JP4914563B2 - Optical scanning device - Google Patents

Description

The present invention relates to an optical scanning device that scans a surface to be scanned with a light beam . Specifically, the present invention relates to an optical scanning device used in a laser printer, a laser facsimile, a digital copying machine, and the like.

  The scanning optical system is used by being incorporated in an optical scanning device that reads an image or forms an image by scanning a light beam. Examples of the optical scanning device include a laser facsimile, a laser printer, and a digital copying machine.

  In a conventional optical scanning device, a semiconductor laser is used as a light source, a diverging beam (diverging light beam) emitted from the semiconductor laser light source is formed into a parallel beam (parallel light beam) by a collimator lens, etc., and then deflected by a deflector such as a polygon mirror. Thus, the beam spot is imaged on the surface to be scanned through the scanning lens having the fθ characteristic. Note that, by changing the deflection angle of the beam emitted from the deflector at a constant angular velocity within a predetermined range, the predetermined range on the scanning surface is scanned with the beam at a constant velocity. In addition, when the deflecting surface is tilted with respect to the rotation axis of the deflector, the surface tilt correction is performed by connecting the deflecting surface of the deflector and the surface to be scanned to a geometrically conjugate relationship. It was. In other words, if there is an inclination with respect to the rotation axis of the deflector, the image quality deteriorates because the position of the light beam that scans the surface to be scanned varies, but this is corrected by using a geometrically conjugate relationship. It was.

Here, the fθ characteristic is a property that satisfies Y = f · θ, where Y is the image height at which the parallel beam incident on the scanning lens having the focal length f at the angle of view θ forms an image on the surface to be scanned. means. In the following, the angle of view is referred to as a deflection angle. When the scanning lens has the fθ characteristic, the maximum deflection angle is θmax, the maximum image height is Ymax, and the focal length of the scanning lens is f, and the relationship of Ymax = f · θmax is satisfied. The maximum image height Ymax means a distance to the limit of the scanning width, and usually corresponds to a width of a desired paper size. The maximum deflection angle θmax denotes deflection angle definitive the limits of the scanning width.

  Conventionally, the scanning optical system has been downsized by shortening the distance from the deflector to the surface to be scanned by designing the maximum deflection angle θmax to be large and the focal length f of the scanning lens to be small.

  Many scanning optical systems are known in which the above-described scanning lens realizes constant-speed scanning and surface tilt correction on the surface to be scanned. For example, a two-group fθ lens system has been proposed that uses a cylindrical lens to correct curvature of field and has a surface tilt correction effect on the deflection surface (see Patent Document 1).

  In addition, a tilted surface composed of a first lens having a negative refractive power on the deflector side and having a negative refractive power as a whole and a second lens having a toric surface having a concave surface on the deflector side. A correction scanning optical system has been proposed (see Patent Document 2).

A surface tilt correction scanning optical system comprising a first lens having a cylindrical surface and a second lens having a toric surface, and comprising a lens having at least one optical axis-symmetric aspheric surface, An optical system for removing pitch unevenness in the direction has been proposed (see Patent Document 3).
JP 58-93021 A Japanese Patent No. 2716428 Japanese Patent Laid-Open No. 7-20398

  In the two-group fθ lens having the deflection surface tilt correction effect disclosed in Patent Document 1, the first lens must be disposed in the vicinity of the scanning surface in order to correct field curvature, and as a result. The first lens having a length approximately the same as the width of the desired paper size is required, leading to an increase in cost.

  In addition, in the surface tilt correction scanning optical system disclosed in Patent Document 2, a cylindrical surface and a toric surface are provided in different lenses to increase the degree of freedom of design. However, the fθ characteristic, field curvature, etc. In order to correct these various aberrations over a wide range, a glass lens having a high refractive index and a large thickness must be used, resulting in a problem that the price increases and the weight increases.

  Further, the surface tilt correction scanning optical system disclosed in Patent Document 3 uses a low-refractive-index and inexpensive resin lens to reduce the cost, but in order to maintain various aberrations over a wide range, it is thick. A thick lens has to be used, resulting in a problem of increased costs. Further, the surface tilt correction scanning optical system disclosed in Patent Document 3 is miniaturized by increasing the maximum deflection angle θmax in the scanning lens. This utilizes the fact that the focal length f of the lens is reduced by increasing the maximum deflection angle θmax under the condition that the maximum image height is constant, that is, the distance from the deflector to the surface to be scanned is shortened. . However, if the maximum deflection angle θmax is to be increased, there is a problem that the width of the deflector in the main scanning direction increases and the deflector becomes larger. Further, when a deflector having a small number of surfaces is used to suppress an increase in the size of the deflector, an expensive motor for rotating the deflector at a high speed is required, resulting in an increase in cost.

Therefore, the present invention realizes a reduction in size and weight in an optical scanning device , improves the accuracy of aberration correction, and reduces pitch unevenness in the sub-scanning direction caused by vibration of the scanning lens. Furthermore, the present invention realizes a configuration that is easy to process and assemble in manufacturing.

Further, according to the present invention, by mounting the optical scanning device of the present invention in an image reading apparatus, it is possible to reduce the size and weight and improve the accuracy of image reading. In the present invention, by mounting the optical scanning device of the present invention in an image forming apparatus, it is possible to reduce the size and weight and improve the accuracy of image formation.

