Displacement detection head and displacement detector including the same

Abstract

To provide a displacement detection head and the like in which an allowable variation of a gap between the displacement detection head and a grating scale is enlarged.SOLUTION: A displacement detection head 20 includes: a light source 22 that emits coherent light; an expander 23 that converts the emitted light into a plane wave; a first beam splitter 24 that splits the converted light into first light that is transmitted light and second light that is reflected light; a first mirror 25 that reflects the first light; a composite phase plate 26 that splits the second light into a plurality of light beams; a second mirror 27 that reflects the split second light toward a grating scale 10 and causes it to intersect the first light; a second beam splitter 29 that generates first interference light in which the first light and the second light are superimposed and irradiates the grating scale 10 with the interference light; a third beam splitter 30 that reflects the reflected light from the grating scale 10; a first light receiving portion 35 that receives the reflected light; and a displacement calculation portion 40 that processes an output signal from the first light receiving portion 35 and calculates a displacement in a direction along a surface of the grating scale 10.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a displacement detection device using light and a displacement detection head used therefor.

Background Art

[0002] Conventionally, as a device for non-contact measurement of the displacement and posture of a member to be measured, an optical displacement detection device has been widely used.

[0003] Patent Document 1 below describes a technique for irradiating a diffraction grating scale with coherent light, receiving the diffracted light from the diffraction grating scale by a light receiving unit, and measuring displacement information of the diffraction grating scale based on a signal output from this light receiving unit.

[0004] In this method, since it is a method of interfering diffracted lights diffracted by a diffraction grating scale, the gap amount between the diffraction grating scale and the detection head has relatively high freedom.

[0005] However, because diffracted light from the diffraction grating scale is used, the diffraction angle is as large as several degrees to several tens of degrees. Therefore, when the gap amount between the diffraction grating scale and the detection head changes by, for example, about several millimeters, a phenomenon occurs in which the optical axis is displaced and the interference intensity decreases, or the optical component is blocked by the aperture. For this reason, generally, the allowable range of the change amount of the gap between the diffraction grating scale and the detection head is limited to about 1 millimeter as the upper limit.

[0006] In addition, Patent Document 2 below discloses an optical encoder (displacement detection device) including a main scale, an index scale having an optical grating with a predetermined pitch slightly shifted from the optical grating pitch of the main scale, light irradiation means for transmitting parallel light through these main scale and index scale to generate moiré fringes, a line sensor for detecting these moiré fringes and outputting a sine wave signal, and a displacement amount detection circuit for detecting the phase angle of this sine wave signal and detecting the relative movement amount of the index scale with respect to the main scale.

[0007] In this optical encoder, if the gap amount between the main scale and the index scale spreads to, for example, several hundred micrometers or more, there is a problem that the contrast of the moiré fringes significantly decreases and a signal with less noise cannot be obtained. Therefore, it is premised that the gap amount between the main scale and the index scale is kept constant.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0009] As described above, among conventional optical displacement detection devices, in the method using light interference, the beam irradiation position on the diffraction grating scale changes due to fluctuations in the gap amount between the detection head and the diffraction grating scale. Therefore, there is a problem that the intensity of the interference signal decreases due to limitations on the optical aperture of the detection head. In addition, in the method using moiré fringes, there is also a problem that the contrast of the moiré fringes decreases due to fluctuations in the gap amount between the detection head and the scale. For this reason, in each conventional optical displacement detection device, the allowable range of changes in the gap between the detection head and the scale has been limited to about several millimeters.

[0010] Therefore, in each conventional optical displacement detection device, displacement detection has been performed by restricting the amount of fluctuation in the gap between the detection head and the scale. Also, based on the above background, even when using a grating scale having a two-dimensional grating pattern as the scale, it has been limited to two-dimensional displacement detection and cannot be applied to three-dimensional spatial displacement detection.

[0011] The present invention has been made in view of the above circumstances, and one of its objects is to significantly improve the allowable range regarding the amount of fluctuation in the gap between the detection head and the grating scale in an optical displacement detection device for detecting the displacement of the grating scale.

[0012] Another object is to expand the allowable range of the gap between the detection head and the grating scale to a range of several hundred millimeters when the grating scale has a two-dimensional grating pattern, so as to enable the detection of two-dimensional displacement due to movement in a direction parallel to the surface of the grating scale in a very wide three-dimensional spatial range.

Means for Solving the Problems

[0013] The present invention for solving the above problems is a detection head that irradiates interference fringe light onto a grating scale, a light source that emits coherent light, An expander that is provided on the optical path of the light emitted from the light source, converts the incident light into a plane wave, and transmits it; A first beam splitter that is provided on the optical path of the light transmitted through the expander and splits the transmitted light into a first light that is transmitted light and a second light that is reflected light; A first mirror that is provided on the optical path of the first light transmitted through the first beam splitter and reflects the first light; A second mirror that is provided on the optical path of the second light reflected by the first beam splitter, reflects the second light toward the grating scale, and intersects the first light reflected by the first mirror; A composite phase plate that is provided on the optical path between the first beam splitter and the first mirror, divides the incident second light into lights in a plurality of areas having different phases from each other, and transmits them; A second beam splitter that is provided at a position where the first light reflected by the first mirror and the second light reflected by the second mirror intersect, reflects the first light toward the grating scale, and transmits the second light to generate first interference fringe light in which the first light and the second light are overlapped; A third beam splitter that is provided on the optical path of the first interference fringe light, transmits the first interference fringe light, irradiates it toward the grating scale, and reflects the reflected light from the grating scale in a predetermined direction; A first light receiving unit that receives the light reflected by the third beam splitter; It relates to a displacement detection head including a displacement calculation unit that receives an output signal from the first light receiving unit and calculates a displacement between the displacement detection head and the grating scale in a direction along the surface of the grating scale.

[0014] According to this displacement detection head, the coherent light emitted from the light source is expanded by the expander and converted into a plane wave, and is split into first light and second light by the first beam splitter. Then, the first light passes through the first mirror and reaches the second beam splitter, and the second light is split into lights with different phases in a plurality of areas by passing through the composite phase plate, and then reaches the second beam splitter through the second mirror. The first light and the second light that reach the second beam splitter are overlapped at the second beam splitter to become first interference fringe light directed toward the grating scale.

[0015] Then, the first interference fringe light is reflected by the grating scale, passes through the third beam splitter, and is received by the first light receiving unit. Based on the output signal from the first light receiving unit, the displacement calculation unit calculates the displacement between the grating scale and the grating scale in the direction along the surface of the grating scale.

[0016] Since the first interference fringe light formed as described above is formed by the first light and the second light intersecting at a predetermined angle, the range in which interference fringes are generated within the first interference fringe light extends over a wide range in the optical axis direction. For this reason, the allowable range of the gap between the displacement detection head and the grating scale can be made significantly wider than in the prior art. Even if the displacement detection head and the grating scale vary greatly in the direction orthogonal to the grating scale, the relative displacement between the displacement detection head and the grating scale in the direction along the surface of the grating scale can be detected.

