JP3045567B2 - Moving object position measurement device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a stage device for controlling the position of a linearly moving table device such as a machine tool, an optical machine, a measuring machine, etc. The present invention relates to an apparatus for measuring

[0002]

[Its Problems prior art As shown in FIG. 4, when the moving body M on the stage of the linear motion, for example, moved along the x-axis, in addition to the positioning error e _x in the x-axis direction, y-axis Displacement error consisting of three components of y-axis displacement error e _{y due to} movement in the direction, ez due to movement in the _z- axis, rolling error α due to rolling around the x-axis, pitching error β due to pitching around the y-axis, It is known that a six-component error occurs with a three-component angle error consisting of a yawing error γ due to yawing around the z-axis.

A conventional measuring instrument is disclosed in, for example,
A laser interferometer disclosed in Japanese Patent No. 22360 is known. In this length measuring device, the object to be measured requires two reflecting mirrors in the case of length measurement. In addition, two biprisms are required for measuring the tilt components (yawing, pitching), and the two components cannot be measured at the same time.
Further, the above three components cannot be measured simultaneously by one measuring instrument.

In general, an x-stage, an xy-stage, and an xyz-stage are used for a device that performs linear motion. However, in order to measure the linear motion accuracy of these moving stages with high accuracy, laser interferometry is used for measuring axial displacement. Long system,
Autocollimators are widely used for angular displacement.

For example, in an xy stage moving in an xy plane, as shown in FIG. 5, two laser length measuring devices 100 and 102 and two autocollimators 104 and
Using the laser interferometer 102 and the orthogonal displacement mirror 106, the x displacement is calculated using the laser interferometer 102 and the laser interferometer 104.
Is used to measure the y displacement, and at the same time, measure the angle errors α and γ using the autocollimator 104 and the angle errors β and γ using the autocollimator 106. In this configuration, two laser interferometers 10
Using 0, 102 and two autocollimators 104, 106, displacement of five components can be measured simultaneously.

However, such a measurement system has a complicated configuration and requires a large space for the measurement. Conversely, for stages of the same size, too much space is taken up in the measurement system and the operating range is reduced. In addition, the number of measurement points increases, which causes a measurement error.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a compact measuring optical system for controlling the linear motion of a moving body such as a stage with high accuracy.

[0008]

Means for Solving the Problems In order to solve such a problem, the present invention provides a moving object position measuring device for measuring the position of a moving object having a reflecting surface, which emits a light beam, A beam splitting unit that splits a light beam into two light beams, comprising object light irradiated toward a reflecting surface of the moving body and reference light that interferes with the object light reflected by the reflecting surface. Based on an interference signal generated by interference between the reflected object light and the reference light, means for detecting a distance to the moving object, and detecting a tilt of the reflected object light with respect to an optical axis, Means for detecting the angular displacement of the moving body.

Further, the beam splitting means includes:
It is characterized by comprising two polarizing beam splitters whose beam splitting planes are orthogonal to each other, and a half-wave plate disposed between them. Further, the angular displacement detecting means comprises a position detecting element for receiving the object light reflected by the reflecting surface and detecting a light receiving position thereof.

[0010]

The light beam incident on the beam splitting means is composed of an object light emitted toward the reflecting surface of the moving object and a reference light interfering with the object light reflected by the reflecting surface of the moving object. The light beam is separated into books. An interference signal is generated by the interference between the object light reflected by the reflecting surface of the moving body and the reference light passing through an optical path different from the object light. The distance to the moving object is detected based on the intensity of the interference signal.

On the other hand, the object light reflected by the reflecting surface of the moving body is also irradiated to means for detecting the angular displacement of the moving body, and the angular displacement of the moving body is detected based on the irradiation position. .

[0012]

FIG. 1 shows an embodiment of a measuring optical system according to the present invention.
The light source 12 includes a laser diode 14 and a collimating lens 16. The laser light emitted from the laser diode 14 is shaped into a parallel beam by the collimating lens 16 and emitted from the light source 12. The parallel beam emitted from the light source 12 passes through the isolator 18, becomes linearly polarized light inclined at 45 degrees with respect to the plane of the paper, is reflected by the mirror 20, and then enters the polarization beam splitter 22. The polarization beam splitter 22 transmits a polarization component parallel to the paper surface and reflects a polarization component perpendicular to the paper surface.

The light beam (object light) reflected by the polarizing beam splitter 22 passes through the λ / 4 plate 24 and reaches the plane mirror 26a of the moving body 26. Here, the light beam is reflected, passes through the λ / 4 plate 24 again, becomes linearly polarized light parallel to the paper surface, passes through the polarization beam splitter 22, and enters the lens. The light beam incident on the lens 28 is incident on the polarization beam splitter 30 while being focused. The polarization beam splitter 30 is provided with a half mirror 30a on the left side and a total reflection mirror 30b on the lower side, and these are located on the focal plane of the lens 28. The light incident on the polarization beam splitter 30 is focused on the half mirror 30a, a part of which is transmitted through the half mirror 30a and is incident on the two-dimensional position detecting element 32, and the remaining light is reflected by the half mirror 30a. The light reflected by the half mirror 30a enters the lens 28 and becomes a parallel beam, passes through the polarizing beam splitter 34 and the λ / 4 plate 36, reaches the plane mirror 26a of the moving body 26, and is reflected. The light beam reflected by the plane mirror 26a is again λ /
The light passes through the four plates 36 to become linearly polarized light perpendicular to the paper surface, is reflected by the polarization beam splitter 34, and enters the λ / 4 plate 40.

On the other hand, a linearly polarized light beam (reference light) parallel to the plane of the paper transmitted through the polarizing beam splitter 22 is λ
The light passes through the 板 plate 38 and becomes linearly polarized light perpendicular to the paper surface, and is reflected by the polarization beam splitter 34. The light beam reflected by the polarization beam splitter 34 enters the polarization beam splitter 30 while being incident on the lens 28 and being focused. The light incident on the polarization beam splitter 30 is reflected by the beam splitting surface 30c, and is reflected by the total reflection mirror 3
0b is focused and reflected. The light reflected by the total reflection mirror 30b is reflected by the beam splitting surface 30c, is incident on the lens 28, becomes a parallel beam, is incident on the polarization beam splitter 22, and is reflected. The light beam reflected by the polarization beam splitter 22 becomes linearly polarized light parallel to the paper when passing through the λ / 2 plate 38, passes through the polarization beam splitter 34, and enters the λ / 4 plate 40.

The two light beams that have passed through the λ / 4 plate 40 are both circularly polarized and combined, and then split by the polarizing beam splitter 42 into two beams. The beam that has passed through the polarizing beam splitter 42 is
, And enters the polarization beam splitter 46 to be further split into two beams.
Is incident on the photodiode PD1.
The beam reflected by the polarization beam splitter 46 enters the photodiode PD3. The beam reflected by the polarizing beam splitter 42 passes through the λ / 4 plate 48 and enters the polarizing beam splitter 50, is further divided into two beams, and the beam reflected by the polarizing beam splitter 50 is transmitted to the photodiode PD2. The beam that has entered and transmitted through the polarizing beam splitter 50 enters the photodiode PD4.

The interference signal intensities S _{1 to} S ₄ detected by the photodiodes PD ₁ to PD ₄ are as follows, respectively.

PD1: S ₁ = a ₁ + b ₁ cos (2π / λ · n · Δ
L) PD2: S ₂ = a ₂ + b ₂ sin (2π / λ · n · Δ)
L) PD3: S ₃ = a ₃ + b ₃ cos (2π / λ · n · Δ)
L) PD4: S ₄ = a ₄ + b ₄ sin (2π / λ · n · Δ)
L) Here, ΔL is the optical path difference between the object light and the reference light, and λ is the wavelength of the laser light. S ₁ − output from the differential amplifier 52
S ₂ is a cos signal, and S ₂ − output from the differential amplifier 54
S ₄ becomes the sin signal. The outputs of the differential amplifiers 52 and 54 are respectively subjected to phase correction and offset adjustment by a preamplifier, sent to a counter, where interference signals are counted, and the displacement of the plane mirror 26a is measured. At this time, since the object light makes two round trips in the optical path to the moving body, the optical path difference is twice as large as the movement of the moving body, so that the measurement sensitivity is doubled. Moreover, since the object light and the reference light pass through substantially the same optical path, fluctuations in the temperature environment and the like are strong.

