# Patent

## Title
Image forming apparatus having three-position support

## Abstract

An image forming apparatus including: a light scanning apparatus having an optical box containing a deflector configured to deflect a light beam scanning a photosensitive member, the light scanning apparatus being mounted to a main body of the image forming apparatus by being inserted through an insertion portion formed in the main body; a supporting unit including a first and a second supporting portions to support, in a direction intersecting an inserting direction of the box, the box in a vicinity of a downstream side wall of the optical box in the inserting direction, and a third supporting portion to support the box in a vicinity of an upstream side wall of the box; and a connecting portion configured to connect the box and the main body in the vicinity of the upstream side wall and on at least one side of the third supporting portion in the direction.

## Background
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image forming apparatus including a light scanning apparatus.
2. Description of the Related Art
An electrophotographic image forming apparatus (hereinafter referred to as “image forming apparatus”) is configured to form an image on a sheet through an electrophotographic process. As the image forming apparatus, for example, there are known an electrophotographic copying machine (such as a digital copying machine), an electrophotographic printer (such as a color laser beam printer), and a facsimile machine. The image forming apparatus not only encompasses an image forming apparatus configured to form a monochrome image but also encompasses a color image forming apparatus.
A light scanning apparatus of the image forming apparatus emits a laser beam (hereinafter referred to as “light beam”), and scans a surface of a rotating photosensitive drum with the light beam, to thereby form an electrostatic latent image on the surface of the photosensitive drum. A developing device develops the electrostatic latent image using toner to form a toner image. A transferring device transfers the toner image, which is formed on the photosensitive drum, onto a sheet. A fixing device fixes the toner image onto the sheet by a thermal fixation. In this manner, an image is formed.
In general, a main body of the image forming apparatus includes a frame or side plates opposed to each other. A supporting member configured to support the light scanning apparatus is stretched over the frame or the side plates. The light scanning apparatus is supported by the supporting member in a vertical direction, and is fixed in a state of being supported by the supporting member. The light scanning apparatus (optical box), which is fixed by the supporting member, may be deformed in conformity with the flatness of the supporting member. Therefore, strict design is necessary regarding the flatness of the supporting member and the flatness of a seating surface of the light scanning apparatus, which is held in abutment against the supporting member.
There is known a method of supporting and fixing the light scanning apparatus at three seating surfaces (three points) as a method of stably supporting the light scanning apparatus by the supporting member while preventing the deformation of the light scanning apparatus, which may be caused in conformity with the flatness of the supporting member (Japanese Patent Application Laid-Open No. 2006-85058).
According to Japanese Patent Application Laid-Open No. 2006-85058, the light scanning apparatus is fixed to the supporting member at three seating surfaces. The three seating surfaces are provided at respective apexes of a substantially isosceles triangle, and are arranged in a bottom portion of the light scanning apparatus in a balanced manner in conformity with the shape of the light scanning apparatus. In Japanese Patent Application Laid-Open No. 2006-85058, the seating surfaces are provided at both horizontal end portions on one side of the light scanning apparatus. Further, the seating surface is provided at the center in a width direction on another side of the light scanning apparatus. The seating surfaces are provided on respective fixing portions provided on the light scanning apparatus. Surfaces opposed to the seating surfaces of the fixing portions in the vertical direction are pressed by plate springs, respectively. With this, the light scanning apparatus is fixed to the supporting member.
The image forming apparatus includes driving sources configured to drive the developing device, the photosensitive drum, and the like. Vibrations of various frequencies, which are generated in the driving sources, are transmitted to the light scanning apparatus via the side plates of the image forming apparatus and the supporting member.
When the three seating surfaces are used as in Japanese Patent Application Laid-Open No. 2006-85058, torsional vibration is generated on the other side of the light scanning apparatus due to the vibrations generated in the driving sources. The torsional vibration causes a rotation about a central axis extending from the other side to the one side of the light scanning apparatus and passing through the seating surface at the center on the other side of the light scanning apparatus. However, the one side of the light scanning apparatus is fixed at the seating surfaces of both the horizontal end portions, and hence the torsional vibration that causes a rotation about the central axis is not generated on the one side of the light scanning apparatus. When the torsional vibration is generated on the other side of the light scanning apparatus due to the vibrations generated in the driving sources, a light beam, which is emitted from the light scanning apparatus, scans the photosensitive drum in a vibrating manner. Therefore, the photosensitive drum is irradiated with the light beam with unevenness in irradiation position. The unevenness of the irradiation positions causes an image defect in a stripe shape, which is called “uneven pitch”.
The optical box of the light scanning apparatus of such a type that the light beams, which are emitted from a plurality of light sources of the single light scanning apparatus, respectively, are deflected by a single rotary polygon mirror at the same time may have a rectangular parallelepiped shape or a polygonal (quadrangular or more) box shape, which is similar to the rectangular parallelepiped shape, due to the large number of mirrors and lenses and the arrangement thereof. Therefore, when such a light scanning apparatus is fixed to the supporting member at the three seating surfaces, the torsional vibration is generated conspicuously, in particular.
SUMMARY OF THE INVENTION
In view of the above-mentioned problem, the present invention provides an image forming apparatus, which reduces torsional vibration of a light scanning apparatus while avoiding the deformation of the light scanning apparatus due to the flatness of a supporting unit by use of three supporting portions.
In order to achieve the above-mentioned object, according to one embodiment of the present invention, there is provided an image forming apparatus, comprising:
a photosensitive member;
a light scanning apparatus including:

    
    
        a deflector configured to deflect a light beam so that the light beam scans a surface of the photosensitive member; and
        an optical box configured to contain the deflector,
        the optical box being inserted through an insertion portion formed in a side wall of a main body of the image forming apparatus so that the light scanning apparatus is mounted to the main body of the image forming apparatus;
    
    


a supporting unit including a first supporting portion, a second supporting portion, and a third supporting portion, the supporting unit being configured to support the optical box, the first supporting portion and the second supporting portion being configured to support, in a direction intersecting an inserting direction of inserting the optical box into the main body of the image forming apparatus, the optical box in a vicinity of a side wall of the optical box on a downstream side in the inserting direction, the third supporting portion being configured to support the optical box in a vicinity of a side wall of the optical box on an upstream side in the inserting direction; and
a connecting portion configured to connect the optical box supported by the supporting unit and the main body of the image forming apparatus in the vicinity of the side wall of the optical box on the upstream side in the inserting direction and on at least one side of the third supporting portion in the direction intersecting the inserting direction of the optical box.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.



BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1A and 1B are perspective views of a light scanning apparatus, which is fixed to supporting members, according to a first embodiment.
FIGS. 2A, 2B, 2C, and 2D are views illustrating a fixing portion, a horizontal mounting portion, a fixing portion, and a fitting protrusion, respectively.
FIGS. 3A, 3B, and 3C are views illustrating the light scanning apparatus, which is fixed to the supporting members, according to the first embodiment.
FIGS. 4A, 4B, and 4C are views illustrating the light scanning apparatus according to the first embodiment.
FIGS. 5A, 5B, 5C, and 5D are views illustrating respective vibration modes of the light scanning apparatus which is mounted on the supporting members.
FIGS. 6A, 6B, and 6C are graphs showing respective results of vibration analyses of the light scanning apparatus.
FIG. 7 is a perspective view of a light scanning apparatus, which is fixed to supporting members, according to a second embodiment.
FIG. 8 is a perspective view of a light scanning apparatus, which is fixed to supporting members, according to a third embodiment.
FIG. 9 is a sectional view of an image forming apparatus.



DESCRIPTION OF THE EMBODIMENTS
The embodiments will be described with reference to the accompanying drawings.
First Embodiment
Image Forming Apparatus
FIG. 9 is a sectional view of an image forming apparatus 600. The image forming apparatus 600 includes four image forming portions 300 (300Y, 300M, 300C, and 300K) configured to form yellow, magenta, cyan, and black toner images, respectively. The image forming portions 300 primarily transfer the respective toner images onto an intermediate transfer belt 400 so as to superimpose the four toner images on the intermediate transfer belt 400. The toner images, which are superimposed on the intermediate transfer belt 400, are secondarily transferred onto a recording medium (hereinafter referred to as a sheet) S to form a color image on the sheet.
The image forming portions 300Y, 300M, 300C, and 300K include photosensitive drums (photosensitive members) 310 (310Y, 310M, 310C, and 310K) as image bearing members, respectively. Around each photosensitive drum 310, there are provided a charging roller 330, a developing device 320, a primary transfer roller 340, and a cleaning device 350. A light scanning apparatus 100 is arranged below the image forming portions 300.
The charging rollers 330 (330Y, 330M, 330C, and 330K) uniformly charge surfaces of the photosensitive drums 310Y, 310M, 310C, and 310K, respectively. The light scanning apparatus 100 scans the uniformly charged surfaces of the photosensitive drums 310Y, 310M, 310C, and 310K with light beams L (LY, LM, LC, and LK) modulated in accordance with image information of the respective colors to form electrostatic latent images on the surfaces of the photosensitive drums 310, respectively.
The developing devices 320 (320Y, 320M, 320C, and 320K) develop the electrostatic latent images with developers (toners) of the respective colors to form the toner images of the respective colors on the photosensitive drums 310.
The primary transfer rollers 340 (340Y, 340M, 340C, and 340K) primarily transfer the toner images on the photosensitive drums 310 onto the intermediate transfer belt 400 to superimpose the four color toner images on the intermediate transfer belt 400.
A secondary transfer roller 410 secondarily transfers the toner images superimposed on the intermediate transfer belt 400 onto the sheet S fed from a feeding portion 200 in a collective manner. The sheet S is conveyed to a fixing device 500. The fixing device 500 fixes the toner images to the sheet S by heat and pressure to form a color image on the sheet S.
[Light Scanning Apparatus]
FIGS. 4A, 4B, and 4C are views illustrating the light scanning apparatus 100 according to a first embodiment. FIG. 4A is a perspective view illustrating an internal structure of the light scanning apparatus 100 in a state in which a cover 7 is removed. FIG. 4B is a sub-scanning sectional view of the light scanning apparatus 100, which is taken along the line IVB-IVB of FIG. 4A. The cover 7, which is omitted in FIG. 4A, is mounted on the light scanning apparatus 100 illustrated in FIG. 4B. FIG. 4C is a view illustrating a bottom portion 5d of an optical box 5 of the light scanning apparatus 100.
The light scanning apparatus 100 includes the optical box 5 as a housing and the cover 7. In the embodiment, the optical box 5 is formed by injection molding of a polycarbonate-based glass-reinforced resin material. The optical box 5 has a rectangular shape when viewed from above (in a first direction described later). The light scanning apparatus 100 has a rectangular parallelepiped shape.
The light scanning apparatus 100 includes a single rotary polygon mirror (hereinafter referred to as a deflector) 1. The deflector 1 is rotated by a motor 21. The optical box 5 contains the deflector 1.
The light scanning apparatus 100 includes two laser units 6a and 6b. The laser unit 6a includes two light sources 20K and 20C for black and cyan. The laser unit 6b includes two light sources 20M and 20Y for magenta and yellow.
The light source 20 (20Y, 20M, 20C, 20K) has a diagonal incidence angle in a vertical direction. The light sources 20K and 20C are arranged so that the light beams LK and LC, which are emitted from the respective light sources 20K and 20C, intersect each other on a deflection surface (reflection surface) 1a of the deflector 1. Similarly, the light sources 20M and 20Y are arranged so that the light beams LM and LY, which are emitted from the respective light sources 20M and 20Y, intersect each other on another deflection surface 1a of the deflector 1. The deflector 1 is configured to deflect the four light beams LY, LM, LC, and LK by being rotated by the motor 21 so as to scan the photosensitive drums 310 with the respective light beams L.
The laser units 6a and 6b each include a collimator lens (not shown) configured to convert the light beam L into a collimated light beam. The optical box 5 holds the deflector 1 and the laser units 6a and 6b. A compound cylindrical lens (not shown) is provided between the deflector 1 and the collimator lens (not shown). The compound cylindrical lens (not shown) is configured to condense the two light beams L, which are emitted from the two respective light sources 20, into a linear shape, which extends in a main scanning direction, on the deflection surface of the deflector 1.
