Image forming apparatus

Abstract

To provide an image forming apparatus that can maintain the positioning accuracy of an exposure head.SOLUTION: An image forming apparatus 1 comprises: a body housing 10 that includes a boss 21; a photoconductor drum 51 that can be accommodated in the body housing 10; an exposure head 40 that exposes the photoreceptor drum 51, the exposure head 40 movable between an exposure position where it exposes the photoreceptor drum 51 and a retreat position where it is separated from the photoreceptor drum 51 compared with the exposure position; and a positioning piece 90 that positions the exposure head 40 with respect to the body housing 10, the positioning piece including a cylinder 91 fitted to the boss 21 of the body housing 10, and an arc surface 92 concentric with a peripheral surface of the cylinder 91 and in contact with the exposure head 40.SELECTED DRAWING: Figure 14

Description

Technical Field

[0001] The present invention relates to an image forming apparatus.

Background Art

[0002] Conventionally, as disclosed in Patent Document 1, there is known an image forming apparatus including a main body housing, a plurality of exposure heads each having an LED at a tip, and a plurality of process cartridges including a developing cartridge and being attachable to the main body housing. The main body housing has a groove for positioning an exposure head at an exposure position in a sub-scanning direction, and a second member (corresponding to a positioning member) into which the exposure head inserted into the groove is positioned.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the image forming apparatus described in Patent Document 1, when the position of the positioning member (second member) in the main body housing is displaced, the exposure head cannot be positioned at the correct position of the main body housing, and there is a risk that the positioning accuracy of the exposure head may be reduced.

[0005] Therefore, in the present invention, there is provided an image forming apparatus capable of maintaining the positioning accuracy of an exposure head.

Means for Solving the Problems

[0006] The image forming apparatus for solving the above problems has the following features.

[0007] That is, the image forming apparatus comprises a housing with bosses, a photoreceptor drum housed in the housing, an exposure head for exposing the photoreceptor drum, the exposure head being movable between an exposure position for exposing the photoreceptor drum and a retracted position further away from the photoreceptor drum than the exposure position, and a positioning piece for positioning the exposure head relative to the housing, the positioning piece comprising a cylinder that fits into the bosses of the housing and an arcuate surface concentric with the circumferential surface of the cylinder that contacts the exposure head.

[0008] With the above configuration, since the arcuate surface is concentric with the cylinder, the positioning accuracy of the exposure head can be maintained even if the positioning piece rotates around the boss.

[0009] Furthermore, the positioning piece comprises a plate extending from the cylinder, and the housing comprises a groove recessed in the axial direction of the cylinder, into which the plate is fitted.

[0010] This means that the plate, fitted into the groove, prevents the positioning piece from rotating relative to the boss.

[0011] Furthermore, the cylinder has a through hole, and the positioning piece comprises a first hook that passes through the through hole of the cylinder and has a first claw that protrudes from the side opposite to the side where the arcuate surface is located relative to the cylinder and engages with the housing.

[0012] This allows the first hook to pass through the through-hole of the cylinder, thus enabling miniaturization of the positioning piece.

[0013] Furthermore, the plate is positioned on the side of the cylinder where the arcuate surface is located, and the positioning piece is a second hook extending from the plate and positioned opposite the first hook, and includes a second hook having a second claw that protrudes on the side of the cylinder where the arcuate surface is located and engages with the housing.

[0014] As a result, the first claw of the first hook and the second claw of the second hook protrude to opposite sides, making it difficult for the positioning piece to detach from the housing.

[0015] Furthermore, the plate includes a pressing surface that presses the exposure head, located at the exposure position, inward in the axial direction of the photoreceptor drum.

[0016] This allows the exposure head to be stably held in the exposure position.

[0017] Furthermore, the housing is equipped with a detachable drum cartridge, and the drum cartridge is equipped with the photoreceptor drum.

[0018] Furthermore, the drum cartridge has positioning ribs for positioning the drum cartridge mounted in the housing, the housing has a first groove for guiding the movement of the positioning ribs, and a second groove that branches off from the first groove and guides the movement of the photoreceptor drum, and the arcuate surface has a first guide surface for guiding the positioning ribs to the first groove and a second guide surface for guiding the photoreceptor drum to the second groove.

[0019] This allows the positioning rib to be guided into the first groove and the photoreceptor drum to be guided into the second groove to be performed on a single arc-shaped surface. This makes it possible to miniaturize the positioning piece.

[0020] Furthermore, the positioning piece is made of a material with higher sliding properties than the housing.

[0021] In this way, by making the positioning piece from a material with higher sliding properties than the housing, the exposure head can be smoothly inserted to the exposure position.

[0022] Furthermore, the radius of curvature of the arcuate surface is greater than the radius of curvature of the cylinder.

[0023] This allows the exposure head to be smoothly guided to the exposure position. [Effects of the Invention]

[0024] According to the present invention, the positioning accuracy of the exposure head can be maintained.

Brief Description of the Drawings

[0025] [Figure 1] It is a central cross-sectional view showing an image forming apparatus. [Figure 2] It is a front view showing an exposure head and a process cartridge located at an exposure position. [Figure 3] It is a perspective view showing an exposure head. [Figure 4] It is a perspective view showing a process cartridge. [Figure 5] It is a side view showing a process cartridge. [Figure 6] It is a perspective view showing the inner side surface of the main body housing. [Figure 7] It is a view for explaining a state in which a process cartridge is mounted on the main body housing and an exposure head is positioned at an exposure position. [Figure 8] It is a partially enlarged view of FIG. 7. [Figure 9] (a) and (b) are perspective views showing positioning pieces. [Figure 10] (a) and (b) are perspective views showing positioning pieces. [Figure 11] It is a side view showing a side frame before attaching a positioning piece. [Figure 12] It is a side view showing a state in which a positioning piece is attached to a side frame. [Figure 13] It is a partially enlarged view of the arrow A portion of FIG. 12. [Figure 14] It is a partially enlarged view of the arrow B portion of FIG. 7. [Figure 15] It is a cross-sectional view taken along the C-C line of FIG. 7. [Figure 16] It is a partially enlarged view of the arrow D portion of FIG. 15.

Modes for Carrying Out the Invention

[0026] Next, embodiments for carrying out the present invention will be described with reference to the attached drawings.

[0027] [Overall configuration of the image forming apparatus] The image forming apparatus 1 shown in Figure 1 is one embodiment of the image forming apparatus according to the present invention, and is a color laser printer that forms a multi-color image on paper S using an electrophotographic method.

[0028] In the following explanation, the image forming apparatus 1 will be positioned horizontally as the reference point. The right side of Figure 1 will be referred to as the "front," and the left side as the "rear." The left and right sides will be defined as the view of the image forming apparatus 1 from the front, with the left and right directions being referred to as the "left" and "right," respectively. That is, the front of Figure 1 is the left side, and the back of Figure 1 is the right side. In addition, the vertical downward direction will be referred to as the "downward side," and the vertical upward direction will be referred to as the "upward side."

[0029] As shown in Figure 1, the image forming apparatus 1 mainly comprises a main body housing 10, which is an example of a housing, a cover 11, and a paper feeding unit 20 and an image forming unit 30 provided inside the main body housing 10. The image forming apparatus 1 is, as an example, a color printer.

[0030] The cover 11 is positioned on the opposite side of the exposure head 40 from the side where the photoreceptor drum 51 is located, specifically on the upper part of the main housing 10. The cover 11 is rotatably supported on the main housing 10 around a pivot axis 11A, and opens and closes an opening 10A formed on the upper part of the main housing 10. More specifically, the cover 11 rotates around an axis parallel to the left-right direction, which is located at a position rearward from the photoreceptor drum 51. As a result, the cover 11 is rotatable between a closed position that closes the opening 10A and an open position that opens the opening 10A.

[0031] The paper feeding unit 20 is located at the bottom of the main body housing 10 and mainly comprises a paper feeding tray 25 for storing paper S and a paper supply mechanism 26 for supplying paper S from the paper feeding tray 25 to the image forming unit 30. The paper S in the paper feeding tray 25 is separated one sheet at a time by the paper supply mechanism 26 and supplied to the image forming unit 30. A transport path P for paper S is configured within the main body housing 10, from the paper feeding tray 25 through the image forming unit 30 to the output tray 11B.

[0032] The image forming unit 30 mainly consists of four exposure heads 40, four process cartridges PC, a transfer unit 70, and a fixing unit 80.

