JP2013041171A - Optical scanner, image reading device, and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent reduction in plane precision of an optical member due to warpage or deformation of a plate member of a dynamic vibration absorber.SOLUTION: The optical scanner 1 includes: a laser light source 19; optical means including lenses 12, 13 and a mirror 17 and guiding a light beam from a light source to a photoreceptor 2; and a dynamic vibration absorber 90 which is attached to the lens or a mirror and reduces vibration of the lens or the mirror by resonating at a natural frequency of the lens or the mirror. The dynamic vibration absorber includes a plate member 91, a plurality of viscoelastic bodies 92, and a weight 93. The plate member is attached to the lens or the mirror via the viscoelastic bodies. The weight is attached between the viscoelastic bodies.

Description

  The present invention relates to an optical scanning device having a dynamic vibration absorber, an image reading device, and an electrophotographic image forming apparatus (hereinafter referred to as an image forming apparatus).

  Image forming apparatuses such as copying machines and laser beam printers have an optical scanning device. The optical scanning device includes a laser light source that emits laser light (light beam) and an optical deflector that deflects and scans the laser light from the laser light source. The optical scanning device emits a laser beam modulated according to image information from a laser light source. The laser light is deflected and scanned by a rotating optical deflector. The laser light is reflected by the mirror toward the photosensitive drum. The reflected laser light is imaged in a spot shape on the photosensitive drum by an fθ lens (imaging optical element) having fθ characteristics. Thereby, an electrostatic latent image is formed on the photosensitive drum according to the image information.

  In such an optical scanning device, there is a problem that an image defect occurs due to vibration of an optical member such as a mirror or an fθ lens. The vibration is transmitted from the motor that rotates the optical deflector to the optical member through the optical housing of the optical scanning device. Further, the vibration is transmitted from the drive source of the image forming apparatus to the optical member through the optical housing of the optical scanning device. The vibration of the optical member appears particularly prominent when the frequency of the vibration transmitted to the optical member matches or is close to the natural frequency of the optical member.

  In recent years, the number of image forming apparatuses having a plurality of process speeds has increased, and there have been a plurality of vibration frequencies transmitted to optical members. Therefore, there is a need for a vibration isolator that effectively prevents vibration in a wide frequency band.

  A dynamic vibration absorber is a technique that can reduce the peak of vibration at a low cost in a wide frequency band. The dynamic vibration absorber is configured by a mass, a spring, and a damper, and is directly attached to the vibration body so that the dynamic vibration absorber absorbs vibration of the vibration body and reduces the vibration level of the vibration body. Generally, a dynamic vibration absorber is designed to resonate at the natural frequency of a vibrating body, and it is known that the higher the mass, the higher the vibration isolation effect.

  The dynamic vibration absorber is also used for vibration isolation of the optical scanning device. For example, by attaching a dynamic vibration absorber made of a cantilever beam that resonates at the rotation frequency of the rotating optical deflector to the optical housing of the optical scanning device, the vibration of the optical housing that occurs as the optical deflector rotates is reduced. Anti-vibration devices have been proposed. By attaching a weight to the node of the secondary vibration mode of the cantilever, a multi-degree-of-freedom dynamic vibration absorber that absorbs vibrations of the rotation primary frequency and rotation sixth-order frequency of the optical deflector is realized (Patent Literature) 1).

JP 2005-10260 A

  However, the dynamic vibration absorber of Patent Document 1 has a cantilever whose center of gravity is located away from the base of the beam, and the cantilever is easily detached from the vibrating body due to heat and vibration during distribution. In order to securely attach the cantilever to the vibrating body, the mounting area of the cantilever on the vibrating body must be increased. When such a dynamic vibration absorber, which is a cantilever vibrating body, is attached to an optical member such as a mirror or a lens, the plate member constituting the cantilever must be attached to the optical member over a wide area. When the plate member is directly attached to the optical member with a wide area, there is a problem that the planar accuracy of the optical member is deteriorated due to the warpage or deformation of the plate member.

  The present invention has been made in view of the above problems, and an optical scanning device of the present invention includes a light source, a lens and a mirror, an optical means for guiding a light beam from the light source to a photoconductor, the lens or the A dynamic vibration absorber attached to a mirror and suppressing vibration of the lens or the mirror by resonating at the natural frequency of the lens or the mirror, and the dynamic vibration absorber includes a plate member and a plurality of viscous vibration absorbers. An elastic body and a weight are provided, the plate member is attached to the lens or the mirror via the plurality of viscoelastic bodies, and the weight is attached between the plurality of viscoelastic bodies.

  ADVANTAGE OF THE INVENTION According to this invention, the fall of the plane accuracy of the optical member by the curvature and deformation | transformation of the plate member of a dynamic vibration damper can be prevented.

1 is a schematic diagram of an image forming apparatus. It is the schematic of an optical scanning device. 1 is a schematic diagram of an image reading apparatus. It is a figure which shows the dynamic vibration absorber of Example 1 attached to the mirror of the optical scanning device. It is a figure which shows the general model of a dynamic vibration absorber. It is a figure which shows the gravity center position of a beam, and the displacement of the vibration of a beam. It is a figure which shows the relationship between the length of a viscoelastic body, and the planar accuracy of a mirror. It is a figure which shows the anti-vibration effect obtained with the dynamic vibration damper of Example 1. FIG. It is the table | surface which showed the conditions of the member affixed as a vibration isolator. It is a figure which shows the dynamic vibration absorber of Example 2 attached to the mirror of the optical scanning device. It is a figure which shows the dynamic vibration absorber of Example 3 attached to the mirror of the optical scanning device. It is a figure which shows the dynamic vibration absorber of Example 4 attached to the mirror of the optical scanning device.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

(Image forming device)
FIG. 1 is a schematic diagram of an image forming apparatus 100. In this embodiment, the image forming apparatus 100 will be described by taking a full-color digital copying machine as an example. The image forming apparatus 100 includes an image reading device 8 and an image forming unit 10. The image forming unit 10 includes a plurality of image forming stations P (Pa, Pb, Pc, Pd), an intermediate transfer unit 60, and a sheet conveying unit 7.

