Image forming apparatus

Abstract

Providing an image forming apparatus capable of suppressing the occurrence of image defects. 【Solution means】The image forming apparatus includes an image carrier, a charging roller, a case, and a bearing. The charging roller is in rolling contact with the surface of the image carrier to charge the surface. The case houses the charging roller. The bearing is rotatably attached to the case about a rotation axis extending in the direction in which the image carrier and the charging roller are aligned, and rotatably supports the axis of the charging roller.

Description

Technical Field

[0001] Embodiments of the present invention relate to an image forming apparatus such as a copying machine or a printer.

Background Art

[0002] An image forming apparatus such as a copying machine or a printer includes a charging device that charges the surface of a photoreceptor drum to a predetermined potential, an exposure device that forms an electrostatic latent image on the surface of the photoreceptor drum, a developing device that supplies toner to the electrostatic latent image formed on the surface of the photoreceptor drum for development, a conveyance device that conveys a sheet to the surface of the photoreceptor drum, a transfer device that transfers the toner image formed on the surface of the photoreceptor drum to the sheet, and a fixing device that fixes the toner image transferred to the sheet.

[0003] The charging device includes, for example, a charging roller that is in contact with the surface of the photoreceptor drum and a cleaning roller that is in contact with the surface of the charging roller. Further, the charging device 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 an assembly having both ends held by the bearings, and a pressing spring that presses the two bearings toward the surface of the photoreceptor drum. The casing is movably attached such that the two bearings face the surface of the photoreceptor drum. The pressing spring is between the casing and the two bearings and presses the two bearings toward the photoreceptor drum.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The casing is approximately the same length as the photoreceptor drum, and when molded from resin, it may flex. If the casing flexes, the bearing attached to the casing may tilt relative to the axis of the charging roller, increasing the contact resistance between the axis and the bearing, which may prevent the charging roller from rotating properly. In this case, an undesirable load is placed on the photoreceptor drum in contact with the charging roller, which will adversely affect the image.

[0006] The problem that this invention aims to solve is to provide an image forming apparatus that can suppress the occurrence of image defects. [Means for solving the problem]

[0007] The image forming apparatus of this embodiment includes an image carrier, a charging roller, a case, and a bearing. The charging roller makes rolling contact with the surface of the image carrier to charge the surface. The case houses the charging roller. The bearing is rotatably mounted to the case around a pivot axis extending in the direction in which the image carrier and the charging roller are aligned, and rotatably supports the axis of the charging roller. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1 is a schematic diagram showing an image forming apparatus according to an embodiment. [Figure 2] Figure 2 is a schematic diagram showing the yellow image forming section of the image forming apparatus shown in Figure 1. [Figure 3] Figure 3 is an exploded perspective view showing the charging device of the image forming section in Figure 2. [Figure 4] Figure 4 is a magnified perspective view of the rear bushing of the charging device shown in Figure 3. [Figure 5] Figure 5 is a perspective view of the bush shown in Figure 4, taken from the direction of arrow F5. [Figure 6] Figure 6 is a partially enlarged cross-sectional view of the area near the rear end of the charging device shown in Figure 3. [Figure 7] Figure 7 is a partially enlarged perspective view of the area near the rear end of the casing shown in Figure 6. [Figure 8] Figure 8 is a partially enlarged plan view of the area near the rear end of the charging device shown in Figure 3. [Figure 9] Figure 9 is a magnified perspective view of the front bushing of the charging device shown in Figure 3. [Figure 10] Figure 10 is a plan view illustrating the function of the charging device shown in Figure 3. [Figure 11] Figure 11 is a plan view illustrating the function of the charging device shown in Figure 3. [Modes for carrying out the invention]

[0009] Hereinafter, an image forming apparatus 100 (hereinafter simply referred to as "apparatus 100") according to one embodiment will be described with reference to the drawings. Note that the scale of each part in the drawings used in the description of the following embodiment may have been appropriately changed. Also, in order to make the explanation easier to understand, some of the components in the drawings used in the description of the following embodiment may be omitted.

