JPH11149053A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device by which excellent write-in is executed by reducing the vibration of a mirror at the time of light write-in to a surface to be scanned. SOLUTION: As for the image forming device provided with an optical scanner 10 having a light source part 11, the mirror 12 reflecting a luminous flux radiated by the light source part 11 to the surface to be scanned 3 and a frame 13 where the mirror 12 is attached, the frame 13 possesses a plane part 21 to support the mirror 12, and both end parts of the mirror 12 in a main scanning direction are held between a plate-like member 22 and the plane part 21, and are fixed to the frame 13.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a printer, a copying machine, a facsimile, etc.
The present invention relates to an optical scanning device which is applied to this image forming apparatus and scans a surface to be scanned with a laser beam or the like to form an electrostatic latent image on the surface to be scanned.

[0002]

2. Description of the Related Art Recent image forming apparatuses are provided with an optical scanning device which forms an electrostatic latent image by scanning the surface of a photosensitive member as a surface to be scanned with a laser beam. This optical scanning device,
It is mainly composed of an optical unit having a laser light source unit, a polygon mirror and an Fθ lens, a mirror for reflecting the laser emitted from the optical unit toward the photoconductor, and a frame to which the optical unit and the mirror are fixed. I have. Then, the laser light emitted from the laser light source section is
The light enters a high-speed rotating polygon mirror, is scanned by the polygon mirror, passes through the Fθ lens, is reflected by the mirror toward the photoconductor, and forms an electrostatic latent image on the surface of the photoconductor.

[0003] The introduction of digital technology has improved image quality. In order to improve image quality, high-precision writing on the photoconductor by laser light is required.
There is a strict requirement for the positional accuracy of each line by laser light. One factor that hinders high-precision writing is laser vibration in which laser light vibrates, and it is necessary to reduce this laser vibration in order to perform high-precision writing. Laser vibration is generated when vibration from a motor that rotationally drives the polygon mirror and a drive system including a gear driven by the motor is transmitted to the frame and the mirror and resonates. The vibration of the mirror is a main cause of the laser vibration. When the laser vibration occurs, the laser light applied to the photoconductor vibrates and fluctuates, and the writing on the photoconductor is disturbed, and the image quality deteriorates.

Japanese Patent Laid-Open Publication No. Sho 60-244921 discloses a technique for reducing the flexural vibration of a mirror by attaching a buffer member and a metal member to the non-reflective surface of the mirror. Japanese Patent Application Laid-Open No. 2-253274 discloses a technique in which a buffer member is provided between a mirror and a frame at the center of the mirror to suppress the vibration of the mirror. Furthermore, Japanese Patent Application Laid-Open No. 8-2000 discloses a technique in which a motor for rotating a polygon and a mirror are fixed to frames separated from each other to prevent transmission of vibration of the motor to the mirror.
In the technologies disclosed in these publications, the vibration of the mirror is reduced by preventing the transmission of the vibration to the mirror.

[0005]

By the way, the relationship between the visual sensitivity of an image and the spatial frequency depends on the characteristics of the human visual system.
It is said that the density change in the spatial frequency range of 0.2 to 2.0 line / mm is most noticeable. Considering this phenomenon in combination with the rotation speed of the photoconductor, vibrations in the frequency range of several Hz to several hundreds Hz disturb writing on the surface to be scanned, and adversely affect the image quality. Also,
If a leaf spring or the like is used for fixing the mirror to the frame, the restrained area of the mirror becomes small, and vibrations may be transmitted to the mirror, which may degrade image quality.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an image forming apparatus capable of reducing the vibration of a mirror during optical writing on a surface to be scanned and performing good writing. The purpose is to eliminate the adverse effects of vibrations in the frequency range.

[0007]

According to the first aspect of the present invention,
In an image forming apparatus including a light source unit, a mirror that reflects a light beam emitted from the light source unit to a surface to be scanned, and a frame to which the mirror is attached, a flat unit in which the frame supports the mirror , And both ends of the mirror in the main scanning direction are sandwiched between a plate-shaped member and a flat portion and fixed to a frame.

According to a second aspect of the present invention, there is provided an image forming apparatus comprising an optical scanning device having a light source, a mirror for reflecting a light beam emitted from the light source to a surface to be scanned, and a frame to which the mirror is attached. In the apparatus, the frame has a flat portion supporting the mirror, and a surface other than the reflection surface of the mirror is fixed to the flat portion.

The invention described in claim 3 is the first or second invention.
In the image forming apparatus described above, the mirror has a triangular prism shape.