In order to solve the above-described problems, an optical scanning device according to the present invention includes a light source that generates a diffused light beam, a light beam shaping lens that is provided on an optical path of the diffused light beam, and forms an image of the diffused light beam in a linear shape. A deflector provided on an optical path of the light beam from the light beam shaping lens, and having a deflection surface that forms an image of the light beam from the light beam shaping lens and deflects the light beam, and the deflection surface of the deflector A deflection control unit that controls the azimuth of the light beam, an fθ characteristic that is provided on the optical path of the light beam from the deflector and that is perpendicular to both the main scanning direction and the optical axis direction. And a scanning lens that focuses the light beam from the deflector on the surface to be scanned, and the light beam incident on the scanning lens from the deflector is converged within a cross section in the main scanning direction. That an optical scanning device is an optical beam, said scanning lens includes, in order from the side of said deflector, and a first lens and the second lens, and the first lens, on the side of the deflector, the A cylindrical surface including a straight line in the sub-scanning direction and having a negative refractive power in a cross-section in the sub-scanning direction perpendicular to the cross-section in the main scanning direction, and the second lens is opposite to the deflector side, The anamorphic surface has a positive refractive power in the cross section in the sub-scanning direction, and the anamorphic surface has a shape in which a line connecting the center of curvature in the cross section in the sub-scanning direction for each cross section in the sub-scanning direction is a non-arc. It is characterized by being .

According to the optical scanning device of the present invention, the first surface of the first lens is a cylindrical surface having negative refractive power in the cross section in the sub-scanning direction, and the fourth surface of the second lens is positive in the cross section in the sub-scanning direction. By using an anamorphic surface having a refractive power of 2 mm, it is possible to reduce the size and weight, improve the accuracy of aberration correction, and reduce pitch unevenness in the sub-scanning direction.

In addition, by mounting the optical scanning device of the present invention in the image forming apparatus, it is possible to achieve a reduction in size and weight, and to improve the accuracy of image reading.

In addition, by mounting the optical scanning device of the present invention in the image reading device, it is possible to realize a reduction in size and weight, and to improve the accuracy of image reading.

As described above, the optical scanning device according to the present invention includes a light source that generates a diffused light beam, a light beam forming lens that is provided on an optical path of the diffused light beam and forms an image of the diffused light beam linearly, and the light beam shaping A deflector provided on the optical path of the light beam from the lens and having the deflection surface for deflecting the light beam while the light beam from the light beam shaping lens is imaged, and controlling the orientation of the deflection surface of the deflector A deflection controller provided on the optical path of the luminous flux from the deflector and a surface tilt correction characteristic in the sub-scanning direction perpendicular to both the main scanning direction and the optical axis direction. And a scanning lens that focuses the light beam from the deflector onto a scanned surface, and the light beam incident on the scanning lens from the deflector is a light beam that converges in a cross section in the main scanning direction. A scanning device, the scanning lens includes, in order from the side of said deflector, and a first lens and the second lens, and the first lens, on the side of the deflector, the sub-scanning direction of the straight line Including a cylindrical surface having a negative refractive power in a sub-scanning direction cross section perpendicular to the main scanning direction cross-section, and the second lens is disposed on the side opposite to the deflector side in the sub-scanning direction cross-section. An anamorphic surface having a positive refractive power, and the anamorphic surface has a shape in which a line connecting the centers of curvature in the sub-scanning direction cross section for each sub-scanning direction cross section is a non-arc. To do . Here, the anamorphic surface implies a surface having a shape such as a free-form surface. The free-form surface means a curved surface that does not have a rotational symmetry axis.

  In this specification, the main scanning direction means a direction orthogonal to the optical axis of the scanning lens on a plane including the locus of the light beam scanned by controlling the deflecting surface of the deflector. The direction means a direction perpendicular to both the main scanning direction and the optical axis of the scanning lens. In this specification, the cross section in the main scanning direction means a cut surface by a plane including a line segment in the main scanning direction and a line segment in the optical axis direction, while the sub scanning direction cross section means the sub scanning direction. And a cut surface by a plane including the line segment in the optical axis direction of the scanning lens.

  With the above configuration, since the magnification in the sub-scanning direction can be reduced, pitch unevenness in the sub-scanning direction caused by the vibration of the scanning lens can be suppressed. That is, the tolerance for lens processing and lens mounting becomes loose, and processing and assembly of the scanning optical system can be easily performed. Further, since the light beam incident on the scanning lens is a convergent light beam, an effect equivalent to reducing the focal length f of the scanning lens while keeping the maximum deflection angle θmax in the scanning lens small can be exhibited. That is, since the scanning lens can be reduced in size without increasing the size of the deflector, the overall size of the scanning optical system can be reduced.

In the optical scanning device according to the present invention, the scanning optical system controls the azimuth of the deflecting surface of the deflector by the deflection control unit so that the light beam is emitted from the deflector in different azimuths at substantially equal angular velocities, and from the deflector to the substantially equiangular speed Thus, it is possible to adopt a configuration in which the surface to be scanned is scanned at a substantially constant speed in the main scanning direction via the scanning lens with the light beams emitted in different directions. With this configuration, for example, a polygon mirror (a polygonal columnar body having a deflecting surface that reflects the light beam on the side surface) is used as a deflector, and the polygon mirror is rotated at a substantially equal angular speed by a motor or the like, whereby the light beam is simply It can be deflected in a desired direction. The lens shapes of the first lens and the second lens constituting the scanning lens are designed so that the surface to be scanned can be scanned at a substantially constant speed in the main scanning direction with the light flux from the deflector.

