WO2006025532A1

WO2006025532A1 - Scan optical system, image formation device using the scan optical system, and image read device using the scan optical system

Info

Publication number: WO2006025532A1
Application number: PCT/JP2005/016128
Authority: WO
Inventors: Daizaburo Matsuki; Motonobu Yoshikawa; Michihiro Yamagata
Original assignee: Matsushita Electric Industrial Co., Ltd.
Priority date: 2004-09-03
Filing date: 2005-09-02
Publication date: 2006-03-09

Abstract

It is possible to provide a small-size scan optical system having little performance deterioration by temperature change at a reasonable cost. The scan optical system forms an image by spotting the beam emitted from a light source onto a surface to be scanned. The scan optical system includes: a deflector for performing main scan by reflecting the beam from the light source by a reflection surface so as to be deflected; a first image formation optical system for forming the beam from the light source into a linear image extending in the main scan direction in the vicinity of the reflection surface of the deflector; and a second image formation optical system formed by a single scan lens for again forming the beam of the linear image extending in the main scan direction in the vicinity of the reflection surface of the deflector again into a spot on the surface to be scanned. The first image formation optical system includes a positive power optical system for converting a diverging beam from the light source into a parallel or converging beam. The positive power optical system has a surface made from resin and having optical power by diffraction.

Description

Scanning optical system, image forming apparatus including scanning optical system, and image reading apparatus including scanning optical system

Technical field

TECHNICAL FIELD [0001] The present invention relates to a scanning optical system that scans a laser beam, and more specifically, an exposure optical system of an image forming apparatus such as a laser printer, a laser facsimile, or a digital copying machine, or a reading of an image reading apparatus such as a scanner. The present invention relates to a scanning optical system used in an optical system. The present invention also relates to an image forming apparatus and an image reading apparatus provided with a scanning optical system.

Background art

A scanning optical system is incorporated in an apparatus that reads and writes an image mainly by scanning a light beam. The scanning optical system is especially useful for image forming devices such as laser printers, laser facsimiles, and digital copiers! It is used in an exposure optical system for forming images. The scanning optical system is also used as a reading optical system of an image reading apparatus such as a scanner.

[0003] A conventional scanning optical system used in the image forming apparatus as described above includes a semiconductor laser, a polygon mirror, and a scanning lens. In recent years, since the high resolution of image forming apparatuses and image reading apparatuses has progressed, the spot diameter tends to become smaller, and the optical performance required for the scanning optical system has been remarkably improved. For this reason, in the scanning optical system, the influence of focus fluctuation due to changes in environmental temperature has become a major issue. Therefore, many technologies have been proposed for the purpose of suppressing focus fluctuations in conventional force scanning optical systems.

[0004] For example, Patent Document 1 discloses a scanning optical system using a diffractive surface. The scanning optical system described in Patent Document 1 is provided with at least two diffractive surfaces on the scanning lens, so that focus change (aberration fluctuation) does not occur even if environmental changes (especially temperature changes) occur! As! /

[0005] Further, Patent Document 2 discloses a scanning optical system using a correction lens. The scanning optical system described in Patent Document 2 includes an imaging optical system composed of a plastic lens and an image plane. And a correction lens composed of a single plastic lens arranged on the side, so that the variation in focus due to temperature changes is kept within the depth of focus.

Patent Document 1: JP-A-11 119133

Patent Document 2: Japanese Patent No. 3072146

Disclosure of the invention

Problems to be solved by the invention

However, since the optical element having a diffractive surface included in the scanning optical system described in Patent Document 1 has a complicated shape that is not rotationally symmetric, it is difficult to produce a mold for manufacturing. There was a problem that the machining accuracy of the mold was severe. In addition, the scanning optical system described in Patent Document 1 is difficult to manufacture a diffractive surface because the scanning lens is large. Furthermore, the scanning lens described in Patent Document 1 employs a method of forming a lattice layer by applying an ultraviolet curable resin on the surface as its manufacturing method. There was a problem.

[0007] On the other hand, the scanning optical system disclosed in Patent Document 2 has a problem that the correction lens is disposed close to the surface to be scanned and is thus increased in size, which makes it difficult to reduce the size and increases costs. In addition, the scanning optical system disclosed in Patent Document 2 has led to an increase in cost, which makes it difficult to arrange and adjust the correction lens during assembly.

An object of the present invention is to provide a small-sized and low-cost scanning optical system in which performance deterioration due to temperature change is small. Another object of the present invention is to provide an image forming apparatus and an image reading apparatus provided with such a scanning optical system.

