JP2018066858A - Image formation apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image formation apparatus which can achieve both of installation of an adjustment function to a positioning structure of an optical writing device and reduction in the number of components/steps in the positioning structure.SOLUTION: A positioning member 410 is supported by a rotational shaft 242 of a photoreceptor 24K so as to be rotatable around the rotational shaft, and fixed to a frame 401 so as to be unable to rotate around the rotational shaft in such a state that an optical writing part 202 and another processing part 22K are positioned. A first surface 412 of the positioning member regulates a distance from the photoreceptor to the processing part by inhibiting the movement of the processing part approaching the photoreceptor. A second surface 413 regulates the distance from the photoreceptor to the optical writing part by inhibiting the movement of the optical writing part approaching the photoreceptor. The contour of the first surface projected to the plane vertical to the rotational shaft of the photoreceptor is the circular arc shape coaxial with the rotational shaft, and the contour of the second surface is the curve changing the distance from the rotational shaft in accordance with an angle around the rotational shaft.SELECTED DRAWING: Figure 5

Description

  The present invention relates to an electrophotographic image forming apparatus, and more particularly to a positioning structure of an optical writing unit with respect to a photoreceptor.

  “Optical writing device” (also referred to as “print head (PH)”) is a processing unit that exposes the surface of a photoreceptor in a print engine included in an electrophotographic image forming apparatus such as a printer or a copier. Say. “Exposure” is a process that irradiates a uniform charged area on the surface of the photoreceptor with light modulated by image data, and forms a charge distribution corresponding to the modulation pattern of the amount of light emitted, that is, an electrostatic latent image It is. The photoreceptor covers the outer peripheral surface of a rotating body such as a drum or a belt that is rotatably supported in the image forming apparatus. The optical writing device exposes a linear region (hereinafter referred to as “one line”) extending in the direction of the rotation axis of the rotating body (hereinafter referred to as “main scanning direction”) on the surface of the photosensitive member. The optical writing device further repeats this exposure operation in synchronization with the rotation of the photosensitive member. As a result, exposed lines continue in the rotation direction (hereinafter referred to as “sub-scanning direction”) on the surface of the photosensitive member, so that the exposure area is expanded two-dimensionally.

  There are two types of optical writing devices: an optical scanning method and a light emitting element arrangement method. In the “optical scanning method”, laser light is periodically deflected by a deflector such as a polygon mirror, and one line on the surface of the photoreceptor is scanned with the laser light during each period. The “light emitting element arrangement method” is a light emitting element such as a plurality of light emitting diodes (LEDs) and semiconductor lasers arranged in the main scanning direction, and a refractive index distribution such as a plurality of rod lenses (registered trademark) and Selfoc (registered trademark) Using the (grandient index: GRIN) lens, the entire surface of the photoreceptor surface is exposed simultaneously.

  In the development of optical writing devices in recent years, the light emitting element arrangement method is the mainstream. Unlike the optical scanning method, the light emitting element array method does not require a deflector, so the noise is relatively low, and each part of one line is individually illuminated with a plurality of light emitting elements and a GRIN lens, so that the light emitting elements to the photoconductor are individually illuminated. The optical path length is relatively short. As a result, the light emitting element array method is advantageous in terms of noise reduction and miniaturization compared to the optical scanning method. Therefore, in order to further spread image forming apparatuses such as laser printers, particularly in offices and homes, it is expected that the use of a light emitting element array method is effective.

  One of the important technologies in the use of the light emitting element arrangement method is an optical writing device positioning structure (see, for example, Patent Documents 1, 2, and 3). Since the GRIN lens has a narrower depth of focus than the optical scanning optical system, a structure in which the image surface of the light emitting element by the GRIN lens is surely aligned with the surface of the photoconductor is necessary to accurately expose the surface of the photoconductor. is there. Specifically, for example, in the structure disclosed in Patent Document 1, a spring presses the PH toward the photoconductor, so that a spacer protruding from the surface of the PH hits a member that holds the bearing of the photoconductor. . As a result, the distance from the rotation axis of the photosensitive member to the PH surface is limited to a predetermined value. In the structure disclosed in Patent Document 2, a pin protruding from each of the PH and the developing unit is fitted into a single member that slides on the outer peripheral surface thereof as the photosensitive member rotates. As a result, both the PH and the developing unit are positioned by the single member. In the structure disclosed in Patent Document 3, a plate-like member is fixed to the rotating shaft of the photosensitive member, and another plate-like member is screwed to the tip thereof. When the tracking roller coaxial with the developing roller comes into contact with the other plate-like member, the distance from the rotation axis of the photosensitive member to the central axis of the developing roller is limited to a predetermined value. This distance can also be adjusted from product to product by changing the screwing position. Therefore, it is possible to eliminate the variation in the distance between the products due to the molding error or assembly error of the parts.

JP 2012-025130 A JP 2005-242119 A Japanese Patent Laid-Open No. 06-167869

  In order to further increase the demand for light-emitting element array type optical writing devices, both high performance and reduction in manufacturing costs are important. For high performance, it is considered to use, for example, an organic light emitting diode (OLED) as a light source. On the other hand, with regard to the reduction of manufacturing costs, for example, attempts have been made to reduce the number of parts and the number of assembly steps by integrating parts having common functions as much as possible.

However, it is difficult to achieve both high performance through the use of OLED and reduction in the number of parts / number of processes related to the positioning structure of the optical writing device. This is due to the reason described below.
OLEDs are advantageous in that they have a low black level, high color expressive power, low power consumption, and easy miniaturization / thinness / lightening compared to LEDs. However, OLEDs emit less light than LEDs. Therefore, the use of OLED requires an increase in the F value of the GRIN lens. Since the increase in the F value reduces the depth of focus, the positioning of the optical writing device with respect to the surface of the photoreceptor must be further improved. For example, when the depth of focus can be suppressed to about 100 μm, only an error of about ± 15 μm is allowed for positioning except for a margin for vibration between the surface of the photoconductor and the rotation shaft accompanying the rotation of the photoconductor. If the molding accuracy of a component that can be used for positioning is, for example, about ± 25 μm, the required positioning accuracy cannot be achieved simply by increasing the processing accuracy of the component. Therefore, like the screwing structure disclosed in Patent Document 3, it is indispensable to provide the positioning member with a function that makes it possible to adjust the position of the optical writing device with respect to the surface of the photoreceptor when the product is assembled.

  However, this device is difficult to achieve both reduction in the number of parts / number of processes. In fact, like the structure disclosed in Patent Document 2, the optical writing device and other processing units of the print engine, that is, the charging unit, the developing unit, the transfer unit, the cleaning unit, or the charge eliminating unit are formed as a single member. When the positioning is performed, it is not obvious how to give the member the function of adjusting the position of the optical writing device while fixing the position of the other processing unit. In the screw fastening structure itself disclosed in Patent Document 3, the backlash of the screw is excessive for the required positioning accuracy.

  An object of the present invention is to solve the above-described problems, and in particular, an image forming apparatus capable of achieving both the mounting of the adjustment function to the positioning structure of the optical writing device and the reduction in the number of parts / processes in the positioning structure. Is to provide.

  An image forming apparatus according to one aspect of the present invention is an electrophotographic image forming apparatus, and includes a photosensitive member, a light writing element array type optical writing unit that exposes a surface of the photosensitive member, and a surface of the photosensitive member. A processing unit for processing, a frame for rotatably supporting the photosensitive member, and an optical writing unit supported by the rotating shaft so as to be rotatable around the rotating shaft of the photosensitive member independently of the rotating shaft; And a positioning member fixed to the frame so that the rotation around the rotation axis of the photosensitive member is impossible in a state where both the processing unit and the processing unit are positioned with respect to the photosensitive member. The positioning member directly or indirectly inhibits the movement of the processing unit approaching the surface of the photosensitive member to restrict the distance from the surface of the photosensitive member to the processing unit, and the surface of the photosensitive member. It integrally includes a second surface that restricts the distance from the surface of the photoreceptor to the optical writing unit by directly or indirectly preventing the approaching optical writing unit from moving. On the first surface, the contour projected onto a virtual plane perpendicular to the rotation axis of the photoreceptor is an arc that is coaxial with the rotation axis. The second surface is a curve in which a contour projected on a virtual plane perpendicular to the rotation axis of the photosensitive member changes a distance from the rotation axis depending on an angle around the rotation axis.