In the optical scanning device according to the present invention, it is preferable that the anamorphic surface has a shape in which a line connecting the centers of curvature in any sub-scanning direction cross section for each sub-scanning direction cross section is a non-arc. This is because various aberrations can be further reduced, surface tilt correction can be performed more favorably, and the scanning optical system can be further downsized.

In the optical scanning device according to the present invention, the distance from the center point of the image on the deflection surface to the surface to be scanned with respect to the light beam propagating on the optical axis of the scanning lens is L, and the focal length of the cross section in the main scanning direction of the scanning lens Is a structure satisfying 0.1 <L / f <1.4 (conditional expression 1). This is because according to this configuration, further reduction in size and weight can be achieved, and various aberrations can be corrected more satisfactorily. Hereinafter, the reason why this configuration is preferable will be described in more detail with reference to FIGS. FIG. 14 is a graph showing the correlation between the distance L and the curvature of field with respect to the main scanning direction when the focal length f is fixed to 200 mm. FIG. 15 is a graph showing the correlation between the distance L and the fθ error amount when the focal length f is fixed to 200 mm. Hereinafter, for the sake of convenience, the distance from the center point of the image on the deflection surface to the scanned surface is also abbreviated as “distance from the deflector to the scanned surface”.

If the optical scanning device has a configuration satisfying L / f ≦ 0.1, the distance L from the deflector to the surface to be scanned can be made very short, so that the optical scanning device can be miniaturized. As the distance L to the surface decreases, the field curvature amount in the main scanning direction (main scanning direction field curvature amount) increases as shown in FIG. 14, and as shown in FIG. The amount of fθ error in the main scanning direction (main scanning direction fθ error amount) increases. As a result, variations in the beam spot diameter and pitch unevenness in the main scanning direction are likely to occur on the surface to be scanned, making it difficult to obtain a uniform image. On the other hand, if the optical scanning device is configured to satisfy 1.4 ≦ L / f, the distance L from the deflector to the surface to be scanned becomes relatively long, and it is difficult to downsize the scanning lens. Furthermore, the amount of jitter generated on the surface to be scanned by the vibration of the scanning lens or deflector (deflection surface) increases in proportion to the cross-sectional magnification in the sub-scanning direction with respect to the amount of vibration, but from the deflector to the surface to be scanned. As the distance L increases, it becomes difficult to set the sub-scanning direction cross-section magnifications to be the same. If the cross-section magnification in the sub-scanning direction is set to be the same, the negative refracting power on the cylindrical surface of the first lens must be increased, and the conditions for mounting tolerance of the scanning lens and lens processing become severe. .

  In the above description, the case where the focal length f of the scanning lens is 200 mm has been described with reference to FIGS. 14 and 15. The correlation between the curvature of field with respect to the scanning direction and the correlation between the distance L and the fθ error amount show the same tendency as in FIGS.

In order to reduce the size and weight of the optical scanning device and to correct aberrations satisfactorily, it is more preferable that the optical scanning device has a configuration satisfying 0.25 <L / f <1.2.

In the optical scanning device according to the present invention, the distance from the center point of the image on the deflection surface to the scanned surface with respect to the light beam propagating on the optical axis of the scanning lens is L, and the distance from the center point of the image on the deflection surface is A configuration satisfying 0.29 <s / L (conditional expression 2), where s is the distance to the two lenses, is preferable. This is because an optical scanning device that can be easily assembled and processed can be obtained according to this configuration. The distance from the center point of the image on the deflection surface to the second lens means the vertex (intersection with the optical axis) on the deflector side surface of the second lens from the center point of the image on the deflection surface. In the following, this distance s is also abbreviated as “distance from the deflector to the second lens” for convenience. Hereinafter, the reason why this configuration is preferable will be described in more detail with reference to FIGS. 16 and 17. FIG. 16 is a graph showing the correlation between the distance s from the deflector to the second lens and the shift amount of the image plane position in the sub-scanning direction when the distance L is fixed to 235 mm. FIG. 17 is a graph showing the correlation between the distance s from the deflector to the second lens and the shift amount of the scanning center with respect to the sub-scanning direction when the distance L is fixed to 235 mm.

If the optical scanning device is configured to satisfy s / L ≦ 0.29, as shown in FIG. 16, the shift amount of the image plane position with respect to the sub-scanning direction (image in the sub-scanning direction) caused by an attachment error or a processing error. (Surface position shift amount) becomes large, and as shown in FIG. 17, the deviation amount of the scanning center with respect to the sub scanning direction (scanning center deviation amount in the sub scanning direction) becomes large. As a result, variations in beam spot diameter and pitch unevenness between scanning lines in the sub-scanning direction are likely to occur on the surface to be scanned, making it difficult to obtain a uniform image. In order to correct variations in beam spot diameter and pitch irregularities between scanning lines in the sub-scanning direction, a strict tolerance is required for the scanning lens.

  In the above description, the case where the distance L is 235 mm has been described with reference to FIGS. 16 and 17. However, even if the focal length L of the scanning lens is another value, the image with respect to the distance s and the sub-scanning direction. The correlation between the shift amount of the surface position and the correlation between the distance s and the shift amount of the scanning center with respect to the sub-scanning direction show the same tendency as in FIGS.

In order to reduce the size and weight of the scanning lens and correct aberrations satisfactorily, it is more preferable that the optical scanning device has a configuration satisfying 0.3 <s / L <0.5.

