JPH07218220A - Fast tracking type laser interference length measuring apparatus - Google Patents

Abstract

PURPOSE:To provide a tracking type laser interferometer which enable the tracking of even a moving object moving fast. CONSTITUTION:In an optical system provided in a rotor 108, a laser beam introduced to the rotor from a laser light source is split and one thereof is admitted to a reverse reflector 106 via an optical path orthogonal to an X axis while the other thereof is emitted on the extension of the optical path to be admitted to a reverse reflector 110 arranged in a moving object. Then, a displacement value of the reverse reflector 110 is detected based on the interference between the reflected lights from the reverse reflectors 106 and 11. The reflected light from the reverse reflector 110 is admitted to a photodiode 112 to generate a positional deviation signal. The rotator 108 follows the moving object based on the positional deviation signal and following errors are corrected by the tilting of a mirror 152 thereby allowing the following of the moving object accurately.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-speed tracking laser interferometer, and more particularly to a high-speed tracking laser interferometer for tracking a moving body and measuring the displacement and position of the moving body with high accuracy. Regarding vessels.

[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. 7 (USP No. 4,790,651). As shown in the figure, this tracking type laser interferometer is constructed so that the reflection mirror 10 at the final stage can be rotated around the X axis and the Y axis via the rotating bodies 14 and 16, respectively. Thus, the retro-reflector (not shown) provided on the moving body can be irradiated with the laser beam. That is, the rotating body 14 that supports the reflection mirror 10 has the bearings 12, 1 with respect to the rotating body 16.
2 is rotatably supported around the X axis via
Reference numeral 6 is supported by a fixed base 18 via bearings 20, 20 so as to be rotatable around the Y axis.

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 tracking laser interferometer is required to track a moving object moving at a high speed on a short distance side at a large angular velocity, whereas For a moving object moving at high speed on the distance side, only a tracking error of a minute angle is allowed. Therefore, the conventional tracking type laser interferometer has a drawback that it cannot accurately track a moving body with a high rotational speed of the rotating bodies 14 and 16 around the X axis and around the Y axis.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a high-speed tracking type laser interferometer, which can accurately track a moving body moving at high speed.

[0008]

In order to achieve the above object, the present invention is rotatable about an X-axis and a Y-axis which are orthogonal to a first retro-reflector provided on a moving body. An optical system comprising a rotating body, means for guiding a laser beam oscillated from a laser light source to the rotating body regardless of rotation of the rotating body, and a plurality of optical components fixedly arranged on the rotating body. , Splitting the laser beam guided to the rotating body, making one of the split laser beams incident on the first retroreflector along an optical path on a straight line passing through the intersection of the X axis and the Y axis, and An optical system that makes a laser beam incident on a second retro-reflector to obtain reflected light from each of the first and second retro-reflectors, and the rotator is tiltably disposed in the rotator. Optics for deflecting the laser beam guided to the camera by a small angle A detecting unit for detecting a moving amount of the first retroreflector based on the interference with the reference light reflected from the reflective light and the second retroreflector from the first retroreflector,
It is fixedly arranged on the rotating body, a part of the reflected light from the first retro-reflector is incident, and outputs a position signal according to the shift amount of the laser beam incident on the first retro-reflector. Position detection means, first control means for controlling the inclination of the reflective optical component at a first response speed based on a position signal from the position detection means so that the displacement amount becomes zero, and the position detection means Based on the position signal from the means and / or the signal indicating the inclination of the reflective optical component from the reference position, the rotary body is moved at the second response speed so as to return the reflective optical component to the reference position. Second control means for controlling the rotational position around the Y-axis.

[0009]

