Image forming apparatus

Abstract

The present invention provides an image forming apparatus that can reduce the occurrence of paper feeding failures while suppressing the occurrence of malfunctions in the apparatus's internal components. [Solution] The image forming apparatus comprises an image forming unit and a paper feeding unit. The paper feeding unit has a pickup roller, a feed roller, and a retard roller. The pickup roller contacts the recording medium contained in the paper feeding cassette and feeds out the recording medium. The feed roller transports the recording medium fed out by the pickup roller. The retard roller is pressed against the feed roller to form a nip portion and transports the recording medium while handling it. At least a portion of the upper part of the feed roller is covered by a first static elimination member. The first static elimination member is grounded.

Description

Technical Field

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[0001] The present invention relates to an image forming apparatus such as a copying machine using an electrophotographic method, a printer, a facsimile machine, and a multifunction machine thereof.

Background Art

[0002] A conventional image forming apparatus is disclosed in Patent Document 1. It includes an image forming unit and a paper feeding unit. The image forming unit forms an image on a recording medium. The paper feeding unit supplies the recording medium to the image forming unit. The paper feeding unit has a pickup roller, a feed roller, and a retard roller. The pickup roller contacts the recording medium accommodated in the paper feed cassette and sends out the recording medium. The feed roller conveys the recording medium sent out by the pickup roller. The retard roller is pressed against the feed roller to form a nip portion and conveys the recording medium while discharging it.

[0003] On the downstream side of the retard roller, a static elimination member is arranged in the paper conveyance path. Thereby, the charged recording medium when passing through the retard roller contacts the static elimination member and is statically eliminated. Therefore, the recording medium is easily peeled off from the retard roller, and the occurrence of paper feeding failure can be reduced.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the configuration of Patent Document 1, when the recording medium was fed at high speed, the material of the retard roller was changed, or the type of recording medium was changed, the amount of charge on the recording medium could increase due to friction with the retard roller. At this time, the charge current flowing from the static elimination member placed in the paper transport path to ground increased, which could cause the power supply voltage level in the device to fluctuate. As a result, substrates and sensors placed near the paper transport path could malfunction.

[0006] In view of the above problems, the present invention aims to provide an image forming apparatus that can reduce the occurrence of paper feeding failures while suppressing malfunctions of the equipment within the apparatus. [Means for solving the problem]

[0007] To achieve the above objective, the first configuration of the present invention comprises an image forming unit and a paper feeding unit. The image forming unit forms an image on a recording medium. The paper feeding unit supplies the recording medium to the image forming unit. The paper feeding unit has a pickup roller, a feed roller, and a retard roller. The pickup roller contacts the recording medium housed in the paper feed cassette and feeds out the recording medium. The feed roller transports the recording medium fed out by the pickup roller. The retard roller is pressed against the feed roller to form a nip portion and transports the recording medium while handling it. At least a portion of the upper part of the feed roller is covered by a first static elimination member. The first static elimination member is grounded. [Effects of the Invention]

[0008] According to the first configuration of the present invention, an image forming apparatus can be provided that can reduce the occurrence of paper feeding failures while suppressing the occurrence of malfunctions in the equipment within the apparatus. [Brief explanation of the drawing]

[0009] [Figure 1] A schematic cross-sectional view showing the overall configuration of the image forming apparatus 100 according to the first embodiment of the present invention. [Figure 2]Perspective view of the paper feeding unit 60 of the image forming apparatus 100 according to the first embodiment of the present invention. [Figure 3] A partially cross-sectional view showing an enlarged portion of the paper feeding unit 60 of the image forming apparatus 100 according to the first embodiment of the present invention. [Figure 4] A partially cross-sectional view showing an enlarged portion of the paper feeding unit 60 of the image forming apparatus 100 according to the second embodiment of the present invention. [Modes for carrying out the invention]

[0010] <First Embodiment> Embodiments of the present invention will be described below with reference to the drawings. Figure 1 is a cross-sectional view showing the internal structure of an image forming apparatus 100 according to the first embodiment of the present invention. For convenience of explanation, the vertical direction is defined as the up-down direction (Z1-Z2) when the image forming apparatus 100 is in a usable installation state (as shown in Figure 1). The front-to-back direction (Y1-Y2) is defined with the front side of the image forming apparatus 100 shown in Figure 1 being the front (front). The left-to-right direction (X1-X2) is defined with reference to the front of the image forming apparatus 100 in its installed state. In this embodiment, the left-to-right direction (X1-X2) is orthogonal to the up-to-down direction (Z1-Z2) and the front-to-back direction (Y1-Y2). The left-to-right direction (X1-X2) is defined as the opposing direction of a pair of sides of the image forming apparatus 100 facing each other, and the front-to-back direction (Y1-Y2) is defined as the axial direction of the feed roller 63a. Note that this definition of the up-to-down direction does not limit the orientation and positional relationship of the image forming apparatus 100 when it is in use.