Means for solving the problem

The above object is achieved by the following scanning optical system. In other words, the scanning optical system of the present invention is a scanning optical system that forms and scans a beam emitted from a light source as a spot on a surface to be scanned, and reflects and deflects the light source power beam by a reflecting surface. The first scanning optical system that forms a beam in the main scanning direction in the vicinity of the deflecting surface of the deflector and the main scanning in the vicinity of the reflecting surface of the polarizer A first imaging optical system comprising a single scanning lens for re-imaging a linearly-formed image beam extending in the direction as a spot on the surface to be scanned. But the divergent behavior from the light source A positive power optical system that converts the beam into a collimated beam or a convergent beam, the positive optical system having a surface made of a resin and having optical power by diffraction.

[0010] Preferably, the scanning lens is made of a resin. Preferably, the surface having optical power by the bending of the positive power optical system has a rotational axis symmetrical shape. Preferably, the positive optical system converts the divergent beam from the light source into a convergent beam, and the beam incident on the scanning lens has a convergence in the main scanning direction.

[0011] Preferably, the scanning lens has an anamorphic surface. The anamorphic surface is preferably a free-form surface, and is more preferably a free-form surface that is a curved non-circular line connecting the centers of curvature in the sub-scanning direction.

[0012] Preferably, the scanning lens has a cylindrical surface. The cylindrical surface may be formed on the scanned surface side or on the deflector side.

[0013] Preferably, when the magnification in the sub-scanning direction in the second imaging optical system is m, the following conditional expression (1):

1. 2 <m <4.5 (1)

Satisfied. The m is more preferably in the range represented by the following conditional expression.

1. 7 <m (1),

2. 2 <m (1) "

m <3.9 (1) "'

[0014] Preferably, when the distance from the reflecting surface of the polarizer to the surface to be scanned is L and the focal length of the scanning lens in the main scanning direction is f, the following conditional expression (2):

0. 5 <L / f <l. 2 (2)

Satisfied. The LZf is more preferably in the range represented by the following conditional expression.

0. 7 <L / f (2) '

L / f <l. 0 (2) "

Preferably, in the scanning lens, when the thickness of the lens is measured in a direction parallel to the optical axis, the thickness of the thinnest portion is t, and the thickness of the center of the scanning lens is T, the following conditional expression ( 3): 0.15 <t / T <0.3 (3)

Satisfied. The tZT is more preferably in the range represented by the following conditional expression. 0. 19 <t / T (3) '

t / T <0. 26 (3) "

The above object is achieved by the following image forming apparatus. That is, the image forming apparatus of the present invention is an image forming apparatus that forms an image based on an image signal, and a light source that controls a beam to be emitted based on an input image signal, and a light source that is emitted from the light source. An exposure optical system that forms an electrostatic latent image on an electrostatic latent image carrier based on a beam; and developing means that develops the electrostatic latent image formed by the exposure optical system, the exposure optical system comprising: A scanning optical system, wherein the scanning optical system reflects a beam of light source power by reflecting it on the reflecting surface and deflects it, and a beam from the light source is scanned near the reflecting surface of the deflector in the main scanning direction. The first image-forming optical system that forms an image in a linear line extending in the direction and the beam formed in a linear form extending in the main scanning direction in the vicinity of the reflecting surface of the polarizer are again connected as spots on the surface to be scanned. A second imaging optical system comprising a single scanning lens for imaging, The first imaging optical system includes a positive power optical system that converts a divergent beam from a light source into a collimated beam or a convergent beam. It has a surface with dynamic power.

The above object is achieved by the following image reading apparatus. That is, the image reading apparatus of the present invention is an image reading apparatus that reads a two-dimensional image and forms an electrical image signal, and includes a light source that controls a beam to be emitted based on an input image signal, and a light source A reading optical system for illuminating a two-dimensional image to be read by a beam emitted from the detector, and a detector for detecting a return beam of two-dimensional image power illuminated by the reading optical system, wherein the reading optical system is a scanning optical system The scanning optical system extends a beam from the light source in the main scanning direction near the reflecting surface of the deflector and a deflector that performs main scanning by reflecting and deflecting the beam of the light source by the reflecting surface. The first image-forming optical system that forms an image in a linear shape and the linearly-formed image that extends in the main scanning direction near the reflecting surface of the polarizer are re-imaged as spots on the surface to be scanned. Second consisting of a single scanning lens An image optical system, and a positive power optical system that converts the divergent beam from the first imaging optical system light source into a parallel beam or a convergent beam. As a material, it has a surface with optical power due to diffraction. The invention's effect

[0018] According to the present invention, it is possible to provide a compact and low-cost scanning optical system in which performance deterioration due to temperature change is small. Further, according to the present invention, it is possible to provide an image forming apparatus and an image reading apparatus including a small and low-cost scanning optical system in which performance deterioration due to temperature change is small.

Brief Description of Drawings

FIG. 1 is a configuration diagram of a scanning optical system according to a first embodiment.

FIG. 2 is an optical configuration diagram in the vicinity of a light source of the scanning optical system according to the first embodiment.

FIG. 3 is a sectional view of the second imaging optical system of the scanning optical system according to Embodiment 1 in the sub-scanning direction.

