JP2000121322A - Laser length measuring machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance the sensitivity of measurement of a travel of a moving substance by reflecting leser beams split into two, by two reflecting means from reverse directions, and returning them to the same direction respectively and causing them to interfere with each other. SOLUTION: A polarizing beam splitter 3 splits a laser beam 2 into first (s-polarized) and second (p-polarized) laser beams. The first laser beam is reflected by rectangular prisms 41, 42, and is emitted in parallel with the direction of movement of a moving substance 90 and in the right direction, and enters a corner cube 31. This reflected beam proceeds in a direction reverse to the incidence, is reflected by the polarizing beam splitter 3, passes a polarizing plate 6 thereafter, and enters a photodetector 7. The second laser beam is reflected by rectangular prisms 43-45, and enters a corner cube 32 from the right direction. The reflected beam strikes the photodetector 7 and both laser beams interfere with each other. In this case the corner cubes 31, 32 move by ΔL by ΔL movement of the moving substance 90 also. The optical path length of the first (second) laser beam becomes shorter (longer) by 2ΔL, and an optical path length difference of 4 ΔL is generated and the sensitivity becomes twice as high as in the condentional art.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser beam split into two laser beams which is reflected by two reflectors, returned in the same direction and interfered with each other. The present invention relates to a laser length measuring device for measuring a moving distance.

[0002]

2. Description of the Related Art Laser length measuring devices are widely used to precisely measure the moving distance of an object. FIG. 1 is a diagram showing a basic configuration of a laser length measuring device. The laser light source 1 is He-N
The laser light source outputs a laser beam having good coherence (long interference distance) such as an e-laser. The laser beam 2 output from the laser light source is split into two laser beams by a polarization beam splitter 3. At this time, the optical axis of the polarizing beam splitter 3 is 4 ° with respect to the polarization plane of the incident laser light.
It is adjusted to be 5 °. In this case, the laser beam transmitted through the polarization beam splitter 3 is called P-polarized light, and the laser beam reflected by the polarization beam splitter 3 is called S-polarized light, and their polarization directions are orthogonal to each other. One of the laser beams (P-polarized light) enters the corner cube 4 arranged on the moving object 90, where it is reflected in the opposite direction and enters the polarization beam splitter 3 again. The other laser beam (S-polarized light) enters the fixed reference corner cube 5 where it is reflected in the opposite direction and again enters the polarizing beam splitter 3. The laser beam that has entered the polarization beam splitter 3 from the corner cube 4 and the laser beam that has entered the polarization beam splitter 3 from the reference corner cube 5 are overlapped by the polarization beam splitter 3 and pass through the polarizing plate 6 to the photodetector 7. Incident. These two laser beams interfere with each other and produce interference fringes. The intensity of the interference fringes is greatest when the optical path difference between the two laser beams is an integral multiple of the wavelength of the laser beam, and the optical path difference is an integral multiple of the wavelength. Is the smallest when it differs by 1/2. Therefore, when the moving object 90 moves and the corner cube 4 arranged there moves, the output intensity of the photodetector 7 periodically changes. Specifically, corner cube 4 is 1 /
When the optical detector moves by two wavelengths, an optical path difference corresponding to the wavelength is generated in a round trip, so that the number of cycles in which the output intensity of the photodetector 7 changes is 1 /
The value obtained by multiplying the two wavelengths is the moving distance of the corner cube 4, that is, the moving object 90. Polarization beam splitter 3,
The reference corner cube 5, the polarizing plate 6, the photodetector 7, and the like are generally housed in an interference unit that is the same housing. Further, in the separation type laser interferometer described in Japanese Utility Model Application No. 62-52869, a laser light source 1
And the photodetector 7 are provided at a position distant from the interference unit housing the polarization beam splitter 3 and the like, and are connected to each other by a polarization-maintaining optical fiber.

[0003] The output signal of the photodetector 7 is amplified by an amplifier 8, compared with an intermediate level of the output signal by a comparator 9, converted into a binary signal, and counted by a counter 10. The length measurement value calculation unit 11 calculates the moving distance from the value of the counter 10. In laser length measuring devices, improvement in sensitivity (resolution) is required. Therefore, by detecting the intensity change of the interference fringes at different phases (for example, 90 degrees) and detecting the intensity ratio, a resolution of about 1/100 of the fringe pitch can be obtained.

