JP2007003726A - Scanning optical apparatus and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the resonance of a reflection mirror and to reduce the irregularity of scanning light. <P>SOLUTION: A scanning optical apparatus has: a deflector which deflects and scans the light emitted from a light source; a reflection mirror which guides the luminous flux scanned with the deflector onto a predetermined imaging face; an apparatus casing which holds these components; and a cover which covers the apparatus casing. The scanning optical apparatus is characterized in that the reflection mirror is mounted on the mounting face of a supporting part provided on the apparatus casing at two points in the longitudinal direction, the both end parts of the reflection mirror are arranged on the mounting face and projected in the longitudinal direction, and at least one end face in the longitudinal direction of the reflection mirror is made contact to a butting member. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a scanning optical device that exposes a photosensitive member by scanning a light beam, and an image forming apparatus using the scanning optical device.

  Conventionally, in a scanning optical device, when a long reflecting mirror vibrates with both ends at the center and near the center due to vibration due to unbalanced rotational drive of the rotary polygon mirror and vibration of the drive system of the image forming apparatus body There is. When the long reflection mirror resonates in this way, the scanning position of the light beam reflected by the reflection mirror is shifted on the surface of the photoreceptor. As a result, the position of the electrostatic latent image does not become a desired image, and image unevenness occurs.

  In order to prevent this, there is a technique of holding the reflection mirror only at both ends in the longitudinal direction (see, for example, Patent Document 1). In addition, the resonance frequency is increased by increasing the thickness of the reflecting mirror or attaching a weight to the reflecting mirror.

JP-A-11-326808

  However, the method disclosed in Patent Document 1 holds the reflecting mirror by a force pushing it in the longitudinal direction. For this reason, in order to hold it securely, the pressing force must be increased. Here, if the pressing force is increased too much, the reflection mirror is curved, which may cause bending of the scanning line on the photosensitive member surface, change in scanning magnification, and deterioration of imaging performance.

  In addition, increasing the thickness of the reflecting mirror or attaching a weight to the reflecting mirror to prevent the reflecting mirror from resonating increases the number of members, resulting in poor assembly, increasing the size of the device, and increasing costs. There is a problem.

  An object of the present invention is to prevent the resonance of the reflection mirror and reduce the unevenness of the scanning light.

  In order to achieve the above object, a typical configuration according to the present invention includes a deflector that deflects and scans light emitted from a light source, and a reflection mirror that guides a light beam scanned by the deflector to a predetermined imaging surface. In the scanning optical device having an apparatus housing that holds them and a cover that covers the apparatus housing, the reflection mirror is placed on a mounting surface of a support portion provided in the apparatus housing at two locations in the longitudinal direction. The both ends of the reflection mirror are placed so as to protrude in the longitudinal direction from the placement surface, and a contact member is in contact with at least one longitudinal end surface of the reflection mirror.

  As described above, the apparent support point distance is shortened by placing the reflecting mirror on the apparatus housing, energizing the longitudinal end faces to each other and arranging the longitudinal end portions so as to protrude from the support portion. As a result, the resonance frequency shifts to a high frequency region, and the reflection mirror hardly resonates. As a result, the unevenness of the scanning light is reduced. Further, when used in an image forming apparatus, image unevenness is reduced.

[First Embodiment]
A first embodiment of the present invention will be described with reference to the drawings. In the description, after describing the image forming apparatus and the scanning optical apparatus, the configuration and operation of the reflection mirror support 20 which is a characteristic part will be described in detail.

(Image forming apparatus 100)
An outline of the image forming apparatus 100 will be described. FIG. 1 is a cross-sectional view of the image forming apparatus 100. Note that the image forming apparatus 100 according to the present embodiment uses a monocolor electrophotographic printer in which one image carrier is disposed to form an image, but is not limited thereto. For example, a full-color image forming apparatus in which a plurality of image carriers are arranged and a plurality of color toner images are superimposed and transferred onto a sheet may be used.

  As shown in FIG. 1, an image forming apparatus 100 according to the present embodiment includes a scanning optical device 1 that generates a laser beam (light beam) 3 and emits it as scanning light 8, and a scanning light 8 emitted from the scanning optical device 1. And a photosensitive drum (image carrier) 32 that forms an electrostatic latent image. Around the photosensitive drum 32, a primary charger 33 that uniformly charges the photosensitive drum 32 before the electrostatic latent image is formed, and development is performed by supplying a developer to the electrostatic latent image. And a developing unit 34 for forming a toner image, and a transfer charging roller 35 for transferring the toner image to the transferred transfer material 36. A fixing device 37 for fixing the transferred toner image on the transfer material 36 and a discharge roller for discharging the transfer material 36 to the outside of the apparatus on the downstream side of the photosensitive drum 32 in the conveyance direction of the transfer material 36. 38 is arranged.