[0010] Device 100 is, for example, an MFP (multifunction peripheral). Device 100 is equipped with printing, scanning, copying, decolorizing, and facsimile functions. The printing function is a function that forms an image on paper P. The scanning function is a function that reads an image from a document on which an image has been formed. The copying function is a function that prints an image read from a document using the scanning function onto paper P using the printing function. The decolorizing function is a function that decolorizes an image formed on paper P with decolorizable toner.

[0011] As shown in Figure 1, the device 100 has a housing 1 that forms the outer shell of the device. The device 100 includes a printer 10, a scanner 20, and an operation panel 30. The device 100 has the printer 10 and scanner 20 inside the housing 1, and the operation panel 30 is located on the front side of the housing 1. In the following description, the device 100 is viewed from the direction shown in Figure 1, and the front-to-back (front, rear), up-and-down, and left-to-right directions are defined for all components.

[0012] The printer 10 includes a plurality of paper feed cassettes 11, a manual feed tray 12, and a plurality of paper feed rollers 13. The paper feed cassettes 11 store the paper P used for printing. The manual feed tray 12 is for manually inserting the paper P. The paper feed rollers 13 selectively take out the paper P from either the paper feed cassettes 11 or the manual feed tray 12 by rotating.

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

[0014] The toner cartridges 141 to 144 each store the toner to be supplied to the image forming units 151 to 154. The toner cartridge 141 stores yellow (Y) toner. The toner cartridge 142 stores magenta (M) toner. The toner cartridge 143 stores cyan (C) toner. The toner cartridge 144 stores black (K) toner. The combination of toner colors is not limited to YMCK, and other color combinations may also be used. Also, the toner may be a toner that fades at a temperature higher than a predetermined temperature.

[0015] The image forming units 151 to 154 each receive the supply of toner from the toner cartridges 141 to 144 and form toner images of different colors. The image forming unit 151 forms a yellow (Y) toner image. The image forming unit 152 forms a magenta (M) toner image. The image forming unit 153 forms a cyan (C) toner image. The 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, referring to FIG. 2, the image forming unit 151 for yellow will be described as a representative, and the description of the image forming units 152 to 154 for other colors will be omitted.

[0017] The image forming unit 151 for yellow includes a photosensitive drum 41, a charging device 90, a developing device 43, a primary transfer roller 44, a cleaner 45, and a charge eliminating lamp 46. The charging device 90 faces downward in the gravitational direction of the photosensitive drum 41.

[0018] The photosensitive drum 41 has an axis extending in the front and rear of the apparatus 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 the yellow toner D supplied from the toner cartridge 141. That is, the developing device 43 forms a yellow toner image on the surface of the photosensitive drum 41.

[0019] The image forming unit 151 includes a primary transfer roller 44 at a position facing the surface of the photosensitive drum 41 with the transfer belt 17 interposed therebetween. The primary transfer roller 44 generates a transfer voltage between itself and the photosensitive drum 41. Thereby, the primary transfer roller 44 transfers (primary transfer) the toner image on the surface of the photosensitive drum 41 to the surface of the transfer belt 17 that is in contact with the photosensitive drum 41.

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

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

[0022] The exposure apparatus 16 emits a light beam BY according to the Y component image data to form an electrostatic latent image for yellow on the surface of the photoreceptor drum 41 of the image forming unit 151. Similarly, the exposure apparatus 16 emits light beams BM, BC, and BK according to the M, C, and K component image data to form electrostatic latent images for each color on the surface of the photoreceptor drum 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 a document 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] As shown in Figure 1, the transfer belt 17 is stretched in an endless manner and rotates by rotating the drive roller 171 around which the transfer belt 17 is wound. As the transfer belt 17 rotates, the toner images of each color that have been superimposed on the surface of the transfer belt 17 by the image forming units 151-154 are transported to the transfer area opposite the secondary transfer roller 18.

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

[0026] The fuser unit 19 heats and pressurizes the paper P. The fuser unit 19 comprises a heating roller 191 and a pressurizing roller 192 that face each other with the paper P transport path in between. The heating roller 191 is equipped with a heat source such as a heater. The heating roller 191, heated by the heat source, contacts the paper P and heats the paper P. The pressurizing roller 192 pressurizes the paper P as it passes between the pressurizing roller 192 and the heating roller 191. As a result, the fuser unit 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 an output tray 60. The duplex unit 50 prepares the paper P for printing on the reverse side. The duplex unit 50 reverses the front and back sides of the paper P by switching it back and feeds it into the transfer area between the transfer belt 17 and the secondary transfer roller 18. The output tray 60 is for ejecting the paper P after printing is complete.

