JP2008015210A - Optical scanner and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical scanner in which an image is efficiently formed in both terms of forwarding and reversing scans with writing and further an excellent quality image with little color shift is formed, and to provide an image forming apparatus. <P>SOLUTION: A vibration mirror 106 has an optical path switching means which switches the optical path of a light beam 201 from a light source unit 107 in a subscanning direction, and scans the surface of a photoreceptor 101 being a face to be scanned in the forwarding scan and scans the surface of a photoreceptor 102 being a different face to be scanned in the reversing scan by the switching in the subscanning direction performed by the optical path switching means. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optical scanning device and an image forming apparatus, and in particular, by deflecting a light beam from the same light source and scanning different scanning surfaces in forward scanning and backward scanning, it is efficient in any section of reciprocating scanning. In particular, the present invention relates to an optical scanning apparatus and an image forming apparatus capable of performing image writing and forming a higher quality image.

  An optical scanning device that deflects a light beam by deflecting means such as an optical deflector, forms an image of the deflected light beam as a fine spot light on a scanned surface, and scans the scanned surface at a constant speed in the main scanning direction. Is conventionally known and applied to latent image writing means of image forming apparatuses such as laser beam printers, laser beam plotters, facsimiles, and digital copying machines. This optical scanning device scans a surface to be scanned such as an image carrier by, for example, deflecting and reflecting laser light emitted from a laser light source with an optical deflector, and at the same time, responds to the laser light in accordance with an image signal. Thus, the image is written on the surface to be scanned by intensity modulation (for example, on and off).

  Polygon mirrors and galvanometer mirrors are widely used as the optical deflectors, but in order to achieve higher resolution images and high-speed printing, the rotational speed of the deflectors must be further increased. Problems such as durability of bearings, heat generation, noise, and increased power consumption occurred, and there was a limit to high-speed scanning.

  In contrast, in recent years, research on optical deflectors using silicon micromachining has been underway, and a silicon substrate is used to integrally form a vibrating mirror and a torsion beam that supports it. There has been proposed a method in which a vibrating mirror that performs reciprocal vibration of a structure is used in an optical deflector (see, for example, Patent Document 1 and Patent Document 2).

  If the vibrating mirror is used as a deflecting means of the optical scanning device, the device is downsized and reciprocally vibrates using resonance, so it has good durability even during high-speed scanning, greatly increasing heat generation, noise, and power consumption. Can be reduced. By using a vibration mirror that performs reciprocal vibration instead of a polygon mirror, noise and power consumption can be reduced, and an image forming apparatus suitable for an office environment or a global environment is provided.

  However, when a vibrating mirror that performs reciprocal vibration is used as a deflecting unit, scanning is performed while the photoconductor, which is a surface to be scanned, moves in a direction orthogonal to the scanning direction (sub-scanning direction). The scanning line is inclined toward. That is, when recording on the photosensitive member is performed also in the backward scan following the forward scan, the trajectory of the reciprocating scan line becomes zigzag, and the density of image writing may become uneven, leading to deterioration in image quality. For this reason, conventionally, a method has been adopted in which image writing is performed only in one of the reciprocating scans of the oscillating mirror (forward scan or return scan) (see, for example, Patent Document 3).

However, for example, a conventional method for writing an image only in one of the reciprocating scans of the oscillating mirror as disclosed in Patent Document 3 is inefficient. On the other hand, two light beams are used to record one scanning line, and the interval between the two beam spots and the light quantity ratio are made variable, so that both forward scanning and backward scanning can be performed without degrading the image quality. A method to be used has been proposed. (Patent Document 4).
Japanese Patent No. 2924200 Japanese Patent No. 30111144 JP 2005-345866 A JP 2005-37557 A

  Certainly, the method proposed in Patent Document 4 improves an inefficient image writing method of image writing in only one of the reciprocating scans of the vibrating mirror. However, in this method, two light sources are required for one scanning line, so that the cost and space for the light source and the accompanying coupling lens, cylindrical lens, member for assembling the light source unit, etc. are additionally required. A new problem will occur. In addition, since the number of light sources is twice that of the prior art, the power for driving the light sources is doubled, resulting in a problem of increased power consumption during image formation.

  Therefore, the present invention has been made in view of the above circumstances, and by scanning a light beam from the same light source on different scanning surfaces in forward scanning and backward scanning, an image can be obtained in any section of reciprocating scanning. It is a first object of the present invention to provide an optical scanning device and an image forming apparatus that can efficiently form an image and write a good quality image with little color shift.

  In addition, the present invention provides an optical scanning device and an image forming apparatus capable of writing an image with a simple configuration, space saving, and excellent cost performance by adopting a configuration having a small number of light sources or other optical components. This is the second purpose.

  A third object is to provide an optical scanning apparatus and an image forming apparatus that can form an image with low power consumption and are more suitable for the environment.

  To achieve this object, the invention according to claim 1 is deflected by a plurality of light sources, an optical deflector for deflecting a light beam from the light sources and reciprocatingly scanning in a main scanning direction, and the optical deflector. An optical deflector driving unit that detects the light beam and controls a deflection angle of the optical deflector, and guides the light beam deflected by the optical deflector to a corresponding scanned surface to form an image. An optical scanning device including an imaging optical system, provided in an optical path of the light beam between the light source and the imaging optical system, in a sub-scanning direction orthogonal to a scanning direction of the optical deflector The optical deflector includes an optical path switching unit that switches the optical path of the light beam and deflects the light beam to the optical deflector. The optical deflector deflects the light beam on the same deflection surface, and moves in the sub-scanning direction performed by the optical path switching unit. By switching the optical path of the light beam, forward scanning and return scanning Wherein the scanning different scanned surface in the 査.

  According to a second aspect of the present invention, in the optical scanning device according to the first aspect, the optical deflector also serves as the optical path switching means.

  According to a third aspect of the present invention, in the optical scanning device according to the first or second aspect, the optical deflector deflects the light beam from the same light source on the same deflection surface, and forward scanning and backward scanning. And a different surface to be scanned is scanned.

  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 imaging optical system includes a scanning line on a surface to be scanned by forward scanning of the optical deflector. The light beam is imaged so that the inclination and the scanning line inclination on the scanning surface by the backward scanning of the optical deflector are in opposite directions.

  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 imaging optical system includes a plurality of scanning lenses arranged closest to the optical deflector. Both the light beams are guided to the surface to be scanned.

  According to a sixth aspect of the present invention, in the optical scanning device according to the fifth aspect, the optical deflector is configured to switch the optical path of the light beam in the sub-scanning direction performed by the optical path switching unit. The light beam is deflected so as to pass through a substantially symmetrical position with respect to a symmetric reference axis that is a horizontal plane that passes through the center of the optical deflector and is parallel to the scanning direction of the optical deflector. The imaging scanning is performed on the scanning surface.

  According to a seventh aspect of the present invention, in the optical scanning device according to the sixth aspect, the optical deflector deflects all the light beams on the same deflection surface.

  According to an eighth aspect of the present invention, in the optical scanning device according to the seventh aspect, the optical deflector deflects all the light beams at the same deflection point.

  According to a ninth aspect of the present invention, in the optical scanning device according to the eighth aspect, the optical deflector rotates a scanning rotation shaft that rotates the optical deflector to reciprocately scan the light beam, and the scanning. An optical path switching rotation axis that is provided in a direction perpendicular to the rotation axis and switches the optical path of the light beam in the sub-scanning direction, and the same rotation point intersects the scanning rotation axis and the optical path switching rotation axis. It is located at a point.

  According to a tenth aspect of the present invention, the optical scanning device according to any one of the first to ninth aspects is mounted, and a light beam from the light source modulated by an image signal is deflected by the optical deflector. Then, an image is formed in a spot shape by the imaging optical system, and an electrostatic latent image is recorded on the image carrier by scanning the image carrier, and the electrostatic latent image is visualized with toner and visualized. An image forming apparatus for transferring an imaged toner image onto a recording medium, wherein a plurality of light sources are used to record an electrostatic latent image on each single image carrier.

  According to an eleventh aspect of the present invention, there is provided an optical scanning device according to any one of the first to ninth aspects, and an image carrier that records an electrostatic latent image corresponding to each of the light beams from the light source. An image forming apparatus comprising: a developing device that visualizes the electrostatic latent image with toner of each color; and a transfer device that transfers the visualized toner image onto a recording medium in a superimposed manner. An image is recorded so that the writing direction in the reciprocating scanning direction of the optical deflector on the body is aligned.

  According to the present invention, since the light beam from the same light source is deflected to scan different surfaces to be scanned in the forward scan and the backward scan, efficient image formation in which an image is written in any section of the reciprocating scan is enabled. Furthermore, an optical scanning apparatus and an image forming apparatus that can form an image of good quality with little color misregistration are realized. In addition, by adopting a configuration with a small number of light sources or other optical components, an optical scanning device and an image forming apparatus that enable simple image writing, space saving, and cost-effective image writing are realized. The In addition, an optical scanning apparatus and an image forming apparatus that can form an image with low power consumption and are more suitable for the environment are realized.

