Optical scanner and image forming apparatus

Abstract

To prevent a reduction in the image quality of an image obtained by developing electrostatic latent images formed on scanning target bodies and superimposing the developed images one on top of the other.SOLUTION: An optical scanner comprises a housing, a deflector, and a pair of scanning optical systems. The scanning optical systems each include an optical path bending mirror. The optical path bending mirror has a normal direction of a reflection surface as a thickness direction. A side end face of the optical path bending mirror is bonded to the housing with an adhesive. The optical path bending mirror of one scanning optical system and the optical path bending mirror of the other scanning optical system are arranged to establish a symmetrical positional relationship with the deflector therebetween. The adhesive bonded to the optical path bending mirror of the one scanning optical system is arranged closer to the reflection surface than the center in the thickness direction of the side end face. The adhesive bonded to the optical path bending mirror of the other scanning optical system is arranged closer to a surface opposite to the reflection surface than the center in the thickness direction of the side end face.SELECTED DRAWING: Figure 8

Description

[Technical Field]

[0001] The present invention relates to an optical scanning device and an image forming apparatus. [Background technology]

[0002] Electrophotographic image forming apparatuses are equipped with an optical scanning device. The optical scanning device scans a photosensitive drum, which serves as a scanned body, with a light beam to form an electrostatic latent image. This electrostatic latent image is developed into a toner image and printed on a sheet. In color printing, electrostatic latent images are formed on multiple photosensitive drums, and the electrostatic latent images on each photosensitive drum are developed and superimposed to form an image that is printed on a sheet.

[0003] The optical scanning device includes an optical path bending mirror to guide the light beam onto the photosensitive drum. The optical path bending mirror reflects the light beam onto the photosensitive drum. Such an optical scanning device is disclosed, for example, in Patent Document 1. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2002-202472 Summary of the Invention [Problem to be solved by the invention]

[0005] For example, the optical path bending mirror is fixed to the housing of the optical scanning device with an adhesive. Here, the adhesive expands due to temperature rise, etc. When the adhesive expands, the position of the optical path bending mirror is displaced from its initial position. In other words, when the adhesive expands, the scanning position of the light beam scanning on the photosensitive drum is shifted. As a result, the quality of the image obtained by developing and superimposing the electrostatic latent images on each photosensitive drum is reduced. Specifically, color shift occurs.

[0006] The present invention has been made to solve the above-mentioned problems, and aims to provide an optical scanning device and an image forming device that can suppress deterioration in image quality of images obtained by developing and superimposing electrostatic latent images formed on each scanned body. [Means for solving the problem]

[0007] To achieve the above object, an optical scanning device according to a first aspect of the present invention is an optical scanning device that deflects a light beam to scan multiple scanned objects and form electrostatic latent images on the scanned objects, and includes a housing, a deflector rotatably arranged within the housing for deflecting the light beam, and a pair of scanning optical systems also arranged within the housing. The scanning optical system includes an optical path bending mirror that reflects the light beam deflected by the deflector and guides the light beam onto an assigned scanned object. The optical path bending mirror is a rectangular parallelepiped member that has a reflective surface with its longitudinal direction aligned with the main scanning direction and a thickness direction normal to the reflective surface, and that reflects the light beam from the reflective surface. The side end face of the optical path bending mirror facing the main scanning direction is bonded to the housing via an adhesive. The optical path bending mirror of one scanning optical system and the optical path bending mirror of the other scanning optical system are arranged symmetrically with respect to each other across the deflector when viewed from the main scanning direction. The adhesive bonded to the optical path bending mirror of one scanning optical system is placed on the side end face closer to the reflecting surface than the center in the thickness direction, and the adhesive bonded to the optical path bending mirror of the other scanning optical system is placed on the side end face closer to the reflecting surface than the center in the thickness direction.

[0008] An image forming apparatus according to a second aspect of the present invention includes a plurality of scanned bodies and the optical scanning device, and prints an image on a sheet by developing and superimposing electrostatic latent images formed on the plurality of scanned bodies. [Effects of the Invention]

[0009] In the present invention, it is possible to suppress deterioration in the quality of the images obtained by developing and superimposing the electrostatic latent images formed on the respective scanned bodies. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a schematic diagram of an image forming apparatus according to an embodiment. [Figure 2] FIG. 2 is a schematic diagram of an image forming unit according to an embodiment. [Figure 3] FIG. 2 is a perspective view of the inside of a housing of the optical scanning device according to the embodiment. [Figure 4] 2 is a schematic diagram of the inside of a housing of an optical scanning device according to an embodiment (a diagram schematically showing the arrangement position of an optical path bending mirror); FIG. [Figure 5] FIG. 2 is a perspective view of an optical path bending mirror according to an embodiment. [Figure 6] 3 is a schematic diagram showing the position of an adhesive relative to an optical path bending mirror (the position of an adhesive placed on the reflecting surface side) according to an embodiment. FIG. [Figure 7] 10 is a schematic diagram showing the position of an adhesive relative to an optical path bending mirror (the position of an adhesive placed on the opposite surface side) according to an embodiment. FIG. [Figure 8] 10A and 10B are diagrams illustrating the position of an adhesive and the displacement direction of an optical-path bending mirror when the adhesive expands according to the embodiment. [Figure 9] 10A and 10B are diagrams illustrating the placement position of an adhesive and the displacement direction of the first and second mirrors when the adhesive expands according to the embodiment. [Figure 10] 10 is a diagram showing the position of an adhesive in a modified example and the displacement directions of the first to third mirrors when the adhesive expands. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0011] An image forming apparatus equipped with an optical scanning device according to an embodiment of the present invention will be described below using a tandem color laser printer as an example. Note that the present invention is not limited to printers, but can also be applied to multifunction peripherals that have functions such as copying.

