JP2675317B2 - Moving amount measuring method and moving amount measuring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial applications]   In the present invention, the measuring standard is a diffraction grating, and the diffracted light is
Depending on the phase of the beat signal obtained by causing the Telodyne interference
The relative movement distance between the diffraction grating and other optical members
Amount measuring method and device therefor
Things. [Conventional technology]   In the field of length and position measurement, there have been
However, using a caliper, micrometer, etc.
Measurements are still being made, but problems with the μm unit
In the area of so-called precision measurement, these measuring tools are
Don't use it. In recent years, electronic measurement equipment has advanced and
Developed a measuring device that uses optical and magnetic technologies together with circuits.
It is often used for processing and inspection. One that uses light
An example is optical wave interferometry based on the wavelength of laser light.
A long instrument is known. The accuracy of this length measuring device is
Although it can sufficiently meet the standard requirements, laser light
Detected by changes in the optical path system environment (pressure, temperature, vibration, etc.)
In addition to the problem of deterioration in accuracy, it is also expensive in price.
You. In addition, as a method using magnetism, a belt-shaped or rod-shaped method is used.
Pre-record a magnetic pattern as a standard for dimensions on the magnetic body
Then, find the mutual positional relationship between this pattern and the magnetic head.
The magnetic scale is known. However, this method
Accuracy is determined by the pitch of the reference pattern that can be stored in the magnetic material.
The pitch that can be stored stably is 5 to 10 μm.
The measurement accuracy is practically about 2 digits compared to the light wave interferometer.
The accuracy is low. On the other hand, an optical interferometer and a magnetic scale
As a length measuring device with intermediate accuracy of
Practical application of a device that combines a laser light is underway.   Conventionally, this type of device is generally shown in FIG. 6 or 7.
In FIG. 6, 1 is a diffraction pattern.
Lattice, 2 is a light source that emits monochromatic light such as laser light, 3, 4
Is a reflection placed on the opposite side of the light source 2 across the diffraction grating 1.
The mirrors 5 are arranged on the light source 2 side to read the interference light.
It is a detector. The light ray L emitted from the light source 2 is a diffraction grating.
The light is transmitted and diffracted by the child 1. Ray L₁Is the diffraction grating 1 times
Assuming the folded n-th order diffracted light, the pitch of the diffraction grating is
p, the minute displacement of the diffraction grating 1 is Δx, and the ray L₁Is 2π
-It contains the phase information of Δxn / p. Meanwhile, the diffraction grating
Ray L that linearly transmitted 1_TwoContains phase information
Absent. Ray L₁, And L_TwoAre reflected by the reflectors 3 and 4, respectively.
Then, it goes backward in the forward path and again enters the diffraction grating 1 to diffract and transmit light.
An error is made. Ray L₁Transmitted light and ray L_Two-N order diffraction
The light is spatially selected, interfered, and is incident on the detector 5.
You. At this time, ray L_Two-N order diffracted light is -2π · Δx ·
Since the phase information of n / p is included, the interference light is 2
Since the phase information of π ・ Δx ・ 2n / p is included, the diffraction grating
1 and other light sources 2 and optical systems such as reflectors 3 and 4 are relative
The movement of the diffraction grating 1 for one cycle is
Therefore, the intensity change of the interference light is 2n cycles. The detection resolution is
It becomes p / 2n.   In addition, the device of FIG. 7 has a light source 2 and a transmission type diffraction grating 1.
The beam splitter 6 is placed between the two
3 and 4 are on the lower side of the diffraction grating 1 at the same angle with respect to the diffraction grating 1.
They are arranged symmetrically. Detector 5 is a beam splitter
It is provided on the reflection side of 6. Therefore, the light emitted from the light source 2
The line L passes through the beam splitter 6 and is paired with another optical system.
And is incident on the movable diffraction grating 1. This diffraction grating 1
The n-th order diffracted light with a different sign is formed in
To select ray L₁, L_TwoIncident on the reflecting mirrors 3, 4 as
Reflected by the mirrors 3 and 4 in the reverse direction, and again the diffraction grating
Incident on 1. + N of the light that has become the + nth order in the first diffraction
Second-order diffracted light and -n-th order of the light that has been changed to -n-th order in the first diffraction
Select diffracted light spatially. By doing this
Two rays L₁, L_TwoThe directions of travel are the same and interfere with each other
Going toward the direction of the light source 2 while matching, beam splitting
It is reflected by the tool 6 and enters the detector 5. Obedience
By diffracting the diffraction grating 1 twice,
The folding grating 1 moves for one cycle with respect to other optical systems.