  Hereinafter, the configuration, operation, action, and the like of the optical scanning device and the image forming apparatus that are the embodiments of the present invention will be described in detail with reference to the drawings.

[Embodiment 1]
An optical scanning device will be described as a first embodiment of the present invention. In an embodiment of the present invention (the same applies to other embodiments described later), a vibrating mirror using a resonance phenomenon is used as an optical deflector. . First, the vibrating mirror will be described.

  FIG. 1 is a perspective view showing a configuration of a vibrating mirror module used in the optical scanning device of the present embodiment. For example, if the dimensions of the movable mirror are the length 2a, the width 2b, the thickness d, the length of the torsion beam L, and the width c, the moment of inertia I and the spring constant K are obtained using the Si density ρ and the material constant G. Is given by Equation 1 below.

  Further, the resonance frequency f is expressed by Equation 2 below.

  Here, since the length L of the beam and the deflection angle θ are in a proportional relationship, θ = A / I × f ^ 2 (A: constant), and the deflection angle θ is inversely proportional to the moment of inertia I. In order to increase the resonance frequency f, the deflection angle θ is reduced unless the moment of inertia I is reduced.

  On the other hand, assuming that the dielectric constant ε of the air, the electrode length H, the applied voltage V, and the interelectrode distance δ, the electrostatic force F between the electrodes is expressed by the following Equation 3.

  The deflection angle θ = B × F / I (B: constant) is also expressed. The longer the electrode length H is, the larger the deflection angle θ is. Double drive torque is obtained. Thus, by increasing the outer peripheral length as much as possible to increase the electrode length, a larger electrostatic torque can be obtained at a low voltage.

  By the way, with respect to the speed υ and area E of the movable mirror, if the density of air is η, the air viscous resistance P = C × ηυ ^ 2 × E ^ 3 (C: constant) is opposed to the rotation of the movable mirror. Will work. Therefore, it is desirable to seal the movable mirror and keep it in a reduced pressure state. Although the vibration mirror has been described above, the optical deflector is not limited to the vibration mirror as long as it can perform reciprocal scanning.

  Next, the optical scanning device of this embodiment will be described. FIG. 4 is a perspective view showing the configuration of the optical scanning device of the present embodiment. The light beams emitted from the light source unit 107 are focused only in the sub-scanning direction by the cylindrical lens 113 having refractive power only in the sub-scanning direction, and a long line image is formed on the vibrating mirror 106 in the main scanning direction. . Each light beam incident on the oscillating mirror 106 is deflected and scanned by the oscillating mirror, and thereafter, a scanning lens (oscillating mirror side) 120, scanning lenses (scanned surface side) 122 and 123, and a folding mirror as an imaging optical system. By passing through 126 to 131, image formation scanning is performed in the direction of the arrow in the figure on the surfaces of the photosensitive drums 101 and 102 which are the scanning surfaces. The same applies to the imaging scan on the photosensitive drums 103 and 104.

  As indicated by the arrows in FIG. 4, the imaging scan directions on the surfaces of the different photoconductors 101 and 102 in the present embodiment are opposite to each other in the forward scan and the backward scan of the vibrating mirror 106. It shows that the photoconductor 101 and the photoconductor 102 are imaged and scanned, respectively. As a result, as shown in FIG. 5, compared to the conventional inefficient image writing method in which the surface of the photoreceptor is imaged and scanned only in one of the reciprocating scans of the vibrating mirror 106, as shown in FIG. Efficient image writing is possible.

  Here, in order to image-form and scan different photoconductors in the forward scan and the backward scan, a means for switching the optical path is required. For example, a liquid crystal polarizing element may be provided as an optical path switching unit between the light source unit 107 and the vibrating mirror 106. In this case, the state of the element changes depending on the voltage applied to the element, and the refraction angle changes when the light beam passes through the element, so that the optical path after the element can be switched.

  In this embodiment, the function of the optical path switching means is given to the vibrating mirror that is an optical deflector. That is, as shown in FIG. 2, the oscillating mirror further has another axis of rotation that is perpendicular to the above-described axis of rotation (torsion beam) in the outer frame of FIG. The angle can be changed by the axis, the optical path can be switched between forward scanning and backward scanning, and different scanning surfaces can be imaged scanned. By adopting such a configuration, no special optical path switching element is required to perform optical path switching in the sub-scanning direction in the present embodiment. Therefore, an increase in cost is prevented by not increasing the number of parts. , Reducing the risk of optical performance degradation.

  FIG. 3 is a diagram illustrating a state of the oscillating mirror 106 having a section (sub-scan section) along the sub-scanning direction of the optical scanning device. (A) shows a state when the oscillating mirror 106 is in an initial state, (b) shows a state during forward scanning of the oscillating mirror 106, and (c) shows a state during backward scanning of the oscillating mirror 106. A represents one incident light beam from one light source, B represents an emitted light beam during forward scanning, and B ′ represents an emitted light beam during backward scanning.

  As shown in FIG. 3, in this embodiment, the oscillating mirror 106 has different angles in the sub-scanning direction during forward scanning and during backward scanning, thereby switching the optical path of each outgoing light beam, and outgoing light in forward scanning. Different scanning surfaces, that is, different photoconductors are image-scanned by the beam B and the outgoing light beam B ′ in the backward scanning. As a result, the two photoconductors 101 and 102 are image-scanned by one light source unit 107. Here, for example, the photosensitive member 101 is imaged and scanned by the outgoing light beam B for forward scanning, and the photosensitive member 102 is imaged and scanned by the outgoing light beam B ′ for backward scanning.

  Here, a method of changing the angle in the sub-scanning direction using the vibrating mirror will be described. FIG. 18 is a diagram showing the angular displacement in the main scanning direction of the oscillating mirror in the present embodiment on the time axis. Since the oscillating mirror uses a resonance phenomenon, its angular change draws a curve having an amplitude of a sinusoidal θ0 as shown in FIG.

  The image writing is performed in the range of + θd to −θd in the drawing. This is because the angle change can be approximated to be approximately linear within this range, and the photosensitive member can be scanned with good linearity. Therefore, the oscillating mirror scans other than the effective image writing area of + θd to −θd, and performs synchronization detection, light amount adjustment, and the like during this period.

  Further, in order to switch the optical path between the forward scanning and the backward scanning, the angle of the vibrating mirror in the sub-scanning direction must be changed, which is outside the effective image writing area between the forward scanning and the backward scanning. It is preferable to carry out at the timing. This is because if the angle in the sub-scanning direction is changed in the effective image writing area, the scanning line tilt or the scanning line bending described later occurs on the photosensitive member for forming an image, and the image quality is greatly deteriorated. It is because it causes.

  In order to prevent such deterioration in image quality, in addition to changing the angle in the sub-scanning direction of the vibrating mirror outside the effective image writing area, the angle of the vibrating mirror in the sub-scanning direction in the effective image writing area The oscillating mirror may be controlled so that is constant. Thereby, it is possible to stably provide good image quality without causing the scanning line inclination or the scanning line bending due to the angle change of the vibrating mirror in the sub-scanning direction.

  In addition to the method described above, the angle changing method in the sub-scanning direction using the vibrating mirror scans at the same scanning frequency in both the main scanning direction and the sub-scanning direction, The phase of the sine wave vibration in changing the angle in the scanning direction may be 90 deg. FIG. 19 is a diagram showing the angular displacement in the main scanning direction and the sub-scanning direction of the oscillating mirror in the present embodiment on the time axis.

  By using resonance vibration to change the angle in the sub-scanning direction by this method, two-dimensional scanning of the vibrating mirror can be performed with lower power consumption, and power consumption generated during image formation can be greatly reduced. A possible optical scanning device and image forming apparatus can be provided.

  In this case, since the angle in the sub-scanning direction sequentially changes in the effective image writing area, the scanning line is bent, but the phase difference of the sine wave vibration in changing the angle in the main scanning direction and the sub-scanning direction is set to 90 deg. As a result, the speed of changing the angle in the sub-scanning direction in the effective writing area is minimized, scanning line bending can be minimized, and image quality can be kept good.

  In order to give an example of a one-side oblique incidence optical system, a description will be given below with reference to FIG. 13 which is a sub-scan sectional view of the optical layout. Since the scanning line bending increases as the exit angle from the vibrating mirror increases, the case where the exit angle is the maximum 3.3 deg will be described.

  When the output angle is 3.3 deg, the distance from the vibrating mirror to the scanning lens (vibrating mirror side) which is the next optical element is 37 mm. Therefore, the incident position in the sub-scanning direction incident on the scanning lens (vibrating mirror side) H is obtained as shown in Equation 4.

  Here, since the angle of view at the end of the effective image writing area is 30 deg, the main scanning direction angle θd of the vibrating mirror at this time is 15 deg. Further, in the present embodiment, the phase of the sine wave vibration in the angle change in the sub-scanning direction has a difference of 90 deg from the phase of the sine wave vibration in the angle change in the main scanning direction, so that the angle in the main scanning direction is 15 deg. The angle in the sub-scanning direction is 75 deg (or 105 deg). At this time, the incident position Hd in the sub-scanning direction, which is incident on the scanning lens (vibrating mirror side), is obtained as in Expression 5.

