JP5802468B2 - Optical scanning device and image forming apparatus using the same - Google Patents

Description

  The present invention relates to an optical scanning device including a deflector that deflects and scans a light beam emitted from a light source while rotating around an axis of a rotation axis, and an image forming apparatus using the same.

  2. Description of the Related Art Conventionally, in an optical scanning device used in a laser printer, a copying machine, or the like, a MEMS (Micro Electro Mechanical Systems) micromirror is used as a deflecting body that deflects and scans a light beam emitted from a light source (for example, Patent Documents). 1). In the optical scanning device of Patent Document 1, a light beam emitted from a light source in an incident optical system is imaged on a micromirror, and scanning light is coupled to a photosensitive drum (scanned surface) via a scanning lens having negative optical power. I am letting you image. According to this optical configuration, there is an advantage that the scanning region can be lengthened with the same optical path length as compared with the case where a scanning lens having a positive optical power is used. However, if the convergence angle with respect to the surface to be scanned is the same, the mirror diameter of the micromirror needs to be larger when the negative scanning lens is used than when the positive scanning lens is used.

  As the mirror diameter increases, the moment of inertia of the micromirror increases, causing problems such as an inability to increase the resonance frequency and an increase in element size. Therefore, a device for reducing the mirror diameter as much as possible is required. The most effective method is to employ a so-called center incident optical system. The center incidence optical system minimizes the incident angle of the light beam with respect to the micromirror in the main scanning section. From the rotation axis of the micromirror, the optical axis of the incident light to the micromirror, and the micromirror in one sub-scanning section. It is an optical system which arrange | positions the optical axis of reflected light. In this case, in order to spatially separate the incident light and the reflected light, the incident light is incident on the micromirror by an oblique incidence method having an angle in the sub-scanning direction.

  When the oblique incidence method is adopted, a scanning curve is generated, and as a result, there arises a problem that imaging performance in the vicinity of the scanning end portion is deteriorated. In order to solve such a problem, Patent Document 2 discloses a technique in which a refracting surface of a scanning lens is a special toric surface. The special toric surface is a refracting surface having a curved shape in which the generatrix shape connecting the vertices of the child lines is curved in the sub-scanning direction.

JP 2006-78520 A Japanese Patent Laid-Open No. 10-73778

  However, in Patent Document 2, the shape of the scanning lens in the sub-scanning section is not specified. Therefore, it is difficult to verify the surface shape. For example, when creating a scanning lens by mold molding, it takes a great deal of effort to design and verify the mold, and to obtain a surface shape having the desired optical performance. There is a problem that the provided scanning lens cannot be easily obtained.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide an optical scanning device and an image forming apparatus that can easily verify the surface shape of a scanning lens.

Optical scanning apparatus according to an aspect of the present invention, a light source for emitting a light beam, before Symbol a deflector for deflecting the scanning by reflecting a light beam emitted from the light source, the refractive surface of the rotationally asymmetric least 1 Menfukumi, the deflection A scanning lens that forms an image of the scanned light beam on the surface to be scanned, an incident light beam incident on the deflecting body, and a reflected light beam that is deflected and scanned by the deflecting body and travels toward the scanned surface do not interfere with each other. And an incident optical system that directs the incident light beam toward the deflecting body with an angle in the sub-scanning direction with respect to the optical path of the reflected light beam, and the refractive surface connects a child line vertex of the refractive surface bus is curved in the sub-scanning direction, the shape of the plane parallel to the sub-scanning cross section made by the optical axis and the sub-scanning axis that leads to the surface to be scanned from the light source is a ellipse with the exception of the image height center, the image height at the center an arc, the ellipse, the optical axis Extremum in direction is on the bus.

  According to this configuration, in the optical scanning device employing the incident optical system that makes the incident light beam incident on the deflector with an angle in the sub-scanning direction, the bus connecting the vertexes of the refracting surface of the scanning lens is sub-scanned. Since it is curved in the direction, it is possible to reduce the size of the deflecting body and to suppress the influence of scanning curvature. Furthermore, since the shape of the sub-scanning section of the refractive surface is specified, the surface shape of the scanning lens can be easily verified.

