JPH05273076A - Dynamic surface shape measuring equipment of polygon mirror - Google Patents

Abstract

PURPOSE:To measure surface shape by dividing laser beam into two parts, measuring deviation which is generated in time interval between incidence of the first beam into a first trigger sensor and that of the second beam into a second trigger sensor and then obtaining inclination of an irradiation beam due to deformation of a surface during rotation. CONSTITUTION:By moving a traveling stage, a second beam B2 is applied to a location closer to the edge of a polygon mirror 12. The mirror 12 is rotating and a trigger generation time difference between a first trigger sensor 16 and a second trigger sensor 17 is adjusted to 0 when a first beam Bl and the second beam B2 are applied to a same position. When the surface of the mirror 12 is completely flat 12a, the beams are applied to the sensors 16 and 17 simultaneously. When the surface of the mirror 12 is deformed as in 12b due to centrifugal force, the angle of reflection light of the beam B2 changes to B2b and then incidence of the beam B2b into the sensor 17 is delayed as compared with the beam B1. By detecting the delay, inclination of the surface of the mirror 12 at this position is obtained, thus measuring the surface shape.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dynamic surface profile measuring instrument used in a laser beam printer or the like for measuring a surface profile during rotation of a polygon mirror.

[0002]

2. Description of the Related Art Conventionally, a surface roughness meter, an interferometer, etc. have been used to measure the surface shape of a polygon mirror.

[0003]

These have the following drawbacks. (A) Since it is possible to measure only in a stationary state, it is impossible to measure a surface shape change due to a centrifugal force generated when rotating at a high speed, for example. (B) Since only the shape is measured, it is not possible to confirm what kind of error occurs in the scanning light when the scanning light beam is actually incident. Therefore, the relation with the jitter, which is a typical numerical value of the scanning light error, was not clear, and the influence of the scanning beam diameter was not clear. The present invention has been made to eliminate these drawbacks.

[0004]

The present invention will be described with reference to FIG. 1, which corresponds to an embodiment. A polygon mirror dynamic surface shape measuring instrument according to the present invention is a first beam splitter for splitting an output beam of a laser 1 into two. 2 and the split first beam B1
A first beam expander 4 for expanding the diameter of the first beam B1, a first lens 6 for condensing the reflected light that impinges the first beam B1 on the polygon mirror 12, and a first lens B1 for converting the condensed first beam B1 into an electric signal. 1 trigger sensor 16, a second beam expander 7 for increasing or decreasing the diameter of the second beam B2 split by the first beam splitter, and a second beam B2
Beam folding means 3 and 8 for directing 1 in a direction parallel to the reflecting surface of the polygon mirror 12 at the moment when the first trigger sensor 16 is incident, and the polygon mirror 12 at the moment when the first beam B1 is incident on the first trigger sensor 16. Moving stage 9 which is movable in a direction parallel to the reflection surface of the second moving stage 9 and the moving stage 9 which causes the second beam B2 to return and enter the polygon mirror 12.
A movement in which the reflected light from the upper two mirrors 10 and 11 and the polygon mirror 12 is folded back and emitted in a direction parallel to the reflecting surface of the polygon mirror 12 at the moment when the first beam B1 enters the first trigger sensor 16. Two mirrors 13 and 14 on the stage 9 and a second lens 5 that collects the emitted light
And a second trigger sensor 17 for converting the collected second beam B2 into an electric signal.

[0005]

When the moving stage 9 is moved, the incident position of the first beam B1 on the polygon mirror 12 is changed. If the reflecting surfaces are not parallel at this time, a time interval between the time when the first beam B1 is incident on the first trigger sensor 16 and the time when the second beam B2 is incident on the second trigger sensor 17 is displaced,
By measuring the deviation, it is possible to know the tilt of the emitted beam due to the deformation of the rotating surface.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram of an embodiment according to the present invention. A beam emitted from a laser 1 is split by a first beam splitter 2 into a first beam B1 and a second beam B2.
The diameter of the first beam B1 is expanded by the second beam expander 4. This is the first by increasing the diameter
This is for making the beam B1 less susceptible to the surface condition of the mirror surface of the polygon mirror 12. After that, the first beam B1 passes through the second beam splitter 5 and is condensed and incident on the polygon mirror 12 by the first cylindrical lens 18 only in the sub-scanning direction. The reflected light again passes through the first cylindrical lens 18. First, second,
The third cylindrical lenses 18, 19 and 20 are for correcting the rising error of the trigger due to the surface tilt of each surface of the polygon mirror 12. The first beam B1 reflected by the polygon mirror 12 then enters the second beam splitter 5 again, is reflected, is condensed by the first lens 6, enters the first trigger sensor 16, and is converted into an electric signal. It is sent to the counter 21.

On the other hand, the second beam B2 is reflected by the first mirror 3 and the beam diameter is adjusted by the second beam expander 7. The beam diameter of the second beam B2 has a similar meaning to the moving average width, and if it is increased, the macroscopic deformation of the surface shape can be read. After that, the second beam B2 is reflected by the second mirror 8 and becomes parallel to the reflecting surface of the polygon mirror 12 at the moment when the first beam B1 enters the first trigger sensor 16.

After that, the second cylindrical lens 19 and the third mirror 1 on the moving stage 9 which can move in the same direction.
0, and then enters the polygon mirror 12 through the fourth mirror 11. The reflected light is similarly reflected by the fifth mirror 13, the sixth mirror 14, and the third cylindrical lens 20 on the moving stage 9.
After passing through the first beam B1, the first beam B1 is made parallel to the reflecting surface of the polygon mirror 12 at the moment when the first beam B1 is incident on the first trigger sensor 16, is condensed by the fixed second lens 15, and is incident on the second trigger sensor 17. Then, it is converted into an electric signal and input to the counter 21.

The second lens 15 has an effect of correcting a change in the position of the surface of the polygon mirror 12. In addition, since the moving stage 9 is mechanically moved, it is inevitable that the moving stage 9 moves, but the incident light is moved twice on the moving stage 9 (the mirror 10,
11), the play of the moving stage 9 can be corrected by returning the emitted light twice (mirrors 13 and 14).

The counter 21 measures the input time interval of the trigger signals of the first trigger sensor 16 and the second trigger sensor 17, and the computer 22 calculates the amount of angular deviation generated on the surface of the polygon mirror 12 from the time interval. The surface shape can be measured.

Next, the measuring principle of the measuring instrument will be described with reference to FIG. Move the moving stage 9 to move the second beam B.
Consider a state in which 2 is incident near the end of the polygon mirror 12. The polygon mirror 12 is rotating clockwise,
When the first beam B1 and the second beam B2 are incident on the same position, the trigger generation time difference between the first trigger sensor 16 and the second trigger sensor 17 is adjusted to 0. If the surface of the polygon mirror 12 is a perfect plane 12a, as shown by the solid line in FIG.
Should always be incident on the second trigger sensor 17 at the same time that the first beam B1 is incident on the first trigger sensor 16. However, as shown by the dotted line in FIG. 2, when the mirror surface is deformed like 12b by the centrifugal force, the angle of the reflected light of the second beam B2 changes like B2b, and as a result, the second beam B2b is transmitted to the second trigger sensor 17. Is the first incident
It lags behind beam B1. By detecting this delay, the inclination of the surface of the polygon mirror 12 at this position in the scanning direction can be obtained.

[0012]

As described above in detail, according to the present invention, since the deformation of the mirror during rotation can be measured, the deformation due to the centrifugal force when the mirror rotates at a high speed can be measured. Moreover, since the optical system is the same as the scanning optical system, it is possible to measure how the shape of the surface and the beam diameter relate to the scanning jitter.

[Brief description of drawings]

FIG. 1 is a plan view showing a configuration of the present invention.

FIG. 2 is a configuration diagram showing the principle of the present invention.

[Explanation of symbols]

 1 Laser 2 1st Beam Splitter 3 1st Mirror 4 1st Beam Expander 5 2nd Beam Splitter 6 1st Lens 7 2nd Beam Expander 8 2nd Mirror 9 Moving Stage 10 3rd Mirror 11 4th Mirror 12 Polygon Mirror 13 5th mirror 14 6th mirror 15 2nd lens 16 1st trigger sensor 17 2nd trigger sensor 18 1st cylindrical lens 19 2nd cylindrical lens 20 3rd cylindrical lens 21 Counter 22 Computer B1 1st beam B2 2nd beam

Claims (1)

[Claims] 1. A first beam splitter (2) for splitting a beam emitted from a laser (1) into two, and a first beam expander (4) for expanding the diameter of the split first beam (B1).
A first lens (6) for converging the first beam (B1) on the polygon mirror (12) and condensing the reflected light; and a first trigger for converting the converging first beam (B1) into an electric signal. The sensor (16), the second beam expander (7) for increasing or decreasing the diameter of the second beam (B2) split by the first beam splitter, and the second beam (B2) for the first beam (B2).
The first beam (B1) and the beam folding means (3) and (8) for making the direction 1) parallel to the reflection surface of the polygon mirror 12 at the moment of incidence on the first trigger sensor 16. A moving stage (9) capable of moving in a direction parallel to the reflecting surface of the polygon mirror (12) at the moment of entering the trigger sensor (16), and a movement in which the second beam (B2) is folded and made to enter the polygon mirror (12). The reflected light from the two mirrors (10) and (11) on the stage (9) and the polygon mirror (12) is turned back to produce the first beam (B1).
Two mirrors (13), (14) on the moving stage (9), which emits light in a direction parallel to the reflecting surface of the polygon mirror (12) at the moment when the light enters the first trigger sensor (16).
And a second lens (15) that collects the emitted light and a second trigger sensor (17) that converts the collected second beam (B2) into an electric signal. Dynamic surface shape measuring instrument of polygon mirror.