  From the above, the scanning line curve generated at this time is H-Hd = 310 μm at the maximum. Although this value is larger than the conventional scanning line bending, the direction of the scanning line bending is opposite to the direction of the scanning line bending that occurs when the oblique incident light is incident on each optical element. The direction of the scanning line cancels each other, and the scanning line curve guided to the photosensitive member has a smaller value than this, and does not cause a problem in image formation. This method can also be realized as an optical scanning device. .

  Further, as will be described later, this can be corrected by the scanning line bending correction mechanism by the holding part of each folding mirror, and the scanning line bending can be improved, so that high-quality image quality can be stably provided. .

  In this embodiment, as can be seen from the fact that the optical scanning device can be constructed in FIG. 4 without the light source unit 108 which is an element necessary for constructing the conventional optical scanning device shown in FIG. Since different photoconductors can be scanned in the forward scan and the backward scan, two photoconductors are scanned by one light source unit in contrast to the conventional method in which one light source unit is required for one photoconductor. The number of light source units can be halved.

  The fact that the number of light source units can be reduced means that power consumption during image formation can be reduced, and the cost and space of the light source and its associated coupling lens, cylindrical lens, light source unit assembly, etc. can be reduced. Therefore, cost performance is improved, and a compact optical scanning device and image forming apparatus in which the optical system on the front side that enters the vibrating mirror is made compact are realized.

  Furthermore, image formation can be performed at the same speed as conventional image formation. This is due to the following reasons. Since the scanning direction is reversed between the forward scanning and the backward scanning of the oscillating mirror, when the reciprocating scanning is used for image formation on the same photosensitive member, the photosensitive member rotates at a constant speed. As shown in FIG. 3, the scanning line is drawn with a zigzag line, resulting in image degradation. For this reason, conventionally, only one of the reciprocating scans has been used for image formation.

  In the present embodiment, since image formation can be performed on two photosensitive members by reciprocating scanning, for example, conventionally, two light source units are used and each of the two photosensitive members is reciprocated between two reciprocating mirrors. Whereas one scanning line is drawn, one light source unit can draw one scanning line on each of the two photosensitive members during one reciprocation of the vibrating mirror. That is, while the number of light source units is halved, the image forming speed can be equivalent to that of the conventional one.

  Further, the phenomenon shown in FIG. 6 described above causes the scanning line inclination to be reversed between the photosensitive members in a full-color tandem image forming apparatus or the like as in the present embodiment. Therefore, when forming a full-color image. This causes color misregistration and causes image quality degradation.

  In order to prevent this, the scanning lens 120 and the scanning lenses 122 and 123 are provided with a characteristic that causes a scanning line inclination. For example, as shown in FIG. 7, the scanning line B during forward scanning has a scanning line inclination on the non-rotating photoconductor from the scanning start end to the scanning end end in an upward direction in the sub-scanning direction. Thus, it is assumed that the scanning line B ′ at the time of backward scanning also has a scanning line inclination on the photosensitive member which is not rotated from the scanning start end to the scanning end end so as to go upward in the sub-scanning direction. As a result, the scanning direction on the photosensitive member is reversed in the reciprocating scanning, so that the direction of each scanning line inclination on the photosensitive member is reversed.

  Then, when the magnitude of this inclination is adjusted, as shown in FIG. 8, when the image is formed by rotating the photosensitive member, the above-described scanning line inclination is canceled with the scanning line inclination generated when the image is formed and rotated. The scanning line inclination in the sub-scanning direction on the photosensitive member can be made substantially zero. By this method, the difference in the scanning line inclination on each photoconductor can be made substantially zero, and the color misregistration, which is the problem described above, can be reduced and the image quality can be improved.

  Further, as an example of a method for adjusting the scanning line inclination, there is a method in which the scanning lenses 122 and 123 are rotated about the optical axis direction as a rotation axis. Since the scanning lenses 122 and 123 for each optical path of each light beam can be individually adjusted, the degree of freedom in correcting each scanning line inclination is high, and color misregistration can be easily reduced, thereby improving the image quality. realizable.

  The scanning line tilt adjustment method described above cannot be used when the scanning lens in each optical path of each light beam is a single lens. However, as another method of adjusting the scan line tilt, for example, the scan line tilt can be adjusted by adjusting the shift amount and tilt of the folding mirror for each optical path of each light beam, and the orientation is aligned to reduce color misregistration. can do. As mentioned above, although the example of the adjustment method of scanning line inclination was given, the adjustment method of scanning line inclination is not restricted to the said example.

  FIG. 9 is a sub-scanning sectional view showing a preferred arrangement of the scanning lens 120 in the present embodiment. In this embodiment, as shown in FIG. 9, it is more preferable that the scanning lens 120 closest to the oscillating mirror 106 is shared by two light beams for the forward scanning and the backward scanning of the oscillating mirror. As a result, the scanning lens 120 in this embodiment may use one point for each of the two light beams, and the cost and space can be reduced by reducing the number of parts.

  In addition, as shown in FIG. 9, it is more preferable that the incident position and incident angle of each light beam incident on the incident surface of the scanning lens 120 have a symmetrical relationship in the sub-scanning direction. By adopting such a configuration, it is possible to configure each imaging optical system that forms and scans a pair of light beams on each scanning surface with an imaging optical system having the same characteristics. It is possible to share components such as the folding mirrors 126 to 131 and the scanning lenses 122 and 123 that cannot be shared due to optical path separation. Thereby, the versatility of each of the components is improved, and the cost from development, design to manufacturing can be reduced.

[Embodiment 2]
Next, an optical scanning device as a second embodiment of the present invention will be described. FIG. 10 is a perspective view showing the configuration of the optical scanning device of the present embodiment. In this embodiment, the light beam from the same light source is guided to different photoconductors in the forward scanning and the backward scanning of the oscillating mirror, and the number of light sources is halved compared to the conventional one. 1 and common.

  On the other hand, the difference from the first embodiment is an optical path for guiding a light beam from the light source unit to each photoconductor. By making the configuration of the optical path as shown in FIG. 10, the number of points of the oscillating mirror 106 and the scanning lens 120 can be reduced from two in the first embodiment to one, thereby reducing the cost and saving space. Can be realized.

  In addition, when a plurality of vibrating mirrors are provided as in the first embodiment, since one image is formed by all the photosensitive members, it is necessary to drive the plurality of vibrating mirrors at a common scanning frequency. If there is one oscillating mirror as in the form, no special control means for adjusting the scanning frequency between the oscillating mirrors is required. For this reason, all the photoconductors are scanned at a uniform scanning frequency, so that stable image formation can be performed. Further, the optical scanning device can be simply configured and the cost can be reduced.

  FIG. 11 is a diagram showing the positional relationship of light beam incidence and emission with respect to the oscillating mirror and the scanning lens in this embodiment. Light beams from two light sources are incident on the oscillating mirror and the angle can be changed in the sub-scanning direction. Several examples of the emission angle and emission position of the outgoing light beam from the vibrating mirror in the sub-scanning direction are shown. In all examples, the oscillating mirror 106 is illustrated vertically and horizontally. Here, the oscillating mirror 106 and the scanning lens 120 are arranged with the horizontal plane as a reference plane (symmetric reference axis). However, the optical scanning apparatus may be arranged to be inclined in the image forming apparatus. Is not limited to the horizontal plane.

  A 107 is a light beam incident on the vibrating mirror 106 from the light source unit 107, and A 108 is a light beam incident on the vibrating mirror 106 from the light source unit 108. B107 is a light beam obtained by deflecting and scanning the light beam A107 by the forward scanning of the vibrating mirror 106, and B'1007. The light beam A 107 is a light beam that has been deflected and scanned by the backward scanning of the oscillating mirror 106. B108 is a light beam obtained by deflecting and scanning the light beam A108 by the forward scanning of the vibrating mirror 106, and B'1008 is a light beam obtained by deflecting and scanning the light beam A108 by the backward scanning of the vibrating mirror 106.

  In FIG. 11A, two light beams are horizontally incident on the vibrating mirror 106, and only one of the vibrating mirrors 106 is reciprocally scanned to provide an angle in the sub-scanning direction. It is a figure radiate | emitted with an angle. In FIG. 11B, two light beams are horizontally incident on the vibrating mirror 106, and the vibrating mirror 106 is provided with an angle in the sub-scanning direction in both reciprocating scans, so that all the light beams are in the sub-scanning direction. It is a figure radiate | emitted with an angle.

  In FIG. 11C, two light beams are incident on the oscillating mirror 106 at an equal angle in the sub-scanning direction, one of the reciprocating scanning beams is emitted horizontally, and the other one is angled in the sub-scanning direction. FIG. FIG. 11D is a diagram in which two light beams are incident on the vibrating mirror 106 at an angle equal to the sub-scanning direction, and all the light beams are emitted with an angle in the sub-scanning direction.

