JP3389799B2 - Length measuring 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 length measuring device for measuring a position or a moving distance of an object on a machine tool or the like.

[0002]

2. Description of the Related Art A conventional interferometer is described below with reference to FIG. In the figure, 1401 is a light source with stable wavelength and coherent, 1402 is a beam splitter,
1403 is a probe corner cube, 1404 is a fixed corner cube, 1405 is a λ / 8 plate, 1406 is a polarization beam splitter, 1407a, 1407b, 140.
7c is a polarizing plate, 1408a, 1408b and 1408c are detectors, 1409a, 1409b and 1409c are amplifiers, 1410a and 1410b are subtractors, and 1411 is a counter.

Next, the operation will be described. Light source 1401
The emitted light wave is split into two by the beam splitter 1402, one enters the probe corner cube 1403, the other passes through the λ / 8 plate 1405, and enters the fixed corner cube 1404. The light waves reflected by the respective corner cubes enter the beam splitter 1402 again, and one of the combined light waves passes through the polarizing plate 1407a toward the detector 1408a and the other goes toward the polarizing beam splitter 1406. Further, the light waves split into two by the polarization beam splitter 1406 are respectively reflected by the polarizing plate 140.
7b, 1407c and detectors 1408b, 140
It is incident on 8c. Each detector has a probe corner cube 1403 and a fixed corner cube 1404.
The interference signal resulting from the optical path difference at
7a, 1407b, and 1407c respectively, the interference outputs of the probe corner cubes 1403 are set according to the movement of the probe corner cube 1403.
With respect to the movement of 03, the phases are output different by 90 °. Each detector 1408a, 1408b,
The signal of 1408c is the amplifier 1409a, 1409b, 1
Subtractors 1410a and 1410 after being amplified by 409c
Counter 1 as a signal with a 90 ° phase shift subtracted by b
It is increased / decreased in 411 and output as a position.

[0004]

Since the conventional interferometric length measuring apparatus is constructed as described above, the interference signal changes one cycle in a sine wave shape as the probe corner cube moves by λ / 2. It appears as a repetitive signal, and the interference period cannot be changed without changing the optical wavelength λ. For this reason, when measuring a length exceeding half wavelength λ / 2, it is necessary to perform an incremental measurement that integrates the number of repeated interference cycles, and if absolute position detection is required, There is a problem that the interferometer is required to return to the origin by another detecting means as an initial operation, and the accumulated error caused by the incorrect counting of the interference cycle cannot be eliminated unless the origin is returned.

The present invention has been made in order to solve the above-mentioned problems, and enables the interference period to be set to a desired value without changing the light wavelength, and the absolute value of the absolute value can be set without returning to the origin. It is an object to provide a length measuring device that can obtain a measurement signal.

[0006]

According to a first aspect of the present invention, a length measuring apparatus irradiates an object with two or more coherent parallel light fluxes having an optical path difference.
More than one light beam is different from each other with respect to the movement axis of the object.
A light <br/> source having an optical system to be incident on said object at an incident angle becomes, fixed to the object, and a reflector for reflecting the two or more light beams in the respective direction of incidence in the same direction, A multiplexer for combining the two or more light fluxes on mutually parallel optical axes and a photodetector for measuring the interference intensity of the two or more light fluxes combined is provided . the above
The position of the object in the moving axis direction is measured .

The length measuring apparatus according to the second structure of the present invention is
In the first configuration, the optical system is one having a demultiplexer for demultiplexing into two or more coherent parallel light flux emitted from the same light source.

The length measuring apparatus according to the third aspect of the present invention is
In the first configuration, at least one of the reflectors is a diffraction grating and has a grating pitch for generating a diffracted wave that reflects incident light in the same direction.

The length measuring apparatus according to the fourth structure of the present invention is
In the first configuration, the reflector includes a prism or a combination mirror having an angle of deviation of 180 °.

The length measuring apparatus according to the fifth aspect of the present invention is
Two or more coherents that have an optical path difference with respect to the object
Irradiate a parallel light beam and raises the above two or more light beams.
The incident angles differ from each other with respect to the moving axis of the object.
A light source having an optical system to be incident on the object, is fixed to the object, the light beam and the reflector, one of the other light beam which reflects one of the two or more light beams in the incident direction in the same direction A reflector that reflects light at an angle opposite to that at the time of incidence, a combiner that combines the two light beams on mutually parallel optical axes, and an interference of the two or more combined light beams. Equipped with a photodetector to measure the intensity,
The position of the object in the moving axis direction is measured .

The length measuring apparatus according to the sixth aspect of the present invention is
Heterodyne length measuring device
And have different optical frequencies and different optical paths.
Irradiates more than two coherent parallel light beams and
Note that two or more light beams can be transmitted to each other with respect to the moving axis of the object.
Has an optical system that makes the above-mentioned target incident at different incident angles.
A light source that is fixed to the object, if the synthesis the two or more light beams and a reflector that reflects in the same direction as each direction of incidence, the two above more light beams onto parallel optical axes mutually comprising a filter, a photodetector for detecting an equal beat signal to the difference of the frequency caused by the interference of two or more light beams above synthesis, and a phase detector to measure the phase variation of the beat signal, measured From the above phase change
The position of the elephant in the moving axis direction is measured .

