JPH11237569A - Aligner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an aligner for scanning plural beams with less degradation of image quality due to deviations in image formation positions between optical beams, and with reduced deterioration in a resolution or fluctuation in a beam diameter or the like by satisfying a specified condition between the distance of a deflection point and an image surface and a paraxial focus distance. SOLUTION: This aligner 1 is provided with a semiconductor laser element 3 for emitting light beam (laser beams) and a deflection device 7 for deflecting (scanning) the laser beam emitted from the semiconductor laser element 3 to image surface S arranged at a prescribed position. F/L<=0.25 is satisfied. In this device, relation F/L<=0.25 is satisfied where L is the distance between a deflection point of deflecting light by a rotary polygon mirror and an image surface S at the time of passing through the center of the effective area of a prescribed image surface S and F is an the paraxial focus distance of the second direction of a vertical direction to the first direction of a lens near the intersection of the light beam passing through the center of the effective area of the prescribed image surface S.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention is used for a monochromatic high-speed laser printer, a monochromatic high-speed digital copier, and the like.
The present invention relates to a multi-beam exposure apparatus that scans a plurality of light beams.

[0002]

2. Description of the Related Art There is a proposal to increase the exposure speed, that is, the image forming speed, by exposing image data of the same color in parallel with a plurality of light beams. According to this method, even when the number of rotations of the reflection surface of the deflecting device is increased, the number of rotations can be reduced to 1 / number of light beams. Therefore,
The cost of the motor and the image frequency can be reduced.

The above-described exposure apparatus includes a plurality of semiconductor laser elements, a first lens group for narrowing a cross-sectional beam diameter of a light beam emitted from each semiconductor laser element to a predetermined size and shape, and a first lens group. A plurality of light beams narrowed down to a predetermined size and shape by the laser beam are continuously formed in a direction (ie, a scanning direction) orthogonal to a direction (an auxiliary scanning direction) in which a recording medium holding an image formed by the light beams is transported (an auxiliary scanning direction). Deflecting device that deflects or scans by reflecting the light beam, the light beam scanned by the deflecting device is set at a predetermined position on the recording medium so that the amount of rotation of the deflecting device and the distance scanned by the deflecting device are proportional. It has a second lens group that forms an image at a speed. Note that so far, at least two fθ lenses have been used as the second lens group.

[0004]

In the above-described exposure apparatus, the number of lenses in the second lens group is two or more. Therefore, when a plurality of light beams are incident, the light beam in the auxiliary scanning direction is not used. It is necessary to accurately maintain the position where each light beam passes through each lens. For this reason, high accuracy is required as the shape and processing accuracy of the lens and the accuracy of assembling the lens, and there is a problem that the cost increases as a result.

[0005] Further, even if the cost problem is ignored,
In an exposure apparatus currently in practical use, for example, there is a problem in that the image density of a halftone image becomes non-uniform due to a variation in the beam diameter in the scanning direction, and jitter occurs in the auxiliary scanning direction to deteriorate the image quality.

SUMMARY OF THE INVENTION An object of the present invention is to provide an exposure apparatus which scans a plurality of beams with little deterioration in image quality due to a shift of an imaging position between light beams, a decrease in resolution, or a change in beam diameter.

[0007]

SUMMARY OF THE INVENTION The present invention has been made based on the above-mentioned problems, and comprises a light emitting source and a rotary polygon mirror for deflecting light from the light emitting source in a first direction at a substantially constant angular velocity. A deflector including, disposed between the deflector and the light-emitting source, pre-deflection optical means for guiding the light from the light source to the rotating polygon mirror of the deflector while having predetermined characteristics,
An exposure having only one lens that forms an image of light deflected by the rotating polygonal mirror at a constant speed such that a rotation amount of the rotating polygonal mirror and a distance in the first direction are proportional to a predetermined image plane; In the apparatus, the lens is formed such that any one surface except a light incident surface and a light exit surface is formed as a symmetric surface in which a line of intersection intersecting each of the light incident surface and the light exit surface is asymmetric, and The distance between the deflection point where the light is deflected by the mirror and the image plane when passing through the center of the effective area of the predetermined image plane is L, in the vicinity where the ray passing through the center of the effective area of the predetermined image plane intersects the lens. When the paraxial focal length of the second lens in the second direction perpendicular to the first direction is F, the following condition is satisfied: F / L ≦ 0.25. is there.

The present invention also provides a light emitting source, a deflector including a rotary polygon mirror for deflecting light from the light emitting source at a substantially constant angular velocity in a first direction, and between the deflector and the light emitting source. The pre-deflection optical means for guiding the light from the light source to the rotating polygon mirror of the deflector while giving predetermined characteristics to the light from the light source, and the light deflected by the rotating polygon mirror to a predetermined image plane, A single lens that forms an image at a constant speed so that the rotation amount of the rotating polygon mirror is proportional to the distance in the first direction,
In the exposure apparatus having the lens, any one surface except the light incident surface and the light exit surface is formed as a symmetric surface in which an intersection line intersecting with each of the light incident surface and the light exit surface is asymmetric. The distance between the deflection point at which the light is deflected by the rotating polygon mirror and the image plane when passing through the center of the effective area of the predetermined image plane is L, and the light passing through the center of the effective area of the predetermined image plane passes through the lens. Provided is an exposure apparatus, wherein 0.35 ≦ L ₃ /L≦0.65 is satisfied when a distance between an emission point and the predetermined image plane is L _3. .

Further, the present invention provides a light emitting source, a deflector including a rotary polygon mirror for deflecting light from the light emitting source in a first direction at a substantially constant angular velocity, and between the deflector and the light emitting source. And a pre-deflection optical means for guiding the light from the light source to the rotating polygon mirror of the deflector while giving the light a predetermined characteristic, and rotating the light deflected by the rotating polygon mirror to a predetermined image plane. In an exposure apparatus having only one lens that forms an image at a constant speed such that the rotation amount of the polygon mirror and the distance in the first direction are proportional, the lens excludes a light incident surface and a light exit surface. An arbitrary surface is formed as a symmetric surface in which an intersection line intersecting with each of the light incident surface and the light exit surface is asymmetric, and a deflection point at which the light is deflected by the rotary polygon mirror and an effective value of the predetermined image surface are determined. The distance between the image planes when passing through the center of the area is L Wherein the distance between the light rays passing through the effective area center of the predetermined image plane from the deflection point of the light is deflected by the rotary polygon mirror and the point of entering the fθ lens L _1, the effective area center of the predetermined image plane An exposure apparatus characterized by satisfying 0.15 ≦ L ₁ × sinΦ / L ≦ 0.27, where Φ is an angle at which the light is deflected by the deflector with respect to an effective area end. Is provided.

Still further, the present invention provides a light emitting source, a deflector including a rotary polygon mirror for deflecting light from the light emitting source at a substantially constant angular velocity in a first direction, and combining the deflector with the light emitting source. Disposed between the light source and the pre-deflection optical means for guiding the light from the light source to the rotating polygon mirror of the deflector while giving predetermined characteristics, the light deflected by the rotating polygon mirror to a predetermined image plane A single lens that forms an image at a constant speed so that the rotation amount of the rotating polygon mirror is proportional to the distance in the first direction,
In the exposure apparatus having the lens, any one surface except the light incident surface and the light exit surface is formed as a symmetric surface in which an intersection line intersecting with each of the light incident surface and the light exit surface is asymmetric. The distance between the deflection point where the light is deflected by the rotating polygon mirror and the image plane when passing through the center of the effective area of the predetermined image plane is L, and the distance from the deflection point where the light is deflected by the rotating polygon mirror is L The distance between a point at which a light ray passing through the center of the effective area of the predetermined image plane enters the fθ lens is L ₁ ,
It is intended to provide an exposure apparatus characterized by satisfying 0.3 ≦ L ₁ /L≦0.65.

Further, the present invention provides a deflector including a plurality of light-emitting sources, a rotary polygon mirror for deflecting each light from the light-emitting sources in a first direction at a substantially constant angular velocity, the deflector and the deflector. A pre-deflection optical unit that is disposed between the light source and guides the light from the light source to the rotating polygon mirror of the deflector while having predetermined characteristics, and respective light beams deflected by the rotating polygon mirror. An exposure apparatus having only one lens that forms an image at a constant speed so that the amount of rotation of the rotating polygon mirror and the distance in the first direction are proportional to a predetermined image plane; An arbitrary surface excluding the incident surface and the light exit surface is formed as a symmetric surface in which an intersection line intersecting with each of the light incident surface and the light exit surface is asymmetric, and the light is deflected by the rotating polygon mirror. Having a deflection point and the predetermined image plane L is the distance between image planes when passing through the center of the area, W is the distance between the center of the effective area of the predetermined image plane and the end of the effective area, and W is the distance between the center of the effective area of the predetermined image plane and the end of the effective area. An exposure apparatus characterized by satisfying 0.8 ≦ tan ⁻¹ (W / L) /Φ≦1.3, where Φ is an angle at which each light is deflected by the deflector. Is provided.