In this case, the main scanning direction is a direction perpendicular to a rotation shaft 1b of the deflector 1. Regarding the main scanning direction, the direction of an optical axis differs between an incidence optical system form the light source 20 to the deflector 1 and an imaging optical system from the deflector 1 to the photosensitive drum 310. A sub-scanning direction is a direction perpendicular to the optical axis of the incidence optical system or the imaging optical system, and in addition, a direction perpendicular to the main scanning direction (direction parallel to the rotation shaft 1b of the deflector 1). A main scanning cross section is a cross section cut along a plane including the optical axis of the imaging optical system and being parallel to the main scanning direction. A sub-scanning cross section is a cross section cut along a plane including the optical axis of the incidence optical system or the imaging optical system and being perpendicular to the main scanning cross section. In the embodiment, as illustrated in FIG. 4A, the optical axis direction of the imaging optical system is represented as an x direction, the main scanning direction is represented as a y direction, and the sub-scanning direction is represented as a z direction.
In FIG. 4A, the light beams LK and LC, which are emitted from the light sources 20K and 20C for black and cyan, are deflected on the deflection surface 1a provided on a right side of the deflector 1. The light beams LM and LY, which are emitted from the light sources 20M and 20Y for magenta and yellow, are deflected on the deflection surface 1a provided on a left side of the deflector 1. An imaging optical system for the light beams LK and LC are independent from an imaging optical system for the light beams LM and LY.
The imaging optical system for the light beams LK and LC for black and cyan is provided on the right side of the deflector 1 as illustrated in FIGS. 4A and 4B. As illustrated in FIG. 4B, the imaging optical system for the light beams LK and LC includes a first lens 2a, second lenses 3a and 3b, and mirrors 4a, 4b, 4e, and 4g. The first lens 2a, the second lenses 3a and 3b, and the mirrors 4a, 4b, 4e, and 4g are fixed to the optical box 5.
The imaging optical system for the light beams LM and LY for magenta and yellow is provided on the left side of the deflector 1 as illustrated in FIGS. 4A and 4B. As illustrated in FIG. 4B, the imaging optical system for the light beams LM and LY includes a first lens 2b, second lenses 3c and 3d, and mirrors 4c, 4d, 4f, and 4h. The first lens 2b, the second lenses 3c and 3d, and the mirrors 4c, 4d, 4f, and 4h are fixed to the optical box 5.
The light beams LY, LM, LC, and LK are condensed by the imaging optical systems onto the surfaces of the photosensitive drums 310Y, 310M, 310C, and 310K, respectively.
FIG. 4B illustrates optical paths of the light beams LY, LM, LC, and LK, which pass inside the light scanning apparatus 100. The light beam L emitted from the laser unit 6 (6a, 6b) is deflected by the deflector 1. The light beam LK for black passes through the first lens 2a and the second lens 3a, and is reflected upward by the mirror 4a so as to be guided onto the photosensitive drum 310K for black. After passing through the first lens 2a, the light beam LC for cyan is reflected by the mirrors 4g and 4e, and passes through the second lens 3b so as to be guided by the mirror 4b onto the photosensitive drum 310C for cyan. The light beam LY for yellow passes through the first lens 2b and the second lens 3d, and is guided by the mirror 4d onto the photosensitive drum 310Y for yellow. After passing through the first lens 2b, the light beam LM for magenta is reflected by the mirrors 4h and 4f, and passes through the second lens 3c so as to be guided by the mirror 4c onto the photosensitive drum 310M for magenta.
To uniform shapes of light spots formed on the respective surfaces of the photosensitive drums 310, it is necessary to set uniform optical path lengths each from the light source 20 to the surface of the photosensitive drum 310. Therefore, to set uniform the optical path lengths of the four light beams LY, LM, LC, and LK, the plurality of mirrors 4b, 4e, and 4g and 4c, 4f, and 4h are arranged in the optical path of the light beam LC for cyan and the optical path of the light beam LM for magenta, respectively.
The optical box 5 is inserted into a main body of the image forming apparatus horizontally in a −x direction through an insertion port (insertion portion), which is formed in a side wall on a left side of the image forming apparatus illustrated in FIG. 9. Note that, the insertion port may be formed in another side wall of the image forming apparatus so that the optical box 5 is mounted to the main body of the image forming apparatus while moving horizontally in a +x direction of the image forming apparatus illustrated in FIG. 9. Further, the insertion port may be formed in the side wall so that the optical box 5 shown in FIGS. 1A and 1B may be mounted to the main body of the image forming apparatus while moving horizontally in the y direction of the image forming apparatus. Still further, an inserting direction (moving direction) at the time when the optical box 5 is mounted to the main body of the image forming apparatus may not be completely the horizontal direction as long as the optical box 5 is inserted at an acute angle with respect to the horizontal direction. In a case of a color image forming apparatus illustrated in FIG. 9, for example, the optical box 5 may be mounted to the main body of the image forming apparatus while the optical box 5 is inserted into the main body of the image forming apparatus in the horizontal direction along or an oblique direction with respect to an arranging direction of the plurality of image forming portions (image forming portions 300Y, 300M, 300C, and 300K).
A fixing portion 108a (near-side fixing portion) and horizontal mounting portions (connecting portions) 101 (101a and 101b) are provided on a side wall 5b of the optical box 5 on the near side (upstream side in the inserting direction or one side) in the inserting direction of the optical box 5 at the time when the optical box 5 is mounted to the main body of the image forming apparatus. The fixing portion (third protrusion) 108a protrudes in a direction (the +x direction) opposite to the inserting direction of the optical box 5 from the side wall 5b, which is provided on the near side of the optical box 5. Further, the horizontal mounting portions 101 are protrusions which extend (protrude) from the side wall 5b on the near side and extend toward a bottom surface (in the −z direction) of the optical box 5.
Note that, the horizontal mounting portion 101 may not protrude from the side wall 5b on the near side as illustrated in FIG. 1A, and may protrude from the bottom surface of the optical box 5 in the −z direction. When the horizontal mounting portion 101 protrudes from the bottom surface of the optical box 5 in the −z direction, it is desired that the horizontal mounting portion 101 protrudes from the vicinity of the side wall 5b on the near side in the −z direction. That is, it is desired that the horizontal mounting portion 101, which protrudes from the bottom surface of the optical box 5 in the −z direction, be provided within the range of 20 mm or less from the side wall 5b on the near side, in order to secure a function of suppressing vibration of the optical box 5, which will be described later.