Furthermore, in the optical scanning device according to the present invention, when the sub-scanning axis is defined as the x direction, the main scanning axis is defined as the y direction, and the optical axis is defined as the z direction, the shape z of the refractive surface in the sub scanning section is Is a shape projected onto the yz plane, f (y), a shape projected onto the yx plane is g (y), and a radius of curvature of a cross section perpendicular to the projected generatrix where the generatrix is projected onto a plane perpendicular to the optical axis. Is an ellipse represented by the following formula (1), where rs is the radius of curvature of the elliptical sub-scan section and rl is the radius of curvature .

  According to this configuration, since the surface shape of the sub-scanning section of the refracting surface is defined by a mathematical expression, the surface shape can be automatically designed using optical software or the like.

In the above-described configuration, it is desirable that the deflecting body has an axis serving as a swing center, and the incident light beam, the reflected light beam, and the axis of the deflecting body are arranged on the same plane. According to this configuration, since the incident optical system is a so-called center incident optical system, the size of the deflecting body can be minimized.

  In the above-described configuration, it is desirable that the at least one refracting surface of the scanning lens is a refracting surface that is decentered parallel to the optical axis in the sub-scanning direction. The scanning curve on the surface to be scanned is changed by decentering the refractive surface in parallel. Therefore, it is possible to further suppress the scanning curvature that occurs when the incident light beam is obliquely incident on the deflecting body with an angle in the sub-scanning direction.

  Moreover, it is desirable to further include a rotation mechanism that rotates the scanning lens about an axis parallel to the main scanning direction. When the scanning lens is rotated around an axis parallel to the main scanning direction, the shape of the generatrix viewed from the surface to be scanned changes, and the scanning curve also changes. Therefore, it is possible to further suppress the scanning curve by the rotation mechanism.

  Furthermore, it is desirable to further include an adjusting unit that gives an operation for adjusting a scanning curve to an optical component arranged in an optical path from the light source to the surface to be scanned. According to this configuration, the scanning curve can be further suppressed by the adjusting means.

  An image forming apparatus according to still another aspect of the present invention includes: an image carrier that carries an electrostatic latent image; and the above-described optical scanning device that irradiates a light beam with a peripheral surface of the image carrier as the scanned surface. Prepare.

  According to the present invention, it is possible to provide an optical scanning device and an image forming apparatus that can easily verify the surface shape of a scanning lens. Therefore, the development cost of the scanning lens and the optical scanning device can be reduced.

1 is a cross-sectional view illustrating a schematic configuration of a printer according to an embodiment of the present invention. It is an optical path figure which shows the structure of the main scanning cross section of an optical scanning device. It is an optical path figure which shows the structure of the subscanning cross section of an optical scanning device. It is a principal part enlarged view of FIG. It is a schematic diagram for demonstrating the scanning area | region of a MEMS mirror. It is a schematic diagram for demonstrating the convergence angle to the to-be-scanned surface by a MEMS mirror. It is a schematic diagram for demonstrating the mirror diameter of a MEMS mirror. It is a typical perspective view which shows the incident light beam which goes to a MEMS mirror, and the reflected light beam reflected by a MEMS mirror. It is a schematic diagram for demonstrating scanning curvature. FIG. 6 is a characteristic diagram illustrating an imaging state when scanning curvature occurs. It is a figure which shows the shape of the main scanning plane of the scanning lens which concerns on embodiment of this invention. It is an arrow line view of the arrow A direction of FIG. It is an optical path figure from a MEMS mirror to a surface to be scanned of an optical scanning device concerning an embodiment of the present invention. It is a characteristic view which shows the image formation state of the optical scanning device of this embodiment. It is a graph which shows the scanning curve of the optical scanning device of this embodiment. It is a graph which shows the fluctuation | variation of the beam pitch of the optical scanning device of this embodiment.