And the interfering light incident on the detector 5 produces a 4n cycle intensity change.
I will. The detection resolution is p / 4n, which is twice that of the example in Fig. 6.
You.   FIG. 8 shows a more specific conventional example, in which the diffraction grating 1 (8
Is a light source 2, two detectors 5a, 5b,
System 9, deflection mirrors 10a and 10b, and deflection beam splitter 7
Place the roof prisms 11 and 12 and the phase difference plates 13 and 14 on the other side.
Deploy. The light source 2 is a light emitting diode, a semiconductor laser, or the like.
Is a semiconductor light emitting element of, and the lens system 9 is emitted from the light source 2.
For making the light beam L to be converted into a substantially parallel light beam.
The deflecting mirrors 10a and 10b, the incident light on the deflecting mirror 10a and the deflecting mirror 10b
These relative angles so that the light emitted from
Is set to 90 degrees. In addition, the phase difference plates 13 and 14 are
When re-entering the linearly polarized light of
It also functions as a left-handed circularly polarized light.   Therefore, the light beam L emitted from the light source 2 is transmitted by the lens system 9.
It is made into a parallel light beam, and is directed to the point A on the diffraction grating 1 by the deflecting mirror 10a.
Incident. Then, the light beam is diffracted by the diffraction grating 1.
L₁, L_TwoVia the phase difference plates 13 and 14, respectively,
It is incident on rhythms 11 and 12. Ray L₁, L_TwoIs the Dach Prism 11,1
2 is reflected by the retardation plates 13 and 14 in the direction parallel to the incident direction.
Right-handed and left-handed circularly polarized light, point A of the diffraction grating 1
Is again diffracted at a different point B in the X direction and further deflected.
It is incident on the polarized beam splitter 7 via the mirror 10a.
Right-handed and left-handed incident on this polarized beam splitter 7.
Ray L that has circular polarization characteristics around₁, L_TwoIs a polarized beam
The prism 7 is transmitted and reflected. Transmitted light and reflected light
Each becomes linearly polarized light and interferes with each other to form detector 5
It will be incident on a and 5b.   The detectors 5a and 5b use the orthogonal components of the two circularly polarized light as interference light.
Since it is detected as intensity, when the diffraction grating 1 moves
The outputs R and S of the detectors 5a and 5b are shown in FIGS. 9 (a) and 9 (b).
So it has a phase difference of 90 degrees. These two signals R and S
Binarization based on a constant level as shown in (c) and (d) of the same figure.
The same figure at the rising and falling timings.
Generate pulses as shown in (e) and measure the number.
Therefore, the movement amount of the diffraction grating 1 can be measured. Ma
Also, when counting, considering the moving direction of the diffraction grating 1,
It may be determined whether to add or subtract. In this case, the diffraction case
Output of interference fringes moves by 4n cycles due to movement of child 1 by 1 cycle
And counting the pulses from that output gives 16n pulses.
You will get the price. [Problems to be solved by the invention]   By the way, in the optical arrangement shown in FIG.
To store it in a small space, use the light L₁And ray L_TwoTimes
It is necessary to make the angles to the folded grid 1 equal,
In this case, the relative position between the optical system and the diffraction grating 1 is
Even if it moves in the Y direction perpendicular to the plane,
Phase information corresponding to the amount of movement of the
The same direction as when moving the child in the array direction, that is, the X direction.
It is said that the measurement accuracy will deteriorate due to the change in the intensity of the light.
There was a problem. In addition, as shown in FIG. 7 and FIG.
When the light ray L is vertically incident, the above-mentioned problems do not occur,
Changes in the amount of light and diffraction due to the detection of changes in the intensity of interference light
The detection accuracy deteriorates due to fluctuations in efficiency. These fluctuations
In order to correct the
Needs a processing system such as feedback to the detection signal processing system
Therefore, while the device becomes complicated, noise is not generated in the detection signal.
