JP2008020481A - Optical scanner and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical scanner that is used in an image forming apparatus such as a digital copying machine and a laser printer, and the like, to provide an image forming apparatus using this optical scanner. <P>SOLUTION: In the image forming apparatus, an electrostatic image is recorded on an image carrier by an optical flux from a light source modulated by an image signal, with the electrostatic image made to appear in image with a toner, and with the image transferred to a recording medium. The apparatus is provided with a light source, a deflection means for deflecting an optical flux emitted from the light source by oscillating a vibration mirror, and a wavefront deforming means for deforming the wavefront of the optical flux made incident on the deflection means, in the optical path from the light source to the deflection means. The electrostatic image is recorded by scanning the image carrier back and forth with the optical flux deflected by the deflection means, thereby suppressing failures of beam spot quality deterioration in an image plane caused by dynamic surface deformation of the vibration mirror. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optical scanning apparatus and an image forming apparatus, and more particularly, to an optical scanning apparatus used in an image forming apparatus such as a digital copying machine and a laser printer, and an image forming apparatus using the same.

  In a conventional optical scanning device, a polygon mirror or a galvanometer mirror is used as a deflector that scans a light beam. To achieve a higher resolution image and high-speed printing, this rotation must be further increased. Durability, heat generation due to wind damage, and noise are issues, and there is a limit to high-speed scanning.

  On the other hand, in recent years, research on a deflecting device using silicon micromachining has been promoted, and as disclosed in Patent Document 1 and Patent Document 2, an oscillating mirror and a torsion beam that pivotally supports it are integrated with a Si substrate. The formed method is proposed. According to this method, there is an advantage that the mirror surface size can be reduced and the size can be reduced, and since reciprocal vibration is performed using resonance, high speed operation is possible but low noise and low power consumption are possible.

  Further, Patent Documents 3 and 4 disclose examples of image forming apparatuses in which a vibrating mirror is provided instead of a polygon mirror.

Further, in the optical scanning device corresponding to the “tandem method” shown in Patent Document 5, conventionally, a temperature distribution is generated in the housing that houses the optical scanning device due to a rise in the temperature of the polygon mirror, and the imaging optical system is installed due to thermal distortion. An optical scanning device that can control the temperature rise by using a vibrating mirror and can perform high-quality image formation in response to the problem that the orientation of the scanning lens and the folding mirror, etc., changes and causes color shift and color change. An example is disclosed.
Japanese Patent No. 2924200 Japanese Patent No. 30111144 Japanese Patent No. 3445691 Japanese Patent No. 3543473 JP 2003-98459 A

  However, the above invention has the following problems.

  If a vapor deposition film or a coil pattern is formed on one side of the mirror, a difference in stress occurs between the surface on which the vapor deposition film or the coil pattern is formed and the back side thereof, and the mirror surface is deformed. At this time, if an isotropic force is applied, a spherical deformation occurs. In addition, a vibrating mirror composed of a Si substrate or the like may not be able to obtain sufficient strength due to the need for weight reduction in order to achieve a large deflection angle and a high resonance frequency. Dynamic surface deformation of the mirror surface occurs. An example of deformation of the mirror is shown in FIG. The horizontal axis represents the position in the direction perpendicular to the rotation axis in the mirror plane, and the origin is the intersection with the rotation axis. When the mirror surface is deformed in this manner, the wavefront of the mirror reflected light is deteriorated as shown in FIG. 1B, and the quality of the beam spot on the image surface (shown in FIG. 1C) is deteriorated. As a result, there is a problem that the image quality deteriorates.

  Accordingly, the present invention provides an optical scanning device having a light source, a deflecting unit that deflects a light beam emitted from the light source by swinging a vibrating mirror, and an imaging optical system that reciprocally scans the light beam deflected by the deflecting unit. In the optical path from the light source to the deflecting means, the wavefront deforming means for deforming the wavefront of the light beam incident on the deflecting means is provided to suppress the defect of the beam spot quality deterioration of the image plane caused by the dynamic surface deformation of the vibrating mirror. It is an object of the present invention to propose an optical scanning device that can be used and an image forming apparatus using the same.