[0028] The scanner 20 reads images from documents and other materials. The scanner 20 includes a reading module 70 and a document feeder 80.

[0029] The reading module 70 shines illumination light onto the surface of the document containing the image to be read (hereinafter referred to as the document surface), receives the reflected light with an image sensor (not shown), and converts it into a digital signal. In this way, the reading module 70 reads 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 the document tray 81 one after another through the document glass 82. The scanning module 70 reads images from the documents transported to the document glass 82. The document feeder 80 may also be equipped with another scanning module for reading images from the back of the documents.

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

[0032] The touch panel 31 is a stacked unit comprising, for example, a display such as a liquid crystal display or an organic EL display, and a pointing device that accepts touch input. The display of the touch panel 31 shows a screen for notifying the operator of the device 100 of various information. The touch panel 31 also accepts touch operations from the operator.

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

[0034] The above-mentioned charging device 90 will now be described with reference to Figures 3 to 9. In the drawings used in the following explanation, arrow X indicates the direction from rear to front of the device 100, arrow Y indicates the direction from left to right, and arrow Z indicates the direction from bottom to top. The direction indicated by arrow Z is the direction in which the photoreceptor drum 41 and the charging roller 91 of the charging device 90 are aligned.

[0035] As shown in Figure 3, the charging device 90 comprises a charging roller 91, a cleaning roller 92, a rear bush 93, a front 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 along substantially the entire length of the photoreceptor drum 41. The rear bush 93 is an example of a bearing. The casing 95 is an example of a case. The pressure springs 96 are an example of a pressing means. The pressure springs 96 push the bushes 93 and 94 upward toward the photoreceptor drum 41 located above the charging device 90, pressing the charging roller 91 against the surface of the photoreceptor drum 41.

[0036] The charging roller 91 has a roller portion 912 coaxially attached to the outside of the shaft portion 911. The charging roller 91 is positioned below the photoreceptor drum 41 and parallel to the photoreceptor drum 41 so that the outer peripheral surface 913 of the roller portion 912 rolls against the surface of the photoreceptor drum 41. The charging roller 91 is pressed against the surface of the photoreceptor drum 41 by the biasing force of two compression springs 96. The charging roller 91 moves along with the photoreceptor drum 41 as the photoreceptor drum 41 rotates. By applying a voltage to the charging roller 91, a discharge occurs in the minute space between the charging roller 91 and the photoreceptor drum 41, and the surface of the photoreceptor drum 41 becomes charged to a predetermined potential.

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

[0038] The cleaning roller 92 is positioned parallel to and below the charging roller 91 so as to partially crush its spiral portion 922 and press it 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 is carried along with the charging roller 91 by the rotation of the charging roller 91. The cleaning roller 92 removes toner from the outer circumferential surface 913 of the roller portion 912 of the charging roller 91.

[0039] As shown in Figures 4 and 5, the rear bush 93 is provided with a bearing groove 931 and a bearing hole 932. The bearing groove 931 rotatably receives the rear end of the shaft portion 911 of the charging roller 91. The bearing hole 932 rotatably receives the rear end of the shaft portion 921 of the cleaning roller 92. The bearing groove 931 and the bearing hole 932 are positioned such that the helical portion 922 of the cleaning roller 92, which receives its shaft portion 921, is pressed against the outer circumferential surface 913 of the roller portion 912 of the charging roller 91, which receives its shaft portion 911 in the bearing groove 931. The bearing groove 931 and the bearing hole 932 extend parallel to each other.

