Image forming apparatus

Abstract

To provide an image forming apparatus that can prevent a trouble that bending of a casing causes an increase in the contact resistance between an electrifying roller and a bearing.SOLUTION: An image forming apparatus has an image carrier, an electrifying roller, a bearing, and pressing means. The electrifying roller is in rolling contact with a surface of the image carrier to electrify the surface. The bearing includes a bottom face and two projections. The bottom face is brought into contact with a shaft of the electrifying roller from the side opposite to the image carrier through line contact in a predetermined length along the shaft. The two projections project toward the shaft from both sides of a direction that is orthogonal to the shaft and intersects a direction in which the image carrier and the electrifying roller are arranged side by side, and each have, at its leading end in the projection direction, an apex that faces the shaft with a backlash therebetween. The pressing means presses the bearing in the direction in which the image carrier and the electrifying roller are arranged side by side, to press the electrifying roller against the surface of the image carrier.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] An embodiment of the present invention relates to an image forming apparatus such as a copier or printer installed in a workplace. [Background technology]

[0002] Image forming devices such as copiers and printers include a charging device that charges the surface of a photosensitive drum to a predetermined potential, an exposure device that forms an electrostatic latent image on the surface of the photosensitive drum, a developing device that supplies toner to the electrostatic latent image formed on the surface of the photosensitive drum to develop it, a transport device that transports paper to the surface of the photosensitive drum, a transfer device that transfers the toner image formed on the surface of the photosensitive drum to the paper, and a fixing device that fixes the toner image transferred to the paper.

[0003] The charging device includes, for example, a charging roller that rolls in contact with the surface of the photosensitive drum, and a cleaning roller that rolls in contact with the surface of the charging roller. The charging device also includes, for example, bearings that rotatably hold both ends of the shaft of the charging roller and both ends of the shaft of the cleaning roller, a casing that houses the assembly in which both ends are held by the bearings, and a pressure spring that presses the two bearings toward the surface of the photosensitive drum. The casing mounts the two bearings so that they can move toward the surface of the photosensitive drum. The pressure spring is located between the casing and the two bearings and presses the two bearings toward the photosensitive drum. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-80304 Summary of the Invention [Problem to be solved by the invention]

[0005] The casing has approximately the same length as the photosensitive drum, and when molded from resin, it can bend. If the casing is bent, the bearings may tilt relative to the shaft of the charging roller, increasing contact resistance between the shaft and the charging roller, which can prevent the charging roller from rotating normally. In this case, an undesirable load is applied to the photosensitive drum in contact with the charging roller.

[0006] The problem to be solved by the present invention is to provide an image forming apparatus that can suppress the problem of increased contact resistance between the charging roller and the bearing due to bending. [Means for solving the problem]

[0007] The image forming apparatus of the embodiment includes an image carrier, a charging roller, a bearing, and a pressing unit. The charging roller rolls against the surface of the image carrier to charge the surface. The bearing has a bottom surface and two protrusions. The bottom surface contacts the shaft from the side opposite the image carrier through line contact of a predetermined length along the axis of the charging roller. The two protrusions protrude toward the shaft from both sides in a direction perpendicular to the axis and intersecting the direction in which the image carrier and the charging roller are aligned, and have opposing peaks at their tips in the protruding direction with some play between them and the shaft. The pressing unit presses the bearing in the alignment direction to press the charging roller against the surface of the image carrier. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic diagram showing an image forming apparatus according to an embodiment. [Figure 2] FIG. 2 is a schematic diagram showing the image forming unit for yellow of the image forming apparatus of FIG. [Figure 3] 3 is an exploded perspective view showing a charging device of the image forming unit of FIG. 2. FIG. [Figure 4] 4 is an enlarged perspective view of a bearing bush on the rear side of the charging device shown in FIG. [Figure 5] FIG. 5 is a plan view of the bearing bush of FIG. 4 as viewed from above (in the direction of arrow F5). [Figure 6]FIG. 6 is a perspective view of the bearing bush of FIG. 4 as viewed in the direction of arrow F6. [Figure 7] FIG. 7 is a perspective view of the bearing bush of FIG. 4 as viewed from the direction of arrow F7. [Figure 8] FIG. 8 is a rear view of the bearing bush of FIG. 4 as seen from the rear (direction of arrow F8). [Figure 9] FIG. 9 is a perspective view showing a bearing bush according to a modified example. [Figure 10] FIG. 10 is a rear view of the bearing bush of FIG. 9 as seen from the rear (direction of arrow F10). DETAILED DESCRIPTION OF THE INVENTION

[0009] An image forming apparatus 100 (hereinafter simply referred to as apparatus 100) according to one embodiment will be described below with reference to the drawings. Note that the scale of each part in the drawings used in the following description of the embodiment may be changed as appropriate. Also, in the drawings used in the following description of the embodiment, the configuration may be omitted to make the description easier to understand.

[0010] The device 100 is, for example, an MFP (multifunction peripheral). The device 100 has a printing function, a scanning function, a copying function, an erasing function, a facsimile function, and the like. The printing function is a function of forming an image on paper P. The scanning function is a function of reading an image from an original document or the like on which an image has been formed. The copying function is a function of printing an image read from an original document or the like using the scanning function onto paper P using the printing function. The erasing function is a function of erasing an image formed on paper P with erasable toner.

[0011] As shown in Fig. 1, device 100 has a housing 1 that forms the outer shell of the device. Device 100 is equipped with a printer 10, a scanner 20, and an operation panel 30. Device 100 is equipped with printer 10 and scanner 20 inside housing 1, and with operation panel 30 on the front side of housing 1. In the following description, the front-rear, up-down, left-right directions of all components are defined when device 100 is viewed from the direction shown in Fig. 1.

[0012] Printer 10 is equipped with multiple paper feed cassettes 11, a manual feed tray 12, and multiple paper feed rollers 13. Paper feed cassette 11 stores paper P to be used for printing. Manual feed tray 12 is for manually feeding paper P. Paper feed roller 13 selectively picks up paper P from either paper feed cassette 11 or manual feed tray 12 by rotating.

[0013] The printer 10 includes four toner cartridges 141, 142, 143, and 144, four image forming units 151, 152, 153, and 154, an exposure device 16, a transfer belt 17, a secondary transfer roller 18, and a fixing device 19.

[0014] Toner cartridges 141 to 144 contain toner to be supplied to image forming units 151 to 154, respectively. Toner cartridge 141 contains yellow (Y) toner. Toner cartridge 142 contains magenta (M) toner. Toner cartridge 143 contains cyan (C) toner. Toner cartridge 144 contains black (K) toner. The toner color combination is not limited to YMCK, and other color combinations may also be used. Furthermore, the toner may be one that loses its color at temperatures higher than a predetermined temperature.

[0015] Image forming units 151 to 154 receive toner from toner cartridges 141 to 144, respectively, and form toner images of different colors. Image forming unit 151 forms a yellow (Y) toner image. Image forming unit 152 forms a magenta (M) toner image. Image forming unit 153 forms a cyan (C) toner image. Image forming unit 154 forms a black (K) toner image.

[0016] The image forming units 151 to 154 have the same configuration except for the difference in toner. Therefore, here, the image forming unit 151 for yellow will be described as a representative with reference to Figure 2, and descriptions of the image forming units 152 to 154 for the other colors will be omitted.

[0017] The yellow image forming unit 151 includes a photosensitive drum 41, a charging device 90, a developing device 43, a primary transfer roller 44, a cleaner 45, and a discharging lamp 46.

[0018] The photosensitive drum 41 has a shaft extending from the front to the rear of the device 100. The photosensitive drum 41 has a surface that receives the light beam BY irradiated from the exposure device 16. The photosensitive drum 41 is an example of an image carrier. The charging device 90 charges the surface of the photosensitive drum 41 to a predetermined potential. The exposure device 16 forms an electrostatic latent image on the surface of the photosensitive drum 41. The developing device 43 develops the electrostatic latent image on the surface of the photosensitive drum 41 using yellow toner D supplied from the toner cartridge 141. In other words, the developing device 43 forms a yellow toner image on the surface of the photosensitive drum 41.

[0019] Image forming unit 151 includes primary transfer roller 44 at a position facing the surface of photosensitive drum 41 with transfer belt 17 sandwiched therebetween. Primary transfer roller 44 generates a transfer voltage between itself and photosensitive drum 41. As a result, primary transfer roller 44 transfers (primary transfer) the toner image on the surface of photosensitive drum 41 onto the surface of transfer belt 17, which is in contact with photosensitive drum 41.

[0020] The cleaner 45 removes toner remaining on the surface of the photosensitive drum 41. The charge removal lamp 46 removes charge remaining on the surface of the photosensitive drum 41.