The light intensity fluctuation cannot be completely removed because it contains
There are drawbacks. In addition, the S / N ratio of the detection signal is large for detection accuracy.
This is done to improve the detection resolution.
There is a limit to the pulse conversion of the detection signal
The resolution is limited to a few tenths of the diffraction grating pitch.
Therefore, it is difficult to obtain a detection resolution higher than this. Ma
When applied to a rotary encoder, etc.,
It is necessary to form a diffraction grating on the
It is possible to increase the grid pitch by making it fine.
Is a mechanical ruling engine, photolithography
, Grid line formation by electron beam lithography
Since there is a limit to the
A possible method is to increase the number of grid lines, but the device itself
There is a problem that the body becomes large. In addition, the above
In devices such as tally encoders, a disc-shaped diffraction grating
Detects changes in the intensity of diffracted light caused by rotation
Then, it is converted into a pulse signal, but the detector or pulse
The frequency response speed of electronic circuits used for counting etc.
Due to limitations, the rotary encoder above
There was a problem that could not be speeded up.   Therefore, the present invention solves the above problems.
In addition to using a diffraction grating, the light source uses monochromatic light of two wavelengths.
Adapting the optical heterodyne interferometry used,
By detecting the phase difference signal instead of the signal,
Faster, higher stability, higher resolution and smaller than
A method for measuring the amount of movement of
It is intended to provide. [Means for solving the problem]   The present invention has been made to achieve the above object,
In the movement amount measuring method of the first invention, the frequencies are mutually different.
Optical heterodyne is synthesized by combining monochromatic light of two different wavelengths.
And generate a reference beat signal, and
Long monochromatic light is symmetric with an angle of incidence adjusting means.
The light is incident on different positions on the diffraction grating provided on the object.
The diffracted light of two wavelengths generated from the diffraction grating in the forward path.
Re-enter the diffraction grating by an optical system that moves backward
Then, these diffraction patterns generated by diffracting twice by the diffraction grating
Before diffracted light of two wavelengths with slightly different wavenumbers
After the incident angle adjustment means, the optical heterodyne interference
And the beat signal of the generated interference light and the reference beat signal
Phase difference and the phase pulse generated from the phase difference signal.
From the diffraction grating by counting
The moving distance of the object is measured.   The movement amount measuring device of the second invention is provided on the object.
Diffraction grating and two waves whose frequencies are slightly different from each other
A light source that emits long monochromatic light and the light emitted from this light source
A standard that combines two wavelengths of monochromatic light and causes optical heterodyne interference
A first photosynthesis detecting means for generating a beat signal;
The monochromatic light of two wavelengths emitted from the source is changed on the diffraction grating.
From a symmetrical direction with a certain angle at
Incident angle adjusting means for making each incident and the diffraction grating
The diffracted light of two wavelengths is reversed in the forward path and again the diffraction grating
Reflected light adjusting means for making the light incident on
The diffracted light of two wavelengths generated by being diffracted once is used for the incident angle adjustment
Optical heterodyne interference beat signal synthesized after passing through stages
And a second photosynthesis detecting means for generating
Reference beats respectively generated by the photosynthesis detection means
Phase difference from signal and optical heterodyne interference beat signal
The signal is calculated and the phase difference signal
The diffraction is generated by generating a loose signal and performing a calculation process.
With a signal processing device that converts the amount of movement of an object consisting of a grid
It is composed. [Action]   The present invention calculates the movement amount of the diffraction grating, that is, the movement amount of the object,
It detects continuously as the phase change of the beat signal.
You. Then, the phase of the beat signal is the intensity fluctuation of the diffracted light.
Therefore, according to the present invention, the light source
Detection due to changes in intensity or changes in diffraction efficiency of the diffraction grating
No error will occur. Further, in the present invention, the movement amount is detected.
The output resolution is determined by the detection accuracy of the phase difference, and
By increasing the detection accuracy of the phase difference,
Or the amount of movement of the object without changing the number of grids, etc.
The detection resolution can be easily increased. 〔Example〕   Hereinafter, the present invention will be described in detail based on embodiments shown in the drawings.