According to a fourth aspect of the present invention, in the image forming apparatus of the first, second or third aspect, an attenuation member for attenuating vibration transmitted from the frame to the mirror is interposed between the mirror and the flat portion. is there.

[0011] The invention according to claim 5 is the invention according to claims 1, 2, and 3.
Alternatively, in the image forming apparatus described in 4, the damping member that is long in the main scanning direction of the mirror and attenuates the vibration of the mirror is provided inside the mirror.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, an image forming apparatus to which a writing unit as an optical scanning device according to the present invention is applied will be described. In this embodiment, a case where a laser printer is used as an image forming apparatus will be described. In FIG. 1, reference numeral 1 denotes a laser printer. In the laser printer 1, first, a sheet P fed from a sheet cassette (not shown) in a direction indicated by an arrow A in the figure is conveyed to a drum-shaped photosensitive member 3, which is a surface to be scanned, at a timing by a pair of registration rollers 2. Is done. When the photoconductor 3 is driven to rotate in the direction of arrow B in the figure, the surface of the photoconductor 3 is uniformly charged by the charging charger 4 at that time, and the writing unit 10 irradiates a laser beam to the surface to be scanned. As a result, an electrostatic latent image is formed on the photoconductor 3. The latent image is visualized by toner when passing through the developing device 5, and the visible image is transferred to a sheet conveyed to the photoconductor 3 by the transfer charger 6, and the visible image on the transferred sheet P is transferred. Is fixed by the fixing device 7. Then, the sheet P that has passed through the fixing device 7 is
In the figure, the sheet is conveyed in the direction of arrow C and is ejected outside the laser printer 1. On the other hand, the residual toner on the photoconductor 3 is removed by a cleaning device (not shown).

As shown in FIG.
Is mainly composed of an optical unit 11 as a light source unit, a folding mirror 12 for reflecting laser light emitted from the optical unit 11 to the photoconductor 3, and a frame 13 on which the optical unit 11 and the folding mirror 12 are mounted. Have been.

The optical unit 11 includes a laser unit 15 including a semiconductor laser, a coupling lens, and a cylinder lens, a polygon mirror 16 for deflecting the laser light from the laser unit 15, and a scanning speed on the photosensitive member 3 which is substantially equal to that of the laser unit. Fθ lens 17 to be constant and laser unit 1
5, a housing 18 for accommodating the polygon mirror 16 and the Fθ lens 17.

Next, scanning by the writing unit 10 will be briefly described. The laser light emitted from the laser unit 15 enters the polygon mirror 16. The polygon mirror 16 is rotated at a high speed by a scan motor (not shown) and deflects the incident laser light. The scanning speed of the laser light is made substantially constant by the Fθ lens 17 and passes through the opening 18 a of the housing 18. further,
The aperture 13 of the frame 13 is reflected by the mirror 12
a, and forms an image on the photoconductor 3. Thereby, an electrostatic latent image is formed on the surface of the photoconductor 3 by the laser beam.

Hereinafter, a first embodiment of the present invention will be described. As shown in FIGS.
Are formed in a substantially flat plate shape. Opening 1 of frame 13
In the vicinity of both ends of the mirror 3a in the main scanning direction, a pair of protrusions 20 for supporting both ends of the folding mirror 12 are provided. The projection 20 has a folding mirror 12
Is provided. Flat part 21
Are inclined so that the reflection surface of the return mirror 12 faces the photoconductor 3.

A bracket 22, which is a plate-like member for fixing the end of the folding mirror 12 to the flat portion 21, is fastened to the flat portion 21 by screws 23,23. The bracket 22 is made of a highly rigid metal, such as aluminum or iron, and has a flat portion 22a. The folding mirror 12 is fixed to the projection 20 by sandwiching the end of the folding mirror 12 between the flat portion 22 a and the flat portion 21. At this time, folding mirror 1
2 is in surface contact with the plane portion 22a and the plane portion 21, respectively.

As described above, since both ends of the folding mirror 12 are sandwiched by the flat portions 22a and 21 in surface contact with each other and fixed to the projections 20, 20, the restrained area of the folding mirror 12 is reduced. , Larger than the fixing by the leaf spring. Therefore, the folding mirror 12
Increases, the frequency of the bending vibration of the folding mirror 12, that is, the resonance frequency increases, and the interval between the vertical patterns on the image that appears depending on the frequency decreases. When the interval between the vertical patterns becomes narrow, the vertical patterns become indistinguishable from image disturbance in a human visual system, that is, become vertical patterns that cannot be visualized. Therefore,
The human visual system cannot recognize the disturbance of the image, and the image quality can be improved.

