JP4458833B2 - Optical scanning apparatus and image forming apparatus - Google Patents

Description

  The present invention relates to an optical scanning device used in a laser printer, a plain paper copying machine (PPF), a digital copying machine, and the like, and an image forming apparatus such as the laser printer and the copying machine using the optical scanning device.

  2. Description of the Related Art Conventionally, an optical scanning device that deflects and reflects a light beam emitted from a light source such as a laser light source by an optical deflector and scans the light beam on a surface to be scanned is known. Simultaneously with the scanning of the light beam on the surface to be scanned, the light beam is turned on and off in accordance with an image signal to write an image on the surface to be scanned. A rotating polygon mirror that rotates at a constant speed is widely used as an optical deflector. However, the rotating polygon mirror requires a large amount of equipment and is accompanied by mechanical high-speed rotation, so that banding due to vibration, temperature rise, noise, and consumption There are problems such as an increase in power. In particular, when the rotational speed of the rotary polygon mirror is increased in order to increase the writing speed, the above problem becomes remarkable.

  On the other hand, a micro mirror using sinusoidal vibration of a resonance structure using micro machine technology has been proposed. The micromirror is supported via a beam portion, and swings or vibrates due to deformation of the beam portion. If the micromirror is used in an optical scanning device, the device can be downsized and various problems due to vibration as described above can be reduced.

The present applicant has applied for a patent on an optical scanning device that uses a sine wave oscillating mirror composed of the above-described micromirrors and that defines conditions for satisfying constant velocity characteristics and an image forming apparatus using the same (for example, Patent Document 1). reference).
JP 2002-82303 A

  However, it can be seen that a micromirror that oscillates (oscillates) due to deformation of the beam part undergoes dynamic surface deformation along with the oscillation, which makes it difficult to obtain a good beam spot diameter. all right.

The present invention has been made in order to solve the problems of the invention described in Patent Document 1, and reduces the influence of dynamic surface deformation caused by the swinging of a deflecting mirror such as a micromirror, and provides a good beam. An object of the present invention is to provide an optical scanning device capable of obtaining a spot diameter.
Another object of the present invention is to provide an image forming apparatus that can output a high-quality image by using the optical scanning device.

The present invention includes a light source, a deflection mirror that deflects a light beam from the light source by deformation of a beam portion, a deflection mirror substrate that holds the deflection mirror, a scanning lens that guides the light beam from the deflection mirror to a surface to be scanned, has the deflection mirror is out beam portion from two different points of the position in the main scanning direction and the main scanning direction in a range in which the light beam is reflected on the deflecting mirror is different positions in the main scanning direction located between the beams of the two positions, wherein the deflection mirror and the beam portion has been integrally molded from the same substrate, the bending stiffness of the deflection mirror is minimum at the center portion and both end portions in the main scanning direction The main feature is that the sectional area in the sub-scanning direction of the deflecting mirror varies depending on the position in the main scanning direction so that one maximum value is obtained from the center to the end.

The reflection area of the deflection mirror may be smaller than the entire outer shape of the deflection mirror.
A plurality of deflecting mirrors may be arranged in the main scanning direction, and light beams from the plurality of deflecting mirrors may scan the surface to be scanned.
The optical scanning apparatus configured as described above can be used as an exposure apparatus for an image forming apparatus.

According to the present invention, a deflection mirror that deflects a light beam from a light source by deformation of a beam portion is used as an optical deflector of an optical scanning device, which causes a problem in an optical deflector that uses a rotary polygon mirror as an optical deflector. Problems such as banding, temperature rise, noise, and increased power consumption can be solved.
Moreover, by satisfying conditional expressions (1) and (2),
a. Good beam spot diameter can be obtained b. High speed scanning becomes possible c. Good constant velocity characteristics can be obtained d. An effect that a wide effective writing width can be obtained can be obtained.

By changing the sectional area of the deflection mirror in the sub-scanning direction according to the position in the main scanning direction, the dynamic surface deformation of the deflection mirror can be reduced, and a good beam spot diameter can be obtained.
The deflection mirror protrudes from two beam positions with different positions in the main scanning direction, and the range in the main scanning direction where the light beam is reflected on the deflection mirror is between two beam positions with different positions in the main scanning direction. By providing it in this way, the influence of dynamic surface deformation can be reduced, and a good beam spot diameter can be obtained.
By making the reflection area of the deflecting mirror smaller than the entire outer shape of the deflecting mirror, the deflecting mirror can be miniaturized to reduce dynamic surface deformation, and the optical scanning device can be miniaturized.
By using the thus configured optical scanning device as the exposure device of the image forming apparatus, it is possible to provide an image forming apparatus capable of obtaining high image quality and to reduce the size of the image forming apparatus. .

  Hereinafter, embodiments of an optical scanning device and an image forming apparatus according to the present invention will be described with reference to the drawings. FIG. 1 shows an example of an optical deflector using a deflecting mirror used in an optical scanning device according to the present invention. In FIG. 1, reference numeral 102 denotes a mirror substrate made of a silicon (hereinafter referred to as “Si”) substrate. The mirror substrate 102 is cut into a quadrangular shape by etching from the back side of the Si substrate, and is formed to a predetermined thickness, leaving the frame portion and the top plate portion. In the top plate portion, the deflection mirror 100 is formed by penetrating the periphery of the top plate portion, and the beam portion 101 for pivotally supporting the deflection mirror 100 is formed by connecting the frame portion and the deflection mirror 100. ing. The beam portion 101 has a form called a torsion bar. In the embodiment, a Si substrate of about 200 μm is used, and the thickness of the deflection mirror 100, that is, the thickness of the top plate portion is about 60 μm. The width of the deflecting mirror 100 is 4 mm × 2 mm, and a metal film such as copper (Au) is deposited on the upper surface to form a reflecting surface.

  Concavities and convexities are formed in comb-like shapes at both ends in the length direction of the deflecting mirror 100, and the irregularities serve as the movable electrode 104. A fixed electrode 105 is formed with a clearance of 5 μm on the end face of the substrate facing the movable electrode 104 so as to mesh with the comb-teeth shape. Each of the electrodes 104 and 105 is configured to face the mirror substrate 102 at the same position in the thickness direction when the deflection mirror 100 is in a horizontal state.

  The beam portion 101 is dimensioned so as to resonate in a vibration mode with the beam portion 101 as a rotation axis in accordance with the scanning frequency or drive frequency of the deflection mirror 100. That is, the deflection mirror 100 is made of a vibrating mirror. In the embodiment, the beam portion 101 has a width of about 100 μm and a length of about 1 mm. Since the mirror substrate 102 has a wafer polishing surface, and a nitride film is formed to insulate the electrode and the mirror substrate 102, the deflecting mirror 100 penetrated by etching is slightly affected by the internal stress difference between the front and back surfaces. The movable electrode 104 and the fixed electrode 105 have a step of several μm. Therefore, when a voltage is applied to one of the fixed electrodes 105, the deflecting mirror 100 is rotated by twisting the beam 101 until it is horizontal due to an electrostatic force, and reciprocally vibrates when an AC voltage is applied. Although the amplitude of this vibration is very small, when the frequency of the AC voltage is applied to a frequency corresponding to the mechanical resonance frequency unique to the deflection mirror 100, the deflection mirror 100 is excited to expand the amplitude. In the embodiment, the sine wave is oscillated at ± 5 °.

  The reason why the electrodes are comb-shaped is to increase the area of the electrodes by increasing the outer peripheral length of the electrodes. By doing so, consideration is given to obtain a larger electrostatic torque at a low voltage.

  FIG. 2 is an overall configuration diagram showing an embodiment of an optical scanning device according to the present invention. 2, reference numerals 200, 201, and 202 denote optical deflectors having the same configuration as that of an optical deflector (hereinafter referred to as “vibrating mirror deflector”) using a deflecting mirror as shown in FIG. The three oscillating mirror deflectors 200, 201, and 202 are mounted on the electrical board 204 with the scanning direction aligned with a common virtual line. The oscillating mirror deflectors 200, 201, and 202 are combined with a semiconductor laser 205, a coupling lens 206, a first scanning lens 207, and a second scanning lens 208 as a light source to constitute three optical scanning units. One optical scanning device is constituted by two optical scanning means. In the illustrated embodiment, the second scanning lens 208 in each optical scanning means having the oscillating mirror deflectors 200, 201, and 202 is connected to the scanning direction, which is the length direction, and is integrally formed. ing.

  The light beams emitted from the respective semiconductor lasers 205 are converted into substantially parallel light beams by the respective coupling lenses 206 and are incident on the vibrating mirror deflector. Each light beam is incident at an angle of about 10 ° in the sub-scanning direction with respect to the normal line of the deflecting mirror in the corresponding oscillating mirror deflector, deflected by the reflecting surface of the deflecting mirror, and emitted from the deflector. Further, the image is formed on the photosensitive drum 210 by passing through the plurality of scanning lenses 207 and 208, and each region obtained by dividing one image into three in the main scanning direction is scanned. A light beam is scanned on the photosensitive drum 210 by each optical scanning unit, and the light beam is modulated by an image signal to be recorded, so that one connected image is formed on the photosensitive drum 210. Written and recorded to form an electrostatic latent image. The joined electrostatic latent image consisting of one image is visualized with toner by a developing device 211 and transferred to printing paper or transfer paper 212 by a transfer device.

  In the embodiment shown in FIG. 2, the surface to be scanned is divided into three regions and scanned by three scanning means to form one continuous image. Thereby, the size of the deflection mirror made of a micromirror can be reduced, and the amount of dynamic surface deformation can be reduced. Note that the entire effective writing width region of the surface to be scanned may be scanned by one deflecting unit.

FIG. 3 shows the amount of dynamic surface deformation with respect to the position of the deflection mirror in the main scanning direction.
The amplitude angle of the mirror is 5 °
Deformation amount 1 is dynamic surface deformation amount 2 when the deflection angle is 2 °, dynamic surface deformation amount 3 when the deflection angle is 3.5 °, and dynamic surface deformation amount 3 when the deflection angle is 5 °. .
Due to such dynamic surface deformation, the beam spot diameter in the main scanning direction on the surface to be scanned deteriorates, and there are the following two ways of deterioration.
1) The beam spot diameter on the surface to be scanned increases due to the change in the beam waist position accompanying dynamic surface deformation, that is, the position where the beam spot diameter becomes the smallest when the evaluation surface is changed in the optical axis direction.
2) The beam waist diameter accompanying dynamic surface deformation, that is, the beam spot diameter at the beam waist position is increased.
The problem 1) can be dealt with by a scanning optical system if the amount of dynamic surface deformation is known in advance. However, the scanning optical system cannot cope with the problem 2).

In the graph of FIG. 3, if the optical power in the region where the position of the deflecting mirror in the main scanning direction is + is positive, the optical power in the region − is negative. The beam waist diameter is increased when the light beam spans both the positive and negative regions. When the range in the positive region is P and the range in the negative region is N, the minimum value of P and N If is reduced, it is possible to reduce the increase in the beam waist diameter due to the wavefront aberration deterioration.
As can be seen from FIG. 3, with respect to the outermost periphery of the outer shape of the mirror of ± 2 mm, the dynamic surface deformation rapidly deteriorates when it exceeds ± 1.8 mm. Therefore, by not using this portion, it is possible to reduce the beam waist diameter increase due to the amount of dynamic surface deformation.