  With this configuration, image formation is performed as follows. The laser beam 3 optically modulated based on the image information becomes the scanning light 8 and is emitted from the scanning optical device 1. Since the surface of the photosensitive drum 32 is uniformly charged by the primary charger 33 in advance, an electrostatic latent image is formed on the surface of the photosensitive drum 32 by the emitted scanning light 8.

  The electrostatic latent image is visualized as a toner image by the developing device 34. Thereafter, the toner image formed on the surface of the photosensitive drum 32 is attracted to the transfer material 36 by the voltage applied to the transfer charging roller 35 in order, thereby transferring the toner image. The toner image transferred onto the transfer material 36 is fixed by being pressurized and heated by a fixing device 37. Finally, the transfer material 36 is conveyed out of the apparatus by the discharge roller 38 and the image formation is completed.

(Scanning optical device)
The scanning optical device will be described. FIG. 2 is a perspective view of the scanning optical device. In FIG. 2, each optical component is visible, but after each optical component is assembled in the optical box 11 as the apparatus housing, the upper portion of the optical box 11 is covered by a cover (not shown). .

  As shown in FIG. 2, the scanning optical device 1 includes a laser unit (light source) 2 that generates a light beam 3, a rotary polygon mirror 5 that deflects and scans the light beam 3, and a deflection that drives the rotary polygon mirror 5. , An incident mirror 13 for guiding the light beam 3 to the rotary polygon mirror 5, and a plurality of imaging lenses (fθ lenses) 4 for imaging the scanning light 8 scanned by the rotary polygon mirror 5 on the photosensitive drum 32, 9 and a reflection mirror 12 that changes the traveling direction of the scanning light 8 to the photosensitive drum 32. These members are assembled in an optical box 11 as an apparatus housing.

  With this configuration, the scanning optical device 1 emits the scanning light 8 as follows. First, the light beam 3 emitted from the laser unit 2 is changed in angle by the incident mirror 13, passes through the first imaging lens 4, and is then condensed on the light beam reflecting surface 6 of the rotary polygon mirror 5. The rotary polygon mirror 5 is rotationally driven by the deflector 7 to deflect the incident light beam 8. The deflected light beam 8 again passes through the first imaging lens 4, is changed in angle by the glass reflection mirror 12, passes through the second imaging lens 9, and then is condensed on the photosensitive drum 32. To do. An electrostatic latent image is formed by the light beam 8 condensed and scanned on the photosensitive drum 32. The upper opening of the optical box 11 is closed by a cover (not shown).

(Configuration of the support part 20 of the reflection mirror 12)
The holding structure of the reflecting mirror 12, which is a characteristic part of this embodiment, will be described in detail. FIG. 3 is a view for explaining the state of the first embodiment in which the reflection mirror 12 is attached to the optical box 11. Specifically, FIG. 3 (a) is an arrow view in the A direction shown in FIG. 2, and FIG. 3 (b) is an arrow view in the B direction shown in FIG. 3 (a).

  The reflecting mirror support portions 20 are formed integrally with the optical box 11 and are disposed at two locations near both ends in the longitudinal direction of the reflecting mirror 12 as shown in FIG. The shape of the reflection mirror support 20 shown in FIG. 3A is the same on the opposite side of the reflection mirror in the longitudinal direction.

  The mirror support unit 20 includes a pedestal 41 that supports the light beam reflection surface 12a of the reflection mirror 12 and a pedestal 43 that supports the adjacent surface 12b adjacent to the light beam reflection surface 12a, as mounting surfaces. The pedestal 41 and the pedestal 43 of the support portion 20 of the reflection mirror are in contact with the reflection mirror 12, thereby positioning the reflection mirror 12 at a position and an angle. Further, the reflection mirror support 20 has a leaf spring-like biasing means 26. The urging means 26 abuts on the surface 12c facing the light beam reflecting surface 12a, and presses the reflecting mirror 12 toward the light beam reflecting surface 12a (P direction in the figure). Thereby, the reflection mirror 12 is held on the support portion 20 of the reflection mirror.

  Further, as shown in FIG. 3B, the reflection mirror 12 is arranged so that one end surface 12d of the end portion in the main scanning direction, that is, the longitudinal direction of the reflection mirror 12 abuts on a stopper 23 as a contact member. . Then, a leaf spring-like elastic member 24 is brought into contact with the other end surface 12e of the reflecting mirror 12 in the longitudinal direction.

(Effects of support point distance of reflection mirror 12 on vibration)
Next, the influence of the support point distance of the reflection mirror 12 on the vibration will be described. FIG. 4 is a diagram showing a mode shape (mode of vibration) of the reflecting mirror. Specifically, FIG. 4A shows a mode shape of the reflecting mirror 12 of this embodiment, and FIG. 4B shows a mode shape in the case where the stopper 23 and the elastic member 24 are not provided. In FIGS. 4A and 4B, the amplitude is exaggerated so that the mode shape of the reflecting mirror can be easily grasped.

  As can be seen from FIG. 4A, in the case of the present embodiment, the reflecting mirror 12 is urged and supported at both end surfaces in the longitudinal direction. That is, one end surface that is one end surface in the longitudinal direction of the reflection mirror 12 is in contact with the stopper 23, and the other end surface that is the other end surface in the longitudinal direction of the reflection mirror 12 is in contact with the elastic member 24. For this reason, the distance between the nodes of the mode shape of the reflecting mirror 12 is shortened as indicated by W in the figure. This means that the support point distance L of the reflection mirror 12 is apparently shortened as indicated by the distance W.

  On the other hand, in the conventional configuration without the stopper 23 and the elastic member 24, the support point distance L between the nodes of the mode shape of the reflection mirror 12 is fixed by the urging means 26 as shown in the figure. Between the positions being.

  Here, the resonance frequency f of the reflection mirror when the reflection mirror is supported at both ends is expressed by the following equation.

  As can be seen from this equation, the resonance frequency f of the reflecting mirror is inversely proportional to the square of the support point distance L.

  Therefore, when the reflection mirror 12 is sandwiched in the longitudinal direction by the stopper 23 and the elastic member 24, the apparent support point distance is shortened from the distance L to the distance W. As a result, the resonance frequency f expressed by Equation 1 is increased. Thus, with the configuration of the present embodiment, the resonance frequency f of the reflection mirror 12 can be increased as compared with the conventional fixing method.

  Conventionally, the resonance frequency is shifted to a high frequency range by increasing the thickness of the reflecting mirror or attaching a weight to the reflecting mirror. In this case, the apparatus becomes large and the cost is increased.

  In the present embodiment, the resonance frequency is increased by using the stopper 23 and the elastic member 24 for fixing the reflection mirror 12 to the pedestal 41 without separately using means for increasing the resonance frequency of the reflection mirror. is doing.

  In this way, since a means for increasing the resonance frequency is not separately used, the cost can be reduced without increasing the number of members. Further, the frequency of vibration applied to the reflection mirror 12 can be shifted from the resonance frequency of the reflection mirror 12, so that resonance does not occur. For this reason, it is possible to prevent the reflection mirror 12 from resonating and to prevent occurrence of image unevenness due to a shift in the scanning position on the surface of the photosensitive drum 32.

(Effect of overhang amount of reflection mirror 12 on vibration)
Next, the relationship between the overhang amount of the reflection mirror 12 and the movement amount of the resonance frequency f will be described. Here, the overhang amount is a distance from the position supported by the pedestal 41 to the end of the reflection mirror, and a distance protruding outward from the pedestal 41. In FIG. 4A, the distance is indicated by H.

  Here, the relationship between the overhang amount of the reflection mirror and the resonance frequency will be described. FIG. 5 is a graph of experimental results showing the relationship between the overhang amount and the resonance frequency when the thickness h of the reflection mirror 12 is 5 mm, the width is 10 mm, and the support point distance L is 260 mm. The vertical axis shows the increase rate of the resonance frequency when the overhang amount H is 0, that is, when the resonance frequency in the conventional fixed system shown in FIG. 4B is 1, and the resonance frequency f [Hz] at that time. ing.

  As shown in FIG. 5, the resonance frequency increases as the overhang amount increases, but a curve with a gradual slope is drawn. The resonance frequency converges to a substantially constant value when the amount of overhang H exceeds 30 mm. The increase rate of the resonance frequency at this time is 1.2. For this reason, it is efficient and preferable to set the overhang amount H to 30 mm or less.

  In this experimental result, the overhang amount H was set to 10 mm, and the resonance frequency of the reflection mirror was 1.1 times that of the conventional fixed method. Specifically, it shifted from 180 Hz to 198 Hz. According to the result of this experiment, the resonance frequency f of the reflection mirror 12 can be moved to the high frequency side simply by bringing the longitudinal end face of the reflection mirror 12 into contact with the optical box 11, and image unevenness occurs due to the resonance of the reflection mirror. Can be prevented.