  The image reading device 8 reads an image of a document pressed against the platen glass by the pressure plate 86 and outputs an image signal to an image processing unit (not shown) of the image forming apparatus 100. Details of the image reading device 8 will be described later.

  The image forming unit 10 forms an image on a recording medium in accordance with image information (image signal) from the image reading device 8. The image forming unit 10 includes four image forming stations P (Pa, Pb, Pc, Pd). The four image forming stations P respectively form toner images on the photosensitive drums (photosensitive members) 2 (2a, 2b, 2c, and 2d) according to the image signals separated into four colors of yellow, magenta, cyan, and black. Form. The image forming station P includes an optical scanning device 1 (1a, 1b, 1c, 1d), a photosensitive drum 2 (2a, 2b, 2c, 2d), a charging device 3 (3a, 3b, 3c, 3d), and a developing device 5. (5a, 5b, 5c, 5d) and the cleaning device 4 (4a, 4b, 4c, 4d).

  The toner images of the respective colors formed on the photosensitive drum 2 are transferred onto the intermediate transfer belt 61 by the primary transfer member 6 (6a, 6b, 6c, 6d). The toner images of the respective colors are sequentially transferred onto the intermediate transfer belt 61, and the four color toner images are superimposed on the intermediate transfer belt 61. The intermediate transfer belt 61 is stretched around a driving roller 62 and a driven roller 63.

  The toner images superimposed on the intermediate transfer belt 61 are transferred onto the sheet S by the secondary transfer rollers 65 and 66. The sheet S is a recording medium on which an image is formed by the image forming apparatus 100, and is, for example, paper, an OHP sheet, a cloth, or the like. In the secondary transfer rollers 65 and 66, the sheet S is fed to the manual feed cassette 70 and fed in time so that the position of the sheet S coincides with the position of the toner image on the intermediate transfer belt 61. The paper is fed from the cassette 78 or the paper feed cassette 79. The belt cleaning device 64 removes the toner remaining on the intermediate transfer belt 61 after the secondary transfer.

  The sheet S to which the toner image has been transferred is heated and pressed by the fixing roller 74, and the toner image is fixed to the sheet S to form a full color image. The sheet S on which the full color image is formed is discharged onto the discharge tray 77.

(Optical scanning device)
Next, the optical scanning device 1 will be described with reference to FIG. FIG. 2 is a schematic diagram of the optical scanning device 1. FIG. 2A is a view showing a mounting portion of the optical housing (optical box) 11 of the optical scanning device 1. FIG. 2B is a diagram illustrating an optical member inside the optical housing 11 of the optical scanning device 1. FIG. 2C is a diagram showing a mounting portion for the mirror 17. FIG. 2 (d) is a view showing a mounting portion for the toric lens 12.

  The optical scanning device 1 has an optical housing 11. As shown in FIG. 2B, the optical housing 11 houses a light source unit (laser light source) 19 that emits laser light (light beam), an optical deflector 16 that deflects laser light, and a plurality of optical members. ing. The plurality of optical members include a cylindrical lens (first optical member) 18, toric lenses (second optical members) 12 and 13, and a mirror (second optical member) 17. The plurality of optical members are optical means that includes a lens and a mirror and guides the laser light from the light source unit 19 to the photosensitive drum 2.

  In FIG. 2A, the light source unit 19, the optical deflector 16, and the plurality of optical members housed in the optical housing 11 are not shown. The optical housing 11 is fixed to the stay 31 with screws 32 as shown in FIG. Both ends of the stay 31 are fixed to opposing side plates 33. The optical housing 11 may be urged against the stay 31 by a leaf spring (not shown) so as to be fixed to the stay 31.

  The optical member inside the optical housing 11 will be described. In FIG. 2B, the light source unit 19 includes a laser holder 19-1, a collimator lens 19-2, and an electric board 19-3. The optical deflector 16 includes a rotary polygon mirror 16-1 and a motor (drive source) 16-2.

  The laser light source is press-fitted into the laser holder 19-1. The laser light emitted from the laser light source passes through the collimator lens 19-2 and becomes parallel laser light. The parallel laser light is collected only in the rotation direction of the photosensitive drum 2 by the cylindrical lens (first optical member) 18. The laser beam condensed by the cylindrical lens 18 is deflected by a rotating polygon mirror 16-1 rotating at a constant speed by a motor 16-2 so as to scan the photosensitive drum 2. The laser beam deflected by the rotating polygon mirror 16-1 passes through a mirror (second optical member) 17 and is predetermined on the photosensitive drum 2 by toric lenses (second optical member) 12 and 13 having fθ characteristics. An image is formed with a spot diameter of. The mirror 17 and the toric lenses 12 and 13 have the scanning direction of the laser light deflected by the rotating polygon mirror 16-1 as the longitudinal direction.