Advantages of the Invention

[0017] As described above, according to the displacement detection head according to the present invention, interference fringes can be formed over a wide range in the optical axis direction within the first interference fringe light, and the allowable range of the gap between the displacement detection head and the grating scale can be made significantly wider than in the prior art. For this reason, even if the displacement detection head and the grating scale vary greatly in the direction orthogonal to the grating scale, the relative displacement between the displacement detection head and the grating scale in the direction along the surface of the grating scale can be detected.

Brief Description of Drawings

[0018]

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Embodiments for Carrying Out the Invention

[0019] Hereinafter, specific embodiments of the present invention will be described with reference to the drawings.

[0020] [First Embodiment] First, a displacement detection device according to the first embodiment will be described. As shown in FIG. 1, the displacement detection device 1 of this example includes a grating scale 10 and a displacement detection head 20 provided opposite to the grating scale 10 and irradiating interference fringe light onto the grating scale 10.

[0021] The grating scale 10 is composed of a scale substrate 11 and a grating pattern 12 formed on its surface. The grating scale 10 exemplified in the present embodiment has a grating pattern 12 in which strip-shaped gratings are formed at a predetermined pitch in a one-dimensional direction (one direction) as shown in FIG. 3. The grating is a portion that reflects light, and the portion where no grating is provided is a portion that transmits or absorbs light. The grating pattern 12 is preferably protected by a protective glass or the like. Note that FIG. 3(a) is a plan view of the grating scale 10, and FIG. 3(b) is a front view of the grating scale 10. Also, in FIG. 3(a), the grating vector 1 indicates the direction in which the grating is provided.

[0022] In this example, as an example, a one-dimensional grating scale 10 having a grating pattern 12 in which gratings are arranged in a one-dimensional direction is used, but the present invention is not limited thereto, and two-dimensional grating scales 13 and 16 shown in FIGS. 4 and 5 may also be used. The two-dimensional grating scale 13 shown in FIG. 4 includes a scale substrate 14 and a grating pattern 15 formed on the surface thereof with circular grating portions (reflective portions) formed at a predetermined pitch in two-dimensional directions (two orthogonal directions). FIG. 4(a) is a plan view of the grating scale 13, and FIG. 4(b) is a front view of the grating scale 13. Further, in FIG. 4(a), grating vectors 1 and 2 indicate the directions in which the gratings are provided.

[0023] Further, the two-dimensional grating scale 16 shown in FIG. 5 includes a scale substrate 17 and a grating pattern 18 formed on the grating portion (reflective portion) formed on the surface thereof with circular non-grating portions (non-reflective portions) formed at a predetermined pitch in two-dimensional directions (two orthogonal directions) by punching out. FIG. 5(a) is a plan view of the grating scale 16, and FIG. 5(b) is a front view of the grating scale 16. Further, in FIG. 5(a), grating vectors 1 and 2 indicate the directions in which the non-grating portions are provided. Also in these two-dimensional grating scales 13 and 16, the grating patterns 15 and 18 are preferably protected by a protective glass or the like.

[0024] As shown in FIG. 1, the displacement detection head 20 is composed of a) a case 21, b) a light source 22, an expander 23, a first beam splitter 24, a first mirror 25, a composite phase plate 26, a second mirror 27, an adjustment mechanism 28, a second beam splitter 29, a third beam splitter 30, a first light receiving portion 35, and a displacement calculation portion 40 disposed in the case 21.

[0025] The case 21 is composed of a housing-shaped member, and an opening 21a from which interference fringe light is emitted is formed on the surface facing the grating scale 10.

[0026] The light source 22 emits coherent light directed towards the grating scale 10. Examples of coherent light include single-mode semiconductor lasers, multi-mode semiconductor lasers, gas lasers such as HeNe lasers, and superluminescent diodes. Hereinafter, the direction orthogonal to the surface of the grating scale 10 is referred to as the Z-axis direction, the grating vector 1 direction is referred to as the X-axis direction, and the grating vector 2 direction is referred to as the Y-axis direction. The X-axis, Y-axis, and Z-axis are mutually orthogonal.

[0027] The expander 23 is provided on the optical path of the light emitted from the light source 22. In the process of the coherent light emitted from the light source 22 passing through, the coherent light is expanded and converted into a plane wave. In order to increase the allowable amount of the gap G between the detection head 20 and the grating scale 10, it is necessary to improve the wavefront accuracy of the plane wave generated by the expander 23. Preferably, within the beam diameter of the coherent light, the wavefront accuracy is λ (= wavelength of the coherent light) or less.

[0028] The first beam splitter 24 is provided on the optical path of the light that has passed through the expander 23, and splits it into a first light that is transmitted light in the Z-axis direction (hereinafter referred to as "plane wave L") and a second light that is reflected light in the X-axis direction (hereinafter referred to as "plane wave R"). Preferably, the light quantity ratio between the plane wave L and the plane wave R is 1:1.

[0029] The first mirror 25 is provided on the optical path of the plane wave L that has passed through the first beam splitter 24, and reflects the plane wave L in the X-axis direction.

[0030] The second mirror 27 is provided on the optical path of the plane wave R reflected by the first beam splitter 24, and reflects the plane wave R towards the opening 21a of the case 21, that is, in the Z-axis direction towards the grating scale 10, so as to intersect with the plane wave L reflected by the first mirror 25.

[0031] The composite phase plate 26 is provided on the optical path between the first beam splitter 24 and the first mirror 27, and splits the incident plane wave R into a plurality of lights, in this example, four lights with different phases from each other, and transmits them. As shown in FIG. 2, the composite phase plate 26 of this example is divided into four regions (areas), that is, regions corresponding to λ / 4, 3λ / 4, λ / 2, and λ. The plane wave R is divided into lights of four areas (area 1, area 2, area 3, area 4) whose phases are λ / 4, 3λ / 4, λ / 2, and λ within the plane wave.

[0032] The second beam splitter 29 is provided at a position where the plane wave L reflected by the first mirror 25 and the plane wave R reflected by the second mirror 27 intersect. The plane wave L is reflected in the Z-axis direction toward the opening 21a of the case 21, that is, toward the grating scale 10, and at the same time, the plane wave R is transmitted, so that the plane wave L and the plane wave R are overlapped to generate first interference fringe light with interference fringes formed at a predetermined pitch in the radial X-axis direction.

[0033] Similarly, when the plane wave L passes through the second beam splitter 29 and the plane wave R is reflected in the X-axis direction by the second beam splitter 29, the plane wave L and the plane wave R are overlapped, and second interference fringe light with interference fringes formed at a predetermined pitch in the radial direction is generated. In this example, the first interference fringe light is used for displacement detection.

