JP2603429B2 - Tracking laser interferometer - Google Patents

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 measuring a displacement and a position of a moving body with high accuracy while tracking the moving body.

[0002]

2. Description of the Related Art FIG. 5 shows a conventional tracking type laser interferometer for directing a laser beam to a moving body (US Pat. No. 4,790,651). As shown in the figure, the tracking type laser interferometer is configured such that the last-stage reflection mirror 10 can be rotated around the X axis and the Y axis, respectively, whereby the retroreflection provided on the moving body is achieved. The body (not shown) can be irradiated with a laser beam. That is, the rotating body 14 that supports the reflection mirror 10 is supported by the rotating body 16 via the bearings 12 and 12 so as to be rotatable around the X axis.
It is supported rotatably around the Y axis via 0 and 20.

A laser beam oscillated from a laser light source (not shown) is split by a polarizing beam splitter 22 fixed to a fixed base 18, and one of the split laser beams is incident on a corner cube 24 and reflected therefrom. 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 coaxially with the Y axis by the prism 28, and then the prism 3 supported by the rotating body 16
It is bent coaxially with the X axis via 0 and 32, and is incident on the reflection mirror 10 at the final stage.

Accordingly, the laser beam emitted from the reflection mirror 10 rotates when the rotating body 16 rotates around the Y axis, and moves vertically when the rotating body 14 rotates around the X axis. By controlling the rotation of the rotating bodies 14 and 16, respectively, a laser beam can be emitted toward the retroreflector provided on the moving body. The reflected light from the retroreflector provided on the moving body enters the detection unit 26 as the measurement light via the reflection mirror 10, the prisms 32, 30, and 28, and the polarization beam splitter 22.

[0005] 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 the mirror and the measuring light reflected by the retroreflector provided on the moving body.

[0006]

However, the above conventional tracking type laser interferometer has a problem that the accuracy of the bearings 12 and 20 affects the measurement accuracy and high-precision measurement cannot be performed. That is, when tracking the moving body, the rotating body 1
The rotation of the rotating body 1 is controlled by bearings 12 and 12.
The rotation of the rotating member 6 is controlled by the bearings 20, 20, and the fluctuation of the rotation center of the rotating bodies 14, 16 appears as a change in the optical path length of the measuring light. The optical path length of the measurement light also changes due to thermal expansion of the rotating bodies 14 and 16 and the like, which affects measurement accuracy.

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

[0008]

According to the present invention, there is provided a first retroreflector disposed at a fixed position, comprising:
A second retroreflector disposed on the moving body, a rotating portion rotatable around an X axis and a Y axis orthogonal to the first retroreflector, respectively; Means for guiding a laser beam to the rotating portion regardless of the rotation of the rotating portion, and an optical system comprising a plurality of optical components fixedly arranged on the rotating portion, wherein the laser beam guided to the rotating portion And splitting one of the split laser beams into the first retroreflector via an optical path orthogonal to the X-axis, and emitting the other laser beam on an extension of the optical path to form the first laser beam. An optical system that is incident on the second retroreflector and obtains reflected light from the first and second retroreflectors, respectively;
A detection unit that detects a movement amount of the second retroreflector based on interference between two reflected lights obtained through the optical system;
A part of the reflected light from the second retroreflector is fixedly disposed on the rotating section, and outputs a position signal according to a shift amount of the laser beam incident on the second retroreflector. Position detecting means, and control means for controlling a rotational position of the rotating section about the X-axis and the Y-axis based on a position signal from the position detecting means so that the displacement amount becomes zero. It is characterized by.

[0009]

According to the present invention, the first retroreflector is fixedly disposed at the position where the X axis and the Y axis intersect, and the first retroreflector is centered around the X axis and the Y axis. Each is provided with a rotatable rotating part. An optical system composed of a plurality of optical components is fixed to the rotating unit. The optical system divides a laser beam guided from a laser light source to the rotating unit, and applies one of the divided laser beams to the X-axis. And the other laser beam is emitted along 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 retroreflector is detected based on the interference of the reflected light from the first and second retroreflectors. Even when a relative displacement occurs between the rotating part and the first retroreflector when detecting the movement amount, the laser beam incident on the first retroreflector and the second retroreflector Since the laser beam incident on the laser beam 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.