[0011] The image forming apparatus 100 comprises an image forming section Pa to Pd, a paper feeding unit 60, a transfer section 50, a fixing section 14, an ejection section 17, a transport roller pair 40, a paper transport path 19, and a branch transport path 20.

[0012] The image forming apparatus 100 (in this case, a color printer) has four image forming units Pa, Pb, Pc, and Pd arranged in order from the upstream side in the transport direction (left side in Figure 1). The image forming units Pa to Pd form an image on the transfer paper (recording medium) P.

[0013] More specifically, the image forming sections Pa to Pd are provided to correspond to images of four different colors (yellow, cyan, magenta, and black). The image forming sections Pa to Pd sequentially form images of yellow, cyan, magenta, and black through the processes of charging, exposure, development, and transfer, respectively.

[0014] The image forming sections Pa to Pd form visible images (toner images) of each color on the photoreceptor drums (image carriers) 1a to 1d. In addition, an intermediate transfer belt (intermediate transfer body) 8, which rotates counterclockwise in Figure 1, is provided adjacent to each image forming section Pa to Pd. The toner images formed on the photoreceptor drums 1a to 1d are sequentially transferred and superimposed onto the intermediate transfer belt 8, which moves while in contact with each photoreceptor drum 1a to 1d.

[0015] The transfer unit 50 transfers the toner image formed in the image forming units Pa to Pd onto the transfer paper P (recording medium). The transfer unit 50 includes a drive roller 11 and a secondary transfer roller 9. Specifically, the toner image that has been primary transferred onto the intermediate transfer belt 8 is secondary transferred onto the transfer paper P, which is an example of a recording medium, by the secondary transfer roller 9. Furthermore, the transfer paper P on which the toner image has been secondary transferred is discharged from the main body of the image forming apparatus 100 after the toner image has been fixed in the fixing unit 14.

[0016] The paper feeding unit 60 supplies transfer paper P to the image forming units Pa to Pd. Specifically, the paper feeding unit 60 has a pickup roller 62, a feed roller 63a, and a retard roller 63b. The paper feeding unit 60 is located above the paper cassette 61 at Z1. The paper cassette 61 is located at the bottom of the main body of the image forming apparatus 100 and contains the transfer paper P on which the toner image is secondarily transferred.

[0017] The pickup roller 62 is pressed against the upper surface of the transfer paper P with a predetermined pressure. Feeding of the transfer paper P is started by rotating the pickup roller 62. That is, the pickup roller 62 contacts the transfer paper (recording medium) P housed in the paper feed cassette 61 and sends out the transfer paper (recording medium) P to the paper conveyance path 19.

[0018] The feed roller 63a and the retard roller 63b constitute the feed roller pair 63. The feed roller 63a conveys the transfer paper (recording medium) P sent out by the pickup roller. Also, the retard roller 63b is pressed against the feed roller 63a to form a nip portion, and conveys the transfer paper (recording medium) P while breaking it.

[0019] Specifically, the retard roller 63b is pressed against the feed roller 63a and rotates in a driven manner. Also, the retard roller 63b incorporates a torque limiter. Further, a driving force transmission gear 66 for transmitting the rotation of the feed roller 63a to the pickup roller 62 is disposed between the feed roller of 63a and the pickup roller 62 (see FIG. 3).

[0020] Thereby, when a plurality of transfer papers P are fed simultaneously by the pickup roller 62, the transfer paper P is broken by the feed roller 63a and the retard roller 63b, and only the uppermost one is separated and sent out toward the paper conveyance path 19. The transfer paper P that has passed through the paper conveyance path 19 reaches the registration roller pair 13 and is conveyed to the nip portion between the secondary transfer roller 9 and the driving roller 11 of the intermediate transfer belt 8 in accordance with the image formation timing. Note that the paper feed unit 60 will be described in detail later.

