JPH07120213A - Tracking type laser interferometer - Google Patents

Abstract

PURPOSE:To follow a traveling body and to measure its displacement and position accurately by increasing and decreasing the optical path length of reference light and measurement light even if the rotary center of a rotary body deviates. CONSTITUTION:Laser beams which are emitted 102, are converted into circular polarization 134, enter a hollow shaft 146 of a rotary part 108 via prisms 136-144, and are split into two straight line polarizations. One straight line polarization enters a cat's eye 106, the other is made incident on a cat's eye 110 of the traveling body via prisms 158 and 162 etc., and each reflection light returns in opposite direction to an incidence optical path as the measurement light. An analysis part 104 outputs interference fringes which are obtained by allowing both to interfere with each other via a signal cable 125, and a signal processing part where it is input, detects the displacement of the traveling body from the number and phase of the interference fringes. In this case, even if the rotary center of the rotary part 108 deviates, control is made 114 so that laser beams entering the cat's eyes 106 and 110 are on the same straight line for increasing and decreasing the optical lengths of the reference light and measurement light, thus preventing the deviation from affecting measurement accuracy.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tracking type laser interferometer, and more particularly to a tracking type laser interferometer for tracking a moving body while accurately measuring the displacement and position of the moving body.

[0002]

2. Description of the Related Art Conventionally, there is also a tracking type laser interferometer for directing a laser beam to a moving body, which is shown in FIG. 5 (USP No. 4,790,651). As shown in the figure, this tracking laser interferometer is configured so that the reflection mirror 10 at the final stage can be rotated around the X axis and the Y axis, respectively. A body (not shown) can be irradiated with a laser beam. That is, the rotating body 14 that supports the reflection mirror 10 is rotatably supported by the rotating body 16 around the X axis via the bearings 12 and 12, and the rotating body 16 is supported by the fixed base 18 by the bearings 2.
It is rotatably supported around the Y axis via 0 and 20.

A laser beam oscillated from a laser light source (not shown) is split by a polarization beam splitter 22 fixed to a fixed table 18, and one of the split laser beams enters a corner cube 24 and is reflected by the corner cube 24. The light enters the detection unit 26 via the polarization beam splitter 22 as reference light. On the other hand, the other split laser beam is bent by the prism 28 coaxially with the Y axis, and thereafter, the prism 3 supported by the rotating body 16 is used.
It is bent coaxially with the X axis through 0 and 32, and is incident on the reflection mirror 10 at the final stage.

Therefore, the laser beam emitted from the reflection mirror 10 turns when the rotator 16 turns about the Y axis, and moves vertically when the rotator 14 turns about the X axis. By controlling the rotations of the rotating bodies 14 and 16, respectively, the laser beam can be emitted toward the retroreflector provided on the moving body. The reflected light from the retro-reflector provided on the moving body enters the detection unit 26 as the measurement light via the reflection mirror 10, the prisms 32, 30, 28 and the polarization beam splitter 22.

In the detector 26, the corner cube 24
The movement of the moving body is measured based on the interference between the reference light reflected by and the measuring light reflected by the retro-reflector provided on the moving body.

[0006]

However, the conventional tracking type laser interferometer described above has a problem in that the accuracy of the bearings 12 and 20 affects the measurement accuracy, and high-precision measurement cannot be performed. That is, when tracking a moving body, the rotating body 1
4 is rotationally controlled via bearings 12 and 12,
The rotation of 6 is controlled via bearings 20 and 20, and the blurring of the rotation centers of these rotating bodies 14 and 16 appears as a change in the optical path length of the measurement light. Also, the optical path length of the measurement light changes due to the thermal expansion of the rotating bodies 14, 16, etc., which affects the measurement accuracy.

The present invention has been made in view of the above circumstances, and is configured so that a measurement error does not occur even if the center of rotation of a rotating body is deviated so that the moving body can be tracked while tracking the moving body. It is an object of the present invention to provide a tracking type laser interferometer capable of measuring displacement and position with high accuracy.

