JP2012108383A - Optical scanning device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical scanning device that solves a problem of cost increase due to necessity of attaching a reinforcement member that covers a wide range of a bottom face of a case of an optical scanning device, in attaching a reinforcement member to the entire area of the bottom face of the case, so as to prevent deformation of the case caused by temperature rise of a drive motor in image formation.SOLUTION: Reinforcement members 401, 402, 403, 404 are attached to a case so as to fit along a bottom face and side walls.

Description

  The present invention relates to an optical scanning device mounted on an electrophotographic image forming apparatus such as a copying machine or a printer.

  In an electrophotographic image forming apparatus such as a laser beam printer or a digital copying machine, an optical scanning device is provided as an exposure device for exposing a photosensitive member. An electrostatic latent image is formed on the photosensitive member by laser light emitted from the optical scanning device, and an image is formed by developing the electrostatic latent image with toner.

  FIG. 9A shows a schematic cross section illustrating an example of an optical scanning device. Laser light emitted from a light source (not shown) is deflected by a polygon mirror 901. The polygon mirror 901 deflects the laser beams respectively emitted from the two light sources to the left and right in FIG. The polygon mirror 901 is rotated by a drive motor 902, and the laser beam incident on the reflecting surface of the polygon mirror 901 that is driven to rotate is converted into scanning light. The light beam emitted from one light source is deflected rightward in FIG. 9A by the polygon mirror 901. This scanning light enters the fθ lens 903 and is then reflected by the reflection mirror 904. Thereafter, the laser light enters the fθ lens 905, is reflected by the reflection mirror 906, and is emitted from the housing 907. By passing through the fθ lenses 903 and 905, the laser light forms a spot image on a photoconductor (not shown) and scans the photoconductor at a constant speed. Further, the light beam emitted from the other light source is deflected leftward in FIG. 9A by the polygon mirror 901. This scanning light enters the fθ lens 908 and is then reflected by the reflection mirror 909. Thereafter, the laser light enters the fθ lens 910, is reflected by the reflecting mirror 911, and is emitted from the housing 907. By passing through the fθ lenses 908 and 910, the laser beam forms a spot image on a photoconductor (not shown) different from one of the light sources, and scans the photoconductor at a constant speed. The laser beams emitted from the housing 907 scan on different photoconductors, whereby a latent image is formed on the photoconductor.

  The bearing portion of the drive motor 902 is fitted into a fitting hole 913 provided in the bottom surface 912 of the housing 907 shown in FIG. 9B, whereby the polygon mirror 901 and the drive motor 902 are positioned with respect to the housing 907. Is done.

  In general, the drive motor 902 rotates the polygon mirror 901 at a high speed (rotational speed of 20,000 to 40,000 rpm). Therefore, as shown in FIG. 11 (vertical axis: bearing temperature, horizontal axis: time (minutes)), the temperature of the bearing portion of the drive motor 902 rises by 15 ° C. or more within a few minutes after starting. Propagates to the bottom surface of the optical scanning device casing 907 (around the fitting hole 913).

  The casing 907 expands from the periphery of the fitting hole 913 that has been heated by this heat. However, since the casing 907 is locally increased in temperature, the casing 907 does not deform evenly and causes distortion. For example, as shown in FIG. 10, the bottom surface of the housing 907 is bent on the mortar with the fitting hole 913 into which the bearing portion of the drive motor 902 is fitted. In FIG. 10, in order to make the deformation easy to understand, the actual deformation amount is exaggerated. Along with this deformation, the side wall of the housing 907 is deformed (see FIGS. 3 and 5). For this reason, the postures of the light source held on the side wall and the mirrors and lenses at various locations in the housing are changed, and the irradiation position of the scanning line on the photosensitive member is shifted. The amount of misregistration of the scanning lines is several tens of μm. In a color image forming apparatus, the quality of the output image is deteriorated as color misregistration.

  In order to suppress such deformation of the bottom surface of the housing on the mortar, an optical scanning device in which a reinforcing plate is attached to the bottom surface outside the housing has been proposed (see Patent Document 1). The reinforcing plate is attached to the housing so as to surround the region where the polygon mirror is fixed.

JP 2009-251308 A

  However, the configuration in which a plate-like reinforcing plate is provided on the bottom surface of the housing as in Patent Document 1 has the following problems. Since sufficient reinforcement is not provided only by providing a reinforcing plate in the vicinity of the region where the polygon mirror is fixed, as shown in FIG. 4 of Patent Document 1, the reinforcing plate covers from one side wall to the other side wall. Thus, when reinforcing by attaching a reinforcement board to the bottom face of a housing | casing, since a reinforcement board needs to have an area more than fixed, component cost will increase.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to reduce the distortion of the housing accompanying the temperature increase of the drive motor that drives the polygon mirror in the optical scanning device with a simple configuration. .

  The optical scanning device according to the present invention includes a rotary polygon mirror that deflects the light beam so that the light beam emitted from the light source scans the object to be scanned, a drive motor that drives the rotary polygon mirror, and the light An optical member that guides the beam to the scanned object; a box-shaped housing having a plurality of surfaces, the housing that houses the rotary polygon mirror, the drive motor, and the optical member; In order to suppress a change in the relative positional relationship between two adjacent surfaces among the two surfaces, a reinforcing member attached to the housing along the two surfaces is provided.

  In order to suppress a change in the relative positional relationship between at least two adjacent surfaces among a plurality of surfaces, a reinforcing member is attached along the two surfaces to suppress distortion of the bottom surface of the housing due to heat generated by the drive motor. Can do.

1 is a schematic cross-sectional view of a main part of an image forming apparatus. The figure which shows the internal structure of an optical scanning device. The figure which shows a deformation | transformation of a housing | casing bottom face and a side wall. FIG. 3 is a diagram illustrating a reinforcing member according to the first embodiment. The figure which shows the deformation | transformation of a side wall. The figure for demonstrating the effect by attaching a reinforcement member. FIG. 10 is a diagram illustrating a reinforcing member according to the second embodiment. FIG. 10 is a diagram illustrating a reinforcing member according to the third embodiment. An embodiment of a conventional optical scanning device. The figure which shows the deformation | transformation of the bottom face of an optical scanning device housing | casing. The figure which shows the temperature rise of the drive motor bearing part with respect to motor drive time.

Example 1
Hereinafter, examples will be described with reference to the drawings. FIG. 1 is a schematic cross-sectional view of a main part of an electrophotographic image forming apparatus according to the present embodiment. The image forming apparatus according to the present embodiment can be broadly divided into a paper feeding unit 101 that supplies paper, image forming units 102Y, 102M, 102C, and 102Bk that form toner images, and a photosensitive member that is a scanning body in the image forming unit. The toner images formed on the photosensitive drums of the optical scanning devices 103 and 104 and the image forming units 102Y, 102M, 102C, and 102Bk that scan the drum (photosensitive member) to form an electrostatic latent image on the photosensitive drum are temporarily formed. An intermediate transfer belt 105 that is transferred and then collectively transferred onto the recording paper, and a fixing unit 106 that fixes the toner image transferred onto the recording paper.

  The image forming apparatus of this embodiment includes an image forming unit 102Y that forms a yellow toner image, an image forming unit 102M that forms a magenta toner image, an image forming unit 102C that forms a cyan toner image, and a black toner image. An image forming unit 102Bk to be formed. Since the components of each image forming unit are the same, the following description will be made using the image forming unit 102Y. The image forming unit 102Y includes a photosensitive drum 107Y that is a photoconductor, a charging device 108Y, and a developing device 109Y. When forming an image, the surface of the photosensitive drum 107Y is charged by the charging device 108Y. The charged photosensitive drum 107Y is exposed by the optical scanning device 103, whereby an electrostatic latent image is formed on the photosensitive drum 107Y. This electrostatic latent image is visualized (developed) with yellow toner held in the developing device 109Y.

  The toner image formed on the photosensitive drum 107Y is transferred to the intermediate transfer belt 105, which is an intermediate transfer body, in the primary transfer portion Ty. In the primary transfer portion Ty, a transfer roller 110Y is provided so as to face the photosensitive drum 107Y, and a toner image on the photosensitive drum 107Y is transferred to the intermediate transfer belt 105 by applying a predetermined bias to the transfer roller 110Y. Is done. The toner images on the photosensitive drums 107M, 107C, and 107Bk of other colors are also transferred onto the intermediate transfer belt 105 by the transfer rollers 110M, 110C, and 110Bk.