  The second surface may be an arc whose outline projected onto a virtual plane perpendicular to the rotation axis of the photoconductor is different from the center of the rotation axis of the photoconductor. The optical writing unit may include a protruding member that contacts the second surface of the positioning member at the tip surface. In this case, the second surface may have a shape in which the tangent plane at the contact point with the tip surface of the protruding member is constant regardless of the angle around the rotation axis of the photosensitive member. The protruding member may have a protruding direction perpendicular to a tangential plane at a contact point with the second surface.

This image forming apparatus may further include a tangential direction positioning member that positions the optical writing unit by directly or indirectly preventing the movement of the optical writing unit approaching in the tangential direction of the surface of the photoreceptor. Good. In this case, the end of the second surface on the side where the tangential positioning member is located with respect to the optical writing unit may be closer to the rotation axis of the photoreceptor than the end on the opposite side.
The optical writing unit includes an array of light emitting elements arranged in the direction of the rotation axis of the photoconductor, an arrangement of refractive index distribution lenses arranged in the direction of the rotation axis of the photoconductor, and a shape elongated in the direction of the rotation axis of the photoconductor And a holding member that holds the arrangement of the light emitting elements and the arrangement of the gradient index lenses may be included. In this case, the image forming apparatus is supported by the rotation shaft so as to be rotatable around the rotation shaft of the photosensitive member independently of the rotation shaft, and positions the optical writing unit with respect to the photosensitive member. There may be further provided an auxiliary positioning member fixed to the frame so that the rotation around the rotation axis of the photosensitive member becomes impossible in the state. The second surface of the positioning member is directly or indirectly in contact with one end in the longitudinal direction of the holding member, and prevents the movement of the optical writing unit approaching the surface of the photoconductor, thereby preventing the surface of the photoconductor from moving. The distance to the optical writing unit may be regulated, and the auxiliary positioning member is brought into contact with the other end in the longitudinal direction of the holding member directly or indirectly to approach the surface of the photosensitive member. The third surface for restricting the distance from the surface of the photosensitive member to the optical writing unit may be included. The third surface is a curve in which the contour projected on a virtual plane perpendicular to the rotation axis of the photoconductor changes the distance from the rotation axis depending on the angle around the rotation axis. The change rate of the distance with respect to the angle or the error of the change rate may be larger than that of the second surface of the positioning member.

  The first surface and the second surface may be arranged symmetrically with respect to the rotation axis of the photoreceptor. The processing performed by the processing unit on the surface of the photosensitive member may be at least one of charging, development, transfer, cleaning, and charge removal. The processing unit may be a transfer unit that transfers a toner image formed on the surface of the photoreceptor from the surface to an intermediate transfer member or a sheet. The positioning member has a rod shape or a plate shape extending between the first surface and the second surface, and may be fixed to the frame at a portion narrower than other portions. The optical writing unit may include an organic light emitting diode as a light emitting element.

  In the image forming apparatus according to the present invention, as described above, the member for positioning both the optical writing unit and the processing unit in the radial direction of the rotating shaft of the photosensitive member is supported by the rotating shaft so as to be rotatable around the rotating shaft. ing. The positioning member integrally includes a first surface for positioning the processing unit and a second surface for positioning the optical writing unit. The first surface is a circular arc surface that is coaxial with the rotation axis of the photosensitive member, and the second surface is a curved surface that varies in distance from the rotation axis depending on the angle around the rotation axis. Therefore, by rotating the positioning member around the rotation axis, it is possible to adjust the distance from the rotation axis to the optical writing unit while keeping the distance from the rotation axis to the processing unit constant. In this way, this image forming apparatus can achieve both the mounting of the adjustment function to the positioning structure of the optical writing device and the reduction in the number of parts / the number of processes in the positioning structure.

FIG. 1A is a perspective view illustrating an appearance of an image forming apparatus according to an embodiment of the present invention. (B) is a schematic cross-sectional view of the printer along the line bb shown in (a). (C) is an enlarged view of one of the photoconductor units shown in (b). (A) is a perspective view of the optical writing unit shown in FIG. 1, and (b) is a cross-sectional view of the optical writing unit along a line bb shown in (a). (C) is a block diagram of the light source substrate shown in (b). (D) is a schematic diagram showing an optical path in one of GRIN lenses included in the lens array shown in (a). (A) is a schematic perspective view showing an intermediate transfer unit of the printer shown in FIG. 1, and (b) is an enlarged view of a portion surrounded by a broken line shown in (a). FIG. 2A is a perspective view illustrating an appearance of a support structure for a photosensitive drum included in one of the photosensitive units illustrated in FIG. 1. (B) is a perspective view showing an appearance when the frame is removed from the support structure shown in (a), and (c) is a partial perspective view showing the vicinity of the end face of the photosensitive drum in the same state from another viewpoint. It is. FIG. 5A is a perspective view showing the positions of the support member and the optical writing unit of the intermediate transfer unit that are in contact with the end face of the positioning member shown in FIG. 4 with respect to the photosensitive drum. (B) is a partial front view of the member which (a) shows. (C) is a side view of the positioning member shown in FIG. (A) is a typical side view of the member shown in FIG. (B) is a typical side view showing the correspondence between the attitude of the positioning member shown in (a) and the positions of other members. (A) is a graph of an equiangular spiral, and (b) is a schematic side view showing a second end face of a positioning member having a contour of a part of the equiangular spiral coaxial with the central axis of the photosensitive drum. is there. (C) is a partial side view schematically showing the correspondence between the posture of the positioning member and the position of the pin of the optical writing unit. (D) is a partial side view schematically showing the pin of the optical writing section tilted so that the contact point with the second end face of the positioning member coincides with the apex thereof. (A) is a side view schematically showing the arrangement of the sub-scanning direction positioning portion relative to the optical writing portion and the shape of the second end face of the positioning member. (B) is a schematic perspective view showing the difference in the shape of the second end face between the positioning members arranged on both sides of the photosensitive drum.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[Appearance of image forming apparatus]
FIG. 1A is a perspective view showing an external appearance of an image forming apparatus 100 according to an embodiment of the present invention. The image forming apparatus 100 is a printer. A sheet discharge tray 41 is provided on the upper surface of the casing, and accommodates sheets discharged from a sheet discharge opening 42 opened in the back thereof. An operation panel 51 is embedded in front of the paper discharge tray 41. A paper feed cassette 11 is attached to the bottom of the printer 100 so that it can be pulled out.

[Internal structure of image forming apparatus]
FIG. 1B is a schematic cross-sectional view of the printer 100 along the line bb shown in FIG. The printer 100 is an electrophotographic color printer, and includes a feeding unit 10, an image forming unit 20, a fixing unit 30, and a paper discharge unit 40.
First, the feeding unit 10 uses the pickup roller 12 to separate the sheets SH1 one by one from the bundle of sheets stored in the sheet feeding cassette 11. Next, the feeding unit 10 uses the timing roller 13 to send the separated sheet to the image forming unit 20 in synchronization with the operation. “Sheet” refers to a thin film or thin plate material, article, or printed material made of paper or resin. The type of sheet that can be stored in the paper feed cassette 11, that is, the paper type, is, for example, plain paper, high-quality paper, color paper, or coated paper, and the size is, for example, A3, A4, A5, or B4. Furthermore, the posture of the sheet can be set to either vertical or horizontal.

  The image forming unit 20 is, for example, a printing engine based on an intermediate transfer method, and is a tandem arrangement of photosensitive units 20Y, 20M, 20C, 20K, an intermediate transfer belt 21, a primary transfer roller 22Y, 22M, 22C, 22K, and a secondary. A transfer roller 23 is included. The intermediate transfer belt 21 is rotatably spanned between a driven pulley 21L and a driving pulley 21R. In the space between these pulleys 21L, 21R, four photosensitive units 20Y,... And four primary transfer rollers 22Y,... Are arranged in pairs, and the intermediate transfer belt 21 is interposed between them. It is opposed to each other. The secondary transfer roller 23 forms a nip with the drive pulley 21R with the intermediate transfer belt 21 interposed therebetween. The sheet SH2 sent from the timing roller 13 is passed through this nip.

  In each of the photosensitive units 20Y,..., The photosensitive drums 24Y, 24M, 24C, and 24K contact the primary transfer rollers 22Y that are opposed to each other with the intermediate transfer belt 21 interposed therebetween to form a nip. Yes. Each of the photosensitive units 20Y,... Has the same surface portion as the primary transfer roller 22Y,... And the photosensitive drum 24Y, while the intermediate transfer belt 21 rotates (counterclockwise in FIG. 1B). When passing through the nip, a toner image of one color different from yellow (Y), magenta (M), cyan (C), and black (K) is formed on the surface portion. As a result, the four color toner images are superimposed on the surface portion to form one color toner image. The sheet SH2 is passed from the timing roller 13 to the nip at the timing when the color toner image passes through the nip between the driving pulley 21R and the secondary transfer roller 23. As a result, the color toner image is transferred from the intermediate transfer belt 21 to the sheet SH2 at the nip.

  The fixing unit 30 thermally fixes the toner image on the sheet SH <b> 3 sent from the image forming unit 20. Specifically, the fixing unit 30 passes the sheet SH2 through the nip between the fixing roller 31 and the pressure roller 32 while rotating the fixing roller 31 and the pressure roller 32. At this time, the fixing roller 31 applies heat of a built-in heater to the surface of the sheet SH3, and the pressure roller 32 applies pressure to the heated portion of the sheet SH3 and presses it against the fixing roller 31. The toner image is fixed on the surface of the sheet SH <b> 3 by the heat from the fixing roller 31 and the pressure from the pressure roller 32. The fixing unit 30 further sends the sheet SH <b> 3 to the paper discharge unit 40 by the rotation of the fixing roller 31 and the pressure roller 32.

The paper discharge unit 40 discharges the sheet SH3 on which the toner image is fixed from the paper discharge port 42 to the paper discharge tray 41. Specifically, the paper discharge unit 40 uses the paper discharge roller 43 disposed inside the paper discharge port 42 to discharge the sheet SH3 that has moved from the upper part of the fixing unit 30 to the paper discharge port 42. And put it on the paper discharge tray 41.
[Structure of photoconductor unit and image forming process thereby]
FIG. 1C is an enlarged view of one photosensitive member unit 20K shown in FIG. The photosensitive unit 20K includes a charging unit 201, an optical writing unit 202, a developing unit 203, a cleaning blade 204, and an eraser 205 in addition to the photosensitive drum 24K. These are arranged around the photoconductive drum 22 and perform an electrophotographic image forming process on the outer peripheral surface thereof other than fixing, that is, charging, exposure, development, transfer, cleaning, and charge removal. The other photoconductor units 20Y, 20M, and 20C also have a common structure.

  The photoconductor drum 24K is a cylindrical member made of a conductor such as aluminum whose outer peripheral surface 241 is covered with a photoconductor, and the center axis thereof (in FIG. 1C, the center of the circular cross section of the photoconductor drum 24K). It is supported so that it can be rotated independently of the central axis 242 around the axis 242 that penetrates perpendicularly to the paper surface. The photoreceptor is a material whose charge amount changes depending on the exposure amount, and includes an inorganic material such as amorphous selenium, a selenium alloy, amorphous silicon, or a stacked structure (OPC) of a plurality of organic materials. Although not shown in FIG. 1C, the central shaft 242 of the photosensitive drum 24K is connected to a drive motor through a rotational force transmission mechanism such as a gear or a belt. When the photosensitive drum 24K rotates once by the rotational force from the driving motor (clockwise in FIG. 1C), each surface portion of the photosensitive member is moved to the surrounding processing units 201, 202, 203, 204, and 205. Face them in order and receive them.

  The charging unit 201 includes a wire or thin plate-like electrode 211 extending in the axial direction at an interval from the outer peripheral surface 241 of the photosensitive drum 24K. The charging unit 201 applies corona discharge between the electrode 211 and the outer peripheral surface 241 of the photosensitive drum 24K by applying a negative high voltage to the electrode 211, for example. This discharge negatively charges the surface portion of the photoreceptor facing the charging unit 201.

  The optical writing unit 202 exposes a linear region extending in the axial direction, that is, the main scanning direction, that is, one line, of the charged portion of the photosensitive drum 24K. At this time, the optical writing unit 202 modulates the amount of light applied to the photosensitive drum 24K based on the gradation value represented by the image data. In one line on the photosensitive drum 24K, the charge amount decreases as the amount of irradiation light increases, so that a charge amount distribution corresponding to the gradation value distribution represented by the image data, that is, an electrostatic latent image is formed. The optical writing unit 202 repeats this exposure operation for one line in synchronization with the rotation of the photosensitive drum 24K. As a result, since the exposed line continues in the rotation direction, that is, the sub-scanning direction, on the outer peripheral surface of the photosensitive drum 24K, the electrostatic latent image spreads two-dimensionally.

  The developing unit 203 develops the electrostatic latent image on the photosensitive drum 24K with K-color toner. Specifically, the developing unit 203 first agitates the two-component developer DVL with the two auger screws 231 and 232 and negatively charges the toner contained in the developer DVL by friction at that time. Next, the developing unit 203 uses the developing roller 233 to convey the developer DVL to the nip with the photosensitive drum 24K. In parallel with this, the developing unit 203 applies a negative high voltage to the developing roller 233. As a result, in the electrostatic latent image, a region with a relatively small charge amount has a higher potential than the developing roller 233, so that an amount of toner corresponding to the decrease in the charge amount is separated from the developer conveyed by the developing roller 233. And adhere. Thus, the electrostatic latent image becomes visible as a toner image.

The toner image moves to the nip between the toner image and the primary transfer roller 22K as the photosensitive drum 24K rotates. Since a positive high voltage is applied to the primary transfer roller 22K, the negatively charged toner image is transferred from the outer peripheral surface of the photosensitive drum 24K to the intermediate transfer belt 21.
The cleaning blade 204 is a thin rectangular plate-like member formed of, for example, a thermosetting resin such as polyurethane rubber. The length of the cleaning blade 204 is substantially the same as the portion of the outer peripheral surface 241 of the photosensitive drum 24K covered with the photosensitive member. equal. Of the plate surface of the blade 204, the one facing the outer peripheral surface 241 of the photosensitive drum 24K is arranged on the outer peripheral surface 241 with one of its long sides (edge) parallel to the axial direction of the photosensitive drum 24K. The toner remaining on the transfer trace of the toner image is scraped off from the outer peripheral surface 241. In this way, the outer peripheral surface is cleaned.