  The invention according to claim 1 is a light source, a deflecting means for deflecting a light beam emitted from the light source by swinging a vibrating mirror, and an imaging optical system for reciprocally scanning the light beam deflected by the deflecting means; In the optical scanning device having the above, the optical path from the light source to the deflecting means has wavefront deforming means for deforming the wavefront of the light beam incident on the deflecting means.

  According to a second aspect of the present invention, in the optical scanning device according to the first aspect, the wavefront deformation means deforms the wavefront of the light beam along a scanning direction.

  According to a third aspect of the present invention, in the optical scanning device according to the first or second aspect, the wavefront deforming unit performs a wavefront deformation in a reverse direction on two light flux regions sandwiching a rotation axis of the deflecting unit. Features.

  According to a fourth aspect of the present invention, in the optical scanning device according to any one of the first to third aspects, the wavefront deforming unit performs wavefront deformation in accordance with a scanning position.

  According to a fifth aspect of the present invention, in the optical scanning device according to any one of the first to fourth aspects, the wavefront deformation means is a liquid crystal element, and the liquid crystal element includes a plurality of regions in which the light distribution state is variable. It is characterized by having.

  According to a sixth aspect of the present invention, in the optical scanning device according to the fifth aspect, the wavefront deformation means is installed in a region where the light beam is parallel between the light source and the deflection means.

  According to a seventh aspect of the present invention, in the optical scanning device according to the fifth aspect, the wavefront deforming means is installed in a region where the light beam is in a converged state between the light source and the deflecting means.

  According to an eighth aspect of the present invention, in the optical scanning device according to any one of the fifth to seventh aspects, the optical scanning device includes a detection unit that detects the light beam deflected by the vibrating mirror, and the detection result by the detection unit is included in the detection result. The wavefront deformation means is controlled based on the above.

  According to a ninth aspect of the present invention, there is provided a light source, a deflecting unit that deflects a light beam emitted from the light source by swinging a vibration mirror, and an imaging optical system that reciprocally scans the light beam deflected by the deflecting unit. In the optical scanning device, the imaging optical system has wavefront aberrations in two light beam regions in the main scanning direction sandwiching the optical axis of the scanned light beam in opposite directions, and the amount of aberration increases as the angle of view increases. Is characterized by an increase.

  According to a tenth aspect of the present invention, in the optical scanning device according to the ninth aspect, the imaging optical system has a wavefront aberration along the main scanning direction.

  According to an eleventh aspect of the present invention, in the optical scanning device according to the ninth or tenth aspect, the imaging optical system is symmetric with respect to the optical axis of the central image height at an angle of view symmetric with respect to the optical axis of the central image height. It has a characteristic wavefront aberration.

  According to a twelfth aspect of the present invention, in the optical scanning device according to the ninth or tenth aspect, the imaging optical system is asymmetric with respect to the optical axis of the central image height at an angle of view symmetric with respect to the optical axis of the central image height. It has a wavefront aberration.

  According to a thirteenth aspect of the present invention, an electrostatic image is recorded on an image carrier with a light beam from a light source modulated by an image signal, the electrostatic image is visualized with toner, and the image is transferred to a recording medium. The forming apparatus includes the optical scanning device according to any one of claims 1 to 12, wherein the light beam from the light source is deflected and imaged in a spot shape by the imaging optical system, and the image is formed. The carrier is scanned.

  The present invention relates to an optical scanning device having a light source, a deflecting unit that deflects a light beam emitted from the light source by swinging a vibration mirror, and an imaging optical system that reciprocally scans the light beam deflected by the deflecting unit. By providing wavefront deforming means for deforming the wavefront of the light beam incident on the deflecting means in the optical path from the light source to the deflecting means, it is possible to suppress defects in beam spot quality degradation on the image plane caused by dynamic surface deformation of the vibrating mirror. it can.

  Hereinafter, configurations and operations of an optical scanning device and an image forming apparatus according to an embodiment of the present invention will be described.