[0010] The rotating section is provided with position detecting means on which a part of the reflected light from the second retroreflector is incident. The position detecting means is provided with a laser beam incident on the second retroreflector. A position signal is output according to the beam shift amount. Therefore, by constantly controlling the rotational position of the rotating section about the X axis and the Y axis based on the position signal from the position detecting means so that the displacement amount becomes zero, the moving body is always irradiated with the laser beam. Can be tracked.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of a tracking type laser interferometer according to the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 is a perspective view showing one embodiment of a tracking laser interferometer according to the present invention. As shown in FIG. 1, this tracking laser interferometer mainly includes a light source unit 102, a light analyzing unit 104, a cat's eye 106, a rotating unit 108, and a moving object ( (Not shown), a cats eye 110, a four-division photodiode 112, and a tracking control unit including motors M _{X and MY} and a control device 114.

The rotating section 108 is supported rotatably about the X axis through bearings 122 and 124 provided between the rotating section 108 and the supporting frame 120.
Are supported rotatably about the Y axis via a bearing 126 provided between the first and second members. Therefore, the rotating unit 108 is supported on the fixed base 100 so as to be rotatable around the X axis and the Y axis, respectively.

The control unit 114 controls the rotating unit 108 based on an output signal from the four-division photodiode 112 (details of this signal will be described later) so that the laser beam enters the cat's eye 110 for measurement light. motor M for rotating the motor M _X and the supporting frame 120 to rotate the
Drive control of _Y. The light source unit 102 and the light detection unit 104 are unitized, and the light source unit 102 receives a laser beam from a laser light source (not shown) via an optical fiber 123, and emits the laser beam as parallel light. The photodetector 104 photoelectrically converts the interference light, which will be described later, and outputs the signal via a signal cable 125 to a signal processor (not shown).

The laser beam emitted from the light source unit 102 is linearly polarized light having a polarization plane inclined at 45 degrees, and can be considered as a vertical polarization component and a horizontal polarization component having the same phase. The two linearly polarized lights are
The light enters the non-polarizing beam splitter 132 through 0.
The laser beam split by the non-polarizing beam splitter 132 is converted into right-handed circularly polarized light and left-handed circularly polarized light by passing through a quarter-wave plate 134, and the two circularly polarized laser beams are converted into a prism 136. , Hollow shaft 138 of support frame 120, prism 14 fixed to support frame 120
0, 142, 144, the rotating part 10 coaxial with the X axis.
8 is input to the hollow shaft 146. A 波長 wavelength plate 148 is provided at the incident end of the hollow shaft 146, and
The two circularly polarized laser beams pass through the quarter-wave plate 148 and are again converted into two linearly polarized lights that vibrate in a direction 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 rotating unit 108 and rotates the rotating unit 108.
Are incident on an 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 enters the polarization beam splitter 154 via the prism 152. The two linearly polarized laser beams are split by the polarizing beam splitter 154 into two linearly polarized lights that oscillate at right angles to each other in a plane perpendicular to the traveling direction, and one linearly polarized light reflected by the polarizing beam splitter 154 is: After being made into a narrow beam by the lens group 156, the beam 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 hemispherical surface formed with a reflecting mirror, 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 converged by the lens group 156, the cat's eye 1
06 can be smaller than 2. The reflected light reflected by the cat's eye 106 is returned as reference light in a direction opposite to the incident light path.