According to the present invention, the tilting position of the reflective optical component provided on the rotating body is controlled so that the amount of deviation from the position detecting means becomes zero, whereby the rotating body is rotated about the X-axis and the Y-axis. The first control means for controlling the deflection direction of the laser beam similarly to the rotation, and the X-axis and the Y-axis so that the amount of displacement of the rotating body from the position detection means and the amount of tilt of the reflective optical component become zero.
Second control means for controlling the rotational position around the axis is provided. The reflective optical component can track the moving body with a small time constant, though it is in a minute range as compared with the rotating body.
When the reflective optical component is tilted, the rotating body rotates so as to return the reflective optical component to the initial position. Therefore, even if the moving body moves at high speed due to sudden acceleration / deceleration or speed fluctuation, the second control means controls the rotation of the rotating body about the X-axis and the Y-axis to track the moving body. By controlling the tilting of the reflective optical component by the control means to compensate the tracking error of the rotating body, it is possible to accurately track the moving body.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of a high speed tracking type laser interferometer according to the present invention will be described in detail below with reference to the accompanying drawings. Figure 1
FIG. 1 is a perspective view showing an embodiment of a high speed tracking type laser interferometer length measuring device according to the present invention. As shown in the figure, this high-speed tracking type laser interferometer length measuring device is mainly composed of a light source section 102, a light detecting section 104 and a cat's eye 10 arranged on a fixed base 100.
6, a rotating body 108, a cat's eye 110 arranged in a moving body (not shown) that moves in space, a photodiode 112 divided into four, motors M _{X and} M _{Y, a} motor drive circuit 114, and piezo drive The tracking control unit includes a circuit 115.

The rotating body 108 is rotatably supported around the X axis via bearings 122 and 124 provided between the rotating body 108 and the supporting frame 120.
It is rotatably supported about the Y-axis via a bearing 126 provided between and. Therefore, the rotator 108 is rotatably supported by the fixed base 100 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 device 114 causes the rotating body 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
_{The Y} is driven and controlled, and the mirror 152 is tilted.

The light source section 102 and the light detecting section 104 are unitized, and a laser beam is applied to the light source section 102 from a laser light source (not shown) through an optical fiber 123, and this laser beam is converted into parallel light. Emit. 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 body 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 light is passed through the hollow shaft 146 of the rotating body 108 to rotate the rotating body 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 mirror 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. The cat's eye 106 can reflect a laser beam incident in a predetermined incident range in a direction opposite to 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. As shown in FIGS. 2 and 3, the mirror 152 is rotatably supported about the y-axis, and the y-axis is sandwiched between the L-shaped mounting plate 153 and the mirror 152, and the balance spring 153C and the piezo element. 153Y is provided. In addition, the mounting plate 153, as shown in FIG.
It is attached to a base plate 155 so as to be rotatable about an axis, and a piezo element 153X and a balance spring (not shown) are provided between the base plate 155 and the attachment plate 153 with the x axis interposed therebetween. . Then, when the piezo element 153Y is driven, the mirror 152 causes an axis (hereinafter, referred to as an axis orthogonal to the plane of FIG. 2).
When the piezo element 153X is driven to rotate about the y-axis and the piezo element 153X is driven, the mirror 152 causes an axis orthogonal to the y-axis (hereinafter, x).
It rotates around the axis.

In this way, by rotating the mirror 152 around the x-axis and the y-axis, the laser beam can be swung in the vertical and horizontal directions. The piezo element 1
Although the turning range of the mirror 152 driven by 53X and 153Y is small, the responsiveness of the mirror 152 is high, so that the moving body can be tracked even when it moves rapidly.

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, the Cat's Eye 110
A part of the reflected light from the polarization beam splitter 15
It is reflected by 4 and is projected onto the photodiode 112 divided into four through 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 receives the light-receiving surface of the photodiode 112 according to the deviation direction and the deviation amount. 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 motor drive circuit 114 and the piezo element drive circuit 115. The piezo element drive circuit 115
Of the four input electrical signals, the piezo element 153 is arranged so that the levels of the electrical signals corresponding to the upper and lower split surfaces match.
While driving X, the piezo element 153Y is driven so that the levels of the electric signals corresponding to the left and right divided surfaces match. As a result, the mirror 152 is rotationally controlled about the X axis and the Y axis, and as a result, the emitting direction of the laser beam is controlled so as to always enter the cat's eye 110.

Similarly, in the motor drive circuit 114, among the four input electric signals, the levels of the electric signals corresponding to the upper and lower split surfaces are the same, and the turning position of the mirror 152 about the x-axis is the initial position. drives the motor M _X as back, the motor M _Y so that the level matches the electrical signal corresponding to the left and right divided surface, and y-axis rotational position of the mirror 152 is returned to the original position To drive. As a result, the rotating body 108 is rotationally controlled around 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.