Further, since the constrained area of the folding mirror 12 becomes large, the relative vibration generated in the folding mirror 12 is suppressed, and the vibration of the folding mirror 12 which affects the image can be reduced.

Next, a second embodiment will be described with reference to FIGS. In these drawings, the same members as those shown in FIGS. 3 and 4 are denoted by the same reference numerals as those used in FIGS. 3 and 4, and the description thereof is omitted, and different points will be described.

As shown in FIG. 5 and FIG.
Numeral 0 is made of glass and is formed in a triangular prism shape having a reflection surface on one surface. The surface of the folding mirror 30 is mirror-finished, and if this surface can be used as a reflecting surface, the material may be a metal such as aluminum or iron instead of glass.

Both ends of the folding mirror 30 are fixed to the flat portions 21 of the projections 20 by plate-like brackets 31, respectively. The bracket 31 is formed in a V-shaped cross section along the shape of the folding mirror 30, and both ends of the bracket 31 are fastened to the flat portion 21 by screws 23. The wall surface forming the V-shaped groove of the bracket 31 is:
It is formed in a planar shape.

Since the folding mirror 30 has a triangular prism shape, the rigidity of the folding mirror 30 is improved, the deformation of the folding mirror 30 is reduced, and the resonance frequency of the folding mirror 30 is higher than the resonance frequency of the flat folding mirror. Get higher. Therefore, the interval between the vertical patterns on the image that appears depending on the frequency becomes narrow, and the vertical pattern cannot be judged as a disturbance of the image by the human visual system, that is, it becomes a vertical pattern that cannot be visualized. Therefore, the human visual system cannot recognize the disturbance of the image, and the image quality can be improved.

Here, the frequency at which bending vibration occurs between the flat mirror 12 in the first embodiment and the triangular mirror 30 in the present embodiment will be described. FIGS. 7 and 8 show vibration modes when the folding mirror 12 and the folding mirror 30 are modeled on a simulation, respectively, and the natural frequencies of both the folding mirrors 12 and 30 are calculated.
The vibration mode is a state in which the folding mirrors 12 and 30 generate flexural vibration, and the frequency at which the flexural vibration occurs is a resonance frequency.

In FIG. 7, when the folding mirror 12 is deformed from the normal shape (the state indicated by reference numeral X1 in the figure) (the state indicated by reference numeral Y1 in the figure), bending vibration occurs in the folding mirror 12. . The frequency at which the flexural vibration occurs at this time is 305 Hz based on the result of simulation, for example, calculation by the finite element method.

In FIG. 8, the folding mirror 30
Is deformed from the normal shape (the state indicated by reference sign X2 in the figure) (the state indicated by reference sign Y2 in the figure), the bending vibration occurs in the folding mirror 30, and the frequency at which the bending vibration occurs at this time Is 782 Hz based on the calculation result of the above simulation.

Therefore, as apparent from the calculation result of this simulation, the frequency of the bending vibration of the folding mirror 30, that is, the resonance frequency becomes higher than the resonance frequency of the folding mirror 12. Although the frequency at which the flexural vibration occurs is calculated by simulation, the frequency may be obtained by experimentally analyzing the frequency. Experimental analysis includes a modal analysis method.

Further, a third embodiment will be described with reference to FIG. 3, the same members as those shown in FIGS. 3 and 4 are denoted by the same reference numerals as those used in FIGS. 3 and 4, and the description thereof will be omitted, and different points will be described.

In the vicinity of the opening 13a of the frame 13, a flat plate 35 extends along the longitudinal direction of the opening 13a.
Are fixed by screws 36. On the upper surface of the plate 35, a flat portion 35a is formed. On the flat portion 35a, one surface other than the anti-slope surface of the triangular prism-shaped folding mirror 37 is attached and fixed in a state of surface contact with the flat portion 35a. I have. The plate 35 is made of a material whose coefficient of thermal expansion is similar to the material of the folding mirror 37. The folding mirror 37 is made of glass and has a reflective surface on one surface, similarly to the folding mirror 30 in the second embodiment.

With this configuration, the portion of the folding mirror 37 that is in surface contact with the flat portion 35a increases, so that the constraint area of the folding mirror 37 increases. Therefore, the folding mirror 37 is constrained to have an area substantially the same as the area of the folding mirror 37, so that the folding mirror 37
The frequency of the flexural vibration, i.e., the resonance frequency, can be improved to a high frequency band, and the human visual system cannot determine a vertical pattern on an image that appears depending on this frequency as a disturbance of the image. That is, it becomes a vertical pattern that cannot be visualized. The human visual system cannot recognize the disturbance of the image, and can improve the image quality of the image. In the present embodiment, even if the resonance frequency is low, it is several kHz, so that image deterioration due to mirror vibration can be greatly reduced.

