JP2517027B2 - Moving amount measuring method and moving amount measuring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention uses a length-measuring standard as diffraction and diffracts light using one diffraction grating and a diffraction grating that can move relative to the diffraction grating. The present invention relates to a moving amount measuring method and a device for measuring the relative moving distance between two diffraction gratings by causing light heterodyne interference and measuring the phase difference between two beat signals respectively obtained from the two diffraction gratings. .

[Conventional technology]

In the field of length and position measurement, measurement with human eyes has traditionally been performed using pure mechanical rulers, calipers, micrometer, etc., but in the area of so-called precision measurement where μm unit is a problem. The measuring tool of does not do that. 2. Description of the Related Art In recent years, electronic measuring devices have been developed, and measuring devices using light, magnetism, and the like as well as electronic circuits have been developed and widely used for processing and inspection. As an example of using light, there is known a light wave interferometer length measuring device based on the wavelength of laser light. The precision of this length measuring instrument can sufficiently meet the requirements of the current industrial level, but there is a problem that the detection precision deteriorates due to the environmental changes (pressure, temperature, vibration, etc.) of the optical path system of the laser beam. The price is expensive. Further, as a method using magnetism, a magnetic scale is known in which a magnetic pattern as a dimensional reference is recorded in advance on a strip-shaped or rod-shaped magnetic body, and the mutual positional relationship between this pattern and the magnetic head is obtained. There is. However, the accuracy of this method is determined by the pitch of the reference pattern that can be stored in the magnetic material, and the pitch that can be stably stored is 5 to 10 μm, and the measurement accuracy is practically two digits compared to the optical wave interferometer. The accuracy is low. On the other hand, a device combining a diffraction grating and a laser beam is being put into practical use as a length measuring device having an intermediate accuracy between a light wave interferometer and a magnetic scale.

Conventionally, this kind of device is generally configured as shown in FIG. 4 or FIG. 5, and in FIG. 4, 1 is a diffraction grating, 2 is a light source for emitting monochromatic light such as laser light, 3 ,Four
Is a reflecting mirror that is placed on the opposite side of the light source 2 across the diffraction grating 1, and 5 is a detector that is placed on the light source 2 side to read the interference light. The light ray L emitted from the light source 2 is transmitted and diffracted by the diffraction grating 1. When light L ₁ is an n-th order diffracted light diffracted by the diffraction grating 1, the light beam L ₁ the pitch of the diffraction grating p, a small displacement of the diffraction grating 1 as [Delta] x 2 [pi
-It contains the phase information of Δxn / p. On the other hand, the light ray L ₂ that has directly transmitted through the diffraction grating 1 does not include phase information. The light rays L ₁ and L ₂ are reflected by the reflecting mirrors 3 and 4, respectively, travel backward, enter the diffraction grating 1 again, and are diffracted and transmitted. The transmitted light of the light ray L ₁ and the −n-th order diffracted light of the light ray L ₂ are spatially selected, interfered with each other, and enter the detector 5. At this time, the -nth-order diffracted light of the ray L ₂ is -2π · Δx ·
Phase information of n / p is included, and therefore,
Since the phase information of 2π · Δx · 2n / p is included, assuming that the diffraction grating 1 and other optical systems such as the light source 2 and the reflecting mirrors 3 and 4 move relatively, the diffraction gratings 1 and 1 The change in the intensity of the interference light due to the movement of the period is 2n periods. The detection resolution is p / 2n.

The device shown in FIG. 5 has a light source 2 and a transmission type diffraction grating 1.
The beam splitter 6 is placed between the two
3, 4 are arranged below the diffraction grating 1 symmetrically with respect to the diffraction grating 1 at the same angle. The detector 5 is provided on the reflection side of the beam splitter 6. Accordingly, the light ray L emitted from the light source 2 is transmitted through the beam splitter 6 and is incident on the diffraction grating 1 which can move with respect to another optical system. This diffraction grating 1
The nth-order diffracted lights with different signs are formed by, and these are spatially selected and are incident on the reflecting mirrors 3 and 4 as the light rays L ₁ and L _{2, and} are reflected by these reflecting mirrors 3 and 4 so as to go backward. Then, the light enters the diffraction grating 1 again. + N of the light that has become the + nth order in the first diffraction
The second-order diffracted light and the -n-th-order diffracted light of the -nth-order diffracted light in the first diffraction are spatially selected. By doing so, the traveling directions of these two light rays L ₁ and L ₂ coincide with each other, and they travel toward the direction of the light source 2 while interfering with each other, and are reflected by the beam splitter 6 and incident on the detector 5. Become. Therefore, when the diffraction grating 1 is moved twice with respect to another optical system by being diffracted twice by the diffraction grating 1, the interference light incident on the detector 5 changes its intensity by 4n cycles. . The detection resolution is p / 4n, which is twice that of the example in FIG.

FIG. 6 more specifically shows a conventional example, in which the diffraction grating 1 (8
Is a light source 2, two detectors 5a and 5b, a lens system 9, deflecting mirrors 10a and 10b, and a polarization beam splitter 7 are arranged on one side of the grid line, and other prisms 11 and 12 and a phase difference plate 13 are arranged on the other side. , 14 are placed. The light source 2 is a semiconductor light emitting element such as a light emitting diode or a semiconductor laser, and the lens system 9 is for making a light beam L emitted from the light source 2 into a substantially parallel light flux.
The relative angles of the deflecting mirrors 10a and 10b are 90 so that the incident light to the deflecting mirror 10a and the outgoing light from the deflecting mirror 10b are parallel to each other.
Set every time. Further, the phase difference plates 13 and 14 have a function of converting the linearly polarized light from the light source 2 into right-handed and left-handed circularly polarized light when re-incident on the diffraction grating 1.

Accordingly, the light beam L emitted from the light source 2 is collimated by the lens system 9 and is incident on the point A of the diffraction grating 1 by the polarizing mirror 10a. Then, the light beam is diffracted by the diffraction grating 1.
As L ₁ and L ₂ , they enter the roof prisms 11 and 12 via the phase difference plates 13 and 14, respectively. Rays L ₁ and L ₂ are roof prisms 11 and ₁ .
2 is reflected in the direction parallel to the incident direction, and is made into circularly polarized light to the right and to the left by the phase difference plates 13 and 14, and is reflected by the point A of the diffraction grating 1.
Is again diffracted at a different point B in the X direction and further enters the polarized beam splitter 7 via the deflecting mirror 10b.
Light rays L ₁ and L ₂ having right-handed and left-handed circularly polarized light incident on the polarized beam splitter 7 are transmitted or reflected by the polarized beam splitter 7. The transmitted light and the reflected light are each linearly polarized light and interfere with each other to form a detector 5
It will be incident on a and 5b.

Since the detectors 5a and 5b detect the orthogonal components of two circularly polarized lights as interference intensity, outputs R and S of the detectors 5a and 5b when the diffraction grating 1 moves are shown in FIGS. 2 (a) and (b). ) Has a phase difference of 90 degrees. These two signals R and S are duplicated on the basis of a constant level as shown in (c) and (d) of the same figure, and pulses are generated at the rising and falling timings thereof as shown in (e) of the figure. The amount of movement of the diffraction grating 1 can be measured by measuring the number. Also, in the measurement, considering the moving direction of the diffraction grating 1,
It may be determined whether to add or subtract. In this case, the movement of the diffraction grating 1 for one cycle causes the output of the interference fringes to move for 4n cycles, and 16n pulses are obtained by counting the pulses from the output.

[Problems to be solved by the invention]

By the way, in the optical arrangement of FIG. 4, in order to store the optical system in a small space, it is necessary to make the angles of the light rays L ₁ and L ₂ with respect to the diffraction grating 1 equal. Even when the relative position with respect to the diffraction grating 1 moves in the Y direction perpendicular to the surface of the diffraction grating 1, phase information corresponding to the amount of movement is included in the diffracted light, and the diffraction grating 1 is arranged in the array direction, that is, Since the intensity of the interference light changes similarly to the case of moving in the X direction, there is a problem that the measurement accuracy deteriorates. Further, when the light ray L is vertically incident as shown in FIGS. 5 and 6, the above-mentioned problem does not occur, but since the intensity change of the interference light is detected, it is detected by the change of the light amount, the change of the diffraction efficiency, or the like. Accuracy deteriorates. In order to correct these fluctuations, it is necessary to have a processing system such as monitoring the light intensity of the laser light and feeding back to the detection signal processing system, which complicates the device, while the detection signal contains a noise component. Therefore, there is a drawback that the fluctuation of light intensity cannot be completely removed. In addition, since the S / N ratio of the detection signal greatly affects the detection accuracy, there is a limit to the pulse conversion of the detection signal that is performed to improve the detection resolution.Therefore, the detection resolution also depends on the number of diffraction grating pitches. The limit is about 1/10, and it is difficult to obtain a detection resolution higher than this. Also, when applied to a rotary encoder, etc., it is necessary to form a diffraction grating on the circumference, and it is possible to make the grating pitch fine in order to improve the detection resolution of the rotation angle, but a mechanical ruling engine, Since there is a limit to the formation of grid lines by photolithography, electron beam lithography, etc., it is possible to increase the diameter of the circle to lengthen the circumference and increase the number of grid lines, but the size of the device itself will increase. There is a problem. Further, in the device such as the rotary encoder, the change in the intensity of the diffracted light caused by the rotation of the disc-shaped diffraction grating is detected and converted into a pulse signal, which is used as a detector or a pulse counting device. Since there is a limit to the frequency response speed of the electronic circuit used, there is a problem that the rotary encoder cannot be operated at high speed.

Therefore, the present invention solves the problems as described above, uses a diffraction grating, and applies an optical heterodyne interferometry method using monochromatic light of two wavelengths to a light source, instead of the intensity signal of the diffracted light. An object of the present invention is to provide a moving amount measuring method and a moving amount measuring device therefor, which are faster, more stable, and have higher resolution than conventional ones by detecting a phase difference signal, and are small in size. .

[Means for solving problems]

The present invention has been made to achieve the above object,
In the movement amount measuring method of the first invention, a monochromatic light beam having two wavelengths slightly different from each other is moved relative to the first diffraction grating provided on the first object and the first object. Is made incident on a second diffraction grating provided on a second object, and diffracted light of two wavelengths generated from the first and second diffraction gratings is re-traveled by an optical system that reverses the forward path. Two wavelengths of slightly different frequencies generated by being incident on the first and second diffraction gratings and diffracted twice by the first and second diffraction gratings are optically heterodyne interference. Then, the first beat signal is detected from the optical heterodyne interference light generated from the first diffraction grating, and the second beat signal is detected from the optical heterodyne interference light generated from the second diffraction grating. First
By counting the phase difference between the beat signal and the second beat signal, and the periodic pulse signal having the phase generated from the phase difference signal, the second diffraction on the first object including the first diffraction grating. The moving distance of the second object formed of a grid is measured.

Further, the movement amount measuring device of the second invention is provided on the first diffraction grating provided on the first object and on the second object,
A second diffraction grating movable relative to the first diffraction grating, a light source for generating monochromatic light of two wavelengths having frequencies slightly different from each other, and a monochromatic light of two wavelengths emitted from the light source. Is incident on the first and second diffraction gratings from directions having a predetermined angle, and the outward path of the diffracted light of two wavelengths generated from the first and second diffraction gratings is reversed. Then, the reflected light adjusting means for making the light incident on the first and second diffraction gratings again and the diffracted light of two wavelengths generated by being diffracted twice by the first and second diffraction gratings are respectively combined, First optical composition detection means for generating a first optical heterodyne interference beat signal from the first diffraction grating, and second optical composition detection means for generating a second optical heterodyne interference beat signal from the second diffraction grating. And the first and Calculating a phase difference signal from the first beat signal and the second beat signal respectively generated by the photosynthesis detecting means, and generating and calculating a phase periodic pulse signal from the phase difference signal. For a first object consisting of the first diffraction grating,
And a signal processing device for converting the amount of movement of the second object composed of the second diffraction grating.

[Action]

The present invention calculates the movement amount of the diffraction grating, that is, the movement amount of the object,
The phase change of the beat signal is continuously detected. Then, the phase of the beat signal is not affected by the intensity fluctuation of the diffracted light, and accordingly, in the present invention, a detection error may occur due to the intensity change of the light source, the diffraction efficiency of the diffraction grating, or the like. Absent. Furthermore, in the detection optical system for the two beat signals obtained by the optical heterodyne interference, the two-wavelength laser beam is used until the two-wavelength laser beams separated by the polarization beam splitter are combined again by the polarization beam splitter. Since the optical path systems of the optical heterodyne interference lights from the two diffraction gratings generated respectively are almost the same, a small vibration of the optical system element,
The effects of disturbances such as atmospheric pressure and temperature cancel each other out at the stage of detecting the phase difference, and a stable phase difference signal is obtained. Further, in the present invention, the detection resolution of the movement amount is determined by the detection accuracy of the phase difference, and by increasing the detection accuracy of the phase difference, the pitch of the diffraction grating or the number of the gratings is not changed. The detection resolution of the movement amount of is easily increased.

〔Example〕

Hereinafter, the present invention will be described in detail based on embodiments shown in the drawings.

FIG. 1 shows a first embodiment of the movement amount measuring device according to the present invention. The same reference numerals as in FIGS. 4 to 6 denote the same members.

In FIG. 1, 1a is a first diffraction grating fixed or integrally formed on a first object (not shown),
1b is a second diffraction grating 3a, 3b, 3c, which can be moved relative to the first diffraction grating fixed or integrally formed on a second object (not shown). 3d, 3e, 3f are reflectors, 5a, 5b are detectors, 7 is a polarized beam splitter, 8a,
8b is a lattice line, 15 is a dual wavelength orthogonal polarization laser light source, 16a, 16
b is a polarizing plate, 17a and 17b are condenser lenses, 18 is a quarter-wave plate, 19
Is a cylindrical lens, and 20 is a triangular reflection mirror.

In the device of the first embodiment, the laser light L emitted from the two-wavelength orthogonally polarized laser light source 15 has two diffraction gratings 1a and 1a.
In order to irradiate b uniformly, the beam shape is changed into an elliptical shape by the cylindrical lens 19 and is incident on the polarized beam splitter 7. The polarized beam splitter 7 separates the p-polarized light having a horizontal polarization direction (frequency is f ₁ ) and the s-polarized light having a vertical polarization direction (frequency is f ₂ ) into the reflecting mirrors 3a and 3b, respectively. And laser light L ₁ , via 3c
As L ₂ , in the first diffraction grating 1a and the second diffraction grating 1b,
Bilateral symmetry with respect to the normal direction (Y direction) perpendicular to the diffraction grating surface enters from the direction of the nth diffraction angle. This diffraction grating
The two n-order reflected diffracted lights of the laser light L _{1 and} the two n-order reflected diffracted lights of the laser light L ₂ by 1a and 1b are directed in the normal direction perpendicular to the diffraction grating surface of the diffraction gratings 1a and 1b. Diffracted lights of two wavelengths emitted from the respective diffraction gratings 1a and 1b are optically combined, and combined into two laser lights, which are then incident on the reflecting mirror 3d via the 1/4 wavelength plate 18.

Here, the two laser beams L ₁ and L ₂ are respectively reflected by the reflecting mirror 3d so as to go backward in the forward direction, and again the diffraction gratings 1a and 1
It is incident on b from the direction normal to the diffraction grating surface. Again, the ± nth-order diffracted lights of the laser light that have entered the diffraction gratings 1a and 1b enter the polarization beam splitter 7 via the reflection mirrors 3a and 3b and via the reflection mirror 3c, respectively. Therefore,
Since the diffracted light of the p-polarized laser light L ₁ passes through the quarter-wave plate 18 twice to rotate the polarization plane by 90 degrees, and becomes s-polarized light and enters the polarization beam splitter 7, It is reflected 90 degrees by the beam splitter 7. On the contrary, the diffracted light of the s-polarized laser light L ₂ has its polarization plane rotated by 90 degrees by passing through the quarter-wave plate 18 twice, and becomes the p-polarized beam splitter. Since it is incident on 7, it passes through the polarized beam splitter 7. That is, the laser beam L ₁ and L ₂ transmitted diffracted light diffracted twice by these diffraction gratings 1 a and 1 b are optically combined by the polarization beam splitter 7. The combined circuit light from the diffraction grating 1a is extracted through the triangular reflection mirror 20 and the reflection mirror 3e, the extracted laser light is condensed by the condensing lens 17a, and optical heterodyne interference is performed by using the polarizing plate 16a. The first beat signal is detected by the detector 5a. On the other hand, the synthetic diffracted light from the diffraction grating 1b is extracted via the triangular reflection mirror 20 and the reflection mirror 3f,
The extracted laser light is condensed by the condenser lens 17b,
The optical heterodyne interference is caused by using the polarizing plate 16b, and the detector 5b
Detected as the second beat signal.

Therefore, by detecting the phase difference Δφ between the first beat signal detected by the detector 5a and the second beat signal detected by the detector 5b, the first object formed of the first diffraction grating 1a is detected. It is possible to measure the relative movement amount Δx of the second object composed of the second diffraction grating 1b.

Here, for example, the grating pitch of the diffraction gratings 1a and 1b is P, the wavelengths of the laser beams of frequencies f ₁ and f ₂ are λ ₁ and λ ₂ , respectively, and the pitch direction perpendicular to the grating line of the diffraction grating 1b with respect to the diffraction grating 1a. Considering the case of detecting the optical heterodyne interference light of the n-th order diffracted light with the movement amount in the (X direction) being Δx,
The change amount of the optical path length of the laser light L ₁ which is one of the optical heterodyne interference lights detected by the detector 5b with respect to the movement amount Δx is 2 × Δ because it is diffracted twice by the diffraction grating 1b.
It becomes longer by x · sin θn ₁ . On the contrary, the amount of change in the optical path length of the other laser light L ₂ of the optical heterodyne interference light is similarly shortened by 2 · Δx · sin θn ₂ . here,
θn ₁ and θn ₂ are nth-order diffraction angles of wavelengths λ ₁ and λ ₂ , respectively, and have a relationship of sin θn ₁ = n · λ ₁ / P (1) sin θn ₂ = n · λ ₂ / P (2).

Therefore, the first diffraction grating 1a composed of the first object is fixed as the reference diffraction grating, and the first beat signal obtained from the first diffraction grating in which the optical path length does not change is used as the reference beat signal, and the second beat signal is used as the second beat signal. When the phase difference Δφ with the second beat signal obtained from the diffraction grating 1b is calculated, Δφ = 2π · 2 · Δx · sin θn ₁ / λ ₁ − (− 2π · 2 · Δx · sin θn ₂ / λ ₂ ) = 4π ・ Δx ・ sin θn ₁ / λ ₁ + 4π ・ Δx ・ sin θn ₂ / λ ₂ ) (3) Then, substituting equations (1) and (2) in (3) below, Δφ = 8π ・ n ・ Δx / P = 2π ・ Δx / (P / (4n))
(4) Therefore, there is a linear relationship between the phase difference Δφ and the relative movement amount Δx of the diffraction grating 1b with respect to the diffraction grating 1a, and the phase difference Δφ is P / (4n) with respect to the relative movement amount Δx of the diffraction grating 1b. Will change as the cycle.

FIG. 2 shows a more specific second embodiment of the movement amount measuring device according to the present invention. In the figure, 3a, 3b,
3c, 3d, 3e, 3f and 3g are reflecting mirrors, 18a and 18b are quarter-wave plates, and 21 is a signal processing unit.

In the device of the second embodiment, the laser light L emitted from the two-wavelength orthogonal polarization laser light source 15 has two diffraction gratings 1a and 1a.
In order to uniformly irradiate from b, the beam shape is changed into an elliptical shape by the cylindrical lens 19 and is incident on the polarized beam splitter 7. The polarized beam splitter 7 separates the p-polarized light having a horizontal polarization direction (frequency is f ₁ ) and the s-polarized light having a vertical polarization direction (frequency is f ₂ ) into the reflecting mirrors 3a and 3b, respectively. , And 3c through laser light L
_{As 1} and L ₂ , a first diffraction grating 1a provided on a first object (not shown) and a second object (Fig. The light is incident on the second diffraction grating 1b provided on the diffraction grating 1b from above in a direction of an nth-order diffraction angle that is bilaterally symmetric with respect to a normal direction (Y direction) perpendicular to the diffraction grating surface. By the diffraction gratings 1a and 1b, two n-order transmitted diffracted lights of the laser light L ₁ and two n-orders of the laser light L ₂ are transmitted.
The transmitted diffracted light of the order is emitted respectively in the normal direction perpendicular to the diffraction grating surface of each diffraction grating 1a, 1b, and the two transmitted diffracted light from the diffraction grating 1a, 1b by the laser light L ₁ and the laser light L _{The two} transmitted diffracted lights from the diffraction gratings 1a and 1b by 2 are
The light enters the reflecting mirrors 3e and 3d via the quarter-wave plates 18a and 18b, respectively.

Here, these four transmitted diffracted lights are reflected by the reflecting mirrors 3b and 3e so as to respectively go backward in the forward path, and again the diffraction grating 1
The light perpendicular to the diffraction grating surface is incident on a and 1b from the normal direction. Again, the ± n-order transmitted diffracted light of the diffracted light that has entered the diffraction gratings 1a and 1b enters the polarized beam splitter 7 via the reflection mirrors 3a and 3b and via the reflection mirror 3c, respectively. Therefore, the transmitted diffracted light of the p-polarized laser light L ₁ has its polarization plane rotated by 90 ° by passing through the quarter-wave plate 18b twice, and is converted into s-polarized light by the polarized beam splitter 7. Since it is incident, it is reflected by 90 degrees by the polarized beam splitter 7. On the contrary, the transmitted diffracted light of the s-polarized laser light L ₂ has a polarization plane by passing through the quarter-wave plate 18a twice.
Polarized beam splitter 7 rotated 90 degrees and converted to p-polarized light
Is incident on the polarized beam splitter 7 and is transmitted through the polarized beam splitter 7. That is, the four transmitted diffracted lights of the laser lights L ₁ and L ₂ diffracted twice by the diffraction gratings 1 a and 1 b are optically combined by the polarization beam splitter 7. Diffraction grating 1a
The synthetic diffracted light from is taken out through the triangular reflecting mirror 20 and the reflecting mirror 3g, the taken-out laser light is condensed by the condenser lens 17a, and optical heterodyne interference is caused by using the polarizing plate 16a, and the detector 5a. Detected by the above, and input to the signal processing unit 21 as the first beat signal. On the other hand, the synthetic diffracted light from the diffraction grating 1b is extracted via the triangular reflection mirror 20 and the reflection mirror 3f, the extracted laser light is condensed by the condenser lens 17b, and optical heterodyne interference is performed by using the polarizing plate 16b. Then, it is detected by the detector 5b and input to the signal processing unit 21 as a second beat signal.

Therefore, in the signal processing unit 21, by detecting the phase difference Δφ between the first beat signal detected by the detector 5a and the second beat signal detected by the detector 5b, the first diffraction grating 1a is detected. It is possible to measure the movement amount Δx of the second diffraction grating 1b that is relatively movable. When the optical heterodyne interference beat signal of the n-th order diffracted light is used, the relationship between the phase difference Δφ and the relative movement amount Δx of the diffraction grating 1b is represented by the above formula (4) as in the first embodiment.

FIG. 3 (a) is a diagram showing a specific example of the phase difference signal Δφ, and the phase difference signal Δφ is the movement amount Δx = −P / of the diffraction grating 1b.
(8n) to + P / (8n) -π (-180 degrees) to + π
It shows linearity in the range of (+180 degrees), and this
Repeat with n). With respect to the phase difference signal of FIG. 9A, for example, a pulse is output at a timing at which the phase difference is changed from +180 degrees to −180 degrees, or vice versa, as shown in FIG. The amount of movement of the diffraction grating 1b can be measured by generating and counting the number. The detection resolution at this time is P / (4n). In this case, since the moving direction of the diffraction grating 1b corresponds to the increasing / decreasing direction of the phase difference value, it can be easily determined. Good.

Further, the phase difference signal Δφ is different from the intensity signal of the diffracted light, and the intensity fluctuation of the light source, the diffraction efficiency of the diffraction grating, the minute vibration of the optical element of the optical path system in which the laser light travels, the laser light traveling atmosphere The signal is almost unaffected by disturbances such as atmospheric pressure and temperature, and is a signal proportional only to the movement amount Δx of the diffraction grating 1b, and a stable signal can be obtained. Therefore, the phase difference detection resolution of about 1 degree can be easily achieved by the phase difference signal detection processing system including an ordinary electronic circuit. Therefore, as shown in FIG.
As the moving amount Δx = −P / (8n) to + P / (8n)
It can be divided into 360. That is, the movement amount Δx of the diffraction grating 1b can be detected with the detection resolution P / (360 · 4n). further,
The value of the division number N can be easily set by the phase difference signal detection processing system, and has a feature that the movement amount Δx of the diffraction grating 1b can be detected with an arbitrary detection resolution P / (N · 4n). When this is applied to a rotary encoder, for example, a rotary encoder that is easily compact and has a highly accurate rotational displacement detection resolution without changing the grating pitch of the diffraction grating formed on the disk or the number of gratings Is shown to be feasible. Furthermore, by appropriately setting the value of N, it is possible to use a diffraction grating with a large grating pitch without impairing the detection resolution, and therefore it is possible to increase the response rotation speed of the rotary encoder.

As described above, the movement amount of the diffraction grating 1b is set to P / (4n) by the stroke corresponding to the number of diffraction gratings 1b.
Can be detected at high speed and roughly by the pulse signal of
Phase difference signals can be used to detect finely between (4n) pulse signals with a resolution of P / (4n).

In the first and second embodiments, the two-wavelength orthogonal polarization laser light source 15 is used as the two-wavelength monochromatic light source.
However, the same effect can be obtained by using light generated by using an acoustooptic device such as a Bragg cell as the monochromatic light of two wavelengths. In this case, by combining the acousto-optic element and the semiconductor laser, the two-wavelength monochromatic light source can be made compact. Further, by using an optical fiber such as a polarization-maintaining optical fiber for the incident optical system of the two-wavelength laser light, the movement amount detection optical system main body and the two-wavelength monochromatic light source are separated, and both are coupled by the optical fiber. By applying the technique, the movement amount detection optical system can be made more compact.

Further, an example in which the direction of the incident light to the diffraction grating 1a, 1b and the direction of the diffracted light from the diffraction grating 1a, 1b are included in the XY plane perpendicular to the diffraction grating surface has been described. Direction of the incident light, and as the direction of the diffracted light from the diffraction grating, oblique incidence not included in the XY plane perpendicular to the diffraction grating surface,
Also, the same effect can be obtained by optically combining two obliquely emitted diffracted lights and detecting the optical heterodyne interference beat signal.

Further, as the diffraction grating 1a, 1b in the present invention, any of an absorption type diffraction grating and a phase type diffraction grating may be used, and not limited to a binary diffraction grating, a sinusoidal diffraction grating, a phrase diffraction grating, etc. It is possible to use a diffraction grating, and it is also possible to use other reflective diffraction gratings of transmission type.

Furthermore, in the first and second embodiments described above, the method of separating the laser light L of two wavelengths by the polarization beam splitter 7 in advance and making them incident on the two diffraction gratings 1a and 1b, respectively, is described. The laser light L from the two-wavelength orthogonal polarization laser light source 15 is directly reflected by the two diffraction gratings 1a, 1
When incident on b and generate optical heterodyne interference light from diffracted light, for example, only laser light of a desired wavelength from diffracted light of two same orders having different signs, for example, polarization beam splitter 7, polarization plates 16a, 16b, etc. The same effect can be obtained by taking out the respective signals and detecting the beat signal by causing optical heterodyne interference.

〔The invention's effect〕

As described in detail above, according to the movement amount measuring method and the measuring apparatus thereof according to the present invention, monochromatic light beams of two wavelengths having slightly different frequencies are respectively incident on two diffraction gratings, and the monochromatic light beams of the two wavelengths are respectively incident. Since the optical heterodyne interference beat is detected by optically combining the diffracted light of two wavelengths from each diffraction grating generated by two times of diffraction, the phase difference signal is detected from the phase change of the detected diffracted light beat signal. The moving amount (that is, the moving amount of the object) can be measured by performing the calculation processing, and further generating the periodic pulse signal of the phase from the phase difference signal and performing the calculation processing. Moreover, even when the diffracted light intensity fluctuates due to fluctuations in the intensity of the light source, fluctuations in the diffraction efficiency of the diffraction grating, etc., the amplitude of the diffracted light beat signal only changes and there is no phase change in the beat signal. This has no influence, and accordingly, the movement amount can be detected with high accuracy.
Further, since the phase difference signal is highly stable, the phase difference can be detected with an accuracy of, for example, 1 ° or less, and high resolution can be obtained.

Furthermore, by arranging two diffraction gratings so that they are irradiated by the same beam spot of incident light, and detecting the phase difference between the two optical heterodyne interference beat signals generated by these diffraction gratings respectively, The influence of disturbance such as atmospheric pressure, temperature, or minute vibration of the optical element in the optical path system in which light travels is canceled, and the relative displacement amount between both diffraction gratings can be detected with high stability.

Furthermore, when it is applied to a rotary encoder or the like, the high detection resolution of phase difference detection is used to reduce the number of diffraction gratings arranged on the disk without degrading the detection resolution, or to downsize the device, or Can increase the pitch of the diffraction grating to speed up rotational movement detection.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a first embodiment of a movement amount measuring method according to the present invention and its measurement position, FIG. 2 is a configuration diagram showing a second embodiment of the present invention, FIG. 3 (a), (B) and (c) are time charts of signals obtained from the embodiment of the present invention, and FIGS. 4, 5, and 6 are configuration diagrams showing an example of a conventional movement amount measuring method, respectively. Figures (a)-(e) are the sixth
It is a time chart of the signal obtained from the measuring method of the figure. 1,1a, 1b …… Diffraction grating, 2 …… Light source, 3,3a to 3g, 4 …… Reflector, 5,5a, 5b …… Detector, 6 …… Beam splitter, 7 …… Polarized beam split Zutter, 8,8a, 8b …… 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 ... Polarizing plate, 17a, 17b ... Condensing lens, 18a, 18b ... 1/4 wavelength plate, 19 ... Cylindrical lens, 20
...... Triangular reflection mirror, 21 …… Signal processing unit.

Claims (2)

(57) [Claims] 1. A diffraction grating is used as a length measuring standard, and diffracted light produced by making monochromatic light incident on this diffraction grating interferes with each other.
In a length measuring device for obtaining a relative moving distance of a diffraction grating with respect to another optical system, monochromatic light having two wavelengths having slightly different frequencies is used as a light source, and the monochromatic light is separated into two polarized lights by a polarization beam splitter. A first diffraction grating provided on the first object with the two polarized lights at a desired angle via an incident angle adjusting means, and a second object movable relative to the first object Let the second diffractive grating provided above enter and let the diffracted light of two wavelengths generated from the first and second diffractive gratings travel backward through the quarter wave plate once. Diffracted by passing through the quarter-wave plate again by the optical system and again entering the first and second diffraction gratings and diffracted twice by the first and second diffraction gratings. Light is allowed to enter the polarization beam splitter through the incident angle adjusting means. By the diffraction light each other of 2 different wavelengths frequencies slightly from each other by an optical heterodyne interference, and detects the first beat signal from the optical heterodyne interference light generated from the first diffraction light, the second
The second beat signal is detected from the optical heterodyne interference light generated from the diffracted light, and the phase difference between the first beat signal and the second beat signal, and the periodic pulse signal of the phase generated from the phase difference signal are detected. A movement amount measuring method characterized by measuring a moving distance of a second object made of the second diffraction grating with respect to a first object made of the first diffraction grating by counting. 2. A first diffraction grating provided on a first object, and a second diffraction grating provided on a second object and movable relative to the first diffraction grating. And a light source for generating monochromatic light of two wavelengths whose frequencies are slightly different from each other, and a polarization beam splitter and an incident angle adjusting means are provided between the light source and the first and second diffraction gratings.
The incident angle adjusting means sets an incident angle of light that is incident on the first and second diffraction gratings and the polarization beam splitter, and is generated from the first and second diffraction gratings.
Between the reflected light adjusting means for reversing the outward path of the diffracted light of the wavelength and for making it enter the first and second diffraction gratings again, and between the first and second diffraction gratings and the reflected light adjusting means. A 1/4 wavelength plate is provided so that the diffracted light passes twice, and the light is generated by being diffracted twice by the first and second diffraction gratings.
First light combining / detecting means for generating diffracted light having a wavelength into the polarization beam splitter via the incident angle adjusting means and combining them to generate a first optical heterodyne interference beat signal from the first diffraction grating. A second photosynthesis detecting means for generating a second optical heterodyne interference beat signal from the second diffraction grating, and a first beat signal generated by each of the first and second photosynthetic detecting means, And a second beat signal, a phase difference signal is calculated, and a phase periodic pulse signal is further generated from the phase difference signal to perform a calculation process, so that a first object including the first diffraction grating is obtained. A moving amount measuring device, comprising: a signal processing device for converting a moving distance of a second object composed of the second diffraction grating.