[0021] In accordance with the input image data, the exposure device 16 irradiates the surfaces of the photosensitive drums 41 of the image forming units 151, 152, 153, and 154 with light beams BY, BM, BC, and BK, respectively. The light beams BY, BM, BC, and BK are based on image data of each color obtained by color-separating the image data into Y, M, C, and K colors, respectively.

[0022] The exposure device 16 emits a light beam BY in accordance with image data for the Y component to form an electrostatic latent image for yellow on the surface of the photosensitive drum 41 of the image forming unit 151. Similarly, the exposure device 16 emits light beams BM, BC, and BK in accordance with image data for the M, C, and K components to form electrostatic latent images for each color on the surfaces of the photosensitive drums 41 of the image forming units 152, 153, and 154.

[0023] The image data input to the exposure device 16 is, for example, image data read from an original or the like by the scanner 20. Alternatively, the image data input to the exposure device 16 is image data transmitted to the device 100 from a device other than the device 100.

[0024] 1, the transfer belt 17 is stretched endlessly and rotates by rotating the drive roller 171 around which the transfer belt 17 is wound. As the transfer belt 17 rotates, it transports the toner images of each color formed by the image forming units 151 to 154 on top of each other on the surface of the transfer belt 17 to a transfer region where the secondary transfer roller 18 faces.

[0025] The secondary transfer roller 18 faces the drive roller 171 with the transfer belt 17 sandwiched therebetween. The secondary transfer roller 18 transfers (secondary transfer) the toner image formed on the transfer belt 17 onto the paper P passing between the secondary transfer roller 18 and the toner image formed on the transfer belt 17.

[0026] The fixing device 19 heats and presses the paper P. The fixing device 19 includes a heating roller 191 and a pressure roller 192 that face each other with the transport path of the paper P sandwiched between them. The heating roller 191 includes a heat source such as a heater. The heating roller 191, heated by the heat source, comes into contact with the paper P and heats it. The pressure roller 192 presses the paper P that passes between the pressure roller 192 and the heating roller 191. In this way, the fixing device 19 fixes the toner image transferred onto the paper P to the paper P.

[0027] The printer 10 also includes a duplex unit 50 and a paper output tray 60. The duplex unit 50 prepares the paper P so that printing can be performed on the reverse side. The duplex unit 50 switches the paper P back to turn it over, and sends it to the transfer area between the transfer belt 17 and the secondary transfer roller 18. The paper output tray 60 is used to eject the paper P after printing has been completed.

[0028] The scanner 20 reads an image from a document, etc. The scanner 20 includes a reading module 70 and a document feeder 80.

[0029] The reading module 70 irradiates the surface of the document having the image to be read (hereinafter referred to as the document surface) with illumination light, receives the reflected light with an image sensor (not shown) and converts it into a digital signal, thereby reading the image from the document surface.

[0030] The document feeder 80 is, for example, an ADF (auto document feeder). The document feeder 80 transports documents placed on a document tray 81 one after another through a document glass 82. The reading module 70 reads images from the documents transported to the document glass 82. The document feeder 80 may be provided with another reading module for reading images from the back side of the documents.

[0031] The operation panel 30 is a man-machine interface that performs input and output between the device 100 and the operator of the device 100. The operation panel 30 includes, for example, a touch panel 31 and an input device 32.

[0032] Touch panel 31 is a stack of a display such as a liquid crystal display or an organic EL display and a pointing device that accepts touch input. The display of touch panel 31 displays a screen that notifies the operator of device 100 of various information. Touch panel 31 also accepts touch operations by the operator.

[0033] The input device 32 accepts operations by an operator of the apparatus 100. The input device 32 is, for example, a keyboard, a keypad, or a touchpad.

[0034] The above-mentioned charging device 90 will be described in detail below with reference to FIGS. In each drawing used in the following description, the direction from rear to front of the device 100 is indicated by an arrow X, the direction from left to right is indicated by an arrow Y, and the direction from bottom to top is indicated by an arrow Z.

[0035] 3, the charging device 90 includes a charging roller 91, a cleaning roller 92, a rear-side bearing bush 93, a front-side bearing bush 94, a casing 95, and two pressure springs 96. The charging roller 91, the cleaning roller 92, and the casing 95 extend in the front-rear direction over substantially the entire length of the photosensitive drum 41. The pressure spring 96 functions as a pressure means that presses the bearing bushes 93 and 94 toward the photosensitive drum 41, thereby pressing the charging roller 91 against the surface of the photosensitive drum 41.

[0036] The charging roller 91 is equipped with a shaft portion 911 and a roller portion 912 that are coaxial with each other. The charging roller 91 is arranged below and parallel to the photosensitive drum 41 so that the outer peripheral surface 913 of the roller portion 912 is in rolling contact with the surface of the photosensitive drum 41. The charging roller 91 is arranged so that it is pressed against the surface of the photosensitive drum 41 by the biasing force of two pressure springs 96, which will be described later. When the photosensitive drum 41 rotates, the charging roller 91 rotates along with the photosensitive drum 41. By applying a voltage to the charging roller 91, discharge occurs in the minute space between the charging roller 91 and the photosensitive drum 41, and the surface of the photosensitive drum 41 is charged to a predetermined potential.

[0037] The cleaning roller 92 includes a shaft portion 921 and a spiral portion 922 arranged coaxially. The spiral portion 922 has a shape in which an elastically deformable, long member such as a sponge is wound spirally around the outer peripheral surface of the shaft portion 921. The cross section of the spiral portion 922 perpendicular to the direction along the spiral is rectangular. The spiral portion 922 has an inner surface in which one side of the rectangular cross section is continuous in the direction along the spiral, and an outer surface opposite the inner surface. The inner surface of the spiral portion 922 is fixed to the outer peripheral surface of the shaft portion 921, and its outer surface is in contact with the outer peripheral surface 913 of the roller portion 912 of the charging roller 91.

[0038] The cleaning roller 92 is disposed below and parallel to the charging roller 91 so that the spiral portion 922 is partially crushed and pressed against the roller portion 912 of the charging roller 91. The shaft portion 921 of the cleaning roller 92 is parallel to the shaft portion 911 of the charging roller 91. The cleaning roller 92 rotates along with the rotation of the charging roller 91. The cleaning roller 92 removes toner from the outer peripheral surface 913 of the roller portion 912 of the charging roller 91.

[0039] As shown in FIGS. 4 to 8, the rear-side bearing bushing 93 has a bearing groove 2 and a bearing hole 3. The bearing groove 2 is a groove that rotatably receives the rear-side end of the shaft portion 911 of the charging roller 91. The bearing hole 3 is a bottomed hole that rotatably receives the rear-side end of the shaft portion 921 of the cleaning roller 92. The bearing groove 2 and the bearing hole 3 are positioned such that the spiral portion 922 of the cleaning roller 92, whose shaft portion 921 is received in the bearing hole 3, is pressed against the outer circumferential surface 913 of the roller portion 912 of the charging roller 91, whose shaft portion 911 is received in the bearing groove 2. The bearing groove 2 and the bearing hole 3 extend parallel to each other.

[0040] The bearing bush 93 integrally comprises a horizontal wall portion 931 extending substantially horizontally and two vertical wall portions 932, 933 spaced apart on the left and right sides and extending in the up-down and front-rear directions, respectively. The left vertical wall portion 932 extends upward from the left end of the horizontal wall portion 931. The right vertical wall portion 933 extends upward from the right end of the horizontal wall portion 931. The bearing groove 2, which receives the rear end of the shaft portion 911 of the charging roller 91, is a groove surrounded by the horizontal wall portion 931 and the two vertical wall portions 932, 933. Both ends of the bearing groove 2 in the front-rear direction are open. The bearing hole 3, which receives the rear end of the shaft portion 921 of the cleaning roller 92, is located below the horizontal wall portion 931. The rear end of the bearing hole 3 is closed.

[0041] The bearing bush 93 has an opening 4 above the bearing groove 2 that can receive the shaft portion 911 of the charging roller 91 from above. The opening 4 is located between the upper ends of the two vertical wall portions 932, 933. The bearing bush 93 has a claw portion 5 that protrudes to the right from the upper end of the rear end side of the vertical wall portion 932 on the left side of the bearing groove 2 to prevent it from coming off. The distance between the tip of the claw portion 5 in the protruding direction and the upper end of the vertical wall portion 933 on the opposite side is slightly smaller than the diameter of the shaft portion 911.

[0042] The bearing bush 93 has a strip-shaped bottom convex portion 6 that protrudes slightly upward from the inner bottom surface of the bearing groove 2, i.e., from the upper surface of the horizontal wall portion 931. The left and right ends of the bottom convex portion 6 are smoothly connected to the inner surfaces of the vertical wall portions 932, 933. The bearing bush 93 has two semi-cylindrical side convex portions 7 that protrude inward from the inner surfaces of the two vertical wall portions 932, 933 in directions approaching each other.

[0043] The bearing bush 93 has two retaining grooves 8 extending in the up-down direction on the outer left-right surfaces of the two vertical wall portions 932, 933. The bearing bush 93 has a boss portion 9 that protrudes downward from the lower surface of the horizontal wall portion 931 on the rear end side of the bearing groove 2. The boss portion 9 has the upper end of a pressure spring 96 attached concentrically thereto.

[0044] The bottom protrusion 6 is located at the bottom of the bearing groove 2, away from the opening 4, toward the rear end of the center of the bearing bush 93 in the front-to-rear direction. The bottom protrusion 6 has a horizontal upper surface 101 that has a certain width in the front-to-rear direction. As shown in FIG. 8 , the upper surface 101 of the bottom protrusion 6 functions as a bottom surface that comes into line contact with the outer peripheral surface 913 of the shaft portion 911 of the charging roller 91 from the side opposite the photosensitive drum 41, with a predetermined length of line contact.

[0045] The width of the top surface 101 of the bottom protrusion 6 in the front-to-rear direction, i.e., the length of line contact with the outer circumferential surface 913 of the shaft portion 911, is desirably set to a predetermined width to prevent abrasion due to sliding contact with the shaft portion 911 of the rotating charging roller 91. However, if the width of the top surface 101 of the bottom protrusion 6 is made too large, it becomes difficult to achieve line contact with the outer circumferential surface 913 of the shaft portion 911, so it is desirably set to an appropriate width for the top surface 101. For example, the width of the top surface 101 of the bottom protrusion 6 in the front-to-rear direction is approximately 70% to 150% of the diameter of the shaft portion 911. The top surface 101 does not necessarily have to be a flat surface, and may be a surface that makes line contact with the outer circumferential surface 913 of the shaft portion 911 of the charging roller 91 over a certain length, and may be a slightly curved surface, for example.

[0046] The two side protrusions 7 are continuous with both left and right ends of the bottom protrusion 6, and extend upward from the center in the width direction of the bottom protrusion 6. The two side protrusions 7 extend in a direction approximately perpendicular to the upper surface 101 of the bottom protrusion 6. The upper ends of the two side protrusions 7 terminate at the upper ends of the two vertical wall portions 932, 933, respectively. The width of the side protrusions 7 in the front-to-rear direction is narrower than the width of the bottom protrusion 6.

[0047] The two side protrusions 7 have a cylindrical shape that bulges inward from the inner surfaces of the two vertical wall portions 932, 933. The two side protrusions 7 have a cylindrical surface 102 facing the bearing groove 2. Therefore, the apex 103 at the tip of the side protrusion 7 in the protruding direction is a straight line parallel to the axis of the cylindrical surface. As shown in FIG. 8 , the apex 103 of the side protrusion 7 faces the outer peripheral surface 913 of the shaft portion 911 of the charging roller 91 with some play. The distance between the apexes 103 of the two side protrusions 7 is slightly larger than the diameter of the shaft portion 911 of the charging roller 91. The surface 102 of the side protrusion 7 does not necessarily have to be cylindrical. The side protrusions 7 may have any shape as long as the apex 103 can be in point contact with the outer peripheral surface 913 of the shaft portion 911 of the charging roller 91.

[0048] The shaft portion 911 of the charging roller 91 is in a non-contact state with other parts of the bearing bush 93, except that its outer peripheral surface 913 is in line contact with the upper surface 101 of the bottom convex portion 6 of the bearing groove 2 and its outer peripheral surface 913 is in point contact with the top portion 103 of the side convex portion 7 of the bearing groove 2. For this reason, the bearing bush 93 has low contact resistance with the shaft portion 911 of the charging roller 91, and it can be said that this structure makes it difficult for the bearing bush 93 to apply an undesired load to the shaft portion 911.

[0049] The two retaining grooves 8 provided on the outer surfaces of the two left and right vertical wall portions 932, 933 of the bearing bush 93 are, for example, rectangular grooves in horizontal cross section perpendicular to the longitudinal direction. The upper ends of the two retaining grooves 8 are closed at positions spaced apart below the upper ends of the vertical wall portions 932, 933. The two retaining grooves 8 are positioned opposite the side protrusions 7 in the left-right direction. The retaining grooves 8 slidably fit into rectangular column-shaped ribs (not shown) extending up and down the casing 95. The bearing bush 93 is attached to the casing 95 via the two retaining grooves 8 so that it can move up and down.

[0050] The boss portion 9 protrudes downward from the lower surface side of the side wall portion 931 of the bearing bush 93. The boss portion 9 is, for example, a substantially cylindrical protrusion having a central axis extending in the up-down direction. The boss portion 9 is located so that its central axis is aligned with an imaginary plane including the linear apexes 103 of the two side protrusions 7. In other words, the boss portion 9 is located so that it overlaps the two side protrusions 7 and the two retaining grooves 8 in the left-right direction. The boss portion 9 is attached to the upper end of the compression spring 96 so that its central axis is aligned with the center of the compression spring 96. The compression spring 96 has its lower end fixed to the casing 95 in an axially compressed state.

[0051] In a compressed state, a pressure spring 96 arranged between the casing 95 and the bearing bush 93 presses the bearing bush 93 in a direction (upward) away from the casing 95, with the point of force on a line passing through the center of the spring. The bearing bush 93 is pushed upward by the pressure spring 96, thereby pushing upward the rear ends of the shaft 911 of the charging roller 91 and the shaft 921 of the cleaning roller 92. The bearing bush 93 prevents the shaft 911 of the charging roller 91 from coming off upward by means of a claw 5 located in a position facing the rear end of the shaft 911 of the charging roller 91.

[0052] The front-side bearing bush 94 basically has the same structure as the rear-side bearing bush 93. The bearing bush 94 has a bearing groove 2 that rotatably receives the front end of the shaft portion 911 of the charging roller 91, and a bearing hole 3 that rotatably receives the front end of the shaft portion 921 of the cleaning roller 92. The bearing bush 94 has configurations equivalent to the bottom convex portion 6, two side convex portions 7, two holding grooves 8, and boss portion 9 described above. Therefore, a detailed description of the front-side bearing bush 94, which has the same structure as the bearing bush 93, will be omitted.

[0053] Next, we will explain the functions of the above-mentioned bearing bushes 93 and 94. Note that here too, a functional explanation of the front-side bearing bush 94, which functions in the same way as the rear-side bearing bush 93, will be omitted.

[0054] When the long casing 95 of the charging device 90 is molded from resin, the casing 95 is more likely to bend than the charging roller 91 and cleaning roller 92, which have metal shafts. When the casing 95 bends and curves, the bearing bushes 93 and 94 attached to both ends of the casing 95 in the longitudinal direction tilt relative to the shaft 911 of the charging roller 91. If the tilt direction of the bearing bushes 93 and 94 due to the bending of the casing 95 is vertical, the bearing bushes 93 and 94 tilt toward the opening 4 of the bearing groove 2, so no load due to contact resistance is applied to the shaft 911 of the charging roller 91. In contrast, if the bearing bushes 93 and 94 tilt left or right, the shaft 911 may approach the inner surfaces of the vertical wall portions 932 and 933 on the left and right of the bearing groove 2, and the shaft 911 may come into contact with the inner surfaces of the vertical wall portions 932 and 933.

[0055] For example, if the shaft portion 911 is received in a conventional bearing groove having a cylindrical bottom surface with a diameter slightly larger than that of the shaft portion 911 without providing side protrusions 7 on the inner surfaces of the left and right vertical wall portions 932, 933 of the bearing groove 2 as in the bearing bush 93 of this embodiment, even a slight tilt of the bearing bush in the left-right direction would cause the shaft portion 911 to bite into the vertical wall portions on the left and right of the bearing groove, resulting in contact resistance. For this reason, in the case of a conventional bearing groove without side protrusions 7, the backlash between the bearing bush and the shaft portion 911 is increased to allow for slight tilt of the bearing bush in the left-right direction. However, in this case, the greater the backlash between the bearing groove of the bearing bush and the shaft portion 911, the lower the left-right positioning accuracy of the shaft portion 911 of the charging roller 91.

[0056] The bearing bush 93 of this embodiment has side protrusions 7 on the inner surfaces of the left and right vertical wall portions 932, 933 of the bearing groove 2. This structure makes it difficult for the shaft portion 911 to come into contact with the inner surfaces of the vertical wall portions 932, 933, even if the bearing bush 93 is tilted left and right due to deflection of the casing 95. When the bearing bush 93 tilts left and right from a state where it is not tilted with respect to the shaft portion 911, the gap (backlash) between the surface 102 of the side protrusions 7 and the outer peripheral surface 913 of the shaft portion 911 gradually decreases. However, because the surface 102 of the side protrusions 7 is cylindrical, the rate at which the gap decreases with respect to the left and right tilt angle of the bearing bush 93 is smaller than in conventional bearing grooves. Therefore, with the bearing bush 93 of this embodiment, as long as the left and right tilt angle of the bearing bush 93 with respect to the shaft portion 911 is within a predetermined tolerance, the above-mentioned wedging problem does not occur, and the charging roller 91 can rotate normally.

[0057] The allowable value of the tilt angle in the left-right direction of the bearing bush 93 is determined by the length of the shaft portion 911 of the charging roller 91 and the curvature of the surface 102 of the side convex portion 7. In other words, by designing the curvature of the surface 102 of the side convex portion 7 to an appropriate value, the allowable value of the tilt angle in the left-right direction of the bearing bush 93 can be set to a desired value. As an example, the allowable value of the tilt angle in the left-right direction of the bearing bush 93 is about 3°.

[0058] Furthermore, as described above, by designing the curvature of the surface 102 of the side convex portion 7 to an appropriate value, it is possible to reduce the gap between the apexes 103 of the two left and right side convex portions 7 and the outer circumferential surface 913 of the shaft portion 911, thereby reducing backlash in the left and right direction of the bearing groove 2. Therefore, according to this embodiment, it is possible to improve the positioning accuracy of the charging roller 91 in the left and right direction.

[0059] Furthermore, because the bearing bush 93 has a flat upper surface 101 in which the bottom convex portion 6 of the bearing groove 2 is disposed horizontally, the bearing bush 93 can make line contact with the outer peripheral surface 913 of the shaft portion 911 even when the bearing bush 93 is tilted left or right. That is, in this case, the vertical position of the shaft portion 911 does not change, and the distance between the bearing bush 93 and the cleaning roller 92 can be maintained constant. In contrast, with a conventional cylindrical bearing groove, when the bearing bush is tilted left or right, the shaft portion 911 is pushed upward, increasing the distance between the bearing bush 93 and the cleaning roller 92. Therefore, according to this embodiment, even when the casing 95 is bent, the distance between the charging roller 91 and the cleaning roller 92 can be maintained constant, allowing the cleaning roller 92 to function normally.

[0060] Furthermore, the bearing bushing 93 has a bottom convex portion 6 with a flat top surface 101 and two side convex portions 7 with cylindrical surfaces 102 on the inner surface of the bearing groove 2. As a result, as shown in FIG. 8 , when the shaft portion 911 of the charging roller 91 is received in the bearing groove 2, a relatively large gap S exists between the outer circumferential surface 913 of the shaft portion 911 and the inner surface of the bearing groove 2. This gap S prevents, for example, problems from occurring, such as toner scattered inside the housing 1 of the device 100 accumulating in the bearing groove 2. Conventional cylindrical bearing grooves do not have such a gap, and therefore, there is a risk of problems such as toner getting between the bearing groove and the outer circumferential surface 913 of the shaft portion 911 of the charging roller 91, causing rotational resistance, or the inner surface of the bearing groove being worn down by the toner sliding against it. In contrast, the bearing bushing 93 of this embodiment, which has a large gap S between the bearing groove 2 and the shaft portion 911, can rotatably support the shaft portion 911 without contact resistance for a long period of time.

[0061] Next, modified examples of the bearing bushes 93 and 94 of the above-described embodiment will be described with reference to Figures 9 and 10. Note that the bearing bush 200 according to the modified example has the same structure as the bearing bush 93 of the above-described embodiment except for the shape of the side convex portion 202. Therefore, components that function in the same way as the bearing bush 93 of the above-described embodiment will be assigned the same reference numerals and detailed description thereof will be omitted.

[0062] The bearing bushing 93 of the embodiment described above has two side protrusions 7 each having a cylindrical surface 102 on either side of the bearing groove 2, but the side protrusions provided on the inner surface of the bearing groove 2 may have any shape as long as they are projections that can make point contact with the outer peripheral surface 913 of the shaft portion 911. For example, a bearing bushing 200 according to a modified example shown in FIGS. 9 and 10 may have a side protrusion 202 having a spherical surface 201 instead of the side protrusion 7. The side protrusion 202 of the modified example includes a spherical surface on its surface with an apex 203 at the tip in the protruding direction. The shape of the side protrusion may also be, for example, a polygonal pyramid or a cone with a curved and chamfered apex.

[0063] The side convex portions 202 are positioned so that the peaks 203 are located at a predetermined height from the upper surface 101 of the bottom convex portion 6. The height position of the peaks 203 may be a position above the upper surface 101 of the bottom convex portion 6 by the radius of the shaft portion 911 of the charging roller 91, or slightly below that. Since the distance between the peaks 203 and the outer peripheral surface 913 of the shaft portion 911 changes depending on the height position of the peaks 203, the protruding height of the peaks 203 may be adjusted according to the height position of the side convex portions 202. In the illustrated modified example, the side convex portions 202 are provided at a position so that the peaks 203 are located at a position higher than the upper surface 101 by the radius of the shaft portion 911.

[0064] The bearing bush 200 of this modified example can also achieve the same effect as the bearing bush 93 of the above-described embodiment, and can rotatably hold the shaft portion 911 of the charging roller 91 for a long period of time, even if the bearing bush 200 is tilted with respect to the shaft portion 911 due to bending of the casing 95. Furthermore, compared to the bearing bush 93 of the above-described embodiment, the bearing bush 200 of this modified example has a larger gap S between the inner surface of the bearing groove 2 and the outer peripheral surface 913 of the shaft portion 911 of the charging roller 91, and therefore can almost completely eliminate the problem of toner accumulating in the bearing groove 2.

[0065] Although the embodiments and modifications of the present invention have been described above, the above-described embodiments and modifications are presented as examples and are not intended to limit the scope of the invention. The above-described embodiments and modifications can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. The detailed embodiments and modifications thereof are included within the scope and spirit of the invention, and are also included in the invention and its equivalents set forth in the claims.

[0066] Other embodiments will be described below. 6. In the image forming apparatus according to claim 1, the bearings are provided at both ends of the shaft of the charging roller. 7. The image forming apparatus according to claim 1 has a casing that houses the charging roller with the pressing means sandwiched between it and the bearing. 8. In the image forming apparatus of claim 1, the protrusion has a spherical surface. 9. In the image forming apparatus according to claim 2, the protrusions have cylindrical surfaces extending in the arranging direction. 10. In the above item "9," the bottom surface is a plane having a width along the axis that is greater than the diameter of the protrusion. [Explanation of symbols]

[0067] 2...bearing groove, 3...bearing hole, 4...opening, 5...claw portion, 6...bottom convex portion, 7, 202...side convex portion, 8...retaining groove, 9...boss portion, 41...photosensitive drum, 90...charging device, 91...charging roller, 911...shaft portion, 913...outer peripheral surface, 92...cleaning roller, 921...shaft portion, 93, 94, 200...bearing bush, 931...horizontal wall portion, 932, 933...vertical wall portion, 95...casing, 96...pressure spring, 100...image forming device, 101...upper surface, 102...surface, 103, 203...top portion, 151, 152, 153, 154...image forming unit, P...paper.

Claims

1. an image carrier; a charging roller that rolls and comes into contact with the surface of the image carrier to charge the surface; a bearing including a bottom surface that contacts the shaft from the side opposite to the image carrier by line contact of a predetermined length along the axis of the charging roller, and two protrusions that protrude toward the shaft from both sides in a direction perpendicular to the axis and intersecting the direction in which the image carrier and the charging roller are aligned, and that have tops at their tips in the protruding direction that face each other with a backlash between them and the shaft; a pressing means for pressing the bearings in the arranging direction to press the charging roller against the surface of the image carrier; An image forming apparatus having the same.

2. The protrusions have the tops extending linearly in the arranging direction. The image forming apparatus according to claim 1 .

3. The bottom surface is a plane having a predetermined width along the axis. The image forming apparatus according to claim 1 .

4. the pressing means presses the bearing toward the image carrier by placing a point of force on a center point in the width direction on a line where the shaft is tangent to the bottom surface and on a line in the aligning direction that passes through a center line of the shaft. The image forming apparatus according to claim 3 .

5. The protrusion has a linear apex that extends symmetrically and parallel to the line on which the force point is placed. The image forming apparatus according to claim 4 .

Images