JPH03100616A - Scanning optical device - Google Patents

Abstract

PURPOSE:To perform plotting with high accuracy by holding optical devices between a laser beam source and a static deflecting system integrally by separating from another optical device. CONSTITUTION:A light source unit providing with components from a laser diode 10 to a prism block 20 is provided with a lower substrate 201 and an upper substrate 202, and two foot parts 210 are fixed at the upper substrate 202, and horizontal plates 211 are suspended on the upper terminals of the foot parts 210, and also, a vertical plate 212 is suspended between the foot parts 210 under the horizontal plate 211. A cylindrical lens barrel 220 in which the laser diode 10 and a collimator lens 11 are assembled and a mirror supporting part 230 to support a folding mirror 12 are fixed at the horizontal plate 211, and a cylinder lens 13 is mounted on the vertical plate 212. Namely, the components from the laser diode 10 to the prism block 20 are unified as one independent unit separately from another component. In such a manner, assembling accuracy can be heightened.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a scanning optical device that forms a pattern on an image plane by scanning a laser beam on the image plane, and particularly relates to a scanning optical device that forms a pattern on an image plane by scanning a laser beam on the image plane. The present invention relates to an apparatus such as a plate-making machine that requires high density in the pattern formed.

[Conventional technology] In order to perform highly accurate drawing, the spot must be narrowed down to a small size. In order to reduce the spot diameter, it is necessary to increase the F number of the optical system, which inevitably reduces the depth of focus. It becomes shallow. Therefore, in order to keep the spot diameter on the scanning plane approximately constant, the curvature of field must be kept small.

However, if the optical axis of the scanning lens and the optical axis of the light beam incident on the polygon mirror do not match within the plane where the light beam is scanned by the polygon mirror, the deflection point will change to the fθ lens as the polygon mirror rotates. It changes asymmetrically between positive and negative image heights across the optical axis. Therefore, there is a problem that the curvature of field at the image plane becomes asymmetric, and cannot be corrected when using a lens that is symmetrical with respect to the optical axis.

In order to solve this problem, a configuration can be considered in which the laser beam is made incident on the polygon mirror through the optical axis of the scanning lens. According to this configuration, the appearance of field curvature is symmetrical, so that it can be corrected with a lens that is symmetrical about the optical axis, and the value is also very small.

However, in order to adopt such a configuration, a static deflector must be placed in the optical path of the light reflected by the polygon mirror to separate the light beam from the light source to the polygon mirror and the light beam incident from the polygon mirror to the fθ lens. It is necessary to do so.

By the way, Japanese Patent Application Laid-Open No. 60-233616 discloses a configuration in which a polarizing beam splitter and a 174-wavelength plate are used to cause a light beam from a light source to enter a polygon mirror through an optical axis of a scanning lens.

In addition, in the configuration of JP-A-60-233616, in order to correct the influence of the inclination of the reflective surface of the polygon mirror with respect to the rotation axis, which is called a surface tilt error, the laser beam is directed to the reflective surface of the polygon mirror within the sub-scanning section. The image is once formed above. Therefore, a total reflection mirror cannot be provided as a static deflector, and it is necessary to use a polarizing beam splitter or the like.

However, in the case of the configuration described in the above publication, the angle of incidence of the light beam on the polarizing beam splitter changes as the polygon mirror rotates, so the transmittance of the polarizing beam splitter gradually decreases from the center to the periphery. This causes unevenness in the amount of light on the image plane.

In order to solve the above-mentioned problems, the present applicant has developed a structure in which a total reflection mirror can be used as a static deflector while employing a structure in which the laser beam is incident on a polygon mirror through the optical axis of a scanning lens. This is proposed in Ganhei 1-63934.

That is, the light beam from the laser light source is once imaged in the sub-scanning cross section before entering the scanning deflector, and a static deflector is placed at this imaging position to guide the light beam from the light source to the scanning deflector. The static deflector has a slit mirror that reflects the light beam or a mirror with a slit that transmits the light beam to the imaging position.

According to such a configuration, most of the light reflected by the scanning deflector is transmitted around the slit mirror or is reflected by the outside of the slit of the slit mirror, and forms a spot on the image plane via the scanning lens. tie.

However, when implementing the above proposed technology, it is desirable to reduce the vignetting of the light beam from the polygon mirror to the scanning lens in order to ensure the amount of light on the image plane. It is preferable to make the area of the mirror slit as small as possible.

However, if the area of the slit mirror or the like is made smaller, there is a strict requirement for precision in converging the light beam on this portion.

[Object of the invention] This invention was made in view of the above problems, and
The purpose is to provide a scanning optical device that can prevent the deterioration of wavefront aberration on the image plane with a relatively simple configuration and that can perform drawing with high precision. An object of the present invention is to provide a scanning optical device that can accurately guide a focused light beam onto a slit mirror or the like even when the area is made small.

[Means for Solving the Problems] In order to achieve the above object, a scanning optical device according to the present invention employs a configuration in which a laser beam is incident on a scanning deflector from the optical path of a beam deflected by the scanning deflector. , a holding mechanism is provided that holds the optical elements from the laser light source to the static deflector integrally, distinguishing them from other optical elements.

[Example] The present invention will be described below based on the drawings. 1 to 4 show an embodiment of a scanning optical device according to the present invention.

First, the arrangement of the optical elements of this device will be explained based on FIG.

The illustrated optical system includes a laser diode lO as a light source, a collimating lens 11 that converts diverging light emitted from the laser diode lO into a parallel light beam, a folding mirror 12 that reflects the collimated light beam, and a line image using this light beam. A prism block 2° has a cylindrical lens 13 as a condensing lens to form a condenser lens, a slit mirror 21 as a static deflector provided in alignment with the line image position of the luminous flux, and a prism block 2° that collects the luminous flux reflected by the slit mirror 21. It includes a polygon mirror 30 as a scanning deflector that reflects and polarizes the light, and an fθ lens 40 as a scanning lens that condenses the light beam reflected by the polygon mirror 30 to form a spot on the scanning surface.

Here, the surface scanned by the light beam by the polygon mirror 30 is defined as a main scanning section, and the surface perpendicular to the main scanning section and including the rotation axis 31 of the polygon mirror is defined as a sub-scanning section.

The prism block 20 has a rectangular parallelepiped shape in which a triangular prism 22 and a trapezoidal prism 23 are bonded together, and a slit mirror 21, which is a total reflection mirror, is deposited on the bonded surface. The angle of the slit mirror 21 with respect to the main scanning section is approximately 45@.

The diverging light emitted from the laser diode IO is collimated and then focused onto the slit mirror 21 by the cylindrical lens 13.
1, the entire amount of light is reflected and passes through the optical axis of the fθ lens 40 toward the polygon mirror 30.

The light beam reflected and polarized by the polygon mirror 30 reaches the prism block 20 again with a predetermined spread. Here, most of the light flux passes through the periphery of the slit mirror 21 and enters the fθ lens 40.

The light beam exiting the fθ lens 40 is deflected to the lower side of the base by a mirror 51 provided at the left end of the base 90, guided by mirrors 52 and 53, and conveyed by a feed roller 60, as shown in FIG. A spot is formed on the panel 61 as a scanning target to be scanned at a constant speed.

The slit mirror 21 provided to separate the optical paths does not change the transmittance due to changes in the rotation angle of the polygon mirror 30, so the image height on the scanning plane does not change as in the case of using a deflection beam splitter. There is no change in spot intensity due to

Next, the specific assembly of each optical element will be explained based on FIGS. 1 to 3, and at the same time, the adjustment direction of each optical element will be explained with reference to FIG. 1.

The coordinates in the figure are determined based on the traveling direction of the light flux, and the direction of the light flux from the laser diode 10 and the optical axis direction of the fθ lens 40 are the X axis, and the polygon mirror 3
The direction of the zero rotation axis 31 is defined as the two axes, and the direction perpendicular to both the x and two axes is defined as the y axis.

Each optical element is attached to a flat base 90 as a unit.

A polygon unit 100 incorporating a polygon mirror 30 and a motor for rotationally driving the polygon mirror 30 is immovably fixed to a base 90.

The light source unit 200, which includes everything from the laser diode IO to the prism block 20, includes a lower substrate 201 that is slidable in the X-axis direction with respect to the base 90, and a lower substrate 201 that is slidable in the X-axis direction with respect to the base 90.
The upper substrate 202 is provided so as to be rotatably adjustable around the X13' axis with respect to the X13' axis.

As shown in FIG. 2, the lower substrate 201 has two abutments fixed to the base 90 whose positions in the y-axis direction are determined by pins 203, and which are screwed into the base 90 through the lower substrate. The base 9 is fixed by the fixing bolts 204 at the four corners that match.
Fixed to 0. The through holes of the lower board 201 into which the fixing bolts 204 are inserted are formed to be larger than the diameter of the bolts, so by loosening these fixing bolts 204, the lower board 201 can be attached to the pins along the
It can be slid in the axial direction.

The sliding adjustment of the light source unit 200 in the X-axis direction has the effect of correcting out-of-focus in the sub-scanning direction on the scanning plane due to errors in the curvature of the lens system, the distance between surfaces, and the like.

The upper substrate 202 is positioned in the L3' direction by abutment pins 205 fixed at three locations on the lower substrate 201. In addition, the upper substrate 202 has screw holes formed at its four corners fitted with adjustment bolts 206 whose tips contact the lower substrate 201 as shown in FIG. Fixing bolt 20 provided as
7 to the lower substrate 201.

Therefore, by loosening the fixing bolt 207 and operating the adjustment bolt 206, the upper substrate 202 can be adjusted with respect to the lower substrate 201 around the Xty axis.

The rotational adjustment of the light source unit 200 including the prism block around the X axis is for correcting the collapse of the spot shape on the scanning plane and the deterioration of the image quality. After the adjustment is completed, it is used to improve the overall performance of the device.

The prism block 20 fixed at the center of the upper substrate is slidable in the y-axis direction with respect to the upper substrate 202. Considering the vignetting of the light beam transmitted from the polygon mirror 30 to the fθ lens 40 side, it is desirable that the area of the slit mirror 21 be as small as possible.Sliding adjustment of the prism block in the y-axis direction can be done by changing the size of the slit mirror. When the size is about the same as the line image formed by the cylinder lens 13, it is necessary to match these positional relationships.

As shown in FIG. 1, on the upper substrate 202, between the upper ends of the zero leg parts 210, two legs 210 are fixed to both sides of the prism block by fixing screws 210a that are screwed together from below. A horizontal plate 211 is installed, and a vertical plate 212 is installed between the legs 210 below the horizontal plate 211.

On the horizontal plate 211, there is a cylindrical lens barrel 220 in which a laser diode 10 and a collimating lens 11 composed of four lenses lla to 4th lens lid are incorporated, and a mirror support part that supports a folding mirror 12. 230 is fixed.

Since the laser diode IO varies in the location where light is emitted from product to product, it is configured to be slidable in the y-z directions so that the oscillation light flux can be aligned with the designed optical axis.

The collimating lens 11 is slidable in the y-axis direction to adjust its relative relationship to the laser diode 10. This is an adjustment for correcting focus deviation mainly in the main scanning direction on the scanning plane due to errors in the curvature of the lens system, interplane distance, etc.

The folding mirror 12 is rotatably adjustable around two axes, the x and y axes.

Further, the vertical plate 212 includes a positive lens 13a and a negative lens 1.
A cylinder lens 13 made up of a combination of lenses 3b and 3b is attached via a holder 240.

Since the cylinder lens 13 may include variations from product to product due to processing errors, it is possible to adjust the slide in the optical axis (X-axis) direction and adjust the rotation around the optical axis. The former adjustment is to adjust the movement of the line image along the optical axis direction to match the focus with the slit mirror.
The latter adjustment is for rotationally adjusting the direction in which the line image is formed to match the direction of the slit mirror 21.

In addition, from the laser diode 10 to the prism block 2
The parts up to 0 are integrated as one unit independent from other parts, which increases assembly accuracy and prevents misalignment between the line image forming position by the cylinder lens 13 and the slit mirror 21. .

The lens unit 300 includes an fθ lens 40 composed of three anamorphic lenses 41, 42, and 43, and a lens substrate 301 on which these lenses are arranged. The lens substrate 301 and the light source unit 200 are fixed to two places on the base 90 using pins 302.
The position in the X-axis direction is determined by abutting against the base 90, and it is fixed to the base 90 with fixing bolts 303 at the four corners.

Therefore, by loosening the fixing bolt 303, the lens substrate 301 can be slid in the y-axis direction using the bottle 302 as a guide.

In addition, the three anamorphic lenses are held down by a holding spring plate 311 provided by a holding plate 310 that covers the central lens.
The lens 42 is fixed to the lens substrate 301 in two axial directions through the lens 42, and the center lens 42 is assembled so as to be rotatably adjustable around the x and y axes.

The adjustment of the fθ lens 40 is to correct the tilt of the image plane and the deterioration of image quality due to eccentricity errors.

As shown in FIG. 3, support members 312 slightly longer than the height of the lens are screwed to the four corners of the holding plate 310 to the lens substrate 301. It is fixed using fixing bolts 313.

In addition, each lens is attached to three locations through the bin 32.
0.320, . ... are applied to the lens substrate 301 and fixed in the x and y directions.

The abutment bin 203 for determining the position of the light source unit 200 and the abutment bin 302 for determining the position of the lens unit are positioned with respect to the center of rotation of the polygon mirror 30.

Additionally, on the lower right side of FIG. 2, as a means for detecting the rotational position of the polygon mirror 30, there is a monitor light source unit 400 that irradiates a monitor light beam onto a surface different from the surface of the polygon mirror 30 that reflects the drawing light beam. , and a monitor light receiving unit 500 that receives the monitor light beam reflected by the polygon mirror 30. Since these units are not directly related to the invention, detailed explanations will be omitted.

[Effects] As explained above, according to the scanning optical device of the present invention, the optical elements from the light source to the static deflector, which require high precision, can be assembled independently as one unit. The positional relationship between the elements, for example, the positional relationship between the line image formed by the condenser lens and the static deflector, can be accurately realized without having to make adjustments again when assembling the device into the main body of the device.

[BRIEF DESCRIPTION OF THE DRAWINGS] FIGS. 1 to 4 show an embodiment of a scanning optical device according to the present invention, and FIG. 1 is a view taken along the line II in FIG. 2 is a plan view of the entire device, FIG. 3 is a view taken along the line ■-■ in FIG. 2, and FIG. 4 is a perspective view showing the arrangement of optical elements. be. lO... Laser diode 13... Cylinder lens 20... Prism block 21... Slit mirror 30... Polygon mirror 40... fθ lens 1st rI! J1]

Claims (5)

[Claims] (1) A laser light source, a scanning deflector that reflects and deflects the light beam from the laser light source to scan within the main scanning cross section, and a scanning lens that focuses the laser light beam reflected by the scanning deflector onto an image plane. , a condenser lens that once forms an image in a sub-scanning section perpendicular to the main scanning section before the light beam from the laser light source enters the scanning deflector; and a condensing lens that forms an image in the optical path of the light reflected by the scanning deflector. a static deflector that is provided at a position where the light beam is imaged and guides the light beam from the laser light source to the scanning deflector and causes the light reflected by the scanning deflector to enter the scanning lens; What is claimed is: 1. A scanning optical device comprising: a holding mechanism that holds one optical element integrally while distinguishing it from other optical elements. (2) The scanning optical device according to claim 1, wherein the scanning deflector is a polygon mirror. (3) The scanning optical device according to claim 1, wherein the condenser lens is a cylindrical lens. (4) The static deflector includes a slit mirror that is long in the main scanning direction and is arranged to coincide with the imaging position of the laser beam by the condenser lens, and reflects the laser beam from the light source toward the scanning deflector. Claim 1 characterized in that it has
4. The scanning optical device according to any one of 3 to 3. (5) The scanning optical device according to any one of claims 1 to 4, characterized in that the light flux incident on the scanning deflector from the static deflector is incident along the optical axis of the scanning lens.