  For this reason, according to this embodiment, compared with increasing the plate thickness of a reflecting mirror or pasting a weight, which has been conventionally used as a means for moving the resonance frequency of the reflecting mirror. Resonance avoidance can be achieved with a very inexpensive configuration.

  Further, as shown in FIG. 5, the resonance frequency f of the reflecting mirror 12 in contact with the stopper 23 varies within a certain range (180 to 217 Hz in the present experimental result) according to the overhang amount H. By utilizing this characteristic, when there are a plurality of reflecting mirrors, the resonance frequency of the plurality of reflecting mirrors can be made uniform by adjusting the overhang amount H of each reflecting mirror.

  Usually, when there are a plurality of reflection mirrors, there are a plurality of resonance frequencies corresponding to the number of the reflection mirrors. For this reason, conventionally, it has been necessary to design the apparatus so as to avoid all of the plurality of resonance frequencies when designing the apparatus.

  However, according to the present embodiment, the resonance frequency of the plurality of reflection mirrors 12 can be made uniform by finely adjusting the overhang amount H of each reflection mirror 12. For this reason, if one aligned resonance frequency is avoided, the occurrence of image unevenness due to resonance of the reflection mirror can be effectively prevented.

  In addition, since the longitudinal direction of the reflecting mirror is pressed by an elastic member, mirror bending in a direction perpendicular to the reflecting surface hardly occurs. Therefore, it is possible to suppress the bending of the scanning line on the surface of the photosensitive drum 32, the change in scanning magnification, and the deterioration of the imaging performance.

  In the above description, the elastic member 24 is used to urge the reflecting mirror 12 to contact the stopper 23. However, the present invention is not necessarily limited to abutting or urging both ends of the reflecting mirror 12, and only one end surface of the reflecting mirror 12 may be abutted against the stopper 23.

  For example, after the one end surface of the reflection mirror 12 is brought into contact with the stopper 23, the surface 12 c facing the reflection surface of the reflection mirror 12 is pressed by the urging means 26, thereby holding the position of the reflection mirror 12. Then, the reflecting mirror 12 is held by the friction between the base 41 and the light beam reflecting surface 12a in the longitudinal direction orthogonal to the direction of the pressing force P, and the position is maintained. As a result, the contact state between the one end surface of the reflecting mirror 12 and the stopper 23 is maintained.

  Thus, by maintaining the contact state between the reflection mirror 12 and the stopper 23 by the pressing force P of the urging means 26, the resonance frequency f of the reflection mirror 12 can be moved to the high frequency side, and the above-mentioned Similar to the configuration with the elastic member 24, the mode shape of the reflecting mirror 12 is the same as that shown in FIG. 4A, and resonance with each means of the apparatus (for example, the deflector 7 and the drive source of the main body) is avoided. can do. Further, by not using the elastic member 24, the number of members can be further reduced.

[Second Embodiment]
A second embodiment of the present invention will be described with reference to the drawings. The same components as those in the above-described embodiment are denoted by the same reference numerals, and description thereof is omitted. FIG. 6 is a diagram for explaining a state of the second embodiment in which the reflection mirror 12 is attached to the optical box 11.

  In the above-described embodiment, the elastic member 24 is used as means for biasing the reflecting mirror 12 in the longitudinal direction. In the present embodiment, as shown in FIG. 6, the elastic member is an elastic portion 50 as a part of the optical box 11.

  Specifically, one end surface 12d of the reflecting mirror 12 is brought into contact with the stopper 23, and the other end surface 12e is urged by the elastic portion 50.

  By integrally forming the elastic portion 50 so as to be a part of the optical box 11, the number of members can be further reduced, contributing to cost reduction, excellent assembly, and stable scanning light 8. can do.

  In addition, if an adhesive means such as an adhesive or a double-sided tape is interposed in the contact portion 51 where the elastic portion 50 and the reflection mirror 12 are in contact, the holding force of the reflection mirror 12 is further increased and the reflection mirror 12 is securely held. Can do. In addition, the urging force of the elastic portion 50 can be reliably transmitted, and the resonance frequency can be adjusted more reliably.

  In the present embodiment, the elastic portion 50 is formed integrally with the optical box 11, but may be provided integrally with a cover (not shown) that covers the scanning optical device 1, and as a part of the cover. You may shape | mold.

[Third Embodiment]
A third embodiment of the present invention will be described with reference to the drawings. The same components as those in the above-described embodiment are denoted by the same reference numerals, and description thereof is omitted. FIG. 7 is a view for explaining the state of the third embodiment in which the reflection mirror 12 is attached to the optical box 11.