  The toric lenses 12 and 13, the mirror 17, and the cylindrical lens 18 are attached to the optical housing 11 using a leaf spring, an adhesive, or the like. As shown in FIG. 2C, the mirror 17 is fixed to the optical housing 11 by urging both ends of the mirror 17 against the inner wall portion of the optical housing 11 by the leaf spring 15. As shown in FIG. 2D, the toric lens 12 is fixed to the optical housing 11 by urging both ends of the toric lens 12 against the inner wall portion of the optical housing 11 by the leaf spring 14. The toric lens 13 is also fixed to the optical housing 11 in the same manner as the toric lens 12.

  Both ends of the mirror 17 and the toric lenses 12 and 13 may be bonded to the inner wall of the optical housing 11 with an adhesive.

  The toric lenses 12 and 13, the mirror 17, and the cylindrical lens 18 are vibrated by vibration transmitted through the optical housing 11. The vibration sources transmitted to the optical housing 11 are a motor 16-2 inside the optical scanning device 1 and a drive source outside the optical scanning device 1, for example, the image forming station P of the image forming unit 10 and the intermediate transfer unit 60. , And a drive source of the sheet conveying unit 7. Vibrations generated by the rotation of the motor, which is a drive source, and vibrations generated by the engagement of the gears that transmit the drive are transmitted to the optical housing 11 of the optical scanning device 1 through the side plate 33 and the stay 31.

(Image reading device)
Next, the image reading device 8 will be described with reference to FIG. FIG. 3A is a schematic diagram of the image reading device 8. FIG. 3B is a view showing a mounting portion for the mirrors 83-1 and 83-2.

  The image reading apparatus 8 includes a light source (illuminating means) 40 (FIG. 1) that illuminates a document, a plurality of optical members, and a line sensor (image sensor) 81. The plurality of optical members include a plurality of mirrors (first optical members) 83 (83-1, 83-2, 83-3) and an imaging lens (second optical member) 82. The plurality of optical members are optical means that includes a lens and a mirror and guides reflected light from the original illuminated by the light source 40 to the line sensor 81.

The light source 40 illuminates the document pressed against the platen glass by the pressure plate 86. Reflected light from the original is imaged on a line sensor (image sensor) 81 by an imaging lens 82 via mirrors 83-3, 83-2, and 83-1. The line sensor 81 outputs an image signal to an image processing unit (not shown) of the image forming apparatus 100 according to the read image.

  The mirrors 83-1, 83-2, and 83-3 are incorporated in the mirror unit 84. When the wire 85 is wound up by a pulley 87 rotated by a driving source (not shown), the mirror unit 84 moves in the direction indicated by the arrow A and reads an image from end to end of the document.

  The imaging lens 82 and the mirror 83 inside the image reading device 8 are attached to the housing of the image reading device 8 using screws, leaf springs, adhesives, or the like. As shown in FIG. 3B, both ends of the mirrors 83-1 and 83-2 are fixed to the stay 89 by being urged by a leaf spring 88 against the stay 89. The stay 89 is attached to the casing of the mirror unit 84.

  Both ends of the mirrors 83-1 and 83-2 may be bonded to the stay 89 with an adhesive.

  The imaging lens 82 and the mirror 83 vibrate due to vibration transmitted through the housing of the image reading device 8 and vibration caused by movement of the mirror unit 84. The vibration sources transmitted to the housing of the image reading device 8 are a driving source for the pulley 87, an image forming station P for the image forming unit 10, an intermediate transfer unit 60, and a driving source for the sheet conveying unit 7.

Example 1
FIG. 4 is a diagram illustrating a dynamic vibration absorber (vibration isolation device) 90 according to the first embodiment attached to the mirror 17 of the optical scanning device 1. FIG. 4A is a cross-sectional view of the dynamic vibration absorber 90. FIG. 4B is a perspective view of the dynamic vibration absorber 90.

  The dynamic vibration absorber 90 is attached to an optical member (mirror or lens), and suppresses vibration of the optical member by resonating at the natural frequency of the optical member. In this embodiment, the dynamic vibration absorber 90 is attached to the back surface 17b of the reflection surface 17a of the mirror 17. The dynamic vibration absorber 90 resonates at the natural frequency of the mirror 17. The dynamic vibration absorber 90 includes a plate member 91 provided with a weight 93 and a plurality of viscoelastic bodies 92 (92-1, 92-2) for attaching the plate member 91 to the mirror 17.

  The plurality of viscoelastic bodies 92 (92-1, 92-2) are attached to one surface 91a of the plate member 91, and the weight 93 is attached to the other surface 91b of the plate member 91.

  The plurality of viscoelastic bodies 92 includes a first viscoelastic body 92-1 and a second viscoelastic body 92-2. The first viscoelastic body 92-1 and the second viscoelastic body 92-2 are attached to different positions of the mirror 17 and the plate member 91 in the longitudinal direction of the mirror 17, respectively. The weight 93 is attached to the plate member 91 between the first viscoelastic body 92-1 and the second viscoelastic body 92-2 that are attached at different positions in the longitudinal direction of the mirror 17. In the first embodiment, the weight 93 only needs to be disposed between the first viscoelastic body 92-1 and the second viscoelastic body 92-2, and the weight 93 is not necessarily the first viscoelasticity. It is not necessary to arrange in the central part between the body 92-1 and the second viscoelastic body 92-2.

  The first viscoelastic body 92-1 and the second viscoelastic body 92-2 are respectively attached to both ends of the plate member 91 in the longitudinal direction. In the first embodiment, the edges of the first viscoelastic body 92-1 and the second viscoelastic body 92-2 do not necessarily need to coincide with the edge of the plate member 91. As can be seen from FIG. 4A, the first viscoelastic body 92-1 and the second viscoelastic body 92-2 are arranged on the center side of the plate member 91 away from the edge of the plate member 91. Good.

  The plate member 91 is attached to the back surface 17b of the reflection surface 17a of the mirror 17 via the first viscoelastic body 92-1 and the second viscoelastic body 92-2. The weight 93 is attached to the other surface 91b of the plate member 91 at a position between the first viscoelastic body 92-1 and the second viscoelastic body 92-2. The viscoelastic bodies (first viscoelastic body 92-1 and second viscoelastic body 92-2) 92 are substances having viscosity and elasticity. The viscoelastic body 92 is, for example, a rubber member, a plastic member, a gelatin member, a gel member, a protein member, or the like.

  In general, optical members such as mirrors and lenses are components that require strict planar accuracy. When the planar accuracy of the optical member decreases, the image quality deteriorates due to the deformation of the spot on the photosensitive drum and the dot position accuracy. When the wide surface of one end of a cantilever of a dynamic vibration absorber is directly fixed to an optical member as in the prior art, the planar accuracy of the optical member is affected by warpage or deformation of the cantilever. There is.

  On the other hand, according to the present embodiment, the plate member 91 of the dynamic vibration absorber 90 is attached to the optical member by the plurality of viscoelastic bodies 92, so that the plate member 91 is separated from the optical member by heat and vibration during distribution. It is possible to prevent peeling. Further, since the plate member 91 is stably attached to the optical member by the plurality of viscoelastic bodies 92, the attachment area of the plate member 91 to the optical member is compared with the attachment area of the cantilever of the conventional dynamic vibration absorber. Can be made smaller. Even if the mounting area of the plate member 91 to the optical member is smaller than the mounting area of the conventional cantilever of the dynamic vibration absorber, the plate member 91 is prevented from peeling off from the optical member due to heat and vibration during distribution. can do. In addition, since the mounting area of the plate member 91 according to the present embodiment to the optical member is smaller than the mounting area of the cantilever of the conventional dynamic vibration absorber, the optical member is not affected by the warp or deformation of the plate member 91. There is an effect that it is hard to receive.

  Next, the principle of vibration suppression of the dynamic vibration absorber 90 will be described with reference to FIG. FIG. 5 is a diagram showing a general model of a dynamic vibration absorber.

  The dynamic vibration absorber 21 is directly attached to the vibrating body 22. The dynamic vibration absorber 21 has the same natural frequency as the natural frequency of the vibrating body 22. The dynamic vibration absorber 21 absorbs vibration energy of the vibrating body 22 by resonating at the natural frequency of the vibrating body 22.

  The vibrating body 22 is represented by a mass 22M and a spring 22K. The dynamic vibration absorber 21 is represented by three elements of a mass 21M, a spring 21K, and a damper 21C. The vibrating body 22 vibrates greatly at a natural frequency ω that is uniquely determined by the mass 22M and the spring 22K. By directly attaching the dynamic vibration absorber 21 having the mass 21M and the spring 21K that resonates at the natural frequency ω of the vibration body 22 to the vibration body 22, the dynamic vibration absorber 21 vibrates positively, Absorbing vibration energy, the vibration level of the vibrating body 22 is reduced.

  In the dynamic vibration absorber 90 of the first embodiment illustrated in FIG. 4, the mirror 17 corresponds to the vibrating body 22. Regarding the three elements of the dynamic vibration absorber 90, the weight 93 corresponds to the mass 21M, the elastic plate member 91 corresponds to the spring 21K, and the viscoelastic body 92 corresponds to the damper 21C.

  The mirror 17 is a both-end fixed beam whose both ends are urged and fixed by a leaf spring 15. When the frequency near the natural frequency ω of the mirror 17 is transmitted to the mirror 17, the mirror 17 vibrates greatly. For example, in the primary mode of vibration, both ends of the mirror 17 are vibration nodes, and the center of the mirror 17 is an antinode of vibration, and vibrates greatly in a direction perpendicular to the reflecting surface 17a of the mirror 17. However, in the first embodiment, the dynamic vibration absorber 90 is attached to the back surface 17b of the reflection surface 17a of the mirror 17, so that the dynamic vibration absorber 90 resonates at the natural frequency ω of the mirror 17. The plate member 91 of the dynamic vibration absorber 90 vibrates greatly in the vibration direction of the mirror 17 with the positions of the first viscoelastic body 92-1 and the second viscoelastic body 92-2 as nodes. When the plate member 91 and the weight 93 attached to the plate member 91 actively vibrate, the dynamic vibration absorber 90 absorbs the vibration energy of the mirror 17. Further, the damping level of the first viscoelastic body 92-1 and the second viscoelastic body 92-2 is also added, and the vibration level of the mirror 17 is reduced.

  Next, it will be described that the dynamic vibration absorber 90 of Example 1 shown in FIG. 4 has a small influence on the planar accuracy of the optical member.

  FIG. 6 is a diagram showing the position of the center of gravity of the beam and the displacement of the vibration of the beam. FIGS. 6A, 6 </ b> B, and 6 </ b> C are diagrams illustrating the center-of-gravity position G when the attachment portions of the plate members 41, 51, and 91 are changed. FIG. 6A shows a cantilever 41. FIG. 6B shows the both-end fixed beam 51. FIG. 6C shows the dynamic vibration absorber 90 according to the first embodiment in which the weight 93 is attached to the both-end fixed beam 91.

  The cantilever 41 shown in FIG. 6A is not stable because the center of gravity G is away from the viscoelastic member (fixed point) 42 at the base of the cantilever 41, and the cantilever 41 is used as an attachment member. The viscoelastic member 42 is easily peeled off. In order to prevent the cantilever 41 from being peeled off due to heat or vibration during distribution, a large mounting area is required. When the mounting area to the mirror 17 is increased, the mirror 17 is easily affected by warpage or deformation of the cantilever 41.