Further, even if the dynamic surface deformation is a completely sinusoidal shape, in the outer shape of the deflection mirror, the width in the main scanning direction is D1, and the range in the main scanning direction in which the light beam is reflected on the deflection mirror is D2. When
0.5 <D2 / D1 <0.9 (1)
The following conditions are satisfied. When D2 / D1 exceeds the upper limit, the minimum values of P and N increase, and the beam waist diameter increases. That is, by making D2 / D1 not exceed the upper limit, the beam spot diameter can be reduced. If D2 / D1 is less than the lower limit, the setting of the beam spot diameter in the initial design becomes thick, or it becomes difficult to increase the speed by increasing the main scanning direction width of the mirror. It can also be seen that the amount of dynamic surface deformation increases as the deflection angle increases.

Usually, the mirror swings due to the deformation of the beam portion vibrates with a characteristic close to a sine wave. Further, when scanning the surface to be scanned with the light beam modulated based on the image signal, it is desirable in terms of electrical control to modulate the light source at the same time interval for each pixel.
FIG. 4 shows the ideal image height with respect to the horizontal axis θ2 / θ1 and the image height by the ideal fθ lens, where θ1 is the amplitude angle of the deflection mirror and θ2 is the maximum deflection angle corresponding to the effective writing width of the deflection mirror. Show the relationship. From FIG.
0.2 <θ2 / θ1 <0.7 (2)
It can be seen that it is desirable to satisfy the following conditions. If θ2 / θ1 exceeds 0.7, the difference between the ideal fθ lens and the ideal image height becomes large, and correction with the scanning optical element becomes difficult, and the constant velocity characteristic is actually deteriorated. On the other hand, if θ2 / θ1 is less than 0.2, the effective writing width becomes extremely narrow.
As is clear from the above description, satisfying the expressions (1) and (2) at the same time can provide a good beam spot diameter, constant velocity characteristics, and a wide effective writing width.

  FIG. 5 shows another example of a deflection mirror applicable to the present invention. In FIG. 5, the beam portion functioning as the beam portion is Y-shaped, and the beam portion comes out from two places having different positions in the main scanning direction. The beam portions coming out from two locations merge into one beam portion on the frame portion side and are connected to the frame portion. The dynamic surface deformation in the range sandwiched between the beam portions is reduced as shown in FIG. Therefore, by setting the range in which the light beam is reflected on the deflection mirror surface between the beam portions, the beam spot diameter increase due to the dynamic surface deformation can be reduced.

  As shown in FIGS. 3 and 6, the amount of dynamic surface deformation varies depending on the mirror position in the main scanning direction. Therefore, as shown in FIG. 5C, by making the rigidity of the micromirror variable according to the position in the main scanning direction, it is possible to achieve both reduction of the dynamic surface deformation amount and securing of the deflection angle. FIG. 5B is a diagram showing the embodiment, and a region surrounded by a plurality of circles is thinned. The circular thinned portions differ in the diameter and arrangement density of the circles depending on the position in the main scanning direction. As a result, the deflection mirror has different cross-sectional areas in the sub-scanning direction due to different positions in the main scanning direction. In other words, the rigidity of the deflection mirror is changed depending on the position in the main scanning direction. By doing so, the dynamic surface deformation of the deflection mirror in the main scanning direction can be reduced.

  In addition, as shown in FIG. 5A, by making the region functioning as a mirror narrower than the entire region of the mirror, problems in processing the deflection mirror are reduced, yield is improved, and cost can be reduced. Become.

  FIG. 7 shows an embodiment of a multicolor image forming apparatus using the optical scanning device according to the present invention. In FIG. 7, oscillating mirror deflectors 220, 221, 222, and 223 are mounted on an electrical board in the same manner as in the above-described embodiment, and include a semiconductor laser 225, a coupling lens 226, a first scanning lens 227, and a second scanning lens 228. These are combined to form an optical scanning unit. Each of the optical scanning units is arranged along the feeding direction of the transfer belt 229, and the photosensitive drums 230, 231, 232, and 233 whose surfaces are uniformly charged in advance are respectively yellow (Y) and magenta (M). , Electrostatic latent images corresponding to cyan (C) and black (K) are recorded. These electrostatic latent images are visualized with each color toner by developing units 234, 235, 236, and 237 disposed around the respective photosensitive drums. The toner images are sequentially transferred as the transfer belt 229 moves, and are superimposed to form a color image. The color image is transferred to the printing paper 238 in the transfer unit, fixed in the fixing unit, and the printing paper 238 on which the image is fixed is discharged to a paper discharge tray (not shown).