The length measuring apparatus according to the seventh aspect of the present invention is
In a sixth configuration, at least one of the two or more parallel light beams is provided with a deflecting means, and a phase difference between the beat signals before and after the deflection is obtained to obtain a position over a distance longer than a repetition cycle of the beat signal. it is obtained so as to make an absolute measurement.

The length measuring apparatus according to the eighth aspect of the present invention is
A plurality of sets of the length measuring devices of the first configuration having different angles of incidence are provided, and the distance corresponding to the interference period of one set of measuring devices is interpolated with the interference period of the other set of measuring devices. It is configured to be longer than the resolution distance.

The length measuring apparatus according to the ninth aspect of the present invention is
A plurality of sets of length measuring devices of the fifth configuration having different angles of incidence are provided, and the distance corresponding to the repetition cycle of the beat signal of one set of measuring devices is set to the beat signal of another set of measuring devices. The length is longer than the interpolating resolution distance of the repetition period of, and at least one of the plurality of length measuring devices has a deflecting means for one of the parallel light beams.

[0015]

DETAILED DESCRIPTION OF THE INVENTION

Embodiment 1. Hereinafter, the drawings of the embodiments of the present invention will be described. FIG. 1 is a configuration diagram showing a first embodiment of the present invention. In the figure, 101 is a light source that generates a coherent parallel beam, 102 is a demultiplexer that splits the parallel beam into two directions, first and second, and a parallel beam that is incident from the first and second directions. Is also a multiplexer / demultiplexer that also serves as a multiplexer for unidirectionally coupling the light beams, 103 and 104 are first and second reflectors that reflect the incident parallel beam without changing the optical axis, and 105 is the first And a position measuring object to which the second reflectors 103 and 104 are attached and which freely moves in one direction. Reference numeral 106 denotes the second reflector which is a parallel beam in the second direction demultiplexed by the multiplexer / demultiplexer 102. 10
4 is a reflecting mirror that is bent so as to be obliquely incident on the optical fiber 4 at a predetermined angle θ, and forms a demultiplexing optical system together with the multiplexer / demultiplexer 102. Reference numeral 107 is a photodetector for detecting the intensity of the parallel beam combined by the multiplexer / demultiplexer 102. In addition, FIG. 2 is a diagram showing an example of the second reflector.
Reference numerals 1 and 202 denote reflecting mirrors, which correspond to the first and second reflectors 103 and 104, respectively.

Next, the operation of this embodiment will be described. In the present embodiment, the object whose position is to be measured is 105 as described above, and is driven by, for example, a linear table in a processing machine that operates in the direction of the arrow drawn below the measuring object 105 in the drawing, In the present embodiment, this is moved by a drive mechanism such as a linear motor or a ball screw. The parallel beam A emitted from the light source 101 attached to the fixed part outside the moving mechanism is the multiplexer / demultiplexer 1
It is incident on 02 and is branched into two directions B and C. In the present embodiment, the direction of the parallel beam B is the measuring object 105.
It is installed so that it is parallel to the moving direction of. The parallel beam B is incident on the reflector 103 mounted on the beam incident side end surface of the measurement object 105, is reflected in the same direction, and returns to the multiplexer / demultiplexer 102. Note that, in the drawing, the incident and reflected beams are intentionally shifted in order to make them easy to understand, but they are actually overlapped, and the same is true for a parallel beam C described later. The parallel beam C branched by the multiplexer / demultiplexer 102 is moved by the reflecting mirror 106 in the moving direction of the measuring object 105, that is, the parallel beam B.
Is incident on the second reflector 104 and is returned to the multiplexer / demultiplexer 102 on the same optical path as the parallel beam B, and is combined / demultiplexed. The beam 102 is combined with the parallel beam B into a parallel beam D, and the intensity thereof is output from the photodetector 107.

Since the light source 101 is coherent as described above, the combined parallel beam D is the reflected parallel beam B.
And C interfere with each other and are modulated according to the respective phase changes. The condition for reflecting a parallel beam on the same optical path by the reflector 104 is that the same phase change as that of a plane mirror arranged so as to be perpendicularly incident to the parallel beam C inclined by an angle θ like the reflecting mirror 201 in FIG. It acts as a reflector given to the parallel beam C, and for the sake of simplicity, the emission point of the parallel beams B and C is set as the origin O, and the phase difference at this position is set to 0. Is L, the optical path difference Δ between the parallel beam B and the parallel beam C is Δ = 2 (L−Lcos θ) = 2L (1−cos θ). On the other hand, in a general interference measurement system such as the Michelson type, since the optical path difference is 2L, the sensitivity of the interferometer is changed to 1-cos θ or the interference cycle is 1 / (in the present embodiment. 1-cos θ). Further, the sensitivity or the interference period can be arbitrarily changed by changing the inclination angle θ without changing the frequency (wavelength) of the light source.

By the way, in the present embodiment, the parallel beam B
Was set to the moving direction of the measuring object 105, but it may have a certain inclination φ as in the case of the parallel beam C, and the sensitivity in that case is represented by (cosφ−cosθ).
Further, although the reflecting mirror 106 is used on the side of the parallel beam C which is inclined in the present embodiment, it may be used on the side of the parallel beam B or both of them, and the branching angle is a desired inclination angle due to the configuration of the multiplexer / demultiplexer 102. If it can be set to θ, the reflecting mirror 106 can be omitted.

Embodiment 2. Next, a second embodiment will be described with reference to the drawings. FIG. 3 is a configuration diagram showing a second embodiment of the present invention. In the figure, reference numeral 301 denotes a reflection type diffraction grating, which corresponds to the reflector 104 in the first embodiment, 301a is a side view of the reflection type diffraction grating for explaining the operation, and 301b is the reflection type diffraction grating. It is a front view.

Next, the operation will be described. Generally, a coherent light beam incident on a diffraction grating having a periodic structure is separated into 0th and ± nth order diffracted beams in the Franhofer region, and the separation angle of the diffracted wave at this time is the wavelength λ and the diffracted wave. It is uniquely determined by the lattice pitch Λ. Therefore, by setting a diffraction grating having an appropriate pitch Λ for a beam having a wavelength λ that is incident on the reflection type diffraction grating 301 at an incident angle θ so that its incident surface is perpendicular to the diffraction grating, ± n It is possible that any one of the following diffracted beams will occur in the same direction as the incident beam. Therefore,
When the reflection type diffraction grating 301 of the present embodiment is applied to the reflector 104 of the first embodiment, a variable sensitivity interferometry system having an action equivalent to that of a reflector arranged obliquely by a reflector having a planar configuration. Can be configured.

Here, the behavior of the reflected beam when the reflected beam coincides with the incident beam as in this configuration will be described by taking the case of the first-order diffracted wave as an example. Considering the optical path difference generated by this configuration similarly to FIG. 2, Δ = 2L (1-1 / cos
θ), the condition that the reflected vibrato coincides with the incident beam when the light beam moves on the diffraction grating is
Since Λ = λ / 2sin θ, the above-mentioned phase change amount P
Is P = 2π / λ · 2Lsin2θ / cosθ, which is 2Lsin2θ / cosθ when converted to the optical path. Therefore, the actual optical path difference is Δ = 2L (1-1 / cosθ + sin2θ / cosθ).
= 2L (1-cos θ), which is the same as in the first embodiment when the reflecting mirrors are obliquely arranged as shown in FIG.

In the case of this structure, since the reflector can be formed by a plane, the two reflectors 103 and 104 in the first embodiment can be formed on one substrate. It is possible to make the diffraction gratings having different pitches or one of the beams enter a simple mirror surface and enter the diffraction grating for the other beam.
Alternatively, the two reflectors may be configured by the same diffraction grating, and diffracted waves of different orders may be used for the two light beams.

Embodiment 3. Next, a third embodiment will be described with reference to the drawings. FIG. 4 is a configuration diagram showing a third embodiment of the present invention. In the figure, 401 is a light source that generates a coherent parallel beam, 402 is a demultiplexer,
403 and 406 are first and second folding mirrors, 40
4 and 405 are corner cube prisms, 407 is a multiplexer, 408 is a photodetector, 409 is a fixed optical system, 410
Is a moving optical system mounted on the object to be measured. Also, FIG.
FIG. 4 is an explanatory diagram showing an optical path when a beam is obliquely incident on a corner cube prism, 501 is a first reflecting mirror, 502 is a second reflecting mirror, 503 is a reference plane, and 504 is a reference plane 503. 1 virtual image by the reflecting mirror 501, 505
Is a virtual image of the virtual image 504 by the second reflecting mirror 502.
The corner cube prism has a three-dimensional shape formed by three planes intersecting at right angles as is generally known, but it is drawn as two-dimensional for convenience of illustration. Also, if the drawing does not require vertical retroreflectivity, the same effect can be obtained by using the same combination of two reflecting mirrors as in the drawing.

Next, the operation will be described. The parallel beam emitted from the light source 401 is branched by the demultiplexer, and then enters the corner cube prisms 404 and 405 which are reflectors directly or through the first bending mirror 403. One of the branched parallel beams, the beam on the side of the corner cube prism 404 in the present embodiment, is installed at a predetermined angle θ with respect to the moving axis of the moving optical system 410 to be measured, and the other corner cube. The beam on the prism 405 side is installed parallel to the moving axis. Due to the nature of the corner cube prism, the beam entering the corner cube prism 404 exits in the same direction as the entrance from a position symmetrical with respect to the center of the corner cube prism, passes through the second bending mirror 406, and then the multiplexer 407. Is combined with the reflected beam on the corner cube prism 405 side, and the interference intensity thereof is output by the photodetector 408. However, in this optical system, with respect to the tilted beam, the optical axis of the reflected beam moves in parallel according to the position of the moving optical system as shown by the broken line in FIG. Therefore, it is necessary to set the width of the parallel beam in the cross-sectional direction so that the parallel movement amount of the optical axis can be absorbed and interference can be obtained in the entire measurement range.

The optical path difference in the system of this embodiment is shown in FIG.
More demanded. Assuming that a plane perpendicular to the beam that is obliquely incident on the corner cube prism is a reference plane 503, the virtual image by the first reflecting mirror 501 is 504. Further, the virtual image of 504 by the second reflecting mirror 502 becomes 505, which is a plane parallel to the reference plane 503. Therefore, the light ray passing through the corner cube prism can be considered by converting the incident beam into a straight line that is extended, and is incident on the reference surface 503, reflected by the corner cube, and again the optical path length reaching the reference surface 503 is the incident position. It is constant regardless of. Since the incident position on the second bending mirror 406 does not affect the total optical path length, the optical path length reaching the corner cube prism 404 is the distance from the exit point of the fixed optical system to the reference surface 503, and the first embodiment and the first embodiment are described. As in the case of 2, the distance between the fixed optical system and the moving optical system is L cos θ, and the optical path difference is represented by 2 L (1−cos θ). Therefore, the detection sensitivity is changed by (1-cos θ) times,
It is possible to freely change the sensitivity by setting θ.