Fixing portions 108b (first far-side fixing portion) and 108c (second far-side fixing portion) and a fitting protrusion 103 are provided on a side wall 5a of the optical box 5 on a far side (downstream side in the inserting direction or another side opposite to the one side) in the inserting direction of the optical box 5 at the time when the optical box 5 is mounted to the main body of the image forming apparatus. The fixing portion (first protrusion) 108b, the fixing portion (second protrusion) 108c and the fitting protrusion (positioning protrusion) 103 protrude from the side wall 5a of the optical box 5, which is provided on the far side in the inserting direction of the optical box 5, in the inserting direction (direction opposite to the x direction, which is hereinafter referred to as −x direction).
As illustrated in FIG. 4C, the bottom portion 5d of the optical box 5 of the light scanning apparatus 100 has three seating surfaces 8a (third supported portion or third abutment portion), 8b (first supported portion or first abutment portion), and 8c (second supported portion or second abutment portion). As described later, the seating surface 8a is provided on the fixing portion 108a. The seating surfaces 8b and 8c are provided on the fixing portions 108b and 108c, respectively. The seating surfaces 8a, 8b, and 8c protrude in a direction opposite to the z direction (hereinafter referred to as −z direction).
The three seating surfaces 8a, 8b, and 8c are arranged on respective apexes of an isosceles triangle. However, the arrangement of the seating surfaces 8a, 8b, and 8c is not limited to the isosceles triangle. The arrangement of the seating surfaces 8a, 8b, and 8c may be changed as long as the light scanning apparatus 100 is not substantially deformed. Further, the seating surfaces 8a, 8b, and 8c are arranged in a relative manner so that the optical box 5, which is supported by those seating surfaces at three points, is stabilized.
[Supporting Member]
FIGS. 1A and 1B are perspective views of the light scanning apparatus 100, which is fixed to supporting members 12 and 13, according to the first embodiment. FIG. 1A is a rear perspective view of the light scanning apparatus 100. FIG. 1B is a front perspective view of the light scanning apparatus 100.
Two side plates 10 and 11 are provided inside the main body of the image forming apparatus 600. The supporting members (supporting units) 12 and 13 are fixed to the two side plates 10 and 11 or a frame with screws (not shown) so as to bridge between (be suspended from) the two side plates 10 and 11. That is, the supporting members 12 and 13 serve as beam members (supporting beams) configured to connect the two side plates 10 and 11. In the embodiment, the two supporting members 12 and 13 are used, but the embodiment is not limited thereto. For example, one supporting member may be used, or three or more supporting members may be used.
Although not illustrated herein, the photosensitive drum 310, the charging roller 330, the developing device 320, the primary transfer roller 340, and the cleaning device 350 of the image forming apparatus 600 are supported by other respective supporting members (not shown) which bridge between the side plates 10 and 11.
FIGS. 2A, 2B, 2C, and 2D are views illustrating the fixing portion 108a, the horizontal mounting portion 101 (101a, 101b), the fixing portion 108b (108c), and the fitting protrusion 103, respectively.
The light scanning apparatus 100 includes the fixing portion 108a, the horizontal mounting portions 101 (101a and 101b), the fixing portions 108b and 108c, and the fitting protrusion 103. As described above, the seating surfaces 8a, 8b, and 8c are provided on the bottom portion 5d of the optical box 5. Specifically, the seating surface 8a is provided on a lower part of the fixing portion 108a as illustrated in FIG. 2A. The seating surfaces 8b and 8c are provided on lower parts of the fixing portions 108b and 108c, respectively, as illustrated in FIG. 2C.
As illustrated in FIG. 2B, a mounting hole 101c is formed in the horizontal mounting portion 101. Further, a receiving portion (reference surface) 12a (FIG. 2A), two screw holes 12b, and a wire spring 9a are provided on the supporting member (first supporting member) 12. The receiving portion 12a supports the fixing portion 108a. 
As illustrated in FIGS. 1B, 2C, and 2D, a fitting hole 13a, two receiving portions (reference surfaces) 13b and 13c, and wire springs 9b and 9c are provided on the supporting member (second supporting member) 13. The supporting member 13 includes a first insertion portion and a second insertion portion. The first insertion portion is provided with the receiving portion 13b. The fixing portion 108b is inserted into the first insertion portion as the optical box 5 is inserted into the main body of the image forming apparatus. The second insertion portion is provided with the receiving portion 13c. The fixing portion 108c is inserted into the second insertion portion as the optical box 5 is inserted into the main body of the image forming apparatus. The fixing portion 108b is inserted into the first insertion portion so that the receiving portion 13b supports the fixing portion 108b. The fixing portion 108c is inserted into the second insertion portion so that the receiving portion 13c supports the fixing portion 108c. 
The light scanning apparatus 100 is positioned by the receiving portion (third supporting portion) 12a and the two screw holes 12b of the supporting member 12 and the fitting hole 13a, the receiving portion (first supporting portion) 13b, and the receiving portion (second supporting portion) 13c of the supporting member 13. The light scanning apparatus 100 is fixed to the supporting members 12 and 13.
(Positioning Method)
Now, a method of positioning the light scanning apparatus 100 with respect to the image forming apparatus 600 in each of the x, y, and z directions will be described.
As illustrated in FIG. 2A, the seating surface 8a of the light scanning apparatus 100 is held in abutment against the receiving portion 12a of the supporting member 12 in the −z direction (first direction). As illustrated in FIG. 2C, the seating surfaces 8b and 8c of the light scanning apparatus 100 are held in abutment against the receiving portions 13b and 13c of the supporting member 13 in the −z direction (first direction), respectively. When the seating surfaces 8a, 8b, and 8c are held in abutment against the receiving portions 12a, 13b, and 13c, respectively, the light scanning apparatus 100 is positioned with respect to the image forming apparatus 600 in the z direction. In the embodiment, the z direction (a supporting direction) corresponds to a vertically upward direction. That is, the fixing portions 108b and 108c are supported by the receiving portions 13b and 13, respectively, so that the optical box 5 is positioned by the supporting member 13 in the z direction (the supporting direction).
As illustrated in FIG. 2D, the fitting protrusion 103 of the light scanning apparatus 100 is fitted into the fitting hole (fitting portion) 13a of the supporting member 13. When the fitting protrusion 103 is fitted into the fitting hole 13a, the light scanning apparatus 100 is positioned with respect to the image forming apparatus 600 in the y direction (third direction) orthogonal to the z direction (the supporting direction).