In the conventional example shown in FIG. 1, a corner cube is used as the reflection means, but a plane mirror may be used. The laser length measuring device is required to further improve the sensitivity, and various methods have been proposed.
For example, FIG. 2 is a diagram showing a configuration of a laser measuring device having a multi-pass method called a double-pass method.

As shown in FIG. 2, in this double-path laser length measuring device, a laser beam 2 is incident on a polarization beam splitter 3, and an S-polarized laser beam is reflected and incident on a reference corner cube 5. This is the same as the conventional example of FIG. P-polarized laser beam is 1/4 wavelength plate 2
3, the light is reflected by the plane mirror 21, passes through the quarter-wave plate 23 again, and enters the polarization beam splitter 3. Since this laser beam has passed through the quarter-wave plate 23 twice, it is an S-polarized laser beam. The laser beam is reflected by the polarization beam splitter 3 and is incident on the corner cube 22. And is further reflected. This laser beam is applied to the 波長 wavelength plate 23
, Is reflected by the plane mirror 21, passes through the quarter-wave plate 23 again, and enters the polarization beam splitter 3.
Similarly, since this laser beam has passed through the quarter-wave plate 23 twice, it is again a P-polarized laser beam,
The light passes through the polarizing beam splitter 3. This laser beam and the reference laser beam reflected by the reference corner cube 5 interfere in the same manner as in the conventional example of FIG.

The laser beam that first passes through the polarizing beam splitter 3 makes two round trips to and from the plane mirror 21, and the optical path difference caused by the amount of movement of the plane mirror 21 is 2 in FIG. It is twice. Therefore, the plane mirror 21
Can be measured with twice the sensitivity. In addition,
In the example of FIG. 2, a plane mirror is used as the reflection means attached to the moving object, but a corner cube may be used instead.

As described above, the sensitivity can be improved by the number of reciprocations by increasing the number of reciprocations between the measurement laser beam and the reflection means attached to the moving object.

[0008]

However, when the number of passes is increased, the deviation of the incident position of the laser beam to the reflecting means due to the deviation of the emission direction from the polarizing beam splitter becomes large, so that the setting becomes difficult. There's a problem. Further, although the sensitivity within one cycle of the interference fringes has been improved, it is difficult to further improve the sensitivity from the viewpoint of the S / N ratio.

An object of the present invention is to improve the sensitivity of a laser length measuring device by a method different from the above-mentioned method, and an object of the present invention is to realize a new laser length measuring method capable of improving the sensitivity.

[0010]

In order to achieve the above object, a laser length measuring apparatus according to the present invention comprises a moving object provided with two reflecting means, one of which is provided with a first reflecting means parallel to the moving direction.
One of the laser beams split from the first direction is made incident, and the other laser beam split from the second direction opposite to the first direction is made incident on the other reflecting means, and reflected by the two reflecting means. Interfere with the laser beam.

That is, a laser length measuring device of the present invention is a laser length measuring device for measuring a moving amount of a moving object, wherein a laser beam from a laser light source is transmitted to a first laser beam and a second laser beam.
And a beam splitter that combines the returning first laser beam and the second laser beam so as to interfere with each other, and the incident first laser beam provided on the moving object in the opposite direction. A first reflecting means for reflecting, and a first laser beam emitted in a first direction parallel to a moving direction of the moving object, made incident on the first reflecting means, and reflected by the first reflecting means. A first optical path means for entering the beam splitter; a second reflecting means provided on the moving object for reflecting the incident second laser beam in a reverse direction; A second optical path means that emits light in a second direction opposite to the direction and makes the light incident on the second reflecting means, and is made to enter the beam splitter after being reflected by the second reflecting means; Synthesized Receiving means for receiving the interference light between the first laser beam and the second laser beam and generating an electric signal corresponding to the interference fringes; and counting means for counting the number of cycles of the change in the electric signal output from the light receiving means. And characterized in that:

In the laser length measuring device according to the present invention, both the first reflecting means and the second reflecting means are provided on the moving object, and the laser beams are respectively incident on the moving object from opposite directions. Accordingly, with the movement of the moving object, one of the first reflecting means and the second reflecting means moves in the direction of increasing the optical path length, and the other moves in the direction of decreasing the optical path length. Since interference occurs between the laser beams reflected by the first reflecting means and the second reflecting means, the change in the optical path length due to the movement of the moving object is twice that of the conventional example. Therefore, the sensitivity is doubled.