In the optical scanning device according to the present invention, the first lens may have a flat surface on the side opposite to the deflector side. In the optical scanning device according to the present invention, the first lens may have a cylindrical surface having a refractive power only in the cross section in the main scanning direction on the side opposite to the deflector side. With these configurations, it becomes easier to process and attach the lens.

The optical scanning device according to the present invention may have a configuration in which a cylindrical surface having refractive power is provided on the deflector side only in the cross section in the main scanning direction. With this configuration, it is possible to achieve constant speed scanning and surface tilt correction while satisfactorily correcting various aberrations.

In the optical scanning device according to the present invention, the second lens may have a flat surface on the deflector side. With this configuration, it becomes easier to process and attach the lens.

In the optical scanning device according to the present invention, the second lens may have a spherical surface on the deflector side. In the optical scanning device according to the present invention, the second lens may have an aspheric surface on the deflector side. With these configurations, it is easy to process the lens, and it is possible to realize constant speed scanning and surface tilt correction while maintaining various aberrations relatively well.

In the optical scanning device according to the present invention, the second lens may have an anamorphic surface on the deflector side. Further, in the optical scanning device according to the present invention, the second lens has a curved surface on the deflector side in which the center of curvature in an arbitrary cross section in the sub-scanning direction and a line connecting each cross section in the sub-scanning direction is a non-arc. Is preferred. With these configurations, it is possible to achieve uniform scanning and surface tilt correction while satisfactorily correcting various aberrations.

In the optical scanning device according to the present invention, it is preferable that each of the first lens and the second lens is a resin lens. If it is this structure, the material cost of a 1st lens and a 2nd lens will become cheap compared with a glass lens, and an optical scanning device can be provided cheaply. Further, if resin lenses are used as the first lens and the second lens, the scanning lens can be reduced in weight compared to the case where a glass lens is used. The resin constituting the first lens and the resin constituting the second lens may be the same substance or different substances. In the optical scanning device according to the present invention, one of the first lens and the second lens may be a resin lens and the other may be a glass lens.

As described above, the image forming apparatus according to the present invention includes the light source, the light source control unit, the optical scanning device according to the present invention, and the image forming unit. With this configuration, by mounting the optical scanning device of the present invention, it is possible to reduce the size and weight, and to improve the accuracy of image formation. Here, the control of the generation of the light flux in the light source control unit means the control of the on / off of the light flux and the control of the on / off of the light flux and the intensity of the light flux.

In the image forming apparatus according to the present invention, the image forming unit includes an image formed on the surface of the photoconductor according to the photoconductor drum whose side surface is coated with the photoconductor whose charge distribution is changed by irradiation of the light beam, and the photoconductor charge distribution. A developing unit for adhering the display material, a transfer device for transferring the image display material adhering to the photosensitive member to an image display medium, and a charger for equalizing the charge distribution of the photosensitive member. It can be set as the structure which is the surface of a body. With this configuration, the surface of the photoconductor can be scanned with the light beam from the light source via the optical scanning device of the present invention, and the charge distribution on the surface of the photoconductor can be changed. Thus, an image corresponding to the image information can be formed on the image display medium using the image display material.

As described above, the image reading apparatus according to the present invention includes a light source, a light beam shaping lens, a deflector, a deflection control device, a first lens, and a second lens, and has an fθ characteristic in the main scanning direction. And a scanning lens having surface tilt correction characteristics in the sub-scanning direction. The surface on the deflector side of the first lens is a cylindrical surface having a negative refractive power in the cross section in the sub-scanning direction, and the surface opposite to the deflector side of the second lens (the side opposite to the first lens side) Is an anamorphic surface having a positive refractive power in the cross section in the sub-scanning direction. In addition, the light beam incident on the scanning lens from the deflector is a light beam that converges in the cross section in the main scanning direction. In addition, with this configuration, by mounting the optical scanning device of the present invention, it is possible to reduce the size and weight, and to improve the accuracy of reading an image.

  The image reading apparatus according to the present invention further includes a separator that is provided between the light source and the deflector and separates a part of the light beam reflected on the image plane as reading light, and the reading light separated by the separator. Is preferably received, and image information is generated in accordance with the reading light. With this configuration, since the reflected light on the image plane can be guided to the separator by the substantially same optical path as the light beam incident on the image plane, further miniaturization can be realized.

(Embodiment 1)
In the first embodiment, an embodiment of an optical scanning device according to the present invention will be described with reference to FIGS. FIG. 1 is a cross-sectional view of a cross section in the main scanning direction schematically showing the structure of the optical scanning device . FIG. 2 is a cross-sectional view of the cross section in the sub-scanning direction schematically showing the structure of the optical scanning device .

The optical scanning apparatus according to the first embodiment shown in FIGS. 1 and 2 includes a semiconductor laser (light source) 1, a light beam forming unit 9 including an axially symmetric lens 2 and a cylindrical lens 3, and a light beam from the semiconductor laser 1. A polygon lens (deflector) 4 that deflects the light, a drive motor (deflection control unit) (not shown) that controls the rotation of the polygon mirror 4, and a scanning lens comprising a first lens 6 and a second lens 7. and a 10.

  The axially symmetric lens 2 is a lens that is rotationally symmetric with respect to the optical axis. The axially symmetric lens 2 focuses the diffused light beam from the semiconductor laser 1 in both the main scanning direction section and the sub-scanning direction section.

  The cylindrical lens 3 is arranged so that its optical axis is included in a plane that includes the normal line of the deflection surface of the polygon mirror 4 and is parallel to the main scanning direction. In the cylindrical lens 3, the surface on the axially symmetric lens 2 side is a cylindrical surface having positive refractive power in the sub-scanning direction, and the surface on the polygon mirror 4 side is a flat surface. The cylindrical lens 3 forms the light beam from the axially symmetric lens 2 as a line image on the deflection surface of the polygon mirror 4. Note that the light beam from the cylindrical lens 3 is incident on the deflection surface of the polygon mirror 4 obliquely with respect to the main scanning direction.

  In FIG. 1, a mirror having eight side surfaces of a regular octagonal prism as deflection surfaces (light reflection surfaces) is shown as the polygon mirror 4. The drive motor 9 rotates the polygon mirror 4 around the rotation center axis 5 of the polygon mirror 4.

  The first lens 6 has a cylindrical surface having a negative refractive power in the cross section in the sub-scanning direction as a surface (first surface) on the polygon mirror 4 side, and a surface (second surface) on the second lens 7 side. As above, it has a cylindrical surface having refractive power only in the cross section in the main scanning direction.

  The second lens 7 has a cylindrical surface having a positive refractive power in the cross section in the main scanning direction as a surface (third surface) on the first lens 6 side, and a surface (fourth surface) on the scanned surface 8 side. As an anamorphic surface having positive refractive power in the main scanning direction and the sub-scanning direction.

  The first lens 6 and the second lens 7 constituting the scanning lens are arranged so that the deflection surface of the polygon mirror 4 serving as a deflector and the surface to be scanned 8 are geometrically optically conjugate with respect to the sub-scanning direction. In addition, the surface tilt of the polygon mirror 4 is corrected, and the field curvature and the fθ characteristic are corrected.

Here, the operation of the optical scanning device shown in FIG. 1 will be described. The diffused light beam from the semiconductor laser 1 is shaped into a focused light beam by the axisymmetric lens 2. The converged light beam from the axially symmetric lens 2 is further converged within the cross section in the sub-scanning direction by the cylindrical lens 3 and forms a linear image on the deflection surface of the polygon mirror 4. The light beam from the polygon mirror 4 rotating around the rotation center axis 5 by the drive motor 9 is deflected in a direction changing at a constant angular velocity within a predetermined deflection angle range, and the deflected light beam constitutes a scanning lens. An image is formed on the scanned surface 8 by the first lens 6 and the second lens 7. Thereby, the surface to be scanned can be scanned with the light beam imaged on the surface to be scanned 8.

(Embodiment 2)
In the second embodiment, an embodiment of an optical scanning device according to the present invention will be described with reference to FIGS. FIG. 3 is a cross-sectional view of the cross section in the main scanning direction schematically showing the structure of the optical scanning device . FIG. 4 is a sectional view of the section in the sub-scanning direction schematically showing the structure of the optical scanning device . The same members as those in the optical scanning device according to the first embodiment are denoted by the same reference numerals as those in FIGS. 1 and 2, and the description thereof is omitted.

In the optical scanning device according to the second embodiment shown in FIGS. 3 and 4, the surface on the first lens 6 side (third surface) is a flat surface, and is on the side opposite to the polygon mirror 4 side (to be scanned). The second lens 27 is an anamorphic surface having a positive refractive power in the main scanning direction section and the sub-scanning direction section. Note that the second lens 7 (see FIGS. 1 and 2) and the second lens 27 in the optical scanning device according to the first embodiment have different third surface shapes.

(Embodiment 3)
In Embodiment 3, an embodiment of an optical scanning device according to the present invention will be described with reference to FIGS. FIG. 5 is a cross-sectional view with respect to the main scanning direction schematically showing the structure of the optical scanning device . FIG. 6 is a cross-sectional view with respect to the sub-scanning direction schematically showing the structure of the optical scanning device . 5 and 6, the same members as those in the optical scanning device according to the first embodiment are denoted by the same reference numerals as those in FIGS. 1 and 2, and the description thereof is omitted.

In the optical scanning device according to the third embodiment shown in FIGS. 5 and 6, the surface on the first lens 6 side (third surface) is a spherical surface, and the side opposite to the polygon mirror 4 side (to be scanned). The second lens 37 which is an anamorphic surface having a positive refractive power in the main scanning direction section and the sub-scanning direction section is provided on the surface 8 side) (fourth surface). Each of the second lens 7 in the optical scanning device according to the first embodiment and the second lens 27 in the optical scanning device according to the second embodiment and the second lens 37 are on the third surface. The shape is different.

(Embodiment 4)
In the fourth embodiment, an embodiment of an image reading apparatus including the optical scanning device according to the present invention will be described with reference to FIG. FIG. 7 is a cross-sectional view of the cross section in the main scanning direction schematically showing the structure of the image reading apparatus. In FIG. 7, the same members as those in the optical scanning device according to the first embodiment are denoted by the same reference numerals as those in FIGS. 1 and 2, and the description thereof is omitted.

The image reading apparatus according to the fourth embodiment shown in FIG. 7 is a half provided between the optical scanning apparatus of the first embodiment and the axis target lens 2 and the cylindrical lens 3 in the optical scanning apparatus . A mirror (separator) 16, a light detector (light receiving unit) 17, and a detection optical system 18 provided between the half mirror 16 and the light detection device 17 are provided.

  The half mirror 16 transmits the light beam from the semiconductor laser 1 and separates part of the reflected light reflected by the reading surface (image surface) 18 in a direction different from that of the semiconductor laser 1 as reading light. The detection optical system guides the reading light separated by the half mirror 16 to the light detector 17 while focusing it on the light receiving surface. Further, the photodetector measures the intensity of the reading light and generates image information (image information signal) according to the measurement value.

Since the image reading apparatus according to the fourth embodiment uses the optical scanning device according to the present invention, the image reading apparatus is small in size, low in cost, and capable of reading an image with high resolution.

In the above description, the case where the optical scanning device of the first embodiment is used has been described, but the same effect can be obtained even if the optical scanning device of the second or third embodiment is used.

(Embodiment 5)
In the fifth embodiment, an embodiment of an image forming apparatus including the optical scanning device according to the present invention will be described with reference to FIG. FIG. 8 is a cross-sectional view schematically showing the structure of the image forming apparatus.

The image forming apparatus according to the fifth embodiment shown in FIG. 8 includes the optical scanning device (not shown), the light source (not shown), and the light source from the above-described first, second, or third embodiment. A scanning optical device 21 having a light source control unit (not shown) for controlling the generation of a light beam, a photosensitive drum 19, a primary charger 20, a developing device 22, a transfer charger 23, a fixing device 25, In this configuration, a cleaner 24 and a paper feed cassette 26 are provided.

  The surface of the photosensitive drum 19 is covered with a photosensitive member whose charge distribution changes when irradiated with light. The primary charger 20 uniformly charges the surface of the photoreceptor by causing electrostatic ions to uniformly adhere to the surface of the photoreceptor of the photosensitive drum 19. The developing device 22 adheres charged toner (image display material) to the photosensitive drum 19 in accordance with the charge distribution of the photosensitive member of the photosensitive drum 19. The transfer charger 23 transfers the charged toner attached to the photosensitive drum 19 onto a sheet (image display medium) supplied from the sheet feeding cassette 26. The cleaner 24 removes toner adhering to the surface of the photosensitive drum 19.

  Here, the operation of the image forming apparatus will be described. First, the photosensitive member of the photosensitive drum 19 is uniformly charged by the primary charger 20. Next, the surface of the uniformly charged photoreceptor is scanned with a light beam corresponding to image information from the light source by the scanning optical device 21. As a result, the charge distribution on the surface of the photoreceptor is changed according to the image information. Next, the developing unit 22 causes charged toner to adhere to the surface of the photoreceptor. Next, the charged toner attached to the surface of the photoconductor is transferred to the paper supplied from the paper feed cassette 26 by the transfer charger 23. Next, the charged toner transferred to the paper is fixed on the paper by the fixing device. As a result, the image information can be displayed (printed) on the paper. Next, the charged toner remaining on the photosensitive drum 19 is removed by the cleaner 24 after the charged toner is transferred onto the paper. By repeating the above process, the entire image information can be printed on a sheet.

Hereinafter, embodiments of the optical scanning device according to the present invention will be described. In each of the embodiments described below, the shape of the first lens 6 constituting the scanning lens on the polygon mirror 4 side is a cylindrical surface having a negative refractive power only in the sub-scanning cross section, and the first lens 6 constituting the scanning lens constitutes the scanning lens. The shape on the scanning surface side of the two lenses 7 is a non-arc curve in which a line connecting the center of curvature of an arbitrary sub-scanning direction section for each sub-scanning direction section is curved.

  The sag amount z (mm) from the vertex at the position of the main scanning direction coordinate y (mm) is assumed to be positive when the direction of the incident light beam is positive, with the vertex of the surface (intersection of each surface and the optical axis) as the origin. The amount z is expressed by the following formula 1. The function P (y) in Equation 1 is expressed by Equation 2 below. In addition, RDx in Equation 1 is expressed by Equation 3.

Here, P (y) is a function representing a non-arc shape in the cross section in the main scanning direction including the optical axis, RDy (mm) is a radius of curvature in the main scanning direction, and K is a conic constant contributing to the main scanning direction. Each of AD, AE, AF, and AG is an even-order constant that contributes to the main scanning direction, and each of AOD, AOE, AOF, and AOG is an odd-order constant that contributes to the main scanning direction. RDx is a function representing the radius of curvature in the sub-scanning direction at each y coordinate, RDs (mm) is the center radius of curvature in the sub-scanning direction, and BC, BD, BE, BF, and BG are even-order constants. Yes, each of BOC, BOD, BOE, BOF and BOG is an odd order constant. By introducing odd-order terms, the curve connecting the centers of curvature of the cross section in the sub-scanning direction can be asymmetric with respect to the optical axis. This makes it possible to highly correct the asymmetrical field curvature in the sub-scanning direction.

  f is the focal length of the scanning lens, θmax is the maximum deflection angle, L is the distance between the deflecting reflecting surface and the scanned surface, s is the distance from the deflecting reflecting surface to the second lens 7, and d0 is from the deflecting reflecting surface. The distance to the first lens 6, i is the surface number, ryi is the radius of curvature of the cross section in the main scanning direction, rxi is the radius of curvature of the cross section in the sub-scanning direction, di is the spacing between the upper surfaces of the axes, and ni is the refractive index of the glass material. Represents. Each unit of f, L, s, d0, ryi, rxi, di, RDy, and RDs is (mm), and the unit of θmax is (deg). The design wavelength is 780 nm.

In Example 1, an example of a scanning lens in the optical scanning device according to Embodiment 1 will be described. Specifications for specifying the scanning lens according to Example 1 were set as follows.

f = 205.58
2θmax = 86.9
L = 182.47
s = 55
d0 = 30.00
Surface number i ryi rxi di ni
1 ∞ -34.48 4.90 1.526
2 -518.10 ∞ 20.10
3 249.80 ∞ 16.28 1.526
4 -275.36 -19.17
The coefficients in the above formulas 1 to 3 are collectively shown in Table 1 below.

  The values necessary for evaluating the conditional expression 1 and the conditional expression 2 are summarized in Table 6 at the end together with the values for the scanning lenses according to Examples 2 to 5 described below. As shown in Table 6, the scanning lens of Example 1 satisfies the above conditional expressions 1 and 2.

  FIGS. 9A and 9B show the correlation between the image height and the fθ error and the correlation between the image height and the curvature of field for the scanning lens of Example 1, respectively. In FIG. 9B, the solid line represents the field curvature in the main scanning direction, and the broken line represents the field curvature in the sub-scanning direction. The same applies to FIGS. 10 (b), 11 (b), 12 (b) and 13 (b) referred to in the second to fifth embodiments.

In Example 2, an example of a scanning lens in the optical scanning device according to Embodiment 1 will be described. Specifications for specifying the scanning lens according to Example 2 were set as follows.

f = 165.8
2θmax = 86.9
L = 198.22
s = 65
d0 = 40.62
Surface number i ryi rxi di ni
1 ∞ -43.48 9.93 1.526
2 -155.78 ∞ 14.44
3 -999.00 ∞ 13.68 1.526
4 -221.00 -20.26
The coefficients in the above formulas 1 to 3 are collectively shown in Table 2 below.

  The values necessary for evaluating the conditional expression 1 and the conditional expression 2 are shown in Table 6 at the end. As shown in Table 6, the scanning lens of Example 2 satisfies the above conditional expressions 1 and 2.

  FIGS. 10A and 10B show the correlation between the image height and the fθ error and the correlation between the image height and the curvature of field for the scanning lens of Example 2, respectively.

In Example 3, an example of a scanning lens in the optical scanning device according to Embodiment 1 will be described. Specifications for specifying the scanning lens according to Example 1 were set as follows.

f = 812.94
2θmax = 63.0
L = 216.95
s = 80
d0 = 45.00
Surface number i ryi rxi di ni
1 ∞ -220.0 3.26 1.526
2 -4139.60 ∞ 31.74
3 430.81 ∞ 10.65 1.526
4 -3822.52 -25.94
The coefficients in the above formulas 1 to 3 are collectively shown in Table 1 below.

  The values necessary for evaluating the conditional expression 1 and the conditional expression 2 are shown in Table 6 at the end. As shown in Table 6, the scanning lens of Example 3 satisfies the above conditional expressions 1 and 2.

  FIGS. 11A and 11B show the correlation between the image height and the fθ error and the correlation between the image height and the curvature of field with respect to the scanning lens of Example 3, respectively.

In Example 4, an example of a scanning lens in the optical scanning device according to Embodiment 2 will be described. Specifications for specifying the scanning lens according to Example 4 were set as follows.

f = 167.0
2θmax = 86.9
L = 193.74
s = 65
d0 = 37.49
Surface number i ryi rxi di ni
1 ∞ -50.00 9.85 1.526
2 -128.72 ∞ 17.66
3 ∞ ∞ 11.87 1.526
4 -244.27 -20.49
The coefficients in the above formulas 1 to 3 are collectively shown in Table 4 below.

  The values necessary for evaluating the conditional expression 1 and the conditional expression 2 are shown in Table 6 at the end. As shown in Table 6, the scanning lens of Example 4 satisfies the above conditional expressions 1 and 2.

  FIGS. 12A and 12B show the correlation between the image height and the fθ error and the correlation between the image height and the curvature of field with respect to the scanning lens of the fourth embodiment, respectively. In FIG. 12B, the field curvature (broken line) in the sub-scanning direction is displayed as being doubled (enlarged in the horizontal axis direction).

In Example 5, an example of a scanning lens in the optical scanning device according to Embodiment 3 will be described. Specifications for specifying the scanning lens according to Example 5 were set as follows.

f = 167.0
2θmax = 86.9
L = 193.24
s = 65
d0 = 38.05
Surface number i ryi rxi di ni
1 ∞ -50.00 10.36 1.526
2 -121.73 ∞ 16.59
3 -3274.28 -3274.28 11.09 1.526
4 304.14 20.38
The coefficients in the above formulas 1 to 3 are collectively shown in Table 5 below.

  The values necessary for evaluating the conditional expression 1 and the conditional expression 2 are shown in Table 6 at the end. As shown in Table 6, the scanning lens of Example 5 satisfies the above conditional expressions 1 and 2.

  FIGS. 13A and 13B show the correlation between the image height and the fθ error and the correlation between the image height and the curvature of field with respect to the scanning lens of the fifth embodiment, respectively. In FIG. 13B, the curvature of field (broken line) in the sub-scanning direction is displayed as being doubled (enlarged in the horizontal axis direction).

INDUSTRIAL APPLICABILITY The present invention can be used to reduce the size and weight of an optical scanning device , improve the accuracy of aberration correction, and reduce pitch unevenness in the sub-scanning direction caused by the vibration of a scanning lens. Moreover, it can utilize in order to perform simply the process and assembly in manufacture of an optical scanning device .

  In addition, the present invention can be used in an image reading apparatus in order to reduce the size and weight and improve the accuracy of image reading.

In addition, the present invention can be used in an image forming apparatus to realize a reduction in size and weight and to improve image forming accuracy by mounting the optical scanning device of the present invention.