The eraser 205 irradiates light to the outer peripheral surface 241 of the photosensitive drum 24K from, for example, LEDs arranged in the axial direction of the photosensitive drum 24K. The remaining charge disappears from the portion of the outer peripheral surface 241 that has received the irradiated light. In this way, the outer peripheral surface 241 is neutralized.
[Structure of optical writing unit]
2A is a perspective view of the optical writing unit 202, and FIG. 2B is a cross-sectional view of the optical writing unit 202 along a line bb shown in FIG. The optical writing unit 202 is a light emitting element array system, and includes a light source substrate 221, a lens array 222, and a holder 223. The light source substrate 221 is a long glass substrate or a resin substrate, and emits light from one side plate surface (upper surface in FIG. 2B) 224. The lens array 222 is a rectangular plate made of glass or resin that is long and transparent in the same direction as the light source substrate 221, and the GRIN lens array is sealed between the two plate surfaces. Each GRIN lens has a cylindrical shape extending in parallel with the short side of the plate surface of the lens array 222, and one end surface (the lower surface in FIG. 2B) faces the light emitting surface 224 of the light source substrate 221. The other end surface (upper surface in FIG. 2B) 226 is directed to the outer peripheral surface of the photosensitive drum 24K. Each GRIN lens emits light incident on one end surface 225 from the light source substrate 221 from the other end surface 226 and forms an image on the outer peripheral surface of the photosensitive drum 24K. The holder 223 is a plate-shaped resin member that is long in the same direction as the light source substrate 221, and includes a concave portion 227 on one side plate surface (the lower surface in FIG. 2B), and the opposite side plate surface (FIG. 2). (B) includes a slit 228 on the upper surface. The space inside the recess 227 communicates with the space inside the slit 228. A light source substrate 221 is fixed to a portion of the inner surface of the recess 227 connected to the slit 228, and the lens array 222 is sandwiched in the slit 228. As described above, the holder 223 holds the light source substrate 221 and the lens array 222.

-Light source substrate-
FIG. 2C is a block diagram of the light source substrate 221. The light source substrate 221 includes a light emitting element array 251, a selection circuit 252, and a driver integrated circuit (IC) 253. The light emitting element array 251 is an array of solid light emitting elements such as LEDs and OLEDs formed directly on the light source substrate 221. In the example shown in FIG. 2C, the light emitting elements 260 are arranged in three rows in a zigzag shape along the longitudinal direction of the light source substrate 221. Each row has thousands of light emitting elements arranged at a pitch of several tens of μm. Each light emitting element changes a drive current amount according to a luminance signal from the outside. The greater the amount of drive current, the higher the amount of light emitted from the light emitting element. The selection circuit 252 is a thin film transistor (TFT) circuit formed directly on the light source substrate 221, and connects the light emitting elements to the driver IC 253 in order. The driver IC 253 is a chip such as an application specific integrated circuit (ASIC) or a programmable integrated circuit (FPGA) mounted on the light source substrate 221. For example, this chip is arranged at one end in the longitudinal direction of the plate surface opposite to the plate surface on which the light emitting element array 251 and the selection circuit 252 are formed. The driver IC 253 is connected to a light source control unit 255 in the printer 100 through a flexible printed circuit board (FPC) 254, and receives digital image data therefrom. The driver IC 253 converts the image data into an analog luminance signal and transmits the analog luminance signal to the light emitting elements connected by the selection circuit 252.

-Lens array-
FIG. 2D is a schematic diagram showing an optical path in one GRIN lens 280 included in the lens array 222. The GRIN lens 280 has a transparent glass or resin cylindrical shape with a diameter of several hundred μm to several mm, and is distributed such that the refractive index decreases in a parabolic shape from the central axis toward the outer peripheral surface. With this refractive index distribution, light incident from one end face 281 of the GRIN lens 280 propagates while drawing a sinusoidal locus along the axial direction, and travels a certain distance (for example, several mm to several tens of mm). Repeat the imaging. Therefore, the light emitted from the other end surface 282 of the GRIN lens 280 forms an erect image or an inverted image in accordance with the axial length AXL of the GRIN lens 280. In FIG. 2D, the image is an inverted image as indicated by the white arrow. This blurring of the image is suppressed to an allowable level before and after the imaging point PBF and within a focal depth DOF (= several hundred μm) of the GRIN lens 280.

[Structure of intermediate transfer unit]
3A is a schematic perspective view showing the intermediate transfer unit 300 of the printer 100, and FIG. 3B is an enlarged view of a portion 310 surrounded by a broken line shown in FIG. (B) is drawn as if portions located before and after this portion 310 were removed. The intermediate transfer unit 300 includes a frame in addition to the intermediate transfer belt 21, the driven pulley 21L, the driving pulley 21R, the primary transfer rollers 22Y, 22M, 22C, and 22K, and the secondary transfer roller 23 illustrated in FIG. 301 is included. The frame 301 has a rectangular shape, for example, and is fixed to a chassis (not shown) of the printer 100. Of the side surfaces 302, 303, 304, and 305 of the frame 301 that correspond to the four sides of the rectangle, the two opposing surfaces (two in the left-right direction in FIG. 3B) 302 and 303 are respectively driven pulleys 21L. And the driving pulley 21R. The secondary transfer roller 23 is disposed outside the drive pulley 21 </ b> R with respect to the center of the frame 301, and both ends are supported by the side surfaces 303 of the frame 301. The intermediate transfer belt 21 extends so as to confine a space sandwiched between two opposite side surfaces (two sheets positioned in the depth direction in FIG. 3B) 304 and 305. One support member 311 is fixed to each end of each primary transfer roller 22Y,. This support member 311 is substantially rectangular plate-shaped, the plate surface is perpendicular to the central axis 311 of the primary transfer roller 22Y,... It is supported so that it can slide inside. The primary transfer roller 22Y,... Is the surface of the intermediate transfer belt 21 facing the space inside the frame 301 (the upper surface of the portion of the intermediate transfer belt 21 that extends below the frame 301 in FIG. 3B). 21A is contacted. Each opening 306 in the side surfaces 304 and 305 of the frame 301 further includes one first spring 312. The first spring 312 is a coil spring, for example, and applies an elastic force to the support member 311 in the same opening 306. This elastic force acts on the primary transfer rollers 22Y through the support member 311 and presses the outer peripheral surface of the rollers against the surface 21A of the intermediate transfer belt 21.

[Photosensitive drum support structure]
FIG. 4A is a perspective view showing the appearance of the support structure of the photosensitive drum 24K included in one of the photosensitive unit 20K. This figure is drawn from a viewpoint positioned slightly above the extension line of the central axis 242 of the photosensitive drum 24K. The other photoconductor units 20Y, 20M, and 20C also include a common support structure.

  This support structure includes a frame 401. The frame 401 is disposed outside each end surface 243 of the photosensitive drum 24K, and extends in parallel to the end surface 243. The frame 401 has each end of the central shaft 242 of the photosensitive drum 24K penetrated through its own hole 402 and rotatably supports them. A part of the outer peripheral surface 241 of the photosensitive drum 24K is exposed from the gap of the frame 401. The intermediate transfer unit 300 is positioned on the exposed portion, and the primary transfer roller 22K is in contact with the intermediate transfer belt 21.

  Further, as shown in FIG. 4A, an optical writing unit 202 is disposed in the gap of the frame 401. In the optical writing unit 202, the bottom surface of the holder 223 is supported by a sheet metal 404 from below. The sheet metal 404 is supported by a second spring 405 so as to be slidable in the radial direction of the photosensitive drum 24K. The second spring 405 is, for example, a coil spring, and pushes the optical writing unit 202 up to the photosensitive drum 24K through the sheet metal 404 by its elastic force.

  4B is a perspective view showing an external appearance when the frame 401 is removed from the support structure shown in FIG. 4A, and FIG. 4C is a view showing the vicinity of the end surface 243 of the photosensitive drum 24K in the same state. It is a fragmentary perspective view shown from a viewpoint. Positioning members 410 are installed between the end surfaces 243 of the photosensitive drum 24K and the frame 401. The positioning member 410 is, for example, an elongated rod-like member or plate-like member made of metal or hard resin. The positioning member 410 includes a hole 411 at the center, and is supported by the end so as to be rotatable around the end of the central shaft 242 of the photosensitive drum 24K. Yes. The positioning member 410 has a first end surface (upper end surface in FIG. 4 (b)) 412 and a second end surface (lower end surface in FIG. 4 (b)) 413, together with a portion connecting the first end surface in the longitudinal direction. Molded. The first end surface 412 contacts one of the support members 311 of the intermediate transfer unit 300, and the second end surface 413 contacts the surface of the optical writing unit 202 (the upper surface in FIG. 4B). In the positioning member 410, an intermediate portion 414 between the central hole 411 and the second end surface 413 is a screw (not shown in FIG. 4), and is fixed to the screw hole 406 of the frame 401 shown in FIG. Is done.