[0012] <Configuration of image forming device> 1, the image forming apparatus 1000 of this embodiment is placed on a substantially flat floor surface FL. The up-down direction of the image forming apparatus 1000 is perpendicular to the floor surface FL.

[0013] The image forming apparatus 1000 includes a sheet cassette CA. The sheet cassette CA accommodates a stack of sheets P. The sheets P are, for example, paper. The sheets P in the sheet cassette CA are used in a print job. The sheet cassette CA is detachable from the main body of the image forming apparatus 1000.

[0014] The image forming apparatus 1000 includes a main transport path MP, which runs from a sheet cassette CA, through a transfer position and a fixing position, and to an ejection tray ET.

[0015] In a print job, a sheet P in a sheet cassette CA is fed to a main transport path MP, and the sheet P is transported along the main transport path MP. An image is formed using toner. The image is then printed on the sheet P as it is being transported. In other words, a transfer process of the image onto the sheet P as it is being transported is performed at a transfer position. A fixing process of the image onto the sheet P is performed at a fixing position.

[0016] The image forming apparatus 1000 includes four image forming units 110. The four image forming units 110 correspond to the colors cyan, magenta, yellow, and black, respectively. The image forming apparatus 1000 also includes an optical scanning device 100. The configuration of the optical scanning device 100 will be described in detail later.

[0017] Each of the four image forming units 110 includes a photosensitive drum 10. The four photosensitive drums 10 are arranged at intervals in a predetermined direction and are rotatably supported. The axial direction in which the rotation axis of the photosensitive drum 10 extends is perpendicular to the up-down direction of the image forming apparatus 1000 and corresponds to the front-rear direction of the image forming apparatus 1000.

[0018] 2, the configuration of one image forming unit 110 will be described, but the configurations of the four image forming units 110 are the same. Therefore, the description of the configurations of the other image forming units 110 will be omitted, as the following description will be used as an example.

[0019] The image forming unit 110 further includes a charging device 1101, a developing device 1102, and a cleaning device 1103. When the image forming unit 110 forms an image, the photosensitive drum 10 rotates. The charging device 1101 charges the outer circumferential surface of the photosensitive drum 10.

[0020] Here, the optical scanning device 100 emits a light beam and scans the outer peripheral surface of the rotating photosensitive drum 10. As a result, the optical scanning device 100 forms an electrostatic latent image on the outer peripheral surface of the photosensitive drum 10. In this configuration, the photosensitive drum 10 corresponds to the "scanned body." The axial direction of the photosensitive drum 10 is the main scanning direction. The rotation direction of the photosensitive drum 10 is the sub-scanning direction, which is perpendicular to the main scanning direction.

[0021] The developing device 1102 supplies toner to the outer peripheral surface of the photosensitive drum 10 and develops the electrostatic latent image into a toner image. The photosensitive drum 10 rotates with the toner image carried on its outer peripheral surface. The cleaning device 1103 removes toner remaining on the outer peripheral surface of the photosensitive drum 10.

[0022] 1, the image forming apparatus 1000 also includes an intermediate transfer belt 120. The intermediate transfer belt 120 is an endless belt. The intermediate transfer belt 120 is rotatably supported. The intermediate transfer belt 120 is tensioned by a plurality of tension rollers.

[0023] One of the multiple tension rollers is connected to a belt motor (not shown). In the following description, the tension roller connected to the belt motor is referred to as a drive roller. In FIG. 1, of the multiple tension rollers, the drive roller is designated by the reference numeral 121, and the reference numerals of the other tension rollers are omitted. The intermediate transfer belt 120 rotates in response to the rotation of the drive roller 121. The other tension rollers rotate in response to the rotation of the intermediate transfer belt 120.

[0024] The image forming apparatus 1000 includes four primary transfer rollers 130. The four primary transfer rollers 130 correspond to the colors cyan, magenta, yellow, and black, respectively. Each primary transfer roller 130 is disposed on the inner circumferential side of the intermediate transfer belt 120. Each primary transfer roller 130 is pressed against the photosensitive drum 10 carrying an image of the corresponding color via the intermediate transfer belt 120.

