JP2002350191A - Optical displacement measuring instrument - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical displacement measuring instrument that uses coherent parallel light with fewer optical components and achieves resolution being equal to or higher than the period of a diffraction lattice for optical displacement measurement. SOLUTION: The optical displacement measuring instrument comprises a light source optical system 1A that has a light source 11 for irradiating coherent light L11a, and a lens 12 for forming parallel coherent light L11b from the radiation light L11a of the light source 11, a transmission type diffraction grating 21 for displacement measurement that moves in parallel with grating vector to the parallel coherent light L11b being radiated from the light source optical system 1A and diffracts the coherent light L11b, a light reception means 3 for receiving interference light DL201 being formed by the interference of diffraction light DL100 where the coherent light L11b is diffracted by the diffraction grating 21 for position measurement, and a position detection means 4 for detecting the relative movement position of the diffraction grating 21 for displacement measurement from the output signal of the light reception means 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical displacement measuring device for detecting a relative moving position of a movable part such as a machine tool or a semiconductor manufacturing device.

[0002]

2. Description of the Related Art Hitherto, as a device for detecting a relative position of a movable portion such as a machine tool or a semiconductor manufacturing device, an optical displacement measuring device using a grating partially transmitting light has been known. For example, the configuration shown in FIG. In FIG. 19, the optical displacement measuring device according to the prior art is configured such that the coherent light L11 transmitted through the displacement measuring movable grating 23 is
After passing through the fixed grating 33 having the same period as that of the light, the light is received by the light receiving element 32 and converted into an electric signal. That is, the relative displacement of the movable grating 23 is measured using the zero-order transmitted light. Therefore, the period of the intensity of the light transmitted through the movable grating 23 is the same as the pattern of the movable grating 23. That is, the optical resolution is the same as the resolution of the movable grating 23.

FIGS. 20 and 21 show another conventional optical displacement measuring apparatus. In FIG. 20, the optical system of the optical displacement measuring device includes a light emitting unit that forms a light source.
72, first imaging means 74, a diffraction grating 71 for measuring displacement,
The second imaging unit 75 and the light receiving unit 73 are provided. In such a configuration, the coherent light La emitted from the light emitting means 72 is condensed by the first imaging means 74, and
An image is formed (condensed) on the top. Of the diffracted light transmitted through the diffraction grating 71, the diffracted light of a predetermined order is condensed and received as diffracted light Lb on the light receiving means 73 via the second imaging means 75.

In FIG. 21, an optical displacement measuring device using this optical system is provided between the first image forming means 74 and the diffraction grating 71 and the second image forming means 75 of the optical system described in FIG. And half-mirrors 76a, 76b and reflectors (77a to 77d) disposed between the diffraction grating 71 and a position detection unit that processes a detection signal received by the light receiving unit 73 to measure a relative displacement of the movable grating 23. And a unit 78.

In such a configuration, the coherent light La from the light emitting means 72 is condensed by the first imaging means 74, and
At 76a, the light is branched into coherent lights La1 and La2, and one of the coherent lights La
1 is reflected by the reflector 77a, and the other coherent light La2 is reflected by the reflector 77b and is collected at a predetermined position q on the diffraction grating 71. The diffracted light Lb1 of the coherent light La1 at the position q is reflected by the reflector 77d, and the diffracted light Lb2 of the coherent light La2 at the position q is reflected by the reflector 77c to form a half mirror 76b.
And diffracted light Lb on the light receiving means 73 by the second imaging means 75.
The image is formed as

In such an optical displacement measuring apparatus, an interference signal is detected by causing two diffracted lights Lb1 and Lb2 to interfere with each other, and a phase difference between the two diffracted lights Lb1 and Lb2 is obtained from the interference signal. The moving position of. In the optical displacement measuring device described above, the diffraction grating itself expands and contracts with a change in ambient temperature, so that the measured value of the displacement has a temperature characteristic.

[0007]

In recent years, with the increase in precision of machine tools and industrial robots, an inexpensive optical displacement measuring device capable of detecting a position with high resolution has been required. . In such a conventional optical displacement measuring device, in order to optically increase the resolution,
It was necessary to reduce the period of the movable grating. On the other hand, in order to collectively manufacture a lattice pattern by a method such as transfer, it is necessary to have a minimum dimensional structure having a size equal to or larger than a certain value. When the dimensional structure is less than a certain value, it is necessary to manufacture by a method such as drawing using an electron beam drawing apparatus or the like, and there is a problem that it is more expensive than a batch manufacturing method such as transfer. .

In the method using diffracted light, coherent light is focused on a diffraction grating for measuring displacement, and the diffracted light transmitted through the diffraction grating is focused on a light receiving means. Therefore, there is a problem that optical components such as a half mirror and a reflector are required. In addition, since the diffraction grating itself expands and contracts with a change in ambient temperature, the measured value of the displacement has a temperature characteristic. As a method for preventing this, for example, a material having a small linear expansion coefficient (for example, , Quartz),
There is a method of installing a temperature sensor, monitoring the temperature, and feeding back the result to a measured value. In the former method, temperature correction cannot be performed essentially, and in the latter method, there is a problem that it is expensive because a temperature sensor needs to be installed.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to solve the above-mentioned problems and to provide a first optical system which uses coherent parallel light with a small number of optical components and has a predetermined grating period. Optical displacement that uses a displacement measurement diffraction grating to optically realize a resolution higher than the period of the first displacement measurement diffraction grating, and compensates for the effect of the expansion and contraction of the diffraction grating itself due to temperature changes at low cost. It is to provide a measuring device.

[0010]

According to the present invention, there is provided a light source comprising: a light source that emits coherent light; and an optical element that forms parallel coherent light from the light emitted from the light source. An optical system, a transmission-type first displacement measuring diffraction grating that moves in a direction parallel to the grating vector with respect to the parallel coherent light emitted from the light source optical system, and diffracts the coherent light; A light receiving unit for receiving interference light formed by the light diffracted by the first displacement measuring diffraction grating interfering with each other, and an output signal of the light receiving unit,
A first method for detecting a relative movement position of the first displacement measuring diffraction grating
And position detecting means.

With this configuration, the principle that the period of the intensity of the interference fringes generated by the interference of the diffracted lights diffracted by the first displacement measuring diffraction grating is smaller than the period of the first displacement measuring diffraction grating itself. , The resolution of the displacement measurement for detecting the relative movement position can be improved and measured. A light source optical system including a light source that emits coherent light and an optical element that forms parallel coherent light from the light emitted from the light source; and a parallel coherent light emitted from the light source optical system. A transmission-type displacement-measuring diffraction grating (hereinafter abbreviated as a reference diffraction grating) that moves in a direction parallel to a grating vector with respect to light and diffracts coherent light, and a substrate on which the reference diffraction grating is formed. And a second displacement measuring diffraction grating formed on a substrate made of a material having a different linear expansion coefficient from the substrate and having a temperature correcting diffraction grating (hereinafter abbreviated as a reference diffraction grating); A reference light receiving means for receiving a reference interference light and a reference interference light formed by diffracted lights formed by being diffracted by the diffraction grating and the reference diffraction grating, respectively; a reference light receiving means; hand In the output signal to be detected is intended to comprise the second position detecting means for detecting the temperature corrected relative movement position of the second displacement-measuring diffraction grating, a.

With this configuration, the reference light receiving means and the reference light receiving means receive the reference interference light and the reference interference light formed by diffracting the reference diffraction grating and the reference diffraction grating formed on the substrates made of materials having different linear expansion coefficients. At the second
The position detection means calculates the output signals of these light-receiving means, corrects the effect of the expansion and contraction of the diffraction grating itself due to the ambient temperature, improves the resolution of displacement measurement for detecting the relative movement position, and measures the temperature as well as temperature dependence. It is possible to measure a relative movement position with less possibility.

Further, the light receiving surface of the light receiving means can be arranged in a slit shape having an interval corresponding to an interval of interference fringes formed by interference light. With this configuration, the first and second
The relative position between the slit on the light receiving surface of the light receiving means and the interference fringe formed by the interference light is displaced by the relative movement position of the displacement measuring diffraction grating, and this displacement can be detected as a change in the detection amount of the light receiving means. .

The light source optical system divides the coherent parallel light from the light source into two parallel lights, and irradiates the split parallel lights from different positions and directions on the first and second displacement measuring diffraction grating surfaces. The optical system can be provided. With this configuration, the coherent parallel light is obliquely incident on the first and second displacement measuring diffraction grating surfaces. Therefore, the ± 1st-order diffracted light of the coherent parallel light has a larger diffraction angle as compared with the case of normal incidence. Having. Therefore, the period of the interference fringes generated by the interference of the ± 1st-order diffracted light having the large diffraction angle can be made smaller, and as a result, a higher resolution can be obtained.

An optical system for irradiating parallel light from different positions and directions on the first and second displacement measuring diffraction grating surfaces is a two-branch for diffracting coherent parallel light from a light source to generate two diffracted lights. A diffraction grating, a reflecting surface that reflects and deflects the branched diffracted light, and a light-shielding plate that shields the zero-order transmitted light in the two-branch diffraction grating can be provided. With this configuration, the 0th-order light of the coherent parallel light can be shielded by the light-shielding plate, so that the 0th-order light weakens the interference intensity of the interference fringes of the ± mth-order diffracted light and reduces the influence of reducing the contrast. Therefore, a higher resolution can be stably obtained.

The first displacement measuring diffraction grating may include a reflection type diffraction grating instead of the transmission type diffraction grating. With such a configuration, the light receiving means is provided on the same side as the light source side, and reflects and diffracts the coherent parallel light applied to the reflection type diffraction grating, and receives the interference light formed by the interference of the diffracted lights with each other. can do.

The substrates of the reference diffraction grating and the reference diffraction grating may be arranged in parallel, and one end of the reference diffraction grating and the reference diffraction grating may be fixed to a third common member. In addition, the grating periods of the reference diffraction grating and the reference diffraction grating can be configured to match at a predetermined reference temperature.

Further, the predetermined reference temperature can be set outside the allowable operating temperature range of the optical displacement measuring device. With this configuration, the scales of the two diffraction gratings, the reference diffraction grating and the reference diffraction grating, are matched at the reference temperature, and the position of the signal light due to the shift of the scales of the two diffraction gratings caused by expansion and contraction of the substrate due to a temperature change. The phase difference can be corrected by detecting the temperature of the diffraction grating substrate and feeding the result back to the displacement measurement value.

In particular, the reference diffraction grating and the reference diffraction grating are provided with a measuring diffraction grating portion for measuring the amount of displacement and a correction diffraction grating portion for temperature correction, and are provided in both diffraction grating portions in advance. At intervals, the interference fringes formed by the interference light are arranged at the measurement position for measuring the amount of displacement and the correction position for performing the temperature correction, and a light-receiving slit-like grating and a light-receiving element are arranged, so that the interference fringes can be finely divided. A reference value for measuring the amount of displacement by counting up a photodetection signal periodically repeated at a predetermined interval can be corrected at a predetermined interval in both diffraction grating portions.

In the reference diffraction grating, a correction position grating can be provided at a predetermined position alongside the reference diffraction grating row. With this configuration, the light reception signals of the reference diffraction grating and the reference diffraction grating are read at the timing position at which the optical signal from the correction position grating is read. As a result, the amount of displacement can be measured and its temperature can be corrected at a fixed position that is a fixed distance away from the position where one end of the reference diffraction grating and the reference diffraction grating are fixed to the third common member.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a diagram showing a main part of an optical displacement measuring device according to a first embodiment of the present invention, FIG. 2 is a diagram showing a main part of an optical displacement measuring device according to a second embodiment, and FIG. FIG. 4 is a main part configuration diagram of an optical displacement measuring device according to a third embodiment, and FIG.
FIG. 5 is a front view of a slit, FIG. 6 is an explanatory view for explaining generation of diffracted light by a diffraction grating and formation of interference fringes, and FIG. 7 is diffraction by a diffraction grating. FIG. 8 is an explanatory view for explaining generation of light, FIG. 8 is an explanatory view of an area where interference fringes of ± 1st-order diffracted light are formed, FIG. 9 is an explanatory view of an area where interference fringes due to oblique incident light are formed, and FIG. Is a main part configuration diagram of an optical displacement measuring apparatus according to a fifth embodiment having a temperature correcting means. FIGS. 11 to 17 relate to the fifth embodiment, and FIG. 11 has a reference diffraction grating and a reference diffraction grating. FIG. 12 is a front view of a slit and a diagram of detection characteristics of a received signal, FIG. 13 is a diagram of an increase / decrease characteristic of a received signal due to movement of the second displacement measurement diffraction grating, FIG. FIG. 15 is a block diagram illustrating position signal generation, and FIG.
FIG. 16 is a partially enlarged view of the second displacement measuring diffraction grating at the temperature T = T0 and a detection characteristic diagram of the received signal. FIG. 16 is a partially enlarged view of the second displacement measuring diffraction grating and the received signal at the temperature T = T0 + ΔT. FIG. 17 is a block diagram for explaining temperature correction of a position signal, and FIG. 18 is a partially enlarged view of a second displacement measuring diffraction grating for explaining another temperature correction method. (Embodiment 1) In FIG. 1, an optical displacement measuring apparatus of the present invention comprises a light source 11 for emitting coherent light L11a,
A light source optical system 1A including an optical element for forming a coherent coherent light L11b from the emitted light L11a, for example, a lens 12,
The parallel coherent light L11b emitted from the light source optical system 1A moves in the direction parallel to the lattice vector, and the coherent light L1
The transmission type first displacement measuring diffraction grating 21 diffracting 1b and the coherent light L11b are formed by the interference between the diffracted light DL100 diffracted by the first displacement measuring diffraction grating 21 and the region DL200. A light receiving means 3 for receiving the interference light, and a first displacement measuring diffraction grating from the output signal of the light receiving means 3
And a first position detecting means 4 for detecting the relative movement position of the reference position 21.

With such a configuration, the period (W) of the intensity of the interference fringe DL201 generated by the interference between the diffracted lights DL100 diffracted by the first displacement measuring diffraction grating 21 is changed by the first displacement measuring diffraction grating 21. By utilizing the principle of becoming smaller than the period (P) of the object itself, the relative movement position can be detected, and the displacement measurement can be performed with improved resolution. Further, on the light receiving surface of the light receiving means 3, a grating having an interval corresponding to the interval w of the interference fringes DL201 formed by the interference light can be arranged in a slit shape.

With such a configuration, the relative position between the slit 31 on the light receiving surface of the light receiving means 3 and the interference fringe DL201 formed by the interference light varies depending on the relative movement position of the first and second displacement measuring diffraction gratings 21, This deviation can be detected as a change in the detection amount of the light receiving unit 3. (Embodiment 2) In FIG. 10, an optical displacement measuring apparatus according to the present invention comprises a light source 11 for emitting coherent light L11a,
A light source optical system 1A including an optical element for forming a coherent coherent light L11b from the emitted light L11a, for example, a lens 12,
The parallel coherent light L11b emitted from the light source optical system 1A moves in the direction parallel to the lattice vector, and the coherent light L1
A transmission type diffraction grating (hereinafter, abbreviated as a reference diffraction grating) 25 for diffracting 1b and a substrate 26a made of a material having a different linear expansion coefficient from the substrate 25a on which the reference diffraction grating 25 is formed. A second displacement measuring diffraction grating 2B including a formed temperature correcting diffraction grating (hereinafter, abbreviated as a reference diffraction grating) 26, and coherent light L11b are formed by the second displacement measuring diffraction grating 2B. Diffracted light DL100S, DL100R formed by being diffracted by the reference diffraction grating 25 and the reference diffraction grating 26, respectively.
Formed by the interference of each other
Reference light receiving means 3S for respectively receiving the reference interference light DL201S and reference interference light DL201R of DL200S, R, and reference light receiving means 3R
And a second position detecting means 4B for detecting, from the output signals of the light receiving means 3S and 3R, the relative movement position corrected by the second displacement measuring diffraction grating 2B.

With this configuration, the reference diffraction grating 25 formed on the substrates 25a and 26a made of materials having different linear expansion coefficients.
And reference interference light formed by diffracting the reference diffraction grating 26
DL201S and the reference interference light DL201R are received by the reference light-receiving means 3S and the reference light-receiving means 3R, and the output signals of these light-receiving means 3S, 3R are processed by the second position detecting means 4B comprising the position signal generators 58S, 58R, Diffraction grating 2 by ambient temperature (T0 + ΔT)
It is possible to improve the resolution of the displacement measurement for detecting the relative movement position by correcting the effect of expansion and contraction of the 5, 26 itself, and to measure the relative movement position with little temperature dependence.

[0025]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Before describing each embodiment of the present invention, the principle of the present invention and its practicality will be described with reference to FIGS. First, referring to FIG. 6, the principle of increasing the resolution, that is, the period w of the interference fringe DL201 between the diffracted lights (L111, L112) is set to the first displacement measuring diffraction grating 21 (hereinafter simply referred to as diffraction grating 21). The principle of becoming smaller than the period p will be described focusing on diffracted light (DL111, DL112) of a specific order (for example, ± 1st order). In FIG. 6, the diffraction grating 21 has a thin plate shape made of, for example, an optical material such as glass or plastic, and its surface has binary surface irregularities (hereinafter abbreviated as “grating”) at a constant period. Engraved with Light incident on such a diffraction grating 21 is reflected by the grating 21
Diffracts according to For example, when light having a wavelength λ is vertically incident on the diffraction grating 21 having a grating period of p, the diffraction angle θm of the diffracted lights L111 and L112 generated by diffraction is

[0026]

Equation 1 θm = sin ⁻¹ (mλ / p) (1) Here, m is an integer indicating the diffraction order. FIG. 6 shows a state in which interference fringes DL201 are generated by interference between wavefronts of two diffracted lights L111 and L112 of m = ± 1. From FIG. 6, the following two points become clear.

(1) The period w of the intensity of the interference fringe DL201 is determined by geometrical considerations.

[0028]

## EQU2 ## w = p / (2. | m |) (2) Since m is an integer, w <p always holds,
It does not depend on the wavelength λ of the incident light L11b. Furthermore, the higher the order | m | of the diffracted light to be interfered, the higher the resolution in principle.

(2) The position where the intensity of the interference fringe DL201 is generated depends on the initial phase of the coherent light source L11b and the shape of the diffraction grating 21.
Therefore, the interference fringe DL201 also moves with the movement of the diffraction grating 21 (assuming that the moving speed of the diffraction grating 21 is sufficiently smaller than the speed of light). (1), (2)
The DL 201 has a smaller period w than the diffraction grating 21 and moves parallel and simultaneously with the diffraction grating 21. In other words, it can be seen that the interference fringe DL201 generated by the diffraction grating 21 has a scale with a finer scale than the diffraction grating 21 itself.

Next, in FIG. 7 and FIG.
The diffracted light DL201 of the DL200 is overviewed, and an area D suitable for signal detection as interference light is examined. In FIG. 6, for the sake of convenience of explanation of the principle, attention has been paid to only the diffracted light of the diffraction order m = ± 1st, and these interferences have been described. By the way, the diffracted light by the diffraction grating 21 is the 0-order transmitted light, ± m-order diffracted light (m = ± 1, ±
2,...) Appear at specific angles. FIG. 7 illustrates the 0th-order transmitted light, ± 1st-order diffracted light, and ± 2nd-order diffracted light. The diffracted light for m = 0 is DL101, the diffracted light for m = + 1 is DL111, the diffracted light for m = -1 is DL112, m
= 121 diffracted light when m = -2, diffracted light when m = -2
DL122, respectively. Diffracted light of each order (DL101, D
In the region where L111, DL112, DL121, DL122,...) Overlap each other, the overlapped diffracted lights interfere with each other. FIG.
As is clear, in the region where the ± 1st-order diffracted light (DL111, DL112) causes interference, higher-order diffracted light (D
L121, DL122...) And zero-order transmitted light (DL101) also exist. These (DL121, DL122 ...) and (DL101) are ± 1st-order diffracted light (DL1
11, DL112) has the effect of reducing the interference intensity and reducing the contrast, resulting in a deterioration in resolution.

Therefore, when the interference fringes (DL200) of the ± 1st-order diffracted lights (DL111, DL112) are used, higher-order diffracted lights (DL121, DL122,. It is desirable that the influence of the above is small. This means that the intensity of the diffracted light of each order can be adjusted to some extent by changing the depth of the diffraction grating 21, but the intensity of the diffracted light other than the ± 1st order cannot be reduced to zero.

In FIG. 7, ± 1st order diffracted light (DL111, DL11
2) is included in the area of the 0th-order transmitted light (DL101), but any of the higher-order diffracted lights (DL1
There is an area DL200 that is not included in the area of 21, DL122. Therefore, this area DL200 is used as the interference signal DL201.
Is used, it is possible to eliminate the influence of the diffracted light (DL111, DL112) of the second or higher order.

Here, the size of the area DL200 is estimated. For example, in FIG. 8, a diffraction grating 21 having a grating period p = 20 μm
Coherent light L11b with wavelength λ = 0.780 μm and beam width A = 5 mm
Is incident perpendicularly. According to equation (1), θ1
= 2.235 (deg) and θ2 = 4.474 (deg). The width L and depth D of the region are respectively

[0034]

L = A · (tanθ2−tanθ1) / (tanθ2 + tanθ1) (3)

[0035]

D = D1−D2 = A · (1 / tanθ1−1 / tanθ2) / 2 (4) Therefore, in this embodiment,
L = 32.1 mm and D = 1.67 mm are calculated, and it can be confirmed that practical dimensions can be obtained.

The optical displacement measuring devices according to the first to fourth embodiments will be described below. (Embodiment 1) In FIG. 1, (A) shows a front view of the optical displacement measuring device of the first embodiment, and (B) shows a side view. The components of this optical displacement measuring device are as follows. That is, the transmission type diffraction grating 2A (2
1), a coherent light source 11 that emits coherent light L11a such as a laser beam, and a coherent light emitted from the coherent light source 11.
A lens 12 for converting L11a into parallel light, a slit 31 for partially transmitting the diffracted light DL100 from the transmission type diffraction grating 21, and a light receiving element 32 for receiving the diffracted light DL201 transmitted through the slit 31
And is configured.

With this configuration, the incident parallel interference light
L11b generates diffracted light DL100 by transmitting through the transmission diffraction grating 2A (21). The slit 31 and the light receiving element 32
It is set in an area DL200 where ± 1st-order diffracted light strongly interferes.
Since the interference fringes also move with the movement of the transmission diffraction grating 2A (21), the light amount signal received by the light receiving element 32 changes in a sine curve shape depending on the movement of the transmission diffraction grating 2A (21). . Position displacement can be detected by discriminating the output signal of the light receiving element 32 with an appropriate threshold. Further, position information can be obtained by integrating the displacements. Also, the displacement direction can be detected from the increase / decrease information of the position displacement information.

In FIG. 5, the slit 33 has the same period (w = p / (2 | m |)) as that of the received interference fringe DL201.
And A and B shifted in phase by π / 2 (= w / 4) from each other
It can be configured by providing two rows of phase slits, and can be provided on the entire surface of the light receiving element 32 instead of the slit 31. With this configuration, the light (DL201) transmitted through the slits of the respective A and B phases
A, DL201B) are received by the optical elements 32A, 32B shown by dotted lines, respectively, so that a signal having a phase shift of π / 2 from each of the A and B phases can be extracted. By processing this signal, the moving direction of the transmission diffraction grating 2A (21) can be detected. (Embodiment 2) FIG. 2A is a front view of an optical displacement measuring apparatus according to a second embodiment of the present invention, and FIG. 2B is a side view. In the second embodiment, a two-branch diffraction grating 13, a light guide plate 14, and a light shielding plate 15 are added to the configuration of the first embodiment. In this configuration, the coherent light beams L11c and L11d divided into two optical paths by the two-branch diffraction grating 13 are reflected by the reflection surface 14 formed on the side surface of the light guide plate 14.
A is reflected by A and becomes coherent light L11e, L11f, and the diffraction grating 21
The light enters obliquely at an angle of ± α from the different positions above, and after being diffracted by the transmission type diffraction grating 2A (21), overlaps and interferes. FIG. 9 shows the formation of interference fringes DL202 in the case of oblique incidence. Since the light enters the diffraction grating 21 obliquely, these ±
The first-order diffracted light (L113, L114) has a larger diffraction angle ± θ2 than in the case of normal incidence. Therefore, the period W2 of the interference fringes DL202 generated by these interferences can be reduced, and as a result, the resolution can be increased. Further, since the light shielding plate 15 functions to block noise light such as the zero-order transmitted light DL101, the contrast of the interference fringe DL202 can be increased.

As described above, in the second embodiment, as compared with the first embodiment, the period W2 of the interference fringe DL202 can be reduced and the contrast thereof can be increased. As a result, a higher resolution can be obtained. be able to. Third Embodiment In FIGS. 3 and 4, the first displacement measuring diffraction grating can be configured to include a reflection diffraction grating 22 instead of the transmission diffraction grating 21.

With this configuration, the light receiving means 3 is provided with the light source 11
The coherent parallel light L11b, (L11e, L11f) irradiated on the reflection type diffraction grating 22 is reflected and diffracted, and the interference lights DL201 and DL202 formed by the interference of the diffracted lights with each other. Can be received. FIG. 3 is a side view of an optical displacement measuring apparatus according to a third embodiment of the present invention. In FIG. 3, the optical displacement measuring apparatus according to the third embodiment is different from the optical displacement measuring apparatus according to the first embodiment in that the transmission type diffraction grating 21 is replaced with a reflection type diffraction grating 22, and a slit 31 or a slit 33 is provided.
The light receiving means 3 including the light receiving element 32 and the light receiving element 32 are arranged on the same side as the light source 11 with respect to the reflection type diffraction grating 22. The operation is the same as that of the first embodiment, but the light source 11 and the light receiving means 3 are on the same side, so that the arrangement and configuration of the electric circuit and the like are easy and the overall size can be reduced. (Embodiment 4) A side view of an optical displacement measuring apparatus according to a fourth embodiment of the present invention is shown in FIG. In FIG. 4, the optical displacement measuring apparatus according to the fourth embodiment differs from the optical displacement measuring apparatus according to the second embodiment in that the transmission type diffraction grating 21 is replaced by the reflection type diffraction grating.
Instead of the light source 11, the light receiving unit 3 including the slit 31 or the slit 33 and the light receiving element 32 is arranged on the same side as the light source 11 with respect to the reflective diffraction grating 22. The operation is the same as that of the second embodiment, but for the same reason as in the third embodiment, there is an advantage that the arrangement and configuration of the electric circuit and the like can be simplified and the overall size can be reduced. (Embodiment 5) Before describing the embodiment of the temperature characteristic correction according to the present invention, an example of the configuration of the optical displacement measuring device described in the first embodiment will be taken up for the sake of simplicity. Hereinafter, the principle of the temperature correction according to the present invention will be described. (Principle of Temperature Correction) In FIG. 10, the optical displacement measuring device including the temperature correcting means according to the present invention moves in the direction parallel to the lattice vector with respect to the parallel coherent light L11b emitted from the light source optical system 1A. The second displacement measuring diffraction grating 2B is formed on a transmission type reference diffraction grating 25 for diffracting the coherent light L11b and a substrate 26a made of a material having a different linear expansion coefficient from a substrate 25a on which the reference diffraction grating 25 is formed. Reference grating 26
And are arranged in parallel. Also, the scales of the two diffraction gratings, the reference diffraction grating 25 and the reference diffraction grating 26, are matched at a predetermined reference temperature T0,
The temperature T (= T + Δ) of the diffraction grating substrates 25a and 26a is determined by the phase difference of the signal light due to the displacement of the scale of the two diffraction gratings 25 and 26 caused by the expansion and contraction of the substrates 25a and 26a caused by the temperature change ΔT.
T) is detected, and the temperature is corrected by feeding back the result to the displacement measurement value.

The principle of the temperature correction will be described below. still,
Here, the diffraction grating for measuring the amount of displacement is the reference diffraction grating 25, and the diffraction grating for temperature correction is the reference diffraction grating.
Call it 26. For the substrate 25a of the reference diffraction grating 25 and the substrate 26a of the reference diffraction grating 26, the parameters are defined as shown in Table 1.

[0042]

[Table 1] Now, when the temperature T = T0, the reference position (for example, (C) of FIG. 11)
The distance from the plane Y shown in FIG. 2, that is, the reference position at which the substrates 25a and 26a made of materials having different linear expansion coefficients are fixed, to the target position where the displacement is measured is defined as L0. Linear expansion coefficient β
Assuming that 1, β2 is constant irrespective of the temperature (T ° C), when the temperature is T = TO + ΔT, the distance from the reference position of the target position of each diffraction grating 25,26 is

[0043]

L1 = L0 + ΔL1 = L0 (1 + β1ΔT) (5)

[0044]

L2 = L0 + ΔL2 = L0 (1 + β2ΔT) (6) Therefore, the temperature change ΔT is obtained by using the difference ΔL (= L2−L1) between the lengths of the two diffraction grating substrates 25a and 26a.

[0045]

ΔT = ΔL / ((β2−β1) · L0) (7) That is, when the reference diffraction grating substrate 25a and the reference diffraction grating substrate 26a having the same length L at the temperature T0 produce a length difference ΔL due to the temperature change ΔT, the temperature change ΔT is
It is expressed by equation (7). At this time, if the expression (7) is substituted into the expression (5), the length of the reference diffraction grating 25 becomes

[0046]

L1 = L0 · (1 + β1 · ΔL / ((β2−β1) · L0)) = L0 + β1 · ΔL / (β2−β1) (8) Equation (8) means that the temperature change of the displacement measurement amount can be corrected by measuring the difference ΔL between the lengths of the two diffraction grating substrates 25a and 26a without detecting the ambient temperature change.

That is, the temperature-corrected true distance Lc from the reference position (for example, the surface Y) at the ambient temperature (T0 + ΔT) to the position of interest at which the displacement is measured is determined by the reference diffraction for measuring the displacement. For the measured value Lm by the grid 25,

[0048]

Lc = Lm + β1ΔL / (β2−β1) (9) (Example) Next, a specific example of the present invention will be described.
First, the configuration of the embodiment will be described. In FIG. 10, the second displacement measuring diffraction grating 2B includes a reference diffraction grating 25 and a reference diffraction grating. The diffracted light DL100S from the reference diffraction grating 25 is transmitted through the slit 35, received by the light receiving elements 37a and 37b, and received signals (voltage values) V37a and V3.
Converted to 7B. Similarly, the diffracted light from the reference diffraction grating 26
After passing through the slit 36, the DL100R is received by the light receiving elements 38a and 38b, and received signals (voltage values) V38a and V38b.
Is converted to The same function can be realized by the combination of the slit 35 and the light receiving elements 37a and 37b depending on the configuration of the light receiving element array arranged in the opening shape of the slit 35. The other basic configuration, the principle of displacement measurement, and the operation are the same as those described in the first to fourth embodiments, and thus description thereof is omitted.

Next, the detailed structure of the second displacement measuring diffraction grating 2B is shown in FIG. 11A is a front view, and FIG.
11B is a side view, and FIG. 11C is a partially enlarged view of FIG. In FIG. 11, the second displacement measuring diffraction grating 2B is
The reference diffraction grating 25 for measuring the amount of displacement when the linear expansion coefficient of 25a is β1 and the reference for performing temperature correction on the measured amount of displacement when the linear expansion coefficient of the substrate 26a is β2 (> β1) It comprises a diffraction grating 26 and a base substrate 27 that supports these two diffraction gratings 25,26. In FIG. 11C, the reference diffraction grating 25 and the reference diffraction grating 26 are independently fixed to the base substrate 27 only on the surface Y, and these members 25, 2
6 and 27 are integrally attached to an object to be measured for measuring the amount of displacement, and can simultaneously move in directions parallel to the grating vectors of the diffraction gratings 25 and 26. Between the reference diffraction grating 25 and the reference diffraction grating 26, and the surface X are not fixed, and each member 25, 26, 27 can expand and contract independently in response to a temperature change according to its linear expansion coefficient. it can. Furthermore, on the open end side of the reference diffraction grating 25 and the reference diffraction grating 26,
At an appropriate distance from the measurement grid ML, the temperature correction grid CL
Can also be prepared.

When the temperature (T = T0), two diffraction gratings 2
The distance from the fixed end (for example, the surface Y) of each of the 5,26 to the temperature correction grating CL is L0, but when the temperature is (T = T0 + ΔT), the distances are expressed by the equations (5) and (6), respectively. L1 and L2 represented.
The same function can be realized by the combination of the slit 35 and the light receiving elements 37a and 37b by the configuration of the light receiving element array arranged in the opening shape of the slit 35.

Next, the prerequisites for convenience of explanation are shown. This condition is an example, and the condition for realizing a necessary function is not limited to this. (1) Set the operating temperature range of the optical displacement measuring device to Tmin <T <
Let Tmax be the reference temperature used for temperature correction, T0 ≦ Tmin. (2) When T = T0, the reference diffraction grating 25 and the reference diffraction grating 26
Have the same lattice period, and the opening positions in the traveling direction also match. (Method of Detecting Position of Displacement Amount) Next, a method of detecting a position signal of the displacement amount will be described. FIG. 12 shows a light receiving element 37a and a light receiving element 37b shown by dotted lines for receiving light transmitted through the reference diffraction grating 25, and a slit 35 shown by a solid line placed on the front surface of the light receiving elements 37a and 37b. Show. Light receiving element 37
a, 37b are arranged in two rows parallel to the direction of travel,
Light transmitted through the opening of the slit 35 is received. slit
The 35 apertures are arranged in parallel with two rows of apertures having an aperture width w at a period p / 2 in the traveling direction and shifted by a distance d. Light transmitted through these aperture rows is received by the light receiving elements 37a and 37b. Is done.

Now, assuming that the grating period of the reference diffraction grating 25 is p, an interference fringe DL201S generated by the diffracted light DL100S.
Has a strong sine wave pattern with a period p / 2. Accordingly, the received signal V37a received by the light receiving element 37a in accordance with the movement of the reference diffraction grating 25 also has a sine wave or a pattern similar to the sine wave that changes with the period p / 2 (shown by a solid line in FIG. 12B). Further, when the reference diffraction grating 25 moves to the right, the reception signal v37b received by the light receiving element 37b becomes the reception signal v3
This is a pattern obtained by translating the pattern 7a in the X direction by a distance d (illustrated by a dotted line in FIG. 12B). Received signal V37a, v
If 37b is a sine wave and the aperture width w is sufficiently small,
If the distance d = p / 8 (equivalent to π / 2 in phase), approximately

[0053]

## EQU10 ## V37a = V0. [1 + cos (4.pi.X / p)] (10)

[0054]

V37b = V0 · [1 + sin (4πX / p)] (11) By obtaining two signals V37a and V37b whose phases are shifted by π / 2, the reference diffraction grating 25
Position and moving direction can be determined.

An example of this operation will be described with reference to an increase / decrease table shown in FIG. 13 and a block diagram shown in FIG. FIG. 13 illustrates the increase and decrease of the signals of V37a and V37b when the diffraction grating moves left and right with reference to the peak position of V37a. First,
In FIG. 14, the peak of V37a is detected by the increase / decrease determiner 53a. At this time, if V37b tends to increase monotonically,
This means that the reference diffraction grating 25 has moved to the right (see FIG.
13 (A) Change table), the peak counter value N1 is increased by one. If V37b tends to decrease monotonically, the diffraction grating
Since 25 indicates that it is moving to the left ((A) increase / decrease table in FIG. 13), the peak counter value N1 is decreased by one. If the peak counter value N1 is obtained by adding the peak value from the reference position of the reference diffraction grating 25, the coarse position of the reference diffraction grating 25 can be expressed as (N1 · p / 2).

Next, from the two values V37a and v37b, the position Xg1 of the slit grating period p / 2 or less can be determined. As a result, the position of the reference diffraction grating 25 is

[0057]

X1 = N1 · p / 2 + XgI (12) (Temperature Correction Method) Next, a temperature correction method will be described. To perform the temperature correction, the second displacement measuring diffraction grating 2B uses a reference diffraction grating 25 and a reference diffraction grating 26 having different linear expansion coefficients. As shown in FIG. 11, the coherent light L11b emitted from the light source 11 includes a reference diffraction grating 25 and a reference diffraction grating 25.
And at the same time. Here, attention is paid to each temperature correction grating CL. When the temperature T = T0, the two diffraction gratings 25 and 26 have the same period, as shown in FIG.
The aperture positions also match, and the distance from the fixed end (for example, the surface Y) of the diffraction gratings 25 and 26 to the temperature correction grating CL matches L0. When the second displacement measuring diffraction grating 2B moves at this time, the signals received by the light receiving elements 37a and 37b become exactly the same as shown in FIG. Next, if the temperature is T
In the case of = T0 + ΔT, as shown in FIG. 16A, the two diffraction gratings 25 and 26 change in accordance with the respective linear expansion coefficients β1 and β2 according to the temperature change ΔT, and the fixed end (surface Y ) To the temperature correction grating CL are L1 and L2, respectively, and the position of the temperature correction grating CL on the two diffraction gratings 25 and 26 is shifted by a distance ΔL = L2−L1 (FIG. 16B). ). As described above, by detecting the displacement ΔL of the grating due to the temperature change caused by the difference between the linear expansion coefficients of the two diffraction gratings 25 and 26, it can be converted into the temperature change ΔT from the equation (7). ) Allows temperature compensation for the measured length. Also, by setting T0 ≦ Tmin, the lattice displacement ΔL can always be a positive value, and thus there is an advantage that the number of signal processing cases can be reduced. (Other temperature correction method) In FIG.
The correction position grating 28 can be provided at a predetermined position (L0) in parallel with the reference diffraction grating array.

With this configuration, the light receiving signals DL201S and DL201R of the reference diffraction grating 25 and the reference diffraction grating 26 are read at the timing where the optical signal from the correction position grating 28 is read. As a result, the displacement X is measured at a fixed position L0 that is a fixed distance away from the position where one end (for example, the surface Y) of the reference diffraction grating 25 and the reference diffraction grating 26 is fixed to the third common member 27, and its temperature is corrected. It can be performed. Although not shown, the light receiving means at this time includes slits 35 and 36, light receiving elements 37a, 37b, 38a and 38b, and a light receiving element 37c for receiving an optical signal from the correction position grating 28. Be composed. The light receiving elements 37a, 37b, 37c, 38a, and 38b use an array sensor such as a CCD, for example, and sequentially call the amount of light received on the array sensor and read the light receiving elements at the same timing as the reading of the optical signal of the correction position grid 28. By reading the amount of received light at 37a, 37b, 38a, 38b, the temperature change Δ
The temperature can be corrected by measuring the amount of deviation due to T.

Although the temperature correction method according to the present invention has been described with reference to the configuration of the first embodiment, instead of the displacement measuring diffraction grating 2A,
By using the second displacement measuring diffraction grating 2B composed of the reference diffraction grating 25 and the reference diffraction gratings 26 having different linear expansion coefficients β1 and β2, the temperature characteristics of the diffraction grating substrates 25a and 26a can be The effect can be corrected.

[0060]

According to the present invention, an optical displacement measuring device having a resolution equal to or less than the grating period can be constructed by utilizing the interference signal of the diffracted light by the diffraction grating. Since the grating period of the diffraction grating can be made larger than the conventional resolution required for the device, it can be manufactured at low cost. Also, as compared with other conventional optical displacement measuring devices, when the incident light to the first displacement measuring diffraction grating is vertical light, coherent parallel light is used,
It has the feature that the degree of freedom of optical positioning can be widened along with the reduction of the number of optical parts, and it uses a coherent parallel light with a small number of optical parts and uses a first displacement measuring diffraction grating having a predetermined grating period. Thus, it is possible to provide an optical displacement measuring device that optically achieves a resolution higher than the period of the first displacement measuring diffraction grating.

Further, according to the present invention, it is possible to perform temperature correction on the measured displacement value without separately installing a temperature sensor.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a main part of an optical displacement measuring device according to a first embodiment of the present invention, (A) is a front view, and (B) is a side view.

FIGS. 2A and 2B are main configuration diagrams of an optical displacement measuring device according to a second embodiment, wherein FIG. 2A is a front view and FIG.

FIG. 3 is a main part configuration diagram of an optical displacement measuring device according to a third embodiment.

FIG. 4 is a configuration diagram of a main part of an optical displacement measuring device according to a fourth embodiment.

FIG. 5 is a front view of a slit.

FIG. 6 is an explanatory view illustrating generation of diffracted light and formation of interference fringes by a diffraction grating.

FIG. 7 is an explanatory diagram illustrating generation of diffracted light by a diffraction grating.

FIG. 8 is an explanatory diagram of a region where interference fringes of ± 1st-order diffracted light are formed.

FIG. 9 is an explanatory diagram of a region where interference fringes due to obliquely incident light are formed;

FIGS. 10A and 10B are main part configuration diagrams of an optical displacement measuring device according to a fifth embodiment having temperature correction means, where FIG. 10A is a front view and FIG.
Is a side view

FIG. 11 shows a first diffraction grating having a reference diffraction grating and a reference diffraction grating.
It is a key block diagram of the diffraction grating for displacement measurement, (A) is a front view, (B) is a side view, (C) is a partially enlarged view.

12A and 12B are a front view of a slit and a detection characteristic diagram of a reception signal, wherein FIG. 12A is a front view and FIG. 12B is a detection characteristic diagram of a reception signal.

FIG. 13 is a graph showing an increase / decrease characteristic of a received signal due to movement of the second displacement measuring diffraction grating.

FIG. 14 is a block diagram illustrating position signal generation.

15A and 15B are a partially enlarged view of a second displacement measuring diffraction grating and a reception signal detection characteristic diagram at a temperature T = T0, where FIG. 15A is a partially enlarged view and FIG. 15B is a reception signal detection characteristic diagram.

16A and 16B are a partially enlarged view of a first displacement measuring diffraction grating and a reception signal detection characteristic diagram at a temperature T = T0 + ΔT, where FIG. 16A is a partially enlarged view and FIG. 16B is a reception signal detection characteristic diagram.

FIG. 17 is a block diagram illustrating temperature correction of a position signal.

FIG. 18 is a partially enlarged view of a second displacement measuring diffraction grating for explaining another temperature correction method.

FIG. 19 is a configuration diagram of a main part of an optical displacement measuring device according to a conventional technique.

FIG. 20 is an explanatory diagram of another optical system according to the related art.

FIG. 21 is a main part configuration diagram of another optical displacement measuring device according to the related art.

[Explanation of symbols]

 1A, 1B Light source optical system 11 Light source 12 Lens 13 Two-branch diffraction grating 14 Light guide plate 14A Reflection surface 15 Light shield plate 2A, 2B, 21 Transmission diffraction grating 22 Reflection diffraction grating 23 Movable slit 3, 3S, 3R73 Light receiving means 31, 33,35,36 Slit 32,32A, 32B, 37a, 37b, 37c, 38a, 38b Light receiving element 4,4B, 58S, 58R Position detecting means 51a, 52b Received signal of light receiving element 53a, 53b Increase / decrease determiner 54 Peak detection Device 55 Moving direction detector 56 Phase detector 57 Peak counter 58S, 58R, 81,82 Position signal generator 71 Diffraction grating 72 Light emitting means 74 First imaging means 75 Second imaging means 76a, 76b Half mirror 77a-77d Reflector 78 Position detector 83 Position deviation detector 84 Temperature converter 85 Temperature corrector for position signal A Beam width L0 Distance of temperature T0 L1 Distance of reference diffraction grating of temperature T L2 Distance of reference diffraction grating of temperature T L11a ~ L11f, La Coherent light DL100, Lb, DL100S, R Diffracted light DL101 0th order diffracted light DL111,112 1st order diffracted light DL121,122 2nd order diffracted light DL200 area DL201, DL 202, DL201S, DL201R Interference fringes m order p Lattice period q Focusing position w, w2 Interference fringe spacing α Incident angle θ, θ +, θ-, ± θ2 Diffraction angle λ Wavelength

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Tetsuya Saito 1-1, Tanabe Nitta, Kawasaki-ku, Kawasaki, Kanagawa Prefecture Inside Fuji Electric Co., Ltd. (72) Inventor Yuji Matsuzoe 1, Tanabe Nitta, Kawasaki-ku, Kawasaki-ku, Kanagawa Prefecture No. 1 Fuji Electric Co., Ltd. (72) Inventor Nobuhiko Tsuji No. 1-1 Tanabe Nitta, Kawasaki-ku, Kawasaki City, Kanagawa Prefecture F-term (reference) 2F065 AA02 AA07 AA09 AA20 BB15 DD03 DD09 EE01 EE02 FF16 FF48 FF52 FF61 HH03 JJ01 JJ02 JJ05 JJ25 LL04 LL28 LL41 LL42 QQ17 QQ51 2F103 BA01 BA02 BA10 BA31 CA02 CA08 DA01 EA05 EA15 EA17 EB01 EB11 ED21 FA12

Claims (10)

[Claims] 1. A light source optical system comprising: a light source which emits coherent light; and an optical element which forms parallel coherent light from the light emitted from the light source; and a parallel light source emitted from the light source optical system. A first displacement measuring diffraction grating of a transmission type that moves in a direction parallel to the lattice vector with respect to the coherent light and diffracts the coherent light; Light receiving means for receiving interference light generated by the diffracted diffracted lights interfering with each other; and first position detecting means for detecting a relative movement position of the first displacement measuring diffraction grating from an output signal of the light receiving means. An optical displacement measuring device, comprising: 2. A light source optical system comprising: a light source that emits coherent light; and an optical element that forms parallel coherent light from the light emitted from the light source; A transmissive displacement measuring diffraction grating (hereinafter abbreviated as a reference diffraction grating) that moves in a direction parallel to the grating vector with respect to the coherent light and diffracts the coherent light; A second displacement measurement diffraction grating formed on a substrate made of a material having a different linear expansion coefficient from a substrate to be formed, the diffraction grating being provided with a temperature-correcting diffraction grating (hereinafter abbreviated as a reference diffraction grating); Reference light receiving means for receiving a reference interference light and a reference interference light formed by interference of diffracted lights formed by diffracting interference light by the reference diffraction grating and the reference diffraction grating, respectively, and a reference light receiving means When From the output signal to be detected by these light receiving means comprises a second position detecting means for detecting the temperature corrected relative movement position of the second displacement-measuring diffraction grating, the optical displacement measuring apparatus, characterized in that. 3. The optical displacement measuring device according to claim 1, wherein the light receiving surface of the light receiving means has a slit-like grating having an interval corresponding to an interval between interference fringes formed by interference light. An optical displacement measuring device. 4. The optical displacement measuring apparatus according to claim 1, wherein the light source optical system divides the coherent parallel light from the light source into two parallel lights, and divides the split parallel light into a second parallel light. 1. An optical displacement measuring device, comprising: an optical system for irradiating a second displacement measuring diffraction grating surface from different positions and directions. 5. An optical displacement measuring apparatus according to claim 4, wherein the optical system for irradiating the parallel light from different positions and directions of the first and second displacement measuring diffraction grating surfaces comprises a coherent parallel light source from a light source. A two-branch diffraction grating that diffracts light to generate two diffracted lights, a reflecting surface that reflects and deflects the branched diffracted light, and a light-shielding plate that shields the zero-order transmitted light in the two-branch diffraction grating is provided. An optical displacement measuring device, characterized in that: 6. An optical displacement measuring apparatus according to claim 1, wherein said first and second displacement measuring diffraction gratings are reflection type diffraction gratings instead of transmission type diffraction gratings. The light receiving means is disposed on the same side as the light source side, and receives coherent parallel light reflected on the reflection type diffraction grating, reflects and diffracts the light, and receives interference light formed by interference of the diffracted lights with each other. An optical displacement measuring device, characterized in that: 7. The optical displacement measuring apparatus according to claim 2, wherein the substrates of the reference diffraction grating and the reference diffraction grating are arranged in parallel, and one ends of the reference diffraction grating and the reference diffraction grating are connected to a third common substrate. An optical displacement measuring device fixed to a member. 8. The optical displacement measuring device according to claim 2, wherein the grating periods of the reference diffraction grating and the reference diffraction grating coincide at a predetermined reference temperature. . 9. The optical displacement measuring device according to claim 8, wherein the predetermined reference temperature is set outside an allowable operating temperature range of the optical displacement measuring device. measuring device. 10. The optical displacement measuring apparatus according to claim 2, wherein the reference diffraction grating is arranged at a predetermined position along the reference diffraction grating row. An optical displacement measuring device, comprising: