JPH08166209A - Polygon mirror evaluating device - Google Patents

Abstract

PURPOSE: To measure eccentricity in the optical axis direction along with the measurement of lateral deviation eccentricity and an angle error relative to the optical axis of a reflection face by mounting a polygon mirror having a plurality of optical reflection faces at an equal division angle and providing a distance measurement means for measuring distance to the reflection faces of the polygon mirror. CONSTITUTION: Light of a pointlike beam 11 transmitted through a collimator lens 3 is converted into a light wave front according to the shape of a reflection plate 9a by a wave front controller 10 to be made incident on the plate 9a, and the position of the image of a target 12 by reflected light is detected and stored by an image position detector 13. Distance to the reflection plate 9a is measured by a triangulation type optical displacement gage 14 exactly opposite to the reflection plate 9a. A highly accurate rotation stage 2 mounting a polygon mirror is rotated in the direction A by 90 deg. so as to face the reflection face 9b to a lens 3, and deviation of the image of the target 12 which is reflected by the reflection face 9b is measured by the device 13. Positions of the images of the reflection faces 9a and 9b are compared so as to understand lateral deviation eccentricity. Distance to the reflection face 9b which is measured by the displacement gage 14 is compared with that to the reflection face 9a so that eccentricity in the optical axis direction is found.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polygon mirror evaluation apparatus for evaluating a light reflecting surface of a polygon mirror, and more particularly to measuring a variation in the distance from the center of rotation of the polygon mirror to each reflecting surface (eccentricity in the optical axis direction). The present invention relates to a polygonal mirror evaluation device capable of accurately performing.

[0002]

2. Description of the Related Art As a conventional polygon mirror evaluation apparatus for measuring an angular error (divided angle error) between respective reflecting surfaces of a rotary polygon mirror, there is, for example, one shown in FIG.

This polygonal mirror evaluation apparatus is equipped with a rotary polygonal mirror 1 and can rotate the polygonal mirror 1 with high precision and at a predetermined angle, and reflecting surfaces 1a to 1d of the rotary polygonal mirror 1.
The collimator lens 3 for irradiating the collimator lens 3, the beam splitter 4 arranged on the opposite side of the collimator lens 3 from the rotary polygon mirror 1, and the collimator lens 3 located on the branch optical path of the beam splitter 4. A focal plate 5 having a focal surface 5A on one surface thereof, a focal plate 6 having a focal surface 6A of the collimator lens 3 located on the other branched optical path of the beam splitter 4 on its one surface, and a light source for illuminating the focal plate 5. 7 and a condenser lens 8 for condensing the light from the light source 7 on the focusing screen 5.

The light source side focusing plate 5 has a scale formed by a crosshair and a scale on one surface of a transparent glass plate, which is illuminated by the light source 7 through the condenser lens 8 and the focus of the collimator lens 3 is scaled. It is arranged to match the surface. A scale similar to that of the focusing screen 5 is also engraved on the observing side focusing screen 6 by a crosshair or a pinhole, and the collimator lens 3 is arranged so that its focus coincides with the scale surface.

A rotary polygon mirror 1 using this polygon mirror evaluation apparatus
The measurement of the division angle formed by the two adjacent surfaces of the reflective surfaces 1a to 1d will be described. Here, since the rotary polygon mirror 1 has four light reflecting surfaces, the ideal division angle is 90 degrees.

First, the rotary polygon mirror 1 is mounted on the high precision rotary stage 2. At this time, the center of rotation of the rotary polygon mirror 1 is made to coincide with the center of rotation of the high-accuracy rotary stage 2, and the reflecting surface 1a is completely opposed to the collimator lens 3. After that, the image of the scale of the focusing screen 5 illuminated by the light source 7 is set so that it is reflected by the reflecting surface 1a and coincides with the scale of the focusing screen 6.

Next, the reflecting surface 1a to 1d of the rotary polygon mirror 1 is rotated by the division angle which the reflecting surfaces 1a to 1d should originally have, that is, 90 degrees, in the direction A to rotate the reflecting surface 1a.
Aim b at the collimator lens 3.

After rotating the rotary polygon mirror 1 by 90 degrees,
The focusing screen 5 which is reflected by the reflecting surface 1b and forms an image on the focusing screen 6.
When the images on the scale of 1 are in agreement, the reflecting surfaces 1a and 1b have an ideal division angle.

