JPH04372804A - Optical system for measuring linear motion - Google Patents

Abstract

PURPOSE:To obtain a measuring optical system having the compact constitution for controlling the linear motion of a moving body such as a stage in high accuracy. CONSTITUTION:Two polarizing beam splitters 22 and 34 whose beam-split faces are intersected at a right angle are provided in parallel in the incident direction of the light beams. Al/2 plate 38 is arranged between the beam splitters. At the part between the polarizing beam splitters 22 and 34 and a reflecting surface 26a of a moving body 26, lambda/4 plates 24 and 36 are provided. At the opposite side of the plates, a lens 28 for refracting the light beams from the polarizing beam splitters 22 and 34 is arranged. A half mirror 30a and a total reflection mirror 30b are provided at the edge of a polarizing beam splitter 30 which is located at the focal plane.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention is particularly applicable to a stage device that controls the position of a table device that moves linearly, such as a machine tool, an optical machine, or a measuring machine. The present invention relates to a device for measuring .

0002

[Prior Art and its Problems] As shown in FIG. 4, when a movable body M on a stage that moves linearly moves along the x-axis, in addition to the positioning error ex in the x-axis direction, Displacement error consisting of three components: y-axis displacement error ey due to movement, ez due to movement in the z-axis direction, rolling error α due to rolling around the x-axis, pitching error β due to pitching around the y-axis, and displacement error around the z-axis. It is known that a six-component error occurs, including a three-component angle error consisting of a yawing error γ due to yawing.

[0003] As a conventional measuring instrument, for example, Japanese Patent Laid-Open No. 62
A laser interferometer length measuring device disclosed in Japanese Patent No. 22360 is known. This length measuring device requires two reflecting mirrors on the object to be measured when measuring the length. Furthermore, two biprisms are required to measure tilt components (yawing, pitching), and two components cannot be measured at the same time. Furthermore, the three components mentioned above cannot be measured simultaneously with one measuring device.

[0004]Generally, x stage, xy stage, and xyz stage are used for linear motion equipment, but
To accurately measure the linear motion accuracy of these moving stages, laser interferometric length measurement systems are widely used to measure axial displacements, and autocollimators are widely used to measure angular displacements.

For example, in an xy stage that moves within the xy plane, two laser length measuring devices 100, 102, two autocollimators 104,
106 and the orthogonal mirror 108, the x displacement is measured using the laser interferometric length measuring device 102, and the x displacement is measured using the laser interferometric length measuring device 104.
A known configuration is known in which the y displacement is measured using an autocollimator 104, and the angular errors β and γ are simultaneously measured using an autocollimator 106. In this configuration, two laser interferometers 10
Using two autocollimators 104 and 106, the displacement of five components can be measured simultaneously.

However, such a measurement system has a complicated configuration and also requires a large space for measurement. Conversely, stages of the same size will take up too much space in the measurement system and the operating range will become smaller. Furthermore, the number of measurement points increases, which may cause measurement errors.

SUMMARY OF THE INVENTION An object of the present invention is to provide a measurement optical system with a compact configuration for controlling the linear motion of a moving body such as a stage with high precision.

[0008]

[Means for Solving the Problems] A measuring optical system of the present invention for measuring the position of a moving body having a reflective surface includes means for emitting a light beam, and beam splitting surfaces arranged in the traveling direction of the light beam and each other. It has two polarizing beam splitters whose polarizing beam splitters are perpendicular to each other, a 1/2 wavelength plate disposed between them, and a 1/4 wavelength plate disposed between the polarizing beam splitter and the reflective surface of the moving body. , beam splitting means for separating the light beam into two light beams, the first polarizing beam splitter emits one of the light beams toward the reflective surface of the moving object, and splits the reflected light beam from there. the second polarizing beam splitter emits the other light beam on its opposite side, the second polarizing beam splitter having lens means for refracting the light beam from the polarizing beam splitter and reflecting means disposed in the focal plane of the lens means. The optical means further comprises an optical means for making the light beam from the first polarizing beam splitter enter the second polarizing beam splitter and making the light beam from the second polarizing beam splitter enter the first polarizing beam splitter. , the second polarizing beam splitter passes the light beam from the optical means and emits it toward the reflective surface of the moving body, reflects the reflected light beam therefrom and outputs it from the beam splitting means, and the second polarized beam splitter passes the light beam from the optical means and emits it toward the reflective surface of the moving body, and reflects the reflected light beam from there and outputs it from the beam splitting means, so that the first polarized light The beam splitter further includes means for reflecting the light beam from the optical means and emitting it from the beam splitting means, receiving the two light beams emitted from the beam splitting means, and detecting the position of the moving body.