[0025] The image forming apparatus 1000 includes a secondary transfer roller 140. The secondary transfer roller 140 is in pressure contact with the intermediate transfer belt 120 at the transfer position. The secondary transfer roller 140 sandwiches the intermediate transfer belt 120 between itself and a drive roller 121, forming a transfer nip between itself and the intermediate transfer belt 120. This forms a transfer nip at the transfer position. The main transport path MP passes through the transfer nip.

[0026] In a print job, a sheet P is transported toward a transfer position (that is, a transfer nip). The sheet P passes through the transfer nip during transport.

[0027] Each image forming unit 110 forms an image using toner of a corresponding color. That is, each image forming unit 110 develops an electrostatic latent image formed on the outer circumferential surface of the corresponding photosensitive drum 10 into a toner image. Each primary transfer roller 130 primarily transfers the image onto the intermediate transfer belt 120. Toner images of each color are sequentially transferred onto the intermediate transfer belt 120, superimposed on each other. As a result, a full-color image is formed on the intermediate transfer belt 120.

[0028] The intermediate transfer belt 120 rotates while carrying the primarily transferred full-color image. As the sheet P passes through the transfer nip, the sheet P comes into contact with the intermediate transfer belt 120. As a result, the full-color image on the intermediate transfer belt 120 is secondarily transferred onto the sheet P passing through the transfer nip.

[0029] The image forming apparatus 1000 includes a fixing unit 150. The fixing unit 150 includes a heating roller and a pressure roller. The fixing unit 150 is disposed at a fixing position. The heating roller has a built-in heater. The pressure roller is in pressure contact with the heating roller. The heating roller and the pressure roller are in pressure contact with each other to form a fixing nip at the fixing position.

[0030] In a print job, the sheet P passes through the fixing position. That is, the sheet P is sandwiched in the fixing nip. The fixing unit 150 heats the sheet P as it passes through the fixing position. At the fixing position, pressure is applied to the sheet P. The fixing unit 150 applies heat and pressure to the sheet P to fix the toner image to the sheet P. The sheet P that has been fixed is discharged to an output tray ET.

[0031] The image forming apparatus 1000 can execute a single-sided print job in which an image is printed on only one side of a sheet P, as well as a double-sided print job in which an image is printed on both sides of a sheet P. To execute a double-sided print job, the image forming apparatus 1000 is provided with a double-sided printing transport path DP.

[0032] The double-sided printing transport path DP branches off from the main transport path MP at a branching position downstream of the fixing position in the sheet transport direction, and merges with the main transport path MP at a merging position upstream of the transfer position in the sheet transport direction.

[0033] If the job being executed is a single-sided print job, the sheet P passes through the transfer nip only once, and a single transfer process is performed on the sheet P while it is passing through the transfer nip. After the first transfer process, the sheet P is discharged directly onto the discharge tray ET.

[0034] If the job being executed is a double-sided printing job, the sheet P passes through the transfer nip twice, with one transfer process performed on each of the front and back sides of the sheet P. Specifically, the first time the sheet P passes through the transfer nip, the transfer process is performed on one side of the sheet P. After the first transfer process, the sheet P is switched back after the rear end of the sheet P passes the branch position but before the sheet P is completely discharged onto the discharge tray ET. This causes the rear end of the sheet P to be drawn into the double-sided printing conveyance path DP.

[0035] Thereafter, the sheet P is transported along the double-sided printing transport path DP. Then, the sheet P on the double-sided printing transport path DP is returned to the main transport path MP from the junction position. The sheet P returned to the main transport path MP is transported along the main transport path MP and passes through the transfer nip again. At this time, the orientation of the front and back surfaces of the sheet P is reversed to the orientation when it passed through the transfer nip the previous time. As a result, when the sheet P passes through the transfer nip for the second time, the transfer process is performed on the other side of the sheet P that is opposite to the one side.

[0036] <Configuration of optical scanning device> As shown in FIGS. 3 and 4, the optical scanning device 100 includes a housing 1. The housing 1 is made of resin. The housing 1 is box-shaped with a bottom and an opening at the top. The opening is closed by a cover member (not shown). The internal area of ​​the housing 1 houses optical components, which will be described later. For example, the housing 1 has an exit opening (not shown) at the bottom into which glass is fitted. The optical scanning device 100 emits a light beam from inside the housing 1 to the outside through the exit opening.

[0037] The optical scanning device 100 includes a deflector 2. The optical scanning device 100 also includes a light source 20. The light source 20 has a plurality of semiconductor lasers corresponding to the colors cyan, magenta, yellow, and black, respectively. A semiconductor laser is assigned to each of the four photosensitive drums 10. Each semiconductor laser emits a light beam that scans the outer circumferential surface of the assigned photosensitive drum 10.

[0038] The deflector 2 is disposed inside the housing 1. The deflector 2 is rotatably supported. The axial direction in which the rotation axis RA of the deflector 2 extends is defined as the vertical direction of the optical scanning device 100. The photosensitive drum 10 is disposed below the optical scanning device 100. The vertical direction of the optical scanning device 100 (i.e., the axial direction of the deflector 2) may coincide with the vertical direction of the image forming device 1000, or may be inclined relative to the vertical direction of the image forming device 1000.