I will tell.   FIG. 1 is a first embodiment of a movement amount measuring device according to the present invention.
It is shown. In addition, the same reference numerals as those in FIGS. 6 to 8 are used.
The numbers indicate the same members. In FIG. 1, 15
Have slightly different frequencies and their planes of polarization are
Dual-wavelength cross-polarization laser that emits monochromatic light of two intersecting wavelengths
Light source. Here, p-polarized light whose polarization planes are orthogonal to each other,
The frequency of the s-polarized laser light is f₁, f_TwoAnd
Therefore, the optical heterodyne interference beat frequency Δf≡ | f₁−f
_Two| 7a and 7b are polarized beam splitters, 16a and 16b are
Polarizing plates 17a and 17b are condenser lenses.   In the device of the first embodiment, a dual wavelength orthogonal polarization laser is used.
Beam splitting a part of the laser light L emitted from the light source 15
It is taken out as transmitted light through the target 6 and taken out.
The laser light is condensed by the condenser lens 17a, and the polarizing plate 16a is used.
Optical heterodyne interference, and the detector 5a detects
Signal. On the other hand, 2 wavelength orthogonal polarization laser light source 15
Part of the light emitted from the beam is transmitted through the beam splitter 6.
In the diffraction grating 1 that can be reflected and move with respect to other optical systems
The light enters from the normal direction (Y direction) perpendicular to the diffraction grating surface.
This diffraction grating 1 forms diffracted light of the same order with different signs.
These are spatially selected and the ray L_Three, L_FourPolarized light as
The light enters the reflecting mirrors 3 and 4 via the beam splitters 7a and 7b.
Where ray L_Three, L_FourThe reflectors 3 and 4
Is reflected by and is incident on the diffraction grating 1 again. Polarized beams
The splitters 7a and 7b can be adjusted by water depending on the polarization direction of the laser light.
Flat polarized laser light (p polarized) and vertically polarized laser light (s
It is an optical element that splits into polarized light)
L_ThreeIs the p-polarized light transmitted through the polarized beam splitter 7a.
Laser light (frequency f₁), And re-enters the diffraction grating 1.
You. On the contrary, laser light L_FourIs a polarized beam split
S-polarized laser light (frequency f_Two)
And similarly enters the diffraction grating 1 again. Again, diffraction
These laser lights L incident on the grating 1_Three, L_FourIs a diffraction grating
1 is diffracted again and diffracted light of the same order with different signs
Optically synthesized in the direction normal to the plane of the grating
Is transmitted through the beam splitter 6, and is collected by the condenser lens 17b.
The light is condensed and converted into optical heterodyne interference light by the polarizing plate 16b.
Then, the detector 5b detects it as a diffracted light beat signal.   Therefore, the reference beat signal detected by the detector 5a and the detector
The phase difference with the diffracted light beat signal detected in 5b can be detected.
With, the amount of movement of the diffraction grating 1 can be measured.   Here, for example, the grating pitch of the diffraction grating 1 is P, and the frequency is
f₁, f_TwoThe wavelength of each laser light is λ₁, λ₂And then times
In the pitch direction (X direction) perpendicular to the grid line of the folded grid 1.
Optical heterodyne interfering light of n-th order diffracted light where the amount of movement is Δx
Considering the case of detecting the
Laser light L detected by_ThreeThe optical path length change of the
Since it is diffracted twice by the grating 1, 2π · Δx · si
nθ_n1Just become longer. On the contrary, laser light L_FourLight of
Similarly, the amount of change in path length is 2 · Δx · sin θ_n2Just shorter
You. Where θ_n1, θ_n2Are the wavelengths λ₁, λ₂N
Is the second diffraction angle, sin θ_n1= N · λ₁/ P (1) sin θ_n2= N · λ_Two/ P (2) There is a relationship.   Therefore, the phase of the reference beat signal and the diffracted light beat signal
The difference Δφ is Then, substituting equations (1) and (2) into equation (3), Δφ = 8π ・ n ・ Δx / P     = 2π · Δx / (P / (4n)) (4) Therefore, the phase difference Δφ and the movement amount Δx of the diffraction grating 1 are linear.
The phase difference Δφ is related to the movement amount Δx of the diffraction grating 1.