[0040] The bearing groove 931 has an inner surface with a U-shaped cross-section in a plane parallel to the YZ plane perpendicular to the axial direction (front-rear direction). Both ends of the bearing groove 931 in the front-rear direction are open. The bearing groove 931 has a substantially rectangular opening 9311 at its upper part, into which the shaft portion 911 of the charging roller 91 can be received from above. The bearing groove 931 has a band-shaped bearing projection 9312 on its rear inner surface that slides against the outer circumferential surface of the shaft portion 911 of the charging roller 91. The inner surface of the bearing projection 9312 includes a cylindrical surface with substantially the same curvature as the outer circumferential surface of the shaft portion 911. The width between the inner surfaces of the bearing projections 9312 on both sides of the opening 9311 in the left-right direction is slightly larger than the diameter of the shaft portion 911. The front inner surface of the bearing groove 931 faces the circumferential surface of the shaft portion 911 with a small gap between them. In other words, the inner surface of the bearing groove 931 has a step 9313 in the middle of the axial direction.

[0041] The bush 93 has a claw portion 933 that is integrally projected inward from near the left edge of the opening 9311, close to the rear end of the bearing groove 931. The distance between the tip of the claw portion 933 in the projection direction and the opposite edge of the opening 9311 is slightly smaller than the diameter of the shaft portion 911 of the charging roller 91. The claw portion 933 prevents the shaft portion 911, which is positioned in the bearing groove 931, from coming out upward. When inserting the shaft portion 911 into the bearing groove 931, for example, the shaft portion 911 is placed into the bearing groove 931 through the opening 9311 in a position away from the front of the claw portion 933, and the shaft portion 911 is slid slightly to the rear side relative to the bearing groove 931 so that the rear end of the shaft portion 911 is positioned below the claw portion 933.

[0042] With the shaft portion 911 inserted into the bearing groove 931 in this manner, the outer circumferential surface near the rear end of the shaft portion 911 of the charging roller 91 contacts the inner surface of the bearing projection 9312 of the bearing groove 931, allowing the shaft portion 911 to rotate coaxially with respect to the bearing groove 931. Furthermore, since the inner surface of the bearing projection 9312 of the bearing groove 931 has approximately the same curvature as the shaft portion 911, it restricts the lateral movement of the shaft portion 911 relative to the bearing groove 931. Note that the upper part of the bearing groove 931 is open toward the photoreceptor drum 41, so a slight upward movement of the shaft portion 911 relative to the bearing groove 931 is possible until the shaft portion 911 contacts the claw portion 933.

[0043] The bearing hole 932 is located below the bearing groove 931, offset in front of the bearing projection 9312 of the bearing groove 931. The rear end of the bearing hole 932 closes in front of the bearing projection 9312 of the bearing groove 931. On the front surface of the rear bottom of the bearing hole 932, there is a projection 9321 with a spherical surface that bulges slightly towards the front. The rear end of the shaft portion 921 of the cleaning roller 92 inserted into the bearing hole 932 can contact the top of the projection 9321 on the bottom surface of the bearing hole 932. The cross-section of the bearing hole 932 by a plane parallel to the YZ plane is approximately U-shaped, and the width of the bearing hole 932 in the left-right direction is slightly larger than the diameter of the shaft portion 921 of the cleaning roller 92. The shaft portion 921 inserted into the bearing hole 932 is restricted from moving left-right relative to the bush 93, but is allowed to move slightly upward toward the charging roller 91.

[0044] The bush 93 integrally includes a cylindrical pivot shaft 934 below the bearing projection 9312 of the bearing groove 931. The pivot shaft 934 has a central axis that extends vertically perpendicular to the bearing groove 931 and the bearing hole 932. The pivot shaft 934 is positioned so that its central axis intersects with the center of the shaft portion 911 of the electrostatic roller 91 that is received in the bearing groove 931.

[0045] As shown in Figure 6, the bush 93 can be attached to the casing 95 by inserting its pivot shaft 934 into the cylindrical sleeve 951 of the casing 95. The inner diameter of the sleeve 951 is slightly larger than the outer diameter of the pivot shaft 934. The sleeve 951 has a hole through which the pivot shaft 934 is inserted so as to be rotatable and slidable in the vertical direction. It is desirable that the sleeve 951 be as long as possible in order to suppress the tilting of the pivot shaft 934 of the bush 93. The hole in the sleeve 951 extends in the vertical direction and penetrates the bottom surface of the casing 95.

[0046] When attaching the bush 93 to the casing 95, the aforementioned compression spring 96 is attached coaxially to the outside of the sleeve 951 of the casing 95, and with the compression spring 96 compressed, the pivot shaft 934 of the bush 93 is inserted into the sleeve 951. In this state, the compression spring 96, due to its restoring force, presses the bush 93 upward along the pivot shaft 934. The bush 93 is rotatable relative to the casing 95 about the pivot shaft 934 and is also movable up and down relative to the casing 95 along the pivot shaft 934.

[0047] As shown in Figure 7, the casing 95 has a housing section 950 that houses an assembly comprising a charging roller 91, a cleaning roller 92, and two bushings 93 and 94. As described above, the assembly is held at the rear end of the shaft portion 911 of the charging roller 91 and the rear end of the shaft portion 921 of the cleaning roller 92 by the bushing 93, and the front ends of the two shaft portions 911 and 921 are held by the front bushing 94, which will be described later. The housing section 950 has a roughly rectangular opening 952 that is long in the front-to-back direction for inserting the assembly from above the casing 95.

[0048] The rear bush 93 is attached to the housing 950 near the rear end of the casing 95 via the opening 952. As described above, the rear bush 93 can be attached to the rear side of the housing 950 by inserting its pivot shaft 934 into a sleeve 951 that protrudes from the bottom of the housing 950. The front bush 94 is attached to the housing 950 near the front end of the casing 95 via the opening 952.

[0049] As shown in Figure 8, the rear bush 93 has columnar surfaces 935 on both sides in the left-right direction that are coaxial with the pivot axis 934. The columnar surfaces 935 are concentric curved surfaces formed by rotating a line parallel to the pivot axis 934 around the pivot axis 934. The casing 95 has sliding contact surfaces 953 on the inner sides of both the left and right sides of the housing 950 that slide against the columnar surfaces 935 of the bush 93. The two left and right sliding contact surfaces 953 are, for example, flat surfaces parallel to the XZ plane. The distance between the two sliding contact surfaces 953 in the left-right direction is slightly greater than the distance between the left and right vertices of the two left and right columnar surfaces 935 of the bush 93. The sliding contact surfaces 953 allow rotation of the bush 93 relative to the casing 95, and restrict the left-right movement (tilting) of the bush 93 relative to the casing 95. The sliding contact surface 953 is not limited to a flat surface; for example, it may be a curved surface with a curvature smaller than the columnar surface 935 of the bush 93.

[0050] The bush 93 does not have a sliding groove or sliding rail for mounting it to the casing 95 so as to be movable in the vertical direction, and the casing 95 also does not have a sliding groove or sliding rail for mounting the bush 93 so as to be movable in the vertical direction. The bush 93 is movable in the vertical direction relative to the casing 95 by sliding its pivot shaft 934 up and down relative to the sleeve 951, and is rotatable relative to the casing 95 around the pivot shaft 934. The columnar surface 935 of the bush 93 and the sliding contact surface 953 of the casing 95 prevent the bush 93 from tilting laterally relative to the casing 95 and guide the rotation of the bush 93 relative to the casing 95.

[0051] As shown in Figure 8, the bush 93 has an engagement step 936 near the left columnar surface 935 to prevent the bush 93 from coming out upward relative to the housing 950. The casing 95 has an engagement claw 955 that faces the engagement step 936, slightly spaced above it, when the bush 93 is installed in the housing 950. When the bush 93 is installed in the housing 950 through the opening 952, the engagement step 936 of the bush 93 overcomes the engagement claw 955 of the casing 95, with the engagement claw 955 deforming, so that the engagement step 936 faces the engagement claw 955 below it. In this state, the bush 93 can be prevented from coming out upward relative to the casing 95. The engagement step 936 and the engagement claw 955 have a shape that allows slight rotation and slight vertical movement of the bush 93 relative to the casing 95, and are positioned to allow slight rotation and slight vertical movement of the bush 93.

[0052] As shown in Figures 6 and 8, the casing 95 includes a leaf spring 97 that presses the rear end of the shaft portion 911 of the charging roller 91 toward the front. The leaf spring 97 is an example of a pressing member. The casing 95 has three bosses 954 for fixing the leaf spring 97 to the rear side of the sleeve 951 through which the pivot shaft 934 of the bush 93 is inserted. The leaf spring 97 is positioned to press toward the front the end of the shaft portion 911 of the charging roller 91 that protrudes toward the rear side of the bearing groove 931 of the bush 93 mounted in the housing portion 950. The shape of the leaf spring 97 can be anything, and other pressing members such as coil springs may be provided instead of the leaf spring 97.

