JPH07120693A - Optical beam scanning device - Google Patents

Abstract

PURPOSE:To provide an optical beam scanning device capable of suppressing the curvature of a scanning line resulted from the slippage of the base line of an image face curvature correcting lens from the scanning surface. CONSTITUTION:A lens holder 61 is rotatable around a rotating shaft 69 extending in parallel to a main scanning direction (y) while holding an image surface curvature correcting lens 42. The image face curvature correcting lens 42 is rotated together with the lens holder 61 according to an external force to be positioned. The posture of the base line L of the image face curvature correcting lens 42 is thus regulated, and the slippage of the base line L from the scanning surface is reduced. Consequently, the curvature of the scanning line formed on a surface to be scanned is suppressed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light beam scanning device used in a laser beam printer, an image recording device for plate making, and the like, and particularly, it is possible to suppress the curvature of a scanning line formed on a surface to be scanned. The present invention relates to a light beam scanning device.

[0002]

2. Description of the Related Art Conventionally, in this type of light beam scanning apparatus, in order to correct the plane tilt of the deflector, the deflecting surface and the scanned surface are optically moved in a direction substantially orthogonal to the scanning surface, that is, in the sub-scanning direction. It is configured so as to be conjugate with each other.
Specifically, the light beam from the light source is condensed by an appropriate optical system only in the sub-scanning direction to form a line image, and the deflector is arranged so that the deflection surface is located on or near the line image. ing. Then, the light beam deflected by this deflector is irradiated onto the surface to be scanned through the scanning lens and the cylindrical lens having power only in the sub-scanning direction.

However, when the light beam scanning device is constructed in this way, the problem of troublesomeness is solved,
The following problems occur. That is, the image plane is curved,
If the image forming position deviates from the surface to be scanned in the optical axis direction, and especially if the amount of deviation deviates from the depth of focus range, the size of the light spot changes. As a result, the quality of the image formed on the surface to be scanned deteriorates.

Therefore, conventionally, in order to correct field curvature while correcting surface tilt, instead of a cylindrical lens, a field curvature correction lens in which a generatrix L is curved in the main scanning direction y as shown in FIG. A technique using 42 has been proposed. Examples of the field curvature correction lens 42 include Japanese Patent Publication No.
There is one disclosed in Japanese Patent Application Laid-Open No. 7082 (Reference 1) and one disclosed in Japanese Patent Laid-Open No. 3-249722 (Reference 2).

(1) The lens described in Document 1 is a curved cylindrical lens in which a cylindrical lens is curved and shaped so as to approach the surface to be scanned as it goes from the optical axis to both ends of the lens (main scanning direction y). By disposing this curved cylindrical lens between the scanning lens and the surface to be scanned, the field curvature can be corrected and the scanning line SL parallel to the main scanning direction y can be formed on the surface to be scanned. it can.

(2) The lens described in Document 2 is an anamorphic lens, and the radius of curvature of one surface of the lens in the sub scanning direction x advances from the optical axis OA to both ends of the lens (main scanning direction y). Therefore, it is shaped to be large. Therefore, the power in the same direction on the one surface of the anamorphic lens decreases as it goes from the optical axis OA to both ends of the lens, and as a result, the field curvature is corrected and the main scanning direction y is applied to the surface to be scanned. Scan line S parallel to
L can be formed.

[0007]

By the way, in order to correct the field curvature, it is necessary to curve the generatrix L of the field curvature correction lens 42 only along the main scanning direction y. However, the lens processing accuracy is limited. As shown in FIG. 10, the generatrix L of the field curvature correction lens 42 is changed as shown in FIG.
Not only the main scanning direction y but also the sub scanning direction x may be curved (the generatrix L is displaced from the scanning surface). In this case, the scanning line SL 'is curved and the image quality is deteriorated. In FIG. 10, the chain double-dashed line is the bus L
Shows the scanning line SL when the curve is not curved in the sub-scanning direction x, that is, the generatrix L is located in the scanning plane.

The present invention has been made to solve the above problems, and reduces the amount of curvature of the generatrix of the field curvature correction lens in the sub-scanning direction to suppress the curvature of the scanning line formed on the surface to be scanned. It is an object of the present invention to provide a light beam scanning device capable of performing the above.

[0009]

According to the present invention, a light beam from a light source is condensed only in the sub-scanning direction to form a line image,
The light beam is deflected by a deflector having a deflection surface on or near the line image, and the deflected light beam has a power in the scanning lens and the sub-scanning direction and is substantially orthogonal to the sub-scanning direction. A light beam scanning device for scanning the surface to be scanned in the main scanning direction by irradiating the surface to be scanned through a field curvature correction lens in which a generatrix is curved along the scanning direction. In order to achieve this, the field curvature correction lens is held rotatably around a rotation axis parallel to the main scanning direction, and the field curvature correction lens is rotated around the rotation axis according to a force applied from the outside. It is equipped with a rotation positioning mechanism for rotating the lens to position it.

[0010]

According to the present invention, the field curvature correcting lens is rotatably held by the rotation positioning mechanism about the rotation axis parallel to the main scanning direction. Then, the field curvature correction lens is rotated around the rotation axis according to a force applied from the outside, the attitude of the generatrix of the field curvature correction lens is adjusted, and the deviation of the generatrix from the scanning surface is deviated. Will be reduced. as a result,
Curvature of the scanning line formed on the surface to be scanned is suppressed.

[0011]

FIG. 1 is a diagram showing an embodiment of a light beam scanning device according to the present invention. As shown in the figure, in this light beam scanning device, a light beam L1 from a light source 10 such as a semiconductor laser is passed through a first imaging optical system 20 to form a mirror surface 31 (deflection of a deflecting surface) of a rotary polygon mirror 30 that functions as a deflector. Surface). The first imaging optical system 20 is composed of a collimator lens 21 and a cylindrical lens 22 having a power only in the sub-scanning direction x. The divergent light beam L1 from the light source 10 is collimated by the collimator lens 21. After being shaped into the beam L2, the cylindrical lens 2
By 2 the focused light beam L3 is focused only in the sub-scanning direction x. As a result, a line image is formed on or near the mirror surface 31 of the rotary polygon mirror 30.

The rotary polygon mirror 30 rotates about a rotation axis 32 in the direction of arrow A and deflects the focused light beam L3. Then, the deflected light beam L deflected by the rotating polygon mirror 30.
4 is imaged on the surface to be scanned (cylindrical surface of the rotary drum) 50 via the second imaging optical system 40 including the scanning lens 41 and the field curvature correction lens 42. By configuring the light beam scanning device in this way, in the sub-scanning direction x,
The mirror surface 31 of the rotary polygon mirror 30 is optically conjugate with the scanned surface 50, and as a result, the surface tilt of the mirror surface 31 is corrected, and the image recorded on the scanned surface 50 is kept in high quality.

Although not shown in FIG. 1, the field curvature correction lens 42 has a rotary positioning mechanism for rotationally positioning the lens 42 around a predetermined rotary axis, and a vertical position (secondary direction). A positioning mechanism 60 including a vertical positioning mechanism for moving and positioning in the scanning direction x) is attached. Hereinafter, the configuration and operation of the positioning mechanism 60 will be mainly described with reference to FIGS. 2 to 4.

FIG. 2 is a top view of the positioning mechanism 60.
3 is a front view of the positioning mechanism 60, and FIG. 4 is a side view of the positioning mechanism 60. This positioning mechanism 60
Has a lens holder 61 extending in the main scanning direction y. On one side surface (lower surface side in FIG. 2) of the lens holder 61, a concave portion 62 extending in the main scanning direction y is formed in the center thereof.
Is provided, and leaf springs 63 and 6 for pressing the lens on both ends are provided.
3 is attached. Therefore, the lens 42 can be held in the lens holder 61 by immersing the lens 42 in the recess 62 and pressing both ends of the lens 42 with the leaf springs 63, 63.

A slit 64 is provided in the center of the other side surface (upper surface side in FIG. 2) of the lens holder 61, and an image plane on which the light beam is held by the lens holder 61 through the slit 64. It is adapted to enter the curvature correction lens 42.

The lens holder 61 has a shaft 65 projecting from both ends thereof in the main scanning direction y, and is freely rotatable on a lens holder column 68 fixed to a base 67 via a vertical positioning mechanism 66 which will be described later. Is supported by. As a result, the lens holder 61 is rotatable about the rotary shaft 69 parallel to the main scanning direction y while holding the lens 42. Further, the both ends of the lens holder 61 are provided with substantially rectangular parallelepiped projections 61a (the projection at one end is not shown). In this embodiment, the rotating shaft 69 passes through both ends of the generatrix L of the lens 42, but the present invention is not limited to this.

The upper end 68 of this lens holder support 68
As shown in FIG. 4, a is finished in a substantially U-shape, and the U-shaped notch 70 has a protrusion 6 of the lens holder 61.
1a is growing. Further, an adjusting push screw 71 is penetrated through one apex portion 68b of the substantially U-shaped upper end portion 68a, and an adjusting spring 72 is attached to the other apex portion 68c. The protrusion 61a of the lens holder 61 is sandwiched and supported. Although not shown in the drawing, the other lens holder support is similarly configured. Therefore, when the adjusting push screw 71 is pushed in the (−z) direction, the tip of the screw 71 pushes the protruding portion 61a of the lens holder 61 against the spring force of the spring 72, and as a result, the field curvature correction is performed. The lens holder 61 that holds the lens 42 has a rotating shaft 6
The lens 42 rotates about 9 degrees, and the lens 42 rotates about the rotation axis 69 at an angle θ.
Is rotated and positioned (see the alternate long and short dash line in FIG. 4). Conversely, if the screw 71 is moved in the (+ z) direction,
The lens holder 61 is rotated in the opposite direction by the spring force of the spring 72, and the lens 42 is positioned.

As described above, in this embodiment, the lens holder 61 is configured to hold the lens 42, and
A rotation positioning mechanism is provided which is rotatable about a rotation shaft 69 extending in parallel with the main scanning direction y while holding the lens 42 and rotates the lens 42 together with the lens holder 61 in accordance with an external force to position the lens 42. Therefore, the posture of the generatrix L of the field curvature correction lens 42 can be adjusted to reduce the amount of curvature of the scanning line in the sub-scanning direction x.

On the other hand, the vertical positioning mechanism 66 is provided between the base 67 and the lens holder support 68, as shown in FIG. The vertical positioning mechanism 66 includes a vertical adjustment screw 73, a guide shaft 74, and a spring 75. That is, the lens holder support 68
A bush 76 is provided at the lower end portion 68d of
A guide shaft 74 protruding from the upper surface of the base 67 is inserted into the bush 76, so that the lens holder support 68 can be smoothly moved up and down. In addition, the base 67 and the lower end 68 of the lens holder support 68
A vertical adjustment screw 73 and a spring 75 are connected between the lens holder d and d, and the lens holder column 68 moves up and down in accordance with the vertical movement of the screw 73 due to rotation, and as a result, the lens held by the lens holder 61. 42 is vertically positioned (sub scanning direction x).

As described above, in this embodiment, since the vertical positioning mechanism 66 is provided, the optical axis of the lens 42 can be easily adjusted. For example, when the lens 42 is rotated around the rotation shaft 69 by using the rotation positioning mechanism, the lens 42
May be significantly deviated from the optical axis OA. In such a case, by using the vertical positioning mechanism 66,
The optical axis of the lens 42 can be easily adjusted.

Next, the rotational positioning mechanism according to the above-mentioned embodiment can reduce the amount of curvature of the scanning line in the sub-scanning direction x and how the scanning line changes, using two models. explain.

(1) First Model FIG. 5 is a first explanatory view for explaining the effect of the rotary positioning mechanism in the embodiment. Here, as shown in the figure, the straight line passing through the end of the generatrix L of the field curvature correction lens 42 is made to coincide with the main scanning direction y, and the point of intersection with the optical axis OA is taken as the origin O and from the origin O. X in sub-scanning direction x
The coordinates are the Y coordinate in the main scanning direction y, and Z in the optical axis direction z.
A three-dimensional coordinate system that takes coordinates will be defined and described. Further, since the field curvature correction lens 42 is often arranged in the vicinity of the scanned surface 50, the curvature of the scanning line on the scanned surface 50 is almost the same as the curvature of the generatrix of the lens 42 in the sub-scanning direction X. Suppose that

As shown in FIG. 5, the projection line Lyz formed when the generatrix L of the lens 42 is projected on the yz plane has a radius R1,
It can be represented by an arc of the center (0, 0, Z0), and the projection line Lxy formed when projected on the xy plane has a radius R2,
If it can be represented by an arc of the center (X0,0,0),
The curvature of the generatrix L in the scanning plane (yz plane) is expressed by the following equation.

[0024]

[Equation 1]

On the other hand, the curvature of the generatrix L in the sub-scanning direction x is

[0026]

[Equation 2]

[0027] These simultaneous equations of Equations 1 and 2 show the bus line L. So, these are X, Y, Z
When transformed into the relational expression of

[0028]

[Equation 3]

It becomes Here, considering only the amount of bending in the sub-scanning direction x at the center of the optical axis OA, the angle θ, that is, the straight line connecting both ends of the generatrix L as the rotation axis, that is,

[0030]

[Equation 4]

The amount of bending can be reduced by rotating only. For example, assuming that the radii R1 and R2 are "2000" and "9999.75" respectively, and the coordinates X0 and Z0 are "-9999.25" and "-1997.5" respectively, the scanning line on the surface 50 to be scanned is shown in FIG. Solid line SL '. On the other hand, when it is rotated about the rotation axis by the angle θ that satisfies the equation 4, the scanning line on the scanned surface 50 becomes the solid line SL, and the curvature of the scanning line formed on the scanned surface 50 is suppressed. You can

(2) Second Model FIG. 7 is a second explanatory view for explaining the effect of the rotary positioning mechanism in the embodiment. As shown in the figure, the projection line Lyz formed when the generatrix L of the lens 42 is projected onto the yz plane can be represented by an arc of radius R1 and center (0,0, Z0), and when projected onto the xy plane. When the projection line Lxy formed at is represented by two straight lines passing "X = X1" at the center of the optical axis OA and "X = 0" at both ends, when analyzed in the same manner as above,

[0033]

[Equation 5]

[0034]

[Equation 6]

Is obtained. The bus L in the sub-scanning direction x
Since the curvature of is symmetric in the xz plane,
Only the case of Y ≧ 0 ″ is considered.

Here, similarly to the above, considering only the amount of curvature in the sub-scanning direction x at the center of the optical axis OA, the angle θ, that is, the straight line connecting both ends of the generatrix L as the rotation axis, that is,

[0037]

[Equation 7]

The amount of bending can be reduced by rotating only. For example, assuming that the radius R1 is "2000" and the coordinate Z0 is "-1997.5" and the coordinate X1 is "0.5", the scanning line on the surface 50 to be scanned is the solid line S in FIG.
It becomes L '. On the other hand, when it is rotated about the rotation axis by the angle θ that satisfies the expression 7, the scanning line on the scanned surface 50 becomes the solid line SL, and the curvature of the scanning line formed on the scanned surface 50 is suppressed. You can

In the above embodiment, the lens holder 61 is configured to hold the lens 42, and
While the lens 42 is held, a rotary positioning mechanism is provided which is rotatable about a rotary shaft 69 extending parallel to the main scanning direction y and which rotates the lens 42 together with the lens holder 61 according to an external force. The configuration of the rotary positioning mechanism is not limited to this, and any configuration is essential as long as the field curvature correction lens 42 can be rotated and positioned according to an external force.

[0040]

As described above, according to the present invention, the field curvature correction lens is rotatably held around the rotation axis parallel to the main scanning direction, and the image is corrected in accordance with the external force. Since the surface curvature correction lens is configured to rotate about the rotation axis, the deviation of the generation line from the scanning surface can be reduced by adjusting the attitude of the generation line of the field curvature correction lens. As a result, the curvature of the scanning line formed on the surface to be scanned can be suppressed.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of a light beam scanning device according to the present invention.

FIG. 2 is a top view of a positioning mechanism.

FIG. 3 is a front view of a positioning mechanism.

FIG. 4 is a side view of a positioning mechanism.

FIG. 5 is a first explanatory diagram for explaining the effect of the rotary positioning mechanism in the embodiment.

FIG. 6 is a diagram showing how the scanning lines change on the surface to be scanned before and after the rotation of the field curvature correction lens.

FIG. 7 is a second explanatory diagram for explaining the effect of the rotary positioning mechanism in the embodiment.

FIG. 8 is a diagram showing how the scanning lines change on the surface to be scanned before and after the rotation of the field curvature correction lens.

FIG. 9 is a diagram showing a relationship between a field curvature correction lens and a scanning line on a surface to be scanned.

FIG. 10 is a diagram showing a relationship between a field curvature correction lens and a scanning line on a surface to be scanned.

[Explanation of symbols]

 10 light source 30 rotating polygon mirror (deflector) 31 mirror surface (deflecting surface) 41 scanning lens 42 field curvature correction lens 50 surface to be scanned 69 rotation axis x sub-scanning direction y main scanning direction

Claims (1)

[Claims] 1. A light beam from a light source is condensed only in the sub-scanning direction to form a line image, and the light beam is deflected and deflected by a deflector having a deflection surface on or near the line image. The light beam is irradiated onto the surface to be scanned through the scanning lens and the field curvature correction lens having power in the sub-scanning direction and having the generatrix curve along the main scanning direction substantially orthogonal to the sub-scanning direction. As a result, in the light beam scanning device that scans the surface to be scanned in the main scanning direction, the field curvature correction lens is rotatably held about a rotation axis parallel to the main scanning direction, and is applied from the outside. A light beam scanning device comprising a rotation positioning mechanism for rotating and positioning the field curvature correction lens around the rotation axis according to a force applied.