Then, it changes with P / (4n) as the period.   FIG. 2 is a second embodiment of the movement amount measuring device according to the present invention.
It shows. In the figure, 3a is a reflecting mirror and 7 is a polarizing mirror.
The light beam splitters 18a and 18b are quarter-wave plates.   In the device of the second embodiment, a dual wavelength orthogonal polarization laser is used.
Beam splitting a part of the laser light L emitted from the light source 15
And take out the laser light
The light is condensed by the condenser lens 17a, and the optical
Interference, detect with detector 5a, and use it as the reference beat signal.
You. On the other hand, the light emitted from the two-wavelength orthogonal polarization laser light source 15
Part of L passes through the beam splitter 6 and
The horizontally polarized laser light (p polarized light) is incident on the splitter 7.
Light, frequency f₁) And vertically polarized laser light (s polarization, frequency
f_Two) L_FiveAnd L₆Is separated into Laser light L_FiveThrough the reflector 3a
And then laser light L₆Directly to other optics
The movable diffraction grating 1 has a normal direction perpendicular to the diffraction grating surface.
It is incident from (Y direction). This diffraction grating 1 has a different sign
Diffracted lights of the same order are formed, and these are spatially selected.
And enters the reflecting mirrors 3 and 4 via the quarter-wave plates 18a and 18b. This
Here, ray L_Five, L₆Use the mirrors 3 and 4 to go backward in the
It is reflected and again enters the diffraction grating 1. Again, the diffraction grating
Ray L incident on 1_Five, L₆Is the diffraction of the same order with different signs
Light is emitted in the direction normal to the diffraction grating surface, that is, in the Y direction.
To the polarized beam splitter 7 via the reflecting mirror 3a, etc.
Re-inject. At this time, ray L_Five, L₆Are each 1/4 wavelength
Since it passes through the plates 18a and 18b twice, the plane of polarization is rotated 90 degrees.
ing. Therefore, in the polarized beam splitter 7,
Ray L_FiveIs reflected because it is s-polarized, and the ray L₆Is p-polarized
Transmitted, optically combined, and condensed by condenser lens 17b
Then, it becomes an optical heterodyne interference light by the polarizing plate 16b and is detected.
It is detected as a diffracted light beat signal by the output device 5b.   Therefore, the reference beat signal detected by the detector 5a and the detector
The phase difference Δφ with the diffracted light beat signal detected in 5b is detected.
Accordingly, the movement amount Δx of the diffraction grating 1 can be measured.
When an optical heterodyne interference beat signal of n-th order diffracted light is used
In this case, the relationship between the phase difference Δφ and the movement amount Δx of the diffraction grating 1 is
As in the first embodiment, it is represented by the above formula (4).   FIG. 3 is a third embodiment of the movement amount measuring device according to the present invention.
It shows. In the figure, 3,3a and 3b are reflectors and 1
8 is a quarter-wave plate.   In the device of the third embodiment, a dual wavelength orthogonal polarization laser is used.
Beam splitting a part of the laser light L emitted from the light source 15
And take out the laser light
The light is condensed by the condenser lens 17a, and the optical
Interference, detect with detector 5a, and use it as the reference beat signal.
You. On the other hand, the light emitted from the two-wavelength orthogonal polarization laser light source 15
A part of L is transmitted through the beam splitter 6 and a polarized light beam is transmitted.
Incident on the horizontal splitter 7 and horizontally polarized laser light (p
Polarization, frequency f₁) L_FiveAnd vertically polarized laser light (s polarized, circular
Wave number f_Two) L₆Is separated into Laser light L_Five, L₆Is the reflector 3a,
Diffraction grating 1 that can move with respect to other optical systems via 3b
Left and right with respect to the normal direction (Y direction) perpendicular to the diffraction grating surface
The light enters from diffraction angles of the same order with different symmetrical signs. this
Laser light L transmitted and diffracted by the diffraction grating 1_Five, L₆Sign of
The diffracted light of the same order is combined with the 1/4 wavelength plate 18
It is incident on the reflecting mirror 3 via. Where ray L_Five, L₆Synthesis of
The diffracted light is reflected by the reflecting mirror 3 so as to go in the backward direction,
It enters the diffraction grating 1 again. It enters the diffraction grating 1 again
Ray L_Five, L₆The synthetic diffracted light of
Diffracted light of the order is formed, and the polarized light is transmitted through the reflecting mirrors 3a and 3b.
Re-enters the Splitter 7. At this time, ray L_Five, L₆
Each of the synthetic diffracted light of passes through the quarter-wave plate 18 twice.
Therefore, the plane of polarization is rotated 90 degrees. Therefore,
Rays L in Moon Splitter 7_FiveDiffracted light is s-polarized
It is reflected by the ray L₆Diffracted light is transmitted as p-polarized light
Then, they are optically combined, condensed by the condenser lens 17b, and polarized.
Optical plate 16b turns into optical heterodyne interference light, and detector 5b
Is detected as a diffracted light beat signal.   Therefore, the reference beat signal detected by the detector 5a and the detector
The phase difference Δφ with the diffracted light beat signal detected in 5b is detected.
Accordingly, the movement amount Δx of the diffraction grating 1 can be measured.
When an optical heterodyne interference beat signal of n-th order diffracted light is used
In this case, the relationship between the phase difference Δφ and the movement amount Δx of the diffraction grating 1 is
As in the first embodiment, it is represented by the above formula (4).   FIG. 4 is a more specific diagram of the movement amount measuring apparatus according to the present invention.
4 shows a fourth embodiment. In the figure, 3,3a, 3
Reference numerals b, 3c and 4 are reflecting mirrors, 8 is a lattice line, and 19 is a signal processing unit.   In the device of the fourth embodiment, a two-wavelength orthogonal polarization laser is used.
Beam splitting a part of the laser light L emitted from the light source 15
And take out the laser light
The light is condensed by the condenser lens 17a, and the optical
In-interference, detected by the detector 5a and used as the reference beat signal.
Input to the signal processing unit 19. On the other hand, a two-wavelength orthogonal polarization laser
A part of the light L emitted from the laser light source 15 is a beam splitter.
-6 is transmitted, it is incident on the polarized beam splitter 7,
Horizontally polarized laser light (p polarization, frequency f₁) L_FiveAnd vertically polarized
Laser light (s polarization, frequency f_Two) L₆Is separated into Leh
The light L_Five, L₆Other light is reflected through the mirrors 3b and 3a and 3c.
Perpendicular to the plane of the diffraction grating 1 that can move with respect to the academic system
Signs symmetrical with respect to the normal direction (Y direction) are different
It is incident from the diffraction angle of the same order. This diffraction grating 1 allows transmission
Folded laser light L_Five, L₆Diffracted light of the same order with different signs
Enter the reflecting mirrors 3 and 4 via the quarter-wave plates 18a and 18b, respectively.
Shoot. Where ray L_Five, L₆Diffracted light goes backwards
Is reflected by the reflecting mirrors 3 and 4, and then enters the diffraction grating 1 again.
I do. Again, the light ray L that is incident on the diffraction grating 1_Five, L₆Diffracted light
Forms diffracted lights of the same order with different signs,
Polarizing beam splitter 7 via mirrors 3a and 3b and 3c
Re-enter. At this time, ray L_Five, L₆The diffracted light is
Since it passes through the quarter-wave plates 18a and 18b twice, the polarization plane is 90 degrees.
It has been rotated. Therefore, the polarized beam splitter 7
At ray L_FiveDiffracted light is reflected by s-polarized light
And ray L₆Is p-polarized light, it is transmitted and optically synthesized.
The light is condensed by the condenser lens 17b, and the light is reflected by the polarizing plate 16b.
It becomes rhodyne interference light, and the diffracted light beat signal is detected by the detector 5b.
Signal and input to the signal processing unit 19.   Therefore, in the signal processing unit 19, detected by the detector 5a
Reference beat signal and diffracted light beat signal detected by detector 5b
By detecting the phase difference Δφ from the
The amount of movement Δx can be measured. Optical heterodyne of n-th order diffracted light
When using the interfering beat signal, the phase difference Δφ and the diffraction grating 1
As with the first embodiment, the relationship with the movement amount Δx is expressed by the above equation.
It is represented by (4).   FIG. 5A is a diagram showing a specific example of the phase difference signal Δφ.
Yes, the phase difference signal Δφ is the amount of movement of the diffraction grating Δx = −P /
(8n) to + P / (8n) -π (-180 degrees) to + π
It shows linearity in the range of (+180 degrees), and this
Repeat with n). For the phase difference signal of FIG.
For example, the phase difference is from +180 degrees to -180 degrees, or vice versa.
Shown in (b) at the timing of switching from +180 degrees
Pulse is generated and the number is counted.
Therefore, the amount of movement of the diffraction grating 1 can be measured. Detection amount at this time
The resolution is P / (4n). In this case, the diffraction grating 1
The direction of movement corresponds to the direction of increase / decrease in the phase difference value.
Since it can be easily determined, consider increasing or decreasing the phase difference value when counting pulses.
It is sufficient to decide whether to add or subtract.   Furthermore, the phase difference signal Δφ is different from the intensity signal of the diffracted light.
The intensity of the light source and the diffraction efficiency of the diffraction grating.
Almost unaffected by disturbance, proportional to the movement amount Δx of the diffraction grating 1
The signal is a stable signal. For this reason,
The phase difference signal detection processing system, which consists of ordinary electronic circuits,
It is possible to easily achieve a detection resolution of about 1 degree. Therefore, the same
As shown in the figure (c), for example, the number of divisions N = 360
The amount of movement Δx = -P / (8n) to + P / (8n) can be divided into 360
Noh. That is, the movement amount Δx of the diffraction grating 1 is determined by the detection resolution.
It can be detected by P / (360 ・ 4n). Furthermore, the number of divisions N
The value can be easily set by the phase difference signal detection processing system.
The amount of movement Δx of the diffraction grating 1 with the desired detection resolution P / (N · 4n)
It has a feature that can detect.   In addition, in the above-described first to fourth embodiments, two wavelengths are used.
2 wavelength orthogonal polarization laser light as monochromatic light source
The source 15 is used, but it is not a Bragg cell as a monochromatic light of two wavelengths.
The same will be true no matter which acousto-optic element is used to generate the light.
The effect can be obtained. In this case, the
Dual wavelength monochromatic light combined with a conductor laser
A compact source is possible. Furthermore, dual wavelength laser
-The optical fiber such as polarization-maintaining optical fiber can be used for the incident optical system of the light.
Using an aver, the amount of movement detection optical system and dual wavelength monochromatic light
Separate the light source and combine them with an optical fiber, etc.
By applying the technology of
It is possible to make it more compact.   In addition, in the above-mentioned first to fourth embodiments,
The application example as a position meter is shown, but the diffraction grating 1 can be rotated.
Applicable to rotary encoders set on various discs
Noh. In this case, the same effect can be obtained.
You. Furthermore, by setting the value of N appropriately, detection
Diffraction grating with large grating pitch without sacrificing resolution
Since it is possible to use the rotary encoder
The response rotation speed can be increased.   Furthermore, the direction of the incident light on the diffraction grating 1 and the diffraction
XY plane where the direction of the diffracted light from the grating 1 is perpendicular to the diffraction grating surface
The example included in
As the direction of the light and the direction of the diffracted light from the diffraction grating,
Oblique incidence and oblique incidence not included in the XY plane perpendicular to the polygonal plane
For this reason, the optical diffracted light of two wavelengths emitted from
Similar effect even if the in-interference beat signal is detected
Can be obtained.   Furthermore, as the diffraction grating 1 in the present invention,
You can use either a converging type diffraction grating or a phase type diffraction grating.
In addition to the binary diffraction grating,
Use various diffraction gratings such as children and phrase diffraction gratings
Is possible, and a reflection type diffraction grating is used in addition to the transmission type.
It is also possible. 〔The invention's effect〕   As described in detail above, the movement amount measurement according to the present invention
According to the method and its measuring device, the diffraction grating has a frequency
Inject monochromatic light of two slightly different wavelengths, and
From the diffraction grating produced by the two diffractions of the monochromatic light of
Optically synthesized diffracted light of different wavelengths is used for optical heterodyne interference
Since it is designed to detect the
The amount of movement of the diffraction grating (that is, the movement of the object
Motion amount) can be measured. In addition, fluctuations in light source intensity and diffraction
The diffracted light intensity fluctuated due to fluctuations in the diffraction efficiency of the child.
Even if the amplitude of the diffracted light beat signal changes
The beat signal has no effect on the phase change of the beat signal.
Therefore, the movement amount can be detected with high accuracy. In addition,
Since the phase difference signal is highly stable, the phase difference is, for example, 1 ° or less.
Can be detected with high accuracy and high resolution can be obtained.
You. Furthermore, when applied to rotary encoders, etc.
When using the high detection resolution of phase difference detection,
Diffraction grating placed on a disk without degrading resolution
To reduce the size of the device by reducing the number of
It is possible to speed up the rotational movement detection by increasing the pitch.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing a first embodiment of a movement amount measuring method and apparatus according to the present invention, and FIG. 2 is a block diagram showing a second embodiment of the present invention. FIG. 4 is a block diagram showing a third embodiment of the present invention, FIG. 4 is a block diagram showing a fourth embodiment of the present invention, and FIGS. 5 (a) to (c) are obtained from the fourth embodiment of the present invention. FIG. 6, FIG. 7, FIG. 8 and FIG. 8 are diagrams showing an example of a conventional movement amount measuring method, and FIG.
8A to 8E are time charts of signals obtained by the measuring method of FIG. 1 ... Diffraction grating, 2 ... Light source, 3,3a, 3b, 3c, 4 ... Reflecting mirror, 5,5a, 5b ... Detector, 6 ... Beam splitter,
7,7a, 7b …… Polarized beam splitter, 8 …… Lattice line,
9 ... Lens system, 10a, 10b ... Deflecting mirror, 11,12 ... Dach prism, 13,14 ... Phase retarder, 15 ... 2-wavelength orthogonal polarization laser light source, 16a, 16b ... 17b ... Condensing lens, 18,18a, 18b ... 1/4 wavelength plate, 19 ... Signal processing unit.

Claims (1)

(57) [Claims] A diffraction grating is used as a length measuring standard, and diffracted light generated by making monochromatic light incident on the diffraction grating interferes to obtain a relative moving distance of the diffraction grating with respect to another optical system. Using monochromatic lights of two wavelengths whose frequencies are slightly different from each other, the monochromatic lights of the two wavelengths are combined to cause optical heterodyne interference to generate a reference beat signal, and the monochromatic lights of the two wavelengths are passed through an incident angle adjusting means. At different angles on the diffraction grating provided on the object at a symmetric angle, and diffracted light of two wavelengths generated from the diffraction grating is made to enter the diffraction grating again by an optical system that reverses the forward path. The diffracted light having two wavelengths, which are slightly different in frequency from each other and are generated by diffracting twice by the diffraction grating, are caused to interfere with each other by optical heterodyne after passing through the incident angle adjusting means. A movement amount characterized by measuring the movement distance of the object formed of the diffraction grating by counting the phase difference between the optical beat signal and the reference beat signal and the periodic pulse signal of the phase generated from the phase difference signal. Measuring method. 2. A diffraction grating provided on the object, a light source for generating monochromatic light of two wavelengths whose frequencies are slightly different from each other, and monochromatic light of two wavelengths emitted from this light source are combined to cause optical heterodyne interference to generate a reference beat signal. First photosynthesis detecting means for generating, and incident angle adjusting means for causing monochromatic light of two wavelengths emitted from the light source to respectively enter at different positions on the diffraction grating from left and right symmetrical directions having a predetermined angle, respectively. Reflected light adjusting means that reverses the outward path of diffracted light of two wavelengths generated from the diffraction grating and makes the diffracted light incident on the diffraction grating again, and diffracted light of two wavelengths generated by being diffracted twice by the diffraction grating, the incident angle adjustment means A second photosynthesis detecting means for generating an optical heterodyne interference beat signal after being synthesized via
A phase difference signal is calculated from the reference beat signal and the optical heterodyne interference beat signal respectively generated by the first and second photosynthesis detecting means, and further, a phase periodic pulse signal is generated from the phase difference signal and calculated. A movement amount measuring device, comprising: a signal processing device for converting the movement amount of an object made of the diffraction grating by processing.