Fourth Embodiment Next, a fourth embodiment will be described with reference to the drawings. FIG. 6 is a configuration diagram showing a fourth embodiment of the present invention. In the figure, 601 is a light source for generating a coherent parallel beam, 602 is a demultiplexer,
Reference numerals 603 and 606 denote first and second folding mirrors, and 60.
4 is a corner-cube-like prism in which the deviation angle is shifted by a predetermined angle 2θ from 180 °, 605 is a corner-cube prism, 607 is a multiplexer, 608 is a photodetector, and 60
Reference numeral 9 is a fixed optical system, and 610 is a moving optical system mounted on a measurement target. FIG. 7 is an explanatory diagram showing an optical path when a beam obliquely enters the corner cube-like prism 604, 701 is a first reflecting mirror, 702 is a second reflecting mirror, and 703 is a first reference. Surface 704 is the first reference surface 7
03 is a virtual image by the second reflecting mirror 702, and 705 is a virtual image 7.
A virtual image of the first reflecting mirror 701 of No. 04, 706 is a second reference plane.

Next, the operation will be described. The parallel beam emitted from the light source 601 is branched by the demultiplexer, and then enters the corner cube-like prism 604 and the corner cube prism 605 which are reflectors directly or through the first bending mirror 603. The parallel beam directed to the corner cube-like prism 604 is installed at a predetermined angle θ with respect to the moving axis of the moving optical system 610 to be measured.
The beam on the 5 side is installed parallel to the moving axis. The corner cube-like prism 604 is constructed by tilting the two reflecting mirrors by θ / 2 with respect to the corner cube prism, and the incident beam is once reflected in the prism in a direction orthogonal to the movement axis. The light is emitted in the direction opposite to the direction of the rear incidence and in the direction opposite to the movement axis with an angle θ. In this case, the optical axis of the outgoing beam does not change even if the corner cube-like prism 604 moves parallel to the moving axis direction, and a stable reflected beam can be obtained. This reflected beam is combined with the reflected beam on the corner cube prism 605 side by the multiplexer 607 on the same optical axis, and the interference output thereof is output by the photodetector 608.

The optical path difference in the system of this embodiment is shown in FIG.
More demanded. Assuming that a plane perpendicular to the beam obliquely incident on the corner cube-like prism 604 is the first reference plane 703, the virtual image by the first reflecting mirror 701 is 704, and further the virtual image by the second reflecting mirror 702. Becomes 705. The inclination of the virtual image 705 at this time is parallel to the second reference surface 706 on the exit side, and the light ray passing through the corner cube prism can be considered by converting the incident beam into an extended straight line. Reference plane 703
The optical path length of the incident light on the second reference surface 706 is constant regardless of the incident position. Therefore, the optical path length to the corner cube prism 604 is the reference plane 7 from the exit point of the fixed optical system.
As shown in the above-mentioned embodiment, L is L cos θ, and the optical path difference is represented by 2L (1−cos θ). Therefore, the detection sensitivity is changed by (1-cos θ) times, and the sensitivity can be freely changed by setting θ.

Embodiment 5. Next, a fifth embodiment will be described with reference to the drawings. FIG. 8 is a configuration diagram showing a fifth embodiment of the present invention. In the figure, reference numeral 801 denotes a light source that generates a coherent parallel beam, 802 demultiplexes the parallel beam into first and second directions, and parallel beams incident from the first and second directions are directed in one direction. It is a multiplexer / demultiplexer that multiplexes, and here is a deflecting beam splitter. Reference numerals 803 and 804 denote first and second reflectors that reflect the incident parallel beam without changing the optical axis.
Reference numeral 5 denotes a position measurement object that is equipped with the first and second reflectors 803 and 804 and is freely movable in one direction. Reference numeral 806 denotes the second direction parallel beam demultiplexed by the multiplexer / demultiplexer 802. A reflecting mirror that is bent so as to be incident on the second reflector 804 at a predetermined angle θ, and 807 is the multiplexer / demultiplexer 10.
A photodetector for detecting the intensity of the parallel beams combined by two, 808 is a frequency modulator that produces at least two parallel beams of slightly different wavelengths from the coherent parallel beams, and 809 and 810 are its optical components. Reference numeral 811 is an analyzer, 812 is a reference frequency generator, and 813 is a phase detector.