FIG. 4 is a cross-sectional view in the sub-scanning direction of a modification of the second imaging optical system of the scanning optical system according to Embodiment 1.

FIG. 5 is a configuration diagram of a scanning optical system according to the second embodiment.

FIG. 6 is a sectional view of the second imaging optical system of the scanning optical system according to Embodiment 2 in the sub-scanning direction.

FIG. 7 is a cross-sectional view showing a configuration of an image forming apparatus according to Embodiment 3.

FIG. 8 is an optical configuration diagram of a scanning optical system applied to the image reading apparatus according to the fourth embodiment.

FIG. 9 is an aberration diagram showing f Θ error on the surface to be scanned of Example 1.

FIG. 10 is an aberration diagram showing field curvature in the main scanning direction on the surface to be scanned of Example 1.

FIG. 11 is an aberration diagram showing field curvature in the sub-scanning direction on the surface to be scanned of Example 1.

FIG. 12 is an aberration diagram showing f Θ error on the scanned surface of Example 2.

FIG. 13 is an aberration diagram showing field curvature in the main scanning direction on the surface to be scanned of Example 2.

FIG. 14 is an aberration diagram showing field curvature in the sub-scanning direction on the surface to be scanned of Example 2. Explanation of symbols

1 Semiconductor laser

2 Collimating lens

3 Cylindrical lens

4 Polygon mirror

5 Rotating axis

6, 6 ', 16 scanning lens

7 Scanned surface

8 Cover glass

10 Reading surface

11 Noof mirror

12 Detector

13 Detection optics

20 Primary charger

21 Exposure optics

22 Developer

23 Transfer charger

24 cleaner

25 Fixing device

26 Paper cassette

27 Photosensitive drum

BEST MODE FOR CARRYING OUT THE INVENTION

(Embodiment 1)

FIG. 1 is a configuration diagram of a scanning optical system according to the first embodiment. The scanning optical system includes a collimating lens 2, a cylindrical lens 3, a polygon mirror 4, and a scanning lens 6. In the scanning optical system, the collimating lens 2 and the cylindrical lens 3 constitute a first imaging optical system, and the scanning lens 6 constitutes a second imaging optical system. The first imaging optical system and the second imaging optical system are different in V and displacement in the main scanning direction and the sub scanning direction orthogonal to the main scanning direction, respectively. This is an anamorphic optical system with optical power. In FIG. 1, the main scanning surface for performing the main scanning by the polygon mirror 4 and the plane including the optical axis of the scanning optical system are described so as to be parallel to the paper surface.

The collimator lens 2 converts a divergent laser beam emitted from the semiconductor laser 1 as a light source into a convergent laser beam. The collimating lens 2 is a lens having a rotational axis symmetrical shape with respect to the optical axis on both the light source side and the polygon mirror side. Further, the collimating lens 2 is made of resin, and a diffractive surface having optical power by diffraction is formed on the surface of the polygon mirror side. The operation of this diffractive surface will be described later. A cover glass 8 which is a parallel plate is disposed between the semiconductor laser 1 and the collimating lens 2.

FIG. 2 is an optical configuration diagram in the vicinity of the light source of the scanning optical system according to the first embodiment. In FIG. 2, the emission point of the semiconductor laser 1 corresponds to the symbol SO. Further, the cover glass 8 corresponds to the surface S1 and the surface S2. Furthermore, collimating lens 2 corresponds to surface S3, surface S4, and surface S5. The surface S4 represents a surface having optical power due to refraction of the collimating lens 2, and the surface S5 represents a surface having optical power due to diffraction of the collimating lens 2.

The cylindrical lens 3 is made of resin and has a flat surface on the light source side and a cylindrical surface that has optical power only in the sub-scanning direction and is formed on the polygon mirror side. The cylindrical lens 3 acts only in the sub-scanning direction of the converging laser beam emitted from the collimating lens 2 and condenses in a linear shape extending in the main scanning direction near the reflection surface of the polygon mirror 4.

The polygon mirror 4 is a rotating polygon mirror that is driven to rotate about the rotation axis 5. The polygon mirror 4 is driven to rotate about the rotation axis 5 to deflect the incident laser beam. The polygon mirror 4 is arranged such that the optical axis of the laser beam incident on the polygon mirror 4 and the scanning center of the laser beam reflected by the reflecting surface in the main scanning direction form a predetermined finite angle.

The scanning lens 6 forms an image of the laser beam deflected and scanned on the surface to be scanned 7 by reflection on the reflecting surface of the polygon mirror 4. The scanning lens 6 has an f Θ characteristic, and scans a laser beam deflected at a constant angular speed by the polygon mirror 4 on the surface to be scanned 7 at a constant speed. The scanning lens 6 is made of resin and has optical power only in the main scanning direction. A cylindrical surface formed on the polygon mirror side, and an anamorphic surface formed on the scanned surface side with optical power in the main scanning direction and the sub-scanning direction.

FIG. 3 is a sectional view of the second imaging optical system of the scanning optical system according to Embodiment 1 in the sub-scanning direction. In the second imaging optical system of the scanning optical system, as shown in FIG. 3, the reflection surface of the polygon mirror 4 and the surface to be scanned 7 are optically conjugate in the sub-scan section. This conjugate relationship realizes so-called surface tilt correction. Even if the reflection surface of the polygon mirror 4 tilts with respect to the rotation axis 5, the sub surface on the surface to be scanned 7 formed by the scanning lens 6 can be obtained. The imaging position in the scanning direction does not change.

In the above configuration, the divergent laser beam emitted from the semiconductor laser 1 enters the collimating lens 2 via the force bar glass 8 and is converted into a convergent laser beam. The laser beam is then imaged by the cylindrical lens 3 into a linear shape extending in the main scanning direction in the vicinity of the reflection surface of the polygon mirror 4. After that, the laser beam is incident on the scanning lens 6 as a divergent laser beam in the sub-scanning direction while maintaining the convergence in the main scanning direction, and is scanned at a constant speed by the scanning lens 6. And imaged as a spot.

Next, a compensation method for environmental temperature changes in the scanning optical system according to Embodiment 1 will be described. As described above, since the collimating lens 2, the cylindrical lens 3, and the scanning lens 6 are all made of resin, when the environmental temperature changes, the shape of the lens itself and the refractive index of the resin change. Due to this change, the optical power due to refraction of each lens also changes, and the spot position is formed at a position shifted from the scanned surface 7.

In the scanning optical system according to the first embodiment, the change in optical power caused by the change in ambient temperature is canceled by the surface having optical power due to diffraction formed in the collimator lens 2. In the scanning optical system according to the first embodiment, the surface having the optical power by diffraction is integrally formed on the refracting surface of the collimating lens 2 so that the shape of the lens itself when the environmental temperature changes is formed. The power change due to the refraction of the lens due to the change in the refractive index of the resin and the resin is offset by the power change due to diffraction!

[0031] In the scanning optical system according to the first embodiment, a collimating lens 2 having a small effective diameter is formed with a surface having optical power due to rotationally symmetric diffraction. This makes it easy to manufacture and assemble the diffractive surface, increasing costs. Do not invite. In addition, since the scanning optical system according to Embodiment 1 forms the collimating lens 2 by means of grease, the refracting surface and the diffractive surface can be formed simultaneously, and a high-precision optical surface can be easily formed. can do.

In addition, since the scanning optical system according to Embodiment 1 has a configuration in which convergent light is formed in the main scanning direction by the collimating lens 2 and is incident on the scanning lens 6, the focal distance of the scanning lens 6 The to-be-scanned surface 7 can be arranged at a shorter position.

[0033] In the first embodiment, it is desirable that the anamorphic surface of the scanning lens 6 is a free-form surface. It is desirable that By configuring the scanning lens in this way, it is possible to satisfactorily correct the fΘ error and the field curvature.

In Embodiment 1, it is desirable that the anamorphic surface of the scanning lens 6 introduces an odd-order term into the surface shape. By introducing odd-order terms, the curve connecting the curvature centers in the sub-scanning plane is asymmetric with respect to the optical axis, and the image plane curve in the sub-scanning direction that occurs asymmetrically can be highly corrected.

In the scanning optical system according to the first embodiment, since the scanning lens 6 is made of resin and has a cylindrical surface, it is easy to manufacture and assemble and adjust the lens including mold processing. This comes out.

Next, numerical conditions that should be satisfied by the scanning optical system according to Embodiment 1 will be described. Each condition described below is preferably satisfied at the same time, but is not limited to this. Each condition can have a corresponding effect by satisfying only the individual conditions.

The scanning optical system according to Embodiment 1 has the following conditional expression (1), where m is the magnification in the sub-scanning direction in the second imaging optical system:

1. 2 <m <4.5 (1)

Is preferably satisfied.

By satisfying conditional expression (1), it is possible to achieve a configuration in which the amount of jitter generated on the surface to be scanned is suppressed in a well-balanced manner due to the vibration of the scanning lens and polygon mirror. In other words, if the lower limit of conditional expression (1) is exceeded, the amount of jitter generated due to the tilting of the polygon mirror is reduced. Therefore, the pitch unevenness occurs between the scanning lines in the sub-scanning direction on the surface to be scanned, and a uniform image cannot be obtained. If the upper limit of conditional expression (1) is exceeded, the amount of jitter generated due to lens vibration increases, resulting in uneven pitch between scanning lines in the sub-scanning direction on the surface to be scanned. I can't get it.

[0039] It should be noted that when the m is in the range represented by any of the following conditional expressions, the above-described effect can be achieved more significantly.

1. 7 <m (1),

2. 2 <m (1) "

m <3.9 (1) "'

[0040] Further, the scanning optical system according to Embodiment 1 has the reflecting surface force of the polygon mirror as the distance to the surface to be scanned where the laser beam forms an image L, and the focal length of the scanning lens in the main scanning direction as f. When the following conditional expression (2):

0. 5 <L / f <l. 2 (2)

It is desirable to satisfy If the upper limit or the lower limit of conditional expression (2) is exceeded, it will be difficult to realize an appropriate scanning optical system.

By satisfying conditional expression (2), it is possible to realize a scanning optical system that is compact and lightweight and has good aberration correction. In other words, if the lower limit of conditional expression (2) is exceeded, the distance from the deflector to the surface to be scanned becomes very short and the size of the apparatus can be reduced, but the amount of field curvature in the main scanning direction and the amount of fΘ error Becomes larger. As a result, variations in the beam spot diameter and pitch unevenness in the main scanning direction occur on the surface to be scanned, so that a uniform image cannot be obtained. If the upper limit of conditional expression (2) is exceeded, the distance between the reflective surface force of the polygon mirror and the surface to be scanned becomes longer, and the apparatus becomes larger. Furthermore, if the upper limit of conditional expression (2) is exceeded, the amount of jitter generated on the scanned surface due to the vibration of the scanning lens and polygon mirror increases in proportion to the magnification in the sub-scanning direction with respect to the vibration amount. Reflective surface force of mirror As the distance to the surface to be driven becomes longer, it becomes difficult to maintain the same magnification in the sub-scanning direction. If the upper limit of conditional expression (2) is exceeded, the negative refractive power of the scanning lens must be increased in order to maintain the scanning lens magnification in the sub-scanning direction at the same value, and as a result, Tolerances during scanning lens mounting and caking are severe and undesirable. [0042] It should be noted that when the LZf is in a range represented by any of the following conditional expressions, the above-described effects can be achieved more remarkably.

0. 7 <L / f (2) '

L / f <l. 0 (2) "

In the scanning lens, when the thickness of the lens is measured in a direction parallel to the optical axis, and the thickness of the thinnest part is t, and the thickness of the center of the scanning lens is T, the following conditional expression (3):

0. 15 <t / T <0. 3 (3)

Is preferably satisfied. If the upper limit or the lower limit of conditional expression (3) is exceeded, the focal length of the scanning lens will be out of the appropriate range, which is not preferable.

[0044] It should be noted that when the tZT is in the range represented by the following conditional expression, the above effect can be achieved more remarkably.

0. 19 <t / T (3) '

t / T <0. 26 (3) "

Note that the scanning lens of the scanning optical system according to Embodiment 1 is configured to have a cylindrical surface having optical power only on the main scanning surface on the polygon mirror side, but is not limited thereto. FIG. 4 is a cross-sectional view in the sub-scanning direction of a modification of the second imaging optical system of the scanning optical system according to Embodiment 1. As shown in FIG. 4, a scanning lens 6 ′ having a cylindrical surface having an optical power only in the main scanning surface may be arranged on the surface to be scanned 7 side.

In addition, the collimator lens of the scanning optical system according to Embodiment 1 converts a divergent beam from a light source into a force-parallel beam that was used to convert the beam into a convergent beam. Also good. In this case, the first imaging optical system of the scanning optical system becomes large, but the sensitivity of the alignment of the polygonal mirror decreases with the cylindrical lens, so that the assembly and adjustment of the scanning optical system becomes easy. There is.

[0047] (Embodiment 2)

Next, the scanning optical system according to the second embodiment will be described with reference to FIGS. FIG. 5 is a configuration diagram of a scanning optical system according to the second embodiment. FIG. 6 is a sectional view of the second imaging optical system of the scanning optical system according to Embodiment 2 in the sub-scanning direction.

[0048] The scanning optical system according to Embodiment 2 has a schematic configuration similar to that of the scanning optical system according to Embodiment 1. Since they are equal, only the differences will be described. 5 and FIG. 6, the configurations with the same reference numerals are the same as those described in the first embodiment.

[0049] In the scanning optical system according to the second embodiment, the scanning optical system according to the first embodiment and the scanning lens 16 of the second imaging optical system are anamorphic on both sides of the polygon mirror side and the scanned surface side. It differs in that it has a surface. In the scanning optical system according to the second embodiment, since the scanning lens 16 has two anamorphic surfaces, aberration correction can be performed more favorably than the degree of freedom for aberration correction is large.

[0050] (Embodiment 3)

FIG. 7 is a cross-sectional view showing the configuration of the image forming apparatus according to the third embodiment. This image forming apparatus is a printer apparatus that forms a monochrome image based on a data signal input from an external camera. The image forming apparatus according to the third embodiment may be mounted with the scanning optical system according to the first embodiment as the exposure optical system 21.

[0051] The image forming apparatus according to Embodiment 3 is a known electrophotographic printer, and includes a primary charger 20, an exposure optical system 21, a developer 22, a transfer charger 23, a cleaner 24, and a fixing device. It includes a device 25, a paper feed cassette 26, and a photosensitive drum 27 (electrostatic latent image carrier). The exposure optical system 21 forms an electrostatic latent image, and print information is written on the photosensitive drum 27 as an electrostatic latent image. The surface of the photosensitive drum 27 is covered with a photosensitive member that changes its charge when irradiated with light. By the primary charger 20, electrostatic ions adhere to the surface of the photosensitive drum 27 and are charged. The charged photosensitive drum 27 is imaged by the developing unit 22 with the charged toner attached to the printing unit. The toner adhering to the photosensitive drum 27 is transferred onto the paper supplied from the paper feed cassette 26 by the transfer charger 23. The transferred toner is fixed on the paper by the fixing device 25. The remaining toner is removed by the cleaner 24.

[0052] Since the image forming apparatus according to the third embodiment uses the scanning optical system according to the first embodiment, it is easy to manufacture and can form a high-quality image. Note that the scanning optical system according to the second embodiment may be used instead of the scanning optical system according to the first embodiment.

[0053] (Embodiment 4)

FIG. 8 is an optical configuration diagram of a scanning optical system applied to the image reading apparatus according to the fourth embodiment. The image reading apparatus according to the fourth embodiment includes the scanning optical system described in the first embodiment. Is mounted as an image reading optical system. In FIG. 8, the scanning optical system of the image reading apparatus according to the fourth embodiment has the same schematic configuration as the scanning optical system according to the first embodiment, so only the differences will be described. Note that, in FIG. 8, configurations with the same reference numerals are the same as those described in the first embodiment.

The scanning optical system applied to the image reading apparatus according to the fourth embodiment includes a half mirror 11, a detector 12, and a detection optical system 13 in addition to the scanning optical system according to the first embodiment. It is equipped with. The half mirror 11 transmits the laser beam from the semiconductor laser 1 and illuminates the reading surface 10 which is a two-dimensional image to be read, and reflects the return light from the reading surface 10 toward the detection optical system 13. The detection optical system 13 returns the light to the detector 12 reflected by the half mirror.

[0055] Since the image reading apparatus according to the fourth embodiment uses the scanning optical system according to the first embodiment, it is easy to manufacture and can read a high-quality image. Note that the scanning optical system according to the second embodiment may be used instead of the scanning optical system according to the first embodiment.

In each of the above embodiments, the collimating lens is not limited to this force, which is a single lens having a rotational axis symmetry shape. For example, the collimating lens may be configured to include a plurality of rotationally symmetrical lenses, and any lens surface may have a surface having an optical power due to diffraction. Further, the collimating lens may include a prism or a mirror in the optical path. That is, instead of the collimating lens, a configuration that functions as a positive power optical system that converts a divergent beam of light source power into a convergent beam or a parallel beam can be used.

In each of the above embodiments, the laser beam is deflected by a polygon mirror. However, the present invention is not limited to this. For example, the deflector may be a galvanometer mirror. That is, a configuration that functions as a polarizer having a reflecting surface that deflects an incident beam can be used instead of a polygon mirror.

[0058] Note that the wavelength of the laser beam is not particularly limited, and a beam having any wavelength such as an infrared region, a visible red region, or a visible blue region is used.

Example

[0059] The scanning optical system according to Embodiment 1 and Embodiment 2 described above is described below. A physical numerical example is shown. Example 1 is a numerical example that embodies the first embodiment shown in FIGS. 1 to 3, and Example 2 is a numerical example that embodies the second embodiment shown in FIGS. 5 and 6. It is.

[0060] With respect to the shape of the lens surface of the scanning lens, the sub-scanning direction coordinate with the vertex of the surface as the origin is represented by X

(mm), the main scanning direction coordinate is y (mm), and the sag amount z (mm) of the apex force is defined by the following formula, where the directional force direction of the incident beam is positive.

+ ρ

+ ACDx ACEX ACFX y ¹ + AOG _xy ⁹

ΚΕλ: (1 + + χ

y ⁷ +

Where P (y) is the shape in the main scanning plane including the optical axis, RDy (mm) is the radius of curvature in the main scanning plane, K is the conic constant contributing to the main scanning direction, AD, AE, AF and AG Is an even-order constant contributing to the main scanning direction, AOD, AOE, AOF and AOG are odd-order constants, RDx is a function representing the radius of curvature in the sub-scanning plane at each y coordinate, and RDs (mm) is the center The radius of curvature in the sub-scanning plane, BC, BD, BE, BF, and BG are even-order constants, and BOC, BOD, BOE, BOF, and BOG are odd-order constants.

Further, in Example 1 and Example 2, the collimating lens and the cylindrical lens are aspherical surfaces, and the shapes thereof are expressed by the following equations.

s = —— ^Ch = + A4x.h ^A + A6x.h ⁶ + A8xh ^s + Al0x.h ^w

\ + ^ l-(\ + k) c ² h ²

However, the sag amount s (mm) is the distance from the tangential plane of the aspherical vertex of the point on the aspherical surface whose height from the optical axis is h, h is the height of the optical axis force, c is the aspherical vertex Curvature (cj = lZR, but the cylindrical lens is only in the sub-scanning direction), k is the conic constant, and An is the nth-order aspheric coefficient of the jth surface of the objective lens.

[0062] The phase grating formed on the diffractive surface of the surface S5 is expressed by the ultrahigh refractive index method (ultrahigh William C. Sweatt "Describing holographic optical elements as lenses (Journal of Optical Society of America, Vol. 6 i, No. 6, June 1977 Holographic Optical Element Ranges, Journal of Optical Society USA, 67th, 6th, June 1977)). A similar phase grating shape can also be expressed by a known phase function method.

[0063] Further, in each table, Si represents the surface number, ryi represents the radius of curvature in the main scanning plane, rxi represents the radius of curvature of the cross section in the sub-scanning direction, di represents the axial top surface spacing, and ni represents the refractive index of the optical material. ing. The design wavelength is 780 nm, the unit of f, L, ryi, rxi, di, RDy and RDs is (mm), and the unit of Θmax is (deg). The surface S8 corresponds to the reflective surface of the polygon mirror. In Tables 3 and 7, f is the focal length of the scanning lens, Θ max is the maximum deflection angle, and L is the distance between the deflection reflecting surface and the scanned surface.

[0064] (Example 1)

For the specific values of Example 1, Table 1 shows the parameters of the first imaging optical system, Table 2 shows the coefficients of the surfaces included in the first imaging optical system, and Table 3 shows the parameters of the second imaging optical system. Table 4 shows the parameters related to the shape of the scanning lens. First imaging optical system

^ 2

Second imaging optical system

FIGS. 9 to 11 are aberration diagrams on the surface to be scanned of Example 1. FIG. In each figure, the vertical axis represents the scanning width corresponding to the maximum deflection angle on the surface to be scanned. In each figure, the optical performance at normal temperature (environmental temperature of the scanning optical system corresponds to 25 ° C) is different from the optical performance at high temperature (environmental temperature of the scanning optical system corresponds to 55 ° C). Shown with lines. Figure 9 shows the f Θ error on the scanned surface, where the side where the f Θ characteristic is compressed is negative and the side where it is stretched is positive. Figure 10 shows the curvature of field in the main scanning direction on the surface to be scanned, where positive is when the imaging position is ahead of the ideal image plane position, and there is an imaging position behind the ideal image plane position. Negative. Fig. 11 shows the field curvature in the sub-scanning direction on the surface to be scanned. The case where the imaging position is in front of the ideal image plane position is positive, and the case where the imaging position is in the rear side of the ideal image plane position. Negative.

[0066] (Example 2)

Regarding specific numerical values of Example 2, the parameters of the first imaging optical system are shown in Table 5, the coefficients of the surfaces included in the first imaging optical system are shown in Table 6, the parameters of the second imaging optical system are shown in Table 7, Table 8 shows the parameters related to the shape of the scanning lens. First imaging optical system

Second imaging optical system

f = 155. 0, 2 0 max = 12O. 4, L = 126. 3

12 to 14 are aberration diagrams on the surface to be scanned of Example 2. FIG. In each figure, the vertical axis represents the scanning width corresponding to the maximum deflection angle on the surface to be scanned. In each figure, the optical performance at normal temperature (environmental temperature of the scanning optical system corresponds to 25 ° C) is different from the optical performance at high temperature (environmental temperature of the scanning optical system corresponds to 55 ° C). Shown with lines. Figure 12 shows the f Θ error on the scanned surface, where the f Θ characteristic is compressed on the negative side and the stretched side is positive. Fig. 13 shows the curvature of field in the main scanning direction on the surface to be scanned. The image forming position is positive when the image forming position is in front of the ideal image surface position, and the image forming position is behind the ideal image surface position. Some cases are negative. Fig. 14 shows the field curvature in the sub-scanning direction on the surface to be scanned. The case where the imaging position is in front of the ideal image plane position is positive, and the case where the imaging position is in the rear side of the ideal image plane position. Negative.

For Example 1 and Example 2, the main optical parameters and the corresponding values of the conditional expressions (1) and (2) are shown in Table 9.

[0069] It should be noted that the expression format of the expression representing the lens shape used in the examples is merely an example, and other expression formats may be used as long as the same shape can be expressed.

Industrial applicability

The present invention is suitable for image forming apparatuses such as laser printers, laser facsimiles, and digital copying machines, and image reading apparatuses such as scanners.