  FIG. 2 shows an example of a system in which four stations are scanned by a single vibrating mirror. As shown in the figure, the optical scanning device that scans each photosensitive drum is integrally formed, and four photosensitive drums (101, 102, 103, 104) arranged at equal intervals along the moving direction 105 of the transfer body. ), The beams from the corresponding light source units are separated again after being deflected by the vibrating mirror 106 and guided to simultaneously form an image.

  The beams from the respective light source units are obliquely incident on the vibration mirror 106 at different incident angles in the sub-scanning direction, so that the beams from the respective light source units are collectively deflected and scanned. Each light source unit (107, 108, 109, 110) is radially arranged such that the light source unit 110 is the highest in the sub-scanning direction and the light source unit 110 is the highest, and decreases in order from the light source unit 109 to the light source unit 107. . A light source unit (109, 108, 107) folded back in a line in the order of beams 202, 203, 204 by a beam 201 from the light source unit 110 and three incident mirrors 111 having different heights in a staircase pattern. ) Are incident on the cylinder lens 113 at different heights in the sub-scanning direction and head toward the vibrating mirror 106.

  Each beam crosses in the sub-scanning direction in the vicinity of the vibrating mirror surface by the cylinder lens 113, and after deflection, enters the first lens 120 of the scanning lens system while widening the distance so that the beams are separated from each other. The first lens 120 is shared by all stations.

  Of the beams from the light source units that have passed through the first lens 120, the beam from the light source unit 107 is reflected by the folding mirror 126 and forms a spot image on the photosensitive drum 101 through the second lens 122. Then, a latent image based on yellow image information is formed as a first image forming station.

  The beam from the light source unit 108 is reflected by the folding mirror 127, forms a spot image on the photosensitive drum 102 via the second lens 123 and the folding mirror 128, and forms a magenta image as a second image forming station. A latent image based on information is formed.

  The beam from the light source unit 109 is reflected by the folding mirror 129, forms an image on the photosensitive drum 103 through the second lens 124 and the folding mirror 130, and forms a cyan image as a third image forming station. A latent image based on information is formed.

  The beam from the light source unit 110 is reflected by the folding mirror 131, forms a spot image on the photosensitive drum 104 via the second lens 125 and the folding mirror 132, and serves as a fourth image forming station. A latent image based on information is formed.

  FIG. 3 is a plan view schematically showing a main scanning section parallel to the scanning direction and a sub-scanning section perpendicular to the scanning direction. In the plan view of the main scanning section, the folding mirror is omitted, and the part after the folding mirror is developed.

  The first lens 120 and thereafter are separated at 4 stations, but only one station is shown in the figure as a representative. Reference numeral 100 denotes an image surface (photosensitive drum 101 surface). In the plan view of the sub-scan section, the optical system from the light source to the vibrating mirror is omitted.

  Here, the optical data of the basic optical system of the present embodiment is shown below. Coordinates for representing the lens surface shape have an intersection of the optical axis and the lens surface as the origin, the optical axis direction as the X axis, the main scanning direction as the Y axis, and the sub scanning direction as the Z axis (see FIG. 13). The lens surfaces are a first surface and a second surface from the light source side.

  The collimating lens in the light source unit is represented by a general rotationally symmetric aspherical expression shown in Equation 1, and the aspherical coefficient of the first surface is shown in Table 1, and the aspherical coefficient of the second surface is shown in Table 2. Here, K is a conical coefficient, R is a radius of curvature, and A1, A2, A3,..., Ai are aspherical coefficients. The curvature radius is positive when the curved surface is convex toward the light source.

  A cover glass (parallel flat plate) exists between the light source and the collimating lens. In the cylinder lens, the first surface has power in the sub-scanning direction, the radius of curvature Rs = 64.5 mm, and the second surface is a plane.

  The first surface of the first lens 120 of the scanning lens system is expressed by Equation 2, and its aspheric coefficient is shown in Table 3. The second surface is expressed as shown in Equation 2, and its aspheric coefficient is shown in Table 4. In particular, the coefficient not in the table is zero. Here, x (y, z) represents a generatrix shape in the main scanning direction, R is a main scanning radius of curvature, K is a conic constant, and A1, A2,..., Ai are coefficients. Rs is a sub-scanning radius of curvature on the optical axis, Cs (y) is a sub-scanning curvature for an arbitrary y, and B1, B2,..., Bi are coefficients.

  The second lens 122 of the scanning lens system includes an outer light beam (201, 204) among the four light beams 204, 203, 202, 201 emitted from the light source units 107, 108, 109, 110 shown in FIG. Different lenses are used for the inner rays (202, 203). The first surface of the second lens 122 is expressed by Equation 2, and the second surface is expressed by Equation 3. Here, R is a main scanning radius of curvature, K is a conic constant, A1, A2,..., Ai and F0, F1, F2,.

  Table 5 shows the aspheric coefficient of the first surface of the second lens 122 with respect to the outer ray, and Table 6 shows the aspheric coefficient of the second surface with respect to the inner ray, and Table 7 shows the aspheric coefficient of the first surface of the second lens 122 with respect to the inner ray. Table 8 shows the aspherical coefficients of the second surface.

光源波長及びレンズ硝材の光源波長での屈折率を表９に示す。

面間隔データを表１０に示す。なお、面間隔は光軸上の値で、単位はｍｍである。

Table 9 shows the refractive index of the light source wavelength and the lens glass material at the light source wavelength.

Table 10 shows the surface distance data. The surface spacing is a value on the optical axis, and the unit is mm.

  4A to 4C are schematic views of a main scanning section from the light source to the oscillating mirror having the configuration shown in FIG. 2, and show the installation position of the wavefront deformation element 150 of the present invention. The wavefront deforming means (element) 150 is an element that reduces wavefront aberration in the effective light beam in the optical scanning device, and partially advances or delays the phase of the wavefront in the effective light beam, thereby obtaining an average phase difference ( It is an element that reduces (wavefront aberration).

  FIG. 4A shows a configuration in which each light source unit includes a wavefront deforming element 150, which has an advantage that the optical axis of each light source unit can be matched with the optical axis of the wavefront deforming element.

  FIG. 4B shows a configuration in which a wavefront deformation element 150 is installed between the incident mirror and the cylinder lens. Here, the optical axes of the light beams from the respective light source units coincide in the main scanning direction and are separated in the sub scanning direction. The light flux from each light source unit is substantially parallel light. In the case of the wavefront deforming element 150 as shown in FIG. 5B, each light beam may be affected by the equivalent wavefront deforming element even if the optical axis of the light beam incident on the wavefront deforming element 150 is shifted in the sub-scanning direction. it can. Therefore, the wavefront deformation of the light beams of a plurality of light sources can be simultaneously achieved with one element.

  FIG. 4C shows a configuration in which a wavefront deforming element 150 is installed between the cylinder lens and the vibrating mirror 106. Since the cylinder lens has power in the sub-scanning direction and each light beam forms a focal line in the vicinity of the vibration mirror 106, the light beam width in the sub-scanning direction becomes smaller as the vibration mirror 106 is approached. Therefore, there is an advantage that the size of the wavefront deformation element 150 can be reduced.

  FIGS. 5A to 5B show examples of the wavefront deformation element 150. Here, a liquid crystal element is assumed and an example of an electrode pattern thereof is shown. Japanese Patent Laid-Open No. 10-20263 discloses an example of wavefront correction by a liquid crystal element.

  FIG. 5A shows a pattern for correcting spherical surface deformation, which is a concentric pattern.

  FIG. 5B shows a pattern for correcting aberration due to sinusoidal surface deformation as shown in FIG. 1, and a pattern similar to the correction pattern for coma aberration described in Japanese Patent Laid-Open No. 10-20263 can be used. At this time, the two regions in the main scanning direction sandwiching the central axis are configured to give opposite phase differences (wavefront aberration).

  At this time, it is desirable to install the liquid crystal element so that the optical axis of the optical system passes through the central axis of the liquid crystal element. Thus, by partially providing a phase difference and dividing the wavefront, the RMS value of the wavefront aberration is reduced, and a good beam spot is obtained on the image plane.

  Further, considering the combination of elements, the patterns shown in FIGS. 5A and 5B can be formed on the front and back of the element, and a single element can be used to correct spherical aberration and sinusoidal aberration.

  In addition, a reflection type liquid crystal element in which one side is a reflection plate may be used instead of the incident mirror 111 in FIG.

  Examples of the wavefront deformation element 150 include a liquid crystal element, a micromirror array having a micromirror that can move in the normal direction of the mirror surface, and a thin Si substrate surface as a mirror surface and a piezo array on the back surface. A mirror element that partially deforms the Si substrate, an element that generates a refractive index distribution by applying a voltage to a crystal that causes a change in refractive index due to the electro-optic effect, using a transparent electrode or the like can be considered.

  In general, in the oscillating mirror 106, the deformation of two regions in the scanning direction (shown in FIG. 15) divided by the rotation axis is substantially symmetric, so the optical axis of the incident light on the oscillating mirror 106 is When the light beam is incident on the surface of the vibrating mirror 106 and the surface formed by the normal axis of the rotating mirror 106 and the normal of the vibrating mirror 106, the wavefront deformation of the light beam by the vibrating mirror 106 is subject to the main scanning direction with respect to the optical axis. Therefore, also in the wavefront deforming element 150, the beam spot on the image plane can be optimized by applying a phase difference in the opposite direction in which the absolute value of the phase difference is substantially equal at a position symmetric with respect to the central axis.

  On the other hand, when the light beams are incident so as not to intersect with each other (shown in FIG. 16), the beam spot on the image plane is obtained by setting the absolute values of the phase differences between the two regions in the main scanning direction across the central axis to different appropriate values. Can be optimized.

  Next, an example of the vibrating mirror 106 substrate will be described with reference to FIG.

  The vibrating mirror 106 cuts the Si substrate by etching to form a movable part. A torsion beam 442 and a planar coil 463 are formed from one side of the Si substrate by a plasma etching dry process, and penetrates the remaining part of the vibrating plate 106 and the vibrating plate 443 to be the vibrating mirror 106 and the frame 446. Form a structure. Here, the width of the torsion beam 442 is about 40 to 60 μm.

  Further, in the structure of the vibrating mirror 106, a metal thin film such as an aluminum thin film or a gold thin film or a dielectric multilayer film can be formed on a portion to be a mirror to form a reflective surface having a high reflectivity. But it can be used as a reflective surface. The reflective surface is formed on one side or both front and back sides. A terminal 464 wired through a coil pattern 463 and a torsion beam 442 is formed by patterning a metal thin film or the like on one surface or both surfaces in the movable portion.

  On the mounting substrate 448, a yoke 449 formed so as to surround the vibration mirror 106 is disposed. The yoke 449 faces the end of the vibration mirror 106 so that the S pole and the N pole face each other, and the rotation axis and A pair of permanent magnets 450 that generate magnetic fields in directions orthogonal to each other are joined. When a current is passed between the terminals 464, Lorentz force is generated on each side parallel to the rotation axis of the coil pattern 463, and a torsion beam 442 is twisted to generate a rotational torque that rotates the mirror 441. It returns horizontally due to the return force of 442. Therefore, the mirror 441 can be reciprocally oscillated by alternately switching the direction of the current flowing through the coil pattern 463. When the current switching period is brought close to the natural frequency of the primary vibration mode of the structure constituting the mirror 441 with the torsion beam 442 as the rotation axis, the so-called resonance frequency f0, the amplitude is excited and a large deflection angle is obtained. Can be obtained. Therefore, in general, the scanning frequency fd is set in accordance with the resonance frequency f0.

  In the above example, the movable part has an electromagnet structure with a coil pattern, and a permanent magnet is installed on the fixed part. However, there is a vibrating mirror with a permanent magnet installed on the movable part and an electromagnet structure on the fixed part. To do.

  FIG. 6 is a block diagram of a drive circuit for amplifying the vibrating mirror. The drive circuit includes a drive pulse generation unit 601, a PLL circuit 602, a gain adjustment unit 603, a movable mirror drive unit 604, an amplitude calculation unit 605, a light source drive unit 606, a write control unit 607, and a pixel clock generation unit 608. Configured. As described above, the planar coil formed on the oscillating mirror 106 is applied with an AC voltage or a pulse wave voltage so that the direction of current flow is switched alternately, so that the deflection angle θ is constant. Adjust the gain of the current to flow through and reciprocate.

  FIG. 7 shows the relationship between the frequency f for switching the direction of current flow and the deflection angle θ. In general, the frequency characteristic has a peak at the resonance frequency f0. When the scanning frequency fd is matched with the resonance frequency f0, the deflection angle can be maximized, but the deflection angle changes steeply in the vicinity of the resonance frequency. Therefore, initially, the drive frequency applied to the fixed electrode in the drive circuit of the oscillating mirror 106 can be set to match the resonance frequency. However, when the resonance frequency fluctuates due to a change in the spring constant accompanying a temperature change, etc. However, there is a drawback that the deflection angle is drastically reduced and the stability over time is poor.

  Conventionally, an example in which the scanning frequency fd is controlled so as to follow the change of the resonance frequency f0 has been proposed, and it can also be used. However, in this embodiment, the scanning frequency fd is fixed to a single frequency that is excluded from the resonance frequency f0, and the deflection angle θ can be increased or decreased according to gain adjustment. Specifically, with respect to the resonance frequency f0 = 2 kHz, the scanning frequency fd is set to 2.5 kHz, and the deflection angle θ is adjusted to ± 25 ° by gain adjustment.

  Over time, the deflection angle θ is scanned with the light beam scanned by the vibrating mirror 106 at the start and end of the scanning region, the synchronization detection sensor 138, or the scan between the synchronization detection sensor 138 and the end detection sensor 139. It is detected according to time and controlled so that the deflection angle θ is constant.

  Here, dynamic surface deformation of the vibrating mirror 106 will be considered. The dynamic surface deformation is a sinusoidal surface deformation as shown in FIG. 1, but the amount of deformation varies depending on the vibration position of the vibration mirror 106, the deformation amount becomes zero at the center of vibration, and becomes the maximum at the maximum amplitude position. . Therefore, since the mirror deformation amount varies depending on the scanning position (mirror vibration position), the wavefront deformation amount of the wavefront deformation element 150 is changed in accordance with the scanning position, so that more accurate wavefront correction can be performed. In this embodiment, a liquid crystal element is used as the wavefront deforming element 150, and the amount of wavefront deformation can be controlled in accordance with the scanning position by switching the liquid crystal using a signal from the synchronization detection sensor or the end detection sensor as a trigger. it can.

  As another embodiment, the wavefront deforming element 150 such as a liquid crystal element is not used, and the imaging optical system (scanning optical system) after the vibrating mirror 106 has an aberration that cancels the wavefront aberration due to the dynamic surface deformation of the vibrating mirror 106. A configuration that can be considered is conceivable. In the configuration of FIG. 2, the imaging optical system after the oscillating mirror 106 is composed of two lenses and two mirrors. Therefore, an optical system having an aberration corresponding to the scanning position may be configured using these components.

  As a specific example, when the dynamic surface deformation as shown in FIG. 8 occurs in the vibration mirror 106 at the maximum image height (h = 110 mm), the optical systems shown in Tables 1 to 10 as shown in FIG. Waveform deformation (aberration) occurs, and the side lobe shown in FIG. 9B is generated in the beam spot on the image plane. Here, by replacing the two scanning lenses after the vibrating mirror 106 with lenses represented by the lens data in Tables 11 to 14, the maximum image height (h = 110 mm) is obtained when there is no surface deformation of the vibrating mirror. As shown in FIGS. 10 (a) and 10 (b), the wavefront shape of FIG. 10A has a wavefront aberration opposite to that of FIGS. 9 (a) and 9 (b) and side lobes around the beam spot.

  Therefore, when the dynamic surface deformation of the oscillating mirror 106 occurs, the lens represented by the data shown in Tables 11 to 14 is used to cause the dynamic surface deformation of the oscillating mirror 106 as shown in FIG. Wavefront aberration is corrected, and a clean beam spot without side lobes is formed as shown in FIG. At this time, the light source wavelength, the lens glass material, the surface interval, and the like remain as shown in Tables 9 and 10. Here, an example relating to the outer light beam has been described, but a correction optical system can be configured similarly for the inner side. In this example, correction is performed using only a lens, but a configuration in which a folding mirror is used as a correction optical system is also possible.

  At this time, in the case of front incidence where the light beam enters the vibrating mirror from the center of the effective scanning area, the dynamic surface deformation of the vibrating mirror is symmetric with respect to the optical axis of the central image height (zero image height) of the effective scanning area. Since the surface deformation is symmetric at a certain angle of view, it is desirable to set the wavefront aberration for correction required for the imaging optical system to be symmetric with respect to the optical axis of the central image height. The examples in Tables 11 to 14 have surface shapes that are symmetrical with respect to the optical axis of the central image height in the main scanning direction.

  On the other hand, when the light beam is incident on the oscillating mirror from other than the center of the effective scanning area as in the configuration shown in FIG. 2, the effective beam width on the oscillating mirror at the image height position symmetric with respect to the optical axis of the central image height. Therefore, the influence of the dynamic surface deformation of the oscillating mirror becomes asymmetric at an angle of view symmetric with respect to the optical axis of the central image height of the effective scanning region. Therefore, it is more desirable to set the wavefront aberration for correction required for the imaging optical system to be asymmetric with respect to the optical axis of the central image height. In this case, the aspherical data of the lens can be achieved by designing with an odd-order term.

  In general, the incident light to the oscillating mirror is incident so that the surface formed by the rotational axis of the oscillating mirror and the normal of the oscillating mirror surface intersects the optical axis of the incident light on the oscillating mirror surface. If they are incident so that they do not intersect, even if they are incident from the front, the influence of the dynamic surface deformation of the oscillating mirror becomes asymmetrical at the image height position symmetric with respect to the optical axis of the central image height. It is more desirable to set the wavefront aberration for correction required for the image optical system to be asymmetric with respect to the optical axis of the central image height.

  FIG. 12 is a cross-sectional view of an image forming apparatus equipped with the optical scanning device described above. A charging charger 902 that charges the photosensitive member to a high voltage around the photosensitive drum 901, a developing roller 903 that attaches the charged toner to the electrostatic latent image recorded by the optical scanning device 900, and visualizes the toner, and a developing roller 903. A toner cartridge 904 for replenishing toner and a cleaning case 905 for scraping and storing the toner remaining on the photosensitive drum 901 are disposed. Image recording is performed on the photosensitive drum 901 by reciprocating scanning of a vibrating mirror. The above-described image forming stations are arranged in parallel in the moving direction of the transfer belt 906, and yellow, magenta, cyan, and black toner images are sequentially transferred onto the transfer belt at appropriate timing, and are superimposed to form a color image. Each image forming station has basically the same configuration except that the toner color is different.

  On the other hand, the recording paper is supplied from the paper supply tray 907 by the paper supply roller 908, and is sent out by the registration roller pair 909 in accordance with the recording start timing in the sub-scanning direction, and the toner image is transferred from the transfer belt 906 and fixed. The toner is fixed by a roller 910 and discharged to a discharge tray 911 by a discharge roller 912.

(A) is a figure showing a modification of a mirror. (B) is a figure which shows the wave front of the light reflected in the deformed mirror. (C) is a figure which shows the beam spot of the image surface of the light with the wave front shown to (b). 1 is a schematic diagram of an optical scanning device according to the present embodiment. (A) is a main scanning cross section parallel to the scanning direction of the optical scanning device according to the present embodiment. (B) is a sub-scanning section perpendicular to the scanning direction of the optical scanning device according to the present embodiment. (A), (b), and (c) are the schematic of the main scanning cross section from the light source of the optical scanning device concerning this embodiment to a vibration mirror. (A) is an electrode pattern of a wavefront deformation element for correcting surface deformation on a spherical surface. (B) is an electrode pattern which correct | amends the aberration by sinusoidal surface deformation. It is a block diagram which shows the structure of the drive circuit which makes a vibration mirror amplitude. It is a figure which shows the relationship between the frequency f which switches the direction through which an electric current flows, and deflection angle (theta). It is a figure which shows the relationship between a surface deformation amount and the main scanning position on a mirror surface. (A) is a figure which shows the wave front of the light which has the aberration which generate | occur | produces in the optical system shown to Tables 1-10. (B) is a figure which shows the beam spot of the image surface of the light with the wave front shown to (a). (A) is a figure which shows the wave front of the light which has the aberration which generate | occur | produces in the optical system shown to Tables 11-14. (B) is a figure which shows the beam spot of the image surface of the light with the wave front shown to (a). (A) is a figure which shows the wave front of the light at the time of using the optical system shown to Tables 11-14 when dynamic surface deformation | transformation generate | occur | produces in a vibration mirror. (B) is a figure which shows the beam spot of the image surface of the light with the wave front shown to (a). 1 is a schematic view of an image forming apparatus according to an embodiment. It is a coordinate for expressing the surface shape of a lens. It is a figure which shows the structural example of a vibration mirror board | substrate. It is a figure which shows a deformation | transformation of two area | regions of the scanning direction divided by a rotating shaft. It is a figure which shows a deformation | transformation of two area | regions of the scanning direction divided by a rotating shaft.

Explanation of symbols

101, 102, 103, 104 Photosensitive drum 106 Vibration mirror 107, 108, 109, 110 Light source unit 111 Incident mirror 113 Cylinder lens 120 First lens 122, 123, 124, 125 Second lens 126, 127, 128, 129, 130, 131, 132 Folding mirror

Claims (13)

In an optical scanning device having a light source, a deflection unit that deflects a light beam emitted from the light source by swinging a vibration mirror, and an imaging optical system that reciprocally scans the light beam deflected by the deflection unit,
An optical scanning apparatus comprising: a wavefront deforming unit configured to deform a wavefront of the light beam incident on the deflecting unit in an optical path from the light source to the deflecting unit.   The optical scanning device according to claim 1, wherein the wavefront deforming unit deforms a wavefront of the light beam along a scanning direction.   3. The optical scanning device according to claim 1, wherein the wavefront deforming unit performs wavefront deformation in opposite directions with respect to two light flux regions sandwiching a rotation axis of the deflecting unit.   4. The optical scanning device according to claim 1, wherein the wavefront deforming unit performs wavefront deformation in accordance with a scanning position.   5. The optical scanning device according to claim 1, wherein the wavefront deforming means is a liquid crystal element, and the liquid crystal element has a plurality of regions in which a light distribution state is variable.   6. The optical scanning device according to claim 5, wherein the wavefront deforming means is installed in a region where the light beam is parallel between the light source and the deflecting means.   6. The optical scanning device according to claim 5, wherein the wavefront deforming means is installed in a region where the light flux is in a converged state between the light source and the deflecting means. Detecting means for detecting the light beam deflected by the vibrating mirror;
8. The optical scanning device according to claim 5, wherein the wavefront deforming unit is controlled based on a detection result by the detecting unit. In an optical scanning device having a light source, a deflection unit that deflects a light beam emitted from the light source by swinging a vibration mirror, and an imaging optical system that reciprocally scans the light beam deflected by the deflection unit,
The imaging optical system is characterized in that the wavefront aberrations of two light beam regions in the main scanning direction across the optical axis of the scanned light beam are opposite to each other, and the amount of aberration increases as the angle of view increases. Optical scanning device.   The optical scanning device according to claim 9, wherein the imaging optical system has a wavefront aberration along a main scanning direction.   11. The optical scanning device according to claim 9, wherein the imaging optical system has a wavefront aberration symmetric with respect to the optical axis of the central image height at an angle of view symmetric with respect to the optical axis of the central image height. .   11. The optical scanning device according to claim 9, wherein the imaging optical system has an asymmetric wavefront aberration with respect to the optical axis of the central image height at an angle of view symmetric with respect to the optical axis of the central image height. In an image forming apparatus that records an electrostatic image on an image carrier with a light beam from a light source modulated by an image signal, visualizes the electrostatic image with toner, and transfers the image to a recording medium.
It has an optical scanning device of a statement in any 1 paragraph of Claims 1-12,
An image forming apparatus characterized in that the light beam from the light source is deflected and imaged in a spot shape by the imaging optical system, and the image carrier is scanned.

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