  Hereinafter, an optical scanning device according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view schematically showing a configuration of an image forming apparatus 1 including an optical scanning device 11 according to an embodiment of the present invention. The image forming apparatus 1 includes an optical scanning device 11, a developing device 12, a charger 13, a photosensitive drum 14 (image carrier), a transfer roller 15, a fixing device 16, and a paper feed cassette 17.

  The photosensitive drum 14 is a cylindrical member, and an electrostatic latent image and a toner image are formed on the peripheral surface thereof. The photosensitive drum 14 receives a driving force from a motor (not shown) and rotates in the clockwise direction in FIG. The charger 13 charges the surface of the photosensitive drum 14 substantially uniformly.

  The optical scanning device 11 includes a light source such as a laser diode, a deflector, a scanning lens, an optical element, and the like. Then, a laser beam corresponding to the image data is irradiated to form an electrostatic latent image of the image data. The optical scanning device 11 will be described in detail later.

  The developing device 12 supplies toner to the peripheral surface of the photosensitive drum 14 on which the electrostatic latent image is formed, thereby forming a toner image. The developing device 12 includes a developing roller that carries toner and a screw that stirs and conveys the toner. The toner image formed on the photosensitive drum 14 is transferred from the sheet feeding cassette 17 to the recording paper conveyed through the conveyance path P. The developing device 12 is supplied with toner from a toner container (not shown).

  A transfer roller 15 is disposed below the photosensitive drum 14 so as to face each other, and a transfer nip portion is formed by both. The transfer roller 15 is made of a conductive rubber material or the like and is given a transfer bias to transfer the toner image formed on the photosensitive drum 14 onto the recording paper.

  The fixing device 16 includes a fixing roller 160 having a built-in heater and a pressure roller 161 provided at a position facing the fixing roller 160, and is formed on the recording paper by heating and conveying the recording paper on which the toner image is formed. The toner image is fixed.

  Next, an image forming operation of the image forming apparatus 1 will be briefly described. First, the surface of the photosensitive drum 14 is charged almost uniformly by the charger 13. The peripheral surface of the charged photosensitive drum 14 is exposed by the optical scanning device 11, and an electrostatic latent image of an image formed on the recording paper is formed on the surface of the photosensitive drum 14. The electrostatic latent image is made visible as a toner image by supplying toner from the developing device 12 to the peripheral surface of the photosensitive drum 14. On the other hand, the recording paper is fed from the paper feed cassette 17 to the transport path P. The toner image is transferred to the recording paper when the recording paper passes through the nip portion between the transfer roller 15 and the photosensitive drum 14. After this transfer operation is performed, the recording paper is conveyed to the fixing device 16 and the toner image is fixed to the recording paper.

  Next, the detailed structure of the optical scanning device 11 will be described. 2 is an optical path diagram showing the configuration of the main scanning section of the optical scanning device 11, FIG. 3 is an optical path diagram showing the configuration of the sub-scanning section, and FIG. 4 is an enlarged view of the main part of FIG. The optical scanning device 11 includes a semiconductor laser 101 (light source), a collimator lens 102, a cylindrical lens 103, a MEMS mirror 104 (deflector), a first scanning lens 105a, a second scanning lens 105b, a first mirror 106, and a second mirror 107. Is provided. In these drawings, the X direction is the sub-scanning direction, the Y direction is the main scanning direction, and the Z direction is the optical axis direction.

  The semiconductor laser 101 is a light source that emits laser light having a predetermined wavelength (incident light beam L0). The collimator lens 102 converts the incident light beam L0 emitted from the semiconductor laser 101 and diffusing into parallel light. The cylindrical lens 103 converts the parallel light beam L0 into linear light that is long in the main scanning direction and forms an image on the MEMS mirror 104. The second mirror 107 is disposed to face the emission surface of the semiconductor laser 101 with the collimator lens 102 and the cylindrical lens 103 interposed therebetween, and reflects the incident light beam L0 so as to be folded back obliquely upward. The first mirror 106 is disposed obliquely in front of the MEMS mirror 104, reflects the incident light beam L0 reflected by the second mirror 107 obliquely downward, and makes it incident on the MEMS mirror 104.