The reference light and the measurement light, which are superposed via the polarization beam splitter 154, have a mirror 152, a prism 150, a quarter wave plate 148, a prism 144,
The reference light and the measurement light that enter the non-polarizing beam splitter 132 via the 142, 140, 136, and the quarter-wave plate 134 and pass through the non-polarizing beam splitter 134 enter the light detecting unit 104.

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 interference fringes, and the interference fringes are 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 of movements and the phase of the interference fringes based on the electric signal indicating the interference fringes.
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 redundancy are provided, and each tracking laser is provided. The position of the moving body in the space can be measured from the displacement of the moving body measured by the interferometer.

Next, a tracking method of the tracking type laser interferometer is described. FIG. 4 is a main part plan view showing the internal structure of the rotating body 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.

FIG. 5 is a plan view of an essential part showing another embodiment of the internal structure of the rotating body. The same parts as those in FIG. 4 are designated by the same reference numerals, and detailed description thereof will be omitted. In FIG. 5, the reflection mirror 150 is rotatably supported only around the x axis, and the reflection mirror 152 is rotatably supported only around the y axis. That is, in the embodiment shown in FIG. 4, one mirror 152 is rotated about the x-axis and the y-axis, but in the embodiment shown in FIG. 5, the two reflecting mirrors 150 and 152 are rotated separately. The laser beam is oscillated vertically and horizontally by controlling the movement.

FIG. 6 shows a control block for controlling the rotating body 108 and the mirror 152. It should be noted that, for simplification, only one-axis control (for example, control of the rotating body 108 about the Y-axis and control of the mirror 152 about the y-axis) will be described with reference to FIG. First, when the moving body moves, the reflected light from the cat's eye 110 shifts and enters from the center of the light receiving surface of the photodiode 112. Based on this, the photodiode 11
From FIG. 2, a shift signal indicating that the laser beam is shifted in the left-right direction from the center of the cat's eye 110 is an integrating circuit 1.
72 and output to the adder circuits 173 and 174. The integrating circuit 172 integrates the input shift signal to convert it into a displacement amount of the piezo element, and outputs it to the adding circuit 173.
The shift signal from the photodiode 112 is also input to the adding circuit 173 for characteristic compensation, and the added value is output to the piezo drive circuit 115. The piezo drive circuit 115 uses the input signal from the adder circuit 173 as the control target of the mirror 152, and drives the piezo element 153Y so that the mirror 152 has the control target angle.

On the other hand, the adder circuit 174 has a photodiode.
The shift signal from the switch 112 and the output signal of the adding circuit 173 are
The addition circuit 174 has been added
The output signal of 173 is added, and the added value is used to drive the motor.
Output to the circuit 114. The motor drive circuit 114 adds
The motor M is rotated at the rotation speed corresponding to the input signal from the path 174. _Y
To drive. 176 is a motor M_YThe rotation speed of
With the tacho generator,_YControl at the required speed
Feedback signal is sent to the motor drive circuit 1
It outputs to 14.

According to the above configuration, the amount of deviation of the laser beam from the center of the cat's eye 110 (photodiode 1
The amount of deviation of the incident light at 12) is that the tilt of the mirror 152 is controlled by the piezo element 153Y, and the rotating position of the rotating body 108 is controlled so that the mirror 152 is mainly returned to the initial position. Modified by. The response speed at the time of correcting the shift by the mirror 152 is
It is fast enough to track a moving body even when the moving body moves rapidly. On the other hand, the response speed of the rotating body 108 is determined by the mirror 15
Although it is slower than the response speed of 2, the rotation range of the rotating body 108 is sufficiently larger than the rotation range of the mirror 152, and the tracking range of the moving body can be made large. In addition, the rotating body 108
The rotation speed of is fast so that the moving body can be tracked even when the moving body moves at high speed.

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, or a sphere whose surface is a mirror surface is used. You may do it. Further, the rotating body is rotatable about the X axis and the Y axis by the gimbal mechanism, but the invention is not limited to this. For example, when the L-shaped bracket is rotated by the motor, and the motor is fixed to the L-shaped bracket. The rotating body may be fixed and the rotating body may be rotated. Furthermore, the introduction of the laser beam into the rotating body 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 body.

Further, although the fringe count type interference length measuring device is used, the present invention is not limited to this, and for example, a heterodyne type interference length measuring device may be used.
Further, although the prism type mirror is used as the reflective optical component in the above-mentioned embodiment, the present invention is not limited to this, and another type of mirror may be used.
Further, although the piezo element is used to drive the mirror in the above-mentioned embodiment, the present invention is not limited to this, and a motor, a galvanometer or the like may be used.