When the scale images of the focusing screen 5 formed on the focusing screen 6 do not coincide with each other and the shift amount is generated in the horizontal direction of the scale, the split angle is calculated from the shift amount and the focal length of the collimator lens 3. The error is calculated, and when the amount of deviation is in the vertical direction of the scale, the angle (tilt angle) of the reflective surface with respect to the vertical direction is calculated. Below, the remaining reflective surface 1
The same operation is performed for c and 1d.

In addition to the above-mentioned method, there is another method for measuring the division angle of the polygonal mirror, which uses beam light, and is disclosed in, for example, Japanese Patent Laid-Open No. 56-112606.

When an attempt is made to evaluate a rotary polygon mirror whose reflecting surface is not a flat surface by the above-described polygon mirror evaluating apparatus, an image of the scale of the focusing plate on the light source side, which is reflected by the reflecting surface and forms an image on the focusing plate on the observation side, is obtained. There is the inconvenience that the position of the image cannot be specified because the image is blurred and spread.

As a means for solving such inconvenience,
The polygonal mirror evaluation apparatus shown in FIG. 5 has been proposed by the present inventor. The polygon mirror evaluation device proposed by the present inventor includes a wavefront shape controller 10 that sets the wavefront shape of the light wavefront so as to follow the reflecting surfaces 9a to 9d of the rotating polygon mirror 9 formed in a non-planar manner. The wavefront shape controller 10 converts the transmitted light into a light wavefront according to the shapes of the reflection surfaces 9a to 9d, and may be, for example, a wavefront conversion lens or a wavefront conversion hologram, and may be a target illuminated by the point light source 11. The image of 12 is not blurred and spread, and is formed on the image position detection device 13 provided on the observation side.

Therefore, as shown in FIG. 6, the reflecting surfaces 9a and 9a
The curvature centers a and d of d are the rotation centers O of the high-accuracy rotary stage.
When there is a deviation of La and Ld with respect to the optical axis of the collimator lens 3 passing through, the deviation of the target image formed on the image position detecting device 13 occurs due to this angular error between the reflecting surfaces 9a and 9d. Such a shift can be detected while preventing blurring of the target image.

As described above, according to the conventional polygon mirror evaluation apparatus, as shown in FIGS. 7A and 7B, the target image of the light source side focusing screen imaged on the observation side focusing plate or Based on the deviation of the image of the light source, the lateral deviation L of the reflecting surface A from the ideal reflecting surface A with respect to the optical axis (FIG. 7A),
The angle error θ of the reflecting surface B (FIG. 7B), or both of them can be measured.

[0015]

However, according to the conventional polygon mirror evaluation apparatus, as shown in FIG. 7C, a variation D in the distance from the rotation center O of the rotary polygon mirror to the reflecting surface A or B occurs. Since the deviation of the target image or the image of the light source does not appear on the observing side reticle during this time, this kind of variation, that is, the measurement of eccentricity error in the direction along the center line of the reflecting surface (optical axis direction eccentricity error) There is a problem that you can not. Recently, a rotating polygon mirror made of plastic has been proposed, but decentering of the reflecting surface in the optical axis direction may occur at the time of molding the plastic. If this occurs, the accuracy of scanning the optical beam of the rotating polygon mirror may be reduced. This also applies to a rotating polygonal mirror whose reflection surface is a flat surface, in and out of a surface in a direction along the surface normal of the reflection surface which is a flat surface, that is, variation in the distance of the reflection surface from the rotation center. Cannot be measured with a conventional polygon mirror evaluation device. Therefore, an object of the present invention is to provide a polygonal mirror evaluation device capable of measuring the eccentricity in the optical axis direction and the variation in the distance from the rotation center.

Another object of the present invention is to provide a polygonal mirror evaluation device capable of measuring the eccentricity in the optical axis direction in addition to measuring the lateral deviation eccentricity of the reflecting surface with respect to the optical axis and the angular error.

[0017]

DISCLOSURE OF THE INVENTION The present invention is directed to eccentricity in the optical axis direction,
And in order to enable the measurement of the variation in the distance from the rotation center, a polygonal mirror having a plurality of light reflecting surfaces at equal division angles is mounted, and a rotation stage that rotates about a center point with a predetermined accuracy, The distance measuring means is provided to face one of the light reflecting surfaces of the polygon mirror at a position at a predetermined distance from the center point, and comprises distance measuring means for measuring the distance to one light reflecting surface,
The distance measuring means has a configuration for detecting a variation in the distance between a plurality of light reflecting surfaces caused by the eccentricity of the polygonal mirror in the optical axis direction when the rotating stage rotates and the variation in the distance from the rotation center. Provide an evaluation device.