As illustrated in FIG. 4A, the horizontal mounting portion 101 (101a, 101b) of the light scanning apparatus 100 has a flat surface 109 (109a, 109b) and a receiving portion (second opposing surface) 110 (110a, 110b). The horizontal mounting portion 101 (101a, 101b) are formed integrally with the optical box 5. The receiving portions 110 are held in abutment against the supporting member 12 in a state in which the fixing portions 108b and 108c on the side wall 5a on the far side of the optical box 5 are fitted into the fitting holes 13b and 13c of the supporting member 13, respectively.
The supporting member 12 is provided immediately below the flat surface 109 (109a, 109b). The flat surfaces 109 are not held in abutment against the supporting member 12. As illustrated in FIGS. 1A and 2B, the receiving portion 110 (110a, 110b) of the horizontal mounting portion 101 (101a, 101b) of the light scanning apparatus 100 is held in abutment against the supporting member 12 in the −x direction (second direction). When the receiving portions 110 of the horizontal mounting portions 101 are held in abutment against the supporting member 12, the light scanning apparatus 100 is positioned with respect to the image forming apparatus 600 in the x direction. In the embodiment, the −x direction (second direction) is perpendicular to the −z direction (first direction). However, the embodiment is not limited thereto. The second direction in which the receiving portion 110 (110a, 110b) is held in abutment against the supporting member 12 only needs to intersect the first direction in which the seating surfaces 8a, 8b, and 8c are held in abutment against the supporting members 12 and 13. The plurality of the horizontal mounting portions 101a and 101b are provided up right from the side wall on the upstream side in the inserting direction of the optical box 5 so as to be opposed to the supporting member 12 in a state in which the optical box 5 is supported by the supporting member 12. The plurality of the horizontal mounting portions 101a and 101b opposed to the supporting member 12 are fixed to the supporting member 12 by the screws 102a and 102b so that vibration generated with the receiving portion 12a of the optical box 5 acting as a fulcrum is suppressed.
(Fixing Method)
Now, a method of fixing the light scanning apparatus 100 to the image forming apparatus 600 will be described. As described above, the light scanning apparatus 100 is fixed to the supporting members 12 and 13 of the image forming apparatus 600 as in the following manner in a state in which the light scanning apparatus 100 is positioned with respect to the image forming apparatus 600.
As illustrated in FIG. 2A, in a state in which the seating surface 8a of the light scanning apparatus 100 is held in abutment against the receiving portion 12a of the supporting member 12 in the −z direction, the fixing portion 108a is biased in the vertically downward direction (−z direction) by the wire spring (elastic member) 9a mounted on the supporting member 12. With the wire spring 9a, the seating surface 8a is fixed to the receiving portion 12a in the z direction. In this case, the wire spring 9a and the receiving portion 12a construct a first fixing section configured to fix the seating surface 8a to the supporting member 12. It is preferred that the wire spring be a wire made of metal, for example.
As illustrated in FIG. 2C, in a state in which the seating surface 8b of the light scanning apparatus 100 is held in abutment against the receiving portion 13b of the supporting member 13 in the −z direction, the fixing portion 108b is biased in the vertically downward direction (−z direction) by the wire spring (elastic member) 9b mounted on the supporting member 13. With the wire spring 9b, the seating surface 8b is fixed to the receiving portion 13b in the z direction. In this case, the wire spring 9b and the receiving portion 13b construct a first fixing section configured to fix the seating surface 8b to the supporting member 13.
Similarly, in a state in which the seating surface 8c of the light scanning apparatus 100 is held in abutment against the receiving portion 13c of the supporting member 13 in the −z direction, the fixing portion 108c is biased in the vertically downward direction (−z direction) by the wire spring (elastic member) 9c mounted on the supporting member 13. With the wire spring 9c, the seating surface 8c is fixed to the receiving portion 13c in the z direction. In this case, the wire spring 9c and the receiving portion 13c construct a first fixing section configured to fix the seating surface 8c to the supporting member 13.
In this manner, in a state in which the light scanning apparatus 100 is positioned with respect to the image forming apparatus 600, the light scanning apparatus 100 is fixed to the supporting members 12 and 13 by the respective first fixing sections while avoiding the deformation of the light scanning apparatus 100 due to the flatness of the supporting members 12 and 13 by the three seating surfaces 8.
The horizontal mounting portions 101a and 101b are fixed to the supporting member 12 by screws (fastening members) 102a and 102b, respectively, in a state in which the receiving portions 110a and 110b of the horizontal mounting portions 101a and 101b are held in abutment against the supporting member 12 in the −x direction. The screws 102a and 102b are screwed into the screw holes 12b of the supporting member 12 through the mounting holes 101c of the horizontal mounting portions 101a and 101b, respectively. The horizontal mounting portions 101a and 101b of the light scanning apparatus 100 are fixed to the supporting member 12 in the x direction by the screws 102a and 102b, respectively.
The mounting hole 101c is sufficiently larger than the screw hole 12b, and hence the screws 102a and 102b do not affect the positioning of the light scanning apparatus 100 in each direction other than the x direction.
As described above, the horizontal mounting portions 101a and 101b are fixed to the supporting member 12 by the screws 102a and 102b, respectively. Thus, torsional vibration in a rotation direction about the seating surface 8a can be reduced. Thus, torsional vibration generated in a case of the fixation at only the three seating surfaces 8a to 8c can be reduced. The specific effect will be described later.
The screw 102 and the screw hole 12b construct a second fixing section configured to fix the receiving portion 110 of the horizontal mounting portion 101 to the supporting member 12. Note that, the horizontal mounting portion 101 may be fixed to the supporting member 12 with an adhesive instead of the screw 102. Alternatively, the horizontal mounting portion 101 may be fixed to the supporting member 12 by a biasing force applied by the elastic member.
(Mounting Procedure)
Next, a mounting procedure of fixing the light scanning apparatus 100 to the supporting members 12 and 13 will be described with reference to FIGS. 3A, 3B, and 3C.