FIG. 1 is a cross-sectional view of the cross section in the main scanning direction schematically showing the structure of the optical scanning device according to the first embodiment. FIG. 2 is a cross-sectional view in the sub-scanning direction schematically showing the structure of the optical scanning device according to the first embodiment. FIG. 3 is a cross-sectional view of the cross section in the main scanning direction schematically showing the structure of the optical scanning device according to the second embodiment. FIG. 4 is a cross-sectional view in the sub-scanning direction schematically showing the structure of the optical scanning device according to the second embodiment. FIG. 5 is a cross-sectional view of the cross section in the main scanning direction schematically showing the structure of the optical scanning device according to the third embodiment. FIG. 6 is a cross-sectional view in the sub-scanning direction schematically illustrating the structure of the optical scanning device according to the third embodiment. FIG. 7 is a cross-sectional view of the cross section in the main scanning direction schematically showing the structure of the image reading apparatus according to the fourth embodiment. FIG. 8 is a cross-sectional view schematically showing the structure of the image forming apparatus according to the fifth embodiment. FIGS. 9A and 9B are graphs showing the correlation between the image height and the fθ error and the correlation between the image height and the curvature of field in the optical scanning device according to the first embodiment. FIGS. 10A and 10B are graphs showing the correlation between the image height and the fθ error and the correlation between the image height and the curvature of field in the optical scanning device according to the second embodiment. FIGS. 11A and 11B are graphs showing the correlation between the image height and the fθ error and the correlation between the image height and the curvature of field in the optical scanning device according to the third embodiment. 12A and 12B are graphs showing the correlation between the image height and the fθ error and the correlation between the image height and the curvature of field in the optical scanning device according to the fourth embodiment. FIGS. 13A and 13B are graphs showing the correlation between the image height and the fθ error and the correlation between the image height and the curvature of field in the optical scanning device according to the fifth embodiment. FIG. 14 is a graph showing the correlation between the distance L from the deflector to the surface to be scanned and the amount of field curvature in the main scanning direction. FIG. 15 is a graph showing the correlation between the distance L from the deflector to the surface to be scanned and the fθ error amount. FIG. 16 is a graph showing the correlation between the distance S from the deflector to the second lens and the shift amount of the image plane position in the sub-scanning direction. FIG. 17 is a graph showing the correlation between the distance S from the deflector to the second lens and the amount of deviation of the scanning center in the sub-scanning direction.

Explanation of symbols

1 Semiconductor laser (light source)
2-axis target lens 3 cylindrical lens 4 polygon mirror (deflector)
5 Rotation Center Axis 6 First Lens 7, 27, 37 Second Lens 8 Scanned Surface 9 Luminous Beam Forming Lens 10 Scanning Lens 16 Half Mirror (Separator)
17 Photodetector (receiver)
18 Detection optical system 19 Photosensitive drum 20 Primary charger (charger)
21 Optical scanning device 22 Developer 23 Transfer charger (transfer device)
24 Cleaner 25 Fixing device 26 Paper cassette

Claims (5)

A light source that generates a diffused light beam, a light beam forming lens that is provided on an optical path of the diffused light beam and forms an image of the diffused light beam in a line, and a light source that is provided on the optical path of the light beam from the light beam forming lens The light beam from the molded lens is imaged and has a deflector that deflects the light beam, a deflection control unit that controls the orientation of the deflecting surface of the deflector, and the light beam from the deflector. An fθ characteristic in the main scanning direction and a surface tilt correction characteristic in the sub-scanning direction perpendicular to both the main scanning direction and the optical axis direction, and the light flux from the deflector A scanning lens for focusing on the optical scanning device, wherein the light beam incident on the scanning lens from the deflector is a light beam that converges in a cross section in the main scanning direction,
The scanning lens includes, in order from the deflector side, a first lens and a second lens, and the first lens includes a straight line in the sub-scanning direction on the deflector side, and the main scanning A cylindrical surface having a negative refractive power in a sub-scanning direction cross section perpendicular to the direction cross section, and the second lens has a positive refractive power in the sub-scanning direction cross section on a side opposite to the deflector side. An anamorphic surface having an anamorphic surface, and the anamorphic surface has a shape in which a line connecting the centers of curvature in the cross section in the sub-scanning direction for each cross section in the sub-scanning direction is a non-arc . Let L be the distance from the center point of the image on the deflection surface to the surface to be scanned with respect to the light beam propagating on the optical axis of the scanning lens, and let f be the focal length of the cross section in the main scanning direction of the scanning lens. ,
0.1 <L / f <1.4
The optical scanning device according to claim 1, wherein: The distance from the center point of the image on the deflection surface to the scanned surface with respect to the light beam propagating on the optical axis of the scanning lens is L, and the distance from the center point on the deflection surface to the second lens is L. Let s be the distance
The optical scanning device according to claim 1, wherein 0.29 <s / L is satisfied.   2. The optical scanning device according to claim 1, wherein the first lens has a cylindrical surface having a refractive power only in a plane or in a cross section in the main scanning direction, on a side opposite to the deflector side.   The second lens has, on the deflector side, a plane, a cylindrical surface having a refractive power only in the cross section in the main scanning direction, a spherical surface, an aspherical surface, an anamorphic surface, or a center of curvature in the sub scanning direction cross section in the sub scanning direction. The optical scanning device according to claim 1, wherein the line connected for each cross section has one of curved surfaces that are non-circular.

Images