[0008]

In order to achieve the above object, the present invention comprises a first retroreflector arranged at a fixed position,
A second retro-reflector disposed on the moving body, a rotary unit rotatable around an X-axis and a Y-axis orthogonal to the first retro-reflector, and oscillated from a laser light source. An optical system including a unit for guiding a laser beam to the rotating unit regardless of the rotation of the rotating unit and a plurality of optical components fixedly arranged on the rotating unit, wherein the laser beam is guided to the rotating unit. And one of the divided laser beams is incident on the first retroreflector via an optical path orthogonal to the X-axis, and the other laser beam is emitted on an extension of the optical path. An optical system which is incident on the second retro-reflector to obtain the reflected light from each of the first and second retro-reflectors;
A detector that detects the amount of movement of the second retro-reflector based on the interference of two reflected lights obtained via the optical system;
A part of the reflected light from the second retro-reflector is fixedly arranged on the rotating unit, and a position signal corresponding to the shift amount of the laser beam incident on the second retro-reflector is output. Position detecting means, and control means for controlling a rotational position of the rotating portion around the X-axis and the Y-axis based on a position signal from the position detecting means so that the displacement amount becomes zero. Is characterized by.

[0009]

According to the present invention, the first retro-reflector is fixedly arranged at a position where the X-axis and the Y-axis cross each other, and the first retro-reflector is centered around the X-axis and the Y-axis. Each is provided with a rotatable part. An optical system composed of a plurality of optical components is fixed to the rotating unit. The optical system splits a laser beam guided from a laser light source to the rotating unit, and splits one laser beam into the X-axis. While being incident on the first retroreflector via an optical path orthogonal to the other, the other laser beam is emitted on an extension of the optical path and is incident on a second retroreflector disposed on the moving body. . Then, the movement amount of the second retro-reflector is detected based on the interference of the reflected light from the first and second retro-reflectors. Even when a relative displacement occurs between the rotating portion and the first retro-reflector when detecting the amount of movement, the laser beam incident on the first retro-reflector and the second retro-reflector Since the laser beam incident on is on the same straight line, the optical path lengths of the reference light and the measurement light both increase or decrease, and as a result, no measurement error appears.

Further, the rotating portion is provided with a position detecting means to which a part of the reflected light from the second retroreflector is made incident, and this position detecting means is a laser to be made incident on the second retroreflector. A position signal corresponding to the beam shift amount is output. Therefore, the moving body is always irradiated with the laser beam by controlling the rotating position of the rotating portion around the X-axis and the Y-axis so that the displacement amount becomes zero based on the position signal from the position detecting means. Can be tracked like.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of a tracking laser interferometer according to the present invention will be described in detail below with reference to the accompanying drawings. FIG. 1 is a perspective view showing an embodiment of a tracking type laser interferometer according to the present invention. As shown in the figure, this tracking type laser interferometer includes a light source unit 102, a light detecting unit 104 and a cat's eye 106, which are mainly arranged on a fixed base 100, a rotating unit 108, and a moving body which moves in space ( (Not shown), a cat's eye 110, a four-divided photodiode 112, a tracking controller including motors M _{X and} M _Y and a controller 114.

The rotating portion 108 is rotatably supported around the X axis through bearings 122 and 124 provided between the rotating portion 108 and the support frame 120.
It is rotatably supported about the Y-axis via a bearing 126 provided between and. Therefore, the rotating unit 108 is supported on the fixed base 100 so as to be rotatable about the X axis and the Y axis.

Based on an output signal from the four-divided photodiode 112 (the details of this signal will be described later), the control unit 114 causes the rotating unit 108 so that the laser beam is incident on the cat's eye 110 for measuring light. motor M for rotating the motor M _X and the supporting frame 120 to rotate the
Drive and control _Y. The light source unit 102 and the light detecting unit 104 are unitized, and a laser beam is applied to the light source unit 102 from a laser light source (not shown) via an optical fiber 123, and the laser beam is emitted as parallel light. The light detecting unit 104 photoelectrically converts the interference light, which will be described later, and then outputs it to a signal processing unit (not shown) via the signal cable 125.

The laser beam emitted from the light source section 102 is a linearly polarized light having a plane of polarization inclined by 45 degrees, which can be considered as a vertically polarized component and a horizontally polarized component having the same phase. The two linearly polarized lights are the prism 13
It is incident on the non-polarization beam splitter 132 via 0.
The laser beam split by the non-polarization beam splitter 132 is converted into right-handed circularly polarized light and left-handed circularly polarized light by passing through the quarter-wave plate 134. The two circularly-polarized laser beams are reflected by the prism 136. The hollow shaft 138 of the support frame 120, the prism 14 fixed to the support frame 120
Rotating unit 10 coaxial with the X-axis via 0, 142, 144
It is incident on the hollow shaft 146 of No. 8. A quarter wavelength plate 148 is provided at the entrance end of the hollow shaft 146, and
By passing through the quarter-wave plate 148, the two circularly polarized laser beams are converted again into two linearly polarized lights vibrating in directions perpendicular to each other in a plane perpendicular to the traveling direction.

The laser beam converted into the two linearly polarized lights passes through the hollow shaft 146 of the rotary unit 108 and rotates the rotary unit 108.
Is incident on the optical system provided on the same plane. That is,
The laser beam is bent in a direction orthogonal to the X axis by a prism 150 provided on the X axis, and then is incident on a polarization beam splitter 154 via a prism 152. The two linearly polarized laser beams are split by a polarizing beam splitter 154 into two linearly polarized lights vibrating in directions orthogonal to each other in a plane perpendicular to the traveling direction, and one linearly polarized light reflected by the polarizing beam splitter 154 is It is made into a narrow beam by the lens group 156 and then enters the cat's eye 106.

The cat's eye 106 is, for example, a true sphere having a refractive index of 2, and a reflecting mirror is formed on the hemispherical surface of the cat's eye 106, and can reflect a laser beam incident in a predetermined incident range in the same direction as the incident direction. . If the laser beam is focused by the lens group 156, the cat's eye 1
The refractive index of 06 can be made smaller than 2. The reflected light reflected by the cat's eye 106 is returned as a reference light in the direction opposite to the incident light path.

On the other hand, the other linearly polarized light transmitted through the polarization beam splitter 154 is prisms 158, 160 and 16
The light is emitted to the cat's eye 110 disposed on the moving body via the 2 and 1/4 wavelength plates 164,
The reflected light reflected by is returned in the direction opposite to the incident light path as measurement light. The quarter-wave plate 164 is for extracting the reflected light for tracking control, and slightly rotates the plane of polarization of the linearly polarized laser beam. As a result, a part of the reflected light from the cat's eye 110 is reflected by the polarization beam splitter 154, and is projected onto the four-divided photodiode 112 via the interference filter 166.
When the laser beam is incident on the spherical center of the cat's eye 110, the reflected light is incident on the center of the light receiving surface of the photodiode 112.

Here, when the laser beam deviates from the spherical center of the cat's eye 110 and enters the cat's eye 110 with the movement of the moving body, the reflected light thereof is in accordance with the deviation direction and the deviation amount thereof, and the light receiving surface of the photodiode 112. It will be incident from the center of. The four-divided photodiode 112 has its light-receiving surface divided into four parts in the vertical and horizontal directions.
Two electric signals are output to the controller 114. Control device 1
Reference numeral 14 denotes a motor M so that the levels of the electric signals corresponding to the upper and lower division planes among the four electric signals to be input match.
While driving _X , the motor M _Y is driven so that the levels of the electric signals corresponding to the left and right divided surfaces match. As a result, the rotating unit 108 is controlled to rotate about the X axis and the Y axis, and as a result, the laser beam is always kept in the cat's eye 1.
The emission direction is controlled so as to be incident on 10.

Now, the reference light and the measurement light, which are superposed via the polarization beam splitter 154, are converted into the prism 152,
150, quarter wave plate 148, prisms 144, 14
The reference light and the measurement light that are incident on the non-polarization beam splitter 132 via the light source 2, 140136, and the quarter-wave plate 134 and are transmitted through the non-polarization beam splitter 134 are analyzed by the light detecting unit 1
Incident on 04.

In the light detecting section 104, the reference light and the measuring light, which are two linearly polarized lights vibrating at right angles to each other, are caused to interfere with each other by an appropriate means to generate an interference fringe, and the interference fringe is photoelectrically converted. The signal is output to a signal processing unit (not shown) via the signal cable 125. As is well known, the signal processing unit detects the displacement of the moving body by obtaining the number and phase of the interference fringes based on the electric signal indicating the interference fringes. still,
In order to measure the position of the moving body in the space, at least four tracking laser interferometers including a tracking laser interferometer for providing redundancy are provided and measured by each tracking laser interferometer. The position of the moving body in the space can be measured from the displacement of the moving body.

Next, the measurement accuracy of the tracking laser interferometer will be described. FIG. 2 is a main part plan view showing the internal configuration of the rotating unit 108 of FIG. As shown in the figure, the laser beam reflected by the polarization beam splitter 154 passes through the optical path orthogonal to the X-axis and then the cat's eye 1 is emitted.
It is incident toward the spherical center of 06. On the other hand, the laser beam transmitted through the polarization beam splitter 154 is reflected by the prism 15
Although it is incident on the cat's eye 110 disposed on the moving body through 8, 160, 162 and the quarter wave plate 164,
At this time, the laser beam emitted from the quarter-wave plate 164 to the cat's eye 110 is the polarization beam splitter 15
4 is emitted to the cat's eye 106 on the extension of the optical path of the laser beam.

The optical path that is a problem in terms of measurement accuracy is the difference in the distance from the position separated by the polarization beam splitter 154 to each cat's eye 106, 110. However, according to the tracking type laser interferometer configured as described above,
The rotating part 108 is a fixedly arranged cat's eye 106.
About the X-axis and the Y-axis (in FIG. 2, an axis that is orthogonal to the plane of the paper passing through the center of the cat's eye 106), so that the center of the cat's eye 106
Even if the intersection of the axis and the Y-axis does not match, the difference in distance from the position separated by the polarization beam splitter 154 to each cat's eye 106, 110 does not change. That is, according to the tracking laser interferometer configured as described above, even if a shake occurs at the center of rotation of the rotating unit 108, the shake does not affect the measurement accuracy and high-precision measurement can be performed.

FIG. 3 is a plan view of the essential parts showing another embodiment of the internal structure of the rotating part. The same parts as those in FIG. 2 are designated by the same reference numerals, and detailed description thereof will be omitted. In the rotating unit 170 shown in FIG. 3, one laser beam transmitted through the polarization beam splitter 154 is incident on the cat's eye 106 through the prism 172, and the other laser beam reflected by the polarization beam splitter 154 is reflected by the prism 174. The light is emitted toward the cat's eye 110 via the 176 and the quarter wave plate 164.

According to the arrangement of the optical components in the rotating unit 170 having this structure, the same effect as that of the rotating unit 108 can be obtained, and even if the rotating unit 170 thermally expands, it is separated by the polarization beam splitter 154. The change in the difference in the distance from the position to each cat's eye 106, 110 is small, and there is no dead path error. FIG. 4 is a plan view of an essential part showing another embodiment of the tracking laser interferometer according to the present invention. As shown in the figure, in this tracking type laser interferometer, the light source section 180 and the light detecting section 182 are arranged on opposite sides of the rotating section 178, and the quarter wave plate 181 from the light source section 180 is disposed. , 184, prisms 186, 188, and 190, and the optical path of the laser beam until it enters the polarization beam splitter 192, and from the polarization beam splitter 192 to the prisms 194, 196, and quarter-wave plates 198, 1
The optical path until it enters the light detecting unit 182 via 83 is different.

Two incident on the polarization beam splitter 192
The two linearly polarized laser beams are split by a polarizing beam splitter 192 into two linearly polarized lights vibrating in directions perpendicular to each other in a plane perpendicular to the traveling direction, and one linearly polarized light reflected by the polarizing beam splitter 192 is a prism. The light is incident on the cat's eye 106 through the 200 and the quarter wavelength plate 202, and the reflected light is reflected by the quarter wavelength plate 202.
And the polarization beam splitter 19 via the prism 200.
2 and is transmitted through the polarization beam splitter 192.

On the other hand, the other linearly polarized light that passes through the polarization beam splitter 192 is emitted to the cat's eye 110 arranged on the moving body via the beam sampler 204, the prisms 206 and 208, and the quarter wavelength plate 210. , The reflected light is a quarter wave plate 210, prisms 208, 20.
6, and enters the polarization beam splitter 192 via the beam sampler 204, and is reflected by the polarization beam splitter 192. The reflected light from the cat's eye 110 reflected by the beam sampler 204 is incident on the four-divided photodiode 212. According to the arrangement of the optical components having this configuration, the same accuracy as that of the configuration of the rotating unit 170 shown in FIG. 3 can be obtained.

In the present embodiment, the cat's eye is used as the retroreflector, but the present invention is not limited to this. For example, a corner cube, a right-angled three-sided mirror, a sphere having a mirror surface, etc. may be used. You may do it. Further, although the rotating portion is rotatable around the X axis and the Y axis by the gimbal mechanism, the invention is not limited to this, and for example, an L-shaped bracket is rotated by a motor and a motor fixed to the L-shaped bracket is used. The rotating part may be fixed and the rotating part may be rotated. Furthermore, the introduction of the laser beam into the rotating unit is not limited to the case where the laser beam is introduced along the X axis and the Y axis, and an optical fiber may be used. However, in this case, it is necessary to prevent the optical fiber from interfering with the rotation of the rotating portion.

Although the fringe count type interferometer is used, the present invention is not limited to this, and for example, a heterodyne type interferometer may be used.

[0029]

As described above, according to the tracking type laser interferometer of the present invention, even if the center of rotation of the rotating body is deviated,
The distance from the beam splitter to the retroreflector for reference,
Since the difference from the distance to the retroreflector for measurement does not change, the displacement or position of the moving body can be measured with high accuracy while tracking the moving body.

[Brief description of drawings]

FIG. 1 is a perspective view showing an embodiment of a tracking laser interferometer according to the present invention.

FIG. 2 is a plan view of a main part showing an internal configuration of a rotating part of FIG.

FIG. 3 is a main part plan view showing another embodiment of the internal structure of the rotating part.

FIG. 4 is a plan view of an essential part showing another embodiment of the tracking laser interferometer according to the present invention.

FIG. 5 is a perspective view showing an example of a conventional tracking laser interferometer.

[Explanation of symbols]

100 ... Fixed base 102, 180 ... Light source part 104, 182 ... Light detecting part 106, 110 ... Cat's eye 108, 170, 178 ... Rotating part 112, 212 ... Quadrant photodiode 114 ... Control device 120 ... Support frame 122, 124 , 126 ... Bearings 123 ... Optical fibers 125 ... Signal cables MX _{, MY} ... Motors

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Mitsuo Goto 1-4, Umezono, Tsukuba-shi, Ibaraki Industrial Technology Institute (72) Inventor, Osamu Nakamura 1-4-1, Umezono, Tsukuba-shi, Ibaraki Industrial technology Inside the Institute of Metrology Institute (72) Yoshihisa Tanimura 1-4 Umezono, Tsukuba, Ibaraki Prefecture Inside the Institute of Metrology Institute of Industrial Technology (72) Inventor Toru Nakamata 9-7 Shirenrenjaku, Mitaka City, Tokyo Stock Company Tokyo Precision (72) Inventor Toshiro Kurosawa 9-7 Shimorenjaku, Mitaka-shi, Tokyo Tokyo Seimitsu Co., Ltd. (72) Inventor Nozomi Takai 9-7 Shimorenjaku, Mitaka-shi, Tokyo Chiseuchi Co., Ltd.

Claims (1)

[Claims] 1. A first retroreflector disposed at a fixed position, a second retroreflector disposed on a moving body, an X axis orthogonal to the first retroreflector, and Rotating parts rotatable about the Y-axis, means for guiding a laser beam oscillated from a laser light source to the rotating parts regardless of the rotation of the rotating parts, and a plurality of fixed parts arranged on the rotating parts. An optical system including the optical components of (1), the laser beam guided to the rotating part is split, and one of the split laser beams is passed through the optical path orthogonal to the X axis to the first retroreflector. An optical system that causes the other laser beam to be emitted on the extension of the optical path and incident on the second retro-reflector while being incident, and to obtain reflected light from the first and second retro-reflectors, respectively. On the basis of the interference of the two reflected lights obtained via the optical system, the second A detection unit that detects the amount of movement of the retro-reflector, and is fixedly disposed on the rotating unit, and a part of the reflected light from the second retro-reflector is incident and is incident on the second retro-reflector. Position detecting means for outputting a position signal according to the amount of deviation of the laser beam, and rotation of the rotating part around the X-axis and the Y-axis so that the amount of deviation becomes zero based on the position signal from the position detecting means. A tracking-type laser interferometer, comprising: a control unit that controls a moving position.