JPH03107738A - Beam shape measuring instrument of scanning optical system - Google Patents

Abstract

PURPOSE:To improve the resolution without using any objective lens which causes a measurement error while a rotary polygon mirror is rotated by arranging a two-dimensional sensor at the image formation position of a projection beam passed through an ftheta lens from the rotary polygon mirror. CONSTITUTION:The two-dimensional sensor 4 is installed at the image formation position P and the sensor 4 is fitted to a support member 5 while enabled to swing vertically in the rotating direction of the rotary polygon mirror 2. Then a beam (a) which is generated by a laser light source 1 is reflected by the polygon mirror 2 and passed through the ftheta lens 3 to form a light image at the image formation point P. A motor 6 which rotates the polygon mirror 2 and the member 5 which swings the sensor 4 vertically in the rotating direction are driven through a controller 10 by a microcomputer 8 which operates in specific relation with picture elements of the sensor 4. In the starting period of measurement, the lateral picture element pitch is divided by an integer and a shift in position by the equally divided length is made in order to totalize the quantity of brightness of each picture element of the sensor 4, thereby measuring the distribution shape of the quantity of brightness of the projection beam.

Description

[Detailed description of the invention] [Industrial application field] The present invention is directed to a scanning optical system. It is related to the device.

Beam shape measurement [Conventional technology] Conventionally, when measuring the brightness shape of a scanning beam from a rotating polygon mirror using a two-dimensional sensor, the rotation of the rotating polygon mirror is stopped; difficult to do.

In addition, as a means of measuring the brightness shape of the beam while stopping the rotation of the rotating polygon mirror, the iI tone value at each pixel is measured, and an interpolation curve is calculated from each pixel and the tone value, and the 61 width ( (about 13.5%) and half-width (about 50%) (Fig. 5).

In this case, the size of one pixel is the resolution, which affects the accuracy of beam shape measurement. In order to improve accuracy, it is necessary to reduce the resolution, and for this reason, as shown in Fig. 6, the beam focal point P and the two-dimensional sensor S
An objective lens L is disposed between the two to expand the beam and reduce the resolution to improve measurement accuracy. F is an rθ lens.

(Problems to be Solved by the Invention) A beam shape measuring device using such a conventional objective lens has a drawback that the luminance shape is measured differently depending on the performance of the objective lens used.

Moreover, it is difficult to keep the rotating polygon mirror stationary at a fixed position because the rotating polygon mirror is supported by an air bearing.

The present invention provides a means for improving resolution when measuring the beam brightness emitted from a rotating polygon mirror and an fθ lens while the rotating polygon mirror is being rotated and without using an objective lens that causes measurement errors. The purpose is to

[Means to solve the problem]

In order to achieve the above object, the present invention disposes a two-dimensional sensor at the imaging position of the emitted beam from the rotating polygon mirror through the fθ lens, and also supports a motor that drives the rotating polygon mirror and the two-dimensional sensor. , a support member that swings the two-dimensional sensor in a direction perpendicular to the rotational direction of the rotating polygon mirror;
During the time when the rotating polygon mirror scans the vertical pixel pitch in the rotation direction with respect to the pixels on the two-dimensional sensor, the two-dimensional sensor The rotational movement of the mirror and the vertical swing of the two-dimensional sensor are controlled by a microcomputer, and the measurement start time is determined by dividing the horizontal pixel pitch into equal integers, and sequentially changing the position by shifting the length of the equal division. The present invention is characterized in that the luminance amount of each pixel of the two-dimensional sensor is accumulated to measure the distribution shape of the luminance amount of the emitted beam.

[Function] With the configuration of the present invention, it is possible to reduce the resolution, improve measurement accuracy, and accurately measure the distribution shape of the luminance amount of the emitted beam without using an objective lens.

〔Example〕

Embodiments of the present invention will be described below based on the drawings.