[0009]

[Operation] The light beam incident on the beam splitting means is divided into two, and one of the light beams is emitted from the first polarizing beam splitter toward the reflective surface of the moving body. The reflected light from the reflective surface passes through the first polarizing beam splitter, enters the optical means, passes through the second polarizing beam splitter, and reaches the reflective surface of the moving body again. The light reflected again by this reflective surface is reflected by the second polarizing beam splitter and enters the means for detecting the position of the moving body.

The other light beam separated by the beam splitting means is emitted from the second polarizing beam splitter, enters the first polarizing beam splitter via the optical means, is reflected there, and determines the position of the moving object. incident on the means for detection.

The means for detecting the position of the moving body detects the position of the moving body from the two incident light beams.

0012

[Embodiment] An embodiment of the measurement optical system of the present invention is shown in FIG. The light source 12 includes a laser diode 14 and a collimating lens 16 , and the laser beam 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 polarizing beam splitter 22. The polarizing beam splitter 22 passes polarized light components parallel to the plane of the paper and reflects polarized light components perpendicular to the plane of the paper.

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 plane of the paper, passes through the polarizing beam splitter 22, and enters the lens 28. The light beam incident on the lens 28 is focused and incident on the polarizing beam splitter 30. The polarizing beam splitter 30 is provided with a half mirror 30a on the left surface and a total reflection mirror 30b on the lower surface, and these are located on the focal plane of the lens 28. The light incident on the polarizing beam splitter 30 passes through the half mirror 3
The light is focused on 0a, a part of which passes through the half mirror 30a and enters the two-dimensional position detection 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,
The light 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 passes through the λ/4 plate 36 again to become linearly polarized light perpendicular to the paper plane, is reflected by the polarizing beam splitter 34, and enters the λ/4 plate 40.

On the other hand, the linearly polarized light beam (reference light) parallel to the plane of the paper that has passed through the polarization beam splitter 22 has a wavelength of λ
The light passes through the /2 plate 38, becomes linearly polarized light perpendicular to the plane of the paper, and is reflected by the polarizing beam splitter 34. The light beam reflected by the polarizing beam splitter 34 enters the lens 28 and is focused, and then enters the polarizing beam splitter 30. The light incident on the polarizing beam splitter 30 is reflected by the beam splitting surface 30c, and is reflected by the total reflection mirror 3.
It is focused on 0b and reflected. The light reflected by the total reflection mirror 30b is reflected by the beam splitting surface 30c, enters the lens 28, becomes a parallel beam, enters the polarizing beam splitter 22, and is reflected. When the light beam reflected by the polarizing beam splitter 22 passes through the λ/2 plate 38, it becomes linearly polarized light parallel to the plane of the paper, passes through the polarizing 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 are then split into two beams by a polarizing beam splitter 42. The beam that has passed through the polarizing beam splitter 42 is transferred to a λ/4 plate 44.
The beam passes through the polarizing beam splitter 46 and is further split into two beams.
The beam that has passed through enters the photodiode PD1,
The beam reflected by the polarizing 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, where it is further split into two beams, and the beam reflected by the polarizing beam splitter 50 enters the photodiode PD2. The incident beam passes through the polarizing beam splitter 50 and enters the photodiode PD4.

The intensities S1 to S4 of the interference signals detected by the photodiodes PD1 to PD4 are as follows.

PD1: S1=a1+b1cos(2π/λ・n・
ΔL) PD2: S2=a2+b2sin(2π/λ・n・
ΔL) PD3: S3=a3+b3cos(2π/λ・n・
ΔL) PD4: S4=a4+b4sin(2π/λ・n・
ΔL) Here, ΔL is the optical path difference between the object light and the reference light, and λ is the wavelength of the laser light. S1- output from the differential amplifier 52
S2 is a cos signal, and S2 output from the differential amplifier 54
-S4 becomes a sin signal. The outputs of the differential amplifiers 52 and 54 are each subjected to phase correction and offset adjustment by a preamplifier, and are 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 travels twice along the optical path to the moving object, the optical path difference is twice as large with respect to the movement of the moving object, so the measurement sensitivity is doubled. Moreover, since the object light and the reference light pass through almost the same optical path, fluctuations in the temperature environment, etc., are strong.