  In FIG. 11E, two light beams are incident on the oscillating mirror 106 at angles equal to each other in opposite directions in the sub-scanning direction, and all the light beams have symmetric angles with respect to the symmetric reference plane. FIG. In addition to this, there is a case where one light beam is incident on the oscillating mirror 106 with an angle in the horizontal direction and another light beam with an angle in the sub-scanning direction. The deflection angle of the vibrating mirror in the sub-scanning direction, the light beam emission angle, etc. are not limited to the example shown in FIG.

  In the present embodiment, the beam spot diameter is increased due to the scanning line bending and wavefront aberration peculiar to the oblique incidence optical system. This is more preferable as shown in FIGS. 11 (b), 11 (d) and 11 (e). This can be reduced by adopting a configuration in which each light beam is incident at an angle substantially equal to an incident position substantially symmetrical in the sub-scanning direction of the scanning lens having a symmetrical shape with respect to the scanning direction. By adopting such a configuration, it is possible to secure the distance that allows the optical path separation by the folding mirror that guides each light beam to each photoconductor with the minimum incident angle in the sub-scanning direction. The beam spot diameter thickening due to the scanning line bending and wavefront aberration peculiar to the oblique incidence optical system depends on the size of the incident angle in the sub-scanning direction to the optical element after deflection by the vibrating mirror and the distance from the scanning lens bus at the incident position. By adopting this configuration, it is possible to reduce the beam spot diameter increase due to scanning line bending and wavefront aberration, and it is possible to stably form a high-quality image.

  Here, the scanning line bending and the beam spot diameter increase due to wavefront aberration, which are specific to the oblique incidence optical system, will be described in detail.

  The scanning line bending in the oblique incidence optical system will be described. For example, unless the shape of the scanning lens constituting the scanning optical system, particularly the scanning lens entrance surface having strong refractive power in the sub-scanning direction, is an arc shape centered on the reflection point of the light beam on the deflecting reflection surface The distance from the deflecting / reflecting surface of the optical deflector to the incident surface of the scanning lens varies depending on the lens height in the main scanning direction. Usually, it is difficult to make the scanning lens in the above shape in order to maintain optical performance. That is, a normal light beam is deflected and scanned by an optical deflector, and does not enter the lens surface perpendicularly at each image height in the main scanning section, but with an incident angle in the main scanning direction. .

  Since the light beam is obliquely incident and has an angle in the sub-scanning direction, the light beam deflected and reflected by the optical deflector is a distance from the deflecting reflection surface of the optical deflector to the scanning lens incident surface due to the image height. In contrast, as shown in FIG. 12, the incident height in the sub-scanning direction to the lens closer to the surface to be scanned (scanning lenses 122 to 125) becomes higher or lower (light beam) from the center as it goes to the periphery. Depending on the angle direction of the sub-scanning direction.

  As a result, when passing through a surface having refracting power in the sub-scanning direction, the refracting power received in the sub-scanning direction differs and scanning line bending occurs. In the case of normal horizontal incidence, the light beam travels horizontally with respect to the scanning lens even if the distance from the deflecting / reflecting surface to the scanning lens incidence surface is different. There is no occurrence of bending of the scanning line.

  Further, a description will be given of fluctuations in the scanning line curve when the temperature changes. In recent years, plastics are commonly used as the material for scanning lenses due to the degree of freedom in lens shape (aspherical shape, etc.) at the time of design for cost and high image quality. The lens shape change is larger than that of the glass lens.

  As described above, in the oblique incidence optical system, scanning is performed with the light beam curved in the sub-scanning direction on the scanning lens incident surface. For this reason, if the radius of curvature and thickness of the scanning lens and the incident angle and incident position of the light beam incident on the scanning lens change due to temperature changes, different refraction changes occur in the main scanning direction and scanning line bending occurs. To do.

  Similarly to the above description, in the case of normal horizontal incidence, the light beam travels horizontally with respect to the scanning lens even if the distance from the deflecting reflection surface to the scanning lens incidence surface is different. The incident position in the scanning direction does not differ at almost the same height as the optical axis, and the occurrence of scanning line bending is extremely small. In other words, since the light beam passes through the generatrix with a normal lens, the imaging position (defocus direction) changes even if the radius of curvature changes due to temperature changes, but refraction of light rays in the sub-scanning direction occurs. Since there is no (or slight) change in the scanning line bending (the position of the scanning line in the sub-scanning direction on the surface to be scanned) is extremely small.

  As described above, the occurrence of a large scanning line bend is a problem peculiar to the oblique incidence optical system, and the generation direction thereof is, for example, on both sides in the sub-scanning direction across the reference plane (symmetric reference plane) in the present embodiment. Different. That is, in FIG. 13, the generation direction is reversed between the light beam incident from the region 1 and the light beam incident from the region 2. This is because the curvature of the scanning line incident on the scanning lens is the direction of the incident angle in the sub-scanning direction of the light beam incident on the scanning lens, that is, the direction of oblique incidence (incident from the region 1 side or region 2 side in FIG. This is because the direction is reversed depending on whether the light is incident from the light source. In particular, the curvature of the scanning line incident on the scanning lens having a strong refractive power in the sub-scanning direction causes the scanning line to be bent for the reason described above.

  Similarly, when a temperature change occurs, the change in the scanning line curve is reversed on both sides in the sub-scanning direction with the symmetrical reference plane interposed therebetween. As described above, when the direction of the scanning line bending is reversed on different scanning surfaces, when the respective colors are overlapped, color misregistration is caused, and the quality of the color image is remarkably deteriorated.

  If the number of folding mirrors in the sub-scanning direction is different from the odd number or even number on both sides in the sub-scanning direction across the symmetry reference plane, the scanning lines folded by the folding mirror in the sub-scanning direction will be Therefore, even when the generation direction of the scanning line is different on both sides in the sub-scanning direction across the symmetry reference plane, the direction can be adjusted to the same direction. As a result, the occurrence of color misregistration can be reduced in color superposition in a color machine, and a good color image can be achieved.

  As the oblique incident angle increases, the curvature of the scanning line incident on the scanning lens increases and the amount of generation of the scanning line bending increases. That is, for example, in the method of FIG. 11E, the amount of scan line bending of the two outer light beams B107 and B′108 is larger than the two inner light beams B108 and B′107. Further, the amount of scan line bending when the temperature fluctuates also increases with the outer light beam.

  However, according to the present embodiment, the generation direction of the scanning line can be matched, so that the occurrence of color misregistration can be suppressed. Further, in order to reduce the influence of scanning line bending and color misregistration generated in the oblique incidence optical system, it is more preferable to suppress the generation of scanning line bending at the time of design.

  Further, by causing the scanning lens having a strong refractive power in the sub-scanning direction to be shifted eccentrically in the sub-scanning direction or tilted eccentrically in the sub-scanning direction, the occurrence of scanning line bending can be reduced. In order to perform better correction, by performing shift decentering or tilt decentering in the sub-scanning direction different in the main scanning direction on the scanning lens, the bus line is curved in the sub-scanning direction, and the light beam directed to each image height is transmitted. You may make it deflect. In this way, it is possible to satisfactorily correct the occurrence of scanning line bending due to the oblique incidence optical system.

  However, as shown in FIG. 14, the surface that curves the generatrix has a curvature in the sub-scanning direction, so that the light beam incident on the lens is sub-beamed due to the effects of assembly errors, processing errors, environmental fluctuations, and the like. When shifted in the scanning direction, the shape of the scanning line curve changes due to the influence of the refractive power of the lens in the sub-scanning direction, and an initial (or design) color shift suppression effect is obtained in a color image. Therefore, there is a problem that color misregistration occurs.

  Therefore, in order to more stably reduce the scanning line bending, in this embodiment, the shape in the sub-scanning direction is a planar shape having no curvature and the lens longitudinal direction (at least one surface of the scanning lens) The scanning line bending is corrected by using a special surface having a decentering angle (tilt amount) different in the lens lateral direction (sub-scanning direction) according to the lens height in the main scanning direction. The tilt amount (eccentric angle) of the special surface refers to a tilt angle in the short direction on the optical surface of the optical element. When the tilt amount is 0, there is no tilt, that is, the same state as a normal lens.

  Furthermore, a special aspect will be explained. The surface shape of the special surface is according to Equation 6 below. However, the content of the present invention is not limited to the following formula, and the same surface shape can be specified using another shape formula. The paraxial radius of curvature in the main scanning section, which is a flat section parallel to the main scanning direction, including the optical axis, is RY, the distance from the optical axis to the main scanning direction is Y, the higher order coefficients are A, B, C, D,. Let RZ be the paraxial radius of curvature in the sub-scan section that is orthogonal to the main scan section.

  However, Cm = 1 / RY and Cs (Y) = 1 / RZ. Further, “(F0 + F1 · Y + F2 · Y ^ 2 + F3 · Y ^ 3 + F4 · Y ^ 4 +...) Z” is a portion representing the tilt amount. When there is no tilt amount, F0, F1, F2. Are all zero. When F1, F2,... Are not 0, the tilt amount changes in the main scanning direction.