Further, a fourth embodiment will be described with reference to FIG. The fourth embodiment is different from the third embodiment in that an attenuation member 38 is interposed between the folding mirror 37 and the flat portion 35a of the plate 35. The damping member 38 will be described in detail.
Attenuates the vibration transmitted from the frame 13 to the return mirror 37. For example, rubber, urethane foam,
It is made of a vibration-proof material such as an acrylic plate. The damping member 38 has a shape substantially similar to the shape of the flat portion 35a, and has a property of absorbing distortion due to thermal expansion between the folding mirror 37 and the frame 13.

When the vibration generated by the writing unit 10 is transmitted to the frame 13, the frame 13 is also vibrated. However, the vibration transmitted from the frame 13 to the return mirror 37 is reduced by the above configuration. Therefore,
Vibration of the return mirror 37 is also reduced, and image deterioration due to vibration of the return mirror 37 is reduced, so that high image quality can be achieved.

Further, a fifth embodiment will be described with reference to FIG. In the vicinity of the opening 13a of the frame 13, a triangular prism-shaped mirror mounting member 40 long in the longitudinal direction of the opening 13a is provided. One surface of the mirror mounting member 40 is attached so as to make surface contact with the frame 13. On the surface 40a of the mirror mounting member 40 facing the opening 13a, a flat mirror 41 is attached via a damping member 42. The damping member 42 is made of substantially the same material as the damping member 38 in the fourth embodiment. With this configuration, it is possible to obtain substantially the same effect as the effect in the fourth embodiment.

Further, a sixth embodiment will be described with reference to FIG. The triangular prism mirror 45 is
It is made of glass. Inside the folding mirror 45, a rod-shaped attenuation member 46 having a circular cross section that is long in the main scanning direction of the folding mirror 45 is provided. Damping member 46
Is inserted through a substantially central portion of the folding mirror 45 and extends from one end to the other end of the folding mirror 45. The attenuating member 46 attenuates the vibration of the folding mirror 45, and is made of, for example, a material having a vibration-proof property such as rubber, urethane foam, or the like.

With this configuration, the folding mirror 45 itself has a property of reducing vibration, and even if the vibration is transmitted to the folding mirror 45, the vibration is reduced.
The image quality can be prevented from deteriorating due to the vibration, and the image quality can be improved.

The outer diameter is the same as that of the folding mirror 45 shown in FIG.
FIG. 13 shows a vibration mode when the natural frequency of the folding mirror whose portion corresponding to is hollow is calculated. The vibration mode at this time, that is, the frequency at which the flexural vibration occurs is 864 Hz according to the calculation result of the simulation. In FIG. 13, the state indicated by reference sign X3 indicates the normal shape of the turning mirror, and the state indicated by reference sign Y3 indicates the deformed shape of the turning mirror.

In the folding mirror 45 shown in FIG. 12, since the rigidity of the damping member 46 is low, the frequency at which the bending vibration occurs in the folding mirror 45 is considered to be close to the frequency at which the bending vibration of the folding mirror shown in FIG. 13 occurs. Can be Therefore, the frequency at which the bending vibration of the folding mirror 45 occurs, that is, the resonance frequency is also considered to be a frequency in the vicinity of 864 Hz. The pattern is indistinguishable by the human visual system as an image disorder,
That is, it becomes a vertical pattern that cannot be visualized. Therefore, the human visual system cannot recognize the disturbance of the image, and the image quality can be improved. The cross-section of the folding mirror 45 may be a quadrangular prism, or its material may be metal. Further, the cross-sectional shape of the damping member 46 may be polygonal.

[0038]

As explained above, according to the first aspect of the present invention, the constraint area of the mirror is increased,
The frequency of the flexural vibration of the mirror, that is, the resonance frequency increases, and the interval between the vertical patterns on the image that appears depending on the frequency becomes narrow. Therefore, this vertical pattern cannot be judged by the human visual system as a disturbance of the image. It becomes possible, that is, a vertical pattern that cannot be visualized. Therefore, the human visual system cannot recognize the disturbance of the image, and the image quality can be improved. Further, since the constraint area of the mirror is increased, the relative vibration generated in the mirror is suppressed, and the vibration of the mirror which affects the image can be reduced.