FIG. 2 shows a state where the plane mirror 26a of the moving body 26 is tilted. In the figure, the optical path when the moving body is not inclined is shown by a broken line. When the moving body 26 is tilted by θ, the light beam incident on the plane mirror 26a is reflected at an angle of 2θ with respect to the incident light, and is incident on the lens 28. The light beam that has passed through the lens 28 is reflected by the half mirror 30a and enters the lens 28 again. The light beam emitted from the lens 28 is emitted in parallel with the light beam incident on the lens 28. This light beam is moving body 2
6 and is reflected by the polarizing beam splitter 34. The beam emitted from the polarizing beam splitter 34 is emitted in parallel with the beam incident on the polarizing beam splitter 22, but its optical path is slightly shifted from the optical path when the plane mirror 26a is not tilted. As described above, the position of the moving body 26 of the light beam emitted from the polarization beam splitter 34 is detected from the interference signal.

On the other hand, the reflecting mirror 26a of the moving body 26
The light beam (object light) reflected by the light enters the two-dimensional position detecting element 32 after passing through the half mirror 30a. On the half mirror 30a, the plane mirror 26a
The deviation d between the irradiation position of the reflected object light when not tilted and the irradiation position of the reflected object light when the plane mirror 26a is tilted θ is:

[0020]

(Equation 1)

Is represented by Here, f is the focal length of the lens 28. Therefore, the inclination angle θ can be derived from the displacement d. This characteristic is the same when the plane mirror 26a of the moving body 26 in FIG. 1 is tilted about an axis parallel to the paper surface. Thereby, the angle components of the plane mirror 26a of the moving body 26 in two directions can be simultaneously detected.

The present invention is not limited to the embodiments described above, and various modifications can be made without departing from the gist of the invention. For example, the polarization beam splitter shown in FIG. 3 can be used instead of the polarization beam splitter shown in FIG. The number of the λ / 4 plates does not need to be two, and only one λ / 4 plate can be used as shown in FIG.

According to the present invention, since the length measurement and the angular displacement (yawing and pitching) can be simultaneously performed by measuring the same location, a compact configuration for controlling the linear motion of a moving body such as a stage with high precision. The moving object position measuring device having the measuring optical system is provided.

[Brief description of the drawings]

FIG. 1 shows an embodiment of a measuring optical system according to the present invention.

FIG. 2 shows an optical path of object light when the moving body is tilted.

FIG. 3 shows a modification of the measurement optical system of FIG.

FIG. 4 shows six errors that occur in a moving object.

FIG. 5 shows a configuration of a moving object measuring apparatus according to a conventional example.

[Explanation of symbols]

12: light source, 22, 34, 30: polarizing beam splitter, 24, 36: λ / 4 plate, 26: moving body, 26a: plane mirror, 28: lens, 30a: half mirror, 30
b: total reflection mirror, 38: λ / 2 plate.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G01B 9/00-11/30 102

Claims (2)

(57) [Claims] 1. A moving object position measuring apparatus for measuring a position of a moving object having a reflecting surface, a means for emitting a light beam, and an object beam irradiated with the light beam toward a reflecting surface of the moving object. Beam splitting means for splitting the object light reflected by the reflection surface and the reference light into two light beams, based on an interference signal generated by the interference between the reflected object and the reference light Means for detecting a distance to the moving body, and means for detecting an angular displacement of the moving body by detecting a tilt of the reflected object light with respect to an optical axis, and the beam splitting means. Is a moving object position measuring device characterized by comprising two polarizing beam splitters whose beam splitting planes are orthogonal to each other, and a half-wave plate disposed therebetween. . 2. The moving object position measuring device according to claim 1, wherein said angular displacement detecting means comprises a position detecting element for receiving said object light reflected by said reflecting surface and detecting a light receiving position thereof. apparatus.