FIGS. 3A, 3B, and 3C are views illustrating the light scanning apparatus 100, which is fixed to the supporting members, according to the embodiment. FIG. 3A is a plan view of the light scanning apparatus 100. FIG. 3B is a front view of the light scanning apparatus 100. FIG. 3C is an enlarged view of a portion IIIC surrounded by the dotted line of FIG. 3B.
First, the light scanning apparatus 100 is inserted into the image forming apparatus 600 in the −x direction (inserting direction), and the fitting protrusion 103 provided on the light scanning apparatus 100 is fitted into the fitting hole 13a of the supporting member 13. With this, the light scanning apparatus 100 is positioned in the y direction.
Next, the seating surfaces 8a, 8b, and 8c are brought into abutment against the respective receiving portions 12a, 13b, and 13c of the supporting members 12 and 13. With this, the light scanning apparatus is positioned in the z direction.
Thereafter, the seating surfaces 8a, 8b, and 8c are fixed to the receiving portions 12a, 13b, and 13c by the wire springs 9a, 9b, and 9c, respectively. The wire springs 9a, 9b, and 9c are used herein, and hence, although the frictional resistance is applied, the light scanning apparatus 100 is movable in the −x direction or the x direction at this time.
Next, the receiving portions 110 of the horizontal mounting portions 101 are brought into abutment against the supporting member 12 in the −x direction. With this, the light scanning apparatus is positioned in the x direction and in the rotation direction about the z axis.
Thereafter, the horizontal mounting portions 101a and 101b are fixed to the supporting member 12 by the screws 102a and 102b, respectively.
In this manner, the light scanning apparatus 100 is positioned with respect to the image forming apparatus 600 in the x direction, the y direction, and the z direction so as to be fixed to the supporting members 12 and 13.
Note that, the mounting hole 101c of each of the horizontal mounting portions 101a and 101b, through which the screw 102 is extended, is sufficiently larger than screw hole 12b of the supporting member 12. Therefore, the fixation of the horizontal mounting portions 101a and 101b by the screws 102 does not interfere with the positioning with the seating surfaces 8a, 8b, and 8c in the z direction.
Note that, stress concentration may occur due to a rotational moment at the time of fixation by the screws 102 so that surrounding parts of the horizontal mounting portions 101a and 101b are deformed. As a measure therefor, a double SEMS screw may be used as the screw 102.
Note that, in the embodiment, for the positioning in the x direction and in the rotation direction about the z axis, the horizontal mounting portions 101a and 101b are provided at two respective positions. However, when positioning means for the x direction and/or the rotation direction about the z axis are additionally provided, the horizontal mounting portion 101 may be provided at one position. This is because, even when only one horizontal mounting portion is provided, a restraining force with respect to a direction of the torsional vibration can be generated, and hence a similar effect can be expected. Further, the above-mentioned positioning method and fixing method are merely an example, and the embodiment is not limited to the above-mentioned methods as long as the light scanning apparatus 100 is appropriately positioned and fixed in all the directions.
[Vibration Reduction for Light Scanning Apparatus]
Verification of anti-vibration property according to the embodiment is performed through analyses. FIGS. 5A, 5B, 5C, and 5D are views illustrating respective vibration modes of the light scanning apparatus 100 which is mounted on the supporting members 12 and 13. The side plates 10 and 11 are omitted in FIGS. 5A, 5B, 5C, and 5D.
FIG. 5A illustrates torsional vibration in which the light scanning apparatus 100 is twisted in a rotation direction R about the seating surface 8a. FIG. 5B illustrates vertical vibration in which the light scanning apparatus 100 is moved parallel to a vertical direction V of FIG. 5B. FIG. 5C illustrates horizontal vibration in which the light scanning apparatus 100 is moved parallel to a horizontal direction H of FIG. 5C. FIG. 5D illustrates bending vibration in which the light scanning apparatus 100 is bent in the vertical direction. The effect of the anti-vibration property in those vibration modes according to the embodiment will be described below.
FIGS. 6A, 6B, and 6C are graphs showing respective results of vibration analyses of the light scanning apparatus 100.
FIG. 6A is a graph showing natural frequencies of a light scanning apparatus, which is fixed at three points and is devoid of the horizontal mounting portions, in respective vibration modes according to the conventional art (ref) and natural frequencies of the light scanning apparatus in the respective vibration modes according to the embodiment.
The light scanning apparatus according to the conventional art (ref) and the embodiment are each fixed to the image forming apparatus 600 for a sheet size of A4 to A3 at the three seating surfaces. Due to the weight of the light scanning apparatus and the stiffness of the rectangular parallelepiped shape that is formed of the polycarbonate-based glass-reinforced resin material, in the light scanning apparatus according to the conventional art (ref), torsional vibration is liable to occur at a natural frequency of about 100 Hz. The natural frequency of about 100 Hz corresponds to a driving vibration frequency of a driving source for the photosensitive drum or the developing device of the image forming apparatus 600. Therefore, the light scanning apparatus according to the conventional art (ref) may cause uneven pitch on an image in resonance with the vibration of the driving source. Further, the frequency of about 100 Hz frequently causes easily visually recognizable uneven pitch in a stripe shape of about 1 mm (=process speed/frequency) at a process speed of 70 to 135 mm/s of the image forming apparatus 600. Therefore, it is required that the natural frequency be shifted (changed) from a frequency band of around 100 Hz.
A natural frequency of the torsional vibration of the light scanning apparatus 100 according to the embodiment is shifted to 331 Hz from the natural frequency of 100 Hz of the torsional vibration of the light scanning apparatus according to the conventional art (ref). This is because the horizontal mounting portions 101 are provided, and thus the stiffness of the light scanning apparatus 100 becomes higher with respect to the direction of the torsional vibration.
It is understood from FIG. 6A that the natural frequencies of the light scanning apparatus 100 according to the embodiment become higher also in the other vibration modes.
According to the embodiment, particularly in the torsional vibration, the shift of the natural frequency by about 100 Hz to 200 Hz can be attained, and hence image deterioration due to the uneven pitch can be reduced.
FIG. 6B shows transfer functions of vibrations transmitted to the light scanning apparatus 100 from a side plate (not shown), on which respective driving sources of the image forming apparatus 600 are mounted, in the respective vibration modes of the natural frequencies shown in FIG. 6A. FIG. 6C is an enlarged view of a part VIC surrounded by the dotted line of FIG. 6B.
As the value of the transfer function is large, the light scanning apparatus 100 is easily vibrated. When the embodiment is compared to the conventional art (ref), the transfer function of the torsional vibration is reduced from 2.2 to about 0.004. That is, the transfer function of the torsional vibration according to the embodiment is reduced by about 550 times as compared to that of the conventional art (ref). The transfer functions of the other vibration modes according to the embodiment are also reduced by about 1.2 to 40 times as compared to those of the conventional art (ref). It is confirmed from this fact that the embodiment has a vibration suppressing effect.
As described above, according to the embodiment, it is possible to increase the natural frequencies and exert the vibration suppressing effect not only in the torsional vibration at the three seating surfaces but also in the other vibration modes, to thereby reduce the uneven pitch in the image forming apparatus 600.
Second Embodiment
FIG. 7 is a perspective view of a light scanning apparatus 700, which is fixed to supporting members, according to a second embodiment. In the second embodiment, components similar to those of the first embodiment are denoted by same reference symbols, and description thereof is omitted herein. The light scanning apparatus 700 according to the second embodiment has a similar configuration to that of the light scanning apparatus 100 according to the first embodiment except that horizontal mounting portions 701 (701a and 701b) are provided instead of the horizontal mounting portions 101 of the light scanning apparatus 100 according to the first embodiment.
In the first embodiment illustrated in FIG. 1A, the horizontal mounting portions 101a and 101b of the light scanning apparatus 100 are formed so as to protrude in a downward direction (−z direction) of the light scanning apparatus 100. On the other hand, as illustrated in FIG. 7, the light scanning apparatus 700 according to the second embodiment includes the horizontal mounting portions 701a and 701b which protrude in a lateral direction (y direction and a direction opposite to the y direction (hereinafter referred to as −y direction)). Specifically, the horizontal mounting portions 701a and 701b protrude in the lateral direction (y direction and −y direction) from a rear surface 705b of an optical box 705 or parts in the vicinity of the rear surface 705b. 
Mounting holes (not shown), through which the screws 102 (102a and 102b) are extended, are formed in the horizontal mounting portions 701a and 701b, respectively. A supporting member 712 includes the fixing portions 104a and 104b to which the horizontal mounting portions 701a and 701b are fixed, respectively. The fixing portions 104a and 104b protrude from the supporting member 712 in the z direction. The fixing portions 104a and 104b each have a screw hole (not shown) formed therein with which the screw 102 is threadedly engaged.
The horizontal mounting portions 701a and 701b include receiving portions (second abutment surfaces) (not shown), which are held in abutment against the fixing portions 104a and 104b of the supporting member 712 in the −x direction (second direction), respectively.
The horizontal mounting portions 701 of the light scanning apparatus 700 are fixed to the fixing portions 104 by the screws 102 in a state in which the receiving portions of the horizontal mounting portions 701 are held in abutment against the fixing portions 104 of the supporting member 712.
The screws 102 and the fixing portions 104 construct a second fixing section configured to fix the receiving portions of the horizontal mounting portions 701 to the supporting member 712.
According to the second embodiment, a similar effect to that of the first embodiment can be obtained.
Third Embodiment
FIG. 8 is a perspective view of a light scanning apparatus 800, which is fixed to supporting members, according to a third embodiment. In the third embodiment, components similar to those of the first embodiment are denoted by same reference symbols, and description thereof is omitted herein. The light scanning apparatus 800 according to the third embodiment has a similar configuration to that of the light scanning apparatus 100 according to the first embodiment except that screw holes (not shown) are formed instead of the horizontal mounting portions 101 of the light scanning apparatus 100 according to the first embodiment.
In the third embodiment, two screw holes (not shown) are formed in a rear surface 805b of an optical box 805 of the light scanning apparatus 800.
Fixing portions 105 (105a and 105b) are provided on a supporting member 812. The fixing portions 105a and 105b protrude from the supporting member 812 in the z direction. Mounting holes (not shown), through which the screws 102 (102a and 102b) are extended, are formed in the fixing portions 105a and 105b, respectively.
Around the screw holes (not shown), the rear surface 805b of the optical box 805 includes receiving portions (second abutment surfaces) (not shown), which are held in abutment against the fixing portions 105 of the supporting member 812 in the x direction (direction opposite to the inserting direction), respectively.
The optical box 805 of the light scanning apparatus 800 is fixed to the fixing portions 105 of the supporting member 812 by the screws 102 in a state in which the receiving portions of the optical box 805 are held in abutment against the fixing portions 105 of the supporting member 812.
The screws 102, the fixing portions 105, and the screw holes (not shown) of the optical box 805 construct a second fixing section configured to fix the receiving portions of the optical box 805 to the supporting member 812.
According to the third embodiment, a similar effect to that of the first embodiment can be obtained.
According to the above-mentioned embodiments, the light scanning apparatus is fixed at the both sides of the seating surface 8a in the horizontal direction, and hence it is possible to exert the vibration suppressing effect not only in the torsional vibration but also in the other vibration modes. Note that, a horizontal mounting portion having a similar positioning function and fixing function to those of the embodiment may be provided on a lower portion, a side portion, and/or an upper portion of the light scanning apparatus.
According to the embodiment, it is possible to reduce the torsional vibration of the light scanning apparatus while avoiding the deformation of the light scanning apparatus due to the flatness of the supporting unit by the three supporting portions.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2014-006828, filed Jan. 17, 2014, and Japanese Patent Application No. 2014-264727, filed Dec. 26, 2014, which are hereby incorporated by reference herein in their entirety.

## Claims

1. An image forming apparatus, comprising:
a photosensitive member;
a light scanning apparatus including:
a deflector configured to deflect a light beam so that the light beam scans a surface of the photosensitive member; and
an optical box configured to contain the deflector, the optical box being inserted through an insertion portion formed in a side wall of a main body of the image forming apparatus so that the light scanning apparatus is mounted to the main body of the image forming apparatus;

a supporting unit including a first supporting portion, a second supporting portion, and a third supporting portion, the supporting unit being configured to support the optical box, the first supporting portion and the second supporting portion being configured to support, in a direction intersecting an inserting direction of inserting the optical box into the main body of the image forming apparatus, the optical box in a vicinity of a side wall of the optical box on a downstream side in the inserting direction, the third supporting portion being configured to support the optical box in a vicinity of a side wall of the optical box on an upstream side in the inserting direction, the third supporting portion being positioned between the first supporting portion and the second supporting portion in the direction intersecting the inserting direction;
a first connecting portion configured to connect the optical box supported by the supporting unit and the main body of the image forming apparatus in the vicinity of the side wall of the optical box on the upstream side in the inserting direction and on one side of the third supporting portion in the direction intersecting the inserting direction of the optical box; and
a second connecting portion configured to connect the optical box supported by the supporting unit and the main body of the image forming apparatus in the vicinity of the side wall of the optical box on the upstream side in the inserting direction and on at least another side of the third supporting portion in the direction intersecting the inserting direction of the optical box.

2. An image forming apparatus according to claim 1, wherein the first and second connecting portions are provided upright from the side wall of the optical box on the upstream side in the inserting direction so that parts of the supporting unit on the one side and the other side of the third supporting portion are opposed to the first and second connecting portions in a state in which the optical box is supported by the supporting unit, and the first and second connecting portions opposed to the parts of the supporting unit are fixed to the parts of the supporting unit by screws so that vibration generated with the third supporting portion of the optical box acting as a fulcrum is suppressed.

3. An image forming apparatus according to claim 1, wherein the optical box is provided with a first protrusion and a second protrusion which protrude in the inserting direction from the side wall of the optical box,
wherein the supporting unit includes:
a first insertion portion into which the first protrusion is inserted when the optical box is inserted into the main body of the image forming apparatus, the first insertion portion being provided with the first supporting portion; and
a second insertion portion into which the second protrusion is inserted when the optical box is inserted into the main body of the image forming apparatus, the second insertion portion being provided with the second supporting portion, and

wherein the first protrusion is inserted into the first insertion portion so that the first supporting portion supports the first protrusion and the second protrusion is inserted into the second insertion portion so that the second supporting portion supports the second protrusion.

4. An image forming apparatus according to claim 3, wherein the optical box includes a positioning protrusion which protrudes in the inserting direction from the side wall of the optical box on the downstream side in the inserting direction,
wherein the supporting unit includes a fitting portion into which the positioning protrusion is inserted when the optical box is inserted into the main body of the image forming apparatus, the positioning protrusion being fitted into the fitting portion in a direction orthogonal to the inserting direction of the optical box and to a supporting direction of the optical box, and
wherein the first insertion portion and the second insertion portion are respectively formed on both sides of the fitting portion in the direction orthogonal to the inserting direction and to the supporting direction.

5. An image forming apparatus according to claim 4, wherein the optical box is provided with a third protrusion which protrudes in a direction opposite to the inserting direction from the side wall,
wherein the supporting unit includes a first support beam and a second support beam provided on both sides of the optical box in the inserting direction and suspended from a frame of the image forming apparatus,
wherein the first support beam is provided downstream of the optical box in the inserting direction and includes the first insertion portion, the second insertion portion, and the fitting portion, and
wherein the second support beam is provided upstream of the optical box in the inserting direction and includes the third supporting portion supporting the third protrusion.

6. An image forming apparatus according to claim 3, wherein the optical box is provided with a third protrusion which protrudes in a direction opposite to the inserting direction from the side wall,
wherein the supporting unit includes a first support beam and a second support beam provided on both sides the optical box in the inserting direction and suspended form a frame of the image forming apparatus,
wherein the first support beam is provided downstream of the optical box in the inserting direction and includes the first insertion portion and the second insertion portion, and
wherein the second support beam is provided upstream of the optical box in the inserting direction and includes the third supporting portion supporting the third protrusion.