Next, the operation will be described. The light source 80
The frequency of the beam emitted from the first parallel beam is f by the frequency modulator 808 and the frequency of the beam in the polarization direction parallel to the paper is f.
It is converted into a second parallel beam of + Δf. The frequency difference Δf at this time is given by the reference frequency generator 812. Next, the beam is split into two beams by the polarization beam splitter 802, and the first parallel beam of one frequency f is reflected by the polarization beam splitter 802 and is divided into ¼.
It passes through the wave plate 809 and goes toward the first reflector 803 in parallel with the moving axis of the position measurement object 805. Further, the second parallel beam transmitted through the polarization beam splitter 802 is ¼
The light passes through the wave plate 810 and is inclined toward the second reflector 804 by an angle θ with respect to the moving axis of the position measurement target 805.
Although the first and second parallel beams reflected by the reflector return through the same optical path due to the characteristics of the reflector and enter the polarization beam splitter 802 again, the quarter wavelength plates 809 and 81
Since 0 passes twice each, the polarization direction is rotated by 90 °, the first parallel beam is transmitted by the polarization beam splitter 802, the second parallel beam is reflected, and multiplexed on the same optical axis. After passing through the analyzer 811, the photodetector 807 outputs the light intensity. Beam of frequency f and f + Δf
Since they are orthogonal to each other, the interference output cannot be obtained as it is. Therefore, the analyzer 811 is for extracting the interference output from the beams whose polarization directions are orthogonal to each other, and is installed with the analysis direction inclined with respect to the orthogonal polarization axes of the two beams. Further, in this embodiment, since a method generally called an optical heterodyne is used in which two light waves having slightly different frequencies are used for interference, the photodetector 807 is used.
The output appearing in is a beat signal of frequency Δf, and there is a characteristic that the change of the phase difference of the light wave due to the movement of the position measurement target 805 corresponds to the change of the phase of the beat signal, and the phase detector 813 uses the reference frequency generator. The phase change of the beat signal is detected by comparison with the reference frequency from 812.

Sixth Embodiment Next, a sixth embodiment will be described with reference to the drawings. FIG. 9 is a configuration diagram showing a sixth embodiment of the present invention. The configuration in this embodiment is the same as that in FIG. 8, and FIG. 9 shows a state in which the second parallel beam in the fifth embodiment is slightly inclined as compared with FIG. FIG. 10 is a diagram showing a change in detection sensitivity when the optical axis is tilted. Reference numeral 1001 denotes a beam emitting / detecting surface, 1002 denotes a bending mirror, which corresponds to 906.
Reference numeral 1003 denotes a reflector corresponding to 904, and 1004 denotes the beam emission by the folding mirror 1002 and the detector surface 10.
It is a virtual image of 01. Further, FIG. 11 is a diagram for explaining vernier type detection by a minute change in detection sensitivity.

Next, the operation will be described. When the optical axis of the second parallel beam is slightly tilted in the same configuration as in FIG. 8, it becomes as shown in FIG. As a method of slightly tilting the beam,
If the frequency modulator 908 is composed of, for example, an acousto-optic modulator, the modulation frequency of the second beam is changed from f + Δf to f
It is possible to slightly deflect by changing to + Δf '. Also, mechanical deflection using rotation of a mirror or the like or electro-optic deflection may be used. When the beam is deflected, the position of the beam incident on the photodetector 907 moves according to the distance to the reflector 904. However, if the deflection angle is sufficiently small, the beam should be placed inside the photodetector 907. It is possible to obtain the interference output with the first parallel beam. The detection sensitivity at this time will be described with reference to FIG. In reality, the beam emitting surface and the detector surface are different and are separated by the deflecting beam splitter 802 or 902 which is a multiplexer / demultiplexer in FIG. 8 or 9.
For simplification, in FIG. 10, virtual images formed by the reflecting surfaces are overlapped to form the same surface 1001. The beam emitted from the exit surface 1001 is directed to the reflector 1003 by the bending mirror 1002, and the reflected light from the reflector is incident on the detector surface 1001 again. As shown in FIG. 8, a beam having a tilt angle with respect to the moving axis when it is not slightly deflected, that is, a beam whose incident angle to the reflector 1003 is θ is a one-dot chain line and is deflected by a minute angle δ as shown in FIG. Is indicated by a solid line. As shown in the figure, considering the virtual image by the bending mirror 1002, the system becomes a straight line and the relationship becomes clear. Emission and detector plane 1 without deflection
Letting the optical path from 001 to the reflector 1003 be L, the optical path of the beam that has been slightly deflected is L
It can be derived that cos θ / cos (θ−δ).

Here, it is assumed that an interference signal of n cycles is obtained for the entire length measuring range L ₀ by the inclination angle θ with the moving axis, and δ
FIG. 11 shows the output when the detection sensitivity is changed by only deflecting so that the interference signal of n-1 can be obtained in the entire measurement range. When the upper stage is not deflected, the middle stage is slightly deflected. In this case, the lower part shows the phase difference between the two. Upper to middle it has become one cycle less relative to the total measuring long distances L _0, the lower part can be specified is the position of the absolute value by the signal to indicate a phase change of 2π in all measurement ranges L _0.

Embodiment 7. Next, a seventh embodiment will be described with reference to the drawings. FIG. 12 is a configuration diagram showing a seventh embodiment of the present invention. In the figure, 1201 is an arithmetic circuit, and 1202a, b, and c are first and second circuits, respectively.
And the nth stage interpolator 1203a, b and c are the first, second and nth stage photodetectors 1204a,
b and c are first, second and nth stage interference optical systems, 1205a, b and c are first, second and nth stage reflectors respectively, 1206 is a position measurement target, 1207 is a signal It is a processing unit.