[0039] Of the directions perpendicular to the axial direction of the deflector 2, one direction is defined as the front-to-rear direction of the optical scanning device 100, and the other direction perpendicular to the one direction is defined as the left-to-right direction of the optical scanning device 100. The front-to-rear direction of the optical scanning device 100 is the main scanning direction.

[0040] The axial direction in which the rotation axes of the photosensitive drums 10 extend is parallel to the front-to-rear direction (i.e., the main scanning direction) of the optical scanning device 100. The arrangement direction of the photosensitive drums 10 is parallel to the left-to-right direction of the optical scanning device 100. The extension direction of a straight line connecting the axial centers of the rotation axes of the photosensitive drums 10 corresponds to the arrangement direction of the photosensitive drums 10.

[0041] In the drawings referred to in the following description, the X direction is the front-to-rear direction of the optical scanning device 100 (i.e., the main scanning direction), the Y direction is the left-to-right direction of the optical scanning device 100, and the Z direction is the up-down direction of the optical scanning device 100.

[0042] The deflector 2 is a polygon mirror having a deflection surface on its outer periphery as a light-reflecting surface. As the deflector 2 rotates, the deflector 2 receives and reflects the light beam emitted from the light source 20 on the deflection surface. In this way, the deflector 2 deflects the light beam emitted from the light source 20.

[0043] The optical scanning device 100 includes a pair of scanning optical systems S. In the following description, when it is necessary to distinguish between one of the pair of scanning optical systems S, one scanning optical system S will be given the symbol S1, and the other scanning optical system S will be given the symbol S2.

[0044] Each of the pair of scanning optical systems S includes two scanning lenses Ls. The scanning lenses Ls receive the light beams deflected by the deflector 2. The scanning lenses Ls are fθ lenses. The scanning lenses Ls focus the light beams and correct the scanning speed to be constant.

[0045] Each of the pair of scanning optical systems S includes three optical path bending mirrors 3. In the following description, when it is necessary to distinguish between the three optical path bending mirrors 3, the three optical path bending mirrors 3 will be denoted by the reference numerals 30, 31, and 32, respectively.

[0046] The optical path bending mirror 3 reflects the light beam deflected by the deflector 2. Specifically, the light beam deflected by the deflector 2 passes through the scanning lens Ls, enters the optical path bending mirror 3, and is reflected by the optical path bending mirror 3. The optical path bending mirror 3 reflects the light beam, thereby directing the light beam onto the outer circumferential surface of the photosensitive drum 10.

[0047] As shown in FIG. 5, the optical path bending mirror 3 is a rectangular parallelepiped member with its longitudinal direction aligned with the main scanning direction (X direction). The optical path bending mirror 3 has one surface extending in its longitudinal direction as a reflective surface 3a. The optical path bending mirror 3 reflects the light beam at the reflective surface 3a. The normal direction of the reflective surface 3a of the optical path bending mirror 3 is the thickness direction Dt. In the following description, the surface of the optical path bending mirror 3 opposite to the reflective surface 3a is designated by the symbol 3b, and this surface will be referred to as the opposite surface 3b.

[0048] Here, the optical paths of the light beams that scan each photosensitive drum 10 (as viewed from the main scanning direction) will be described with reference to FIG. 4. In FIG. 4, the photosensitive drums 10 are distinguished by being assigned different reference symbols (10a, 10b, 10c, and 10d). The light beam that scans photosensitive drum 10a is assigned reference symbol La, the light beam that scans photosensitive drum 10b is assigned reference symbol Lb, the light beam that scans photosensitive drum 10c is assigned reference symbol Lc, and the light beam that scans photosensitive drum 10d is assigned reference symbol Ld. The same applies to the drawings referred to in the following description.

[0049] The light beam La is reflected by the optical path bending mirror 30 of the scanning optical system S1. The optical path bending mirror 30 of the scanning optical system S1 reflects the light beam La and guides the light beam La toward the photosensitive drum 10a. In other words, the optical path bending mirror 30 of the scanning optical system S1 is assigned to the photosensitive drum 10a.

[0050] The light beam Lb is reflected by the optical path bending mirrors 31 and 32 of the scanning optical system S1. The optical path bending mirror 31 of the scanning optical system S1 reflects the light beam Lb deflected by the deflector 2 toward the optical path bending mirror 32 of the scanning optical system S1. The optical path bending mirror 32 of the scanning optical system S1 reflects the light beam Lb reflected by the optical path bending mirror 31 of the scanning optical system S1, thereby guiding the light beam Lb toward the photosensitive drum 10b. In other words, the optical path bending mirrors 31 and 32 of the scanning optical system S1 are assigned to the photosensitive drum 10b.

[0051] The light beam Lc is reflected by the optical path bending mirrors 31 and 32 of the scanning optical system S2. The optical path bending mirror 31 of the scanning optical system S2 reflects the light beam Lc deflected by the deflector 2 toward the optical path bending mirror 32 of the scanning optical system S2. The optical path bending mirror 32 of the scanning optical system S2 reflects the light beam Lc reflected by the optical path bending mirror 31 of the scanning optical system S2, thereby guiding the light beam Lc toward the photosensitive drum 10c. In other words, the optical path bending mirrors 31 and 32 of the scanning optical system S2 are assigned to the photosensitive drum 10c.

[0052] The light beam Ld is reflected by the optical path bending mirror 30 of the scanning optical system S2. The optical path bending mirror 30 of the scanning optical system S2 reflects the light beam Ld and guides the light beam Ld toward the photosensitive drum 10d. In other words, the optical path bending mirror 30 of the scanning optical system S2 is assigned to the photosensitive drum 10d.

[0053] <Position of optical path bending mirror> The optical members of the optical scanning device 100 are disposed at positions as shown in FIG. 4. One scanning optical system S1 (optical path bending mirrors 30, 31, and 32) and the other scanning optical system S2 (optical path bending mirrors 30, 31, and 32) are disposed symmetrically with respect to the rotation axis RA of the deflector 2 when viewed from the main scanning direction (X direction). In other words, one scanning optical system S1 and the other scanning optical system S2 are disposed symmetrically with respect to the rotation axis RA of the deflector 2, which serves as the axis of symmetry, when viewed from the main scanning direction. In other words, one scanning optical system S1 is disposed on one side (left side in FIG. 4) in the left-right direction (Y direction) of the rotation axis RA of the deflector 2, and the other scanning optical system S2 is disposed on the other side (right side in FIG. 4) of the rotation axis RA of the deflector 2 in the left-right direction.

[0054] Specifically, when viewed from the main scanning direction (X direction), the optical path bending mirrors 30 of the one scanning optical system S1 and the other scanning optical system S2 are arranged so as to be line-symmetric with respect to the rotation axis RA of the deflector 2. When viewed from the main scanning direction, the optical path bending mirrors 31 of the one scanning optical system S1 and the other scanning optical system S2 are arranged so as to be line-symmetric with respect to the rotation axis RA of the deflector 2. When viewed from the main scanning direction, the optical path bending mirrors 32 of the one scanning optical system S1 and the other scanning optical system S2 are arranged so as to be line-symmetric with respect to the rotation axis RA of the deflector 2. That is, the optical path bending mirrors 30 of the one scanning optical system S1 and the other scanning optical system S2 are paired, the optical path bending mirrors 31 of the one scanning optical system S1 and the other scanning optical system S2 are paired, and the optical path bending mirrors 32 of the one scanning optical system S1 and the other scanning optical system S2 are paired.

[0055] <Adhesive fixing of optical path bending mirror> As shown in Figures 6 and 7, the optical path bending mirror 30 is adhered to the housing 1 via an adhesive GL. The type of adhesive GL is not particularly limited. For example, an acrylic resin-based or epoxy resin-based adhesive may be used as the adhesive GL. Alternatively, an ultraviolet-curing adhesive may be used as the adhesive GL.

[0056] The adhesive GL is applied to a side end face 3c of the optical path bending mirror 3 that faces the main scanning direction (X direction). The side end face 3c of the optical path bending mirror 3 is then adhered to the housing 1 via the adhesive GL. That is, the adhesive GL is disposed between the side end face 3c of the optical path bending mirror 3 and the housing 1. The adhesive GL is hardened by a hardening process (for example, a process of irradiating the adhesive GL with ultraviolet light).

[0057] For example, mirror support portions are provided in the housing 1. The mirror support portions are arranged on both sides in the front-to-rear direction (X direction) within the interior area of ​​the housing 1. The mirror support portions support both ends of the optical path bending mirror 3 in the main scanning direction (X direction).

[0058] Of the side end faces 3c at both ends of the optical path bending mirror 3, the side end face 3c at one end is adhered to the housing 1, while the side end face 3c at the other end is not adhered to the housing 1. The other end of the optical path bending mirror 3 is urged toward a mirror support part of the housing 1 by an urging member (not shown) such as a leaf spring. The optical path bending mirror 3 is supported at two points with respect to the housing 1 so that the orientation of the reflecting surface 3a does not change when viewed from the main scanning direction (X direction), i.e. so that it does not rotate.

[0059] However, this is not limited to this, and of the side end faces 3c at both ends of the optical path bending mirror 3, both the side end face 3c at one end and the side end face 3c at the other end may be adhered to the housing 1 via adhesive GL.

[0060] <Adhesive placement position> The position where the adhesive GL is placed varies depending on the position of the optical path bending mirror 3 to be bonded. The position where the adhesive GL is placed is shown in Figures 6 and 7. In some optical path bending mirrors 3, the adhesive GL is placed on the side end face 3c closer to the reflecting surface 3a than the center in the thickness direction Dt (see Figure 6), while in other optical path bending mirrors 3, the adhesive GL is placed on the side end face 3c closer to the reflecting surface 3a than the center in the thickness direction Dt (see Figure 7). In Figures 6 and 7, the center in the thickness direction Dt is indicated by a dashed line. This also applies to the drawings referred to in the following explanation.

