JPH04344439A - Scanning face trip measurement in scanning optical system and its device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention]

0001

[Industrial Field of Application] The present invention relates to a method and apparatus for measuring the inclination of the scanning surface of a scanning beam in a scanning optical system using a rotating polygon mirror, and relates to a method and apparatus for measuring lens assembly, inspection adjustment, and scanning of a scanning optical system such as a laser printer. This can be applied to measurements of bending, etc.

0002

BACKGROUND OF THE INVENTION In recent years, the present inventor has been conducting research and development on measuring the inclination and bending of the scanning surface of a scanning beam in a scanning optical system. A plurality of sensors are arranged in the range of the imaging position of the scanning beam, and units to be measured, such as a rotating polygon mirror and an fθ lens, are placed on a rotating stage and rotated to set a reference position. The rotating polygon mirror is rotated with the rotation stage fixed, the center of gravity of each sensor is measured, and the center of gravity of each surface is compared with each sensor to measure the surface inclination of each surface of the rotating polygon mirror. can do.

0003

[Problems to be Solved by the Invention] In the above-described means for measuring the curvature and surface inclination of the scanning beam, there is a time difference between the measurement of the reference center of gravity position and the measurement of the center of gravity position of the scanning beam by each reflecting surface. As a result, the beam shape of the light source changes due to changes in the environment, resulting in changes in the measurement of the center of gravity position, making it difficult to measure surface tilt with high precision.

The present invention provides a means for simultaneously measuring the center of gravity position of the scanning beam by each reflecting surface even if there is a change in the environment. It is an object of the present invention to provide a method and apparatus that can measure the scanning surface tilt of a scanning beam with high accuracy in a short time even when the scanning surface tilt is not used.

[0005]

[Means for Solving the Problems] In order to achieve the above-mentioned object, the present invention has a scanning optical system that scans a beam emitted from a light source by rotating a rotating polygon mirror and using an fθ lens at a plurality of imaging positions. In a scanning surface inclination measurement method in a scanning optical system in which a sensor is disposed, a beam reflected by a half mirror disposed between a light source and a rotating polygon mirror is converted to fθ in the same way as a scanning beam passing through a reflecting surface of a rotating polygon mirror. The scanning beam from the reflecting surface of the rotating polygon mirror is focused on a sensor placed at the imaging position, and the center of gravity is measured by each sensor. In addition to measuring the position, each barycenter position measured by each scanning beam is corrected using the barycenter position measured by this half mirror, and the barycenter position of each reflecting surface is compared.

The present invention also provides scanning in a scanning optical system in which line sensors are arranged at a plurality of image formation positions of a scanning optical system in which a beam emitted from a light source is scanned by a rotating polygon mirror and an fθ lens. In a surface tilt measurement device, a half mirror is placed between a light source and a rotating polygon mirror, and the beam reflected by the half mirror is guided to a line sensor placed at an imaging position via an fθ lens, and a scanning beam and a half mirror are generated. Each line sensor that forms an image of the reflected beam is connected to an A/D converter and a microcomputer, and a light receiving sensor for identifying reflective surfaces is installed within the scanning range of the scanning optical system. The light receiving sensor is connected to the A/D converter and the microcomputer via an amplifier.

Furthermore, in the scanning surface inclination measuring device in the scanning optical system, the present invention connects an LD power supply connected to a microcomputer according to a signal from the light receiving sensor for determining the reflective surface, and detects the reflection of the rotating polygon mirror. The light source is turned on according to the surface, and each line sensor measures the light center of gravity of the scanning light.
A shielding plate is disposed between the θ lens and the θ lens to prevent each scanning beam from reaching a line sensor that images the beam reflected by the half mirror.

[0008]

[Operation] In the configuration of the present invention, the center of gravity of the beam is measured by the half mirror installed between the light source and the rotating polygon mirror, and at the same time, the center of gravity of the scanning beam is measured by the reflective surface of the rotating polygon mirror. , it becomes possible to measure the absolute position of the center of gravity on each reflective surface of a rotating polygon mirror, and even if the beam shape changes due to environmental changes or fluctuations over time of the light source, this change in beam shape is absolute. It does not affect the measurement of the center of gravity position, and even if the measurement is started when the light source is not stable, it does not affect the measurement results.
It is possible to measure the inclination of the scanning beam with high precision.

[0009]

Embodiments Hereinafter, embodiments of the present invention will be explained based on the drawing of FIG. In FIG. 1, the scanning optical system A to be measured consists of a laser light source 1 that emits a beam B, a cylindrical lens 2, a rotating polygon mirror 3 that reflects and scans the beam B, and an fθ lens 4 that focuses the beam B. System A is placed on the unit frame 5. The rotating polygon mirror 3 is the drive motor 6
When the laser light source 1 rotates around the rotation axis 0, the beam B generated by the laser light source 1 is scanned by the reflecting surface of the rotating polygon mirror 3 as beams Bc, B3, B1, and B2. At the focal position of each beam, a surface discrimination sensor 9 and a line sensor 8 are provided.
3, 81, and 82 are arranged.