[0053] As shown in Figure 9, the front bush 94 has a bearing groove 941 that rotatably receives the front end of the shaft portion 911 of the charging roller 91, and a bearing hole 942 that rotatably receives the front end of the shaft portion 921 of the cleaning roller 92. The front end of the bearing groove 941 is closed by an end wall 9411. The bearing hole 942 is a bottomed hole with a closed front end. The bearing groove 941 is located in front of and opposite to the bearing groove 931 of the rear bush 93, and the bearing hole 942 is located in front of and opposite to the bearing hole 932 of the rear bush 93. The bush 94 functions essentially the same as the rear bush 93.

[0054] The front bush 94 has a boss 944 for attaching the upper end of the compression spring 96 at a position corresponding to the pivot axis 934 of the rear bush 93. The boss 944 is a cylindrical projection with an axis along the vertical direction. The boss 944 is positioned perpendicular to the bearing groove 941 and the bearing hole 942. The central axis of the boss 944 intersects with the center of the shaft portion 911 of the electrostatic roller 91 received in the bearing groove 941. The lower end of the compression spring 96 is fixed to the bottom of the casing 95. The compression spring 96 is installed in a compressed state between the bottom of the casing 95 and the boss of the bush 94.

[0055] The outer surface of the bush 94 in the left-right direction has two sliding grooves 945 that extend in the vertical direction. The two sliding grooves 945 are positioned opposite each other in the left-right direction. The casing 95 has two rails (not shown) on the left and right sides of the housing 950 at the position where the bush 94 is to be installed. The two rails extend in the vertical direction at positions where they fit into the two sliding grooves 945 of the bush 94 when the bush 94 is installed in the housing 950. The bush 94 is movable relative to the casing 95 in the vertical direction along the sliding grooves 945.

[0056] The compression spring 96, positioned between the casing 95 and the bush 94 in a compressed state, applies force to the bush 94 upward, with the point of force passing through its center. The bush 94 is pushed upward by the compression spring 96 in the direction of the slide groove 945, thereby pushing upward the front ends of the shaft portion 911 of the charging roller 91 and the shaft portion 921 of the cleaning roller 92. As a result, the front side of the charging roller 91 is pressed against the photoreceptor drum 41.

[0057] As shown in Figures 7 and 8, the casing 95 is provided with two engagement pins 956 near its rear end. The rear end of the casing 95 is a free end. The two engagement pins 956 protrude outward from the left-right outer surface of the casing 95, spaced apart from each other, and are arranged coaxially. A frame (not shown) to which the photoreceptor drum 41 is rotatably mounted has two grooves (not shown) that engage with the two rear engagement pins 956 of the casing 95 of the charging device 90, respectively. The grooves in the frame are located below the photoreceptor drum 41 near its rear end, extending in the front-rear direction at opposing positions on the left and right, with their rear ends open. To engage the rear end of the casing 95 with the grooves in the frame, the engagement pins 956 of the casing 95 are inserted into the grooves from the rear side of the grooves, and the two engagement pins 956 are engaged with the grooves in the frame. Therefore, the rear end of the casing 95 is slightly movable in the front-to-back direction along the groove.

[0058] As shown in Figure 3, the casing 95 is provided with two engaging claws 957 near its front end. The front end of the casing 95 is a fixed end. The engaging claws 957 protrude outward from the left-right outer surface of the casing 95. A frame (not shown) to which the photoreceptor drum 41 is attached has a stepped portion (not shown) that engages with the two engaging claws 957 of the casing 95. When attaching the front end of the casing 95 to the frame, the casing 95, with its two engaging pins 956 at the rear end hooked into grooves in the frame, is rotated around the two engaging pins 956 in a direction approaching the photoreceptor drum 41, causing the engaging claws 957 to engage with the stepped portion of the frame through elastic deformation of the claws 957. In this state, the front portion (not shown) of the casing 95 is fastened and fixed to the frame of the photoreceptor drum 41 with screws (not shown).

[0059] Furthermore, the grooves and steps (not shown) of the frame to which the photoreceptor drum 41 is attached are positioned such that the outer surface 913 of the charging roller 91 is pressed against the surface of the photoreceptor drum 41 when the rear side of the casing 95 is hooked into the grooves of the frame and the front side is fixed to the frame.

[0060] Next, the functions of the charging device 90 described above will be explained. When the long casing 95 of the charging device 90 is molded from resin, the casing 95 is more prone to bending than the charging rollers 91 and cleaning rollers 92 which have metal shafts 911 and 921. When the casing 95 bends and curves, it is conceivable that undesirable stresses will be applied to the bushings 93 and 94 attached to both ends of the casing 95 in the longitudinal direction.

[0061] If the casing 95 is deflected in the vertical direction, the bushes 93 and 94 will be inclined in the direction of the openings of the bearing grooves 931 and 941, so there will be almost no load on the shaft portion 911 of the charging roller 91 due to contact resistance. In contrast, if the casing 95 is deflected and bent in the horizontal direction, a stress will act on the shaft portion 911 of the charging roller 91, which is less flexible, causing it to bite into the left and right inner surfaces of the bearing grooves 931 and 941 of the bushes 93 and 94.

[0062] For example, if the bushing 93 on the rear side of this embodiment is not mounted so as to be rotatable relative to the casing 95 around the pivot axis 934, but is mounted so as to be slidable only vertically relative to the casing 95 by means of a slide groove or rail, similar to the bushing 94 on the front side, then the left-right curvature of the casing 95 will cause the bushings 93 and 94 to tilt left-right relative to the shaft portion 911 of the charging roller 91. In this case, even a slight tilt of the bushings 93 and 94 relative to the shaft portion 911 will cause the shaft portion 911 to bite into the inner surfaces of the bearing grooves 931 and 941, creating contact resistance between them.

[0063] As described above, the rear bush 93 of this embodiment is rotatably mounted to the casing 95 around the pivot axis 934. Therefore, even if the casing 95 bends in the left-right direction, the bush 93 can rotate in the left-right direction relative to the casing 95, and the shaft portion 911 of the charging roller 91 and the bearing groove 931 of the bush 93 can always be positioned straight. For this reason, according to this embodiment, even if the casing 95 bends in the left-right direction, it is possible to prevent the problem of unwanted stress being applied to the shaft portion 911 of the charging roller 91 from the bush 93, and the charging roller 91 can rotate normally.

[0064] For example, as shown in Figure 10, if the casing 95 is curved in such a way that its center in the front-to-back direction bulges to the left, the rear end of the casing 95, which is fixed to the frame of the photoreceptor drum 41 at the front, will tilt slightly to the right (downward in the figure). In this case, the casing 95 rotates slightly clockwise around the pivot axis 934 relative to the bush 93 that supports the rear side of the shaft portion 911 of the charging roller 91, thereby suppressing the problem of undesirable stress acting on the bush 93.

[0065] Furthermore, for example, as shown in Figure 11, if the casing 95 is curved in such a way that its center in the front-to-back direction bulges to the right, the rear end of the casing 95, which is fixed to the frame of the photoreceptor drum 41 at the front, will tilt slightly to the left (upward in the figure). In this case, the casing 95 rotates slightly counterclockwise around the pivot axis 934 relative to the bush 93 that supports the rear side of the shaft portion 911 of the charging roller 91, thereby suppressing the problem of undesirable stress acting on the bush 93.

[0066] As described above, according to this embodiment, even if the casing 95 of the charging device 90 becomes deflected, it is possible to prevent unwanted stress from acting on the shaft portion 911 of the charging roller 91, the charging roller 91 can always rotate normally, no unnecessary load is placed on the photoreceptor drum 41, and the occurrence of image defects can be suppressed.

[0067] Furthermore, according to this embodiment, even if the casing 95 is deflected, no unwanted stress is applied to the charging roller 91. Therefore, the play between the bearing grooves 931 and 941 of the bushings 93 and 94 and the shaft portion 911 of the charging roller 91 can be reduced, and the positioning accuracy of the charging roller 91 relative to the photoreceptor drum 41 can be improved.