[0034] At this time, the optical path length (R1 + R2) of the plane wave R from the first beam splitter 24 to the second beam splitter 29 and the optical path length (L1 + L2) of the plane wave L from the first beam splitter 24 to the second beam splitter 29 are preferably equal at the order of several μm. This is because if the difference between the optical path length (R1 + R2) of the plane wave R and the optical path length (L1 + L2) of the plane wave L is large, the interference fringes formed will drift due to environmental changes such as air pressure. Therefore, in this example, an adjustment mechanism 28 for adjusting the position and orientation of the second mirror 27 is provided, and the adjustment mechanism 28 can adjust the optical path length (R1 + R2) of the plane wave R. In this example, the adjustment mechanism 28 is configured to be able to move the second mirror 27 in the H direction of advancing and retreating with respect to the first mirror 25 and in the D direction of rotating about an axis orthogonal to the optical axis of the plane wave R. Incidentally, this adjustment mechanism 28 may be provided on the first mirror 25, or may be provided on both the first mirror 25 and the second mirror 27.

[0035] The plane wave R and the plane wave L are overlapped by the second beam splitter 29, thereby forming interference fringes with a predetermined pitch in the radial direction. Fig. 6 shows the mode of the interference fringes formed by overlapping the plane wave R and the plane wave L. The relationship between the incident angles θ1 and θ2 of the two plane waves R and L and the pitch d of the interference fringes is shown by the following formula. sinθ1 + sinθ2 = λ / d λ is the wavelength of the coherent light. For example, when λ = 655 nm and θ1 = θ2 = 0.4°, the pitch d of the interference fringes is 47 μm.

[0036] As can be seen from the explanatory diagram shown in FIG. 6, in order to form interference fringes in a wide range with respect to the gap direction between the detection head 20 and the grating scale 10, it is preferable that the incident angles θ1 and θ2 are small. On the other hand, when the incident angles θ1 and θ2 are reduced, the pitch d of the interference fringes increases, resulting in a trade-off with the resolution required for the grating scale 10. However, when λ is about 655 nm, if the pitch d of the interference fringes is made as fine as 1 μm, the amount of diffracted light by the diffraction grating increases. Therefore, the grating pitch of the grating scale 10 and the pitch of the interference fringes are set within a range where the amount of reflected light from the grating scale 10 can be ensured.

[0037] Regarding the stability in the atmosphere, by housing the optical path from the first beam splitter 24 to the second beam splitter 29 in the case 21, the influence of air fluctuations can be suppressed. On the other hand, in the optical path from the detection head 20 to the grating scale 10, since the plane wave R and the plane wave L overlap, the influence of air fluctuations is canceled. However, when the pitch d of the interference fringes is greatly enlarged, the influence of air fluctuations is also enlarged. Therefore, it is preferable to set the pitch d of the interference fringes to an optimum value according to the purpose of use. The adjustment of the pitch d of the interference fringes may be performed by rotating the second mirror 27 in the direction indicated by the arrow D by the adjustment mechanism 28.

[0038] The range G in which the interference fringes shown in FIG. 6 are formed is represented by the following equation. G = (beam radius of plane wave R and plane wave L) / tan(θ1 + θ2) Here, when the beam radii of the plane wave R and the plane wave L are 5 mm and θ1 = θ2 = 0.4°, G becomes 716 mm, and interference fringes are formed in a sufficiently wide range. Since the actual effective diameter is about half of the beam diameter, the gap between the detection head 20 and the grating scale 10 is about G / 2.

[0039] In addition, as a means of overlapping two such plane waves at a small angle, there is also a means of overlapping diffracted lights of a diffraction grating. However, when the diffraction angle is reduced, even higher-order diffracted lights overlap, so it is not appropriate for overlapping two plane waves at a small angle.

[0040] The third beam splitter 30 is provided on the optical path of the first interference fringe light, transmits the first interference fringe light, irradiates it toward the grating scale 10, and reflects the reflected light from the grating scale 10 toward the first light receiving part 35.

[0041] The interference fringes formed by the plane wave R and the plane wave L are preferably formed perpendicular to the surface of the grating scale 10. By forming the interference fringes perpendicular to the surface of the grating scale 10, the interference fringes are formed at the same pitch d at any position within the range G where the interference fringes are formed. And the effective range of displacement detection using this interference fringe light is set to, for example, G / 2 from empirical values. From the above, the allowable range of the gap between the detection head 20 and the grating scale 10 is G / 2. In other words, if the gap between the detection head 20 and the grating scale 10 is within G / 2, displacement detection is possible. In a specific example where the beam radii of the plane wave R and the plane wave L are 5 mm and θ1 = θ2 = 0.4°, G / 2 = 716 / 2 = 358 mm, The allowable range of the gap between the displacement detection head 20 capable of displacement detection and the grating scale 10 is 358 mm.

[0042] The required coherence distance of the coherent light source is such that the optical path length difference between the plane wave R and the plane wave L is zero in the optical path from the first beam splitter 24 to the second beam splitter 29, and is 2 × beam radius of the plane wave × tan(θ1 + θ2) or more. In this case, it holds if it is 0.07 mm or more.

[0043] FIG. 7 shows an image of the first interference fringe light incident on the grating scale 10, and FIG. 8 shows an image of the first interference fringe light reflected by the grating scale 10. Note that the pitch d of the interference fringes of the first interference fringe light formed in the detection head part 20 coincides with the grating pitch of the grating scale 10. For example, when the pitch d of the interference fringes is 47 μm, the grating pitch is also set to 47 μm, and the substrate is manufactured so that the grating pitch becomes 47 μm.

[0044] In FIGS. 7 and 8, the convex portions of the grating scale 10 are reflecting portions that reflect light, and the concave portions without reflecting portions are portions where light is transmitted or absorbed. The interference fringes of the first interference fringe light reflected by the grating scale 10 are formed only on the reflecting portions of the grating scale 10. Therefore, when the bright portion of the interference fringe coincides with the reflecting portion of the grating scale 10, the amount of reflected light becomes maximum.

[0045] Here, as shown in FIG. 8, in the reflected first interference fringe light, interference fringes whose light amount changes are formed in the reflection direction, that is, in the optical axis direction which is the Z-axis direction shown in FIG. 8. Since the first interference fringe light reflected by the grating scale 10 is the interference fringe formed by the plane wave R and the plane wave L shown in FIG. 6, interference fringes whose light amount changes in the Z-axis direction are formed in the portion where the reflected light exists, and the portion where the reflected light does not exist becomes dark. The interval, that is, the period A, of the interference fringes along the Z-axis direction is expressed by the following formula when θ1 = θ2 = θ. A = d / tanθ

[0046] In other words, in the first interference fringe light reflected by the grating scale 10, a pattern of interference fringes whose light amount changes with a period A is formed in the space directed in the Z-axis direction which is the reflection direction. For example, when the grating scale 10 is displaced in the Z-axis direction, the pattern formed in the space in the Z-axis direction also moves accordingly. That is, when the grating scale 10 moves by A in the Z-axis direction, the change in the light amount of the interference fringes received by the first light receiving portion 35 makes one round.

[0047] Further, when the grating scale 10 moves in the X-axis direction (the grating vector 1 direction shown in FIG. 3), when the bright portion of the first interference fringe light coincides with the convex portion (reflecting portion) of the grating scale 10 and the dark portion of the first interference fringe light coincides with the concave portion (non-reflecting portion) of the grating scale 10, the amount of light reflected by the reflecting portion becomes maximum. Conversely, when the dark portion of the first interference fringe light coincides with the reflecting portion of the grating scale 10 and the bright portion of the first interference fringe light coincides with the non-reflecting portion of the grating scale 10, the amount of light reflected by the reflecting portion becomes minimum. Therefore, when the grating scale 10 moves by one grating pitch in the X-axis direction, the brightness and darkness of the amount of light reflected by the grating scale 10 make one round.

[0048] Further, the first interference fringe light has four areas within the beam diameter by the composite phase plate 26. When the plane wave R passes through the composite phase plate 26, there are phase differences of λ / 4, 3λ / 4, λ / 2, and λ among the respective areas. Therefore, the bright and dark phases of the first interference fringe light also have phase differences corresponding to the phase differences. Interference fringes whose reflected light amount changes due to the displacement of the grating scale 10 in the X-axis direction are also formed on the first light receiving portion 35.

[0049] As described above, the first light receiving portion 35 receives the first interference fringe light reflected by the grating scale 10 and further reflected by the third beam splitter 30.

[0050] Also, the displacement calculation unit 40 receives the output signal from the first light receiving portion 35, calculates the displacement between the first light receiving portion 35 and the grating scale 10 in the direction along the surface of the grating scale 10, and outputs displacement information.

[0051] As shown in FIG. 9, the first light receiving portion 35 includes a first element portion 36 provided on the optical path of the first interference fringe light reflected by the third beam splitter 30, a beam splitter 38 provided between the third beam splitter 30 and the first element portion 36 for splitting the first interference fringe light reflected by the third beam splitter 30 into transmitted light and reflected light, and a second element portion 37 provided on the optical path of the reflected light reflected by the beam splitter 38.

[0052] The first element part 36 is composed of the light-receiving elements 1a, 2a, 3a, and 4a arranged side by side. These elements are reflected by the third beam splitter 30 and arranged to coincide with four areas formed by the first interference fringe light transmitted through the beam splitter 38, namely, area 1, area 2, area 3, and area 4. Also, the second element part 37 is composed of the light-receiving elements 1b, 2b, 3b, and 4b arranged side by side. Similarly, these elements are also arranged to coincide with the four areas formed by the first interference fringe light reflected by the beam splitter 38, namely, area 1, area 2, area 3, and area 4.

[0053] By arranging them in this way, the first interference fringe light with a phase of λ / 4 is incident on the light-receiving elements 1a and 1b, the first interference fringe light with a phase of 3λ / 4 is incident on the light-receiving elements 2a and 2b respectively, the first interference fringe light with a phase of λ / 2 is incident on the light-receiving elements 3a and 3b, and the first interference fringe light with a phase of λ is incident on the light-receiving elements 4a and 4b. Then, the light-receiving elements 1a, 2a, 3a, 4a, and the light-receiving elements 1b, 2b, 3b, 4b output electrical signals obtained by photoelectric conversion according to the received light amount respectively.

[0054] By the way, as described above, the first interference fringe light incident on the first light-receiving part 35 forms interference fringes with the light amount changing at a period A in the direction of its optical axis due to being reflected by the grating scale 10. Therefore, when the grating scale 10 moves in the Z-axis direction, the light amounts received by the light-receiving elements 1a, 2a, 3a, 4a change. As a result, the signals obtained by photoelectric conversion by each element change.

[0055] Therefore, in order to solve this problem, light-receiving elements 1b, 2b, 3b, and 4b, which are the second element unit 37, are arranged. Note that the positional relationship between the first element unit 36 and the second element unit 37 is as shown in FIG. 9. Let the distance from the center of the second element unit 37 to the light-receiving surface of the first element unit 36 in the optical axis direction of the first interference fringe light incident on the first element unit 36 be A1, and the distance from the center of the first element unit 36 to the light-receiving surface of the second element unit 37 in the optical axis direction of the first interference fringe light incident on the second element unit 37 be A2. Then, these and the period A of the interference fringes have the following relationship. A1 - A2 = A / 2

[0056] By arranging in this way and taking the sum of each output signal from light-receiving elements 1a, 2a, 3a, and 4a and each output signal from light-receiving elements 1b, 2b, 3b, and 4b, it is possible to cancel the change in the output signal from each element caused by the movement of the grating scale 10 in the Z-axis direction.

[0057] As shown in FIG. 10, the displacement calculation unit 40 is composed of a first differential amplifier 41, a second differential amplifier 42, a third differential amplifier 43, a fourth differential amplifier 44, A / D converters 45, 46, 47, 48, a clock 49, a waveform correction processing unit 50, an incremental signal generation unit 51, and a displacement information calculation unit 52.

[0058] The phase of the first interference fringe light received by the light-receiving element 1a and the phase of the first interference fringe light received by the light-receiving element 2a are shifted by 180°. The first differential amplifier 41 outputs a displacement detection signal (displacement detection signal A1 phase) as phase A (first phase), which is an amplified electrical signal (differential signal) with the DC component canceled, based on the electrical signals output from the light-receiving element 1a and the light-receiving element 2a. Similarly, the phase of the first interference fringe light received by the light-receiving element 3a and the phase of the first interference fringe light received by the light-receiving element 4a are shifted by 180°. The second differential amplifier 42 outputs a displacement detection signal (displacement detection signal B1 phase) as phase B (second phase), which is an amplified electrical signal (differential signal) with the DC component canceled, based on the electrical signals output from the light-receiving element 3a and the light-receiving element 4a. By canceling the DC component in this way, the influence of the DC offset of the signal due to the change in the light amount of the coherent light source 22 can be canceled.

[0059] When the grating scale 10 moves in the X-axis direction (i.e., the grating vector 1 direction), which is the direction along its surface, the light amounts of the first interference fringe light received by the light-receiving element 1a, the light-receiving element 2a, the light-receiving element 3a, and the light-receiving element 4a change periodically with the movement of the grating scale 10. Therefore, the displacement detection signals A1 phase and B1 phase as differential signals respectively output from the first differential amplifier 41 and the second differential amplifier 42 are sine waves that change periodically.

[0060] The phase of the displacement detection signal A1 phase and the phase of the displacement detection signal B1 phase are shifted by 90°, in other words, they are shifted by 1 / 4 cycle. Generally, the displacement detection signal A1 phase is treated as a sin signal, and the displacement detection signal B1 phase is treated as a cos signal. Then, using the displacement detection signals A1 phase and B1 phase with different phases of 90°, it is possible to determine whether the displacement detection signal B1 phase is ahead of or behind the displacement detection signal A1 phase. Thereby, it is possible to determine whether the relative displacement direction between the grating scale 10 and the displacement detection head 20 is in the positive direction or the negative direction.

[0061] Similarly, the phase of the first interference fringe light received by the light receiving element 1b and the phase of the first interference fringe light received by the light receiving element 2b are shifted by 180°. The third differential amplifier 43 outputs a displacement detection signal (displacement detection signal A2 phase) as the A phase (first phase), which is an amplified electrical signal (differential signal) with the DC component canceled, based on the electrical signals output from the light receiving element 1b and the light receiving element 2b. Similarly, the phase of the first interference fringe light received by the light receiving element 3b and the phase of the first interference fringe light received by the light receiving element 4b are shifted by 180°. The fourth differential amplifier 44 outputs a displacement detection signal (displacement detection signal B2 phase) as the B phase (second phase), which is an amplified electrical signal (differential signal) with the DC component canceled, based on the electrical signals output from the light receiving element 3b and the light receiving element 4b. By canceling the DC component in this way, the influence of the DC offset of the signal due to the change in the light amount of the coherent light source can be canceled.

[0062] When the grating scale 10 moves in the X-axis direction (i.e., the grating vector 1 direction), which is the direction along its surface, the light amounts of the first interference fringe light received by these light receiving elements 1b, 2b, 3b, and 4b change periodically with the movement of the grating scale 10. Therefore, the displacement detection signals A2 phase and B2 phase as differential signals respectively output from the third differential amplifier 43 and the fourth differential amplifier 44 are sine waves that change periodically.

[0063] The phase of the displacement detection signal A2 phase and the phase of the displacement detection signal B2 phase are shifted by 90°, in other words, they are shifted by 1 / 4 cycle. Generally, the displacement detection signal A2 phase is treated as a sin signal and the displacement detection signal B2 phase is treated as a cos signal. Then, by using the displacement detection signals A2 phase and B2 phase with different phases of 90°, it is possible to determine whether the displacement detection signal B2 phase is ahead of or behind the displacement detection signal A2 phase, and thereby determine whether the relative displacement direction between the grating scale 10 and the displacement detection head 20 is in the plus direction or the minus direction.

[0064] The A / D converters 45, 46, 47, and 48 convert the analog signals output from the first differential amplifier 41, the second differential amplifier 42, the third differential amplifier 43, and the fourth differential amplifier 44 into digital signals and output them at the sampling timing based on the clock signal output from the clock 49.

[0065] The waveform correction processing unit 50 synthesizes and adds the displacement detection signal A1 phase output from the first differential amplifier 41 and converted into a digital signal by the A / D converter 45 and the displacement detection signal A2 phase output from the third differential amplifier 43 and converted into a digital signal by the A / D converter 47, and corrects them into a sine wave shape as the displacement detection signal A phase. Further, the waveform correction processing unit 50 synthesizes and adds the displacement detection signal B1 phase output from the second differential amplifier 42 and converted into a digital signal by the A / D converter 46 and the displacement detection signal B2 phase output from the fourth differential amplifier 44 and converted into a digital signal by the A / D converter 48, and corrects them into a sine wave shape as the displacement detection signal B phase.

[0066] When the grating scale 10 moves in the X-axis direction, the light-receiving elements 1a and 1b, the light-receiving elements 2a and 2b, the light-receiving elements 3a and 3b, and the light-receiving elements 4a and 4b each detect the light amount change of the same phase, and the difference is the light amount change when the grating scale 10 moves in the Z-axis direction. The light amount change when the grating scale 10 moves in the Z-axis direction is canceled by the above processing of the waveform correction processing unit 50.

[0067] The incremental signal generation unit 51 detects the phase change per unit time based on the displacement detection signal A phase and the displacement detection signal B phase output from the waveform correction processing unit 50, and the displacement information calculation unit 52 calculates the relative displacement between the grating scale 10 and the displacement detection head 20 in the X-axis direction based on the phase change per unit time detected by the incremental signal generation unit 51 and outputs it as displacement information. Generally, the resolution of the displacement information is determined by the number of divisions by the A / D converters 45, 46, 47, and 48. The signal period is 47 μm, and the number of divisions of the A / D converters 45, 46, 47, and 48 is 2 16, that is, in the case of 65536 divisions, the resolution of the displacement information by the incremental signal generation unit 51 is 0.7 nm.

[0068] As described above, according to the displacement detection device 1 of this example, after the coherent light emitted from the coherent light source 22 is expanded by the expander 23 and converted into a plane wave, it is split into a plane wave R and a plane wave L by the first beam splitter 24, and then these are overlapped by the second beam splitter 29 to generate the first interference fringe light. Therefore, in the direction in which the first interference fringe light is irradiated on the grating scale 10, that is, in the direction along the optical axis of the first interference fringe light, an area where interference fringes are formed can be formed over a wide range.

[0069] For example, when the beam radii of the plane wave R and the plane wave L are set to 5 mm and θ1 = θ2 = 0.4°, interference fringes can be formed over a range of 716 mm in the optical axis direction of the first interference fringe light. And since the actual effective diameter of the interference fringes is about half of the beam diameter, the allowable range of the gap between the displacement detection head 20 and the grating scale 10 is 358 mm.

[0070] In this way, according to the displacement detection device 1 of this example, the allowable range of the gap between the displacement detection head 20 and the grating scale 10 can be made significantly wider than in the past. Therefore, even if the displacement detection head 20 and the grating scale 10 fluctuate greatly in the Z-axis direction orthogonal to the grating scale 10, the relative displacement between the displacement detection head 20 and the grating scale 10 in the X-axis direction along the surface of the grating scale 10 can be detected.

[0071] Furthermore, in this example, the first interference fringe light reflected by the grating scale 10 is split by the beam splitter 38 and received by the first element unit 36 and the second element unit 37 arranged so that the light receiving surfaces are orthogonal. Therefore, changes in the output signals from each element caused by the movement of the grating scale 10 in the Z-axis direction can be canceled.

[0072] By appropriately adjusting the pitch of the interference fringes formed by superimposing plane wave R and plane wave L, and setting the lattice pattern pitch of the lattice scale 10 according to the pitch of the interference fringes, high-resolution displacement detection can be performed.

[0073] [Second Embodiment] Next, a second embodiment of the present invention will be described. As shown in FIGS. 11 and 12, the displacement detection device 100 of this example is obtained by providing a second displacement detection unit 125 in the displacement detection device 1 according to the first embodiment. The displacement detection unit mechanism in the displacement detection device 1 is designated as the first displacement detection unit 115, and the same reference numerals are assigned to the same components. Also, in this example, the two-dimensional lattice scale 13 shown in FIG. 4 is used.

[0074] The displacement detection device 100 of this example is composed of a displacement detection head 120 and a lattice scale 13. The displacement detection head 120 is composed of a) a case 121 and b) a first displacement detection unit 115 and a second displacement detection unit 125 disposed in the case 21. Note that the first displacement detection unit 115 includes a displacement detection unit 140 instead of the displacement calculation unit 40 in the above example.

[0075] The case 121 is composed of a housing-shaped member. An opening 121a through which the first interference fringe light from the first displacement detection unit 115 is emitted is formed on the surface facing the lattice scale 13, and an opening 121b through which the second interference fringe light from the second displacement detection unit 125 is emitted is also formed.

[0076] The second displacement detection unit 125 is composed of a third mirror 126, a fourth mirror 127, a fourth beam splitter 128, and a second light receiving unit 135. The third mirror 126 is provided on the optical path of the second interference fringe light irradiated in the X-axis direction generated by the second beam splitter 29, and reflects this second interference fringe light at an angle of 90° in the Y-axis direction along the surface of the lattice scale 13.

[0077] The fourth mirror 127 is provided on the optical path of the second interference fringe light reflected by the third mirror 126, and reflects this second interference fringe light in the Z-axis direction toward the grating scale 13. The fourth beam splitter 128 is provided on the optical path of the second interference fringe light reflected by the fourth mirror 127, transmits the second interference fringe light reflected by the fourth mirror 127, irradiates it toward the grating scale 13, and reflects the reflected light from the grating scale 13 toward the second light receiving part 35. By passing through such an optical path, on the grating scale 13, the interference fringes of the second interference fringe light are oriented at 90° orthogonal to the interference fringes of the first interference fringe light.

[0078] When the grating scale 10 moves in the Y-axis direction (the grating vector 2 direction shown in FIG. 4), when the bright part of the second interference fringe light coincides with the convex part (reflective part) of the grating scale 13 and the dark part of the second interference fringe light coincides with the concave part (non-reflective part) of the grating scale 13, the amount of light reflected by the reflective part becomes maximum. Conversely, when the dark part of the second interference fringe light coincides with the reflective part of the grating scale 13 and the bright part of the second interference fringe light coincides with the non-reflective part of the grating scale 13, the amount of light reflected by the reflective part becomes minimum. Therefore, when the grating scale 13 moves by one grating pitch in the Y-axis direction, the brightness and darkness of the amount of light reflected by the grating scale 13 make one full cycle.

[0079] Also, the second interference fringe light has four areas within the beam diameter by the composite phase plate 26. The plane wave R has a phase difference of λ / 4, 3λ / 4, λ / 2, and λ between each area when passing through the composite phase plate 26. Therefore, the bright and dark phase of the second interference fringe light also has a phase difference corresponding to the phase difference. The interference fringes whose reflected light amount changes due to the displacement of the grating scale 13 in the Y-axis direction are also formed on the second light receiving part 135.

[0080] The second light receiving unit 135 receives the second interference fringe light that is reflected by the grating scale 13 and further reflected by the fourth beam splitter 128. Further, the displacement calculation unit 140 receives the output signal from the second light receiving unit 135, calculates the displacement between the grating scale 13 in the directions along the surface of the grating scale 13 (X-axis and Y-axis directions), and outputs displacement information.

[0081] As shown in FIG. 13, the second light receiving unit 135 includes a third element unit 136 provided on the optical path of the second interference fringe light reflected by the fourth beam splitter 128, and a beam splitter 138 provided between the third beam splitter 128 and the fourth element unit 136 for splitting the second interference fringe light reflected by the fourth beam splitter 128 into transmitted light and reflected light, and a second element unit 137 provided on the optical path of the reflected light reflected by this beam splitter 138.

[0082] The third element unit 136 is composed of a light receiving element 1c, a light receiving element 2c, a light receiving element 3c, and a light receiving element 4c. These elements are arranged to coincide with four areas, namely, area 1, area 2, area 3, and area 4, formed by the second interference fringe light that is reflected by the fourth beam splitter 128 and transmitted through the beam splitter 138. Further, the fourth element unit 137 is composed of a light receiving element 1d, a light receiving element 2d, a light receiving element 3d, and a light receiving element 4d. Similarly, these elements are also arranged to coincide with four areas, namely, area 1, area 2, area 3, and area 4, formed by the second interference fringe light reflected by the beam splitter 138.

[0083] Still, this second light-receiving unit 135 has the same configuration as the above-described first light-receiving unit 35. The third element unit 136 corresponds to the first element unit 36, and the fourth element unit 137 corresponds to the second element unit 37. That is, the light-receiving elements 1c, 2c, 3c, and 4c respectively correspond to the light-receiving elements 1a, 2a, 3a, and 4a, and the light-receiving elements 1d, 2d, 3d, and 4d respectively correspond to the light-receiving elements 1b, 2b, 3b, and 4b. The operations and the like in this second light-receiving unit 135 are the same as those in the above-described first light-receiving unit 35, and therefore, a detailed description thereof will be omitted.

[0084] As shown in FIG. 14, the displacement calculation unit 140 has a configuration for calculating the displacement in the Y-axis direction in addition to the configuration of the displacement calculation unit 40 for calculating the displacement in the X-axis direction described above. Specifically, it includes a fifth differential amplifier 141, a sixth differential amplifier 142, a seventh differential amplifier 143, an eighth differential amplifier 144, A / D converters 145, 146, 147, 148, a waveform correction processing unit 150, an incremental signal generation unit 151, and a displacement information calculation unit 152.

[0085] The fifth differential amplifier 141, the sixth differential amplifier 142, the seventh differential amplifier 143, and the eighth differential amplifier 144 respectively correspond to the first differential amplifier 41, the second differential amplifier 42, the third differential amplifier 43, and the fourth differential amplifier 44 described above. Also, the A / D converters 145, 146, 147, 148 respectively correspond to the A / D converters 45, 46, 47, 48 described above. Also, the waveform correction processing unit 150, the incremental signal generation unit 151, and the displacement information calculation unit 152 respectively correspond to the waveform correction processing unit 50, the incremental signal generation unit 51, and the displacement information calculation unit 52 described above.

[0086] With the configurations of the second light-receiving unit 135, the fifth differential amplifier 141, the sixth differential amplifier 142, the seventh differential amplifier 143, the eighth differential amplifier 144, the A / D converters 145, 146, 147, 148, the waveform correction processing unit 150, the incremental signal generation unit 151, and the displacement information calculation unit 152, the relative displacement along the Y-axis direction between the displacement detection head 120 and the grating scale 13 is calculated.

[0087] Also, as shown in FIG. 14, in this displacement calculation unit 140, when each signal is processed by the A / D converters 45, 46, 47, 48, 145, 146, 147, 148, it is based on the clock signal with the same clock 49, and each signal is processed synchronously. Therefore, in the displacement detection device 100 of this example, the displacements in the X-axis direction and the Y-axis direction can be calculated at the same timing.

[0088] In addition, in this example, for the sake of explanation, the detection directions are set to be at 90° like the X-axis direction and the Y-axis direction, but it is not limited to this, and a device with detection directions at different angles may also be used.

[0089] Also, in this displacement detection device 100, a phase plate may be provided between the third beam splitter 30 and the fourth beam splitter 128 and the grating scale 13. FIG. 15 illustrates a configuration in which a phase plate 129 is provided between the fourth beam splitter 128 and the grating scale 13. Although the illustration is omitted, a similar phase plate is also provided between the third beam splitter 30 and the grating scale 13. By passing through the phase plate in this way, the polarization of the interference fringes formed in the first light-receiving unit 35 and the second light-receiving unit can be changed. By doing so, while suppressing the return light to the light source 22, the outputs of the first light-receiving unit 35 and the second light-receiving unit 135 can be increased. [Third Embodiment] Next, a third embodiment of the present invention will be described. The displacement detection device 150 in this example is obtained by changing the configuration of the first light receiving unit 35 in the above-described displacement detection device 1 to the first light receiving unit 151 having the configuration shown in FIG. 16, and changing the displacement calculation unit 40 to the displacement calculation unit 160 having the configuration shown in FIG. 17. In the displacement calculation unit 160, the same reference numerals are given to the same constituent parts as those in the displacement calculation unit 40.

[0090] As described with reference to FIG. 8, the interference fringe light reflected by the grating scale 10 (13, 16) forms a pattern in which the light amount of the interference fringes changes with a period A in the space heading in the reflection direction (Z-axis direction). For example, when the grating scale 10 is displaced in the Z-axis direction, the pattern formed in the space in the Z-axis direction also moves accordingly. That is, when the grating scale 10 moves by A in the Z-axis direction, the change in the light amount of the first interference fringe light received by the first light receiving unit 35 makes one round. The period A is, when θ1 = θ2 = θ, A = D / tanθ and appears in the Z-axis direction with this period A. Specifically, when θ = 0.4° and the pitch d of the interference fringes is 47 μm, the period A is about 6.7 mm.

[0091] And the configuration of the first light receiving unit 35 shown in FIG. 9 is adopted for the purpose of canceling the change in the light amount in the optical axis direction of the first interference fringe light.

[0092] As shown in FIG. 16, the first light receiving unit 151 in this example is composed of a first element unit 152, a second element unit 153, a third element unit 154, a fourth element unit 155, and beam splitters 156, 157, 158.

[0093] The third element section 154 is provided on the optical path of the first interference fringe light reflected by the third beam splitter 30 and receives the first interference fringe light. Also, beam splitters 156, 157, and 158 are arranged in parallel between the third beam splitter 30 and the third element section 154, and are arranged at intervals of period A in the order of beam splitters 156, 157, and 158 from the side closer to the third element section 154, and each split the first interference fringe light into transmitted light and reflected light. Then, the first element section 152 is arranged to receive the reflected light reflected by the beam splitter 156, the fourth element section 155 is arranged to receive the reflected light reflected by the beam splitter 157, and the second element section 153 is arranged to receive the reflected light reflected by the beam splitter 158.

[0094] The third element section 154 is composed of light receiving elements 1c, 2c, 3c, and 4c arranged in parallel, and these elements are arranged to coincide with four areas, namely area 1, area 2, area 3, and area 4, formed by the first interference fringe light transmitted through the beam splitter 156. Also, the first element section 152 is composed of light receiving elements 1a, 2a, 3a, and 4a arranged in parallel, and these elements are arranged to coincide with area 1, area 2, area 3, and area 4 formed by the first interference fringe light reflected by the beam splitter 156.

[0095] Similarly, the fourth element section 155 is composed of light receiving elements 1d, 2d, 3d, and 4d arranged in parallel, and these elements are arranged to coincide with area 1, area 2, area 3, and area 4 formed by the first interference fringe light reflected by the beam splitter 157. Similarly, the second element section 153 is composed of light receiving elements 1b, 2b, 3b, and 4b arranged in parallel, and these elements are arranged to coincide with area 1, area 2, area 3, and area 4 formed by the first interference fringe light reflected by the beam splitter 158.

[0096] With such an arrangement, the first interference fringe light with a phase of λ / 4 is incident on the light receiving elements 1a, 1b, 1c, and 1d, the first interference fringe light with a phase of 3λ / 4 is incident on the light receiving elements 2a, 2b, 2c, and 2d respectively, the first interference fringe light with a phase of λ / 2 is incident on the light receiving elements 3a, 3b, 3c, and 3d, and the first interference fringe light with a phase of λ is incident on the light receiving elements 4a, 4b, 4c, and 4d. Then, each light receiving element outputs an electrical signal obtained by photoelectric conversion according to the received light amount.

[0097] Also, taking the period of the interference fringes in the optical axis direction formed by the first interference fringe light as A, the distance from the light receiving surface of the first element portion 152 to the center of the third element portion 154 is set to A / 2, the distance from the light receiving surface of the fourth element portion 155 to the center of the third element portion 154 is set to 3A / 4, and the distance from the light receiving surface of the second element portion 153 to the center of the third element portion 154 is set to A. Further, the distance from the center of the first element portion 152 to the light receiving surface of the third element portion 154 is set to A / 4.

[0098] By arranging in this way, the phase between the first element portion 152 and the second element portion 153 is shifted by 180°, and the phase between the third element portion 154 and the fourth element portion 155 is also shifted by 180°. Also, the phase between the first element portion 152 and the third element portion 154 is shifted by 90°. That is, when the grating scale 13 moves by A in the Z-axis direction, if the output signal from the first element portion 152 is a sin signal (sine wave) with a period of A, the output signal from the second element portion 153 is a -sin signal (sine wave), the output signal from the third element portion 154 is a cos signal (sine wave), and the output signal from the fourth element portion 155 is a -cos signal (sine wave), and the displacement amount of the grating scale 10 in the Z-axis direction can be calculated from these signals. That is, according to the displacement detection device 150 in this example, the relative displacement in the Z-axis direction between the grating scale 10 and the displacement detection head 20 can be detected.

[0099] As shown in FIG. 17, the displacement calculation unit 160 is configured such that the light receiving elements 1a and 2a of the first element unit 152 are connected to the first differential amplifier 41, and the light receiving elements 3a and 4a are connected to the second differential amplifier 42. Also, the light receiving elements 1b and 2b of the second element unit 153 are connected to the third differential amplifier 43, and the light receiving elements 3b and 4b are connected to the fourth differential amplifier 44. Then, the output signals from the first differential amplifier 41, the second differential amplifier 42, the third differential amplifier 43, and the fourth differential amplifier 44 are converted into digital signals by the A / D converters 45, 46, 47, 48 respectively, and then sequentially processed by the waveform correction processing unit 50, the incremental signal generation unit 51, and the displacement information calculation unit 52, so as to calculate the relative displacement in the X-axis direction between the grating scale 10 and the displacement detection head 20. Generally, the resolution of the displacement information is determined by the number of divisions by the A / D converters 45, 46, 47, 48. When the signal period is 47 μm and the number of divisions of the A / D converters 45, 46, 47, 48 is 2 16 , that is, 65536 divisions, the resolution of the displacement information by the incremental signal generation unit 51 is 0.7 nm.

[0100] Also, the light receiving elements 1a, 2a, 3a, and 4a of the first element unit 152 are connected to the first addition amplifier 161, and the light receiving elements 1b, 2b, 3b, and 4b of the second element unit 153 are connected to the second addition amplifier 162. Also, the light receiving elements 1c, 2c, 3c, and 4c of the third element unit 154 are connected to the third addition amplifier 163, and the light receiving elements 1d, 2d, 3d, and 4d of the fourth element unit 155 are connected to the fourth addition amplifier 164.