  The toner images of the respective colors transferred to the intermediate transfer belt 105 are transferred to a recording sheet as a recording medium conveyed from the paper feeding unit 101 in the secondary transfer unit T2. The recording paper on which the toner image has been transferred in the secondary transfer portion T2 is conveyed to the fixing device 106, and the toner image carried on the recording paper is heated and fixed by the fixing device 106. The recording paper subjected to the fixing process is discharged to a paper discharge unit (not shown).

  Next, the optical scanning devices 103 and 104 will be described. The image forming apparatus of this embodiment includes an optical scanning device 103 that exposes the photosensitive drum 107Y and the photosensitive drum 107M, and an optical scanning device 104 that exposes the photosensitive drum 107C and the photosensitive drum 107Bk. Since the optical scanning device 103 and the optical scanning device 104 have the same configuration, the optical scanning device 103 will be described as an example.

  FIG. 2A is a main scanning sectional view in which the optical path of the optical scanning device 103 shown in FIG. 1 is developed on one plane. The main scanning section here is a plane whose normal is the rotation axis of a drive motor that drives a polygon mirror described later.

  In FIG. 2A, the laser light (light beam) emitted from the light source 201 based on the image data is converted into parallel light by the collimator lens 202, and only the sub-scanning light is converged by the cylindrical lens 203 immediately after that. Then, after being shaped into a predetermined shape by the diaphragm 204, a linear image is formed on the reflection surface of the polygon mirror 205 which is a rotary polygon mirror. The laser light imaged on the reflecting surface of the polygon mirror 205 is converted into scanning light by the rotation of the polygon mirror 205, and then passes through fθ lenses 206 and 207, which are one of the optical members, to be scanned (photosensitive drum). The top surface is scanned at a constant speed. That is, the spot of the laser beam moves at a constant speed on the scanned object.

  The optical scanning device 103 includes a light source 208 that emits laser light guided to a photosensitive drum different from the photosensitive drum to which the laser light emitted from the light source 201 is guided. Laser light (light beam) emitted from the light source 208 is converted into parallel light by the collimator lens 209, and is converted into convergent light only by sub-scanning by the cylindrical lens 210 immediately after. Then, after being shaped into a predetermined shape by the diaphragm 211, a linear image is formed on the reflection surface of the polygon mirror 205, which is a rotary polygon mirror. The laser light imaged on the reflection surface of the polygon mirror 205 is scanned by the rotation of the polygon mirror 205, and then passes through the lenses 212 and 213 to scan at a constant speed on the object to be scanned (surface of the photosensitive drum).

  As shown in FIG. 2A, the polygon mirror 205 deflects the laser light emitted from the light source 201 in the left direction in FIG. 2A and deflects the laser light emitted from the light source 208 in the right direction. . Laser light emitted from the light source 201 is scanned in the direction of arrow C (second scanning path). On the other hand, the laser beam emitted from the light source 208 is scanned in the direction of arrow D (first scanning path).

  FIG. 2B is a schematic diagram illustrating the optical scanning device 103 and the photosensitive drums 107Y and 107M described with reference to FIG. In FIG. 2A, the optical system has been described as being developed on a plane, but in reality, a three-dimensional optical path is formed using a mirror as shown in FIG. 2B. Specifically, the laser light emitted from the light source 201 passes through the fθ lens 206, is reflected by the first mirror 214 that is one of the optical members, and is guided to the fθ lens 207. The laser light that has passed through the fθ lens 207 is reflected by the second mirror 215 and guided to the photosensitive drum 107M. The laser light emitted from the light source 208 is reflected by the third mirror 216 after passing through the fθ lens 212 and guided to the fθ lens 213. The laser beam that has passed through the fθ lens 213 is reflected by the fourth mirror 217 and guided to the photosensitive drum 107Y.

  As shown in FIG. 2B, the polygon mirror 205 is rotationally driven by a drive motor 218. As shown in FIG. 9C, a fitting hole 908 is provided at the center of the housing 219. A bearing of a drive motor 218 that rotationally drives the polygon mirror 205 is fitted into the fitting hole 908, whereby the position of the polygon mirror 205 with respect to the housing 219 is determined. The polygon mirror 205 is supported by a drive motor 218, and in this embodiment, the polygon mirror 205 and the drive motor 218 are integrally formed as a deflection scanning unit.