[0033] The exposure head 40 has multiple LEDs at its tip and is supported by the cover 11 so as to be suspended from the cover 11. When the cover 11 is closed, it is positioned opposite the photoreceptor drum 51. Specifically, the exposure head 40 can move between an exposure position where the photoreceptor drum 51 is exposed and a retracted position further away from the photoreceptor drum 51 than the exposure position, by opening and closing the cover 11. The exposure head 40 exposes the surface of the photoreceptor drum 51 by having the multiple LEDs blink based on the image data. The structure of the exposure head 40 will be described in detail later.

[0034] As shown in Figure 2, the main housing 10 comprises a right side frame 200 and a left side frame 201, which are spaced apart from each other in the left-right direction. The right side frame 200 is located at the right end of the main housing 10 and extends in the front-rear and up-down directions. The left side frame 201 is located at the left end of the main housing 10 and extends in the front-rear and up-down directions.

[0035] The process cartridge PC is positioned between the right side frame 200 and the left side frame 201, and is detachably supported by the side frames 200 and 201. In other words, the process cartridge PC is detachably (housed) in the main body housing 10. The side frame 200 is located to the right of the process cartridge PC and supports the right end of the process cartridge PC.

[0036] The side frame 201 is located to the left of the process cartridge PC and supports the left edge of the process cartridge PC. The process cartridge PC is an example of a drum cartridge. Each process cartridge PC is provided to correspond to the colors black, yellow, magenta, and cyan.

[0037] Each process cartridge PC is arranged in parallel along the front-to-back direction between the cover 11 and the paper feed tray 25. Each process cartridge PC can be installed into the main body housing 10 through the opening 10A when the cover 11 is open. Each process cartridge PC comprises a drum unit 50 and a developing cartridge 60 that can be attached to or removed from the drum unit 50.

[0038] The drum unit 50 includes a cylindrical photoreceptor drum 51, a charger 52 for charging the photoreceptor drum 51, a pressure spring 53 for biasing the developing cartridge 60 toward the photoreceptor drum 51, a cleaning roller 54, and a drum frame 55 for supporting the photoreceptor drum 51 and the like.

[0039] The cleaning roller 54 is a roller that removes foreign matter such as toner remaining on the photoreceptor drum 51. The cleaning roller 54 is rotatable in contact with the photoreceptor drum 51.

[0040] The developing cartridge 60 mainly comprises a toner storage section 61 for storing toner and a developing roller 62 for supplying the toner from the toner storage section 61 to the photoreceptor drum 51.

[0041] The transfer unit 70 is located between the paper feed tray 25 and the process cartridge PC. The transfer unit 70 mainly comprises a drive roller 71, a driven roller 72, an endless conveyor belt 73 stretched between the drive roller 71 and the driven roller 72, and four transfer rollers 74. The outer surface of the conveyor belt 73 is in contact with each photoreceptor drum 51, and the inner side of the conveyor belt 73 is arranged so as to sandwich the conveyor belt 73 between itself and each photoreceptor drum 51.

[0042] The fixing unit 80 is located behind the process cartridge PC and the transfer unit 70, and mainly comprises a heating roller 81 and a pressure roller 82 positioned opposite the heating roller 81 to press against it.

[0043] In this image forming unit 30, the surface of the photoreceptor drum 51 is uniformly charged by the charger 52 and then exposed by the exposure head 40, thereby forming an electrostatic latent image on the photoreceptor drum 51 based on image data. Then, toner is supplied to the photoreceptor drum 51 from the developing roller 62, causing the electrostatic latent image to become visible and forming a toner image on the photoreceptor drum 51.

[0044] The toner images formed on each photoreceptor drum 51 are sequentially transferred onto the paper S being transported on the transport belt 73 by the transfer roller 74. The paper S on which the toner images have been transferred is transported between the heating roller 81 and the pressure roller 82, whereupon the toner images are heat-fixed. After that, the paper S is discharged from inside the main body casing 10 to the outside by the transport roller 100 and placed on the output tray 11B formed on the upper surface of the cover 11.

[0045] [Exposure head] Next, we will describe the exposure head 40 and the structure surrounding the exposure head 40. As shown in Figure 2, in this embodiment, the rotation axis X of the photoreceptor drum 51 extends in the left-right direction. In the following description, the direction in which the rotation axis X extends, that is, the left-right direction, will also simply be referred to as the "axial direction".

[0046] As shown in Figures 2 and 3, the exposure head 40 includes a first frame 110 and a second frame 120, a spacing adjustment member 130 positioned between the second frame 120 and the drum unit 50, a pressing member 160, and a rib 170. The spacing adjustment member 130 is a member that contacts one end of the drum unit 50 to define the distance in the optical axis direction from the lens array 112 to the surface of the photoreceptor drum 51.

[0047] The first frame 110 and the second frame 120 are made of resin.

[0048] The first frame 110 has a roughly rectangular base portion 111 that is elongated in the left-right direction. The base portion 111 is made of resin.

[0049] Multiple LED arrays (not shown) are provided within the base portion 111. The multiple LED arrays are arranged in the direction of the rotation axis. A lens array 112, which is an example of an optical element that images light from the LED array onto the surface of the photoreceptor drum 51, is provided in the opening at the bottom of the base portion 111.

[0050] The LED array is a semiconductor element having multiple light-emitting units (LEDs) arranged in the direction of the rotation axis, and the surface of the photoreceptor drum 51 is scanned and exposed by the sequential blinking of each light-emitting unit in the direction of the rotation axis. The lower surface of the lens array 112 is the light-emitting surface and faces the surface of the photoreceptor drum 51.

[0051] The direction in which the photoreceptor drum 51 is scanned in the direction of the rotation axis by multiple LED arrays aligned in the direction of the rotation axis is the main scanning direction. The optical axis direction of the light emitted from the LED array (light emitted from the lens array 112 to the photoreceptor drum 51) is the optical axis direction. Furthermore, the direction perpendicular to both the optical axis direction and the main scanning direction is the sub-scanning direction. In this embodiment, the sub-scanning direction substantially coincides with the direction in which each process cartridge PC is aligned and the front-to-back direction.

[0052] The second frame 120 is a frame that supports the first frame 110 and is supported by a resin holder that is rotatably supported by the cover 11. The second frame 120 integrally has a roughly rectangular base portion 121 that is long in the left-right direction and two protrusions 125 that protrude downward from both the left and right ends of the base portion 121.

[0053] As shown in Figure 3, the pressing member 160 is provided on one side of the second frame 120 in the direction of the rotation axis, in this embodiment, on the right side. The pressing member 160 is a member that presses the exposure head 40, which is in the exposure position, in the sub-scanning direction. The pressing member 160 has a base portion 161, a pressing portion 162, and a spring 163 (see Figure 8). As will be described later, the pressing member 160 is a member that enters into groove 210 or groove 210B (see Figure 6), which is an example of a second groove in the right side frame 200 of the main body housing 10, and is positioned relative to the main body housing 10.

[0054] The base portion 161 has a box shape and a spring 163 is located inside. The base portion 161 also has a projection 161A on the side surface of its axial end. The pressing portion 162 is located in front of the base portion 161 and is supported so as to be movable relative to the base portion 161 in the sub-scanning direction. The pressing portion 162 has a sliding contact surface 162A that is bent in a convex shape when viewed from the optical axis direction. The pressing portion 162 is made of a highly sliding resin such as polyacetal (POM). The pressing portion 162 is biased forward in the sub-scanning direction by the spring 163 inside the base portion 161.

[0055] The projection 161A is biased to the right by a spring 122 (see Figure 2) located inside the second frame 120. The spring 122 imparts a biasing force to the projection 161A in the rightward direction.

[0056] The rib 170 is located on the other side of the second frame 120 in the direction of the rotation axis, which in this embodiment is on the left side. The rib 170 is a member that fits into a groove in the left side frame 201 (see Figures 2 and 15) of the main housing 10 and is positioned relative to the main housing 10. The rib 170 has a plate shape that extends in the direction of the optical axis.

[0057] As shown in Figures 4 and 5, the drum frame 55 has an arc portion 55A and a guided portion 55B. The arc portion 55A is an arc-shaped part that extends along the circumference centered on the axis of rotation X. The arc portion 55A is provided on both sides of the drum frame 55 in the axial direction.

[0058] The guided portion 55B is the part that engages with the groove 210 or groove 210C (see Figure 7) of the main housing 10 to guide the mounting of the drum unit 50. The groove 210 branches off from the middle of the groove 220 and guides the movement of the photoreceptor drum 51. The guided portion 55B protrudes axially from one side of the drum frame 55 in the axial direction, in this embodiment from the right side, compared to the photoreceptor drum 51.

[0059] The guided portion 55B may have a plate shape extending in the mounting direction of the drum unit 50. More specifically, the tip portion 55C of the guided portion 55B in the mounting direction is tapered. As will be described in detail later, when the drum unit 50 is mounted on the main housing 10, a portion of the guided portion 55B contacts the groove to position the drum unit 50. The position of the drum unit 50 when mounted on the main housing 10 is called the mounting position.

[0060] The developing cartridge 60 has a protrusion 61A on its right side in the axial direction. The protrusion 61A passes through a groove 220 in the main housing 10 when the process cartridge PC containing the developing cartridge 60 is mounted in the main housing 10. The protrusion 61A is an example of a positioning rib for positioning the process cartridge PC mounted in the housing. The groove 220 guides the movement of the protrusion 61A. The groove 220 is an example of a first groove.

[0061] As shown in Figure 6, the right-side frame 200 of the main housing 10 has two drum positioning units 230, corresponding to each process cartridge PC.

[0062] As shown in Figure 7, the drum positioning sections 230 are positioned below the rotation axis X of the mounted drum unit 50, with one located in front of and one behind the rotation axis X. When the drum unit 50 is mounted in the main housing 10, the arc portion 55A of the drum frame 55 contacts the drum positioning sections 230 of the main housing 10 to position the drum unit 50. In particular, the arc portion 55A positions the rotation axis X of the photoreceptor drum 51 supported by the drum unit 50.

[0063] The drum units 50 are arranged in a row of four in the front-to-back direction (sub-scanning direction), corresponding to black, cyan, magenta, and yellow, respectively, from rear to front. The four exposure heads 40 correspond to the four photoreceptor drums 51 that are exposed, with the photoreceptor drums 51 arranged in a row in the sub-scanning direction.

[0064] The main casing 10 has three grooves 210 and one groove 210C as grooves to guide the installation of the drum unit 50. Each groove 210, 210C extends downward from the upper end on the inner surface of the side frame 200.

[0065] Groove 210C is the rearmost of the four grooves 210,210C, and guides the mounting of the rearmost drum unit 50 of the four drum units 50. Three grooves of the same shape are arranged in a line in the sub-scanning direction in front of groove 210C. Groove 210 is the second groove that guides the mounting of the drum unit 50.

[0066] The three grooves 210 not only guide the mounting of the drum unit 50, but also have the function of positioning the exposure heads 40 in the sub-scanning direction when the three exposure heads 40 are in the exposure position. In other words, the three grooves 210 guide the mounting of the drum unit 50 and position the exposure heads 40 in the exposure position in the sub-scanning direction.

[0067] Grooves 210 and 210C guide the guided portion 55B of the drum unit 50 by engaging with it. Grooves 210C and 210 each have a frame positioning surface 213 that contacts the upper part of the guided portion 55B of the drum unit 50 in the mounting position. The frame positioning surface 213 is part of the rear surface of grooves 210 and 210C.

[0068] The main housing 10 further has grooves 210B for positioning the frontmost exposure head 40 in the sub-scanning direction.

[0069] As shown in Figure 8, grooves 210 and 210B have a recess 211 into which at least a portion of the pressing member 160 fits, and an arcuate surface 92 of the positioning piece 90, which will be described in detail later. The recess 211 has a contact surface 211A that extends in the vertical direction, and an auxiliary guide surface 211B that extends diagonally downward from the lower end of the contact surface 211A. When the exposure head 40 is in the exposure position, a portion of the pressing portion 162 of the pressing member 160 enters the recess 211 and contacts the contact surface 211A.

[0070] The arcuate surface 92 is the part that the base portion 161 of the exposure head 40 in the exposure position contacts (see Figure 14). The main body housing 10 has a side frame 200 which is a component that constitutes the main body portion (parts other than the positioning piece 90) of the grooves 210 and 210B, and a positioning piece 90 which has an arcuate surface 92 on which the exposure head 40 corresponding to the grooves 210 and 210B is positioned. The positioning piece 90 is made of a material with higher sliding properties than the material that constitutes substantially the entire side frame 200. High sliding properties here mean that the coefficient of friction with respect to the base portion 161 is small.

[0071] When the drum unit 50 is mounted in the main housing 10, the rotation axis X does not coincide with the groove 210 when viewed from the axial direction. Also, when the drum unit 50 is mounted in the main housing 10, the photoreceptor drum 51 does not coincide with the groove 210 when viewed from the axial direction. In other words, the photoreceptor drum 51 is inserted deep into the main housing 10 relative to the groove 210, and is not directly positioned by the groove 210. As described above, it is positioned by the arc portion 55A contacting the drum positioning portion 230.