[0101] The first adder amplifier 161 adds the output signals from each element of the first element section 152, the second adder amplifier 162 adds the output signals from each element of the second element section 153, the third adder amplifier 163 adds the output signals from each element of the third element section 154, and the fourth adder amplifier 164 adds the output signals from each element of the fourth element section 155. Then, the output signals from the first adder amplifier 161, the second adder amplifier 162, the third adder amplifier 163, and the fourth adder amplifier 164 are each converted into digital signals by A / D converters 165, 166, 167, 168 and then input to the waveform correction processing section 169.

[0102] The waveform correction processing section 169 calculates the difference between the output value of the first adder amplifier 161 and the output value of the second adder amplifier 162 to generate a sin signal (sine wave signal) with the DC component canceled, and calculates the difference between the output value of the third adder amplifier 163 and the output value of the fourth adder amplifier 4 to generate a cos signal (sine wave signal) with the DC component canceled. Then, the incremental signal generation section 170 detects the phase change per unit time using the generated sin signal and cos signal, and the displacement information calculation section 171 calculates the relative displacement in the Z-axis direction between the grating scale 10 and the displacement detection head 20 based on this phase change per unit time. Generally, the resolution of the displacement information is determined by the number of divisions by the A / D converters 165, 166, 167, 168. When the signal period is 6.7 mm and the number of divisions of the A / D converters 165, 166, 167, 168 is 2 16 , that is, 65536 divisions, the resolution of the displacement information by the incremental signal generation section 170 is 0.1 μm.

[0103] As described above, according to the displacement detection device 150 of this example, the relative displacement in the Z-axis direction between the grating scale 10 and the displacement detection head 20 can be calculated. Further, by applying the detection mechanism in the Y-axis direction shown in the second embodiment to this displacement detection device 150, the relative displacement between the grating scale 10 and the displacement detection head 20 in the three orthogonal axes of the X-axis, Y-axis, and Z-axis, in other words, in a three-dimensional space can be detected.

[0104] Regarding the drawings referred to in the above examples, the interference fringe light illustrated in each figure is merely for the convenience of explanation and shows the concept in an easy-to-understand manner, but does not accurately illustrate the actual interference fringe light. Therefore, the interference fringe light illustrated in each figure does not necessarily match each other.

[0105] Although the specific embodiments of the present invention have been described above, the descriptions of the above-described embodiments are illustrative in all respects and not restrictive. Modifications and changes are appropriately possible for those skilled in the art. The scope of the present invention is indicated not by the above-described embodiments but by the claims. Furthermore, the scope of the present invention includes modifications from the embodiments within the scope equivalent to the claims.

Explanation of Reference Numerals

[0106] 1 Displacement detection device 10 Grating scale 11 Scale substrate 12 Grating pattern 20 Displacement detection head 21 Case 22 Light source 23 Expander 24 First beam splitter 25 First mirror 26 Composite phase plate 27 Second mirror 28 Adjustment mechanism 29 Second beam splitter 30 Third beam splitter 35 First light receiving part 36 First element part 37 Second element part 40 Displacement calculation part 41 First differential amplifier 42 Second differential amplifier 43 Third differential amplifier 44 Fourth differential amplifier 45, 46, 47, 48 A / D converter 49 Clock 50 Waveform correction processing part 51 Incremental signal generation part 52 Displacement information calculation unit

Claims

1. A detection head that irradiates interference fringe light onto a grating scale, comprising: a light source that emits coherent light; an expander provided on the optical path of the light emitted from the light source, which converts the incident light into a plane wave and transmits it; a first beam splitter provided on the optical path of the light transmitted through the expander, which splits the transmitted light into a first light that is transmitted light and a second light that is reflected light; a first mirror provided on the optical path of the first light transmitted through the first beam splitter, which reflects the first light; a second mirror provided on the optical path of the second light reflected by the first beam splitter, which reflects the second light toward the grating scale and intersects the first light reflected by the first mirror; a composite phase plate provided on the optical path between the first beam splitter and the first mirror, which divides the incident second light into lights in a plurality of areas with different phases and transmits them; a second beam splitter provided at the position where the first light reflected by the first mirror and the second light reflected by the second mirror intersect, which reflects the first light toward the grating scale and transmits the second light, thereby generating first interference fringe light by overlapping the first light and the second light; a third beam splitter provided on the optical path of the first interference fringe light, which transmits the first interference fringe light, irradiates it toward the grating scale, and reflects the reflected light from the grating scale in a predetermined direction; a first light receiving unit that receives the light reflected by the third beam splitter; a displacement calculation unit that receives the output signal from the first light receiving unit and calculates the displacement between the grating scale and the grating scale in the direction along the surface of the grating scale. A displacement detection head comprising:

2. The displacement detection head according to claim 1, wherein a first optical path length from the first beam splitter to the second beam splitter for the first light and a second optical path length from the first beam splitter to the second beam splitter for the second light are set to the same length.

3. The displacement detection head according to claim 2, further comprising an adjustment mechanism for adjusting the position and angle of at least one of the first mirror and the second mirror.

4. The first light receiving unit is configured to detect the intensity of the light that appears in the optical axis direction among the interference fringes included in the first interference fringe light reflected by the grating scale. The displacement calculation unit is configured to calculate the displacement between the grating scale in the direction along the surface and the direction orthogonal to the surface of the grating scale, for the displacement detection head according to claim 1.

5. The second beam splitter is further configured to generate second interference fringe light by transmitting the first light reflected by the first mirror and reflecting the second light reflected by the second mirror, thereby superimposing the first light and the second light. Furthermore, a third mirror that reflects the second interference fringe light in a direction orthogonal to its optical path. A fourth mirror that reflects the second interference fringe light reflected by the third mirror toward the grating scale. A fourth beam splitter provided on the optical path of the second interference fringe light reflected by the fourth mirror, configured to transmit the second interference fringe light, irradiate it toward the grating scale, and reflect the reflected light from the grating scale in a predetermined direction. A second light receiving unit that receives the light reflected by the fourth beam splitter. The displacement calculation unit is configured to receive the output signals from the first light receiving unit and the second light receiving unit, and calculate the displacement between the grating scale in two orthogonal directions along the surface of the grating scale, for the displacement detection head according to claim 1.

6. The first light receiving unit is configured to detect the intensity of the interference fringes included in the first interference fringe light reflected by the grating scale and appearing in the direction of its optical axis. The second light receiving unit is configured to detect the intensity of the interference fringes included in the second interference fringe light reflected by the grating scale and appearing in the direction of its optical axis. The displacement calculation unit is configured to calculate the displacement between the grating scale in two orthogonal directions along the surface of the grating scale and the direction orthogonal to the surface, for the displacement detection head according to claim 5.

7. A displacement detection head according to any one of claims 1 to 6, A displacement detection device comprising a grating scale having a one-dimensional or two-dimensional grating pattern on its surface and arranged to face the displacement detection head.

Images