[0061] Here, the adhesive GL may expand due to a rise in temperature of the optical scanning device 100. When the adhesive GL expands, the optical path bending mirror 3 is displaced from its initial position. The initial position is the position of the optical path bending mirror 3 before the adhesive GL expands.

[0062] If the adhesive GL is positioned closer to the reflecting surface 3a than the center in the thickness direction Dt on the side end surface 3c (see FIG. 6), when the adhesive GL expands, the end of the optical path bending mirror 3 on one side in the main scanning direction (X direction) to which the adhesive GL is adhered will be displaced in the direction from the reflecting surface 3a toward the opposite surface 3b. In FIG. 6, the outer shape of the optical path bending mirror 3 displaced by the expansion of the adhesive GL is shown by a dashed line. In FIG. 6, the optical path bending mirror 3 is displaced diagonally downward to the left of the drawing.

[0063] If the adhesive GL is positioned on the side end surface 3c closer to the opposite surface 3b than the center in the thickness direction Dt (see FIG. 7), when the adhesive GL expands, the end of the optical path bending mirror 3 on one side in the main scanning direction (X direction) to which the adhesive GL is adhered is displaced in the direction from the opposite surface 3b toward the reflecting surface 3a. In FIG. 7, the outer shape of the optical path bending mirror 3 displaced by the expansion of the adhesive GL is shown by a dashed line. In FIG. 7, the optical path bending mirror 3 is displaced diagonally upward to the left of the drawing.

[0064] When such expansion occurs in the adhesive GL, the reflecting surface 3a of the optical path bending mirror 3 is displaced from its initial position when viewed from the main scanning direction (X direction). As a result, the scanning position of the light beam on the photosensitive drum 10 is shifted in the sub-scanning direction when viewed from the main scanning direction. As a result, the writing start position of the electrostatic latent image is shifted. In other words, the formation position of the electrostatic latent image is shifted.

[0065] If the electrostatic latent image is misaligned on any of the photosensitive drums 10, when the toner image obtained by developing that electrostatic latent image is transferred to the intermediate transfer belt 120 and superimposed on the toner images of other colors, a misalignment occurs between the toner images of other colors. In other words, color misalignment occurs. As a result, image quality deteriorates.

[0066] For example, suppose the scanning position of the light beam relative to a certain photosensitive drum 10 (referred to here as the first photosensitive drum 10) is shifted when viewed from the main scanning direction (X direction). In this case, if the scanning position of the light beam relative to another photosensitive drum 10 (referred to here as the second photosensitive drum 10) is also shifted in the same direction, the misalignment on the intermediate transfer belt 120 between the toner image obtained by developing the electrostatic latent image on the first photosensitive drum 10 and the toner image obtained by developing the electrostatic latent image on the second photosensitive drum 10 is suppressed. On the other hand, if the scanning position of the light beam relative to the second photosensitive drum 10 does not shift or shifts in the opposite direction, the amount of misalignment on the intermediate transfer belt 120 between the toner image obtained by developing the electrostatic latent image on the first photosensitive drum 10 and the toner image obtained by developing the electrostatic latent image on the second photosensitive drum 10 becomes large.

[0067] Therefore, in this embodiment, the adhesive GL of each of the one optical path bending mirror 3 and the other optical path bending mirror 3, which are positioned symmetrically on either side of the deflector 2, is bonded to the opposite side, that is, the reflective surface 3a side and the opposite surface 3b side. If the adhesive GL bonded to the side end surface 3c of one optical path bending mirror 3 is arranged on the reflective surface 3a side, then the adhesive GL bonded to the side end surface 3c of the other optical path bending mirror 3 is arranged on the opposite surface 3b side.

[0068] In this embodiment, the positional relationship of the optical path bending mirrors 30 of the scanning optical systems S1 and S2 is symmetrical with respect to the deflector 2. The positional relationship of the optical path bending mirrors 31 of the scanning optical systems S1 and S2 is symmetrical with respect to the deflector 2. The positional relationship of the optical path bending mirrors 32 of the scanning optical systems S1 and S2 is symmetrical with respect to the deflector 2.

[0069] The arrangement position of the adhesive GL that is adhered to these optical path bending mirrors 3 will be specifically described below with reference to Figures 8 and 9. Figures 8 and 9 are diagrams that schematically show the arrangement position when the optical path bending mirror 3 is viewed from the main scanning direction (X direction). In Figures 8 and 9, the arrangement position of the adhesive GL is schematically shown by a dot pattern.

[0070] In this embodiment, as shown in the upper diagram of Fig. 8, the adhesive GL that is adhered to the optical path bending mirror 30 of the scanning optical system S1 is placed on the reflective surface 3a side. In this case, the adhesive GL that is adhered to the optical path bending mirror 30 of the scanning optical system S2 is placed on the opposite surface 3b side.

[0071] 9, in this embodiment, the adhesive GL adhered to the optical path bending mirror 31 of the scanning optical system S1 is arranged on the reflective surface 3a side, and the adhesive GL adhered to the optical path bending mirror 32 of the scanning optical system S1 is arranged on the reflective surface 3a side. In this case, the adhesive GL adhered to the optical path bending mirror 31 of the scanning optical system S2 is arranged on the opposite surface 3b side, and the adhesive GL adhered to the optical path bending mirror 32 of the scanning optical system S2 is arranged on the opposite surface 3b side.

[0072] The optical path bending mirror 31 reflects the light beam deflected by the deflector 2 toward the optical path bending mirror 32. The optical path bending mirror 32 reflects the light beam reflected by the optical path bending mirror 31, thereby directing the light beam to the assigned photosensitive drum 10. In other words, the optical path bending mirror 31 corresponds to the "first mirror," and the optical path bending mirror 32 corresponds to the "second mirror."

[0073] In this configuration, when the adhesive GL expands, the optical path bending mirror 30 is displaced as shown in the lower diagram of FIG. 8, and the optical path bending mirrors 31 and 32 are displaced as shown in the lower diagram of FIG. 9. Specifically, each optical path bending mirror 3 is displaced in the direction of the white arrow in the diagram when viewed from the main scanning direction (X direction). Note that in FIGS. 8 and 9, each optical path bending mirror 3 before the adhesive GL expands is shown by a solid line, and each light beam is shown by a solid arrow. Furthermore, each optical path bending mirror 3 after the adhesive GL expands is shown by a dotted line, and each light beam is shown by a dotted arrow.

[0074] As a result, when the adhesive GL expands, the reflecting surface 3a of each optical path bending mirror 3 is displaced from its initial position, but the light beams reflected by each optical path bending mirror 3 and directed toward each photosensitive drum 10 are displaced in the same direction, so that it is possible to suppress relative displacement of the scanning position relative to each photosensitive drum 10. This makes it possible to suppress color shifts in color images obtained by developing and superimposing the electrostatic latent images formed on each photosensitive drum 10. In other words, it is possible to suppress degradation in the image quality of color images.

[0075] <Modification> In this modification, the optical path of the light beam directed toward the photosensitive drum 10 is as shown in FIG.

[0076] Specifically, in the modified example, one scanning optical system S1 and the other scanning optical system S2 each include three optical path bending mirrors 3, namely, optical path bending mirrors 301, 302, and 303. Optical path bending mirror 301 corresponds to the "first mirror" and will be referred to as first mirror 301 in the following description. Optical path bending mirror 302 corresponds to the "second mirror" and will be referred to as second mirror 302 in the following description. Optical path bending mirror 303 corresponds to the "third mirror" and will be referred to as third mirror 303 in the following description.

[0077] First mirror 301 reflects the light beam deflected by deflector 2 toward second mirror 302. Second mirror 302 reflects the light beam reflected by first mirror 301 toward third mirror 303. Third mirror 303 reflects the light beam reflected by second mirror 302, thereby directing the light beam onto the outer circumferential surface of the assigned photosensitive drum 10. As a result, one optical path is formed by the three mirrors: first mirror 301, second mirror 302, and third mirror 303.

[0078] Here, the first mirrors 301 of the one scanning optical system S1 and the other scanning optical system S2 are disposed symmetrically with respect to each other across the deflector 2 when viewed from the main scanning direction. The second mirrors 302 of the one scanning optical system S1 and the other scanning optical system S2 are disposed symmetrically with respect to each other across the deflector 2 when viewed from the main scanning direction. The third mirrors 303 of the one scanning optical system S1 and the other scanning optical system S2 are disposed symmetrically with respect to each other across the deflector 2 when viewed from the main scanning direction.

[0079] 10, the adhesive GL adhered to the first mirror 301 of one scanning optical system S1 and the adhesive GL adhered to the first mirror 301 of the other scanning optical system S2 are arranged on opposite sides of the reflective surface 3a and the opposite surface 3b, respectively. The adhesive GL adhered to the first mirror 301 of one scanning optical system S1 is arranged on the reflective surface 3a side, and the adhesive GL adhered to the first mirror 301 of the other scanning optical system S2 is arranged on the opposite surface 3b side.

[0080] The adhesive GL adhered to the second mirror 302 of one scanning optical system S1 and the adhesive GL adhered to the second mirror 302 of the other scanning optical system S2 are arranged on opposite sides of the reflective surface 3a and the opposite surface 3b, respectively. The adhesive GL adhered to the second mirror 302 of one scanning optical system S1 is arranged on the reflective surface 3a side, and the adhesive GL adhered to the second mirror 302 of the other scanning optical system S2 is arranged on the opposite surface 3b side.

[0081] The adhesive GL adhered to the third mirror 303 of one scanning optical system S1 and the adhesive GL adhered to the third mirror 303 of the other scanning optical system S2 are arranged on opposite sides of the reflective surface 3a and the opposite surface 3b, respectively. The adhesive GL adhered to the third mirror 303 of one scanning optical system S1 is arranged on the reflective surface 3a side, and the adhesive GL adhered to the third mirror 303 of the other scanning optical system S2 is arranged on the opposite surface 3b side.