  The MEMS mirror 104 has a mirror surface 104M and a rotation axis 104P parallel to the sub-scanning direction Z. This rotating shaft is rotationally driven (sinusoidally swung) by a driving source (not shown). The MEMS mirror 104 deflects and scans the incident light beam L0 emitted from the semiconductor laser 101 and imaged through the collimator lens 102 and the cylindrical lens 103 while rotating around the rotation axis.

  The collimator lens 102, the cylindrical lens 103, the first mirror 106, and the second mirror 107 are an incident optical system that causes the incident light beam L0 to enter the MEMS mirror 104. In this embodiment, the collimator lens 102, the cylindrical lens 103, and the second mirror 107 are configured as a center incident optical system. . That is, as shown in FIG. 4, on the plane parallel to the sub-scanning direction X including the optical axis Z, the center of the cylindrical lens 103, the rotation axis 104P of the MEMS mirror 104, the first mirror 106, and the second mirror 107. The normal line is arranged.

  When viewed in the sub-scanning direction X with respect to the optical axis from the MEMS mirror 104 toward the peripheral surface 14a of the photosensitive drum 14, the second mirror 107 is disposed below the optical axis, and the first mirror 106 is aligned with the optical axis. It is arranged above. The first mirror 106 and the second mirror 107 are arranged in this manner so that the incident light beam L0 is obliquely incident on the MEMS mirror 104. The incident light beam L0 and the reflected light beam from the MEMS mirror 104 (the deflected light beam L1 and the deflected light beam L2). This is to separate them from each other spatially.

  The first scanning lens 105a and the second scanning lens 105b are lenses having fθ characteristics, and are lenses having a lens surface (rotationally asymmetric refracting surface) formed of a special toric surface. These scanning lenses 105a and 105b are arranged opposite to each other on the optical axis from the MEMS mirror 104 toward the peripheral surface 14a of the photosensitive drum 14, and collect the reflected light flux reflected by the MEMS mirror 104 to An image is formed on the surface 14a (scanned surface).

  Next, advantages of the center incident optical system employed in this embodiment will be described. FIG. 5 is an optical path diagram showing a side incidence optical system as employed in the optical scanning device disclosed in Patent Document 1 described above. In this side incident optical system, an incident light beam emitted from a light source (not shown) is a plane parallel to the main scanning section and from the side of the plane including the optical axis from the MEMS mirror 21 toward the scanned surface 23. The light enters the MEMS mirror 21. Here, when a lens having negative optical power is used as the scanning lens 22, under the condition that the deflection angle θ of the MEMS mirror 21 is the same and the optical path length from the MEMS mirror 21 to the scanned surface 23 is the same. Compared with the case where a lens having positive optical power is used as the scanning lens 22, the scanning area can be made longer.

  Therefore, it can be said that it is advantageous to use the scanning lens 22 having negative optical power from the viewpoint of shortening the optical path length. However, from the viewpoint of reducing the mirror diameter of the MEMS mirror 21, the scanning lens 22 having positive optical power is advantageous. FIG. 6 is a diagram showing the convergence angle φ of the light beam that greatly affects the spot diameter of the light beam irradiated on the scanned surface 23. Under the condition that the convergence angle φ is constant, the image formed by the scanning lens 22 having the positive optical power at the position where the MEMS mirror 21 is disposed is more than the image formed by the scanning lens 22 having the negative optical power. Becomes smaller. That is, when forming a beam spot having the same convergence angle φ, the image width Dp of the reflected light beam Lp on the MEMS mirror 21 when using a lens having a positive optical power as the scanning lens 22 has a negative optical power. It is smaller than the image width Dn of the reflected light beam Ln when using the lens having it. Therefore, in order to reduce the mirror diameter of the MEMS mirror 21, it is disadvantageous to use the scanning lens 22 having a negative optical power.