Next, FIG. 2 shows the situation when the plane mirror 26a of the movable body 26 is tilted. In the figure, the optical path when the moving body is not tilted 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 parallel to the light beam incident on the lens 28. This light beam
6 is reflected by the plane mirror 26a, and then reflected by the polarizing beam splitter 34. The beam emitted from the polarizing beam splitter 34 is emitted parallel to the beam incident on the polarizing beam splitter 22, but its optical path is slightly deviated from the optical path when the plane mirror 26a is not tilted. As described above, the position of the moving object 26 is detected from the interference signal of the light beam emitted from the polarizing beam splitter 34.

On the other hand, the light that has passed through the half mirror 30a is incident on the two-dimensional position detection element 32. half mirror 3
On 0a, the deviation d between the irradiation position of the reflected light when the plane mirror 26a is not tilted and the irradiation position of the reflected light when the plane mirror 26a is tilted by θ is:

[0020]

[Math 1]

It is expressed as follows. Here, f is the focal length of the lens 28. Therefore, the tilt angle θ can be derived from the displacement d. This characteristic is the same even when the plane mirror 26a of the movable body 26 is tilted about an axis parallel to the plane of the paper in FIG. Thereby, angular components in two directions of the plane mirror 26a of the moving body 26 can be detected simultaneously.

The present invention is not limited to the embodiments described above, but can be modified in many ways without departing from the gist of the invention. For example, instead of the polarizing beam splitter shown in FIG. 1, a polarizing beam splitter shown in FIG. 3 may be used. Further, it is not necessary to use two λ/4 plates, and it is also possible to use only one λ/4 plate as shown in FIG.

[0023]

[Effects of the Invention] According to the measurement optical system of the present invention, length measurement and angular displacement (yawing and pitching) can be simultaneously measured at the same location, so the linear motion of a moving object such as a stage can be controlled with high precision. A measurement optical system with a compact configuration is provided for.

[Brief explanation of the drawing]

FIG. 1 shows an embodiment of the measurement optical system of the present invention.

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

FIG. 3 shows a modification of the measurement optical system in FIG. 1.

FIG. 4 shows six errors occurring in a moving body.

FIG. 5 shows the configuration of a measuring device for a moving object 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.

Claims (2)

[Claims] 1. An optical system for measuring the position of a moving body having a reflective surface, comprising means for emitting a light beam;
Two polarizing beam splitters lined up in the traveling direction of this light beam and whose beam splitting planes are perpendicular to each other, a 1/2 wavelength plate placed between them, and a reflecting surface of the moving object between the polarizing beam splitter and the moving object. a 1/4 wavelength plate provided between the two, and beam splitting means for separating the light beam into two light beams, the first polarizing beam splitter splitting one of the light beams into lens means for refracting the light beam from the polarizing beam splitter, with the second polarizing beam splitter projecting the other light beam on the opposite side thereof; reflecting means disposed in the focal plane of the lens means, the optical means comprising: directing the light beam from the first polarizing beam splitter to the second polarizing beam splitter and directing the light beam from the second polarizing beam splitter; The second polarizing beam splitter passes the light beam from the optical means and emits the light beam toward the reflective surface of the moving body, and the second polarizing beam splitter allows the light beam to be reflected from the moving body. The first polarizing beam splitter reflects the light beam from the optical means and exits from the beam splitting means, and receives the two light beams emitted from the beam splitting means. A linear motion measurement optical system further comprising means for detecting the position of a moving object. 2. The optical means includes a third polarizing beam splitter that separates a light beam from the first polarizing beam splitter and a light beam from the second polarizing beam splitter, and the reflecting means includes a third polarizing beam splitter that separates a light beam from the first polarizing beam splitter. A total reflection mirror provided on the end face of a third polarizing beam splitter that is irradiated with the light beam from the second polarizing beam splitter, and a third polarizing beam splitter that is irradiated with the light beam from the first polarizing beam splitter. and a half mirror provided on the end face of the movable body, and further includes means for receiving the light passing through the half mirror and detecting the inclination of the reflecting surface of the moving object from the position of the light beam irradiated to the half mirror. A linear motion measuring optical system according to claim 1.