  The both-end fixed beam 51 in FIG. 6B is stable because the center of gravity G is at the center of the two viscoelastic members (fixed points) 52. For this reason, it is harder to peel off than the cantilever 41 shown to Fig.6 (a). Therefore, the mounting area to the mirror (vibrating body) 17 can be reduced. When the mounting area to the mirror 17 is reduced, the mirror 17 is less susceptible to warping and deformation of the both-end fixed beam 51.

  Here, the relationship between the attachment area of the viscoelastic body and the planar accuracy of the mirror will be described with reference to FIG. FIG. 7 is a diagram showing the relationship between the length of the viscoelastic body and the planar accuracy of the mirror.

FIG. 7 shows a case where a sheet metal (sheet member) having a warp amount of 0.3 mm is attached to the vicinity of the center of a 165 mm long mirror having a distance between fixed positions of both ends of 157 mm through a viscoelastic body. The relationship between the length of a viscoelastic body and the planar accuracy of a mirror is shown. When the width of the viscoelastic body is constant, the length of the viscoelastic body in the longitudinal direction of the mirror is proportional to the attachment area of the viscoelastic body.
In FIG. 7, F represents the plane accuracy at one end in the longitudinal direction of the mirror, C represents the plane accuracy at the center in the longitudinal direction of the mirror, and R represents the plane accuracy at the other end in the longitudinal direction of the mirror. . From FIG. 7, it can be seen that the longer the length of the viscoelastic body in the longitudinal direction of the mirror, that is, the larger the mounting area, the lower the plane accuracy of the mirror.

  The dynamic vibration absorber 90 according to the first embodiment is attached to the mirror 17 by two viscoelastic members 92. Therefore, the attachment area of one viscoelastic member 92 can be made smaller than the attachment area of one viscoelastic member 42 of the cantilever 41. Further, since the plate member 91 is fixed to the mirror 17 at both ends and is stable, the mounting area of one viscoelastic member 92 is made to be less than half of the mounting area of the viscoelastic member 42 of the cantilever 41. The mounting strength of the plate member 91 can be sufficiently maintained. That is, according to the first embodiment, the mounting area of the viscoelastic member 92 to the mirror can be reduced. Therefore, it can be seen from FIG. 7 that the dynamic vibration absorber 90 of Example 1 has a small effect on the planar accuracy of the optical member.

  Next, it will be described that the length of the plate member 91 can be shortened by attaching the weight 93 to the plate member 91. In general, both-end fixed beams are less likely to vibrate than cantilever beams.

数式（１）は、梁の固有振動数ωを表す式である。Ｌは梁の長さ、ｂは梁の幅、ｔは梁の厚み、Ｅは梁のヤング率、ρは梁の密度を表す。片持ち梁の定数λは１．８７５、両端固定梁の定数λは３．７３であるため、同じ幅ｂ及び同じ厚みｔの板部材を用いた片持ち梁と両端固定梁とでは、同じ固有振動数ωを有するようにするために、両端固定梁の長さを片持ち梁の長さの約２倍にする必要がある。

Equation (1) is an equation representing the natural frequency ω of the beam. L is the length of the beam, b is the width of the beam, t is the thickness of the beam, E is the Young's modulus of the beam, and ρ is the density of the beam. Since the constant λ of the cantilever beam is 1.875 and the constant λ of the fixed beam at both ends is 3.73, the cantilever beam using the same width b and the same thickness t and the fixed beam at both ends are the same. In order to have the frequency ω, it is necessary to make the length of the both ends fixed beam about twice the length of the cantilever beam.

  Therefore, in the dynamic vibration absorber 90 of the present embodiment, the weight 93 is attached to the plate member 91 to shorten the length of the plate member 91. According to Equation (1), the beam thickness t is proportional to the beam length L. If the thickness of the plate member 91 is made thinner and the weight 93 is attached without changing the mass of the dynamic vibration absorber 90, the length of the plate member 91 can be shortened. By reducing the length of the plate member 91, the size of the dynamic vibration absorber 90 can be reduced.

  In general, it is known that a dynamic vibration absorber has a higher vibration isolation effect as the mass is heavier. If the mass of the dynamic vibration absorber is reduced in order to reduce the thickness of the plate member, the vibration isolation effect is impaired. Therefore, according to the present embodiment, by attaching the weight 93 to the plate member 91, the dynamic vibration absorber 90 can be downsized without impairing the vibration isolation effect of the dynamic vibration absorber 90.

  Next, it will be described that by attaching the weight 93 to the plate member 91, the dynamic vibration absorber 90 can be further reduced in weight while maintaining the vibration isolation performance of the dynamic vibration absorber 90.

  FIG. 6 (d) is a diagram showing the mass of the both-ends fixed beam to which no weight is attached and the displacement of the vibration of the beam. FIG. 6E is a diagram showing the mass of the both-end fixed beam to which the weight of this embodiment is attached and the vibration displacement of the beam.

梁の振動エネルギーＴの数式（２）における有効質量は、梁全体の質量ｍの３３/７０である。質量が梁全体に分散しているために、梁全体の質量ｍのすべてが振動エネルギーＴとして機能しているわけではないことがわかる。 As shown in FIG. 6 (d), in the dynamic vibration absorber having only the plate member, the mass is dispersed over the entire region in the longitudinal direction of the plate member. The vibration displacement is reduced. The vibration energy T of such a both-ends fixed beam is expressed as in Equation (2) using the vibration displacement x at the center of the beam and the mass m of the entire beam.