Still further, the present invention provides a light emitting source, a deflector including a rotary polygonal mirror for deflecting light from the light emitting source in a first direction at a substantially constant angular velocity, and combining the deflector with the light emitting source. Disposed between the light source and the pre-deflection optical means for guiding the light from the light source to the rotating polygon mirror of the deflector while giving predetermined characteristics, the light deflected by the rotating polygon mirror to a predetermined image plane A single lens that forms an image at a constant speed so that the rotation amount of the rotating polygon mirror is proportional to the distance in the first direction,
In the exposure apparatus having the lens, any one surface except the light incident surface and the light exit surface is formed as a symmetric surface in which an intersection line intersecting with each of the light incident surface and the light exit surface is asymmetric. The distance between the deflection point where the light is deflected by the rotating polygon mirror and the image plane when passing through the center of the effective area of the predetermined image plane is L, and the distance from the deflection point where the light is deflected by the rotating polygon mirror is L The distance between a point at which a light ray passing through the center of the effective area of the predetermined image plane enters the fθ lens is L ₁ ,
When the distance between the point at which light passing through the center of the effective area of the predetermined image plane exits the lens and the predetermined image plane is L ₃ , 0.17 ≦ L ₁ × L ₃ / L ² ≦ 0 .23 are satisfied.

Still further, the present invention provides a light emitting source, a deflector including a rotary polygon mirror for deflecting light from the light emitting source in a first direction at a substantially constant angular velocity, and combining the deflector with the light emitting source. Disposed between the light source and the pre-deflection optical means for guiding the light from the light source to the rotating polygon mirror of the deflector while giving predetermined characteristics, the light deflected by the rotating polygon mirror to a predetermined image plane A single lens that forms an image at a constant speed so that the rotation amount of the rotating polygon mirror is proportional to the distance in the first direction,
In the exposure apparatus having the lens, any one surface except the light incident surface and the light exit surface is formed as a symmetric surface in which an intersection line intersecting with each of the light incident surface and the light exit surface is asymmetric. The angle at which the light is deflected by the deflector between the center of the effective area and the end of the effective area of the predetermined image plane is Φ, the deflection point at which the light is deflected by the rotating polygon mirror, and the effective point of the predetermined image plane The distance between the image planes when passing through the center of the area is L, the distance between the center of the effective area of the predetermined image plane and the end of the effective area is W, and light passing through the center of the effective area of the predetermined image plane passes through the lens. Provided is an exposure apparatus characterized by satisfying φ × (L / W) / L ₃ ≦ 0.009 when a distance between an emission point and the predetermined image plane is L _3. is there.

Still further, the present invention provides a light emitting source, a deflector including a rotary polygon mirror for deflecting light from the light emitting source in a first direction at a substantially constant angular velocity, and combining the deflector with the light emitting source. Disposed between the light source and the pre-deflection optical means for guiding the light from the light source to the rotating polygon mirror of the deflector while giving predetermined characteristics, the light deflected by the rotating polygon mirror to a predetermined image plane A single lens that forms an image at a constant speed so that the rotation amount of the rotating polygon mirror is proportional to the distance in the first direction,
In the exposure apparatus having the lens, any one surface except the light incident surface and the light exit surface is formed as a symmetric surface in which an intersection line intersecting with each of the light incident surface and the light exit surface is asymmetric. The distance between the deflection point where the light is deflected by the rotating polygon mirror and the image plane when passing through the center of the effective area of the predetermined image plane is L, and the light beam passing through the center of the effective area of the predetermined image plane is the lens. The paraxial focal length of the lens in the second direction perpendicular to the first direction near the intersection is F,
The distance between the point at which light passing through the effective area center of the predetermined image plane exits the lens and the predetermined image plane is L ₃ , and the predetermined image is obtained from a deflection point at which the light is deflected by the rotating polygon mirror. The distance between the point at which the ray passing through the center of the effective area of the surface enters the fθ lens is L ₁ , and the light is deflected by the deflector between the center of the effective area of the predetermined image plane and the end of the effective area. Assuming that the angle is Φ and the distance between the center of the effective area of the predetermined image plane and the end of the effective area is W, F / L ≦ 0.25, 0.35 ≦ L ₃ /L≦0.65, 0 _{.15 ≦ L 1 × sinΦ / L} ≦ 0.27, 0.3 ≦ L 1 / L ≦ 0.65, 0.8 ≦ tan -1 (W / L) Φ ≦ 1.3, 0.17 ≦ L provide an exposure _apparatus characterized by ^{_{1 × L 3 / L 2 ≦}} 0.23, and φ × (L / W) / L 3 ≦ 0.009 is satisfied Is shall.

Further, the present invention provides a light emitting source, a deflector including a rotary polygon mirror for deflecting light from the light emitting source in a first direction at a substantially constant angular velocity, and combining the deflector with the light emitting source. Disposed between the light source and the pre-deflection optical means for guiding the light from the light source to the rotating polygon mirror of the deflector while giving predetermined characteristics, the light deflected by the rotating polygon mirror to a predetermined image plane A single lens that forms an image at a constant speed so that the rotation amount of the rotating polygon mirror is proportional to the distance in the first direction,
In the exposure apparatus having the lens, any one surface except the light incident surface and the light exit surface is formed as a symmetric surface in which an intersection line intersecting with each of the light incident surface and the light exit surface is asymmetric. The distance between the deflection point where the light is deflected by the rotating polygon mirror and the image plane when passing through the center of the effective area of the predetermined image plane is L, and the light beam passing through the center of the effective area of the predetermined image plane is the lens. The paraxial focal length of the lens in the second direction perpendicular to the first direction near the intersection is F,
The distance between the point at which light passing through the effective area center of the predetermined image plane exits the lens and the predetermined image plane is L ₃ , and the predetermined image is obtained from a deflection point at which the light is deflected by the rotating polygon mirror. The distance between the point at which the ray passing through the center of the effective area of the surface enters the fθ lens is L ₁ , and the light is deflected by the deflector between the center of the effective area of the predetermined image plane and the end of the effective area. Assuming that the angle is Φ and the distance between the center of the effective area of the predetermined image plane and the end of the effective area is W, F / L ≦ 0.25, 0.35 ≦ L ₃ /L≦0.65, 0 _{.15 ≦ L 1 × sinΦ / L} ≦ 0.27, 0.3 ≦ L 1 / L ≦ 0.65, 0.8 ≦ tan -1 (W / L) Φ ≦ 1.3, 0.17 ≦ L It is characterized in _that the ^{_{1 × L 3 / L 2 ≦}} 0.23, and φ × (L / W) / L 3 ≦ 0.009 of at least two are satisfied There is provided an exposure apparatus.

Still further, the invention provides a light emitting source, a deflector including a rotary polygon mirror for deflecting light from the light emitting source in a first direction at a substantially constant angular velocity, and combining the deflector with the light emitting source. Disposed between the light source and the pre-deflection optical means for guiding the light from the light source to the rotating polygon mirror of the deflector while giving predetermined characteristics, the light deflected by the rotating polygon mirror to a predetermined image plane A single lens that forms an image at a constant speed so that the rotation amount of the rotating polygon mirror is proportional to the distance in the first direction,
In the exposure apparatus having the lens, any one surface except the light incident surface and the light exit surface is formed as a symmetric surface in which an intersection line intersecting with each of the light incident surface and the light exit surface is asymmetric. The distance between the deflection point where the light is deflected by the rotating polygon mirror and the image plane when passing through the center of the effective area of the predetermined image plane is L, and the light beam passing through the center of the effective area of the predetermined image plane is the lens. The paraxial focal length of the lens in the second direction perpendicular to the first direction near the intersection is F,
The distance between the point at which light passing through the effective area center of the predetermined image plane exits the lens and the predetermined image plane is L ₃ , and the predetermined image is obtained from a deflection point at which the light is deflected by the rotating polygon mirror. The distance between the point at which the ray passing through the center of the effective area of the surface enters the fθ lens is L ₁ , and the light is deflected by the deflector between the center of the effective area of the predetermined image plane and the end of the effective area. Assuming that the angle is Φ and the distance between the center of the effective area of the predetermined image plane and the end of the effective area is W, F / L ≦ 0.25, 0.35 ≦ L ₃ /L≦0.65, 0 _{.15 ≦ L 1 × sinΦ / L} ≦ 0.27, 0.3 ≦ L 1 / L ≦ 0.65, 0.8 ≦ tan -1 (W / L) Φ ≦ 1.3, 0.17 ≦ L and wherein _{the ^{1 × L 3 / L 2 ≦}} 0.23, and φ × (L / W) / any combination of L ₃ ≦ 0.009 is satisfied There is provided a that exposure apparatus.

Still further, the present invention provides a light emitting source, a deflector including a rotary polygonal mirror for deflecting light from the light emitting source in a first direction at a substantially constant angular velocity, and combining the deflector with the light emitting source. Disposed between the light source and the pre-deflection optical means for guiding the light from the light source to the rotating polygon mirror of the deflector while giving predetermined characteristics, the light deflected by the rotating polygon mirror to a predetermined image plane A single lens that forms an image at a constant speed so that the rotation amount of the rotating polygon mirror is proportional to the distance in the first direction,
In the exposure apparatus having the lens, any one surface except the light incident surface and the light exit surface is formed as a symmetric surface in which an intersection line intersecting with each of the light incident surface and the light exit surface is asymmetric. The distance between the deflection point where the light is deflected by the rotating polygon mirror and the image plane when passing through the center of the effective area of the predetermined image plane is L, and the light beam passing through the center of the effective area of the predetermined image plane is the lens. The paraxial focal length of the lens in the second direction perpendicular to the first direction near the intersection is F,
The distance between the point at which light passing through the effective area center of the predetermined image plane exits the lens and the predetermined image plane is L ₃ , and the predetermined image is obtained from a deflection point at which the light is deflected by the rotating polygon mirror. The distance between the point at which the ray passing through the center of the effective area of the surface enters the fθ lens is L ₁ , and the light is deflected by the deflector between the center of the effective area of the predetermined image plane and the end of the effective area. Assuming that the angle is Φ and the distance between the center of the effective area of the predetermined image plane and the end of the effective area is W, F / L ≦ 0.25, 0.35 ≦ L ₃ /L≦0.65, 0 _{.15 ≦ L 1 × sinΦ / L} ≦ 0.27, 0.3 ≦ L 1 / L ≦ 0.65, 0.8 ≦ tan -1 (W / L) Φ ≦ 1.3, 0.17 ≦ L an exposure _apparatus characterized by ^{_{1 × L 3 / L 2 ≦}} 0.23, and φ × (L / W) / L 3 ≦ 0.009 is satisfied, this An image forming apparatus comprising: a developing device that develops a latent image formed on an image carrier by an exposure device; and a transfer device that transfers a developer image developed by the developing device to a material to be transferred. Is provided.

[0018]

Embodiments of the present invention will be described below in detail with reference to the drawings.

As shown in FIG. 1, an image forming apparatus 10
Reference numeral 0 denotes an exposure device 1 that simultaneously outputs a plurality of light beams toward an exposure target, and an image forming unit 51 that forms an image corresponding to the light beam output from the exposure device 1 and outputs the image to recording paper. doing.

As shown in FIG. 2, the exposure apparatus 1 has a semiconductor laser element 3 as a light emitting source for emitting a light beam (laser beam) of a predetermined wavelength, and a rotatable reflecting surface. Is rotated at a predetermined speed, so that the laser beam emitted from the semiconductor laser element 3 is transferred to an image plane S disposed at a predetermined position, that is, a photosensitive member as an image carrier, which will be described in detail after the image forming section 51. It has a deflecting device 7 that deflects (scans) at a predetermined linear velocity toward a predetermined position on the drum. A pre-deflection optical system 5 that arranges the cross-sectional beam shape of the laser beam emitted from the laser element 3 into a predetermined size and a predetermined shape is disposed between the deflection device 7 and the semiconductor laser element 3. . Further, between the deflecting device 7 and the image plane S, the laser beam deflected by the rotation of the reflecting surface of the deflecting device 7 is reflected by a reflection angle defined by the rotation of the reflecting surface and a distance on the image surface. A post-deflection optical system 9 that forms an image at a constant speed is disposed so as to be proportional. Note that
The direction in which the laser beam is deflected by the deflecting device 7 is the main scanning direction (the axial direction of the photosensitive drum described in detail below), and the direction orthogonal to the main scanning direction (the direction in which the photosensitive drum is rotated) is the sub-scanning. Direction.

As shown in FIG. 3, the semiconductor laser element 3 has a first light emitting point 3a for emitting a first laser beam A.
And a second light emitting point 3b for emitting the second laser beam B is a laser element arranged on the same element at a predetermined interval, and at the time of assembly, the laser beams A and B is fixed to a housing (not shown) so as to have a predetermined interval in the sub-scanning direction.

The pre-deflection optical system 5 includes a finite focus lens 11 for giving predetermined convergence to the laser beams A and B emitted from the first and second light emitting points 3a and 3b of the laser element 3, and a finite focus lens. The laser beam A and the laser beam B, which are disposed at the focal position on the rear side of the lens 11 and have predetermined convergence by the finite focus lens 11, adjust the respective sectional beam shapes of the laser beams A and B into a predetermined shape. A cylinder lens 15 that gives a predetermined convergence to each of the laser beams A and B only in the sub-scanning direction.
The first and second laser beams A and B emitted from the respective light emitting points 3a and 3b are given predetermined convergence and a sectional beam shape, respectively, so that the reflecting surface of the deflecting device 7 (polyhedral mirror 7a) To guide. Note that, as shown in FIG. 2A, the laser beams A and B substantially overlap in the main scanning direction. Also, in the sub-scanning direction, when the laser beam is emitted from the semiconductor laser element 3, it can be regarded as a substantially single laser beam from the vicinity of the two passing through the aperture 13.

The finite focus lens 11 is provided with, for example, UV (Urt) on at least one of the laser incidence surface and the emission surface of an aspherical glass lens or a spherical glass lens.
A lens in which a plastic lens (not shown) of a curable type is attached (or a plastic lens (not shown) is integrally molded) is used.

As shown in FIG. 3, the stop 13 is located at the rear focal position of the finite focus lens 9. Thereby, the fluctuation of the light amounts of the two laser beams emitted from each of the two light emitting points 3a and 3b is suppressed to a minimum.

The cylinder lens 15 is made of, for example, PMMA
A plastic cylinder lens 15p formed of (polymethyl methacryl) or the like and a glass cylinder lens 15g formed of, for example, LAH78 or the like are provided integrally, and the curvature of the lens surface on the joint surface side of both lenses is substantially Are formed in the same manner, and are bonded to each other by, for example, adhesion. The cylinder lens 15 is fixed at an accurate distance from the finite focus lens 11 by a positioning portion formed integrally with a holding member (not shown) that holds the finite lens 11.

The plastic cylinder lens 15p
The surface in contact with air is formed on a part of the cylindrical surface, and power is given in the sub-scanning direction. The cylinder lens 15 may be integrally formed by pressing the glass cylinder lens 15g and the PMMA cylinder lens 15p from a predetermined direction toward a positioning member (not shown). Further, the cylinder lens 15 can also be provided by molding a plastic cylinder lens 15p integrally with the incident surface of the glass cylinder lens 15g.

The deflecting device 7 includes, for example, a polygon mirror 7a having six plane reflecting mirrors (surfaces) arranged in a regular polygonal shape, and a motor 7b for rotating the polygon mirror 7a at a predetermined speed in the main scanning direction. have. The polygon mirror 7a is formed of, for example, aluminum. Further, after each reflecting surface of the polygon mirror 7a is cut out along a plane including a direction in which the polygon mirror 7a is rotated, that is, a plane orthogonal to the main scanning direction, that is, a sub-scanning direction parallel to the axial direction of the motor 7b, For example, a surface protective layer such as SiO ₂ and a high-brightness reflective layer are provided on the cut surface by vapor deposition.

The post-deflection optical system 9 includes only one imaging lens 21 having a shape and characteristics similar to a well-known fθ lens, and a laser which has passed through the lens 21 and has given imaging characteristics. An emission mirror 23 that bends the beams LA and LB toward the photosensitive drum of the image forming unit 51 described below, and a dust-proof glass 25 that is positioned between the emission mirror 23 and the photosensitive drum and hermetically seals the exposure device 1. And the laser beam L deflected at a predetermined speed by the deflector 7
A and LB are imaged at a constant speed in the axial direction of the photosensitive drum.

The lens surface shape of the post-deflection optical system is as follows:

(Equation 1)

Has a shape represented by

In the equation (A), when the m term of “a _mn” is an odd number, it indicates that the main scanning direction is asymmetric, and thereby the rotation of the polygon mirror 7 a of the deflecting device 7 is performed. , The influence of the movement of the deflection point can be corrected. As a result of the optimization, as shown in Example 1 of Table 1, when the m terms of “a _mn ” are all “0”, the defocus amount in the main scanning direction and the defocus amount in the sub scanning direction In the case where a plurality of laser beams are used, the characteristics are degraded with respect to the displacement of the laser beams in the sub-scanning direction. Further, when the n term of “a _mn ” having a function of shifting the cross section in the sub-scanning direction from the arc shape is other than “0”, the focusing state in the sub-scanning direction is deteriorated, and the beam diameter of the laser beam is reduced. Can't squeeze, but? This section? , The minimum beam diameter of the laser beam can be reduced to a smaller beam diameter as compared with a conventional exposure apparatus.

Further, by setting the shape of the lens surface of the imaging lens 21 to a shape having no rotationally symmetric axis as shown in the equation (A), the intervals of the plurality of laser beams in the sub-scanning method can be reduced. Under the condition that it is kept constant in the scanning area,
In the case of a toric lens having a rotationally symmetric axis or a rotationally symmetric aspherical lens, when trying to use only one imaging lens,
It has been confirmed by simulation that the minimum beam diameter can be reduced to about 50 μm as compared with a conventional optical system in which the wavefront aberration cannot be completely removed.

Referring again to FIG. 1, the image forming unit 51
Is bent by the emission mirror 23 of the exposure apparatus 1,
A photosensitive drum 53 is formed at a position where the laser beams LA and LB that have passed through the dustproof glass 25 are emitted, and is formed in a cylindrical drum shape so as to be rotatable in the direction of an arrow, and forms an electrostatic latent image corresponding to an image. have.

Around the photosensitive drum 53, a charging device 55 for providing a predetermined potential to the surface of the photosensitive drum 53, and the surfaces of the photosensitive drum 53 are irradiated with laser beams LA and LB from the exposure device 1. A developing device 57 for visualizing the electrostatic latent image formed by supplying toner to the photosensitive drum 53 in a state where a recording medium, that is, a recording sheet P is interposed between the developing device 57 and the photosensitive drum 53, Transfer device 59 and transfer device 5 for transferring the toner image (toner) on the photosensitive drum 53 to the paper P conveyed by the conveyance mechanism that does not
9, a cleaner 61 for removing the residual toner remaining on the photosensitive drum 53 after the toner is transferred, and a residual potential remaining on the photosensitive drum 53 after the toner image is transferred by the transfer device 59. Static eliminator 63
Are sequentially arranged along the rotation direction of the photosensitive drum 53.

Below the photosensitive drum 53, a paper cassette 65 for accommodating paper P on which an image formed by the image forming section 51 is transferred is disposed. The sheet P is fed from the top by a delivery roller 67 provided at one end of the sheet cassette 65 and having a substantially semicircular cross section.
The leading edge of the sheet P and the leading edge of the image formed on the photosensitive drum 53 are aligned by the registration roller 69, and the transfer area between the transfer device 59 and the photosensitive drum 53 is determined at a predetermined timing. To be fed.

The paper P to which the toner (toner image) has been transferred is conveyed by a conveyance belt 71 to a fixing device 73, where the toner is fixed.

Next, the optical (shape) characteristics of the imaging lens 21 and the positional relationship of the lens 21 in the exposure apparatus 1 shown in FIG. 2 will be described.

FIGS. 4 to 11 denote L as the deflection point at which the laser beams LA and LB are deflected by the polygon mirror 7a of the deflecting device 7, and the center of the effective area of the predetermined image plane where the laser beams LA and LB are located. the distance between the image plane when passing through, the L _1,
Laser beams LA and LB by polygon mirror 7a of deflecting device 7
Laser but through laser beam LA through the effective area center point of deflection and a predetermined image surface to be deflected, the distance between the point where LB is incident to the imaging lens 21, an L _3, the effective area center of a predetermined image surface The distance between the point at which the beam exits the imaging lens 21 and the predetermined image plane, F, is the distance in the sub-scanning direction of the lens near the point where a ray passing through the center of the effective area of the predetermined image plane intersects the imaging lens 21. The axial focal length, Φ, is defined as the angle [rad], W, at which the laser beams LA, LB are deflected by the polygon mirror 7a of the deflecting device 7 between the center of the effective area of the predetermined image plane and the end of the effective area.
Is defined as the distance between the center of the effective area of the predetermined image plane and the end of the effective area, and the optical characteristics obtained when each parameter is optimized, that is, the polygon mirror 7a of the deflecting device 7 Laser beam L in the case where each of the reflecting surfaces is non-parallel to the rotation axis, that is, the surface tilt is 1 minute.
A, LB, the amount of deviation of the imaging position in the sub-scanning direction (1), ie, F / L (C-1), defocus in the sub-scanning direction (each laser beam LA, LB
Is the difference between the position at which is the minimum beam diameter and the image plane S) (2), that is, L ₃ / L (C-2), the defocus in the main scanning direction (the laser beams LA and LB).
(3), ie, L ₁ × sin Φ / L (C-3), when each of the laser beams LA and LB passes through the imaging lens. The range (4) of the variation of the laser beam in the main scanning direction indicating the maximum distance on S, that is, L ₁ / L (C-4), and the wavelengths of the laser beams LA and LB emitted from each light emitting source are The shift amount (5) of the imaging position in the main scanning direction when it fluctuates by 100 nm, that is, tan ^-1 (W / L) / Φ (C-5), and fθ in the main scanning direction with respect to each of the laser beams LA and LB. Characteristic (6), that is, L ₁ × L ₃ / L ² (C-6) and the effect (7) due to the deviation of the transmittance of the lens 21, that is, optimization data obtained by simulation for each of φ × (L / W) L ₃ (C-7) are shown. 4 to 11 show the first embodiment.
A series of data are shown for Nos. 62 through 62, and the conditions shown in FIG. 4 are applied to all the examples. 4 to 11, the arrangement and paraxial characteristics of the pre-deflection optical system 5, the lens 2
1, the laser beams LA, L on the image plane
The distance in the sub-scanning direction between the first light-emitting point 3a and the second light-emitting point 3b that can set the distance between B to 3 dots is also
It is shown at the same time.

FIGS. 12 to 19 correspond to FIGS.
6 is a graph for evaluating the degree of correlation between the conditional expressions (C-1) to (C-7) and the significance of each conditional expression in the optical characteristics shown in FIG.

FIG. 12 is a graph showing the relationship between the deviation amount of the imaging position of each laser beam and the conditional expression (C-1) when the surface tilt is 1 minute, and the same deviation amount as F / L. And a strong correlation is observed between In addition, in order to reduce the amount of deviation to 3 μm or less in consideration of individual errors of the imaging lens 21, the housing (not shown), the semiconductor laser element 3, and the like on the actual manufacturing surface, F / L ≦ 0.25 ( It is necessary to set F / L so as to satisfy B-1).

FIG. 13 is a graph showing the relationship between the amount of defocus in the sub-scanning direction (deviation between the position where each of the laser beams LA and LB has the minimum beam diameter and the image plane S) and the conditional expression (C-2). And a strong correlation is recognized between L ₃ / L and the defocus amount in the sub-scanning direction. In order to reduce the defocus amount to 2 mm or less in consideration of an individual error of the imaging lens 21, the housing (not shown), the semiconductor laser element 3 and the like on the actual manufacturing surface, 0.35 ≦ L ₃ / It is necessary to set L ₃ / L so as to satisfy L ≦ 0.65 (B-2).

FIG. 14 is a graph showing the relationship between the amount of defocus in the main scanning direction (the deviation between the position where each of the laser beams LA and LB has the minimum beam diameter and the image plane S) and the conditional expression (C-3). And a strong correlation is recognized between L ₁ × sin Φ / L and the defocus amount in the main scanning direction. In order to reduce the defocus amount in the main scanning direction to 2 mm or less in consideration of the individual error of the imaging lens 21, the housing (not shown), the semiconductor laser element 3 and the like on the actual manufacturing surface, 0.15 ≦ L ₁ It is necessary to set L ₁ × sin φ / L so as to satisfy × sin φ / L ≦ 0.27 (B-3).

FIG. 15 is a graph showing the range of variation of the laser beam in the main scanning direction and the conditional expression (C−C) indicating the maximum distance of all the laser beams passing through the imaging lens on the image plane S.
4 is a graph showing the relationship with 4), and a strong correlation is observed between L ₁ / L and the same variation. Incidentally, the actual imaging of manufacturing surface lens 21, taking into account the individual error of 3 such housing and a semiconductor laser device not shown, to the extent of the variation in 20μm or less, 0.3 ≦ L ₁ / It is necessary to set L ₁ / L so as to satisfy L ≦ 0.65 (B-4).

FIG. 16 shows the relationship between the laser beam in the sub-scanning direction over the entire scanning range when the center value of the interval between the laser beams in the sub-scanning direction is set to 42.3 μm. It is a graph which shows the fluctuation amount of an interval. According to FIG. 16, L ₁ / L shows a correlation similar to the variation shown in FIG. 15 with respect to the variation of the interval between the laser beams in the sub-scanning direction. The range of variation shown in FIG.
When the distance is equal to or less than μm, that is, in a range satisfying the expression (B-4), the deviation of the interval between the laser beams in the sub-scanning direction is 3 μm or less.

FIG. 17 shows the light emitting source 3 of the semiconductor laser device 3.
a, laser beam LA emitted from each of 3b
10 is a graph showing the relationship between the amount of deviation of the imaging position in the main scanning direction and the conditional expression (C-5) when the wavelength of LB fluctuates by 100 nm.
^-1 (W / L) / Φ has a strong correlation.

By the way, when the temperature of the light emitting point (including the package and the mount) changes, the light emitting wavelength of the emitted laser beam fluctuates, and the mode hopping phenomenon causes the semiconductor laser element to emit 0.1 ° at an arbitrary temperature. 3n emission wavelength for temperature change of about C
It is known to fluctuate by about m. For this reason, it is difficult to make not only the emission wavelength of the laser beam emitted from each emission point of the semiconductor laser element, but also all the wavelengths emitted from the arbitrarily used semiconductor laser element uniform. Therefore, even if the emission wavelengths can be matched under a certain condition, the emission wavelength varies under all conditions including the temperature condition.

Note that the allowable value at which the deviation of the laser beams in the sub-scanning direction on the sheet P cannot be identified is 15 μm or less. Therefore, by suppressing the variation of the emission wavelength to about 3 nm, the emission wavelength is reduced by mode hopping. Fluctuates, it becomes difficult to identify on the paper P. For this reason, in FIG. 17, the position shift amount in the main scanning direction is set to 0.
If the condition that can be made 5 mm or less is applied to the conditional expression (C-5), assuming that the mode hopping that may occur in a general semiconductor laser is 3 nm, the amount of positional deviation in the main scanning direction is shown in FIG. It is about 3/100 of the shift amount, and even if a wavelength variation of 3 nm occurs, 100 nm is required to reduce the shift amount on the paper to 15 μm or less.
In this case, the range may be specified so as to be 0.5 mm or less in the wavelength variation (the condition in FIG. 17).

Therefore, it is only necessary to set (W / L) Φ so as to satisfy 0.8 ≦ tan ⁻¹ (W / L) Φ ≦ 1.3 (B-5).

FIG. 18 is a graph showing the relationship between the fθ characteristic and the conditional expression (C-6). The fθ characteristic and L ₁ × L ₃ / L
There is a strong correlation between the ^two . In order to suppress the maximum value of the variation of the characteristics to about 0.4% in consideration of individual errors of the imaging lens 21, the housing (not shown), the semiconductor laser element 3 and the like on the actual manufacturing surface, _{0.17 ≦ L 1 × L 3 /} L 2 ≦ 0.23 to meet the (B-6), it is necessary to set the ^{_{L 1 × L 3 / L 2}} .

FIG. 19 is a graph showing the relationship between the influence of the deviation of the transmittance of the lens 21 and the conditional expression (C-7). The deviation (variation) of the transmittance and φ × (L / W) / L _Three
It is recognized that there is a strong correlation between In addition,
In consideration of individual errors of the imaging lens 21, the housing (not shown), the semiconductor laser element 3 and the like on the actual manufacturing surface,
In order to make the deviation (variation) of the transmittance 10% or less, it is preferable that φ × (L / W) / L ₃ ≦ 0.009 (B-7).

In FIGS. 12 to 19 described above, the data indicated by crosses is the data of the embodiment 1 of the embodiments 1 to 62 shown in FIGS. _Shows a case where all the m terms of “a _mn ” are “0”, and satisfies the above-mentioned optimization conditions set using FIGS. 12 to 19, ie, (B-1) to (B-7). As compared with Embodiments 2 to 25 which are examples in which many parameters shown in FIG. 4 are changed, a case where a defocus amount in the main scanning direction, a defocus amount in the sub-scanning direction, and a plurality of laser beams are used. Regarding the deviation of the position of the laser beam in the sub-scanning direction, the characteristics are deteriorated.

Therefore, the shape of the lens surface of the imaging lens 21 is set to a shape having no axis of rotational symmetry as shown in the equation (A), and L is changed by the polygon mirror 7a of the deflecting device 7 to the laser beam LA, L. LB is the respective laser beams LA and deflection point being deflected, the distance between the image plane when the LB passes through the center of the effective region of the predetermined image plane, the L _1, polygon mirror 7a of the deflection device 7
The laser beam LA, a laser beam LA through the effective area center of the deflection point and the predetermined image plane LB is deflected, the distance between the point where LB is incident to the imaging lens 21, an L _3, a predetermined image surface The distance between the point at which the laser beam passing through the center of the effective area exits the imaging lens 21 and the predetermined image plane, F, is a lens in the vicinity where the light beam passing through the center of the effective area of the predetermined image plane intersects the imaging lens 21. , The paraxial focal length in the sub-scanning direction
The angle [rad] and W at which the laser beams LA and LB are deflected by the polygon mirror 7a of the deflecting device 7 between the center of the effective area of the predetermined image plane and the end of the effective area are determined by the values of the effective area of the predetermined image plane. The distance between the center and the end of the effective area, respectively, is defined, and based on conditional expression (C-1), the amount of displacement of the position where each laser beam is imaged when the surface tilt is 1 minute 3μ
m, the range of F / L is set to F / L ≦ 0.25, and based on conditional expression (C-2), L ₃ / L is set so that the defocus amount in the sub-scanning direction is set to 2 mm or less. Is set to 0.35 ≦ L ₃ /L≦0.65, and L ₁ × sin Φ / L is set so that the defocus amount in the main scanning direction is set to 2 mm or less based on the conditional expression (C-3).
Is set to 0.15 ≦ L ₁ × sinΦ / L ≦ 0.27, and based on the conditional expression (C-4), when the laser beams LA and LB pass through the imaging lens 21 in the main scanning direction. The range of L ₁ / L is set to 0.3 ≦ L ₁ /L≦0.65, and the conditional expression (C-5) is set so that the range of the maximum deviation on the image plane S is 20 μm or less. ) Based on tan ^-1 (W / L) such that when the mode hopping is 3 nm, the deviation of the imaging position in the main scanning direction on the paper P is 15 μm or less.
The range of Φ is set to 0.8 ≦ tan ⁻¹ (W / L) Φ ≦ 1.3, and the maximum value of the change amount of the fθ characteristic is set to 0.4% or less based on the conditional expression (C-6). Thus, based on the range of L ₁ × L ₃ / L ² as 0.17 ≦ L ₁ × L ₃ / L ² ≦ 0.23 and based on the conditional expression (C-7), the deviation (variation) of the transmittance is obtained. Φ (L / W) so that is not more than 10%.
By setting the range of / L ₃ to φ × (L / W) / L ₃ ≦ 0.009, only one imaging lens 21 can be used and the minimum beam diameter can be reduced to about 50 μm. .

FIGS. 20 to 32 show the embodiments of FIGS. 4 to 11 in which all the m terms of "a _mn" shown in equation (A) are not set to "0", that is, m terms include odd terms. The shape of the entrance surface and the exit surface of each of the imaging lenses 21 of Examples 2 to 25 is shown by numerical data.

Embodiments 2 to 25 described above are:
The amount of deviation of the imaging position of each laser beam when the surface tilt is 1 minute is 3 μm or less, and the amount of defocus in the sub-scanning direction is 2 μm.
mm or less, the defocus amount in the main scanning direction is 2 mm or less, and the variation range of the passing position on the image plane S in the main scanning direction when the laser beam passes through the imaging lens 21 is 20 μm or less. Even when 3 nm mode hopping occurs, the deviation of the imaging position in the main scanning direction on the paper P is set to 15 μm or less, and the maximum value of the change amount of the fθ characteristic is set to 0.
It is possible to provide only one imaging lens 21 that can be set to 4% or less and the transmittance deviation (variation) to 10% or less. The detailed description of the shape of the lens surface in Examples 26 to 62 shown in FIGS. 4 to 11 is omitted.

FIG. 33 is a schematic diagram showing an example in which the light source 3 of the pre-deflection optical system 5 is constituted by a plurality of semiconductor laser elements 103a and 103b in the exposure apparatus 1 shown in FIG. In this case, the finite focus lenses 111a, 111
An exposure apparatus similar to that shown in FIG. 2 can be provided by the half mirror 117 that combines the first and second laser beams LA and LB having predetermined convergence by both lenses.

In the example shown in FIG.
A general-purpose low-cost laser element can be used for 03a and 103b, and when one of the laser elements stops emitting light or the degree of mode hopping is large, only the corresponding laser element can be replaced. Therefore, the cost of the entire exposure apparatus can be reduced.

[0057]

As described above, according to the exposure apparatus of the present invention, a plurality of laser beams deflected at a predetermined speed by a deflecting device by only one imaging lens are applied to the axis of the photosensitive drum. An image can be formed at a constant speed in the direction.

The imaging lens is

(Equation 2)

An arbitrary surface excluding the light incident surface and the light emitting surface represented by the following expression is a rotationally symmetric axis formed on a symmetrical surface where the line of intersection intersecting each of the light incident surface and the light emitting surface is asymmetric. Defocus amount in the main scanning direction, defocus amount in the sub-scanning direction, and position of the laser beam in the sub-scanning direction when a plurality of laser beams are used, even though there is only one lens. Can be set within a predetermined range, and the minimum beam diameter on the image plane can be converged to about 50 μm.

Therefore, it is possible to provide a low-cost, high-speed, small-size and high-quality exposure apparatus.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an image forming apparatus in which an exposure apparatus according to an embodiment of the present invention is incorporated.

FIG. 2 is a schematic diagram showing an example of an arrangement of optical members of an exposure device incorporated in the image forming apparatus shown in FIG.

FIG. 3 is a schematic diagram showing a semiconductor laser element (light source) incorporated in the exposure apparatus shown in FIG.

FIG. 4 is a data table showing an embodiment of the imaging lens 21 shown in FIG.

5 is a data table showing an embodiment of the imaging lens 21 of FIG. 2 subsequent to the data table shown in FIG. 4;

FIG. 6 is a data table showing an embodiment of the imaging lens 21 of FIG. 2 subsequent to the data table shown in FIG. 5;

FIG. 7 is a data table showing an embodiment of the imaging lens 21 of FIG. 2 subsequent to the data table shown in FIG. 6;

8 is a data table showing an embodiment of the imaging lens 21 of FIG. 2 subsequent to the data table shown in FIG. 7;

9 is a data table showing an embodiment of the imaging lens 21 of FIG. 2 subsequent to the data table shown in FIG. 8;

FIG. 10 is a view following FIG. 2 following the data table shown in FIG. 9;
9 is a data table showing an embodiment of the imaging lens 21 of FIG.

11 is a data table showing an embodiment of the imaging lens 21 of FIG. 2 subsequent to the data table shown in FIG. 10;

FIG. 12 shows a case where each of the reflecting surfaces of the polygon mirror 7a of the deflecting device 7 is non-parallel to the rotation axis, that is, the surface tilt is one minute in the imaging lens shown in FIGS. 9 is a graph showing the relationship between the amount of deviation of the imaging position of the laser beams LA and LB in the sub-scanning direction and the optimization condition (C-1).

FIG. 13 shows the defocusing in the sub-scanning direction (each laser beam LA,
9 is a graph showing a relationship between a position where LB is a minimum beam diameter and a shift amount between the image plane S and an optimization condition (C-2).

FIG. 14 shows a defocusing in the main scanning direction (each laser beam LA,
9 is a graph showing a relationship between a position where LB is a minimum beam diameter and a shift amount between the image plane S and the optimization condition (C-3).

FIG. 15 shows a laser beam in the main scanning direction indicating the maximum distance on the image plane S when each of the laser beams LA and LB passes through the imaging lens in the imaging lens shown in FIGS. 4 to 11; Range and its optimization conditions (C
4) is a graph showing the relationship with 4).

16 is a graph showing the variation of the interval between laser beams in the sub-scanning direction corresponding to the optimization condition obtained from FIG. 15 in the imaging lens shown in FIGS.
The graph calculated | required about the whole area within a scanning range as 2.3 micrometers.

FIG. 17 shows the amount of deviation of the imaging position in the main scanning direction when the wavelengths of the laser beams LA and LB emitted from each light emitting source fluctuate by 100 nm in the imaging lens shown in FIGS. The graph which shows the relationship with the optimization condition (C-5).

FIG. 18 is a graph showing the relationship between the laser beams LA and LB in the main scanning direction in the imaging lens shown in FIGS. 4 to 11;
7 is a graph showing the relationship between θ characteristics and its optimization condition (C-6).

19 is a graph showing the relationship between the influence of the deviation of the transmittance of the lens 21 and the optimization condition (C-7) in the imaging lens shown in FIGS. 4 to 11. FIG.

FIG. 20 is a diagram showing lens surface shapes obtained when the optimization conditions obtained from FIGS. 12 to 19 are applied to Embodiments 2 and 3 of the imaging lens shown in FIGS. 4 to 11. table.

FIG. 21 is a diagram showing lens surface shapes obtained when the optimization conditions obtained from FIGS. 12 to 19 are applied to Embodiments 4 and 5 of the imaging lens shown in FIGS. 4 to 11; table.

FIG. 22 is a diagram showing data indicating lens surface shapes obtained when the optimization conditions obtained from FIGS. 12 to 19 are applied to Embodiments 6 and 7 of the imaging lens shown in FIGS. 4 to 11. table.

FIG. 23 is a diagram showing lens surface shapes obtained when the optimization conditions obtained from FIGS. 12 to 19 are applied to Embodiments 8 and 9 of the imaging lens shown in FIGS. 4 to 11; table.

FIG. 24 shows an embodiment 10 of the imaging lens in which the optimization conditions obtained from FIGS. 12 to 19 are shown in FIGS. 4 to 11;
21 is a data table showing the shape of a lens surface obtained when applied to Example 11;

FIG. 25 shows an embodiment 12 of the imaging lens in which the optimization conditions obtained from FIGS. 12 to 19 are shown in FIGS. 4 to 11;
15 is a data table showing the shape of a lens surface obtained when applied to Example 13;

FIG. 26 shows an embodiment 14 of the imaging lens in which the optimization conditions obtained from FIGS. 12 to 19 are shown in FIGS. 4 to 11;
15 is a data table showing the shape of a lens surface obtained when applied to Example 15;

FIG. 27 shows Embodiment 16 of the imaging lens in which the optimization conditions obtained from FIGS. 12 to 19 are shown in FIGS. 4 to 11.
And a data table showing the shape of the lens surface obtained when applied to Example 17.

FIG. 28 shows an embodiment 18 of the imaging lens in which the optimization conditions obtained from FIGS. 12 to 19 are shown in FIGS. 4 to 11;
And a data table showing the shape of the lens surface obtained when applied to Example 19.

FIG. 29 shows an embodiment 20 of the imaging lens in which the optimization conditions obtained from FIGS. 12 to 19 are shown in FIGS. 4 to 11;
23 is a data table showing the shape of a lens surface obtained when applied to Example 21.

FIG. 30 shows an embodiment 22 of the imaging lens in which the optimization conditions obtained from FIGS. 12 to 19 are shown in FIGS. 4 to 11.
24 is a data table showing the shape of a lens surface obtained when applied to Example 23.

FIG. 31 shows an embodiment 24 of the imaging lens in which the optimization conditions obtained from FIGS. 12 to 19 are shown in FIGS. 4 to 11.
26 is a data table showing the shape of a lens surface obtained when applied to Example 25.

FIG. 32 shows Embodiment 26 of the imaging lens in which the optimization conditions obtained from FIGS. 12 to 19 are shown in FIGS. 4 to 11;
9 is a data table showing the shape of the lens surface obtained when the method is applied to FIG.

FIG. 33 is a schematic view showing another embodiment of the exposure apparatus shown in FIG. 2;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Multi-beam exposure apparatus 3 ... Light source 3a ... 1st light emission point 3b ... 2nd light emission point 5 ... Pre-deflection optical system 7 ... Deflection device 7a: a polygon mirror, 9: post-deflection optical system, 11: finite focal length lens, 13: stop, 15: cylinder lens, 15g: glass cylinder lens, 15p ... Plastic cylinder lens, 21 ... imaging lens, 23 ... mirror, 25 ... dustproof glass, 51 ... image forming unit, 100 ... image forming apparatus.

Claims (12)

[Claims] A light source, a deflector including a rotary polygon mirror for deflecting light from the light source in a first direction at a substantially constant angular velocity, and disposed between the deflector and the light source; Pre-deflection optical means for guiding the light from the light source to the rotating polygon mirror of the deflector while giving predetermined characteristics to the light, and rotating the rotating polygon mirror to rotate the light deflected by the rotating polygon mirror to a predetermined image plane. An exposure apparatus having only one lens that forms an image at a constant speed such that the amount is proportional to the distance in the first direction, wherein the lens has an arbitrary surface excluding a light incident surface and a light exit surface. An intersection line that intersects each of the light incident surface and the light exit surface is formed on a symmetric surface where the light is deflected by the rotary polygon mirror and a center of an effective area of the predetermined image surface with a deflection point at which the light is deflected. Let L be the distance between image planes when passing, When a paraxial focal length in a second direction perpendicular to the first direction of the lens near the point where a ray passing through the center of the effective area intersects the lens is F, F / L ≦ 0.25 is satisfied. An exposure apparatus, comprising: 2. A light source, a deflector including a rotary polygon mirror for deflecting light from the light source in a first direction at substantially constant angular velocity, and disposed between the deflector and the light source. Pre-deflection optical means for guiding the light from the light source to the rotating polygon mirror of the deflector while giving predetermined characteristics to the light, and the light deflected by the rotating polygon mirror is converted into a predetermined image plane by the rotating polygon mirror. An exposure apparatus having only one lens that forms an image at a constant speed such that the amount of rotation is proportional to the distance in the first direction, wherein the lens is an arbitrary surface excluding a light incident surface and a light exit surface Are formed on a symmetrical plane in which intersection lines intersecting each of the light incident surface and the light emitting surface are asymmetric, and a deflection point at which the light is deflected by the rotating polygon mirror and a center of an effective area of the predetermined image plane. L is the distance between image planes when passing through the predetermined image plane When the light passing through the effective region center and L ₃ the distance between the predetermined image plane and that emits the lens, characterized in that 0.35 ≦ L ₃ / L ≦ 0.65 is satisfied Exposure apparatus. 3. A light source, a deflector including a rotary polygon mirror for deflecting light from the light source in a first direction at substantially constant angular velocity, and disposed between the deflector and the light source. Pre-deflection optical means for guiding the light from the light source to the rotating polygon mirror of the deflector while giving predetermined characteristics to the light, and rotating the rotating polygon mirror to rotate the light deflected by the rotating polygon mirror to a predetermined image plane. An exposure apparatus having only one lens that forms an image at a constant speed such that the amount is proportional to the distance in the first direction, wherein the lens has an arbitrary surface excluding a light incident surface and a light exit surface. An intersection line that intersects each of the light incident surface and the light exit surface is formed on a symmetric surface where the light is deflected by the rotary polygon mirror and a center of an effective area of the predetermined image surface with a deflection point at which the light is deflected. The distance between the image planes when passing through is L, the rotating polygon mirror L ₁ the distance between the point at which rays from the deflection point to more the light is deflected through the effective area center of the predetermined image plane incident on the fθ lens, and the effective area center and the effective area end of the predetermined image plane An exposure apparatus characterized by satisfying 0.15 ≦ L ₁ × sin φ / L ≦ 0.27, where φ is the angle at which the light is deflected by the deflector. 4. A deflector including a light emitting source; a deflector including a rotary polygon mirror for deflecting light from the light emitting source in a first direction at substantially constant angular velocity; and a deflector disposed between the deflector and the light emitting source. Pre-deflection optical means for guiding the light from the light source to the rotating polygon mirror of the deflector while giving predetermined characteristics to the light, and rotating the rotating polygon mirror to rotate the light deflected by the rotating polygon mirror to a predetermined image plane. An exposure apparatus having only one lens that forms an image at a constant speed such that the amount is proportional to the distance in the first direction, wherein the lens has an arbitrary surface excluding a light incident surface and a light exit surface. An intersection line that intersects each of the light incident surface and the light exit surface is formed on a symmetric surface where the light is deflected by the rotary polygon mirror and a center of an effective area of the predetermined image surface with a deflection point at which the light is deflected. The distance between the image planes when passing through is L, the rotating polygon mirror When light from the deflection point to more the light is deflected through the effective area center of the predetermined image surface to the distance between the point of entering the fθ lens and _{L 1, 0.3 ≦ L 1 /} L ≦ 0 65. An exposure apparatus, characterized by satisfying the following. 5. A deflector including a plurality of light-emitting sources, a deflector including a rotary polygon mirror for deflecting each light from the light-emitting sources in a first direction at a substantially constant angular velocity, and between the deflector and the light-emitting sources. And a pre-deflection optical unit for guiding each light from the light source to the rotary polygon mirror of the deflector while giving the light a predetermined characteristic, and converting each light deflected by the rotary polygon mirror into a predetermined image. An exposure apparatus having, on a surface, only one lens that forms an image at a constant speed so that a rotation amount of the rotary polygon mirror and a distance in the first direction are proportional to each other; An arbitrary surface excluding a surface is formed as a symmetric surface in which an intersection line intersecting each of the light incident surface and the light exit surface is asymmetric, and a deflection point at which the light is deflected by the rotary polygon mirror and the predetermined point. When passing through the center of the effective area of the image plane L is the distance between the image planes of the predetermined image plane, and W is the distance between the center of the effective area of the predetermined image plane and the end of the effective area. An exposure apparatus, wherein when an angle deflected by the deflector is Φ, 0.8 ≦ tan ⁻¹ (W / L) /Φ≦1.3 is satisfied. 6. A deflector including a light emitting source, a deflector including a rotary polygon mirror for deflecting light from the light emitting source at a substantially constant angular velocity in a first direction, and disposed between the deflector and the light emitting source. Pre-deflection optical means for guiding the light from the light source to the rotating polygon mirror of the deflector while giving predetermined characteristics to the light, and rotating the rotating polygon mirror to rotate the light deflected by the rotating polygon mirror to a predetermined image plane. An exposure apparatus having only one lens that forms an image at a constant speed such that the amount is proportional to the distance in the first direction, wherein the lens has an arbitrary surface excluding a light incident surface and a light exit surface. An intersection line that intersects each of the light incident surface and the light exit surface is formed on a symmetric surface where the light is deflected by the rotary polygon mirror and a center of an effective area of the predetermined image surface with a deflection point at which the light is deflected. The distance between the image planes when passing through is L, the rotating polygon mirror The light passing through the distance L _1, the effective area center of the predetermined image surface between the point where light rays passing through the effective area center of the predetermined image plane from the deflection point is incident to the fθ lens more the light is deflected Exposure apparatus characterized by satisfying 0.17 ≦ L ₁ × L ₃ / L ² ≦ 0.23 where L ₃ is the distance between the point at which the lens exits and the predetermined image plane. . 7. A light source, a deflector including a rotary polygon mirror for deflecting light from the light source at a substantially constant angular velocity in a first direction, and a deflector disposed between the deflector and the light source. Pre-deflection optical means for guiding the light from the light source to the rotating polygon mirror of the deflector while giving predetermined characteristics to the light, and rotating the rotating polygon mirror to rotate the light deflected by the rotating polygon mirror to a predetermined image plane. An exposure apparatus having only one lens that forms an image at a constant speed such that the amount is proportional to the distance in the first direction, wherein the lens has an arbitrary surface excluding a light incident surface and a light exit surface. An intersection line intersecting with each of the light incident surface and the light exit surface is formed on a symmetric surface where the line is asymmetric, and the light is deflected by the deflector between an effective area center and an effective area end of the predetermined image plane. Is the angle to be formed, and the light is L is the distance between the point of deflection and the image plane when passing through the center of the effective area of the predetermined image plane; W is the distance between the center of the effective area of the predetermined image plane and the end of the effective area; when the distance between the point at which light passing through the effective area center of the surface to emit the lens and the predetermined image plane and _{L 3, φ × (L /} W) / L 3 ≦ 0.009 is satisfied An exposure apparatus, comprising: 8. A deflector including a light emitting source; a deflector including a rotary polygon mirror for deflecting light from the light emitting source in a first direction at a substantially constant angular velocity; and a deflector disposed between the deflector and the light emitting source. Pre-deflection optical means for guiding the light from the light source to the rotating polygon mirror of the deflector while giving predetermined characteristics to the light, and rotating the rotating polygon mirror to rotate the light deflected by the rotating polygon mirror to a predetermined image plane. An exposure apparatus having only one lens that forms an image at a constant speed such that the amount is proportional to the distance in the first direction, wherein the lens has an arbitrary surface excluding a light incident surface and a light exit surface. An intersection line that intersects each of the light incident surface and the light exit surface is formed on a symmetric surface where the light is deflected by the rotary polygon mirror and a center of an effective area of the predetermined image surface with a deflection point at which the light is deflected. Let L be the distance between image planes when passing, The paraxial focal length in a second direction perpendicular to the first direction of the lens near the intersection of the ray passing through the effective area center with the lens is F, and the light passing through the effective area center of the predetermined image plane is The distance between the point at which the lens exits and the predetermined image plane is L ₃ , and a ray passing through the center of the effective area of the predetermined image plane from the deflection point where the light is deflected by the rotating polygon mirror enters the fθ lens. L ₁ , the angle at which the light is deflected by the deflector between the center of the effective area of the predetermined image plane and the end of the effective area is Φ, and the center of the effective area of the predetermined image plane. Assuming that the distance from the edge of the effective area is W, F / L ≦ 0.25, 0.35 ≦ L ₃ /L≦0.65, 0.15 ≦ L ₁ × sinΦ / L ≦ 0.27 _{, 0.3 ≦ L 1 / L ≦} 0.65, 0.8 ≦ tan -1 (W / L) Φ ≦ 1.3, 0. _{7 ≦ L 1 × L 3 /} L 2 ≦ 0.23, and φ × (L / W) / L 3 ≦ 0.009 exposure apparatus, wherein a is satisfied. 9. A deflector including a light emitting source, a deflector including a rotary polygon mirror for deflecting light from the light emitting source in a first direction at substantially constant angular velocity, and disposed between the deflector and the light emitting source. Pre-deflection optical means for guiding the light from the light source to the rotating polygon mirror of the deflector while giving predetermined characteristics to the light, and rotating the rotating polygon mirror to rotate the light deflected by the rotating polygon mirror to a predetermined image plane. An exposure apparatus having only one lens that forms an image at a constant speed such that the amount is proportional to the distance in the first direction, wherein the lens has an arbitrary surface excluding a light incident surface and a light exit surface. An intersection line that intersects each of the light incident surface and the light exit surface is formed on a symmetric surface where the light is deflected by the rotary polygon mirror and a center of an effective area of the predetermined image surface with a deflection point at which the light is deflected. Let L be the distance between image planes when passing, The paraxial focal length in a second direction perpendicular to the first direction of the lens near the intersection of the ray passing through the effective area center with the lens is F, and the light passing through the effective area center of the predetermined image plane is The distance between the point at which the lens exits and the predetermined image plane is L ₃ , and a ray passing through the center of the effective area of the predetermined image plane from the deflection point where the light is deflected by the rotating polygon mirror enters the fθ lens. L ₁ , the angle at which the light is deflected by the deflector between the center of the effective area of the predetermined image plane and the end of the effective area is Φ, and the center of the effective area of the predetermined image plane. Assuming that the distance from the edge of the effective area is W, F / L ≦ 0.25, 0.35 ≦ L ₃ /L≦0.65, 0.15 ≦ L ₁ × sinΦ / L ≦ 0.27 _{, 0.3 ≦ L 1 / L ≦} 0.65, 0.8 ≦ tan -1 (W / L) Φ ≦ 1.3, 0. _{7 ≦ L 1 × L 3 /} L 2 ≦ 0.23, and φ × (L / W) / exposure apparatus, wherein at least two are satisfied L ₃ ≦ 0.009. 10. A light source, a deflector including a rotary polygon mirror for deflecting light from the light source in the first direction at substantially constant angular velocity, and disposed between the deflector and the light source. Pre-deflection optical means for guiding the light from the light source to the rotating polygon mirror of the deflector while giving predetermined characteristics to the light, and rotating the rotating polygon mirror to rotate the light deflected by the rotating polygon mirror to a predetermined image plane. An exposure apparatus having only one lens that forms an image at a constant speed such that the amount is proportional to the distance in the first direction, wherein the lens has an arbitrary surface excluding a light incident surface and a light exit surface. An intersection line that intersects each of the light incident surface and the light exit surface is formed on a symmetric surface where the light is deflected by the rotary polygon mirror and a center of an effective area of the predetermined image surface with a deflection point at which the light is deflected. The distance between the image planes when passing is L, the predetermined image plane The paraxial focal length in the second direction perpendicular to the first direction of the lens near the intersection of the ray passing through the center of the effective area with the lens is F, and the light passing through the center of the effective area on the predetermined image plane is The distance between the point at which the lens exits and the predetermined image plane is L ₃ , and a ray passing through the center of the effective area of the predetermined image plane from the deflection point where the light is deflected by the rotating polygon mirror enters the fθ lens. L ₁ , the angle at which the light is deflected by the deflector between the center of the effective area of the predetermined image plane and the end of the effective area is Φ, and the center of the effective area of the predetermined image plane. Assuming that the distance from the edge of the effective area is W, F / L ≦ 0.25, 0.35 ≦ L ₃ /L≦0.65, 0.15 ≦ L ₁ × sinΦ / L ≦ 0.27 _{, 0.3 ≦ L 1 / L ≦} 0.65, 0.8 ≦ tan -1 (W / L) Φ ≦ 1.3, 0 _{17 ≦ L 1 × L 3 /} L 2 ≦ 0.23, and φ × (L / W) / L 3 ≦ 0.009 exposure apparatus characterized by any combination are satisfied. 11. An exposure apparatus according to claim 1, wherein said light emitting source includes at least two or more light sources. 12. A light source, a deflector including a rotary polygon mirror for deflecting light from the light source in a first direction at substantially constant angular velocity, and disposed between the deflector and the light source. Pre-deflection optical means for guiding the light from the light source to the rotating polygon mirror of the deflector while giving predetermined characteristics to the light, and rotating the rotating polygon mirror to rotate the light deflected by the rotating polygon mirror to a predetermined image plane. An exposure apparatus having only one lens that forms an image at a constant speed such that the amount is proportional to the distance in the first direction, wherein the lens has an arbitrary surface excluding a light incident surface and a light exit surface. An intersection line that intersects each of the light incident surface and the light exit surface is formed on a symmetric surface where the light is deflected by the rotary polygon mirror and a center of an effective area of the predetermined image surface with a deflection point at which the light is deflected. The distance between the image planes when passing is L, the predetermined image plane The paraxial focal length in the second direction perpendicular to the first direction of the lens near the intersection of the ray passing through the center of the effective area with the lens is F, and the light passing through the center of the effective area on the predetermined image plane is The distance between the point at which the lens exits and the predetermined image plane is L ₃ , and a ray passing through the center of the effective area of the predetermined image plane from the deflection point where the light is deflected by the rotating polygon mirror enters the fθ lens. L ₁ , the angle at which the light is deflected by the deflector between the center of the effective area of the predetermined image plane and the end of the effective area is Φ, and the center of the effective area of the predetermined image plane. Assuming that the distance from the edge of the effective area is W, F / L ≦ 0.25, 0.35 ≦ L ₃ /L≦0.65, 0.15 ≦ L ₁ × sinΦ / L ≦ 0.27 _{, 0.3 ≦ L 1 / L ≦} 0.65, 0.8 ≦ tan -1 (W / L) Φ ≦ 1.3, 0 _{17 ≦ L 1 × L 3 /} L 2 ≦ 0.23, and φ × (L / W) / an exposure apparatus characterized by L ₃ ≦ 0.009 is satisfied, the image carrier by the exposure device An image forming apparatus comprising: a developing device that develops a latent image formed in a developing device; and a transfer device that transfers a developer image developed by the developing device to a material to be transferred.