  These optical components are accommodated in a box-shaped housing 219 and integrally constitute the laser scanning device 103 or 104. A lid 220 is attached to the housing 219 so that dust does not enter inside. The housing 219 and the lid 220 are formed of a material reinforced by mixing glass fiber with a synthetic resin of polyphenylene ether (PPE) and polystyrene (PS).

  As shown in FIGS. 2B and 2C, the first mirror 214 and the third mirror 216 have a bottom surface 220 on which the drive motor 218 is installed and a side wall 221 (side surface) that stands substantially perpendicularly from the bottom surface. It is installed along the corner (corner) formed by. When the width direction of the image forming apparatus is downsized, the optical scanning apparatus needs to be downsized accordingly. Even in a downsized apparatus, it is necessary to provide a predetermined distance (optical path length) between the polygon mirror and the photosensitive drum in consideration of the length of scanning on the photosensitive drum. Therefore, in the optical scanning device of this embodiment, as shown in FIG. 2B, the housing formed by the bottom surface 220 and the side surface 221 in order to secure the optical path length by making the maximum use of the space inside the housing. A first mirror 214 and a third mirror 216 are arranged in a corner portion of the body.

  In a general image forming apparatus, the drive motor 218 rotates the polygon mirror 205 at a high speed of about 20,000 to 40,000 rpm, and the temperature of the bearing portion of the drive motor 218 is 15 in a few minutes after the rotation starts. In some cases, the temperature rises above ℃. When such a temperature rise occurs, a portion (fitting portion) in which the bearing portion of the drive motor 218 of the housing 219 is fitted (fitting portion) is heated to cause linear expansion. As a result, the bottom surface 220 is deformed into a mortar shape as shown in FIG.

  Here, when the bottom surface 220 is deformed into a mortar shape, the side wall 221 of the housing 219 is also folded inward so as to bow as shown in FIG. Due to the overall distortion of the housing 219, the postures of the lenses and mirrors arranged in various places in the housing 219 change, and as a result, as shown by arrows in FIG. Changes. In particular, as shown in FIG. 2B, the first mirror 214 and the third mirror 216 in the present embodiment are determined by the bottom surface 220 and the side wall 221 of the housing 219, and further, fθ on the optical path. It is provided upstream of the lenses 207 and 213. Therefore, the postures of the first mirror 214 and the third mirror 216 have a great influence on the change of the optical path, and the position of the scanning line is finally shifted by 40 to 50 μm when the installation angle of each mirror fluctuates by several minutes. End up.

  This scan position shift becomes apparent as a color shift when an image is formed by superimposing four colors, which causes a reduction in image quality. Further, in the image forming apparatus that employs the optical scanning device that performs the opposing scanning with the polygon mirror 205 sandwiched as in the present embodiment, the irradiation position fluctuates symmetrically due to the deformation of the housing 219, and therefore the relative color The amount of deviation doubles to 80-100 μm.

  When the bottom surface is deformed on the mortar, the relative positional relationship between two adjacent surfaces constituting the housing 219 is broken. That is, as shown in FIG. 3, the angle between the bottom surface 220 and the side surface 221 standing from the bottom surface and forming the side wall of the housing changes. For example, the angle formed between the bottom surface and the side wall shown in FIG. 3 changes in an acute angle direction due to heat deformation of the motor bearing. Moreover, as shown in FIG. 5, the relative positional relationship between two surfaces of adjacent side walls varies.

  As described above, the deformation of the bottom surface and the change in the relative positional relationship between the housing constituent surfaces are related. That is, it is considered that deformation of the bottom surface of the housing can be suppressed if fluctuations in the relative positional relationship between the housing constituent surfaces can be suppressed.

  In view of this, the optical scanning device of the present embodiment is provided with a reinforcing member for suppressing fluctuations in the relative positional relationship between the casing constituent surfaces. An aluminum die cast is used as the reinforcing member in this embodiment. As the reinforcing member, other metal materials such as iron, stainless steel, zinc, and brass, or a resin material having higher rigidity than the housing may be used.