The effective mass in Equation (2) of the vibration energy T of the beam is 33/70 of the mass m of the entire beam. It can be seen that not all of the mass m of the entire beam functions as vibration energy T because the mass is dispersed throughout the beam.

図６（ｄ）に示す梁と図６（ｅ）に示す梁とで、ｍ＝Ｍ＋ｍ´として、動吸振器全体の質量を同じにした場合、重錘９３を取り付けた図６（ｅ）に示す梁ほうが、振動エネルギーが大きい。動吸振器の振動エネルギーが大きいほど、振動体の振動エネルギーを大きく吸収するため、防振性能が高い。そのため、板部材９１に重錘９３を取り付けることにより、防振性能を維持しつつ、動吸振器９０をより軽量化することができる。 On the other hand, as shown in FIG. 6E, the dynamic vibration absorber 90 of the first embodiment in which the weight 93 is attached to the center portion of the beam has a concentrated mass point at the center portion of the beam having the maximum amplitude. The vibration energy T of the beam is expressed by Equation (3) using the vibration displacement x at the center of the beam, the mass M of the weight, and the mass m ′ of the entire beam.

When the mass shown in FIG. 6D and the beam shown in FIG. 6E are equal to m = M + m ′ and the mass of the entire dynamic vibration absorber is the same, the weight 93 is attached to FIG. The beam shown shows greater vibration energy. The greater the vibration energy of the dynamic vibration absorber, the greater the vibration energy of the vibrating body is absorbed. Therefore, by attaching the weight 93 to the plate member 91, the dynamic vibration absorber 90 can be further reduced in weight while maintaining the vibration-proof performance.

  Next, an example of Example 1 will be specifically described. In one example of the first embodiment, the mass of the weight 93 is about 12.5 g, the mass of the beam excluding the attachment portion is about 6.5 g, and the effective mass in the mathematical expression (3) of the vibration energy T of the beam is about 15 .5g. On the other hand, in a dynamic vibration absorber having no weight 93 and a beam mass excluding the attachment portion of about 19 g, the effective mass of Expression (2) is about 9 g. When both are compared, the effective mass is larger by about 6.5 g in this embodiment, and the vibration energy of the vibrating body can be greatly absorbed by the difference of the effective mass.

  FIG. 8 is a diagram illustrating the vibration isolation effect obtained by the dynamic vibration absorber 90 of the first embodiment. An affixing member having the conditions shown in FIG. 9 was attached to a mirror which is a vibration-proof member (vibrating body). With respect to the vibration of a single mirror that has not been provided with an anti-vibration device, the three types of pasting members can exhibit the same anti-vibration effect. And it turns out that the dynamic vibration absorber 90 of Example 1 has implement | achieved the most compact and lightweight structure.

  In the present embodiment, the mirror 17 of the optical scanning device 1 has been described as a vibration-proof member. Even if the dynamic vibration absorber 90 according to this embodiment is attached to an optical member other than a mirror such as the toric lenses 12 and 13 and the cylindrical lens 18 in the optical scanning device 1, the influence on the planar accuracy of the optical member is similarly reduced. Meanwhile, the vibration of the optical member can be reduced.

  In this embodiment, the dynamic vibration absorber 90 is attached to the back surface of the mirror reflection surface that is perpendicular to the vibration direction of the beam. However, even if the dynamic vibration absorber 90 is attached to either one of the two side surfaces extending in the longitudinal direction other than the mirror reflecting surface and the back surface, the effect on the planar accuracy of the optical member is similarly reduced while reducing the optical accuracy. The vibration of the member can be reduced.

(Example 2)
FIG. 10 is a diagram illustrating a dynamic vibration absorber (vibration isolation device) 190 according to the second embodiment that is attached to the mirror 17 of the optical scanning device 1. The dynamic vibration absorber 190 is attached to the back surface 17 b of the reflection surface 17 a of the mirror 17. FIG. 10A is a cross-sectional view of the dynamic vibration absorber 190. FIG. 10B is a perspective view of the dynamic vibration absorber 190.

  The dynamic vibration absorber 190 is a two-stage series type in which a first dynamic vibration absorber 190a and a second dynamic vibration absorber 190b are connected in series. The second dynamic vibration absorber 190b is mounted on the first dynamic vibration absorber 190a.

  Similar to the dynamic vibration absorber 90 of the first embodiment, the first dynamic vibration absorber 190 a includes three elements: a weight 193, a plate member 191, and a viscoelastic body 192. The plate member 191 provided with the weight 193 is attached to the back surface 17b opposite to the reflecting surface 17a of the mirror 17 by the first viscoelastic body 192-1 and the second viscoelastic body 192-2.

  The dynamic vibration absorber 190 has another plate member 194 attached to the weight 193. The plate member 194 has elasticity. The plate member 194 is attached to a surface opposite to the surface of the weight 193 to which the plate member 191 is attached. The plate member 194 is attached to the weight 193 at or near the center of the plate member 194 in the longitudinal direction. The second dynamic vibration absorber 190b is configured by a plate member 194 attached on the first dynamic vibration absorber 190a. Since the 1st dynamic vibration absorber 190a and the 2nd dynamic vibration absorber 190b absorb the vibration energy of the mirror (vibrated member) 17, a higher vibration isolation effect can be obtained.