[0072] As shown in Figure 7, the main housing 10 has four grooves 220 through which the protrusions 61A of the four developing cartridges 60 pass. The four grooves 220 are arranged in a line in the sub-scanning direction. More specifically, the grooves 220 are formed separately from grooves 210, 210B, and 210C, and are located between groove 210C and groove 210, between grooves 210, or between groove 210 and groove 210B.

[0073] Furthermore, the left side frame 201 of the main housing 10 has a different groove than the right side frame 200. While a detailed explanation is omitted, the left end of the drum unit 50 and the exposure head 40 are positioned using a different configuration than the right end.

[0074] [Main casing (right side frame)] The right side frame 200 and the left side frame 201 of the main housing 10 are positioned opposite each other with a gap between them in the left-right direction. As shown in Figure 11, the right side frame 200 includes a boss 21, a fitting groove 22, a first engagement hole 23, and a second engagement hole 24, all located in the middle of the groove 210.

[0075] The boss 21 is located midway through each groove 210 in the vertical direction. The boss 21 is cylindrical and protrudes to the left. The boss 21 is positioned opposite the recess 211 of the groove 210 in the front-rear direction. The cylindrical 91 of the positioning piece 90 is fitted onto the boss 21.

[0076] The fitting groove 22 is located behind the boss 21. The fitting groove 22 is formed in a roughly rectangular shape in side view, recessed outward in the left-right direction (recessed in the axial direction of the cylinder 91), and the plate 93 of the positioning piece 90 can be fitted into it. The fitting groove 22 is the part that positions the positioning piece 90 relative to the side frame 200 by fitting the plate 93 into it.

[0077] The engagement hole 23 is a hole that engages with the first claw 94a of the first hook 94, which will be described later. The engagement hole 23 is opened in the main housing 10 (side frame 200) at a position corresponding to the first claw 94a of the first hook 94.

[0078] The engagement hole 24 is a hole that engages with the second claw 95a of the second hook 95, which will be described later. The engagement hole 24 is opened in the main housing 10 (side frame 200) at a position corresponding to the second claw 95a of the second hook 95.

[0079] [Positioning piece] The positioning piece 90 positions the exposure head 40 relative to the main housing 10. As shown in Figures 9 and 10, the positioning piece 90 comprises a cylinder 91 that fits into a boss 21 of the main housing 10, an arcuate surface 92 that is concentric with the circumferential surface of the cylinder 91 and contacts the exposure head 40, a plate 93 extending rearward from the cylinder 91, a first hook 94, and a second hook 95.

[0080] The cylinder 91 has a through hole 91a that penetrates in the axial direction (left-right direction). The boss 21 of the side frame 200 is fitted into the through hole 91a. The arcuate surface 92 is the part that the base portion 161 of the exposure head 40, which is in the exposure position, contacts (strikes) with. The arcuate surface 92 is concentric with the circumferential surface of the cylinder 91 and is positioned to overlap the front portion of the cylinder 91 in a side view.

[0081] According to the above configuration, when the positioning piece 90 is placed on the side frame 200 of the main housing 10, the arcuate surface 92 is concentric with the cylinder 91. Therefore, even if the positioning piece 90 rotates around the boss 21 of the main housing 10, for example, the positioning accuracy of the exposure head 40 can be maintained.

[0082] The plate 93 is approximately rectangular in side view and comprises a plate-shaped plate body 93a and a rectangular pressing surface 93b provided on the surface of the plate body 93a. The pressing surface 93b protrudes to the left from the left end face of the plate body 93a. The plate 93 is positioned on the side (rear side) where the arcuate surface 92 is located relative to the cylinder 91. The plate 93 is fitted into a fitting groove 22 that is recessed in the axial direction of the cylinder 91 in the main body housing 10. The pressing surface 93b presses the pressing member 160 of the exposure head 40, which is located at the exposure position, in the axial direction inward (leftward) of the photoreceptor drum 51 against the rightward biasing force of the projection 161A of the pressing member 160 (see Figure 16).

[0083] In this way, the plate 93 fits into the fitting groove 22 of the main housing 10, preventing the positioning piece 90 from rotating relative to the boss 21 of the main housing 10. Furthermore, by pressing the pressing member 160 of the exposure head 40 with the pressing surface 93b, the exposure head 40 can be stably held in the exposure position.

[0084] As shown in Figure 10(a), the first hook 94 is formed to pass through the through hole 91a of the cylinder 91. The first hook 94 has a first claw 94a that protrudes in the axial direction of the cylinder 91 on the side opposite to the side where the arcuate surface 92 is located relative to the cylinder 91 and engages with the engagement hole 23 of the main housing 10.

[0085] As described above, since the first hook 94 is provided so as to pass through the through hole 91a of the cylinder 91, the positioning piece 90 can be made smaller compared to the case where the first hook 94 is provided on the outside of the cylinder 91.

[0086] The second hook 95 extends outward from the plate 93 in the left-right direction and is positioned opposite the first hook 94. The second hook 95 has a second claw 95a that protrudes toward the side (rear side) where the arcuate surface 92 is located relative to the cylinder 91 and engages with the engagement hole 24 of the main housing 10. As a result, the first claw 94a of the first hook 94 and the second claw 95a of the second hook 95 protrude toward opposite sides, ensuring secure engagement with the engagement hole 23 and the engagement hole 24, making it difficult for the positioning piece 90 to come off the main housing 10.

[0087] The positioning piece 90 is attached to the side frame 200 of the main housing 10 by fitting the boss 21 into the through hole 91a of the cylinder 91, fitting the plate 93 into the fitting groove 22 of the main housing 10, engaging the first claw 94a of the first hook 94 into the engagement hole 23 of the main housing 10, and engaging the second claw 95a of the second hook 95 into the engagement hole 24 of the main housing 10 (see Figures 12 and 13).

[0088] Furthermore, the arcuate surface 92 has a first guide surface 92a that guides the protruding portion 61A, which is an example of a positioning rib, to the first groove, groove 220, and a second guide surface 92b that guides the photoreceptor drum 51 to the second groove, groove 210. As a result, guiding the protruding portion 61A to the first groove, groove 220, and guiding the photoreceptor drum 51 to the second groove, groove 210, can be performed with a single arcuate surface 92. This makes it possible to miniaturize the positioning piece 90.

[0089] The positioning piece 90 is made of a separate component from the side frame 200 of the main housing 10. In this embodiment, the side frame 200 is made of ABS (acrylonitrile butadiene styrene) resin. The positioning piece 90 is made of a resin such as POM (polyoxymethylene), which has higher sliding properties than the main housing 10. The positioning piece 90 is made of a material with a lower coefficient of friction than the side frame 200.

[0090] Thus, by making the positioning piece 90 from a material with higher sliding properties than the side frame 200 of the main housing 10, the exposure head 40 can be smoothly inserted to the exposure position when it comes into contact with the positioning piece 90.

[0091] Furthermore, the positioning piece 90 is preferably made of a resin with better sliding properties than ABS resin, for example, and may be made of a resin other than POM.

[0092] Furthermore, it is preferable that the radius of curvature of the arcuate surface 92 is larger than the radius of curvature of the cylinder 91.

[0093] This allows the exposure head 40 to be smoothly guided to the exposure position.

[0094] In the image forming apparatus 1 configured as described above, when mounting the process cartridge into the main body housing 10, the guided portion 55B of the drum unit 50 is inserted into the groove 210 or groove 210C. As a result, the process cartridge PC is mounted while its approximate orientation is restricted by the grooves 210 and 210C. As the process cartridge PC is lowered, the protruding portion 61A of the process cartridge PC (developing cartridge 60) is guided into the groove 220 by the first guide surface 92a of the positioning piece 90, and the photoreceptor drum 51 is guided into the second groove, groove 210, by the second guide surface 92b. As the process cartridge PC is lowered as far as possible, the arc portion 55A of the drum unit 50 abuts against and is supported by a pair of drum positioning portions 230, and the photoreceptor drum 51 and the rotation axis X are positioned in a predetermined position.

[0095] When the lower surface of the guided portion 55B comes into contact with the frame positioning surface 213, the orientation of the drum frame 55 is determined to a predetermined position. When the drum unit 50 is in the mounting position, the protruding portion 61A of the developing cartridge 60 does not come into contact with the sides of the grooves 220 located in front of and behind the protruding portion 61A. In other words, the grooves 220 play a role in preventing the protruding portion 61A from interfering with the side frame 200 when the drum unit 50 is in the mounting position.

[0096] After each process cartridge PC is installed, as the cover 11 is closed, the pressing member 160 of the exposure head 40 is inserted into the groove 210 or groove 210B. The pressing member 160 moves downward through the groove 210 or groove 210B. When the cover 11 is completely closed, as shown in Figure 7, the base portion 161 of the pressing member 160 contacts the arcuate surface 92 of the positioning piece 90, and the pressing portion 162 contacts the contact surface 211A.

[0097] At this time, the pressing portion 162 is biased toward the contact surface 211A by the spring 163, so that the base portion 161 makes firm contact with the arcuate surface 92 and the exposure head 40 is positioned at a predetermined position in the sub-scanning direction. Almost simultaneously, as shown in Figure 16, the projection 161A of the pressing member 160 makes contact with the pressing surface 93b of the positioning piece 90. At this time, the projection 161A is biased toward the pressing surface 93b by the spring 122, so that the projection 161A makes firm contact with the pressing surface 93b of the positioning piece 90 and the exposure head 40 is positioned at a predetermined position in the left-right direction. [Explanation of Symbols]

[0098] 1. Image forming apparatus 10. Main unit (casing) 21 Boss 40 Exposure Heads 51 Photoconductor Drum 90 Positioning piece 91 Cylinder 92 Circular arc surface

Claims

1. A cabinet equipped with a boss, A photosensitive drum that can be housed in the aforementioned housing, An exposure head for exposing the photoreceptor drum, the exposure head being movable between an exposure position for exposing the photoreceptor drum and a retracted position further away from the photoreceptor drum than the exposure position, An image forming apparatus comprising a positioning piece for positioning the exposure head relative to the housing, the positioning piece having a cylinder that fits into the boss of the housing, and an arcuate surface that is concentric with the circumferential surface of the cylinder and contacts the exposure head.

2. A cabinet equipped with a boss, A photosensitive drum that can be housed in the aforementioned housing, An exposure head for exposing the photoreceptor drum, the exposure head being movable between an exposure position for exposing the photoreceptor drum and a retracted position further away from the photoreceptor drum than the exposure position, A positioning piece for positioning the exposure head relative to the housing, comprising a cylinder that fits into the boss of the housing, and a positioning piece having an arcuate surface concentric with the circumferential surface of the cylinder and in contact with the exposure head, The positioning piece comprises a plate extending from the cylinder, The image forming apparatus is characterized in that the housing has a groove recessed in the axial direction of the cylinder, and the plate is fitted into the groove.

3. The image forming apparatus according to claim 2, characterized in that the cylinder has a through hole, and the positioning piece is a first hook that passes through the through hole of the cylinder and has a first claw that protrudes from the side opposite to the side where the arcuate surface is located relative to the cylinder and engages with the housing.

4. The plate is positioned on the side of the cylinder where the arcuate surface is located. The image forming apparatus according to claim 3, characterized in that the positioning piece comprises a second hook extending from the plate and positioned opposite the first hook, the second hook having a second claw that protrudes from the cylinder on the side where the arcuate surface is located and engages with the housing.

5. The image forming apparatus according to claim 2 or 4, characterized in that the plate has a pressing surface that presses the exposure head located at the exposure position in the axial direction of the photoreceptor drum.

6. The aforementioned housing is equipped with a detachable drum cartridge, The image forming apparatus according to any one of claims 1, 2, or 4, characterized in that the drum cartridge comprises the photosensitive drum.

7. The drum cartridge has positioning ribs for positioning the drum cartridge mounted in the housing, The housing has a first groove that guides the movement of the positioning rib, and a second groove that branches off from the first groove and guides the movement of the photoreceptor drum. The image forming apparatus according to claim 6, characterized in that the arcuate surface has a first guide surface for guiding the positioning rib to the first groove and a second guide surface for guiding the photoreceptor drum to the second groove.

8. The image forming apparatus according to any one of claims 1, 2, or 4, characterized in that the positioning piece is made of a material with higher sliding properties than the housing.

9. A cabinet equipped with a boss, A photosensitive drum that can be housed in the aforementioned housing, An exposure head for exposing the photoreceptor drum, the exposure head being movable between an exposure position for exposing the photoreceptor drum and a retracted position further away from the photoreceptor drum than the exposure position, A positioning piece for positioning the exposure head relative to the housing, comprising a cylinder that fits into the boss of the housing, and a positioning piece having an arcuate surface concentric with the circumferential surface of the cylinder and in contact with the exposure head, An image forming apparatus characterized in that the radius of curvature of the arcuate surface is larger than the radius of curvature of the cylinder.

Images