Further, in the above embodiment, the motor drive circuit 11
4 is controlled based on the shift signal and the signal from the adder circuit 173, but may be controlled based on either one of the signals.

[0032]

As described above, according to the high speed tracking type laser interferometer according to the present invention, since the reflective optical component which swiftly follows the moving body is provided on the rotating body which tracks the moving body. It is possible to accurately track even a moving body that moves at high speed with rapid acceleration / deceleration.

[Brief description of drawings]

FIG. 1 is a perspective view showing an embodiment of a high-speed tracking type laser interferometer length measuring device according to the present invention.

FIG. 2 is an explanatory diagram showing a piezo element that rotates a mirror.

FIG. 3 is a perspective view of the mirror of FIG.

FIG. 4 is a plan view of an essential part showing the internal configuration of the rotating body of FIG.

FIG. 5 is a plan view of an essential part showing another embodiment of the internal structure of the rotating body.

FIG. 6 is a control block diagram of a motor and a piezo element.

FIG. 7 is a perspective view showing an example of a conventional tracking laser interferometer.

[Explanation of symbols]

100 ... Fixed stand 102 ... Light source part 104 ... Light detecting part 106, 110 ... Cat's eye 108 ... Rotating body 112 ... Quadrant photodiode 114 ... Motor drive circuit 115 ... Piezo drive circuit 120 ... Support frame 123 ... Optical fiber 125 ... Signal Cable M _X, M _Y ... Motor 152 ... Mirror 152X, 152Y ... Piezo element

Front page continuation (72) Inventor Mitsuo Goto 1-4, Umezono, Tsukuba-shi, Ibaraki Institute of Industrial Technology (72) Inventor Osamu Nakamura 1-4-1, Umezono, Tsukuba-shi, Ibaraki Institute of Industrial Technology (72) Inventor Yoshihisa Tanimura 1-4 Umezono, Umezono Tsukuba-shi, Ibaraki Institute of Industrial Science and Technology (72) Inventor Toru Nakamata 9-7 Shirenrenjaku, Mitaka-shi, Tokyo Tokyo Seimitsu Co., Ltd. ( 72) Inventor Toshiro Kurosawa, 9-7 Shimorenjaku, Mitaka City, Tokyo, Tokyo Seimitsu Co., Ltd. (72) Inventor Nozomi Takai 9-7, Shimorenjaku, Mitaka City, Tokyo

Claims (2)

[Claims] 1. A first retro-reflector disposed on a moving body, a rotator rotatable about an X-axis and a Y-axis orthogonal to each other, and a laser beam oscillated from a laser light source. An optical system comprising a means for guiding the rotating body regardless of the rotation of the body and a plurality of optical components fixedly arranged on the rotating body, for dividing the laser beam guided to the rotating body and dividing the laser beam. The one laser beam is made incident on the first retroreflector along an optical path on a straight line passing through the intersection of the X axis and the Y axis, and the other laser beam is made incident on the second retroreflector. An optical system for obtaining reflected light from each of the first and second retroreflectors, and a reflective optical component that is tiltably disposed in the rotating body and deflects a laser beam guided to the rotating body by a minute angle. , Reflected light from the first retro-reflector and second anti-reflection A detection unit that detects the amount of movement of the first retro-reflector based on interference with reference light reflected from the body; and a detection unit that is fixedly disposed on the rotating body and that reflects light from the first retro-reflector. Position detecting means for outputting a position signal according to the amount of deviation of the laser beam that is incident on the first retroreflector, and the amount of deviation is zero based on the position signal from the position detecting means. A first control means for controlling the inclination of the reflective optical component at a first response speed so that the position signal from the position detecting means and / or a signal indicating the inclination of the reflective optical component from the reference position And a second control means for controlling the rotational position of the rotating body around the X-axis and the Y-axis at a second response speed so as to return the reflective optical component to the reference position. High-speed tracking laser interferometer length measuring device. 2. The reflective optical component includes a first reflective optical component that is tiltable in a first direction in the rotating body, and a second reflective optical component.
The high-speed tracking type laser interferometer length measuring instrument according to claim 1, comprising a second reflective optical component which is tiltable in the direction of.