  When two dynamic vibration absorbers are connected in series and the first dynamic vibration absorber is a cantilever beam as shown in FIG. 6A, the second dynamic vibration absorber is attached to the tip of the cantilever beam. become. In this case, the position of the center of gravity of the dynamic vibration absorber connected in series is further away from the base of the beam, so that the stability further decreases. If the first dynamic vibration absorber is a both-ends fixed beam having no weight as shown in FIG. 6B, the length of the first dynamic vibration absorber in the longitudinal direction needs to be increased. Therefore, it is necessary to lengthen the length in the longitudinal direction of the second dynamic vibration absorber attached on the first dynamic vibration absorber. In order to attach a long plate member as the second dynamic vibration absorber, a spacer (a spacing member) is required to secure a space that allows the long plate member to vibrate in the thickness direction of the long plate member. Become. In the dynamic vibration absorber 190 of the second embodiment, the weight 193 attached to the plate member 191 also serves as a spacer, so that the first dynamic vibration absorber 190a and the second dynamic vibration absorber 190b can be easily connected in series. It has become.

(Example 3)
FIG. 11 is a diagram illustrating a dynamic vibration absorber (antivibration device) 290 of Example 3 attached to the mirror 17 of the optical scanning device 1.

  Similar to the first embodiment, the dynamic vibration absorber 290 is attached to the back surface 17 b opposite to the reflection surface 17 a of the mirror 17. The dynamic vibration absorber 290 resonates at the natural frequency of the mirror 17. The dynamic vibration absorber 290 includes a plate member 291 provided with a weight 293 and a plurality of viscoelastic bodies 292 (292-1, 292-2) for attaching the plate member 291 to the mirror 17. The plurality of viscoelastic bodies 292 includes a first viscoelastic body 292-1 and a second viscoelastic body 292-2, and the weight 293 includes the first viscoelastic body 292-1 and the second viscoelastic body 292-2. Are attached to the plate member 291.

  The difference from the first embodiment is that the edge portion 292-1a of the first viscoelastic body 292-1 is arranged to coincide with one edge portion 291a of the plate member 291, and the edge portion of the second viscoelastic body 292-2 is arranged. 292-2a is arranged to coincide with the other edge 291b of the plate member 291. Thereby, the distance between the 1st viscoelastic body 292-1 and the 2nd viscoelastic body 292-2 can be lengthened. The distance between the first viscoelastic body 292-1 and the second viscoelastic body 292-2 corresponds to the length of the both-end fixed beam. Accordingly, by aligning the edge portions 292-1a and 292-2a of the first viscoelastic body 292-1 and the second viscoelastic body 292-2 with the both edge portions 291a and 291b of the plate member 291, respectively, The dynamic vibration absorber 290 having a shorter length that resonates at the natural frequency can be provided.

Example 4
FIG. 12 is a diagram illustrating a dynamic vibration absorber (antivibration device) 390 according to the fourth embodiment attached to the mirror 17 of the optical scanning device 1.

  Similar to the first embodiment, the dynamic vibration absorber 390 is attached to the back surface 17 b opposite to the reflection surface 17 a of the mirror 17. The dynamic vibration absorber 390 resonates at the natural frequency of the mirror 17. The dynamic vibration absorber 390 includes a plate member 391 provided with a weight 393 and a plurality of viscoelastic bodies 392 (392-1, 392-2) for attaching the plate member 391 to the mirror 17. The plurality of viscoelastic bodies 392 includes a first viscoelastic body 392-1 and a second viscoelastic body 392-2, and the weight 393 includes the first viscoelastic body 392-1 and the second viscoelastic body 392-2. Are attached to the plate member 391.

  The difference from the first embodiment is that the weight 393 is attached to the central portion between the first viscoelastic body 392-1 and the second viscoelastic body 392-2 in the longitudinal direction of the plate member 391. is there. The longitudinal distance D between the inner edge 392-1a of the first viscoelastic body 392-1 and the center of gravity 393a of the weight 393 is equal to the inner edge 392-2a of the second viscoelastic body 392-2. It is the same as the distance D in the longitudinal direction between the weight 393 and the center of gravity 393a.

  The antinode of the primary vibration mode of the plate member 391 that is a both-ends fixed beam is in the center between the first viscoelastic body 392-1 and the second viscoelastic body 392-2. Since the weight 393 is attached to the vibration belly having the largest vibration displacement, the weight 393 works most efficiently.

(Example 5)
In the fifth embodiment, the same dynamic vibration absorber as that of the first to fourth embodiments is replaced with the mirrors 83-1, 83-2, 83-3, or the image reading apparatus 8 illustrated in FIG. It is attached to an optical member such as the imaging lens 82. Similar to the optical member of the optical scanning device 1, the optical member of the image reading device 8 requires strict planar accuracy. By attaching the dynamic vibration absorbers of the first to fourth embodiments to the optical member of the image reading device 8, the influence of the warpage or deformation of the plate member on the planar accuracy of the optical member is the same as in the first to fourth embodiments. The vibration of the optical member can be reduced while reducing the size.

(Example 6)
In the sixth embodiment, the optical scanning device of the first to fourth embodiments or the image reading device of the fifth embodiment is provided in the image forming apparatus. By providing a small and lightweight optical scanning device or image reading device having a small and lightweight vibration isolator in the image forming apparatus, the image forming apparatus is reduced in size and weight while reducing the planar accuracy of the optical member and the image quality due to vibration. Can be prevented.

  In the first to sixth embodiments described above, the dynamic vibration absorber is attached to the optical member by at least two viscoelastic bodies, so that the weight is disposed between the at least two viscoelastic bodies. A dynamic vibration absorber having a certain shape can be provided. Thus, even if the mounting area of the dynamic vibration absorber to the optical member is reduced as compared with the conventional cantilever-shaped dynamic vibration absorber, the dynamic vibration absorber is less likely to be peeled off from the optical member due to heat and vibration during distribution. Further, since the mounting area can be reduced, it is possible to reduce the influence of warping and deformation of the plate member of the dynamic vibration absorber on the planar accuracy of the optical member.