According to the second aspect of the present invention, the mirror is restrained in an area substantially similar to the area of the mirror, so that the frequency of the flexural vibration of the mirror, that is, the resonance frequency can be improved to a high frequency band. Yes, in the human visual system,
The vertical pattern on the image that appears depending on the frequency becomes indistinguishable as a disturbance of the image, that is, a vertical pattern that cannot be visualized. Therefore, the human visual system cannot recognize the disturbance of the image, and the image quality can be improved.

According to the third aspect of the present invention, since the mirror has a triangular prism shape, the rigidity of the mirror is improved, and the frequency of the bending vibration of the mirror, that is, the resonance frequency is higher than the resonance frequency of the flat folding mirror. That is, in the human visual system, a vertical pattern on an image that appears depending on the resonance frequency cannot be determined to be a disturbance of the image, that is, a vertical pattern that cannot be visualized. Therefore, the human visual system cannot recognize the disturbance of the image, and the image quality can be improved.

According to the fourth aspect of the present invention, since the vibration transmitted from the frame to the mirror is reduced, the vibration of the mirror is also reduced, the image deterioration due to the vibration of the mirror is reduced, and the image quality can be improved.

According to the fifth aspect of the present invention, the mirror itself has a property of reducing vibration, and even if vibration is transmitted to the mirror, the vibration is reduced, so that a deterioration in image quality due to mirror vibration can be prevented. High image quality can be achieved. In addition, since the frequency at which the bending vibration of the mirror occurs, that is, the resonance frequency, can be improved, the interval between the vertical patterns on the image that appears depending on the frequency becomes narrower. It is impossible to judge it as disorder. Therefore, the human visual system cannot recognize the disturbance of the image, and the image quality can be improved.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a laser printer.

FIG. 2 is a perspective view illustrating a schematic configuration of an optical scanning device.

FIG. 3 is an enlarged perspective view of a mounting portion of a folding mirror to a frame.

FIG. 4 is a sectional view taken along line IV-IV of FIG. 3;

FIG. 5 is an enlarged perspective view of a portion where a folding mirror is attached to a frame according to a second embodiment of the present invention.

FIG. 6 is a sectional view taken along line VI-VI of FIG.

FIG. 7 is a simulation analysis diagram showing a vibration mode of a flat folding mirror.

FIG. 8 is a simulation analysis diagram showing a vibration mode of a triangular prism-shaped folding mirror.

FIG. 9 is an enlarged perspective view of a portion where a folding mirror is attached to a frame according to a third embodiment of the present invention.

FIG. 10 is an enlarged perspective view of a portion where a folding mirror is attached to a frame according to a fourth embodiment of the present invention.

FIG. 11 is an enlarged perspective view of a portion where a folding mirror is attached to a frame according to a fifth embodiment of the present invention.

FIG. 12 is an enlarged perspective view of a partly broken mirror of a folding mirror showing a sixth embodiment of the present invention.

FIG. 13 is a simulation analysis diagram showing a vibration mode of a triangular prism-shaped folding mirror having a hollow portion inside.

[Explanation of symbols]

 Reference Signs List 3 photoconductor (scanned surface) 10 writing unit (optical scanning device) 11 optical unit (light source unit) 12 folding mirror 13 frame 20 protrusion 21 flat portion 22 bracket (plate-shaped member) 38, 46 attenuation member

Claims (5)

[Claims] 1. An image forming apparatus comprising: a light source unit; a mirror that reflects a light beam emitted from the light source unit to a surface to be scanned; and a frame to which the mirror is attached. An image forming apparatus having a flat portion for supporting the mirror, wherein both ends of the mirror in the main scanning direction are sandwiched between a plate-shaped member and the flat portion and fixed to the frame. 2. An image forming apparatus comprising: a light source unit; a mirror for reflecting a light beam emitted from the light source unit on a surface to be scanned; and a frame to which the mirror is attached. An image forming apparatus, comprising: a flat portion that supports the mirror; and a surface other than the reflection surface of the mirror is fixed to the flat portion. 3. The image forming apparatus according to claim 1, wherein said mirror has a triangular prism shape. 4. An image forming apparatus according to claim 1, wherein a damping member for damping vibration transmitted from said frame to said mirror is interposed between said mirror and said plane portion. Image forming apparatus. 5. The image forming apparatus according to claim 1, wherein an attenuating member which is long in a main scanning direction of the mirror and attenuates vibration of the mirror is provided inside the mirror. Characteristic image forming apparatus.