[0021] A sheet made of a dielectric resin is used for the intermediate transfer belt 8, and a seamless belt having no seam is mainly used. Also, a blade-shaped belt cleaner 25 for removing toner and the like remaining on the surface of the intermediate transfer belt 8 is disposed on the downstream side of the secondary transfer roller 9.

[0022] Around and below the rotatable photosensitive drums 1a to 1d, charging devices 2a, 2b, 2c, and 2d, an exposure device 5, developing devices 3a, 3b, 3c, and 3d, and cleaning devices 7a, 7b, 7c, and 7d are provided. The charging devices 2a, 2b, 2c, and 2d charge the photosensitive drums 1a to 1d. The exposure device 5 exposes the photosensitive drums 1a to 1d with image information. The developing devices 3a, 3b, 3c, and 3d form toner images on the photosensitive drums 1a to 1d. The cleaning devices 7a, 7b, 7c, and 7d remove developers (toner) and the like remaining on the photosensitive drums 1a to 1d.

[0023] When image data is input from a host device such as a personal computer, first, the charging devices 2a to 2d uniformly charge the surfaces of the photosensitive drums 1a to 1d. Next, the exposure device 5 irradiates light according to the image data, and forms an electrostatic latent image corresponding to the image data on each of the photosensitive drums 1a to 1d. The developing devices 3a to 3d are filled with a predetermined amount of a two-component developer containing yellow, cyan, magenta, and black toner, respectively. When the ratio of the toner in the two-component developer filled in each of the developing devices 3a to 3d falls below a specified value due to the formation of the toner image, toner is replenished from the toner containers 4a to 4d to each of the developing devices 3a to 3d.

[0024] The toner in the developer is supplied onto the photosensitive drums 1a to 1d by the developing devices 3a to 3d and adheres electrostatically. Thereby, a toner image corresponding to the electrostatic latent image formed by the exposure from the exposure device 5 is formed.

[0025] Then, an electric field is applied at a predetermined transfer voltage between the primary transfer rollers 6a to 6d and the photosensitive drums 1a to 1d by the primary transfer rollers 6a to 6d, and the yellow, cyan, magenta, and black toner images on the photosensitive drums 1a to 1d are primarily transferred onto the intermediate transfer belt 8. These images are formed with a predetermined positional relationship. Thereafter, in preparation for the formation of a new electrostatic latent image that is subsequently performed, the toner and the like remaining on the surfaces of the photosensitive drums 1a to 1d after the primary transfer are removed by the cleaning devices 7a to 7d.

[0026] The intermediate transfer belt 8 is stretched between the upstream driven roller 10 and the downstream drive roller 11. As the drive roller 11 rotates due to a belt drive motor (not shown), the intermediate transfer belt 8 begins to rotate counterclockwise, and the transfer paper P is transported from the resist roller pair 13 to the drive roller 11 and the secondary transfer roller 9 located adjacent to it at a predetermined timing to the secondary transfer nip section N. The toner image on the intermediate transfer belt 8 is then secondarily transferred onto the transfer paper P as it passes through the secondary transfer nip section N.

[0027] The transfer paper P on which the toner image has been secondarily transferred is transported to the fuser unit 14. The fuser unit 14 has a fuser belt 14a and a pressure roller 14b. The fuser belt 14a is heated by a heating device (not shown), such as a heater or an induction heating unit. The pressure roller 14b is pressed against the fuser belt 14a to form a fuser nip, and imparts rotational driving force to the fuser belt 14a.

[0028] The transfer paper P, transported to the fixing unit 14, is heated and pressurized by the fixing belt 14a and pressure roller 14b, fixing the toner image to the surface of the transfer paper P and forming a predetermined full-color image.

[0029] The transfer paper P on which the full-color image has been formed is directed in a different direction by a transport guide member 15 located at the branching point of the paper transport path 19, after passing through a transport roller pair 40. It is then discharged into the discharge tray 18 by a discharge roller pair (discharge section) 17 (or after being sent to the branching transport path 20 where images are formed on both sides).

[0030] The transport roller pair 40 feeds the transfer paper (recording medium) P from the fixing unit 14 to the discharge roller pair (discharge unit) 17.

[0031] The paper transport path 19 connects the paper feeding section 60, the transfer section 50, the fixing section 14, and the discharge section 17. The branch transport path 20 branches off from the paper transport path 19 downstream of the transport roller pair 40 and communicates with the paper transport path 19 upstream of the registration roller pair 13. The branch transport path 20 extends vertically (Z1-Z2) along the side surface 102 of the image forming apparatus 100 and is curved in a roughly C-shape.

[0032] Figure 2 is a perspective view of the paper feeding unit 60, and Figure 3 is a partial cross-sectional view showing an enlarged portion of the paper feeding unit 60. In Figure 3, the transport direction of the transfer paper P is indicated by a dashed line.

[0033] The paper feeding unit 60 further comprises a housing 69 that holds a pickup roller 62, a feed roller 63a, and a retard roller 63b. The paper feeding unit 60 constitutes a part of the transport surface of the paper transport path 19. The paper feeding unit 60 can be mounted on the main body of the image forming apparatus 1 along guide rails 71 and 72 located in the housing 69.

[0034] The guide rails 71 and 72 are made of sheet metal and are conductive. In this embodiment, they extend parallel to the axial direction (Y1-Y2) of the feed roller 63a. Furthermore, the guide rail 71 functions as a first static elimination member and covers at least a portion of the feed roller 63a above it. That is, at least a portion of the feed roller 63a above it is covered by the guide rail (first static elimination member) 71.

[0035] In this embodiment, the guide rail 71 is made of sheet metal, but it may also be made of molded resin as long as a conductive member is arranged on the surface facing the feed roller 63a.

[0036] The guide rail 71 is grounded via the main frame of the image forming apparatus 100. As a result, the charge on the transfer paper P, which is charged by friction with the feed roller 63a, is discharged via the feed roller 63a and the guide rail 71. Therefore, the amount of charge on the transfer paper P passing through the feed roller 63a is reduced, making it easier for the transfer paper P to peel off the feed roller 63a. This reduces the occurrence of paper feeding failures. In addition, the guide rail (first static discharge member) 71 is located outside the paper transport path 19, and the static charge current flows at a position away from the paper transport path 19. This prevents malfunctions of substrates and sensors located near the paper transport path 19, and suppresses malfunctions of equipment within the apparatus.

[0037] Furthermore, the first static elimination member is composed of a guide rail 71, allowing static elimination of the transfer paper P without increasing the number of parts in the paper feeding unit 60. This helps to suppress an increase in the manufacturing cost of the paper feeding unit 60.

[0038] Furthermore, the guide rail 71 is longer in the axial direction (Y1-Y2) than the axial length (Y1-Y2) of the feed roller 63a. This allows the charge on the charged transfer paper P to be efficiently removed via the feed roller 63a and the guide rail 71.

[0039] Furthermore, in this embodiment, the feed roller 63a and the guide rail (first static elimination member) 71 face each other with a gap of 2.5 mm between them, but it is preferable that the gap be between 2 mm and 4 mm. If the gap is smaller than 2 mm, the feed roller 63a and the guide rail 71 may come into contact. Also, if the gap is larger than 4 mm, the static elimination effect will decrease.

[0040] Furthermore, the guide rail (first static elimination member) 71 is bent radially outward in a convex shape along the feed roller 63a. This allows for a larger area where the guide rail (first static elimination member) 71 and the feed roller 63a face each other at an equal radial distance. Therefore, the static elimination effect can be improved.

[0041] <Second Embodiment> Next, a second embodiment of the present invention will be described. Figure 4 is a partially cross-sectional view showing an enlarged portion of the paper feeding unit 60 according to the second embodiment. In Figure 4, the transport direction of the transfer paper P is indicated by a dashed line. For convenience of explanation, the same reference numerals are used for parts that are the same as those in the first embodiment shown in Figures 1 to 3 above. In the second embodiment, the paper feeding unit 60 further includes a guide member 73. The other parts are the same as in the first embodiment.

[0042] The guide member 73 is positioned on the transport surface of the paper transport path 19 connecting the pickup roller 62 and the feed roller 71, and supports the lower surface of the transfer paper (recording medium) P. By positioning the guide member 73, the transfer paper (recording medium) P is smoothly transported from the pickup roller 62 to the nip portion of the feed roller pair 63. Therefore, the occurrence of paper feeding failures can be further reduced.

[0043] Furthermore, the upper surface of the guide member 73 is composed of a grounded second static elimination member 74. The second static elimination member 74 is made of, for example, a conductive sheet metal, and stainless steel (SUS material) is preferably used. The charge on the transfer paper P, which is charged by friction with the feed roller 63a, is eliminated via the second static elimination member 74. As a result, the amount of charge on the transfer paper P passing through the feed roller 63a can be further reduced. In addition, the charging current can be passed through the second static elimination member 74 at a position away from the paper transport path 19. This prevents damage to substrates and sensors located near the paper transport path 19 and further suppresses malfunctions of equipment within the device.

[0044] The guide member 73 and the second static elimination member 74 may be made of the same material or of different materials. For example, the guide member 73 may be made of a resin molded product, and the plate-shaped second static elimination member 74 may be placed on the upper surface of the guide member 73.

[0045] The axial width (Y1-Y2) of the second static elimination member 74 is greater than the axial width (Y1-Y2) of the nip portion between the feed roller 63a and the retard roller 63b. This allows the charge on the charged transfer paper P to be efficiently removed via the second static elimination member 74.

[0046] The second static elimination member 74 is grounded via the main frame of the image forming apparatus 100. Specifically, the second static elimination member 74 and the main frame of the image forming apparatus 100 are connected via a wire spring, wire, or conductive tape. Alternatively, the second static elimination member 74 and the guide rail 71 may be connected via a wire spring, wire, or conductive tape.

[0047] Furthermore, the present invention is not limited to the above embodiments, and various modifications are possible without departing from the spirit of the invention. For example, in the above embodiment, the first static elimination member is made of a guide rail 71, but the first static elimination member may also be made by arranging a plate-shaped stainless steel (SUS material) in the housing 69. [Industrial applicability]

[0048] The present invention is not limited to color copiers, but can also be used in other vertical transport type image forming devices such as analog copiers, digital multifunction printers, monochrome and color printers, and facsimile machines. [Explanation of symbols]

[0049] 1a~1d Photoconductor drum 2a~2d Charging device 3a~3d developing device 4a~4d Toner container 5. Exposure apparatus 6a~6d Primary transfer roller 7a~7d Cleaning equipment 8. Intermediate transfer belt 9. Secondary transfer roller 10 Driven rollers 11 Drive rollers 12 Paper feed rollers 13 Resist Roller vs 14 Fixing section 14a Fixing belt 14b Pressure Roller 15 Conveyor guide member 16 paper cassettes 17 Discharge roller pair (discharge section) 18 Output tray 19. Paper transport path 25 Belt Cleaner 38 Conveyor Unit 40 Conveyor Rollers 50 Transfer section 60 Paper feed unit 61 Paper Cassette 62 Pickup Roller 63 Feeding roller pair 63a Feed Roller 63b Retard Roller 66 Power transmission gear 69 Housing 71, 72 Guide rail (first static elimination member) 73 Guide member 74 Second static elimination member 100 Image forming apparatus N Secondary transfer nip section P Transfer paper (recording medium) Pa~Pd Image Forming Unit

Claims

1. An image forming unit that forms an image on a recording medium, The system includes a paper feeding unit that supplies a recording medium to the image forming unit, The aforementioned paper feeding unit is A pickup roller that contacts the recording medium contained in the paper feed cassette and feeds out the recording medium, A feed roller that transports the recording medium ejected by the pickup roller, It has a retard roller that is pressed against the feed roller to form a nip portion and conveys the recording medium while handling it, The feed roller is covered by a first static elimination member at least on its upper part. The first static elimination member is grounded in the image forming apparatus.

2. The image forming apparatus according to claim 1, wherein the feed roller and the first static elimination member are facing each other with a gap of 2 mm or more and 4 mm or less between them.

3. The image forming apparatus according to claim 1 or claim 2, wherein the first static elimination member is longer in the axial direction than the axial length of the feed roller.

4. The image forming apparatus according to claim 1 or claim 2, wherein the first static elimination member is bent convexly outward in the radial direction along the feed roller.

5. The paper feeding unit further comprises a housing that holds the pickup roller, the feed roller, and the retard roller. The paper feeding unit can be mounted on the main body of the device along guide rails arranged in the housing. The image forming apparatus according to claim 1 or claim 2, wherein the first static elimination member is composed of the guide rail.

6. The aforementioned paper feeding unit is The system further includes a guide member positioned on the transport surface of the paper transport path connecting the pickup roller and the feed roller, and supporting the lower surface of the recording medium. The image forming apparatus according to claim 1 or claim 2, wherein the upper surface of the guide member is composed of a second static elimination member.

7. The image forming apparatus according to claim 6, wherein the axial width of the second static elimination member is greater than the axial width of the nip portion.

8. The image forming apparatus according to claim 6, wherein the second static elimination member is grounded.

Images