  In Examples 1 to 6 described above, since the weight is provided on the plate member of the dynamic vibration absorber, the dynamic vibration absorber resonates at the natural frequency of the optical member using a shorter plate member. Moreover, since the weight is attached and the mass of the dynamic vibration absorber is concentrated on the weight, the thickness of the plate member can be made thinner and the length of the plate member can be made shorter. Therefore, a lighter dynamic vibration absorber can be provided.

  In addition, by using the weight, the mass of the dynamic vibration absorber is concentrated at the center of the plate member, which is the antinode of the vibration of the fixed beams at both ends, so that the mass of the dynamic vibration absorber can absorb the vibration energy more effectively. Can be used for. Therefore, it can be set as a lighter dynamic vibration absorber, maintaining vibration isolation performance.

  In this embodiment, a weight separate from the plate member is attached to the plate member, but the present invention is not limited to this. The weight may be integral with the plate member. In the two-stage series dynamic vibration absorber, the weight may be integrated with the first plate member and the second plate member. In this embodiment, the weight is a hexahedron, but the present invention is not limited to this. As long as the weight can be attached to the plate member or formed integrally with the plate member, the weight may have other shapes such as a disk shape, a column shape, a conical shape, and a polyhedron.

1 Optical scanning device 2 Photosensitive drum (photosensitive material)
8 Image reader 12 Toric lens (second optical member)
13 Toric lens (second optical member)
16 Optical deflector 17 Mirror (second optical member)
18 Cylindrical lens (first optical member)
19 Light source unit (laser light source)
82 Imaging lens (second optical member)
83 Mirror (first optical member)
90, 190, 290, 390 Dynamic vibration absorber 92, 192, 292, 392 Viscoelastic body 91, 191, 291, 391 Plate member 93, 193, 293, 393 Weight 100 Image forming apparatus

Claims (16)

An optical scanning device,
A light source;
An optical means including a lens and a mirror, and guiding a light beam from the light source to a photoreceptor;
A dynamic vibration absorber attached to the lens or the mirror and suppressing vibration of the lens or the mirror by resonating at the natural frequency of the lens or the mirror;
The dynamic vibration absorber includes a plate member, a plurality of viscoelastic bodies, and a weight, the plate member is attached to the lens or the mirror via the plurality of viscoelastic bodies, and the weight is the plurality of weights. An optical scanning device which is attached between viscoelastic bodies.   2. The light according to claim 1, wherein the plurality of viscoelastic bodies are attached to one surface of the plate member, and the weight is attached to the other surface of the plate member. Scanning device. The plurality of viscoelastic bodies includes a first viscoelastic body and a second viscoelastic body,
3. The weight according to claim 1, wherein the weight is attached to the plate member between the first viscoelastic body and the second viscoelastic body in a longitudinal direction of the plate member. Optical scanning device.   4. The optical scanning device according to claim 3, wherein the first viscoelastic body and the second viscoelastic body are respectively attached to both end portions of the plate member in the longitudinal direction.   5. The weight according to claim 3, wherein the weight is attached to a central portion between the first viscoelastic body and the second viscoelastic body in the longitudinal direction of the plate member. Optical scanning device.   The optical scanning device according to claim 1, further comprising another plate member attached to the weight. The other plate member is attached to a surface opposite to the surface of the weight to which the plate member is attached;
The optical scanning device according to claim 6, wherein the another plate member is attached to the weight at a central portion in a longitudinal direction of the other plate member. An image forming apparatus,
An image forming unit having a photoreceptor;
The optical scanning device according to any one of claims 1 to 7, wherein the photosensitive member is scanned with laser light.
An image forming apparatus comprising: An image reading device,
Illumination means for illuminating the document;
An optical unit that includes a lens and a mirror and guides reflected light from an original illuminated by the illumination unit to an image sensor;
A dynamic vibration absorber attached to the lens or the mirror and suppressing vibration of the lens or the mirror by resonating at the natural frequency of the lens or the mirror;
The dynamic vibration absorber includes a plate member, a plurality of viscoelastic bodies, and a weight, the plate member is attached to the lens or the mirror via the plurality of viscoelastic bodies, and the weight is the plurality of weights. An image reading apparatus mounted between viscoelastic bodies.   The image according to claim 9, wherein the plurality of viscoelastic bodies are attached to one surface of the plate member, and the weight is attached to the other surface of the plate member. Reader. The plurality of viscoelastic bodies includes a first viscoelastic body and a second viscoelastic body,
11. The weight according to claim 9, wherein the weight is attached to the plate member between the first viscoelastic body and the second viscoelastic body in the longitudinal direction of the plate member. Image reading device.   The image reading apparatus according to claim 11, wherein the first viscoelastic body and the second viscoelastic body are respectively attached to both ends of the plate member in the longitudinal direction.   The weight is attached to a central portion between the first viscoelastic body and the second viscoelastic body in the longitudinal direction of the plate member. Image reading device.   The image reading apparatus according to claim 9, further comprising another plate member attached to the weight. The other plate member is attached to a surface opposite to the surface of the weight to which the plate member is attached;
The image reading apparatus according to claim 14, wherein the another plate member is attached to the weight at a central portion in a longitudinal direction of the other plate member. An image forming apparatus,
The image reading apparatus according to any one of claims 9 to 15, which reads an image of a document;
An image forming unit that forms an image on a recording medium in accordance with image information from the image reading device;
An image forming apparatus comprising:

Images