It is desirable that the first reflecting means and the second reflecting means are integrally housed in the same housing and can be handled integrally.

[0014]

FIG. 3 is a diagram showing a configuration of a laser length measuring device according to a first embodiment of the present invention. Here, only the optical path portion is shown, and the laser light source, the electric circuit, and the like are the same as in the related art, and are not shown. As shown in FIG. 3, two corner cubes 3 serving as reflecting means
1 and 32 are fixed to the reflection unit 30 and are integrally treated. The reflection unit 30 is fixed to the moving object 90. The laser beam 2 enters the polarization beam splitter 3 and is split into a first laser beam and a second laser beam. The first laser beam is s-polarized and the second laser beam is p-polarized. The first laser beam is reflected by the right-angle prisms 41 and 42, emitted in a direction substantially parallel to the moving direction of the moving object 90 toward the right side, and enters the corner cube 31. The first laser beam reflected by the corner cube 31 forms right-angle prisms 42 and 41
After being reflected by the polarization beam splitter 3, the light enters the polarization beam splitter 3.
The first laser beam is reflected by the S-polarized light, passes through the polarizing plate 6, and enters the light receiver 7. The second laser beam is reflected by the right-angle prisms 43, 44, and 45, emitted in a direction substantially parallel to the moving direction of the moving object 90 toward the left, and enters the corner cube 32. That is, the first laser beam incident on the corner cube 31 and the second laser beam incident on the corner cube 32 are beams traveling in opposite directions. The first laser beam reflected by the corner cube 32 enters the polarization beam splitter 3 after being reflected by the right-angle prisms 45, 44, and 43. Since the second laser beam is P-polarized light, it is transmitted, passes through the polarizing plate 6, and enters the light receiver 7. The first and second laser beams that have passed through the polarizing plate 6 interfere with each other to generate interference fringes.

When the moving object 90 moves leftward by ΔL,
The corner cubes 31 and 32 also move leftward by ΔL.
When the corner cube 31 moves leftward by ΔL, the optical path length of the first laser beam decreases by 2ΔL, and when the corner cube 32 moves leftward by ΔL, the optical path length of the second laser beam increases by 2ΔL. Therefore, Δ of the moving object 90
Since the optical path difference of 4ΔL is generated according to the movement of L, the sensitivity is doubled as compared with the conventional example.

FIG. 4 is a diagram showing a configuration of a laser length measuring device according to a second embodiment of the present invention. The second embodiment is an embodiment in which the present invention is applied to a double-path laser length measuring device. As shown in FIG. 4, in the laser length measuring device of the second embodiment, a laser beam 2 enters a polarization beam splitter 3 and is split into a first S-polarized laser beam and a second P-polarized laser beam. You. As in the first embodiment, the first laser beam passes through right-angle prisms 41 and 42, and the corner cube 3
1, the light is reflected there, returns to the polarization beam splitter 3 again, is reflected, passes through the polarizing plate 6, and enters the light receiver 7. After passing through the quarter-wave plate 23, the second laser beam is reflected by the corner cube 32 via right-angle prisms 43, 44 and 45, and is reflected by the right-angle prisms 43, 44,
After passing through 45, the light again passes through the quarter-wave plate 23 and enters the polarization beam splitter 3. The second laser beam is 1/4
Since the light has passed through the wave plate 23 twice, it has become S-polarized light, is reflected by the polarization beam splitter 3, and has a corner cube 4
6 and further reflected by the polarizing beam splitter 3. The second laser beam reflected by the polarizing beam splitter 3 passes through the quarter-wave plate 23, passes through right-angle prisms 43, 44, 45, is reflected by the corner cube 32, and passes through right-angle prisms 43, 44, 45. The light again passes through the quarter-wave plate 23 and enters the polarization beam splitter 3. Since the second laser beam has passed through the quarter-wave plate 23 twice again, it has become P-polarized light, passes through the polarizing beam splitter 3 and the polarizing plate 6, and enters the light receiver 7. The first and second laser beams passing through the polarizing plate 6 interfere with each other. Thus, the second laser beam reciprocates twice in the optical path.