Next, the operation will be described. The photodetector 1203, the interference optical system 1204, and the reflector 12 in FIG.
The configuration of 05 has the configuration of FIG. 1 or 8.
In a, b, and c, the detection sensitivities are different from each other by setting the inclination of the beam obliquely incident on the reflector. The optical system of a is set so that an interference signal of one cycle or less can be obtained in the entire movement range of the position measurement target 1206, and the interference position within one cycle is within the interpolation accuracy by the first interpolation circuit. Specified. The optical system of b is set so as to output the interference output at a cycle that does not exceed the interpolation accuracy of a, and the optical systems of the following stages each have an interference signal at a cycle that does not exceed the interpolation accuracy of the upper optical system. Are set up to obtain n. The interference position signal obtained by each interpolation circuit 1202 is calculated by the arithmetic circuit 12.
01 and outputs the position of the position measurement target. This time,
The second-stage optical system is constructed so as to generate an interference signal in a cycle that does not exceed the interpolation accuracy of the first stage.
The absolute position of the interference cycle can be uniquely specified by referring to the signal of the stage. Furthermore, the optical system in the lower stage is configured to generate interference signals in a cycle that does not exceed the interpolation accuracy in the upper stage, so that the absolute position of the interference period can be uniquely determined by sequentially referring to the signals in the upper stage. Can be specified. For example, if the interpolation accuracy in one stage can divide the interference cycle into m, in n stages, the absolute position of the maximum m-th power division can be obtained.

Embodiment 8. Next, an eighth embodiment will be described with reference to the drawings. FIG. 13 is a configuration diagram showing an eighth embodiment of the present invention. In the figure, 1301 is a light source that generates coherent parallel light, 1302 is a demultiplexer, and 1303 is an optical modulator that gives a frequency shift of δf to the light wave from the light source 1301 and deflects a minute angle by external control. 1304 is a light source optical system, 1305a
And b are first and second interference optical systems, 1306a and b.
Is the first and second reflectors, 1307 is the position measurement object, 1
308 is a reference frequency generator for generating a frequency equal to δf, 1309a and b are optical path switching elements for beams of first and second frequencies f, and 1310a and b are optical paths for beams of first and second frequencies f + δf. Switching elements, 1311a and b are first and second multiplexers, and
Reference numerals 312a and b denote first and second photodetectors, 1313a.
And b are first and second phase detectors, and 1314 is an arithmetic circuit.

Next, the operation will be described. Light source 1301
The more coherent parallel beam emitted is incident on the optical modulator 1303 after being branched by the demultiplexer. If the optical modulator is, for example, an acousto-optic element, the diffracted light emitted is subjected to frequency modulation of δf when the acousto-optic element is driven at δf, and the diffraction angle changes when the driving frequency δf is changed. It is possible to give a minute deflection. However, as the function of the light source optical system 1304, it is sufficient if two beams of the frequency f and f + δf, which are slightly different in frequency from each other, are generated and one of them is slightly deflected. For example, a Zeeman laser other than the configuration of this embodiment is used. It is also possible to use a two-frequency laser such as the above and attach a mechanical or electro-optical deflector on the beam side of one frequency. The first parallel beam of the frequency f emitted from the light source optical system 1304 is branched into two directions by the optical path switching element 1309a for the beam of the first frequency f, one of which is the optical path parallel to the moving direction of the position measurement object 1307. The other parallel beam branched toward the first reflector 1306a by the optical path switching element 1309a for the beam of the first frequency f is moved in the moving direction of the position measurement object 1307 by the optical path switching element 1309b for the beam of the second frequency f. The second reflector 13 with an optical path parallel to
Head towards 06b. The parallel beams reflected by the first and second reflectors 1306a and 1306b return on the same optical path as that of the incident light, respectively, and the first and second combined beams are returned by the optical path switching elements for the beams of the first and second frequencies f, respectively. Wave 131
It is incident on 1a and b. On the other hand, the first parallel beam of the frequency f + δf is branched into two directions by the optical path switching element 1310a for the beam of the first frequency f + δf, and one of the beams is in the optical path inclined by a predetermined angle with respect to the moving direction of the position measurement object 1307. Optical path switching element 1 for the beam of the first frequency f + δf toward the first reflector 1306a.
The other parallel beam split by 310a is the second
Optical path switching element 13 for a beam of frequency f + δf
The optical path tilted at a predetermined angle different from that of the interference optical system 1305a in the moving direction of the position measurement target 1307 by the second optical fiber 10b is used.
Toward reflector 1306b. First and second reflector 1
The parallel beams reflected by 306a and b return on the same optical paths as the respective incidents, and enter the first and second multiplexers 1311a and 13b by the optical path switching elements for the beams of the first and second frequencies f + δf, respectively. , Photodetectors 1312a and b combined with the first collimated beam of frequency f
Causes an interference signal to be output. The interference signal is a heterodyne beat signal of frequency δf, and the phase difference from the reference frequency generator is compared and detected by the first and second phase detectors 1313a and 1313b, and the output is sent to the arithmetic circuit 1314.