  As shown in FIG. 3B, the support member 311 of the intermediate transfer unit 300 receives a pressing force from the first spring 312 and approaches the central shaft 242 of the photosensitive drum 24K. Since the first end surface 412 of the positioning member 410 is in contact with the support member 311, the distance from the central axis 242 of the photosensitive drum 24 </ b> K to the support member 311 is from the hole 411 at the center of the positioning member 410 to the first end surface 412. The length is limited. That is, the first end surface 412 restricts the distance from the outer peripheral surface 241 of the photosensitive drum 24K to the primary transfer roller 22K by indirectly blocking the movement of the primary transfer roller 22K approaching the photosensitive drum 24K. .

  As shown in FIG. 4A, the optical writing unit 202 receives a pressing force in the radial direction of the photosensitive drum 24K from the second spring 405, and brings the upper surface closer to the central axis 242 of the photosensitive drum 24K. On this upper surface, as shown in FIG. 2A, projecting members 271 are installed at respective end portions in the longitudinal direction. The protruding member 271 is, for example, a metal or hard resin pin, and protrudes from the upper surface of the holder 223 in the radial direction of the photosensitive drum 24K. The tip surface of the pin 271 is, for example, a part of a spherical surface. Since the second end surface 413 of the positioning member 410 is in contact with the leading end surface, the distance from the central axis 242 of the photosensitive drum 24K to the optical writing unit 202 is from the hole 411 in the central portion of the positioning member 410 to the second end surface 413. The length is limited. In other words, the second end surface 413 restricts the distance from the outer peripheral surface 241 of the photosensitive drum 24K to the optical writing unit 202 by directly preventing the movement of the optical writing unit 202 approaching the photosensitive drum 24K.

[Structure of positioning member]
FIG. 5A is a perspective view showing the positions of the support member 311 and the optical writing unit 202 of the intermediate transfer unit 300 in contact with the end surfaces 412 and 413 of the positioning member 410 with respect to the photosensitive drum 24K. 5B is a partial front view of the members 24K, 410, 311 and 202 shown in FIG. 5A, and FIG. 5C is a side view of the positioning member 410. The first end surface 412 of the positioning member 410 is an arc surface that is coaxial with the central axis 242 of the photosensitive drum 24K. That is, as shown in FIG. 5C, the outline of the first end face 412 projected onto a virtual plane perpendicular to the central axis 242 is an arc having the same central axis 242 and the center CT1. Therefore, the first end surface 412 is located at the same distance R1 from the center CT1 in any part. As shown in FIG. 5C, the second end surface 413 of the positioning member 410 has a contour projected onto a virtual plane perpendicular to the central axis 242 of the photosensitive drum 24K, as a center CT1 of the central axis 242. It is a curve that changes the distance RA from the central axis 242 depending on the surrounding angle θ. Therefore, in the second end surface 413, portions having different positions in the circumferential direction of the photosensitive drum 24K are located at different distances from the center CT1 of the central axis 242.

  FIG. 6A is a schematic side view of the members 24K, 410, 311 and 202 shown in FIG. In this figure, the overall shape of the positioning member 410 is simplified and the shapes of the both end surfaces 412 and 413 are exaggerated so that the difference in shape between the both end surfaces 412 and 413 of the positioning member 410 can be easily understood. ing. Further, the tip surface of the pin 271 of the optical writing unit 202 is exaggerated in a hemispherical shape. The first end surface 412 of the positioning member 410 is an arc surface having a radius R1, and the center axis 242 of the photosensitive drum 24K is equal to the center CT1. That is, the first end face 412 is located at the same distance R1 from the center CT1 in any part. On the other hand, the second end surface 413 is an arc surface having a radius R2 different from that of the first end surface 412, and its center CT2 is deviated from the center CT1 of the center axis 242 of the photosensitive drum 24K. As a result, the distance RA from the center CT1 of the central axis 242 to each part of the second end surface 413 differs depending on where the part is located in the circumferential direction of the photosensitive drum 24K. In particular, the distance RA is equal to the maximum value RL at the one end 601 of the second end surface 413 in the circumferential direction, and decreases monotonously as it approaches the other end 602 located on the opposite side from the one end 601, and the other end 602. The minimum value RS is reached.

  FIG. 6B is a schematic side view showing a correspondence relationship between the posture of the positioning member 410 and the positions of the other members 311 and 202. Also in this figure, simplification and exaggeration of the same shape as in FIG. All portions of the first end surface 412 of the positioning member 410 are located at the same distance R1 from the center CT1 of the central shaft 242 of the photosensitive drum 24K. Therefore, regardless of the rotation angle of the positioning member 410 around the center CT1, the support member 311 continues to contact the first end face 412 at the point CP1 located at a certain distance R1 from the center CT1. In contrast, the second end surface 413 of the positioning member 410 has a different distance RA from the center CT1 of the central axis 242 of the photosensitive drum 24K for each portion where the circumferential position of the photosensitive drum 24K is different. In particular, the distance RA decreases monotonously from the maximum value RL to the minimum value RS from one end 601 to the other end 602 in the circumferential direction of the second end surface 413. Here, the shape of the second end face 413, for example, the radius shown in FIG. 6 (a), so that the average value of the distance RA is sufficiently larger than the difference RL-RS between the maximum value RL and the minimum value RS. R2 and the position of the center CT2 are designed. Therefore, even if the contact CP2 between the second end surface 413 and the pin 271 of the optical writing unit 202 is displaced on the tip surface of the pin 271 due to the rotation of the positioning member 410, the center CT1 of the central shaft 242 of the photosensitive drum 24K is displaced. The distance to the tip of the pin 271 can be regarded as being equal to the distance RA from the center CT1 to the contact CP2. As a result, this distance is equal to the maximum value RL when the contact CP2 is positioned at the one end 601 of the second end surface 413, and the contact CP2 moves from the one end 601 of the second end surface 413 toward the other end 602. As the contact CP2 reaches the other end 602, the minimum value LS is reached.

  In this way, the positioning member 410 rotates from the central axis 242 to the optical writing unit 202 while maintaining the distance R1 from the central axis 242 to the support member 311 constant by the rotation around the central axis 242 of the photosensitive drum 24K. The distance RA is changed. Specifically, for example, as the rotation angle of the positioning member 410 changes in the range of ± several degrees, the distance RA changes in the range of ± ten and several μm.

  This feature regarding the structure of the positioning member 410, particularly the shape of the second end surface 413, is used for positioning the optical writing unit 202 with respect to the outer peripheral surface 241 of the photosensitive drum 24 </ b> K in the manufacture of the printer 100. Specifically, when assembling the photosensitive unit 20K, before fixing the positioning member 410 to the frame 401, the dummy of the intermediate transfer unit and the optical writing unit are actually mounted around the photosensitive drum 24K. , 202. The dummy of the support member contacts the first end surface 412 of the positioning member 410, and the pin dummy contacts the second end surface 413. In this state, the positioning member 410 is rotated around the central axis 242 of the photosensitive drum 24K. Since the positioning accuracy with respect to the primary transfer roller 22K is sufficient with the molding accuracy of the support member 311 and the first end surface 412, the distance R1 from the central axis 242 of the photosensitive drum 24K to the support member 311 is the rotation angle of the positioning member 410. Regardless of the design value, the design value remains within the allowable range. On the other hand, the distance RA from the central axis 242 to the optical writing unit 202 depends on the rotation angle of the positioning member 410 and varies within the range from the maximum value RL to the minimum value RS. If an error from the design value of the distance RA falls within an allowable range due to this change, the intermediate portion 414 of the positioning member 410 is fixed to the screw hole 406 of the frame 401 with a screw. In this way, the positioning member 410 independently positions both the primary transfer roller 22K and the optical writing unit 202 in the radial direction of the photosensitive drum 24K. In particular, the positioning accuracy can be adjusted to be higher than the molding accuracy of the second end surface 413 for the optical writing unit 202 while maintaining the molding accuracy of the first end surface 412 for the primary transfer roller 22K.