In the second embodiment, when the moving object 90 moves .DELTA.L to the left, the corner cubes 31 and 32 also move .DELTA.L to the left. Corner cube 31 moves leftward ΔL
When moved, the optical path length of the first laser beam decreases by 2ΔL, and when the corner cube 32 moves leftward by ΔL, the optical path length of the second laser beam increases by 4ΔL. Therefore,
An optical path difference of 6ΔL occurs according to the movement of the moving object 90 by ΔL.

If a quarter-wave plate 48 is provided in the optical path of the first laser beam indicated by a broken line in FIG.
The first laser beam reflected by the first laser beam and re-entering the polarization beam splitter 3 becomes P-polarized light after passing through the quarter-wave plate 48 twice, and passes through the polarization beam splitter 3 to become a corner cube 46. Incident on. The first laser beam reflected by the corner cube 46 passes through the polarizing beam splitter 3 and reaches the corner cube 31 again, where it is reflected and enters the polarizing beam splitter 3 again. This laser beam passes through the quarter-wave plate 48
Since the light has passed twice, it returns to S-polarized light, is reflected by the polarization beam splitter 3, passes through the polarizing plate 6, and enters the light receiver 7. Thus, when the quarter-wave plate 48 is provided in the optical path of the first laser beam, the first laser beam also reciprocates twice in the optical path. Therefore, an optical path difference of 8ΔL is generated according to the movement of the moving object 90 by ΔL.

[0019]

As described above, according to the present invention,
A laser length measuring device capable of measuring the moving distance of a moving object with twice the sensitivity of the related art can be realized.

[Brief description of the drawings]

FIG. 1 is a diagram showing a basic configuration of a conventional laser length measuring device.

FIG. 2 is a diagram illustrating a conventional example of a laser length measuring device of a double pass system with improved sensitivity (resolution).

FIG. 3 is a diagram showing a configuration of a laser length measuring device according to the first embodiment of the present invention.

FIG. 4 is a diagram showing a configuration of a laser length measuring device according to a second embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Laser light source 2 ... Laser beam 3 ... Polarization beam splitter 4, 5, 31, 32, 46 ... Corner cube

 ──────────────────────────────────────────────────続 き Continued on front page F term (reference) 2F064 AA01 EE01 FF01 FF05 GG13 GG16 GG23 GG38 HH01 HH05 JJ11 2F065 AA06 AA09 BB15 DD03 FF12 FF49 FF52 GG04 GG08 HH04 JJ01 LL11 LL17 LL46 LL37

Claims (2)

[Claims] 1. A laser length measuring device for measuring a moving amount of a moving object, wherein the laser beam from a laser light source is divided into a first laser beam and a second laser beam, and the laser beam is returned. A beam splitter that combines the first laser beam and the second laser beam so as to interfere with each other; a first reflecting unit that is provided on the moving object and reflects the incident first laser beam in a reverse direction; The first laser beam is emitted in a first direction parallel to the moving direction of the moving object, is incident on the first reflecting means, and is incident on the beam splitter after being reflected by the first reflecting means. A first optical path means, a second reflecting means provided on the moving object, for reflecting the incident second laser beam in a reverse direction, and the second laser beam for the first object. A second optical path means which emits light in a second direction opposite to the direction and makes the light incident on the second reflection means, and is made to enter the beam splitter after being reflected by the second reflection means; A light receiving unit that receives interference light of the first laser beam and the second laser beam combined by the beam splitter and generates an electric signal corresponding to interference fringes; and the electric signal output by the light receiving unit. Counting means for counting the number of cycles of change of the laser. 2. The laser length measuring device according to claim 1, wherein the first reflecting means and the second reflecting means are integrally housed in a same housing.