  The surface of each of the photosensitive drums after transferring the toner image is subjected to charge removal and cleaning in the cleaning unit, and then uniformly charged in the charging unit, and preparation for the next exposure is performed. As described above, the image forming apparatus forms an image on printing paper or transfer paper by executing a series of electrophotographic processes including charging, exposure, development, transfer, fixing, and cleaning. Of the series of electrophotographic processes, the optical scanning device is responsible for the exposure process.

Note that here, an example of a multi-color image forming apparatus is described, but the optical scanning apparatus according to the present invention can also be applied to a single-color image forming apparatus.
Further, although the semiconductor laser as the light source has been described as a single beam, it may be multi-beamed to increase the speed.
The material of the scanning lens is not particularly limited. However, if a resin lens is used, it is easy to perform the molding process, so that the cost can be reduced.

  The present invention can be used as an optical scanning device in an image forming apparatus such as a laser printer, a plain paper copying machine (PPF), a digital copying machine, and a facsimile, and as various image forming apparatuses including the optical scanning device. it can. The present invention can be used in the computer peripheral device field or the OA device field.

It is a disassembled perspective view which shows the example of the deflection | deviation mirror which can be used for this invention. It is a perspective view which shows the Example of the optical scanning device concerning this invention using the said deflection | deviation mirror. It is a graph which shows the amount of dynamic surface deformations with respect to the position of the deflection mirror in the main scanning direction. A graph showing the relationship between the ideal image height with respect to θ2 / θ1 and the image height by an ideal fθ lens, where the amplitude angle of the deflection mirror is θ1 and the maximum deflection angle corresponding to the effective writing width of the deflection mirror is θ2. is there. FIG. 5 shows another example of a deflection mirror applicable to the present invention, where (a) is a front view, (b) is a bottom view, and (c) is a graph showing the bending rigidity of the deflection mirror. It is a graph which shows the dynamic surface deformation | transformation of the range pinched | interposed into the beam part in another example of the said deflection | deviation mirror. 1 is a perspective view showing an example of a multi-color image forming apparatus using an optical scanning device according to the present invention.

Explanation of symbols

100 Deflection mirror 101 Beam (beam)
DESCRIPTION OF SYMBOLS 102 Mirror substrate 104 Movable electrode 105 Fixed electrode 205 Semiconductor laser as a light source 206 Coupling lens 207 1st scanning lens 208 2nd scanning lens 210 Photosensitive drum

Claims (4)

A light source, a deflection mirror that deflects the light beam from the light source by deformation of the beam portion, a deflection mirror substrate that holds the deflection mirror, and a scanning lens that guides the light beam from the deflection mirror to a surface to be scanned,
Said deflection-mirror is out beam portion from two different points of the position in the main scanning direction, and the beam at two positions having different positions in the main scanning direction in a range in the main scanning direction in which the light beam is reflected on the deflecting mirror Between the departments
Wherein the deflection Mirror and the beam portion has been integrally molded from the same substrate,
The cross-sectional area of the deflection mirror in the sub-scanning direction is the main scanning direction so that the bending mirror has the smallest bending rigidity at the center and both ends in the main scanning direction and takes one maximum value from the center to the end. An optical scanning device characterized in that the optical scanning device changes depending on the position.   2. The optical scanning device according to claim 1, wherein a reflection area of the deflection mirror is smaller than an entire outer shape of the deflection mirror.   3. The optical scanning device according to claim 1, wherein a plurality of deflection mirrors are arranged in the main scanning direction, and light beams from the plurality of deflection mirrors scan the surface to be scanned in a shared manner. . 4. An image forming apparatus that obtains an image by executing an electrophotographic process, and uses the optical scanning device according to claim 1 as an apparatus that executes an exposure process of the electrophotographic process.

Images