Claims

The scope of the claims

[I] A scanning optical system that images and scans a beam emitted from a light source as a spot on a surface to be scanned,

A deflector that performs main scanning by reflecting and deflecting a beam from a light source by a reflecting surface, and a beam from the light source forms an image in the vicinity of the reflecting surface of the deflector in a line extending in the main scanning direction. An image optical system;

A second imaging optical system comprising a single scanning lens that re-images a linearly focused beam extending in the main scanning direction near the reflecting surface of the polarizer as a spot on the surface to be scanned; e,

The first imaging optical system includes a positive power optical system that converts a divergent beam from a light source into a parallel beam or a converging beam, and the positive power optical system is made of a resin and is diffracted. A scanning optical system having a surface with optical power.

2. The scanning optical system according to claim 1, wherein the scanning lens is made of a resin.

[3] The scanning optical system according to [1], wherein the surface having optical power due to diffraction of the positive power optical system has a rotational axis symmetrical shape.

[4] The scanning according to claim 1, wherein the positive power optical system converts the divergent beam from the light source into a converging beam, and the beam incident on the scanning lens has convergence in the main scanning direction. Optical system.

5. The scanning optical system according to claim 1, wherein the scanning lens has an anamorphic surface.

6. The scanning optical system according to claim 5, wherein the anamorphic surface is a free-form surface.

[7] The scanning optical system according to [6], wherein the anamorphic surface is a free-form curved surface in which a line connecting the centers of curvature in the sub-scanning direction is a curved non-arc.

8. The scanning optical system according to claim 1, wherein the scanning lens has a cylindrical surface.

9. The scanning optical system according to claim 8, wherein the cylindrical surface is formed on the deflector side.

10. The scanning optical system according to claim 8, wherein the cylindrical surface is formed on the surface to be scanned.

[II] When the magnification in the sub-scanning direction in the second imaging optical system is m, the following conditional expression (1):

1. 2 <m <4.5 (1)

The scanning optical system according to claim 1, wherein:

[12] The following conditional expression (1) ':

1.7 <m (1),

The scanning optical system according to claim 11, wherein:

[13] The following conditional expression (1) '':

2.2 <m (1) "

The scanning optical system according to claim 11, wherein:

[14] The following conditional expression (1) '":

m <3.9 (1) "'

The scanning optical system according to claim 11, wherein:

[15] Reflector surface force of the polarizer If the distance to the surface to be scanned is L and the focal length of the scanning lens in the main scanning direction is f, the following conditional expression (2):

0.5 <L / f <l.2 (2)

The scanning optical system according to claim 1, wherein:

[16] The following conditional expression (2) ':

0.7 <L / f (2) '

The scanning optical system according to claim 15, wherein:

[17] The following conditional expression (2) '':

L / f <l.0 (2) "

The scanning optical system according to claim 15, wherein:

[18] In the scanning lens, the thickness of the lens is measured in the direction parallel to the optical axis, where t is the thickness of the thinnest part and T is the thickness of the center of the scanning lens, the following conditional expression (3):

0.15 <t / T <0.3 (3)

The scanning optical system according to claim 1, wherein:

[19] The following conditional expression (3) ':

0.19 <t / T (3) '

The scanning optical system according to claim 18, wherein:

[20] The following conditional expression (3) '':

t / T <0.26 (3) " The scanning optical system according to claim 18, wherein:

[21] An image forming apparatus for forming an image based on an image signal,

A light source in which a beam to be emitted is controlled based on an input image signal;

An exposure optical system for forming an electrostatic latent image on an electrostatic latent image carrier based on a beam emitted from a light source;

Development means for developing the electrostatic latent image formed by the exposure optical system,

The exposure optical system is a scanning optical system, and the scanning optical system is

A deflector that performs main scanning by reflecting and deflecting a beam of light source power by a reflecting surface and a beam of light source power form a linear image extending in the main scanning direction in the vicinity of the reflecting surface of the deflector. An image optical system;

A second imaging optical system comprising a single scanning lens that re-images a linearly focused beam extending in the main scanning direction near the reflecting surface of the polarizer as a spot on the surface to be scanned ,

The first imaging optical system includes a positive power optical system that converts a divergent beam from a light source into a parallel beam or a convergent beam. Having a surface with dynamic power,

Image forming apparatus.

[22] An image reading device for reading a two-dimensional image and forming an electrical image signal,

A reading optical system for illuminating a two-dimensional image to be read by a beam emitted from a light source; and a detector for detecting a return beam of the two-dimensional image force illuminated by the reading optical system. And the scanning optical system is

A deflector that performs main scanning by reflecting and deflecting a beam of light source power by a reflecting surface and a beam of light source power form a linear image extending in the main scanning direction in the vicinity of the reflecting surface of the deflector. An image optical system; A second imaging optical system consisting of a single scanning lens that re-images a linearly focused beam extending in the main scanning direction near the reflecting surface of the polarizer as a spot on the surface to be scanned ,

Image reading device.