When the MEMS mirror 21 increases in size, the moment of inertia increases and a problem occurs on the driving surface. As shown in FIG. 7, the mirror diameter of the MEMS mirror 21 depends on the angle α at which the incident light beam enters the MEMS mirror 21. Since the MEMS mirror 21 swings in the range of the deflection angle θ, the incident angle α is an angle α _min (minimum incident) when the angle formed by the optical axis of the incident light beam and the mirror surface of the MEMS mirror 21 is the maximum. Angle) to an angle α _max (maximum incident angle) at which the formed angle is minimum. The mirror diameter D ₁ of the MEMS mirror 21 required for the angle α _min is relatively small, but the mirror diameter D ₂ required for the angle α _max is relatively large and varies greatly depending on the maximum incident angle. .

Therefore, it is required to make the maximum incident angle (angle α _max ) as small as possible, but the optical path configuration that can minimize the maximum incident angle is a configuration in which an incident light beam is incident from the front of the MEMS mirror 21. is there. That is, it is a center incident optical system employed by the present embodiment. In this case, when the MEMS mirror 21 is at the center rotational position of the swing range, the incident angle α in the main scanning direction is zero.

  FIG. 8 is a schematic perspective view showing a relationship between an incident light beam directed to the MEMS mirror 104 and a reflected light beam (deflected light beam) reflected by the MEMS mirror 104 in the center incident optical system. In the center incident optical system, the incident light beam is incident on the MEMS mirror 104 at an angle in the sub-scanning direction (hereinafter referred to as oblique incidence) so that the incident light beam and the reflected light beam do not interfere with each other.

  When the incident light beam is obliquely incident on the MEMS mirror 104, a scanning curve is generated as shown in FIG. That is, a phenomenon occurs in which the scanning line in which the reflected light beam scans the scanning region is curved like a bow. When the scanning curve occurs, the incident position on the scanning lens 105a is shifted in the sub-scanning direction between the deflected light beam L1 (see FIG. 2) at the center of the scanning region and the deflected light beam L2 at the end of the scanning region. Become. Due to this deviation, distortion occurs in the electrostatic latent image drawn on the peripheral surface 14 a of the photosensitive drum 14.

  Furthermore, the imaging performance near the end of the scanning area is also reduced by the scanning curve. As shown in FIG. 9, the deflected light beams L1 and L2 are elliptical light beams having a major axis in the main scanning direction. In this case, the deflected light beam L2 at the end is incident on the scanning lens 105a in a state where the major axis is inclined with respect to the main scanning direction along the scanning line where the scanning curve is generated. On the other hand, the power direction of the conventional general scanning lens is set in accordance with the main scanning direction and the sub-scanning direction. Therefore, for the central deflected light beam L1, the major axis and minor axis direction of the light beam and the lens power direction coincide with each other, but for the deflected light beam L2 at the end, the major axis and minor axis direction of the light beam and the lens power direction. Does not match. This significantly reduces the imaging performance for the deflected light beam L2. 10A shows a spot image of the central deflected light beam L1, and FIG. 10B shows a spot image of the deflected light beam L2 at the end.

  9 can be suppressed as the angle formed by the optical axis of the reflected light beam from the MEMS mirror 104 to the peripheral surface 14a and the optical axis of the incident light beam is smaller. In the present embodiment, in order to suppress the bending amount e, the incident light beam is not directly incident on the MEMS mirror 104 from the second mirror 107 but is further incident on the first mirror 106 disposed in the vicinity of the MEMS mirror 104. Is reflected and then incident on the MEMS mirror 104. That is, by arranging the first mirror 106 on the opposite side of the second mirror 107 across the optical axis of the reflected light beam and in the closest position of the MEMS mirror 104, the optical axis of the reflected light beam and the optical axis of the incident light beam are changed. The angle formed is made as small as possible (see FIG. 4).

  However, even if the above-described device is applied, the scanning curve does not disappear. Therefore, in this embodiment, at least one surface of the scanning lens (in this embodiment, the first scanning lens 105a and the second scanning lens 105b) is a rotationally asymmetric refracting surface (toric surface) as described below.

  FIG. 11 is a diagram schematically showing one scanning lens 105 on the main scanning plane, and FIG. 12 is a diagram of the scanning lens 105 viewed from the direction of arrow F in FIG. Based on these drawings, the surface shape of the refractive surface R (toric surface) of the scanning lens 105 employed in the present embodiment will be described. In these drawings, the X direction is the sub-scanning direction, the Y direction is the main scanning direction, and the Z direction is the direction in which the optical axis O extends.

The toric surface is a surface having a semi-cylindrical shape, and the direction in which the cylinder extends is the generatrix direction, and the direction perpendicular to the generatrix is the subwire direction. The child line is a line indicating the curved surface of each cross section of the cylinder, and the line connecting the vertices of the child line is a bus line. Referring to FIG. 12, the refractive surface R is
(A) The bus P is curved in the sub-scanning direction,
(B) The shape of the sub-scanning section Rl parallel to the surface formed by the optical axis O and the sub-scanning axis X extending from the MEMS mirror 104 to the scanned surface is an ellipse.
(C) The extreme value of the ellipse in the optical axis O direction is on the bus P.
(D) The shape of the cross section Rs perpendicular to the projected generatrix Pa (projected generatrix Pa shown in FIG. 12) obtained by projecting the generatrix P onto a plane perpendicular to the optical axis O is an arc.
It has the following four geometric features. In the above item (D), the term “arc-shaped” is used because the radius of curvature changes depending on the scanning direction, so that it is not a complete arc. However, the optical performance of the toric surface can be handled as an arc.

The shape z of the refracting surface R in the sub-scanning section is defined as follows. When the sub-scanning axis is defined as the x direction, the main scanning axis is defined as the y direction, and the optical axis is defined as the z direction, The shape of the generatrix P projected onto the yz plane is f (y), the shape of the generatrix P projected onto the yx plane is g (y), and the section perpendicular to the projected generatrix is projected onto the plane perpendicular to the optical axis. when the radius of curvature rs, and rl curvature radius of the sub-scan section is expressed by the following equation (1).

  However, in the above formula (1), f (y), g (y), rs and rl are represented by the following formulas (2) to (5).

The main significance of the refractive surface R having the above-mentioned shape is the following two points.
(A); As shown in (D) above, the lens shape of the cross section Rs perpendicular to the curve obtained by projecting the generatrix P onto the yx plane is substantially equal to the arc of curvature radius rs. As a result, the minor axis of the elliptically deflected light beam incident on the refracting surface R coincides with the direction of the optical power of the refracting surface R. Therefore, it is possible to improve the imaging performance at the end of the scanning region.
(A); As shown in (B) above, since the shape of the sub-scanning section Rl is an ellipse, the sectional shape is symmetrical with the extreme value in the z-axis direction in the section as the apex. Moreover, as shown in (C) above, the extreme value of the ellipse is on the bus P. For this reason, the surface shape of the refracting surface R can be easily verified.

Even if the ellipse (B) and the arc (D) are interchanged in the shape of the refracting surface R, substantially the same effect can be obtained. That is, the refractive surface R is
(A) The bus P is curved in the sub-scanning direction,
(B) ′ The shape of the cross section Rs perpendicular to the projected generatrix Pa obtained by projecting the generatrix P onto a plane perpendicular to the optical axis O is an arc.
(C) ′ The extreme value of the arc in the direction of the optical axis O is on the bus P.
(D) ′ The shape of the sub-scanning cross section Rl parallel to the surface formed by the optical axis O and the sub-scanning axis X extending from the MEMS mirror 104 to the surface to be scanned is elliptical.
It is good also as what has the following four shape characteristics. In the above item (D) ′, the term “elliptical” is used because it is not a complete ellipse. However, the optical performance of the toric surface can be treated as an ellipse.

Such a refracting surface R also has the following two points.
(A) '; As shown in (D)' above, the shape of the sub-scanning cross section Rl is almost elliptical. As a result, the minor axis of the elliptically deflected light beam incident on the refracting surface R coincides with the direction of the optical power of the refracting surface R. Therefore, it is possible to improve the imaging performance at the end of the scanning region.
(A) '; As shown in (B)' above, since the lens shape of the section Rs perpendicular to the curve obtained by projecting the generatrix P onto the yx plane is an arc, the extrema in the z-axis direction in the section As a vertex, the cross-sectional shape is symmetric. Moreover, the extreme value of the arc is on the bus P, as indicated by (C) ′ above. For this reason, the surface shape of the refracting surface R can be easily verified.

  Subsequently, specific examples will be illustrated. FIG. 13 is an optical path diagram showing the optical system from the MEMS mirror 104 to the peripheral surface 14a of the photosensitive drum 14 which is a surface to be scanned, in a main scanning section. Note that the optical path from the light source to the MEMS mirror 104 is omitted in FIG. The first scanning lens 105a has a positive optical power with a convex meniscus shape toward the surface to be scanned, and the second scanning lens 105b has a negative optical surface having a concave surface on the light source side on the optical axis O. It is a lens with power. In the present embodiment, all four surfaces of the incident surface AR1 and the exit surface AR2 of the first scanning lens 105a and the entrance surface BR1 and the exit surface BR2 of the second scanning lens 105b are the above-described special refracting surfaces R. Yes.

  Table 1 shows construction data of the entrance surface AR1 and the exit surface AR2 of the first scanning lens 105a according to the present embodiment, and the entrance surface BR1 and the exit surface BR2 of the second scan lens 105b. The distance between the surfaces indicates the distance (mm) between the shaft upper surfaces on the optical axis O to the next surface. In Table 1, this distance is represented with a minus sign. The distance from the MEMS mirror 104 to the incident surface AR1 of the first scanning lens 105a is −20 mm.

  The configuration of the sub-scan section of the optical system according to the present embodiment is the same as the configuration shown in FIGS. The incident angle at which the incident light beam L0 enters the MEMS mirror 104 via the first mirror 106 is 7 degrees, and the opening angle between the incident light beam L0 and the reflected light beams (deflected light beams L1 and L2) is 14 degrees. The second scanning lens 105b is arranged with an offset (parallel eccentricity) of 0.6 mm in the sub-scanning direction with respect to the optical axis from the first scanning lens 105a to the peripheral surface 14a. That is, the incident surface BR1 (refractive surface) is offset with respect to the optical axis. In this embodiment, since the incident light beam L0 is obliquely incident on the MEMS mirror 104, a scanning curve is generated, but the scanning curve can be further suppressed by the offset.

  As another method of further suppressing the influence of scanning curvature, a rotation mechanism that rotates at least one of the first scanning lens 105a and the second scanning lens 105b around an axis parallel to the main scanning direction may be provided. When the scanning lens is rotated around an axis parallel to the main scanning direction, the shape of the generatrix viewed from the surface to be scanned changes, and the scanning curve also changes. Therefore, the scanning curve can be further suppressed by appropriately rotating at least one of the first scanning lens 105a and the second scanning lens 105b by the rotation mechanism.

  Or it is good also as a structure which provides the adjustment means which gives adjustment operation of a scanning curve with respect to the optical component arrange | positioned in the optical path from the semiconductor laser 101 to the surrounding surface 14a. The adjusting means is a means capable of deforming the scanning curve by applying a mechanical force to the optical component. For example, mechanical means for applying a force for physically bending the first scanning lens 105a and the second scanning lens 105b, and mechanical means capable of bending the first mirror 106 and the second mirror 107. Such adjustment means can further suppress the scanning curvature.

  The optical performance of the optical system (optical scanning device 11) according to the present embodiment described above is shown. FIG. 14 is a characteristic diagram showing the imaging state of the optical system. FIG. 14A is a position −110 mm from the center of the peripheral surface 14a in the main scanning direction (y direction), and FIG. The center in the main scanning direction (0 mm) and FIG. 14C show the spot images of the deflected light flux at a location +110 mm from the center in the main scanning direction. 14A to 14C, the imaging position is changed by 2 mm in the z-axis direction (the center figure is 0 mm, the left figure is -2 mm defocused, and the right figure is only +2 mm). Defocused) and a spot image is acquired. As is clear from FIGS. 14A to 14C, it can be seen that a good imaging state is obtained not only at the center of the scanning area but also at the end of the scanning area.