  Further, the reason why the special surface has a planar shape with no curvature in the sub-scanning direction will be described. As shown in FIG. 14B, when the incident light beam is shifted in the sub-scanning direction, the special surface does not have a refractive power, so only the traveling direction of the light beam is shifted, and the change in the direction is small. On the other hand, as shown in FIG. 14A, on a surface having a curvature in the sub-scanning direction, that is, a surface having a refractive power, such as a curved surface of the bus, when the incident light beam is shifted in the sub-scanning direction, the refractive power is By changing, the traveling direction of the light beam changes. If the amount of change in the advancing direction is different at each image height, the scanning line is greatly bent. In addition, a skew of the light beam occurs, which causes deterioration of wavefront aberration and beam spot diameter. For the above reasons, the shape in the sub-scanning direction on the special surface needs to be a planar shape having no curvature.

  Then, the scanning line bending can be corrected by optimally giving a different tilt amount in the main scanning direction of the scanning lens with respect to the direction of the sub-scanning direction of the light beam directed to each image height by the special surface. .

  Optimum setting of the special surface for each light beam directed to different scanned surfaces, that is, for each angle (oblique incidence angle) in the sub-scanning direction with respect to the symmetrical reference surface, makes it possible to correct the scanning line curvature and Wavefront aberration correction can be performed. In this case, even if the oblique incidence angle is different, it can be coped with by designing optimally by changing the coefficient of the shape formula using the special surface.

  Further, as described above, the special surface can correct the deterioration of the wavefront aberration generated by the oblique incidence optical system. Here, wavefront aberration deterioration due to oblique incidence will be described.

  As described above, the deflection of the optical deflector depends on the image height unless the shape in the main scanning direction of the entrance surface of the scanning lens constituting the scanning optical system is an arc shape centered on the reflection point of the light beam on the deflection reflection surface. The distance from the reflecting surface to the scanning lens entrance surface is different. Usually, it is difficult to make the scanning lens in the above shape in order to maintain optical performance. That is, a normal light beam is deflected and scanned by an optical deflector, and does not enter the lens surface perpendicularly at each image height in the main scanning section, but with an incident angle in the main scanning direction.

  The light beam deflected and reflected by the optical deflector has a certain width in the main scanning direction, and the light beams at both ends in the main scanning direction within the light beam are incident from the deflection reflecting surface of the optical deflector to the scanning lens incident surface. The distance is different and the angle is in the sub-scanning direction (because it is obliquely incident), so that the light enters the scanning lens in a twisted state. As a result, the wavefront aberration is significantly degraded and the beam spot diameter is increased. The incident angle in the main scanning direction becomes tighter toward the peripheral image height, the twist of the light beam increases, and the beam spot diameter increases due to the wavefront aberration deterioration toward the periphery.

  In order to satisfactorily correct the wavefront aberration and the scanning line bending, it is desirable to configure at least two scanning lenses and to use the special surfaces described above for each. That is, wavefront aberration correction is performed on a special surface of the scanning lens close to the optical deflector (at least the scanning lens closer to the optical deflector than the scanning lens having strong refractive power in the sub-scanning direction), and the scanning lens close to the scanned surface (sub-scan By separating each correction function so that scanning line bending correction is performed on a special surface of a scanning lens having a strong refractive power in the scanning direction, it is possible to further reduce the beam spot diameter and reduce scanning line bending. It becomes. Of course, it is not necessary to completely separate the functions, and each special surface may be configured to handle a part of wavefront aberration correction and a part of scanning line bending correction.

  Further, a description will be given of wavefront aberration correction. As described above, the incident angle in the main scanning direction to the scanning lens becomes tighter as it goes to the peripheral image height, the twist becomes larger as the light beam that draws the peripheral image height, and the beam spot diameter increases due to the deterioration of the wavefront aberration. growing. Therefore, it is desirable that the special surface has a surface shape in which the amount of eccentricity increases as the distance from the optical axis in the main scanning direction increases. Since the light beam near the optical axis, that is, near the central image height, is incident on the lens surface substantially perpendicularly, the deterioration of the wavefront aberration due to the light beam having an angle in the sub-scanning direction is small. Therefore, by increasing the amount of decentering as it moves away from the optical axis in the main scanning direction and correcting the wavefront aberration deterioration due to the torsion of the light beam, good optical performance and beam spot diameter can be obtained.

  As described above, good image quality can be obtained by correcting the occurrence of scanning line bending by the oblique incidence optical system at the time of design. From the viewpoint of color misregistration, both the scanning line bend caused by oblique incidence and the scan line bend caused by temperature fluctuation are reduced by matching the direction by optimally setting the number of folding mirrors in the sub-scanning direction. However, by using the special surface, it is possible to reduce the absolute amount of remaining scanning line bending and to obtain better image quality.

  In the one-side scanning method, the amount of scanning line bending that occurs at the time of design differs depending on the angle of oblique incidence. However, as described above, by correcting the scanning line bending at any time by design, As a result, the remaining amount of scanning line bending that occurs is reduced, so that color misregistration is greatly improved.

  As described above, the scanning line bending and wavefront aberration peculiar to the oblique incidence optical system cause image quality degradation such as color shift. This is because the sub-scan to the optical element after deflection by the vibrating mirror as described above. Since it depends on the size of the incident angle in the direction and the distance from the bus line of the scanning lens at the incident position, as shown in FIGS. 11B, 11D, and 11E, the scanning lens having a symmetrical shape with respect to the sub-scanning direction, By adopting a configuration in which each light beam is incident at a substantially equal angle to an incident position that is substantially symmetric in the sub-scanning direction, the distance by which the optical path can be separated by the folding mirror that guides each light beam to each photoreceptor is reduced to the minimum sub-scanning direction. It can be ensured at an incident angle in the scanning direction, and scanning line bending and wavefront aberration can be reduced, and a high-quality image can be stably formed.

  More preferably, as shown in FIG. 11E, a system in which two incident light beams have an intersection at a deflection point C on the vibrating mirror 106 may be used. This is because the size of the oscillating mirror 106 can be reduced by having approximately one deflection point on the oscillating mirror 106. Thereby, the cost required for one oscillating mirror is reduced, the resonance frequency f and the deflection angle θ of the oscillating mirror are improved by reducing the moment of inertia I in Equation 1, and the necessary driving torque is reduced. The drive voltage can be reduced.

  Although not shown in the figure, the deflection point C can be made substantially one point at the time of driving the oscillating mirror by moving the deflection point C near the intersection of the two rotation axes of the oscillating mirror, and the deflection point moves. Accordingly, it is possible to obtain the effect of eliminating the influence of the sag on the scanning line, to obtain good optical performance, and to stably provide a good quality image. The two rotation axes of the oscillating mirror refer to, for example, a rotation axis (twisted beam) that performs reciprocal scanning as shown in FIG. 2 and a rotation axis for switching an optical path provided in the perpendicular direction.

  Here, the sag will be described. FIG. 15 is a diagram showing a main scanning cross section in the vicinity of the oscillating mirror, and shows a state of an incident beam to the oscillating mirror and an outgoing beam having two types of deflection angles. The deflection angles of the outgoing beam 1 and the outgoing beam 2 in FIGS. 15A and 15B are equal. FIG. 15A shows a case where the light beam is incident on the rotation axis that changes the deflection angle of the vibrating mirror in the main scanning direction, and the deflection point is on the rotation axis. On the other hand, FIG. 15B shows the case where the position where the incident beam enters the vibrating mirror is far away from the rotation axis.

  In FIG. 15A, since the deflection point is on the rotation axis, both the outgoing beam 1 and the outgoing beam 2 are deflected at substantially the same spatial point, whereas in FIG. There is a spatial deviation between the deflection point deflecting in the direction of the beam 1 and the deflection point deflecting in the direction of the outgoing beam 2. This deviation of the deflection point becomes a sag.

  If there is a deviation of the deflection point, the optical path lengths on the plus side and the minus side with respect to the image height of 0 in one scanning line are not symmetric. The image forming characteristics in the sub-scanning direction vary between image heights, and the sub-scanning beam spot diameter cannot be made uniform between image heights, resulting in image degradation.

  Ideally, the light beam is narrowed down in the sub-scanning direction on the optical deflector, and the optical deflector and the surface to be scanned have a one-to-one conjugate relationship, which is resistant to tolerances such as surface tilt of the optical deflector. In general, an optical scanning device is used. However, if there is a deviation of the deflection point, the optical path length to the deflection point also varies between image heights. For example, when the optical deflector undergoes dynamic surface deformation, the optical performance on the surface to be scanned is greatly deteriorated.

  In order to improve the above problems, as described above, the deflection point C in FIG. 11 (e) is in the vicinity of the intersection of the two rotation axes of the oscillating mirror, so that the deflection point is always kept approximately one point, It would be more desirable to eliminate sag and to provide a stable and stable image.

[Embodiment 3]
FIG. 16 is a perspective view showing a configuration of an optical scanning device according to a third embodiment of the present invention, and the optical scanning device is a counter scanning system. Also in this embodiment, the light beam from the same light source is guided to different photoconductors in the forward scanning and the backward scanning of the vibrating mirror, and the number of light sources is halved compared to the conventional embodiment. And in common.

  The present invention can also be applied to the opposed scanning method as in the present embodiment. In this embodiment, as shown in FIG. 9, the light is incident horizontally on the vibrating mirror 106, and the vibrating mirror is subjected to forward scanning and backward scanning. Are preferably opposite to each other in the sub-scanning direction, and each outgoing light beam is emitted with a symmetrical angle with respect to a horizontal plane.

  Thereby, as described above, the size of the oscillating mirror can be reduced by making the deflection point substantially one point, the cost of the oscillating mirror can be reduced by minimizing the emission angle of each light beam, and the resonance frequency f or Improvement of the deflection angle θ, reduction of driving voltage, reduction of scanning line bending, wavefront aberration, and the like can be realized.

[Embodiment 4]
FIG. 17 is a perspective view showing the configuration of an optical scanning device according to the fourth embodiment of the present invention. When adopting the counter scanning method, it is more preferable to adopt a method as shown in FIG. This is because the deflection surfaces of the two oscillating mirrors of Embodiment 3 are formed on both surfaces of the oscillating mirror, and the number of oscillating mirrors can be reduced from two to one. As a result, the cost of the oscillating mirror itself can be reduced as described above, and since it is not necessary to match the scanning frequency between the oscillating mirrors, all the photoconductors are scanned at a uniform scanning frequency. It is possible to stabilize image formation and simplify the configuration of the optical scanning device.

[Embodiment 5]
Next, as a fifth embodiment of the present invention, an image forming apparatus equipped with any one of the optical scanning devices of Embodiments 1 to 4 will be described. An image forming apparatus using a cross-type multi-beam light source device as an example of an optical scanning device will be described.

  First, the crossing type multi-beam light source device used in this embodiment will be described in detail. FIG. 20 is an exploded perspective view showing the configuration of the multi-beam light source device in the present embodiment.

  The semiconductor lasers 403 and 404 are individually fitted in fitting holes (not shown) formed on the back side of the base member 405. The fitting hole is inclined at a predetermined angle in the main scanning direction, in this embodiment, about 1.5 °, and the semiconductor lasers 403 and 404 fitted in the fitting hole are also about 1 in the main scanning direction. Inclined 5 °. Further, the semiconductor lasers 403 and 404 have notches formed in the cylindrical heat sink portions 403-1 and 404-1, and the protrusions 406-1 and 407 formed in the center round holes of the pressing members 406 and 407. By aligning -1 with the notch of the heat sink, the arrangement direction of the light emitting sources is adjusted.

  The holding members 406 and 407 are fixed to the base member 405 with screws 412 from the back side, so that the semiconductor lasers 403 and 404 are fixed to the base member 405. Further, the collimating lenses 408 and 409 are adjusted in the optical axis direction along the outer circumferences of the semicircular mounting guide surfaces 405-4 and 405-5 of the base member 405, respectively, and the diverging beams emitted from the light emitting points. Is positioned and bonded so as to be a parallel light beam.

  In the present embodiment, since the light beams from the respective semiconductor lasers are set so as to intersect within the main scanning plane, the fitting hole and the semicircular mounting guide surface 405-4 along the light beam direction, the mounting guide The surface 405-5 is formed to be inclined. Then, the cylindrical engagement portion 405-3 of the base member 405 is engaged with the holder member 410, and the screw 413 is passed through the through hole 410-2 and screwed into the screw holes 405-6 and 405-7. A base member 405 is fixed to the holder member 410 and constitutes a light source unit.

  The holder member 410 of the light source unit has a cylindrical portion 410-1 fitted into a reference hole 411-1 provided in the mounting wall 411 of the optical housing, and a spring 611 is inserted from the front side of the mounting wall 411 to stop the stopper member 612. Is held in close contact with the back side of the mounting wall 411, thereby holding the light source unit. Further, one end of the spring 611 is hooked on the protrusion 411-2 of the mounting wall 411, and the other end of the spring 611 is hooked on the light source unit, thereby generating a rotational force about the center of the cylindrical portion in the light source unit.

  An adjustment screw 613 is provided so as to lock the rotational force of the light source unit. The adjustment screw 613 rotates the entire unit in the θ direction around the optical axis to adjust the pitch. It is configured to be able to. An aperture 415 is disposed in front of the light source unit. The aperture 415 is provided with a slit corresponding to each semiconductor laser, and is configured to be attached to an optical housing to define an emission diameter of the light beam.

  As the semiconductor laser, a semiconductor laser array having a plurality of light emitting points may be used. In addition, a multi-beam may be configured independently without having a plurality of semiconductor laser arrays.

  In this light source device, each light beam crosses the main scanning direction in the vicinity of the deflecting reflection surface of the optical deflector, thereby achieving miniaturization of the deflecting reflecting surface and each light after deflecting reflection. Since the beams can pass through almost the same optical path of the imaging optical system, the difference in optical performance between the respective light beams can be suppressed to a small value. Further, since an inexpensive LD is used and there are few components, a very inexpensive multi-beam light source device and optical scanning device can be provided.

  Conventionally, in an oblique incidence optical system using a polygon mirror as an optical deflector, there has been a problem that sub-scanning beam pitch deviation occurs when multi-beam conversion is performed in order to achieve high speed and high density. Hereinafter, the generation of the sub-scanning beam pitch deviation will be described.

  A multi-beam optical scanning device using a polygon mirror as an optical deflector of an oblique incidence optical system and using a cross-type multi-beam light source will be described as an example. As shown in FIG. 21, the light beams of LD1 and LD2 are incident on the deflection reflection surface with an angle in the main scanning direction. At this time, in order to deflect each light beam to the same image height, it is necessary to change the rotation angle of the polygon mirror. At this time, since the rotation axis of the polygon mirror is not on the deflecting reflection surface, an optical sag is generated.

  In the oblique incidence optical system, as shown in FIG. 22, for example, when looking at the sag of the deflecting reflecting surface toward the image height of ± 150 mm, the sag amount changes between LD1 and LD2. An example of the change in the sag amount is shown in FIG. The sag amount of the deflecting reflecting surface toward the image height of ± 150 mm is inverted between LD1 and LD2, and as shown in FIG. 22, the sub-scanning direction between the light beams (LD1 and LD2) after deflecting and reflecting. The pitch changes. That is, since the pitch in the sub-scanning direction after deflection reflection varies between image heights, the sub-scanning beam pitch on the scanned surface after passing through the imaging optical system differs between image heights, that is, has a deviation. End up.

  Specifically, as shown in FIG. 24, the sub-scanning beam pitch increases from the image height one side to the opposite side. When this optical system is used in a full-color image forming apparatus or the like, if the light beams superimposed between the colors differ between LD1 and LD2, the occurrence of color misregistration in the sub-scanning direction at the peripheral image height increases, resulting in image quality. Will be significantly reduced.

  As described above, when multi-beam formation is performed in an oblique incidence optical system, the sub-scanning beam pitch deviation is affected by the optical sag because the rotation angle of the polygon mirror of the light beam toward the same image height is different. Will occur. For this reason, when a polygon scanner is used as an optical deflector as in the prior art, the thickness in the sub-scanning direction of the deflecting reflection surface can be greatly reduced by employing an oblique incidence optical system. And by reducing the thickness in the sub-scanning direction, the cost of the polygon scanner, which has a high cost weight in the optical scanning device, can be reduced, the inertia as a rotating body can be reduced and the start-up time can be shortened. Although it was possible to obtain effects such as electric power, it was difficult to develop high speed and high density.

  As a method for avoiding this difficulty, there is a method in which the rotation angles of the polygon mirrors of light beams directed to the same image height are substantially matched. However, in order to realize this, it is necessary to use an expensive LDA as a light source, or to use a plurality of inexpensive LDs to match the incident angles in the main scanning direction incident on the polygon mirror by a prism or the like. This raises the problem of increasing the cost of the optical scanning device or increasing the size of the optical scanning device by arranging the prism.

  In the present embodiment, the above problem can be solved by using a vibrating mirror as the optical deflector. As described above, the multi-beam formation in the oblique incidence optical system is largely due to the influence of the optical sag generated in the polygon mirror. According to the present embodiment, an optical sag generated when deflecting a light beam can be reduced by using a vibrating mirror as an optical deflector. Also, since the rotation center of the oscillating mirror is located substantially on the deflection reflection surface, no sag is generated or becomes very small even if the deflection angle changes.

  As a result, the change in the spacing of each light beam in the sub-scanning direction on the deflecting / reflecting surface can be greatly reduced over the entire image height, greatly increasing the sub-scanning beam pitch deviation on the scanned surface. It becomes possible to reduce it. In other words, it can be improved until it becomes equivalent to the optical scanning device that is incident in parallel to the normal line of the deflection reflection surface of the conventional polygon scanner. For this reason, the multi-beam conversion in the oblique incidence optical system, which has been difficult to achieve in the past, can be achieved also in the cross-type multi-beam light source described above.

  Next, the image forming apparatus of this embodiment will be described. FIG. 25 is a diagram showing a schematic configuration of the image forming apparatus of the present embodiment. The image forming apparatus includes a photoreceptor 7, a charging unit 8, an optical writing unit 9, a developing unit 10, a transfer unit 11, a fixing unit 24, and a cleaning unit 12.

  The photoconductor 7 has a drum shape and carries a latent image exposed by the optical writing unit 9. The charging unit 8 charges the photoconductor 7. The optical writing unit 9 exposes the charged photoconductor 7 with a light beam according to image information to form a latent image. The developing means 10 develops the latent image formed on the photoconductor 7 with, for example, toner to make a visible image. The transfer unit 11 transfers the visible image (toner image) on the photoconductor 7 to a transfer material 17 such as recording paper. The fixing unit 24 fixes the visible image (toner image) transferred to the transfer material 17. The cleaning unit 12 cleans the surface of the photoconductor 7 after the transfer. With the above configuration, an image is formed on a transfer material and output by processes (electrophotographic process) of charging, exposure, development, transfer, fixing, and cleaning.

  Each configuration will be further described in detail. The photoconductor 7 is obtained by forming a photoconductor layer (photosensitive layer) made of an inorganic material or an organic material on the surface of a drum-shaped conductive substrate, and the surface of the photoconductor becomes a scanned surface. In addition to the drum shape, a belt shape may be used as the photoreceptor. The charging means 8 is shown as a corona charger in FIG. 25, but various other devices such as a charging roller and a charging brush can be used. Further, as the optical writing means 9, the one described in the above embodiment is used.

  The developing means 10 has various configurations, such as a developing device using a one-component developer containing only toner as a developer, or a developing device using a two-component developer consisting of toner and carrier as a developer. Can be used. The transfer means 11 is represented as a transfer charger in FIG. 25, but various other devices such as a transfer roller, a transfer belt, and a transfer brush can be used. The fixing unit 24 fixes an image on a transfer material by heating and / or pressing, and a roller fixing unit using a heating roller and a pressing roller, or a belt fixing unit using a belt and a heating unit. The thing of various structures, such as these, can be used. As the cleaning means 12, various types of structures such as a blade type, a brush type, and a roller type can be used.

  As described above, in this embodiment, by writing a photoconductor with multiple beams, the image writing density can be improved or the printing speed can be increased. It is possible to provide an image forming apparatus that can realize reduction in cost and cost.

[Embodiment 6]
Next, a full color image forming apparatus will be described as a sixth embodiment of the present invention. The optical scanning device according to the embodiment of the present invention can be applied to the optical writing unit even when the configuration is a multicolor image forming apparatus or a full color image forming apparatus of two or more colors. In the present embodiment, as shown in FIG. 25, a plurality of light beams from a plurality of light sources corresponding to yellow, magenta, cyan, and black color materials are separated by a plurality of folding mirrors, and a plurality of images corresponding to the respective light beams are separated. A full-color image forming apparatus that guides light to the carriers 7Y, 7M, 7C, and 7K.

  In this embodiment, by using any one of the optical scanning devices according to the first to fourth embodiments as an optical scanning device in a full-color tandem image forming apparatus, printing speed is increased, image quality is improved, power consumption is reduced, and size is reduced. Therefore, it is possible to provide a full-color tandem image forming apparatus that can realize cost reduction.

  The above-described embodiment is a preferred embodiment of the present invention, and the scope of the present invention is not limited to the above-described embodiment alone, and various modifications are made without departing from the gist of the present invention. Implementation is possible.

  According to the above embodiment, a plurality of light sources, an optical deflector that deflects a light beam from the light source and reciprocally scans in the main scanning direction, and an optical deflector that detects the light beam deflected by the optical deflector. An optical scanning device comprising: an optical deflector driving unit that controls a deflection angle of the light; and an imaging optical system that guides a light beam deflected by the optical deflector to a corresponding scanned surface and forms an image. The scanning device is provided on the optical path of the light beam between the light source and the imaging optical system, and switches the optical path of the light beam in the sub-scanning direction orthogonal to the scanning direction of the optical deflector to deflect it to the optical deflector. A scanning surface having a switching unit, wherein the optical deflector deflects the light beam on the same deflection surface, and the scanning path is different in the forward scanning and the backward scanning by switching the optical path of the light beam in the sub-scanning direction performed by the optical path switching unit. By reciprocating scanning of a vibrating mirror as an optical deflector. In contrast to the conventional method in which image writing is performed only in one of the sections and only one scanning line can be written for one reciprocation of the vibrating mirror, one line on two different scanning surfaces, ie, one reciprocating vibration mirror, A total of two lines of scanning lines can be written, and efficient image writing can be performed.

  According to the above embodiment, in the optical scanning device, the optical deflector also serves as the optical path switching unit, so that the optical path is switched without using other optical elements when scanning different surfaces to be scanned. Therefore, a simpler configuration can be achieved without increasing the number of parts constituting the optical scanning device and the image forming apparatus, and an assembly error or the like that occurs when the optical element is assembled to the optical scanning device housing. The risk of degrading the optical performance is reduced, and a more stable quality image can be formed. Further, in the case where the optical path is switched in front of the optical deflector, the size of the optical deflector is increased in order to guide each light beam to each scanned surface. Such a problem is solved, the size of the vibrating mirror as the optical deflector can be reduced, the moment of inertia of the vibrating mirror is reduced, the scanning speed can be increased, and high-speed printing is possible. Furthermore, the deflection angle of the vibrating mirror can be increased and the dynamic surface deformation can be reduced, and the optical performance can be improved, so that it is possible to stably provide a better quality image.

  According to the above embodiment, in the optical scanning device, the optical deflector deflects the light beam from the same light source on the same deflection surface, and scans different scanning surfaces in the forward scanning and the backward scanning. Thus, it is possible to reduce the number of light sources, which is conventionally required by the number of scanned surfaces on which image writing is performed, and it is possible to form an image having the same quality as the conventional one with fewer light sources. As a result, power consumption during image formation can be kept low as the number of light sources to be driven is reduced. In addition, the cost and space of the light source and its associated coupling lens, cylindrical lens, and light source unit assembly can be reduced, improving cost performance and providing a front optical system that is incident on the vibrating mirror as an optical deflector. It is possible to provide a compact optical scanning device and image forming apparatus that are compact.

  Further, according to the above embodiment, in the optical scanning device, the imaging optical system includes a scanning line inclination on the surface to be scanned by the forward scanning of the optical deflector and a surface to be scanned by the backward scanning of the optical deflector. By forming the light beam in such a manner that the scan line tilt is relatively opposite to the scan line tilt, it is possible to uniformly align the scan line tilts on different scan surfaces. When configuring a full-color tandem image forming apparatus that supports toner development of each color, it is possible to reduce color misregistration by aligning the scan line inclination corresponding to each color, and to produce a high-quality image. Can be formed.

  According to the above embodiment, in the optical scanning device, the imaging optical system includes a scanning lens arranged closest to the optical deflector to guide a plurality of light beams to the surface to be scanned. The deflector is substantially symmetrical with respect to a symmetrical reference axis that is a horizontal plane that passes through the center of the scanning lens and is parallel to the scanning direction of the optical deflector by switching the optical path of the light beam in the sub-scanning direction performed by the optical path switching means. The light beam is deflected so as to pass through the position, and image scanning is performed on different scanning surfaces for forward scanning and backward scanning, so that the paired light beams are connected to each scanning surface. Each imaging optical system that scans an image can be configured with an imaging optical system having the same characteristics, and the cost from development to design to manufacturing can be kept low by sharing and sharing parts. it can. Further, when securing the distance in the sub-scanning direction between the light beams necessary for separating each light beam to guide each surface to be scanned, the emission angle in the sub-scanning direction can be minimized. Therefore, the beam spot diameter thickening due to the scanning line bending and wavefront aberration deterioration peculiar to the oblique incidence optical system can be suppressed low, the color shift can be reduced, the effect of forming a good quality image, the optical scanning device and the image forming device The effect of reducing the size in the sub-scanning direction can be obtained.

  Further, according to the above embodiment, in the optical scanning device, the optical deflector deflects all the light beams on the same deflection surface, thereby separating each light beam for guiding it to each scanned surface. When securing the distance in the sub-scanning direction between the light beams necessary for the scanning, the emission angle in the sub-scanning direction can be minimized, so that the beam due to scan line bending and wavefront aberration degradation peculiar to the oblique incidence optical system The increase in spot diameter can be suppressed low, color misregistration can be reduced, and an effect of forming a high-quality image and the effect of reducing the size in the sub-scanning direction of the optical scanning device and the image forming device can be obtained. In addition, since all the light beams can be guided to each scanned surface with a single deflection surface, and a writing optical system can be realized with one oscillating mirror, the cost can be reduced and a plurality of oscillating mirrors can be realized. This eliminates the need to adjust the scanning frequency between the vibrating mirrors, which is necessary when using the, and reduces the cost of the complicated scanning frequency adjustment control means and can stably form a good quality image. An optical scanning device and an image forming apparatus can be provided.

  According to the above embodiment, in the optical scanning device, the optical deflector deflects all the light beams at the same deflection point, so that the size of the oscillating mirror as the optical deflector can be reduced. As a result, the moment of inertia of the vibrating mirror is reduced, the scanning speed can be increased, and high-speed printing is possible. Furthermore, the deflection angle of the vibrating mirror can be increased and the dynamic surface deformation can be reduced, and the optical performance can be improved, so that it is possible to stably provide a better quality image.

  According to the above embodiment, in the optical scanning device, the optical deflector is provided in a direction perpendicular to the scanning rotation axis and a scanning rotation axis that rotates the optical deflector to reciprocately scan the light beam. An optical path switching rotation axis that switches the optical path of the light beam in the sub-scanning direction, and the same deflection point is located at a point where the scanning rotation axis and the optical path switching rotation axis intersect, thereby driving a vibrating mirror as an optical deflector The deflection point at the time is always substantially the same point, and the effect of being able to reduce the size of the oscillating mirror as described above can be obtained, and at the same time, since the sag of the scanning line is eliminated, good optical performance can be obtained and good It becomes possible to provide quality images stably.

  Further, according to the above-described embodiment, the optical scanning device is mounted, the light beams from the plurality of light sources modulated by the image signal are deflected, and imaged in a spot shape by the imaging optical system, thereby carrying the image. In an image forming apparatus that records an electrostatic image on an image carrier by scanning the body, visualizes the electrostatic image with toner, and transfers the image to a recording medium, each of the single image carriers By using multiple light sources to record an electrostatic image, multiple light beams are scanned at the same time to record multiple lines simultaneously, improving the image writing density or increasing the printing speed. It is possible to provide an image forming apparatus that can realize improvement in image quality, reduction in power consumption, size reduction, and cost reduction.

  Further, according to the above-described embodiment, the optical scanning device, the image carrier that records the electrostatic image corresponding to each by the light beam from each light source, and the development that visualizes the electrostatic image with each color toner. The image forming apparatus includes the apparatus and a transfer device that transfers the visualized toner image to a recording medium so that the writing direction in the reciprocating scanning direction of the optical deflector on each image carrier is aligned. By recording an image, it is possible to provide a full-color tandem image forming apparatus capable of realizing an increase in printing speed, an improvement in image quality, a reduction in power consumption, a reduction in size, and a reduction in cost.

It is the perspective view which showed the structure of the vibration mirror module in embodiment of this invention. It is the perspective view which showed the structure of the vibration mirror module in embodiment of this invention. It is the figure which showed the mode of the vibration mirror 106 in the cross section along the subscanning direction of the optical scanning device which concerns on embodiment of this invention. It is the perspective view which showed the structure of the optical scanning device concerning embodiment of this invention. It is the perspective view which showed the structure of the conventional optical scanning device. It is the figure which showed the scanning line inclination by the reciprocating scanning of an optical scanning device. FIG. 6 is a diagram illustrating scanning lines obtained by scanning different photosensitive members by reciprocating scanning in the optical scanning device according to the embodiment of the present invention. FIG. 6 is a diagram showing scanning lines obtained by scanning different photosensitive members by reciprocating scanning in the optical scanning device according to the embodiment of the present invention (when forming an image). It is the figure which showed the mode of the light beam in the scanning lens entrance plane in the optical scanner which concerns on embodiment of this invention. It is the perspective view which showed the structure of the optical scanning device concerning embodiment of this invention. It is the figure which showed the mode of the light beam in the vibration mirror deflection | deviation surface in the optical scanner which concerns on embodiment of this invention. It is a figure for demonstrating the scanning line curve in the scanning lens entrance plane in an oblique incidence optical system. It is the figure which showed the subscanning cross section in an oblique incidence optical system. It is the figure which showed the mode of the emitted light beam when an incident light beam was shifted to the scanning lens in the sub-scanning direction in the oblique incidence optical system. It is a figure for demonstrating the shift | offset | difference (sag) of the deflection position in a vibration mirror. It is the perspective view which showed the structure of the optical scanning device concerning embodiment of this invention. It is the perspective view which showed the structure of the optical scanning device concerning embodiment of this invention. It is the figure which represented the angular displacement of the main scanning direction of the vibration mirror in embodiment of this invention with the time axis. It is the figure which represented the angular displacement of the main scanning direction of the vibration mirror in the embodiment of this invention, and a subscanning direction on the time axis. It is the disassembled perspective view which showed the structure of the multi-beam light source unit in embodiment of this invention. It is the figure which showed the mode of the light beam in the deflection surface in the multi-beam oblique incidence optical system using a polygon mirror. It is the figure which showed the mode of the sag generation | occurrence | production in the multi-beam oblique incidence optical system using a polygon mirror. It is the figure which showed the mode of the sag of the polygon mirror reflective surface in the multi-beam oblique incidence optical system using a polygon mirror. It is the figure which showed the mode of the subscanning beam pitch deviation in the multi-beam oblique incidence optical system using a polygon mirror. 1 is a diagram illustrating a schematic configuration of an image forming apparatus according to an embodiment of the present invention.

Explanation of symbols

3,120,121 Scanning lens (vibrating mirror side)
4,122,123,124,125 Scanning lens (scanned surface side)
5,106 Vibrating mirrors 6Y-6K, 201, 202, 203 Light beams 7Y-7K, 101, 102, 103, 104 Photosensitive drums 8Y-8K Charging means 9 Optical writing means 10Y-10K Developing means 11Y-11K Transfer means 12Y-12K Cleaning means 17 Transfer material 24 Fixing means 105 Transfer belt 107, 108, 109 Light source unit 111 Incident mirror 113, 116 Cylindrical lenses 126-128, 129-131, 132-134, 135-137 Folding mirrors 138-141 Synchronization Detection sensor 403, 404 Semiconductor laser 405 Base member 406, 407 Holding member 408, 409 Collimate lens 410 Holder member 411 Mounting wall 412 Fixing screw 413 Screw 415 Aperture 611 Spring 612 Stopper member 613 adjustment screw

Claims (11)

Multiple light sources;
An optical deflector that deflects a light beam from the light source to reciprocate in the main scanning direction;
An optical deflector driver that detects the light beam deflected by the optical deflector and controls a deflection angle of the optical deflector;
An optical scanning device comprising: an imaging optical system configured to guide and image the light beam deflected by the optical deflector to a corresponding scanned surface;
Provided on the optical path of the light beam between the light source and the imaging optical system, and switches the optical path of the light beam in the sub-scanning direction orthogonal to the scanning direction of the optical deflector to deflect it to the optical deflector Having optical path switching means
The optical deflector deflects the light beam on the same deflecting surface, and switches the optical path of the light beam in the sub-scanning direction performed by the optical path switching unit, so that different scanning surfaces are obtained in the forward scanning and the backward scanning. An optical scanning device characterized by scanning.   The optical scanning device according to claim 1, wherein the optical deflector also serves as the optical path switching unit.   3. The light according to claim 1, wherein the optical deflector deflects a light beam from the same light source on the same deflection surface, and scans different surfaces to be scanned in forward scanning and backward scanning. Scanning device.   The imaging optical system has a direction in which a scanning line inclination on the scanning surface by the forward scanning of the optical deflector is relatively opposite to a scanning line inclination on the scanning surface by the backward scanning of the optical deflector. The optical scanning apparatus according to claim 1, wherein the light beam is imaged so as to be.   5. The image forming optical system according to claim 1, wherein a scanning lens disposed closest to the optical deflector guides the plurality of light beams to a surface to be scanned. The optical scanning device according to 1.   The optical deflector is a symmetrical reference axis which is a horizontal plane passing through the center of the scanning lens and parallel to the scanning direction of the optical deflector by switching the optical path of the light beam in the sub-scanning direction performed by the optical path switching means. The light according to claim 5, wherein the light beam is deflected so as to pass through a substantially symmetric position, and imaging scanning is performed on different scanning surfaces in forward scanning and backward scanning. Scanning device.   The optical scanning device according to claim 6, wherein the optical deflector deflects all the light beams on the same deflection surface.   8. The optical scanning device according to claim 7, wherein the optical deflector deflects all the light beams at the same deflection point. The optical deflector is provided in a direction perpendicular to the scanning rotation axis for rotating the optical deflector for reciprocating scanning of the light beam, and switches the optical path of the light beam to the sub-scanning direction. An optical path switching rotation axis,
9. The optical scanning device according to claim 8, wherein the same deflection point is located at a point where the scanning rotation axis and the optical path switching rotation axis intersect. 10. The optical scanning device according to claim 1 is mounted, a light beam from the light source modulated by an image signal is deflected by the optical deflector, and is spotted by the imaging optical system. An electrostatic latent image is recorded on the image carrier by forming an image and scanning the image carrier, the electrostatic latent image is visualized with toner, and the visualized toner image is recorded on a recording medium. An image forming apparatus for transferring,
An image forming apparatus, wherein a plurality of light sources are used to record an electrostatic latent image on each single image carrier. 10. The optical scanning device according to claim 1, an image carrier for recording an electrostatic latent image corresponding to each by a light beam from the light source, and the electrostatic latent image with each color toner. An image forming apparatus comprising: a developing device that makes a visible image; and a transfer device that superimposes the visualized toner image and transfers it to a recording medium,
An image forming apparatus for recording an image so that the writing direction in the reciprocating scanning direction of the optical deflector on each image carrier is aligned.

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