On the other hand, the other linearly polarized light transmitted through the polarizing beam splitter 154 is converted into prisms 158, 160, 16
The light is emitted to the cat's eye 110 disposed on the moving object via the two- and quarter-wave plates 164,
The reflected light is returned as measurement light in a direction opposite to the incident light path. The quarter-wave plate 164 is for extracting 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 polarizing beam splitter 154 and projected to the four-division 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 shifts from the center of the cat's eye 110 and enters the cat's eye 110 with the movement of the moving body, the reflected light is reflected on the light receiving surface of the photodiode 112 according to the shift direction and the shift amount. Is incident off the center. The light receiving surface of the four-division photodiode 112 is divided into four parts in the upper, lower, left, and right directions.
The two electrical signals are output to the controller 114. Control device 1
Reference numeral 14 designates a motor M so that the levels of the electric signals corresponding to the upper and lower division planes of the four electric signals to be input are the same.
_X is driven, and the motor _MY is driven so that the levels of electric signals corresponding to the left and right division planes match. As a result, the rotation of the rotation unit 108 is controlled around the X axis and the Y axis.
The outgoing direction is controlled so as to be incident on.

Now, the reference light and the measurement light superimposed via the polarization beam splitter 154 are combined with the prism 152,
150, quarter wave plate 148, prisms 144, 14
The reference light and the measurement light that enter the non-polarization beam splitter 132 through the 2, 140136 and the quarter-wave plate 134 and pass through the non-polarization beam splitter 134
04.

The analyzer 104 generates interference fringes by causing the reference light and the measurement light, which are two linearly polarized lights oscillating in the direction perpendicular to each other, to interfere with each other by appropriate means, and photoelectrically converts the interference fringes. The signal is output to a signal processing unit (not shown) via the signal cable 125. The signal processing unit detects the displacement of the moving body by calculating the number and phase of the interference fringes based on the electric signal indicating the interference fringes, as is well known. 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 the measurement is performed 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 in 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 to the cat's eye 1.
06 toward the spherical center. On the other hand, the laser beam transmitted through the polarizing beam splitter 154 is
The light enters the cat's eye 110 disposed on the moving object via the 8, 160, 162, and １ ／ wavelength plate 164,
At this time, the laser beam emitted from the quarter-wave plate 164 to the cat's eye 110 is polarized by the polarization beam splitter 15.
4 is emitted on the extension of the optical path of the laser beam emitted to the cat's eye 106.

An optical path that poses a problem in measurement accuracy is a difference in distance between the position separated by the polarizing beam splitter 154 and each of the cat's eyes 106 and 110. However, according to the tracking type laser interferometer having the above configuration,
The rotating part 108 is a fixedly arranged cat's eye 106.
Is rotated around the X axis and the Y axis (in FIG. 2, an axis perpendicular to the plane of the drawing passing through the center of the cat's eye 106), the center of the cat's eye 106 and the X
Even when the intersection of the axis and the Y axis does not match, the difference in the distance from the position separated by the polarizing beam splitter 154 to each of the cat's eyes 106 and 110 does not change. That is, according to the tracking type laser interferometer having the above-described configuration, even if a shake occurs at the rotation center 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 a main part showing another embodiment of the internal structure of the rotating unit. Note that parts common to those in FIG. 2 are denoted by the same reference numerals, and detailed description thereof will be omitted. In the rotation unit 170 shown in FIG. 3, one laser beam transmitted through the polarization beam splitter 154 is incident on the cat's eye 106 via the prism 172, and the other laser beam reflected by the polarization beam splitter 154 is The light is emitted toward the cat's eye 110 via the 176 and the 波長 wavelength plate 164.

According to the arrangement of the optical components in the rotating section 170 having this configuration, the same effect as that of the rotating section 108 can be obtained, and even if the rotating section 170 is thermally expanded, it is separated by the polarization beam splitter 154. The change in the difference between the distance from the position to each of the cat's eyes 106 and 110 is small, and there is no dead path error. FIG. 4 is a plan view of a principal 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, a light source section 180 and an analyzing section 182 are disposed on opposite sides of a rotating section 178, and a 波長 wavelength plate 181 is provided from the light source section 180. , 184, the optical path of the laser beam until it enters the polarization beam splitter 192 via the prisms 186, 188 and 190, and the prism 194, 196 and the quarter-wave plate 198, 1 from the polarization beam splitter 192.
An optical path before the light enters the light detection unit 182 via 83 is different.

The light incident on the polarizing beam splitter 192
The two linearly polarized laser beams are split by a polarizing beam splitter 192 into two linearly polarized lights that oscillate at right angles 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 enters the cat's eye 106 via the 200 and the quarter-wave plate 202, and the reflected light is reflected by the quarter-wave plate 202.
And the polarizing beam splitter 19 via the prism 200
2 and passes through the polarizing beam splitter 192.

On the other hand, the other linearly polarized light transmitted through the polarizing beam splitter 192 is emitted to the cat's eye 110 disposed 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 １ ／ wavelength plate 210, prisms 208 and 20.
6, and enters the polarization beam splitter 192 via the beam sampler 204, and is reflected by the polarization beam splitter 192. Light reflected from the cat's eye 110 reflected by the beam sampler 204 is incident on a four-division photodiode 212. According to the arrangement of the optical components having this configuration, the same accuracy as the configuration by the rotating unit 170 shown in FIG. 3 can be obtained.

In this embodiment, a cat's eye is used as the retroreflector. However, 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, or the like may be used. You may make it. The rotating part is rotatable around the X axis and the Y axis by a gimbal mechanism. However, the present invention is not limited to this. For example, the L-shaped bracket is rotated by a motor and the motor fixed to the L-shaped bracket is used. The rotating unit may be fixed and the rotating unit may be rotated. Further, the introduction of the laser beam to the rotating section 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 hindering the rotation of the rotating unit.

Although the fringe-counting interferometer is used, the invention is not limited to this. For example, a heterodyne-type interferometer may be used.

[0029]

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

[Brief description of the drawings]

FIG. 1 is a perspective view showing one 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 unit of FIG. 1;

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

FIG. 4 is a main part plan view showing another embodiment of the tracking type 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]

Reference Signs List 100: fixed base 102, 180 ... light source unit 104, 182 ... analysis unit 106, 110 ... cat's eye 108, 170, 178 ... rotating unit 112, 212 ... four-division photodiode 114 ... control unit 120 ... support frames 122, 124 , 126 ... Bearing 123 ... Optical fiber 125 ... Signal cable MX _{, MY} ... Motor

Continuing from the front page (72) Inventor Osamu Nakamura 1-1-4 Umezono, Tsukuba, Ibaraki Pref., National Institute of Industrial Science and Technology (72) Inventor Yoshihisa Tanimura 1-4-1 Umezono, Tsukuba, Ibaraki Pref. (72) Inventor Toru Nakamata 9-7-1 Shimorenjaku, Mitaka-shi, Tokyo Tokyo Incorporated Tokyo Seimitsu Co., Ltd. Inventor Nozomi Takai 9-7-1, Shimorenjaku, Mitaka-shi, Tokyo Examiner, Tokyo Seimitsu Co., Ltd. Takuya Okada (56) References JP-A-5-302813 (JP, A) JP-A-4-74914 (JP) , A)

Claims (1)

(57) [Claims] A first retroreflector disposed at a fixed position; a second retroreflector disposed at a movable body; and an X-axis orthogonal to the first retroreflector. A rotating unit rotatable around the Y axis, a unit for guiding a laser beam oscillated from a laser light source to the rotating unit regardless of the rotation of the rotating unit, and a plurality of fixed units disposed on the rotating unit. An optical system comprising the optical components of the above, wherein the laser beam guided to the rotating portion is divided, and one of the divided laser beams is applied to the first retroreflector via an optical path orthogonal to the X axis. And an optical system that emits the other laser beam on the extension of the optical path and enters the second retroreflector to obtain reflected light from the first and second retroreflectors, Based on the interference of two reflected lights obtained through the optical system, the second A detector for detecting the amount of movement of the retroreflector; fixedly disposed on the rotating section, a part of the reflected light from the second retroreflector is incident and incident on the second retroreflector; Position detection means for outputting a position signal corresponding to the amount of deviation of the laser beam; and rotation of the rotating section about the X-axis and Y-axis based on the position signal from the position detection means so that the amount of deviation becomes zero. A tracking laser interferometer, comprising: control means for controlling a moving position.