  FIGS. 4A and 4B are perspective views of the outside of the optical scanning device showing the plurality of reinforcing members 401, 402, 403, 404 before and after the attachment. As shown in FIG. 4A, the reinforcing members 401, 402, 403, and 404 are attached along the bottom surface 220 and the side wall 221. The reinforcing members 401, 402, 403, and 404 are each fixed to the housing 219 with screws. Screw fixing is performed at a plurality of points on each of the bottom surface 220 and the side wall 221, and the housing 219 surface and the reinforcing members 401, 402, 403, 404 are firmly coupled by screw fixing.

  The reinforcing members 401, 402, 403, and 404 are attached to the circled portions in FIG. 3 (the corners of the sides formed by the outer bottom surface and the side walls of the housing 219). A corner formed by the outer bottom surface and side wall of the housing 219 is a portion corresponding to the inner corner of the housing 219 along which the first mirror 214 and the third mirror 216 are installed. As described above, by attaching the reinforcing members 401, 402, 403, and 404 to the housing 219, position fluctuations of the first mirror 214 and the third mirror 216 can be suppressed.

  In addition, since the rib protrudes from the housing 219 for reinforcement as shown in FIG. 4, the shape is drawn in a complicated manner, so it is difficult to specify which portion the bottom surface 220 and the side wall 221 are. Therefore, in this embodiment, in FIG. 4, a surface that extends in substantially the same direction as the bottom surface 220 shown in FIG. 3 is a bottom surface, and in FIG. 4, a surface and side wall that extends in substantially the same direction as the side wall 221 shown in FIG.

  The mortar-shaped deformation of the bottom surface 220 of the casing 219 described above is a phenomenon that occurs with a change in angle between the constituent surfaces of the casing 219 due to a rapid temperature rise of the bearing of the drive motor 218. When the change in the angle between the constituent surfaces of the housing 219 is suppressed, mortar-shaped deformation of the bottom surface 220 is also suppressed as a result. Further, in this embodiment, a reinforcing member is attached to a portion where the first mirror 214 and the third mirror 216, which are mirrors most desired to avoid the change in angle, are installed. Thereby, a change in the installation angle of the first mirror 214 and the third mirror 216 can be suppressed.

  FIG. 6 is a graph in which the effect of attaching the reinforcing members 401, 402, 403, and 404 according to the present embodiment is verified by experiment. FIG. 6 is a graph showing the amount of variation with respect to time of the relative irradiation positions of the first optical path and the second optical path when the reinforcing member is attached to the housing and when it is not attached. The vertical axis represents the relative fluctuation amount of the irradiation position, and the horizontal axis represents time. The amount of color misregistration increases as the relative irradiation positions of the first optical path and the second optical path change.

  According to this, when a reinforcing member having a width of 30 mm and a thickness of 3 mm is attached, the amount of change in the relative irradiation position of the first optical path and the second optical path for 20 minutes after starting the drive motor 218 is as follows: The result of 40% reduction compared to the case where 402, 403, and 404 are not attached is obtained.

  As described above, by attaching the reinforcing members 401, 402, 403, and 404 that join the bottom surface and the side surface of the housing of the optical scanning device, the relative positional relationship between the bottom surface and the side wall (side surface) of the housing can be improved. The variation can be suppressed, and as a result, the mortar-like deformation of the bottom surface can be suppressed. As a result, it is possible to reduce the amount of variation in the relative irradiation position between the first optical path and the second optical path, that is, color misregistration in the image forming apparatus.

  In the present embodiment, the configuration in which the reinforcing member 401 is attached to the outside of the housing 219 has been described. However, the reinforcing member 401 may be attached to the inside of the housing 219. Further, the number of reinforcing members may be one instead of a plurality.

(Example 2)
In the first embodiment, a measure for suppressing the change in angle between the bottom surface 220 and the side wall 221 of the housing 219 has been implemented. However, in the second embodiment, the relative positional relationship between adjacent side walls is changed (angle change). Take measures.

  FIG. 7 is a schematic view of the deformation of the housing 219 when the drive motor 218 is operated as viewed from the axial direction of the drive motor 218. As shown in FIG. 5, when the polygon motor operates and the housing 219 is deformed, the amount of change in the position of the side wall 221 from the ideal position becomes the maximum at the center of each wall, and the amount of change is between the side walls. It decreases while curving toward the connection point. That is, at the corner of the housing 219, the peripheral walls on both sides are deformed inward leaving a ridgeline, and the angle between the two surfaces changes in an acute angle direction.

  With respect to such deformation of the housing 219, as shown in FIG. 7, in the second embodiment, reinforcing members 701, 702, 703, and 704 that connect the side surfaces of the housing are attached. FIGS. 7A and 7B are perspective views of the outside of the optical scanning device showing the plurality of reinforcing members 701, 702, 703, and 704 before and after attachment. The reinforcing members 701, 702, 703, and 704 are made of the same material and fixing method as the reinforcing members 401, 402, 403, and 404 in the first embodiment, and are fixed with screws. This guarantees the angle between the side walls circled in FIG. 5 and increases the resistance against the force to tilt the wall inward, so that the bottom surface deforms into a mortar shape even when the temperature of the bearing of the drive motor 218 rises. As a result, deformation of the entire housing 219 can be suppressed.

(Example 3)
FIG. 8 is a diagram illustrating the third embodiment. The third embodiment reinforces adjacent side walls of the housing 219 as in the second embodiment, but the fixing method is different from the second embodiment. In the second embodiment, the reinforcing members 701, 702, 703, and 704 are fixed along a plurality of surfaces of the side wall of the housing 219. However, in the third embodiment, the target side surface (the side wall 801 and the side wall 802 in FIG. 8). The ribs are once projected from, and the reinforcing member 803 is fixed to the projected ribs.

  As this effect, the deformation suppressing effect is equivalent to that of the reinforcing members 701, 702, 703, 704 in the second embodiment, but the shape of the second embodiment is screwed from the side when the reinforcing members 701, 702, 703, 704 are attached. Therefore, compared with the case of screwing from above, the workability is inferior in terms of the visibility of the screw holes and how to apply torque at the time of tightening. In addition, in order to improve them, it is necessary to change the posture of the housing 219 once and to turn one of the reinforcing members 701, 702, 703, 704 upward, increasing the assembly process. Will be invited. In contrast, the shape of the third embodiment allows the reinforcing member 803 and other components to be assembled in the same direction, so that the reinforcing member 803 is screwed from one direction without changing the posture of the housing 219. This greatly improves workability when assembling the device.

  In addition, although each Example was described as an independent example so far, for example, Example 1 and Example 2 or Example 1 and Example 3 can be implemented simultaneously with respect to one housing | casing 219. It is possible, and there may be a case where a more effective effect can be obtained by combining them.

218 Drive motor 219 Housing 220 Bottom surface 221 Side wall 401, 402, 403, 404 Reinforcing member

Claims (5)

A rotating polygon mirror that deflects the light beam so that the light beam according to the image data emitted from the light source moves on the scanned object;
A drive motor for driving the rotary polygon mirror;
An optical member for guiding the light beam to the scanned body;
A box-shaped housing having a plurality of surfaces, the housing containing the rotary polygon mirror, the drive motor, and the optical member;
An optical scanning device comprising: a reinforcing member attached to the casing so as to straddle two adjacent surfaces among the plurality of surfaces. The housing has a bottom surface on which the drive motor is installed and a plurality of side surfaces standing from the bottom surface and forming side walls of the housing.
The optical scanning device according to claim 1, wherein the reinforcing member is attached to the housing so as to straddle any one of the plurality of side surfaces and the bottom surface. The housing has a bottom surface on which the drive motor is installed and a plurality of side surfaces standing from the bottom surface and forming side walls of the housing.
The optical scanning device according to claim 1, wherein the reinforcing member is attached to the casing so as to straddle two adjacent side surfaces of the side surface. The optical member is a mirror that reflects the scanning light deflected by the rotating polygonal mirror and is disposed along a corner portion of the housing formed by the bottom surface and the side wall,
The reinforcing member is attached to the casing so as to cover an outer corner of the casing corresponding to an inner corner of the casing formed by the bottom surface and the side wall. Item 3. The optical scanning device according to Item 2.   The optical scanning device according to claim 1, wherein a plurality of the reinforcing members are attached to the housing.

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