[0068] Furthermore, according to this embodiment, since the compression spring 96 that biases the rear bush 93 toward the photoreceptor drum 41 is coaxially attached to the outside of the sleeve 951 of the casing 95 through which the pivot shaft 934 of the bush 93 is rotatably inserted, the central axis of the charging roller 91 can be positioned on the center line of the compression spring 96, and the charging roller 91 can be pushed straight upward toward the photoreceptor drum 41.

[0069] Furthermore, according to this embodiment, since a compression spring 96 is mounted around the outside of the sleeve 951 that rotatably and slidably supports the pivot shaft 934 of the rear bush 93, a sliding groove or rail for supporting the bush 93 to slide up and down is unnecessary, and the boss that holds the upper end of the compression spring 96 can be used interchangeably with the pivot shaft 934, thereby simplifying the configuration.

[0070] Furthermore, according to this embodiment, since the rear bush 93 has a columnar surface 935 that can slide against the sliding contact surface 953 of the casing 95 in addition to the pivot shaft 934, tilting of the bush 93 in the left-right direction can be suppressed at a position spaced above the pivot shaft 934, allowing the bush 93 to rotate in a straight position and suppressing the generation of unwanted stress.

[0071] Furthermore, according to this embodiment, a bush 93 that can rotate relative to the casing 95 is provided on the free end side (i.e., the rear side) opposite to the fixed end of the casing 95 that is fixed to the frame supporting the photoreceptor drum 41. This ensures the positional accuracy of the charging roller 91 relative to the photoreceptor drum 41 via the casing 95 and bush 94.

[0072] While embodiments of the present invention have been described above, these embodiments are presented as examples only and are not intended to limit the scope of the invention. The embodiments described above 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 embodiments described above are included in the scope and spirit of the invention, as well as in the claims of the invention and its equivalents. [Explanation of Symbols]

[0073] 41...Photoreceptor drum, 90...Charging device, 91...Charging roller, 911...Shaft, 913...Outer surface, 92...Cleaning roller, 921...Shaft, 93, 94...Bushing, 931, 941...Bearing groove, 932, 942...Bearing hole, 934...Rotating shaft, 935...Columnar surface, 945...Slide groove, 95...Casing, 950...Housing section, 951...Sleeve, 953...Sliding contact surface, 96...Pressure spring, 97...Leaf spring, 100...Image forming apparatus, 151, 152, 153, 154...Image forming section, P...Paper.

Claims

1. Image carrier and, A charging roller that makes rolling contact with the surface of the image carrier and charges the surface, A case housing the aforementioned charging roller, A bearing is rotatably mounted to the case around a pivot axis extending in the direction in which the image carrier and the charging roller are aligned, and which rotatably supports the axis of the charging roller. An image forming apparatus having

2. The charging rollers are biased in the direction they are aligned and pressed against the surface of the image carrier, The image forming apparatus according to claim 1.

3. The pressing means includes a pressing spring arranged coaxially with the pivot axis between the case and the bearing. The image forming apparatus according to claim 2.

4. The bearing includes the pivot shaft, The case has a sleeve through which the pivot shaft is rotatably inserted. The image forming apparatus according to claim 3.

5. The sleeve has a hole that penetrates the case, The image forming apparatus according to claim 4.

6. The compression spring is attached coaxially to the outside of the sleeve. The image forming apparatus according to claim 4.

7. The bearing has a columnar surface formed by rotating a line parallel to the pivot axis around the pivot axis, The case has a sliding contact surface that can slide against the columnar surface, The image forming apparatus according to claim 1.

8. The case has a fixed end that is positioned and fixed relative to the image carrier, and a free end opposite to the fixed end along the axis of the charging roller. The bearing is attached to the free end side of the case. The image forming apparatus according to claim 1.

9. The bearing has a groove that opens on the image carrier side to receive the shaft of the charging roller, The case includes a pressing member that presses the shaft received in the groove toward the fixed end in the axial direction. The image forming apparatus according to claim 8.

10. The end of the groove on the pressing member side is open. The image forming apparatus according to claim 9.

Images