  In the present embodiment, two elastic portions 50 that are part of the optical box 11 described in the second embodiment are provided on both end faces of the reflection mirror 12. Each elastic part 50 is configured such that both ends of the reflection mirror 12 face each other, and the reflection mirror 12 is urged by the elasticity of the elastic part 50. Thereby, since the stopper 23 becomes a part of the optical box 11, it is possible to achieve the effects of reducing the number of members, reducing the cost, and improving the assemblability.

  When the temperature inside or outside the scanning optical device 1 changes due to the environmental change around the device, the optical box 11 and the reflection mirror 12 expand and contract by different linear expansion coefficients unique to each member.

  Here, as in this embodiment, when both ends of the reflection mirror 12 are formed as part of the optical box 11 and the elastic portion 50 is biased in the opposing direction, the optical box 11 and the reflection mirror 12 Differences in linear expansion coefficient can be absorbed. For this reason, even if the surrounding environment changes, the elastic part 50 of the optical box 11 can always reliably hold the reflection mirror 12 and maintain the resonance frequency of the reflection mirror 12 at a high frequency.

  In the present embodiment, the elastic portion 50 formed integrally with the optical box 11 is used. However, the elastic portion 50 is not limited to this. For example, the same effect can be obtained even when the elastic portion 50 is configured to provide an elastic portion on the optical lid (not shown) of the scanning optical device 1 that covers the optical box 11 and urge the end face of the reflection mirror 12. it can.

  In order to hold the contact state between the optical box 11 and the reflection mirror 12 more reliably, an adhesive may be interposed in the contact portion 51, or a double-sided tape may be interposed.

  In the present embodiment, the elastic part 50 is provided integrally with the optical box 11, but may be provided integrally with a cover (not shown) that covers the scanning optical device 1, and as a part of the cover. You may shape | mold.

2 is a cross-sectional view of the image forming apparatus 100. FIG. 1 is a perspective view of a scanning optical device 1. FIG. The figure explaining the state of 1st Embodiment which attached the reflective mirror 12 to the optical box 11. FIG. The figure which shows the mode of a vibration of a reflective mirror. The figure which shows the relationship between the amount of overhangs, resonance frequency, etc. The figure explaining the state of 2nd Embodiment which attached the reflective mirror 12 to the optical box 11. FIG. The figure explaining the state of 3rd Embodiment which attached the reflective mirror 12 to the optical box 11. FIG.

Explanation of symbols

H: Overhang amount, L: Support point distance, W ... Distance, 1 ... Scanning optical device, 2 ... Laser unit (light source), 3 ... Light beam, 5 ... Rotating polygon mirror, 6 ... Light beam reflecting surface, 7 ... Deflector 8 ... scanning light, 11 ... optical box (housing), 12 ... reflecting mirror, 12a ... light beam reflecting surface, 12b ... adjacent surface, 12d ... one end surface, 12e ... other end surface, 20 ... reflecting mirror support, 23 ... Stopper, 24 ... elastic member, 26 ... biasing means, 32 ... photosensitive drum (image carrier), 41 ... pedestal (mounting surface), 43 ... pedestal (mounting surface), 50 ... elastic portion, 51 ... contact Part

Claims (6)

A deflector that deflects and scans light emitted from a light source, a reflection mirror that guides a light beam scanned by the deflector to a predetermined imaging surface, a device housing that holds them, and a cover that covers the device housing In a scanning optical device having
The reflection mirror is mounted on a mounting surface of a support portion provided in the apparatus housing at two locations in the longitudinal direction,
Both end portions of the reflection mirror are arranged to protrude in the longitudinal direction from the placement surface,
An abutting member contacts at least one longitudinal end face of the reflecting mirror.   The scanning optical device according to claim 1, wherein one end surface of the reflection mirror is abutted and supported by the abutting member, and the other end surface is urged and supported by an elastic member.   The scanning optical device according to claim 1, wherein both ends of the reflection mirror are urged and supported by an elastic member.   The scanning optical device according to claim 2, wherein at least one of the contact member and the elastic member is a part of the device housing or the cover.   The scanning optical device according to any one of claims 1 to 4, wherein a length of both end portions of the reflection mirror projecting in the longitudinal direction from the mounting surface is 30 mm or less. In an image forming apparatus comprising: an image carrier; and a scanning optical device that forms an electrostatic latent image by irradiating the image carrier with scanning light.
The image forming apparatus according to claim 1, wherein the scanning optical device is a scanning optical device.

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