In FIG. 1, a beam a generated by a laser light source 1
is reflected by the rotating polygon mirror 2, passes through the fθ lens 3, and forms an optical image at the imaging point P.

In the present invention, a two-dimensional sensor 4 is installed at the imaging point P,
The two-dimensional sensor 4 is attached to a support member 5 so as to be able to swing in a direction (Z direction) perpendicular to the direction of rotation (Y direction) of the rotating polygon 1'12.

An A/D converter 7 and a microcomputer 8 are connected to the two-dimensional sensor 4, and the microcomputer 8 includes:
A display 9 is connected.

The rotation of the rotating polygon mirror 2 is driven by a motor 6.

In the present invention, the motor 6 that rotates the rotating polygon mirror 2 and the support member 5 that swings the two-dimensional sensor 4 perpendicularly to the rotation direction operate in a predetermined relationship with respect to the pixels of the two-dimensional sensor 4. , the motor 6 and the support member 5 are driven by the microcomputer 8 via the controller 10.

In FIG. 2, a pixel 40 of the two-dimensional sensor 4 is shown in (a).
1.402. . . , the measurement state is shown as the rotating polygon mirror 2 moves in the rotational direction with respect to the vertical pitch LI of . The measurement time T is set to be an integer multiple of the length of the pixels in the vertical direction, and is set to be one time in the embodiment.

In response to the rotation of the rotating polygon mirror 2 as described above, the two-dimensional sensor 4 is swung in the vertical direction by the support member 5. FIG. 2(b) shows the relationship between the swinging of the two-dimensional sensor 4 and the pixel pitch, showing the pixels 411, 412, . . . of the two-dimensional sensor 4 arranged in the horizontal direction. ... is taken as the vertical axis, and the horizontal pitch of the pixels is indicated by L2.

The vertical swing width of the two-dimensional sensor 4 is set to an integral multiple of the horizontal pitch L2 of the pixels, and in this embodiment, it is set to twice the horizontal pitch L2 of the pixels, as shown in FIG. 2(a). The position corresponding to the measurement start time is one swing end S0, and when the two-dimensional sensor 4 moves in the other direction by the swing width from this position S0, the injection The center P0 of the beam is at a position S corresponding to the end of the swing width
Leading to I.

The measurement time T shown in FIG. 2(a) corresponds to the time for moving the two-dimensional sensor 4 through the swing width (movement time from position S0 to position S) in FIG. 2(b).

That is, due to the rotation of the rotating polygon mirror 2 and the swinging of the two-dimensional sensor 4, the center P0 of the emitted beam changes from the measurement start time to the vertical pitch of the pixels of the two-dimensional sensor 4, which is an integer multiple (one time in the example). ), and corresponding to this measurement time T, the two-dimensional sensor 4 moves through a positive movement width that is an integral multiple of the lateral pitch L2 of the pixels. This measurement time T corresponds to -half of the swing cycle time of the two-dimensional sensor 4.

In the measurement corresponding to the pixel pitch of the two-dimensional sensor 4 as described above, the luminance measurement value shown in FIG. The resolution can be improved by sequentially shifting to the positions divided into the above-mentioned number of equal parts.

In the embodiment, the vertical pitch L1 of pixels of the two-dimensional sensor 4 is
is divided into four equal parts, the first measurement start time is set from the left end of the vertical pixel pitch LL, and the next measurement start time is set as shown in Fig. 2 (a).
), the position of the pixel is shifted to the right by -4/Δa from the left end of the vertical pixel pitch L1, the imaging center point P1 is aligned here, and the next measurement start time is set as follows.
By sequentially shifting the vertical pitch L1 of the pixels from the left end to half - (twice Δa) and three-quarters (twice Δa) to the right, the measurement accuracy 2 resolution is improved, as shown in Figure 3 (b). The brightness measurements shown in can be obtained.

The pixel pitch of the two-dimensional sensor is moved by Δa, L,
/Δa, one pixel is repeatedly measured several to several thousand times depending on the required resolution, and the luminance amount (gradation value) of each pixel is measured by the A/D converter 7. The microcomputer 8 accumulates the amount of brightness (gradation value) at each pixel position, and calculates the shape of the emitted beam by interpolation calculation, that is, e-1
The shape of the beam is calculated from the width (approximately 13.5%) and the half width (approximately 50%), and the measurement results are displayed on the display 9.

In order to measure with high accuracy, it is desirable to set the value of L1/Δa to be an integer. Further, by using a two-dimensional sensor in which the pixel pitch L1 in the vertical direction and the pixel pitch L2 in the horizontal direction are equal, the resolution can be made equal.

FIG. 4 shows another embodiment of the present invention, which differs from the previous embodiment in that the beam a from the laser light source 1 is transmitted to the rotating polygon mirror 2. Beams al and ax are formed by the fθ lens 3
ta3 and each of its beams al ya2
Two-dimensional sensors 4a, 4b, 4c are placed at the imaging position of ya3.
The two-dimensional sensors 4a, 4b, and 4c are supported by swinging support members 5a, 5b, and 5c, respectively.

Each beam a+wax! As described above, in a3, the brightness shape of the beam can be measured by synchronizing the rotation of the rotating polygon mirror and the swinging of the two-dimensional sensor.

〔effect〕

With the configuration of the present invention, it is possible to measure the brightness shape of the beam while the rotating polygon mirror is rotated, eliminating the need for optical axis alignment, and by directly measuring the optical image with a two-dimensional sensor, there is no need for an objective lens. This has the effect that the beam shape is not affected by lens performance, and that the resolution is improved and brightness distribution measurement can be performed with high precision.

[Brief explanation of drawings]

FIG. 1 is a schematic explanatory diagram showing an embodiment of the beam shape measuring device of the present invention, and FIG. 2 (a), Φ) shows the relationship of the emitted beam to the vertical pitch and horizontal pitch of the pixels of the two-dimensional sensor. Graphs, Fig. 3(a), Φ) are graphs showing one luminance measurement value corresponding to the pixel pitch and a luminance measurement value obtained by dividing the pixel pitch and summing up several measurements, and Fig. 4 is a graph showing the luminance measurement value obtained by dividing the pixel pitch and summing up several measurements. 5 is a graph showing brightness measurement values by a conventional beam shape measuring device. FIG. 6 is a schematic explanatory diagram showing a conventional beam shape measuring device. be. 1... Laser light source, 2... Rotating polygon mirror, 3... f
θ lens, 4 * 4 a, 4 b s 4 c ・
・Two-dimensional sensor, 401.402,411,412・
... Pixel, L,, L2... Pixel pitch, T... Measurement time, D... Swing width, 5°5a, 5b, 5c... Swing support member, 6... Motor, 7... A/D converter, 8... Microcomputer, 9... Display, 10... Controller.

Claims (1)

[Claims] A two-dimensional sensor is disposed at the imaging position of the emitted beam from the rotating polygon mirror through the fθ lens, and a motor that drives the rotating polygon mirror and a two-dimensional sensor are provided to support the two-dimensional sensor in the rotation direction of the rotating polygon mirror. A support member that swings the sensor in a direction perpendicular to the sensor is provided, and during the time when the rotating polygon mirror scans the vertical pixel pitch in the rotation direction with respect to the pixels on the two-dimensional sensor, the two-dimensional sensor swings vertically and horizontally. The rotational movement of the rotating polygon mirror and the vertical swing of the two-dimensional sensor are controlled by a microcomputer so that the amplitude is an integer multiple of the pixel pitch, and the horizontal pixel pitch is set to an integer at the start of measurement. In a scanning optical system, the distribution shape of the luminance amount of the emitted beam is measured by sequentially changing the positions shifted by the equally divided length and summing the luminance amount of each pixel of the two-dimensional sensor. Beam shape measuring device.