Further, in the present invention, in addition to the measurement of the lateral deviation eccentricity of the reflecting surface with respect to the optical axis and the angular error, the eccentricity in the optical axis direction and the variation of the distance from the rotation center can be measured. A rotary stage that mounts a polygonal mirror having surfaces at equal division angles and rotates about a center point at a predetermined angle; and lens means for irradiating one of the light reflecting surfaces of the polygonal mirror with light. A light branching unit arranged on the opposite side of the polygonal mirror with respect to the lens unit, and a reference provided on one light path of the branching light path branched by the light branching unit and located at the light beam condensing point of the lens unit. The object and the image position detecting means for detecting the image forming position of the reference object image reflected by the light reflecting surface of the polygonal mirror provided on the other optical path of the branch optical path of the optical branching means, and the rotary stage are provided. Obtained each time you rotate a specified angle Evaluation means for evaluating the angular error of each light reflecting surface of the polygonal mirror based on the image position, and a distance from the center of rotation of the rotary stage to a predetermined distance to measure the distance to the light reflecting surface of the polygonal mirror. Provided is a polygon mirror evaluation device including distance measuring means.

Further, in order to achieve the above-mentioned object, the present invention comprises a beam source for irradiating a light beam on a light reflecting surface and a reflected light for detecting the position of the light beam reflected by the light reflecting surface. It is preferably composed of a beam position detection unit and a calculation unit that calculates the distance from the position of the light beam detected by the reflected light beam position detection means to the light reflection surface.

[0020]

According to the polygon mirror evaluation apparatus of the present invention, the rotary stage is provided with a predetermined accuracy, that is, an eccentricity in the optical axis direction and a distance from the rotation center by an angle equal to the ideal branch angle of the light reflecting surface of the polygon mirror. Rotate with accuracy according to the measurement accuracy of the variation. The distance to each light reflecting surface is measured next to a predetermined rotation angle of the rotary stage with reference to a position at a predetermined distance from the center point of the rotary stage. Therefore, the eccentricity error in the optical axis direction of each light reflecting surface and the variation in the distance from the rotation center can be measured with high accuracy simply by setting the center axis of the rotary polygon mirror at the center point of the rotary stage.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A polygon mirror evaluation apparatus of the present invention will be described below in detail with reference to the drawings. The same reference numerals are attached to the same configurations and functions as those of the conventional art, and thus duplicated description will be omitted.

FIG. 1 shows a polygon mirror evaluation apparatus according to an embodiment of the present invention. In FIG. 1 (A), the polygonal mirror evaluation device is opposed to the curved reflecting surfaces 9a to 9d, and a predetermined distance from the rotation center of the high precision rotation stage 2 is set. A non-contact type triangulation type optical displacement meter 14 for measuring the distance to the reflection surface is provided at the position of the distance. Other configurations are common to those of the polygon mirror evaluation apparatus of FIG. 5, and thus redundant description will be omitted.

FIG. 1B shows a triangulation type optical displacement meter 14, in which laser light is emitted from a semiconductor laser 14a onto a reflecting surface 9a of a rotary polygon mirror 9, and the light reflected or scattered by the reflecting surface 9a is imaged. The position sensor 1 collects light with the lens 14b.
Light is received at 4c. The image received by the position sensor 14c is detected as an electric signal, and the calculation unit 14d performs comparison calculation processing to measure the eccentricity of the reflecting surface in the optical axis direction. When the reflecting surfaces 9a and 9b are at the positions indicated by the solid line and the positions indicated by the dotted line, the light collecting position of the position sensor 14c is different. Thereby, the eccentricity in the optical axis direction is detected.

The measurement of each reflecting surface by the above-mentioned polygon mirror evaluation apparatus will be described below. Here, the reflecting surface 9a is the first measurement surface.

First, the light of the point light source 11 that has passed through the collimator lens 3 is converted into a light wavefront corresponding to the shape of the reflecting surface 9a by the wavefront shape controller 10 and is incident, and the image of the target 12 due to the reflected light is formed. The position is detected by the image position detecting device 13 and stored. Then, the distance to the reflecting surface 9a is measured by the triangulation type optical displacement meter 14 facing the reflecting surface 9a.

Next, the high-precision rotary stage 2 equipped with the rotary polygon mirror 9 is rotated by 90 degrees in the A direction so that the reflecting surface 9b faces the collimator lens 3 and the image of the target 12 reflected by the reflecting surface 9b shifts. Is measured by the image position detecting device 13.

The position of the image of the target 12 at the time of measuring the reflecting surface 9a stored in the image position detecting device 13 at the time of this measurement is compared with the position of the image of the target 12 at the time of measuring the reflecting surface 9b. Here, when the image of the target 12 is deviated in the horizontal direction when the reflection surface 9b is measured, the reflection surface 9b has a lateral deviation eccentricity with respect to the reflection surface 9a.

Further, the distance to the reflecting surface 9b is measured by the triangulation type optical displacement meter 14 and compared with the distance to the reflecting surface 9a, whereby the reflecting surface 9b with respect to the reflecting surface 9a is measured.
The eccentricity in the optical axis direction is required.

By performing the above-mentioned operation on the reflecting surfaces 9c and 9d in the same manner, the lateral deviation eccentricity and the optical axis direction eccentricity on each reflecting surface of the rotary polygon mirror 9 are measured. Further, the distance measurement of the reflecting surfaces 9a to 9d by the triangulation type optical displacement meter 14 is not limited to the direction parallel to the optical axis of the collimator lens 3 as shown in FIG. Alternatively, the triangulation type optical displacement meter 14 may be provided so as to face the reflecting surface 9b, and the distance of the reflecting surface 9b may be measured when the lateral displacement of the reflecting surface 9a is being measured.

FIG. 2 shows a polygon mirror evaluation apparatus according to another embodiment of the present invention, which includes a collimator lens 3 and a rotary polygon mirror 9.
And a wavefront conversion lens 17 for converting the light wavefront according to the shapes of the reflection surfaces 9a to 9d, and a triangulation type light whose distance measuring direction is set in a direction perpendicular to the optical axis of the collimator lens 3. And a displacement gauge 14. The set position of the wavefront conversion lens 17 is the reflecting surfaces 9a to 9 of the rotary polygon mirror 9.
It is set based on the shape of d.

A TV camera 16 having a focal plane 16A of the collimator lens 3 is provided on the transmission side of the beam splitter 4, and an image of the focusing plate 5 illuminated by the laser light source 15 and the condenser lens 8 is a focal plane 16A. The image pickup surface is formed so as to coincide with.

The operation of the polygon mirror evaluation apparatus having the above configuration will be described below. First, after setting the optical axis of the collimator lens 3 and the rotation axis of the high-accuracy rotary stage 2 to coincide with each other, the reflecting surface 9a is directly opposed to the collimator lens 3.
In this state, laser light is emitted from the laser light source 15. The image of the focusing screen 5 due to this laser light is reflected by the reflecting surface 9a and transmitted through the beam splitter 4, so that T
It is set so as to come to the origin (not shown) of the focal plane 16A of the V camera 16.

In this state, the distance to the reflecting surface 9b is measured by the triangulation type optical displacement meter 14 directly facing the reflecting surface 9b. The triangulation type optical displacement meter 14 is provided so as to face the reflecting surface 9b when the reflecting surface 9a faces the collimator lens 3, and the distance measuring direction ideally divides each reflecting surface of the rotary polygon mirror 9. The angle is set to be equal to the angle at which the collimator lens 3 is set, and the angle is 90 degrees with respect to the optical axis of the collimator lens 3.

Next, the high-accuracy rotary stage 2 is divided by the division angle A which the reflecting surfaces 9a to 9d of the rotary polygon mirror 9 should originally have.
The reflecting surface 9b is directed toward the collimator lens 3 by rotating in the direction, and the deviation of the image of the focusing screen 5 reflected by the reflecting surface 9b is measured by the TV camera 16.

At the time of this measurement, the focal plane 16 of the TV camera 16
When the vertical line of the image of the focusing screen 5 has a horizontal shift amount with respect to the origin formed in A, the shift amount is proportional to the lateral shift eccentricity of the reflecting surface 9b with respect to the reflecting surface 9a.

Further, by the rotation of the high-accuracy rotary stage 2, the reflecting surface 9c facing the triangulation type optical displacement meter 14 is faced.
The eccentricity in the optical axis direction is measured. By performing the above operation on the reflecting surfaces 9a to 9d, the lateral deviation eccentricity of the reflecting surface and the eccentricity in the optical axis direction are measured.

On the other hand, FIG. 3 shows still another embodiment of the present invention, and the measurement of the division angle error of the rotary polygon mirror 1 having the reflecting surfaces 1a to 1d formed in the same plane as the above-mentioned embodiment. In addition to this, it is possible to obtain the error (radius mutual difference) in the distance from the rotation center of each reflecting surface by the triangulation type optical displacement meter 14. In each of the above embodiments, the triangulation type optical displacement meter was used as the distance measuring device, but the present invention is not limited to this.

[0038]

As described above, according to the polygon mirror evaluation apparatus of the present invention, since the distance measuring means for measuring the distance to the reflecting surface of the polygon mirror is provided, the lateral deviation of the reflecting surface with respect to the optical axis and the measurement of the angular error. In addition, it is possible to measure the eccentricity in the optical axis direction and the variation in the distance of the reflecting surface from the center of rotation.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a polygon mirror evaluation device according to an embodiment of the present invention, and FIG. 1B is an explanatory diagram of a distance measurement device in FIG.

FIG. 2 is an explanatory diagram showing a polygon mirror evaluation apparatus according to another embodiment of the present invention.

FIG. 3 is an explanatory diagram showing a polygon mirror evaluation apparatus according to another embodiment of the present invention.

FIG. 4 is an explanatory diagram showing a conventional polygon mirror evaluation apparatus.

FIG. 5 is an explanatory diagram showing a conventional polygon mirror evaluation apparatus.

FIG. 6 is an explanatory diagram showing a conventional polygon mirror evaluation apparatus.

FIG. 7 is an explanatory diagram showing lateral displacement, angular error, and eccentricity in the optical axis direction of the polygon mirror.

[Explanation of symbols]

 1, rotating polygon mirrors 1a to 1d, reflecting surface 2, high precision rotating stage 3, collimator lens 4, beam splitter 5, 6, focusing plate 5A, 6A, focal plane 7, light source 8, condenser lens 9, rotating polygon mirror 9a to 9d, reflecting surface 10, wavefront shape controller 11, point light source 12, target 13, image position detecting means 14, triangulation type optical displacement meter 14a, semiconductor laser 14b, imaging lens 14c, position sensor 14d, calculation Part 15, laser light source 16, TV camera 16A, focal plane 17, wavefront conversion lens

Claims (3)

[Claims] 1. A rotary stage equipped with a polygonal mirror having a plurality of light-reflecting surfaces at equal division angles, and rotating about a center point with a predetermined accuracy, and a rotary stage at a predetermined distance from the center point. The polygonal mirror is provided so as to face one of the light reflecting surfaces, and is composed of distance measuring means for measuring a distance to the one light reflecting surface, and the distance measuring means is provided when the rotary stage rotates. Evaluation of polygonal mirror having a configuration for detecting variation in distance between the plurality of light reflecting surfaces caused by eccentricity in the optical axis direction of the polygonal mirror and variation in distance of the reflecting surface from the rotation center apparatus. 2. A rotary stage that mounts a polygonal mirror having a plurality of light reflecting surfaces at equal division angles and rotates about a center point at a predetermined angle, and one of the light reflecting surfaces of the polygonal mirror. A lens means for irradiating light onto the optical path, a light branching means arranged on the opposite side of the polygonal mirror with respect to the lens means, and one light path of a branching light path branched by the light branching means. A reference object image located at the light beam condensing point of the lens means, and another optical path of the branch optical path of the light branching means, which is reflected by the light reflecting surface of the polygon mirror. Image position detecting means for detecting an image forming position of the reference object image, and angular error and eccentricity of each light reflecting surface of the polygonal mirror based on the image forming position obtained each time the rotary stage rotates by a predetermined angle. An evaluation means for evaluating an error, and A polygon mirror evaluation apparatus, comprising a distance measuring unit fixed to a position of a predetermined distance from the rotation center point of a rotary stage and configured to measure a distance to the light reflecting surface of the polygon mirror. 3. The distance measuring means includes a beam light source for irradiating the light reflecting surface with a light beam, a reflected light beam position detecting section for detecting the position of the light beam reflected by the light reflecting surface, and the reflection. The polygonal mirror evaluation device according to claim 2, further comprising a calculation unit that calculates a distance from the position of the light beam detected by the light beam position detection means to the light reflection surface.