  FIG. 15 is a graph showing the scanning curve of the optical system (optical scanning device 11) of this example. As shown in FIG. 15, although the scanning curve is slightly generated, the height in the sub-scanning direction is 6 μm or less, and it was confirmed that there is no practical problem. FIG. 16 is a graph showing fluctuations in the beam pitch on the imaging surface (scanned surface) when a plurality of light sources are used. The fluctuation of the beam pitch is 0.2 mm or less, and it can be seen that the beam pitch can be sufficiently handled.

  According to the optical scanning device 11 according to the present embodiment described above, the optical scanning that can not only improve the imaging performance at the end of the scanning region but also can easily verify the surface shape of the scanning lens. An apparatus and an image forming apparatus can be provided. Therefore, the development cost of the scanning lens and the optical scanning device can be reduced.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 11 Optical scanning apparatus 14 Photosensitive drum (image carrier)
14a Circumferential surface (scanned surface)
101 Semiconductor laser (light source)
102 Collimator lens 103 Cylindrical lens 104 MEMS mirror (deflector)
105a First scanning lens 105b Second scanning lens 106 First mirror 107 Second mirror

Claims (6)

A light source that emits a luminous flux;
A deflector for deflecting the scanning by reflecting a light flux emitted from the front Symbol source,
A scanning lens including at least one rotationally asymmetric refracting surface, and imaging the deflection-scanned light beam on a surface to be scanned;
An angle in the sub-scanning direction is set with respect to the optical path of the reflected light beam so that the incident light beam incident on the deflecting body does not interfere with the reflected light beam deflected and scanned by the deflecting body and directed toward the scanned surface. An incident optical system for directing the incident light flux toward the deflecting body,
The refractive surface is
The bus connecting the child vertexes of the refractive surface is curved in the sub-scanning direction,
The shape of the sub-scanning section parallel to the surface formed by the optical axis extending from the light source to the scanned surface and the sub-scanning axis is an ellipse except for the center of the image height, and is an arc at the center of the image height,
In the optical scanning device , the extreme value of the ellipse in the optical axis direction is on the generatrix ,
In the case where the sub-scanning axis is defined as the x-direction, the main scanning axis is defined as the y-direction, and the optical axis is defined as the z-direction, the shape z of the refractive surface in the sub-scanning cross section is the shape obtained by projecting the generatrix onto the yz plane. ), G (y) is a shape obtained by projecting the generatrix onto the yx plane, rs is a radius of curvature of a cross section perpendicular to the projected generatrix where the generatrix is projected onto a plane perpendicular to the optical axis, and a radius of curvature of the sub-scanning cross section is An optical scanning device that is an ellipse represented by the following formula (1) when rl.
The optical scanning device according to claim 1 ,
The deflecting body has an axis serving as a swing center,
The optical scanning device, wherein the incident light beam, the reflected light beam, and the axis of the deflecting body are arranged on the same plane. The optical scanning device according to claim 1,
The optical scanning device, wherein the at least one refracting surface of the scanning lens is a refracting surface that is decentered parallel to the optical axis in the sub-scanning direction. The optical scanning device according to claim 1,
An optical scanning device further comprising a rotation mechanism for rotating the scanning lens about an axis parallel to the main scanning direction. The optical scanning device according to claim 1,
An optical scanning apparatus, further comprising: an adjustment unit that applies an adjustment operation of a scanning curve to an optical component disposed on an optical path from the light source to the surface to be scanned. An image carrier for carrying an electrostatic latent image;
The optical scanning device according to any one of claims 1 to 5 , which irradiates a light beam with the peripheral surface of the image carrier as the surface to be scanned.
An image forming apparatus comprising: