JPH0954250A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To correct eccentric distortion aberration generated due to an assembling error, etc., by adjusting the eccentricity of the lens of an optical image forming system on at least two places. SOLUTION: A first lens frame 2a on which a condenser lens G1 is arranged and a second lens frame 2b on which a the image side lens group G2 of a first lens group is arranged is enabled to adjust eccentricity by means of a first and a second eccentricity adjusting mechanisms 3a, 3b respectively. The eccentricity adjusting mechanisms 3a, 3b is provided with a micrometer and an actuator, translate the respective lens groups in (y) direction and (z) direction in a plane perpendicular to the direction X of the optical axis or tilt them around the y and z axes. By adjusting two directions at the time of translation and two axes at the time of inclination, the eccentricity is corrected even when the eccentricity is generated in either direction. A third lens frame 2c is driven in the direction X of the optical axis by means of a focusing mechanism 3c so that a focus of a reducing optical system 20 is matched with a photoreceptor P.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus for forming a two-dimensional pattern formed on a light source section on an image plane via an image forming optical system.

[0002]

When a two-dimensional pattern of a light source unit is imaged on an image plane and a positional deviation occurs due to an assembling error of an imaging optical system, the image of the pattern has an eccentric distortion such as a trapezoidal distortion. There is a problem in that aberration occurs and drawing accuracy is reduced.

[0003]

The present invention has been made in view of the above-mentioned problems, and forms a two-dimensional pattern formed on a light source unit on an image plane via an image forming optical system. In the image forming apparatus, at least two lenses in the image forming optical system including a plurality of lenses can be independently adjusted for eccentricity, and by this adjustment, eccentric distortion aberration such as trapezoidal distortion of an image can be obtained. The feature is that it can be corrected.

The configuration in which at least two lenses can be adjusted independently of eccentricity is because eccentric distortion aberration caused by an error in assembling the lens includes two components, and thus eccentricity adjustment of one lens is not possible. This is because the distortion may not be completely corrected in some cases. The eccentric distortion aberration is described, for example, in "Third-order aberration theory of an optical system having eccentricity" (Yoshiya Matsui, June 1990, Japan Optomechatronics Association).

Looking at two components of the eccentric distortion aberration in a phenomenological manner, one of them has a trapezoidal shape in which a rectangular pattern forms a trapezoidal shape because the imaging magnification has a substantially linear gradient in one direction in the image plane. As the distortion component, the other appears as a V-shaped distortion component in which an image is formed by bending a linear pattern in a V-shape in the image plane in the same direction as the above with a line including the optical axis as a boundary. When yz orthogonal coordinates are set in the plane orthogonal to the optical axis of the imaging optical system, if some lenses are decentered in the y-axis direction and the above two distortions appear at the same time, the position of the image point becomes the reference. The position is displaced in both the y and z directions.

If it is possible to identify the lens in which eccentricity causes distortion and the state of eccentricity, correction can be performed by returning the lens to the reference position, but such identification is generally difficult. Since the ratio of the trapezoidal distortion component and the V-shaped distortion component generated by the constant eccentricity differs depending on the lens, at least two adjustments are necessary to simultaneously correct the trapezoidal distortion component and the V-shaped distortion component. .

The image forming optical system is constructed by arranging, for example, a first lens group having a condenser lens closest to the light source section and a second lens group arranged on the image plane side in order from the light source section side. The condenser lens, the image side lens group of the first lens group excluding the condenser lens, and the second lens group are arranged in independent first, second, and third lens frames, respectively. In this case, at least two of the three lens frames can be eccentrically adjusted.

The "decentering adjustment" is performed by a parallel movement in a plane perpendicular to the optical axis of the image forming optical system and the optical axis of the lens held by the lens frame with respect to the optical axis of the image forming optical system. It is used as a concept that includes both tilting and tilting.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of an image forming apparatus according to the present invention will be described below. The embodiment shows an example in which the image recording apparatus of the invention is applied to a multi-beam recording apparatus. As shown in FIG. 1, in this apparatus, a light source unit 10 arranged in a casing 1, a reduction optical system 20 as an imaging optical system, and a table 30 on which a photoconductor P to be recorded is placed. Composed of and.

The optical system unit provided in the casing 1 is movable in the y direction in a yz plane perpendicular to the optical axis direction x of the reduction optical system 20, and the table 30 is in the z direction in the same plane. Can be slid onto.

The light source unit 10 has a plurality of LEDs (light emitting diodes) 12 mounted in a two-dimensional array on a top panel 11, and an aperture panel 13 having apertures corresponding to the plurality of LEDs 12 in a one-to-one correspondence. Composed of and. The beam emitted from the LED 12 and transmitted through the aperture reaches the photoconductor P via the reduction optical system 20, and forms an image of the aperture on the surface of the photoconductor P.

The reduction optical system 20 has a condenser lens G1 (21a) and an image side lens group G2 in order from the light source section 10 side and has a first lens group 21 having a positive power as a whole.
And a second lens group G3 (22) having a positive power and arranged on the image plane side. The condenser lens G1, the image side lens group G2 of the first lens group, and the second lens group G3 are arranged in independent first, second, and third lens frames 2a, 2b, and 2c, respectively, and are assembled to the casing 1. Has been.

The first lens frame 2a in which the condenser lens G1 is arranged and the second lens frame 2b in which the image side lens group G2 of the first lens group is arranged are the first and second lenses, respectively.
The eccentricity adjustment mechanism 3a, 3b can adjust the eccentricity. The eccentricity adjusting mechanisms 3a and 3b include a micrometer and an actuator, and translate each lens group in the y and z directions in a plane perpendicular to the optical axis direction x, or tilt about the y and z axes. Let By enabling adjustment in two directions in the case of parallel movement and in two directions in the case of tilting, it is possible to correct when eccentricity occurs in either direction.

A third lens unit in which the second lens unit G3 is arranged
The focus of the reduction optical system 20 of the lens frame 2c of
In accordance with an output from a focus detector (not shown), the focusing mechanism 3c drives in the optical axis direction x.

As shown in this example, when the lens group is divided into three groups and housed in independent lens frames, two arbitrary groups among them can be adjusted. Thus, the eccentric distortion aberration can be corrected. However, when the second lens group G3 moves in the optical axis direction for focusing as in this example, the mechanism becomes complicated if this lens group is also used for eccentricity adjustment. It is desirable to adjust with the lens group.

The reduction optical system 20 is individually corrected for aberrations so that the overall performance does not deteriorate even when the second lens group 22 is moved alone in the optical axis direction x by the focusing mechanism 3c. Even if the first lens group and the second lens group, which are independently corrected for aberrations, are independently adjusted for decentering, it is possible to correct decentration distortion while suppressing the amount of coma generated. Further, since the condenser lens G1 is close to the light source unit 10 and the height of the marginal ray is low, the amount of coma aberration generated is small even if the decentering is similarly adjusted.

[0017]

EXAMPLE Next, the reduction optical system 2 shown in the above embodiment
A specific example of 0 will be described. 2 shows the overall configuration of the imaging optical system according to the embodiment, FIG. 3 shows its various aberrations, FIG. 4 shows the first lens group, and FIG. 5 shows the second lens group.

In the embodiment, the first lens group (first surface to eighth surface)
The surface 21 is a positive first lens 21a (condenser lens G1), a positive second lens 21b, and a negative third lens 2 from the object side.
1c, a positive fourth lens 21d is composed of 4 elements in 4 groups, and the second lens group (9th surface to 27th surface) 22 is a negative first lens 2
2a, the positive second lens 22b, the positive third lens 22c,
The negative fourth lens 22d, and the negative fifth lens across the aperture.
Lens 22e, positive sixth to tenth lenses 22f to 22j
It consists of 10 sheets in 9 groups. The fifth lens 22e and the sixth lens 22f of the second lens group 22 are integrally attached.

FIG. 4A shows spherical aberration SA at 450 nm,
Aberration diagram showing sine condition SC, (B) 400nm, 450nm, 550nm
, Chromatic aberration represented by spherical aberration, (C) chromatic aberration of magnification represented by 400 nm and 550 nm, (D) astigmatism (S: sagittal,
(M: meridional), (E) shows distortion.

Table 1 shows specific numerical configurations of the embodiments. In the table, symbol f is the focal length (mm), FNO is the F number, d0 is the distance (mm) on the optical axis from the aperture plate to the object side surface of the first lens L1, and fB is the back focus (m
m), M is the magnification, r is the radius of curvature (mm), d is the lens thickness on the optical axis and the air gap (mm), n450 is the refractive index at 450 nm,
ν is the Abbe number.

In the embodiment, d0 is the LED 12
The light fluxes emitted from and emitted from the first lens group 21 are set to be parallel light fluxes. Further, a diaphragm S is arranged between the fourth lens 22d and the fifth lens 22e of the second lens group 22, and the inter-lens distance d16 is
The sum of the distance from the 4th lens to the aperture is 5.15mm and the distance from the aperture to the 5th lens is 4.09mm.

[0022]

[Table 1] f = 138.46 FNo = 1: 2.5 d0 = 17.25 fB = 18.00 M = -0.040 surface number r d n450 ν surface number r d n450 ν 1 ∞ 47.00 1.52485 64.1 17 -5.743 1.20 1.66888 33.8 2 -370.000 360.48 18 -25.828 4.00 1.50347 81.6 3 198.800 18.00 1.49480 70.2 19 -9.200 0.25 4 -533.000 69.40 20 -24.120 4.00 1.50347 81.6 5 -73.562 5.00 1.63114 49.8 21 -12.800 0.20 6 81.685 19.92 22 59.800 3.50 1.50347 81.6 7 135.029 9.80 1.49480 70.2 0.10 8 -65.656 35.30 24 40.040 3.50 1.50347 81.6 9 93.720 2.00 1.50347 81.6 25 -131.719 0.10 10 20.790 6.50 26 50.000 3.00 1.50347 81.6 11 31.514 3.50 1.71354 31.1 27 ∞ 12 -2324.027 0.35 13 10.000 5.30 1.50347 81.6 14 35.190 0.70 15 20.874. 33.8 16 7.400 5.15 Aperture 4.09

Table 2 shows a specific correction example when decentering distortion occurs in the optical system of the above embodiment. Since the influence of the eccentric distortion becomes larger as the distance from the optical axis increases, here, as shown in FIG. 6, the point A, which is one of the points farthest from the optical axis in the rectangular imaging region, is focused. , And the ideal image formation position (y =-
The amount of eccentric distortion is shown as the amount of displacement (5.12 mm, z = 2.48 mm). If the displacement amount at this point, that is, the error becomes small,
The error at other points is also reduced, and the image formation area substantially coincides with the rectangular area indicated by the broken line.

The amount of error of the image forming point due to the eccentric distortion is shown in FIG. 7, which is an enlarged view of the area within the chain double-dashed line in FIG. The distance to the image position is expressed as projections y and z on the y and z axes.

When eccentric distortion aberration occurs, the image is distorted and moves, so that the coordinates of the point A are affected by both displacement due to distortion and displacement due to movement. However, here, focusing only on the displacement due to the distortion, the position of the point A is set as the distance from the reference image point corresponding to the object point on the axis to the point A, that is, when the reference image point is returned to the coordinate origin. Is shown as the coordinates of point A.

Table 2 shows, for each of the cases (1) to (4), the method of correcting the condenser lens G1 and the image side lens group G2 with respect to the amount of error, the correction amount, and the effect of each correction alone, and The value of the error after correction is shown. G in the cases of (1) and (2)
Decentering distortion is corrected by translating both 1 and G2, and in the cases of (3) and (4), translating G1 and tilting G2.

For example, in the case of (1), when decentering distortion such that point A is displaced by −0.19 μm in the y direction and −0.06 μm in the z direction from the reference position, the condenser lens G1 is moved in the z axis direction. By moving 0.30 mm in parallel with the image side lens group G2 of the first lens group in the z-axis direction by -0.36 mm, the error from the ideal image forming position of the point A in the y direction is − 0.01 μm, 0.04 μm for z direction
Is reduced to

[0028]

[Table 2] Pre-correction error G1 correction amount effect G2 correction amount effect post-correction error (1) Δy -0.19μm 0.30mm 0.45μm -0.36mm -0.27μm -0.01μm Δz -0.06μm (parallel) -0.55μm (parallel) ) 0.65μm 0.04μm (2) Δy 0.29μm -0.85mm -1.28μm 1.25mm 0.95μm -0.04μm Δz 0.65μm (parallel) 1.56μm (parallel) -2.25μm -0.04μm (3) Δy 0.38μm -0.40mm -0.60 μm -6.0 min 0.23 μm 0.01 μm Δz -0.90 μm (parallel) 0.74 μm (tilt) 0.07 μm -0.09 μm (4) Δy 0.29 μm 0.20 mm 0.30 μm 15.5 min -0.59 μm 0.00 μm Δz 0.65 μm (parallel) -0.37 μm (tilt) -2.25 μm 0.09 μm

In the example of Table 2, when the influence of the eccentric distortion aberration occurs line-symmetrically with respect to the z axis, that is, the trapezoidal distortion component occurs due to the gradient of the magnification in the z axis direction, and V
Only the case where the character distortion component is symmetrical about the z axis is shown. Therefore, the direction of correction is the z-axis direction in the case of parallel movement and the y-axis direction in the case of tilting.

Specifically, the error in each case is that the image side lens group G2 of the first lens group in (1) and the second lens group G3 in (2) and (4) are 5 minutes around the y-axis. (min) It is the same as the amount of aberration when tilted, and in (3) it is the same as the amount of aberration when the image-side lens group G2 is translated by 0.5 mm in the z-axis direction.

[0031]

As described above, according to the present invention, the decentering adjustment of the lens of the imaging optical system can be performed at at least two places, so that the decentering distortion aberration caused by the assembly error or the like can be corrected. it can.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an embodiment of an image recording apparatus according to the present invention.

FIG. 2 is a lens diagram showing an overall configuration of a reduction optical system according to an example.

FIG. 3 is a graph showing various aberrations of the lens of FIG.

FIG. 4 is a lens diagram of a first lens group of the lens in FIG.

FIG. 5 is an enlarged lens diagram showing a second lens group of the lens in FIG.

FIG. 6 is an explanatory diagram showing distortion of an image forming area due to decentering distortion.

FIG. 7 is an explanatory diagram showing an enlarged area surrounded by a chain double-dashed line in FIG. 6;

[Explanation of symbols]

 1 Casing 2a, 2b, 2c Lens frame 3a, 3b Decentering adjustment mechanism 10 Light source unit 20 Reduction optical system 21 First lens group G1 (21a) Condenser lens G2 Image side lens group G3 (22) Second lens group 30 Table

Claims (7)

[Claims] 1. An image forming apparatus for forming a two-dimensional pattern formed on a light source unit on an image plane through an image forming optical system, wherein a lens in the image forming optical system is composed of a plurality of lenses. An image forming apparatus, characterized in that at least two of the plurality of lenses are capable of independently adjusting decentering so as to correct decentering distortion of an image. 2. The image forming optical system comprises, in order from the light source section side, a first lens group having a condenser lens closest to the light source section and a second lens group arranged on the image plane side. And the condenser lens, the image side lens group of the first lens group excluding the condenser lens, and the second lens group are arranged in independent first, second, and third lens frames, respectively, and at least 2 The image forming apparatus according to claim 1, wherein the two lens frames are adjustable in eccentricity. 3. The image forming apparatus according to claim 2, wherein the first lens group and the second lens group are independently corrected for aberrations. 4. The first and second lens frames are adjustable in decentering, and the third lens frame is adjustable in the optical axis direction of the imaging optical system for focusing. The image forming apparatus according to claim 2. 5. The image forming apparatus according to claim 2, wherein at least one of the lens frames is movable in parallel in a plane perpendicular to the optical axis of the imaging optical system. 6. At least one of the lens frames is tiltable so that an optical axis of a lens held by the lens frame is tilted with respect to an optical axis of the image forming optical system. The image forming apparatus described. 7. The image forming apparatus according to claim 1, wherein the light source unit includes a plurality of light sources arranged in a two-dimensional manner.