superimposed manner on the intermediate transfer belt 18 moving in the arrow B direction.

  At the same time as the primary transfer of black is completed, the secondary transfer roller 44 and the cleaning blade 47 are pressed against the intermediate transfer belt 18. Subsequently, the superimposed toner image formed on the intermediate transfer belt 18 reaches the secondary transfer region 46 as the intermediate transfer belt 18 moves. In this secondary transfer region 46, the superimposed toner images are collectively sent onto the sheet S fed from the paper feed cassette 48 to the conveyance path 52 by the action of the secondary transfer roller 44 and then supplied by the timing roller pair 56. Secondary transferred. When the secondary transfer is completed, the secondary transfer roller 44 is separated from the intermediate transfer belt 18. Further, the toner remaining on the intermediate transfer belt 18 after the secondary transfer is removed by the blade 47.

  The sheet S on which the toner image is secondarily transferred is sent to the fixing roller pair 57 through the conveyance path 52, and the toner image is fixed on the sheet S there. Then, the paper S is discharged to the paper discharge unit 60 via the paper discharge roller pair 58.

  By the way, if the joint positions of the resin rollers of the support rollers 14, 28, 30, 32 that stretch the intermediate transfer belt 18 coincide with each other, the resin scraping becomes remarkable, and if the scraped powder accumulates on the inner surface of the belt, the intermediate transfer is performed. The shape of the belt 18 is locally altered. Further, damage to the inner surface of the belt becomes remarkable, and the electric resistance value of the intermediate transfer belt 18 is locally altered. As a result, poor cleaning, uneven transfer, etc. occur and image quality deteriorates.

  On the other hand, in the present embodiment, since the seam positions that may damage the intermediate transfer belt 18 are dispersed in the belt width direction, damage to the inner surface of the belt can be minimized, and deterioration in image quality is prevented. be able to.

  The above description relates to an embodiment of the present invention, and the present invention is not limited to this and can be variously modified. For example, in the above-described embodiment, the present invention has been described by taking an example of an image forming apparatus that primarily transfers a toner image onto the intermediate transfer belt 18 and secondarily transfers the toner image onto a sheet. However, the present invention is not limited thereto. The present invention can also be applied to a type of apparatus that directly transfers a toner image onto a sheet conveyed on a sheet conveying belt having the same configuration as the intermediate transfer belt.

  Further, there are various methods for changing the position of the joint of the support roller over which the intermediate transfer belt 18 is stretched, in addition to making the number of each support roller different as in the above embodiment. Is not limited. For example, the number of resin rollers is the same for all the support rollers, and the length of the resin rollers constituting each support roller is different from the length of the resin rollers constituting the other support rollers (in this case, between the support rollers). (The axial length is different.)

  Further, the length of each resin roller constituting the support roller for stretching the intermediate transfer belt 18 may be different. FIG. 4 shows an example in which the length of the resin roller of the roller 30 ′, which is a driven roller, is varied. A gear 70 is fixed to the end of the resin roller 38a 'located at one end of the roller 30'. The gear 70 is drivingly connected to a driven body (not shown) (for example, another driven roller) via a gear train (not shown), and the roller 30 ′ is moved by the movement of the intermediate transfer belt stretched around the roller 30 ′. Torque is transmitted to the driven body. By making the resin roller 38a 'longer than the remaining resin rollers 38a ", it is possible to transmit a stable torque to the driven body.

  In addition, in the above-described embodiment, all the seam positions of the respective support rollers do not completely coincide with all the seam positions of the other support rollers, but a configuration in which they partially coincide is also included in the scope of the present invention. It is.

  If the transport system uses a transport belt, a resin roller having a plurality of frustoconical resin rollers can be applied to a support roller (drive roller, driven roller) that stretches the belt. In this case, since the seam positions that may damage the transport belt are dispersed in the belt width direction, damage to the inner surface of the belt can be minimized, and thus the paper can be transported stably. As a result, a toner image can be stably formed by the image forming unit on the stably transported paper.

1 is a configuration diagram showing an embodiment of an image forming apparatus according to the present invention. (A) The side view which shows the resin roller used for one of the support rollers which stretch the intermediate transfer belt of FIG. (B) The perspective view which shows the resin roller which comprises the resin roller of Fig.2 (a). FIG. 3 is a diagram illustrating a relationship between joint positions of a plurality of support rollers that stretch the intermediate transfer belt of FIG. 1. The figure which shows an example of the support roller from which the length of a resin roller differs.

Explanation of symbols

2 Printer (image forming device)
18 Intermediate transfer belt (endless belt)
14, 28, 30, 32 Resin roller (support roller)
38 Tapered resin roller 38L Large diameter end surface 38S Small diameter end surface

Claims (2)

An image carrier for carrying a toner image;
An endless belt in which a toner image on an image carrier is transferred or transferred onto a sheet conveyed on the belt;
A plurality of support rollers that rotatably stretch the endless belt;
With
Each support roller includes a core shaft and a plurality of resin rollers that are supported by the core shaft and have a truncated cone shape having a large-diameter end surface and a small-diameter end surface. Adjacent resin rollers have a core shaft in a state in which the end surfaces are aligned. Is supported by
An image forming apparatus characterized in that a joint between adjacent resin rollers of each support roller has a position different from a joint between adjacent resin rollers of another support roller in the belt width direction. A transport system having an endless belt for transporting paper;
A plurality of support rollers that rotatably stretch the endless belt;
An image forming unit that forms a toner image on a sheet conveyed by a conveyance system;
With
Each support roller includes a core shaft and a plurality of resin rollers that are supported by the core shaft and have a truncated cone shape having a large-diameter end surface and a small-diameter end surface. Adjacent resin rollers have a core shaft in a state in which the end surfaces are aligned. Is supported by
An image forming apparatus characterized in that a joint between adjacent resin rollers of each support roller has a position different from a joint between adjacent resin rollers of another support roller in the belt width direction.

Images