A half mirror 7 is arranged between the laser light source 1, the cylindrical lens 2, and the rotating polygon mirror 3.
The beam B0 reflected by the half mirror 7 passes through the fθ lens 4 and can reach the line sensor 84 installed on the same plane as the line sensors 83 , 81 , 82 .

Scanning beam B, which is the measurement width of the scanning beam
The scanning beam Bc is located outside the range of 2 to B3,
A photodiode 9 as a surface discrimination sensor is installed at the image plane position of the scanning beam Bc. This photodiode 9 detects the scanning beam Bc and counts the number of scans made by the rotation of the rotating polygon mirror 3, that is, the number of surfaces multiplied by the number of rotations. The photodiode 9 is connected to an amplifier 11 and an A/D converter 12, and line sensors 81, 82, 83
, 84 are connected to the microcomputer 13 and the display 16 via the A/D converter 12, and the microcomputer 13 is connected to the laser light source 1 via the LD power supply 15.
It is connected to the.

Between the rotating polygon mirror 3 and the fθ lens 4,
A shielding plate 10 is arranged parallel to the optical axis of the fθ lens 4 so that the scanning beams Bc, B3, B1, and B2 do not reach the line sensor 84.

The operation of the embodiment of the present invention shown in FIG. 1 will be explained with reference to FIGS. 2 and 3. The rotating polygon mirror 3 includes eight reflective surfaces 31 to 38. The beam B emitted from the laser light source 1 is transformed into beams Bc, B3, and B1 by each of the reflecting surfaces 31 to 38 of the rotating polygon mirror 3 that rotates around the axis 0.
, B2. In this case, FIG.
The result will be as shown in a).

Regarding the measurement of the center of gravity of the first surface 31 of the rotating polygon mirror 3, the laser light source 1 is controlled by the surface discrimination sensor 9, the amplifier 11, the A/D converter 12, the microcomputer 13, and the LD power supply 15. 31 is turned on when scanning the line sensors 83 , 81 , 82 , and the laser light source 1 is turned off by the LD power supply 15 for a certain period of time on the other second to eighth surfaces (FIG. 2(b)). And Figure 2 (
By the cycle shown in c), the line sensors 83,
Image points P3 and P1 of the beams that have reached 81 and 82
, P2 to measure the center of gravity.

At this time, of the beam B directed toward the first surface 31, the beam B0 reflected by the half mirror 7 and passed through the fθ lens 4 reaches the line sensor 84, and the center of gravity is measured from the beam imaging position P0. I do. The absolute center of gravity position of the first surface 31 of the rotating polygon mirror 3 is determined by subtracting the center of gravity position determined by the line sensor 84 from the position of the center of gravity determined by each line sensor 83 , 81 , 82 .

Next, the second surface 32 of the rotating polygon mirror 3 is similarly connected to the surface discrimination sensor 9, the amplifier 11, the A/D converter 12, the microcomputer 13, and the LD power source 15.
Accordingly, the laser light source 1 is turned on when scanning the line sensors 83 , 81 , 82 with the second surface 32 , and is turned off by the LD power supply 15 for a certain period of time on the other surface (FIG. 2(d)). Then, in the cycle shown in FIG. 2(e), the center of gravity is measured from the imaging points P3, P1, P2 of the beams that have reached each line sensor 83, 81, 82 and the imaging point P0 of the beam that has reached the line sensor 84, respectively. Similarly, from the difference, the second surface 3 of the rotating polygon mirror 3
2. Calculate the absolute center of gravity position.

Similar measurements are made for the third to eighth surfaces of the rotating polygon mirror 3. Thereafter, with the first surface 31 of the rotating polygon mirror 3 as a reference, the line sensor 81 is
An example of measurement of the inclination of each surface of the rotating polygon mirror 3 is obtained. By a similar method, line sensors 82 and 83
It is possible to measure the surface tilt.

The scanning beam BC reflected by the reflecting surface of the rotating polygon mirror 3 passes through the fθ lens 4 and reaches the photodiode 9, and the photodiode 9, which has formed the imaging point P0 by the scanning beam BC, is connected to the amplifier 13, A Since it is connected to the /D converter 14 and the microcomputer 15, the image forming point P0 is counted to obtain a timing chart as shown in FIG. 2(A).

According to the timing chart of FIG. 2(A), the scanning timing (FIG. 2(B)) of the first reflective surface 31 of the rotating polygon mirror 3 is set at eight intervals of 1st, 9th, and 17th. Therefore, for each scanning beam B3, B1, B2 at each of the eight intervals, each line sensor 8
Image points P3, P1, P2 on 3, 81, 82
By measuring and calculating the center of gravity position of the first reflecting surface 31 of the rotating polygon mirror 3 by measuring and calculating the center of gravity position using the A/D converter 14 and the microcomputer 15, it is possible to know the center of gravity position of the first reflecting surface 31 of the rotating polygon mirror 3.

As for the second reflecting surface 32 of the rotating polygon mirror 3, the scanning timings are the 2nd, 10th, and 18th as shown in FIG. 2(C), and the image forming points P3, P1, The center of gravity of P2 is
By measuring in the same manner as in the case of the reflective surface 31 of the surface, the position of the center of gravity of the second reflective surface 32 of the rotating polygon mirror 3 can be determined. You can know the location. Then, for each surface, a1, a2, a3, which is the origin of the scanning beam
By comparing the positions of the centers of gravity of the imaging points P3, P1, and P2, it is possible to measure the curvature of the scanning line as shown in FIG.

[0021]

Effects of the Invention In the configuration of the present invention, the center of gravity of the beam reflected by the half mirror installed between the light source and the rotating polygon mirror, and the beam scanned by the reflecting surface of the rotating polygon mirror after passing through the half mirror. The absolute center of gravity position is calculated from the center of gravity position of The present invention has the effect that it is possible to measure the inclination of the scanning beam with high precision without affecting the measurement results even if the measurement is started when the light source is not stable.

[Brief explanation of the drawing]

FIG. 1 is a schematic perspective view showing a means for measuring the inclination of a scanning surface of a scanning line according to an embodiment of the present invention.

FIG. 2 shows measurement timing charts by the measurement means of the embodiment of the present invention, (a) is a light reception timing chart of a surface discrimination sensor, (b) is a timing chart of a light source with respect to the first reflective surface of a rotating polygon mirror, (c) is a timing chart of the measurement of the first reflecting surface of the rotating polygon mirror, (d) is the timing chart of the light source for the second reflecting surface of the rotating polygon mirror, and (e) is the measurement of the second reflecting surface of the rotating polygon mirror. This is a timing chart.

FIG. 3 shows an example of surface tilt measurement results according to the embodiment of the present invention.

[Explanation of symbols]

Claims (4)

[Claims] 1. A scanning surface inclination measurement method in a scanning optical system comprising sensors arranged at a plurality of imaging positions of a scanning optical system in which a beam emitted from a light source is scanned by rotation of a rotating polygon mirror and an fθ lens. , the beam reflected by a half mirror placed between the light source and the rotating polygon mirror is passed through an fθ lens and imaged on a sensor placed at the imaging position, similar to the scanning beam that passes through the reflective surface of the rotating polygon mirror. , the center of gravity position of the scanning beam from the reflecting surface of the rotating polygon mirror is measured by each sensor, and at that time, the center of gravity position of the beam reflected by the half mirror is measured by the sensor, and the center of gravity position measured by the half mirror is used to measure the center of gravity position of the beam reflected by the half mirror. A scanning surface inclination measurement method in a scanning optical system, characterized by correcting each gravity center position measured by each scanning beam and comparing the gravity center positions of each reflecting surface. 2. A scanning surface inclination measuring device in a scanning optical system, comprising line sensors arranged at a plurality of image formation positions of a scanning optical system that scans a beam emitted from a light source by a rotating polygon mirror and an fθ lens. A half mirror is placed between the light source and the rotating polygon mirror, and the beam reflected by the half mirror is guided to a line sensor placed at the imaging position via an fθ lens, and the scanning beam and the beam reflected by the half mirror are Each line sensor that images the
A conversion device and a microcomputer are connected, and a light receiving sensor for reflective surface discrimination is installed within the scanning range of the scanning optical system.
The light receiving sensor for determining the reflective surface is connected to the A via an amplifier.
1. A scanning surface tilt measuring device in a scanning optical system, characterized in that it is connected to a /D conversion device and a microcomputer. 3. Based on the signal from the light receiving sensor for determining reflective surfaces, an LD power source connected to a microcomputer is connected, the light source is turned on according to the reflective surface of the rotating polygon mirror, and each line sensor generates scanning light. 3. The scanning surface inclination measuring device for a scanning optical system according to claim 2, wherein the scanning surface inclination measuring device measures the optical gravity center position of the scanning optical system. [Claim 4] Between the rotating polygon mirror and the fθ lens,
3. The scanning surface inclination measuring device in a scanning optical system according to claim 2, further comprising a shielding plate arranged to prevent each scanning beam from reaching a line sensor that images the beam reflected by the half mirror.