In the interference optical system 1305b, the interference optical system 13
The inclination angle of the second parallel beam is smaller than that of 05a, and it is set so that a phase change of n cycles appears in the moving range of the position measurement target 1307.
Beam is deflected by a small angle and n-
The sensitivity is changed so that a phase change of one cycle appears, and the vernier detection is performed by the method of the sixth embodiment to detect the absolute value in the entire movement range. The decomposition score of the position at this time is
If the phase interpolation accuracy is m and n × m, and the sensitivity of the interference optical system 1305a is set so that a phase change of one cycle appears at the resolution of the interference optical system 1305b, the first and second interferences are obtained. By referring to the output of the optical system, a resolution of n × m × l can be obtained with the phase interpolation accuracy of the interference optical system 1305a being 1. As a matter of course, if the number of interference optical systems is increased so as to obtain a detection output with higher sensitivity, it is possible to obtain an absolute value length measuring device with arbitrary resolution.

[0039]

According to the first embodiment of the present invention, the length measuring apparatus has two or more coherers having an optical path difference with respect to the object.
Irradiate a parallel collimated light beam and at least two of the above light beams
At different incident angles with respect to the axis of movement of the object.
A light source having an optical system to be incident on the object, is fixed to the pair <br/> elephant was a reflector for reflecting the two or more light beams in the respective direction of incidence in the same direction, the two or more And a photodetector for measuring the interference intensity of the two or more combined light fluxes, and based on the measured interference intensity of the object, the above
Since the position in the moving axis direction is measured , the position and moving distance of the object can be measured with arbitrary sensitivity longer than the wavelength.

The length measuring apparatus according to the second configuration of the present invention is
In the first configuration, the optical system is so equipped with a duplexer for demultiplexing a light beam in coherent collimated light beam of two or more from the same source, Ya position of the object in the long any sensitive than the wavelength The distance traveled can be measured.

The length measuring apparatus according to the third structure of the present invention is
In the first configuration, at least one of the reflectors is a diffraction grating and has a grating pitch for generating a diffracted wave that reflects incident light in the same direction. Therefore, the position of the object at an arbitrary sensitivity longer than the wavelength is detected. And moving distance can be measured.

The length measuring apparatus according to the fourth structure of the present invention is
In the first configuration, since the reflector includes the prism or the combination mirror having the deflection angle of 180 °, the position and the moving distance of the object can be measured with an arbitrary sensitivity longer than the wavelength.

The length measuring apparatus according to the fifth aspect of the present invention is
Two or more coherents that have an optical path difference with respect to the object
Irradiate a parallel light beam and raises the above two or more light beams.
The incident angles differ from each other with respect to the moving axis of the object.
A light source having an optical system to be incident on the object, is fixed to the object, the light beam and the reflector, one of the other light beam which reflects one of the two or more light beams in the incident direction in the same direction A reflector that reflects light at an angle opposite to that at the time of incidence, a combiner that combines the two light beams on mutually parallel optical axes, and an interference of the two or more combined light beams. Equipped with a photodetector to measure the intensity,
Since the position of the object in the direction of the moving axis is measured ,
The position and movement distance of an object can be measured with any sensitivity longer than the wavelength.

The length measuring apparatus according to the sixth structure of the present invention is
Heterodyne length measuring device
And have different optical frequencies and different optical paths.
Irradiates more than two coherent parallel light beams and
Note that two or more light beams can be transmitted to each other with respect to the moving axis of the object.
Has an optical system that makes the above-mentioned target incident at different incident angles.
A light source that is fixed to the object, if the synthesis the two or more light beams and a reflector that reflects in the same direction as each direction of incidence, the two above more light beams onto parallel optical axes mutually comprising a filter, a photodetector for detecting an equal beat signal to the difference of the frequency caused by the interference of two or more light beams above synthesis, and a phase detector to measure the phase variation of the beat signal, measured From the above phase change
Since the position of the elephant in the moving axis direction is measured , the position and the moving distance of the object can be measured with arbitrary sensitivity longer than the wavelength.

The length measuring apparatus according to the seventh aspect of the present invention is
In a sixth configuration, at least one of the two or more parallel light beams is provided with a deflecting means, and a phase difference between the beat signals before and after the deflection is obtained to obtain an object over a distance longer than a repetition cycle of the beat signal. Absolute measurement of the position of is possible.

The length measuring apparatus according to the eighth structure of the present invention is
A plurality of sets of the length measuring devices of the first configuration having different angles of incidence are provided, and the distance corresponding to the interference period of one set of measuring devices is interpolated with the interference period of the other set of measuring devices. Since it is configured to be longer than the resolution distance, the absolute position of the object can be measured.

The length measuring apparatus according to the ninth structure of the present invention is
A plurality of sets of length measuring devices of the fifth configuration having different angles of incidence are provided, and the distance corresponding to the repetition cycle of the beat signal of one set of measuring devices is set to the beat signal of another set of measuring devices. Is longer than the interpolating resolution distance of the repetition period of, and at least one of the plurality of length measuring devices has a deflecting means for one of the parallel light fluxes, so that the absolute position of the object can be measured. Is possible.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a first embodiment of the present invention.

FIG. 2 is a diagram for explaining the operation of the first embodiment of the present invention.

FIG. 3 is a diagram showing a configuration and an operation of a second embodiment of the present invention.

FIG. 4 is a diagram showing a configuration of a third exemplary embodiment of the present invention.

FIG. 5 is a diagram for explaining the operation of the third embodiment of the present invention.

FIG. 6 is a diagram showing a configuration of a fourth exemplary embodiment of the present invention.

FIG. 7 is a diagram for explaining the operation of the fourth embodiment of the present invention.

FIG. 8 is a diagram showing a configuration of a fifth exemplary embodiment of the present invention.

FIG. 9 is a diagram showing a configuration of a sixth exemplary embodiment of the present invention.

FIG. 10 is a diagram for explaining the operation of the sixth embodiment of the present invention.

FIG. 11 is a diagram for explaining the operation of the sixth embodiment of the present invention.

FIG. 12 is a diagram showing a configuration of a seventh exemplary embodiment of the present invention.

FIG. 13 is a diagram showing a configuration of an eighth embodiment of the present invention.

FIG. 14 is a diagram showing a configuration of an example of a conventional length measuring device.

[Explanation of symbols]

101 light source, 102 multiplexer / demultiplexer, 103, 104 reflector, 105 object, 106 reflecting mirror, 301a, 3
01b Diffraction grating, 404, 405, 604, 605
Corner cube prism, 802 polarization beam splitter, 808 frequency modulator, 811 analyzer, 812
Reference frequency generator, 813 phase detector.

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazuo Takashima 2-3-3 Marunouchi, Chiyoda-ku, Tokyo Mitsubishi Electric Corporation (72) Inventor Hirokazu Sakuma 2-3-2 Marunouchi, Chiyoda-ku, Tokyo Mitsubishi Electric Incorporated (72) Inventor Takao Mizutani 2-3-3 Marunouchi, Chiyoda-ku, Tokyo Mitsubishi Electric Corporation (72) Inventor Yukio Aoki 2-3-2 Marunouchi, Chiyoda-ku, Tokyo Mitsubishi Electric Corporation ( 56) References JP-A-8-43136 (JP, A) JP-A-6-186004 (JP, A) JP-A-5-210006 (JP, A) JP-B-51-42495 (JP, B1) US Patent 4022532 (US, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G01B 9/02 G01B 11/00

Claims (9)

(57) [Claims] 1. An object is irradiated with two or more coherent parallel light fluxes having an optical path difference, and the two light fluxes.
The above luminous flux is different from the moving axis of the object.
A light source having an optical system for causing an incident angle is incident on the object that is fixed to the object, and a reflector for reflecting the two or more light beams in the respective direction of incidence in the same direction, the two
A combiner for combining two or more light beams on mutually parallel optical axes, and a photodetector for measuring the interference intensity of the two or more combined light beams are provided .
Characterized by measuring the position of the object in the direction of the movement axis
Length measuring device that. Wherein said optical system, measuring apparatus according to claim 1, wherein those having two or more demultiplexer for demultiplexing the coherent parallel light flux emitted from the same light source. 3. The length measuring apparatus according to claim 1, wherein at least one of the reflectors is a diffraction grating, and has a grating pitch for generating a diffracted wave that reflects incident light in the same direction. Wherein said reflector length measuring apparatus according to claim 1, wherein those having a prism or combination mirror with a deflection angle of 180 °. 5. An object is irradiated with two or more coherent parallel light fluxes having an optical path difference, and the two light fluxes.
The above luminous flux is different from the moving axis of the object.
A light source having an optical system to be incident on said object at an incident angle that is fixed to the object, and a reflector for reflecting one of the two or more light beams in the incident direction and the same direction, the other light beam and one reflector for reflecting at an angle with an inclination of an incident during the reverse relative to the light beam, and a multiplexer for combining said two light beams on the optical axes parallel to each other, two that are above synthetic It is equipped with a photodetector that measures the interference intensity of the above luminous flux
From the interference intensity, the position of the object in the moving axis direction
A length measuring device characterized by measuring. 6. An object is irradiated with two or more coherent normal light fluxes having different frequencies and optical path differences , and the two or more light fluxes are paired with each other.
The above target with different incident angles with respect to the moving axis of the elephant
A light source having an optical system to be incident on the object, is fixed to the object, and a reflector for reflecting the two or more light beams in the respective direction of incidence in the same direction, parallel to each other a light beam of two or more above A multiplexer for synthesizing on the optical axis, a photodetector for detecting a beat signal equal to the difference in frequency caused by the interference of the two or more synthesized light fluxes, and a phase for measuring a phase change of the beat signal Equipped with a detector and measured
The position of the object in the moving axis direction from the phase change
Heterodyne type length measuring device characterized by measuring 7. At least one of the two or more parallel light beams.
One to comprise a deflection means, the deflection by obtaining the difference between the phase of the beat signal before and after, measuring device according to claim 6, wherein performing absolute measurements of position over a longer distance than the repetition period of the beat signal. 8. A plurality of sets of length-measuring devices according to claim 1, wherein the angle differences of the incident angles are different, and a distance corresponding to an interference cycle of one set of length-measuring devices is set to that of another set of length-measuring devices. A length measuring device configured to be longer than the interpolating resolution distance of the interference period. 9. A plurality of sets of length-measuring devices according to claim 5, wherein the angle differences of the incident angles are different, and the distance corresponding to the repetition cycle of the beat signal of one set of length-measuring devices is measured by another set of length-measuring devices. The length measuring device is configured to be longer than the interpolating resolution distance of the repetition period of the beat signal of the length measuring device, and at least one length measuring device of the plurality of length measuring devices is provided with a deflecting means for one of the parallel light beams. Long device.