[0082] In this modification, when the adhesive GL expands, each optical path bending mirror 3 is displaced as shown in the lower diagram of FIG. 10. Each optical path bending mirror 3 is displaced in the direction of the outline arrow in the diagram. As a result, in this modification, as in the above embodiment, it is possible to suppress relative deviations in the scanning position with respect to each photosensitive drum 10, thereby suppressing color shifts in color images. In other words, it is possible to suppress degradation of image quality.

[0083] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present invention is defined by the claims rather than the description of the above embodiments, and further includes all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0084] 1 chassis 2 deflector 3, 30 Optical path bending mirror 3a Reflective surface 3b Opposite side 3c Side end surface 10 Photosensitive drum (scanned body) 31 Optical path bending mirror (first mirror) 32 Optical path bending mirror (second mirror) 100 Optical scanning device 301 Optical path bending mirror (first mirror) 302 Optical path bending mirror (second mirror) 303 Optical path bending mirror (third mirror) 1000 Image forming device Dt thickness direction GL Adhesive La, Lb, Lc, Ld light beams S, S1, S2 scanning optics

Claims

1. An optical scanning device that deflects a light beam to scan a plurality of scanned bodies and forms an electrostatic latent image on the scanned bodies, The housing and a deflector rotatably disposed within the housing and configured to deflect the light beam; a pair of scanning optical systems disposed inside the housing; the scanning optical system includes an optical path bending mirror that reflects the light beam deflected by the deflector to guide the light beam onto the assigned scanned object, the optical path bending mirror is a member having a reflective surface whose longitudinal direction is the main scanning direction and whose thickness direction is a direction normal to the reflective surface, and which reflects the light beam at the reflective surface, a side end surface of the optical path bending mirror facing the main scanning direction is bonded to the housing via an adhesive; the optical path bending mirror of one of the scanning optical systems and the optical path bending mirror of the other of the scanning optical systems are arranged to be symmetrical with each other across the deflector when viewed from the main scanning direction, the adhesive bonded to the optical path bending mirror of one of the scanning optical systems is disposed on the side end surface closer to the reflecting surface than the center in the thickness direction, an optical scanning device, wherein the adhesive bonded to the optical path bending mirror of the other scanning optical system is positioned on the side of the side end face opposite to the reflecting surface side from the center in the thickness direction.

2. the scanning optical system includes a first mirror and a second mirror as the optical path bending mirrors, the first mirror reflects the light beam deflected by the deflector toward the second mirror; the second mirror reflects the light beam reflected by the first mirror, thereby directing the light beam onto the assigned scanned object; the first mirrors of one of the scanning optical systems and the other of the scanning optical systems are arranged to be symmetrical with each other across the deflector when viewed from the main scanning direction, the second mirrors of one of the scanning optical systems and the second mirrors of the other of the scanning optical systems are arranged to be symmetrical with each other across the deflector when viewed from the main scanning direction, the adhesive bonded to the first mirror of one of the scanning optical systems and the adhesive bonded to the first mirror of the other of the scanning optical systems are bonded to the reflective surface side and the opposite surface side, respectively, in an opposite manner to each other; 2. The optical scanning device of claim 1, wherein the adhesive bonded to the second mirror of one of the scanning optical systems and the adhesive bonded to the second mirror of the other of the scanning optical systems are bonded to opposite sides of the reflective surface and the opposite surface.

3. the scanning optical system includes a first mirror, a second mirror, and a third mirror as the optical path bending mirrors; the first mirror reflects the light beam deflected by the deflector toward the second mirror; the second mirror reflects the light beam reflected by the first mirror toward the third mirror; the third mirror reflects the light beam reflected by the second mirror, thereby directing the light beam onto the assigned scanned object; the first mirrors of one of the scanning optical systems and the other of the scanning optical systems are arranged to be symmetrical with each other across the deflector when viewed from the main scanning direction, the second mirrors of one of the scanning optical systems and the second mirrors of the other of the scanning optical systems are arranged to be symmetrical with each other across the deflector when viewed from the main scanning direction, the third mirrors of one of the scanning optical systems and the other of the scanning optical systems are arranged to be symmetrical with each other across the deflector when viewed from the main scanning direction, the adhesive bonded to the first mirror of one of the scanning optical systems and the adhesive bonded to the first mirror of the other of the scanning optical systems are bonded to the reflective surface side and the opposite surface side, respectively, in an opposite manner to each other; the adhesive bonded to the second mirror of one of the scanning optical systems and the adhesive bonded to the second mirror of the other of the scanning optical systems are bonded to the reflective surface side and the opposite surface side, respectively, in an opposite manner to each other; 2. The optical scanning device of claim 1, wherein the adhesive bonded to the third mirror of one of the scanning optical systems and the adhesive bonded to the third mirror of the other of the scanning optical systems are bonded to opposite sides of the reflective surface and the opposite surface.

4. A plurality of scanned objects; and an optical scanning device according to any one of claims 1 to 3 that forms electrostatic latent images on a plurality of the scanned bodies, An image forming apparatus that prints an image on a sheet by developing and superimposing the electrostatic latent images formed on the plurality of scanned bodies.

Images