[Advantages of the embodiment]
In the printer 100 according to the embodiment of the present invention, as described above, the positioning member 410 alone positions both the optical writing unit 202 and the primary transfer roller 22K in the radial direction of the photosensitive drum 24K. In particular, the first end surface 412 of the positioning member 410 contacts the support member 311 to indirectly block the movement of the primary transfer roller 22K approaching the photosensitive drum 24K, and the second end surface 413 contacts the optical writing unit 202. Thus, the movement of the optical writing unit 202 approaching the photosensitive drum 24K is directly blocked. The first end surface 412 is an arc surface coaxial with the central axis 242 of the photosensitive drum 24K, and the second end surface 413 is a curved surface having a different distance RA from the central axis 242 depending on an angle around the central axis 242. It is. Therefore, by rotating the positioning member 410 around the central axis 242 of the photoconductor drum 24K, the optical writing unit is moved from the central axis 242 to the optical writing unit while maintaining the distance R1 from the central axis 242 to the support member 311 constant. The distance RA up to 202 can be adjusted. In particular, since the positioning member 410 is integrally formed with the first end surface 412 and the second end surface 413 that are connected to each other, there is no backlash when rotating around the central axis 242 of the photosensitive drum 24K. As a result, the positioning accuracy with respect to the primary transfer roller 22K is maintained at the molding accuracy of the first end surface 412 and the positioning accuracy with respect to the optical writing unit 202 is improved more than the molding accuracy of the second end surface 413. Thus, the positioning member for the optical writing unit 202 is integrated with the positioning member for the primary transfer roller 22K without impairing the positioning accuracy of each. Therefore, the printer 100 can achieve both the mounting of the adjustment function to the positioning structure of the optical writing unit 202 and the reduction in the number of parts / the number of processes in the positioning structure.

[Modification]
(A) The electrophotographic image forming apparatus 100 shown in FIG. 1 is an intermediate transfer type color printer including a tandem arrangement of photoreceptor units 20Y,... And an intermediate transfer belt 21. In addition, the image forming apparatus according to the embodiment of the present invention may be a direct transfer type color printer, a monochrome printer, a facsimile machine, a copier, or a multifunction peripheral (MFP).

(B) The structure of the photoconductor unit 20K shown in FIG. 1C is merely an example. For example, the charging unit may be a proximity discharge type using a roller or the like instead of the corona discharge type 201 using the electrode 211. Further, the eraser 205 may be closer to the primary transfer roller 22K than the cleaning blade 204.
(C) In FIG. 1C, the outer peripheral surface of the drum 24K is covered with a photoconductor. In addition, the outer peripheral surface of the belt may be covered with a photosensitive member instead of the drum 24K. Similar to the drum 24K, this belt is disposed so as to be surrounded by a charging unit, a developing unit, a cleaning blade, and an eraser. When the belt rotates once, the surface portions of the photoreceptor face the processing portions in order, and are subjected to charging, exposure, development, transfer, cleaning, and charge removal processing. In this case, the positioning member 410 may be supported by a rotating shaft of a pulley that drives the belt, instead of the central shaft 242 of the drum 24K.

(D) In the light source substrate 221 shown in FIG. 2C, the solid light emitting elements 260 are arranged in three rows in a staggered pattern along the longitudinal direction of the light source substrate 221. In addition, the number of rows of the light emitting elements may be 1, 2, or 4 or more, and may be a lattice shape instead of the staggered shape.
The solid state light emitting device may in particular be an OLED. Since the OLED emits less light than the LED, the lens array 222 is designed to have a large F-number for the GRIN lens. The positioning accuracy of the optical writing unit 202 by the positioning member 410 is sufficiently high to cope with the narrowing of the focal depth of the GRIN lens.

  (E) In FIG. 4, the intermediate portion 414 of the positioning member 410 is fixed to the screw hole 406 of the frame 401 with a screw. This fixing may be performed with an adhesive instead of the screw. Since the intermediate portion 414 has a narrower width than the center portion and the end portion, the intermediate member 414 is fixed to the frame 401 so that the positioning member 410 against vibration / impact from the outside such as vibration accompanying rotation of the photosensitive drum 24K. The strength of is improved. As a result, a decrease in positioning accuracy due to deformation of the positioning member 410 can be prevented. However, if the intermediate portion 414 already has sufficient strength, another portion may be secured to the frame 401.

  (F) As shown in FIGS. 4 and 5, the positioning member 410 positions both the support member 311 and the optical writing unit 202. Since the support member 311 is positioned symmetrically with the optical writing unit 202 with respect to the central axis 242 of the photosensitive drum 24K, the pressing force received by the positioning member 410 from each of the support member 311 and the optical writing unit 202 is mutually The reverse direction. Further, the elastic forces of the springs 312 and 405 that press the support member 311 and the optical writing unit 202 are set so that the magnitudes of the pressing forces are almost the same. Therefore, depending on the presence or absence of these pressing forces, either the bending moment that the central shaft 242 of the photosensitive drum 24K receives from the positioning member 410 or the frictional force that the positioning member 410 receives from the central shaft 242 of the photosensitive drum 24K when rotating. However, it does not change substantially. As a result, a decrease in positioning error due to bending deformation of the central shaft 242 of the photosensitive drum 24K is prevented, and the smoothness of the rotation of the positioning member 410 is maintained to such an extent that the operability is not impaired. Furthermore, since the positioning member 410 does not substantially receive the bending moment associated with the pressing force from the support member 311 and the optical writing unit 202, a decrease in positioning accuracy due to the bending deformation is prevented.

  However, the positioning member for the optical writing unit 202 may position another member, for example, the developing roller 233 in addition to or instead of the support member 311. Both the pressing force applied to the positioning member by the member to be positioned and the bending moment applied to the central axis of the photosensitive drum due to the pressing force are maintained to such an extent that the positioning accuracy is not lowered. As long as a single positioning member is used, a member to be positioned together with the optical writing unit 202 can be freely set.

  (G) As shown in FIG. 5, the first end surface 412 of the positioning member 410 contacts the support member 311 included in the intermediate transfer unit 300 and indirectly moves the primary transfer roller 22K approaching the photosensitive drum 24K. The second end face 413 contacts the optical writing unit 202 and directly prevents the movement of the optical writing unit 202 approaching the photosensitive drum 24K. In addition, the first end surface 412 may come into contact with the central axis of the primary transfer roller 22K and the like, and the movement of the primary transfer roller 22K approaching the photosensitive drum 24K may be directly blocked. The second end surface 413 may be in contact with another member fixed to the optical writing unit 202 and indirectly block the movement of the optical writing unit 202 approaching the photosensitive drum 24K.

  (H) The second end surface 413 of the positioning member 410 shown in FIG. 6 is an arc surface having a radius R2 different from that of the first end surface 412, and its center CT2 deviates from the center CT1 of the center axis 242 of the photosensitive drum 24K. ing. However, the second end face is not limited to this shape, and the contour projected on the virtual plane perpendicular to the central axis 242 of the photosensitive drum 24K depends on the angle around the central axis 242 from the central axis 242. Any curve that changes the distance may be used. An example of such a curve is a helix that is coaxial with its central axis 242. When this curve is an equiangular spiral, the second end face is always kept in contact with the same portion of the pin 271 of the optical writing unit 202 regardless of the rotation angle of the positioning member 410 as described below. it can.

  7A is a graph of an equiangular spiral, and FIG. 7B is a schematic side view showing a second end face 713 whose contour is a part of the equiangular spiral coaxial with the central axis of the photosensitive drum 24K. FIG. In FIG. 7B, simplification and exaggeration of the same shape as in FIG. The equiangular spiral is a planar curve represented by the formula r = aexp (bθ) (a, b: constant) in polar coordinates (radial radius r, declination angle θ), and the radial radius and tangent are at a constant angle α. It has a feature of crossing at> 0 (hereinafter referred to as “feature angle”). A part of the equiangular spiral has the second end surface 713 on a contour projected onto a virtual plane perpendicular to the central axis of the photosensitive drum 24K. As shown in FIG. 7B, the second end surface 713 has a different distance RA from the center CT1 of the central axis of the photosensitive drum 24K for each portion having a different position in the circumferential direction of the photosensitive drum 24K. RA decreases monotonously from the maximum value RL to the minimum value RS from one end 701 to the other end 702. Further, the straight line connecting the point TPL with the center axis CT1 of the photosensitive drum 24K intersects the plane TPL that is in contact with any point on the second end surface 713 at the same angle α.

  FIG. 7C is a partial side view schematically showing a correspondence relationship between the posture of the positioning member 410 and the position of the pin 271 of the optical writing unit. As shown by the solid line in this figure, the initial arrangement of the pins 271 satisfies the following two conditions. (1) The plane TPL that contacts the tip surface of the pin 271 and its polar angle (inclination angle with respect to the protruding direction of the pin 271) β> 0 is the optical writing accompanying the expansion and contraction of the second spring 405 (see FIG. 4). It is inclined with respect to the moving direction MVD of the insertion portion 202 by the characteristic angle α of the equiangular spiral that forms the contour of the second end surface 713 of the positioning member 410. (2) The center CT1 of the central axis of the photosensitive drum 24K with respect to the point CP2 of the polar angle β is located in the moving direction MVD of the optical writing unit 202. From these conditions, the straight line connecting the point CP2 of the polar angle β on the pin 271 to the center CT1 of the central axis of the photosensitive drum 24K intersects the tangential plane TPL at the point CP2 at the characteristic angle α of the equiangular spiral. On the other hand, as shown in FIG. 7B, a straight line connecting the contact point to the center CT1 of the central axis of the photosensitive drum 24K intersects with the same angle α on the plane TPL contacting the second end surface 713 of the positioning member 410. . When the second end surface 713 comes into contact with the pin 271, the contact plane between the members 271 and 713 coincides with each other, so that the contact coincides with the point CP 2 of the polar angle β on the pin 271. Furthermore, even if the pin 271 moves as the positioning member 410 rotates around the central axis of the photosensitive drum 24K, the condition (2) remains satisfied. Therefore, the second end surface 713 is in contact with the pin 271 after the movement at the point CP2 of the polar angle β as shown in FIG. 7C by a broken line and a two-dot chain line by the same consideration as described above.

  Thus, the positioning member 410 can keep the second end surface 713 always in contact with the same part CP2 of the pin 271 regardless of the rotation angle. In this case, the change rate of the movement amount of the optical writing unit 202 with respect to the rotation angle of the positioning member 410 is not easily influenced by the difference between the shape of the tip surface of the pin 271 and the ideal spherical surface. Therefore, if the second end surface 713 of the positioning member 410 is sufficiently smooth, the amount of movement of the optical writing unit 202 accompanying the rotation of the positioning member 410 can be changed smoothly. Furthermore, the rate of change of the movement amount with respect to the rotation angle is sufficient even if the molding accuracy of the tip surface of the pin 271 varies as long as the molding accuracy of the second end surface 713 of the positioning member 410 is sufficiently uniform between products. It is made uniform. As a result, it is easy to align the positioning accuracy with respect to the optical writing unit 202 among products.

  FIG. 7D is a partial side view schematically showing the pin 771 tilted so that the contact CP2 with the second end face 713 coincides with the vertex TPV. The pin 271 shown in FIG. 7C is a positioning member at a point CP2 where the polar angle = 0, that is, the protruding direction is parallel to the moving direction MVD of the optical writing unit 202, and the polar angle β> 0. It contacts the second end surface 713 of 410. In this case, as shown in FIG. 7D, the direction of the polar angle = 0 of the pin 771 is inclined by the angle β with respect to the moving direction MVD of the optical writing unit 202. In spherical processing, in general, the point where the polar angle is 0, that is, the molding accuracy near the apex is the highest, and the variation between products is the smallest. Therefore, when the pin 771 comes into contact with the second end surface 713 at the vertex TPV, the change rate of the movement amount of the optical writing unit 202 with respect to the rotation angle of the positioning member 410 is further uniformized between products.

  (I) As shown in FIG. 4A, the optical writing unit 202 is positioned by being pressed against the positioning member 410 by the second spring 405 in the radial direction of the photosensitive drum 24K. Further, the optical writing unit 202 may be similarly positioned in the rotation direction of the photosensitive drum 24K, that is, in the sub-scanning direction. In this case, the second end surface of the positioning member 410 may have a shape as described below in accordance with the direction of the pressing force received by the optical writing unit 202 in the sub-scanning direction.

  FIG. 8A is a side view schematically showing the arrangement of the sub-scanning direction positioning unit 800 with respect to the optical writing unit 202 and the shape of the second end surface 813 of the positioning member 410. The sub-scanning direction positioning unit 800 includes an auxiliary positioning member 801 and a third spring 802. The auxiliary positioning member 801 is a wall-like member fixed to the frame 401 shown in FIG. 4A, and its wall surface is opposed to one side 229 extending in the longitudinal direction of the holder 223 of the optical writing unit 202. Yes. A plurality of protrusions 803 protrude from the wall surface toward the side surface 229 of the opposing holder 223. The third spring 802 is, for example, a coil spring, and is disposed on the side opposite to the auxiliary positioning member 801 with respect to the optical writing unit 202, and in the sub-scanning direction with respect to the other side 22A extending in the longitudinal direction of the holder 223 (FIG. 8). The pressing force FH (rightward in (a)) is applied. The optical writing unit 202 approaches the auxiliary positioning member 801 by the pressing force FH. The auxiliary positioning member 801 prevents this approach by the protrusion 803, thereby defining the position of the optical writing unit 202 in the sub-scanning direction.

  As shown in FIG. 8A, the second end surface 813 of the positioning member 410 is such that the end 811 on the auxiliary positioning member 801 side with respect to the optical writing unit 202 is more photosensitive than the end 812 on the opposite side. Close to the central axis 242 of 24K. Such an inclination of the second end surface 813 is advantageous in that the stability of the optical writing unit 202 in the sub-scanning direction is higher than the opposite inclination. This is due to the following two reasons. <1> The force for pressing the optical writing unit 202 against the auxiliary positioning member 801 is strong. <2> When the optical writing unit 202 receives an external force and moves away from the auxiliary positioning member 801, the pin 271 receives a stronger frictional force from the second end surface 813 than when approaching the optical writing unit 202.

  <1> A first component force parallel to the tangential plane TPL common to the second end surface 813 and the pin 271 is applied to the radial pressing force FV of the photosensitive drum 24K received by the optical writing unit 202 from the second spring 405. A case is assumed where the FT and the second component force FN perpendicular to the FT are decomposed. The first component force FT acts to raise the pin 271 along the tangential plane TPL. In particular, the component force FA in the sub-scanning direction (left-right direction in FIG. 8A) of the first component force FT presses the entire optical writing unit 202 against the auxiliary positioning member 801. As a result, the force pressing the optical writing unit 202 against the auxiliary positioning member 801 is strengthened more than the pressing force FH in the sub-scanning direction.

  <2> For example, assume that the optical writing unit 202 receives an external force in a direction away from the auxiliary positioning member 801 due to external vibration / impact. Among these external forces, the component force perpendicular to the common tangential plane TPL between the second end surface 813 and the pin 271 is that the second end surface 813 is inclined as shown in FIG. Is pressed against the second end face 813. As a result, the force perpendicular to the tangential plane TPL received by the second end face 813 from the pin 271 is strengthened more than the second component force FN, so that the vertical drag received by the pin 271 from the second end face 813 is the first reaction. It is strengthened more than 2 component FN. With respect to this reaction, the frictional force that the pin 271 receives from the second end surface 813 as the optical writing unit 202 moves in the sub-scanning direction is in a proportional relationship. Therefore, the higher the external force in the direction of pulling the optical writing unit 202 away from the auxiliary positioning member 801, the stronger the frictional force. The opposite is true when the optical writing unit 202 receives an external force in a direction approaching the auxiliary positioning member 801, and the stronger the external force in the direction in which the optical writing unit 202 approaches the auxiliary positioning member 801, the weaker this frictional force.

(J) In FIG. 4B, the second end surface 413 of the positioning member 410 has the same shape with the same molding accuracy on both sides of the photosensitive drum 24K. In addition, the shape or molding accuracy may be different between the second end faces.
FIG. 8B is a schematic perspective view showing positioning members 810 and 820 having such second end surfaces 823 and 833. FIG. One of these second end faces (the one shown in FIG. 8B by a solid line) 823 has a gentler inclination than the other one (the one shown in FIG. 8B by a broken line) 833, that is, the photosensitive drum 24K. The radial displacement rate with respect to the rotation angle around the central axis 242 is low. The difference in inclination may be intentionally designed or may result from the difference in surface roughness associated with the molding accuracy of one 823 being higher than the other 833.

  Such a difference in shape between the second end surfaces 823 and 833 is used as follows in the positioning process of the optical writing unit 202 with respect to the photosensitive drum 24K. After arranging the dummy of the intermediate transfer unit and the optical writing unit around the photosensitive drum 24K, first, the second end face having a high radial displacement rate with respect to the rotation angle around the central axis 242 of the photosensitive drum 24K. A position of the optical writing unit 202 in the circumferential direction is adjusted by a positioning member 830 having 833. If the error from the design value of the position falls within the allowable range, then the optical writing from the central axis 242 in the radial direction is performed by the positioning member 820 having the second end surface 823 having a low radial displacement rate with respect to the rotation angle. The distance to the unit 202 is adjusted. By repeating these adjustments alternately as necessary, the optical writing unit 202 is positioned in both the circumferential direction and the radial direction. Since the positioning accuracy of the optical writing unit 202 may generally be lower in the circumferential direction than in the radial direction, the second end surface 833 used for positioning in the circumferential direction is inclined more than the second end surface 823 used for positioning in the radial direction. It may be steep or the surface may be rough. In this way, the manufacturing cost of the positioning member can be reduced.

  The present invention relates to a structure for determining the position of an optical writing unit with respect to a photosensitive member in an electrophotographic image forming apparatus. As described above, one end surface of a single positioning member is an arc surface coaxial with the rotational axis of the photosensitive member. In addition, the other end surface is a curved surface having a different distance from the rotation axis depending on the angle around the rotation axis. Thus, the present invention is clearly industrially applicable.

100 Printer 20Y, 20M, 20C, 20K Photosensitive unit 21 Intermediate transfer belt 21L Driven pulley 21R Drive pulley 22Y, 22M, 22C, 22K Primary transfer roller 23 Secondary transfer roller 24Y, 24M, 24C, 24K Photosensitive drum 202 Light Writing unit 221 Light source substrate 222 Lens array 223 Holder 241 Photosensitive drum outer peripheral surface 242 Photosensitive drum central axis 243 Photosensitive drum end surface 271 Pin 300 Intermediate transfer unit 301 Frame 302, 303, 304, 305 of intermediate transfer unit Side surface of frame 311 Support member 312 First spring 401 Frame of photosensitive unit 404 Sheet metal 405 Second spring 410 Positioning member 411 Hole at center of positioning member 412 First end surface 413 of positioning member Second end surface of positioning member 414 Intermediate portion of positioning member 601, 602 End portion of second end surface in circumferential direction of photosensitive drum

Claims (11)

An electrophotographic image forming apparatus,
A photoreceptor,
A light-emitting element array type optical writing unit that exposes the surface of the photoreceptor;
A processing section for processing the surface of the photoreceptor;
A frame that rotatably supports the photoreceptor;
The optical writing unit and the processing unit are positioned with respect to the photoconductor, supported by the rotary shaft so that the photoconductor can rotate independently of the rotary shaft. A positioning member fixed to the frame so that rotation around the rotation axis of the photoconductor becomes impossible in a state where
The positioning member is
A first surface that regulates a distance from the surface of the photosensitive member to the processing unit by directly or indirectly preventing movement of the processing unit that approaches the surface of the photosensitive member;
Integrated with a second surface that regulates the distance from the surface of the photosensitive member to the optical writing unit by directly or indirectly preventing the movement of the optical writing unit approaching the surface of the photosensitive member Included in
In the first surface, the contour projected onto a virtual plane perpendicular to the rotation axis of the photoconductor is an arc coaxial with the rotation axis,
The second surface is a curve in which a contour projected onto a virtual plane perpendicular to the rotation axis of the photoconductor changes a distance from the rotation axis depending on an angle around the rotation axis. An image forming apparatus.   The contour of the second surface projected onto a virtual plane perpendicular to the rotation axis of the photoconductor is an arc whose center is different from the rotation axis of the photoconductor. Image forming apparatus. The optical writing unit includes a protruding member that comes into contact with the second surface of the positioning member at a tip surface,
2. The shape according to claim 1, wherein the second surface has a shape in which a tangent plane at a contact point with a tip end surface of the protruding member is constant regardless of an angle around a rotation axis of the photosensitive member. Image forming apparatus.   The image forming apparatus according to claim 3, wherein the protruding member has a protruding direction perpendicular to a tangential plane at a contact point with the second surface. A tangential positioning member that positions the optical writing unit by directly or indirectly blocking the movement of the optical writing unit approaching in the tangential direction of the surface of the photoreceptor;
2. The second surface is characterized in that an end portion on a side where the tangential positioning member is located with respect to the optical writing portion is closer to a rotation axis of the photoconductor than an end portion on the opposite side. The image forming apparatus according to claim 4. The photosensitive member is supported by the rotation shaft so as to be rotatable around the rotation shaft of the photosensitive member, and the optical writing unit is positioned with respect to the photosensitive member. An auxiliary positioning member fixed to the frame so that rotation around the rotation axis is impossible;
The optical writing unit
An array of light emitting elements arranged in the direction of the rotation axis of the photoreceptor;
An array of gradient index lenses arranged in the direction of the rotation axis of the photoreceptor;
A shape that is elongated in the direction of the rotation axis of the photoconductor, and includes a holding member that holds the arrangement of the light emitting elements and the arrangement of the gradient index lenses,
The second surface of the positioning member is in direct or indirect contact with one end in the longitudinal direction of the holding member, thereby preventing the movement of the optical writing unit approaching the surface of the photoreceptor. Regulating the distance from the surface of the photoreceptor to the optical writing unit,
The auxiliary positioning member is
By directly or indirectly contacting the other end of the holding member in the longitudinal direction, the movement of the optical writing unit approaching the surface of the photoconductor is prevented, thereby preventing the optical writing from the surface of the photoconductor. Including a third surface that regulates the distance to the insert,
The third surface is a curve in which a contour projected onto a virtual plane perpendicular to the rotation axis of the photoconductor changes a distance from the rotation axis depending on an angle around the rotation axis, 6. The image forming apparatus according to claim 1, wherein a change rate of the distance with respect to the angle or an error of the change rate is larger than that of the second surface of the positioning member.   The image forming apparatus according to claim 1, wherein the first surface and the second surface are arranged symmetrically with respect to a rotation axis of the photoconductor.   The process performed by the processing unit on the surface of the photoconductor is at least one of charging, development, transfer, cleaning, and charge removal. The image forming apparatus described in 1.   The image forming apparatus according to claim 8, wherein the processing unit is a transfer unit that transfers a toner image formed on the surface of the photoconductor from the surface to an intermediate transfer member or a sheet.   The positioning member has a bar shape or a plate shape extending between the first surface and the second surface, and is fixed to the frame at a portion narrower than other portions. The image forming apparatus according to claim 1.   The image forming apparatus according to claim 1, wherein the optical writing unit includes an organic light emitting diode as a light emitting element.

Images