JP6231297B2 - Displacement measuring device and displacement measuring method - Google Patents

Description

  The present invention relates to a displacement measuring apparatus and a displacement measuring method using optical interference.

  For example, Patent Document 1 discloses a displacement measuring device using optical interference. This displacement measuring device includes a laser light source, a collimator lens, a first diffraction grating, a second diffraction grating, and an optical sensor in this order from the light source side. The optical sensor diffracted light (for example, 1st order) diffracted by the first diffraction grating and diffracted light (for example, 1st order) generated by diffracting the 0th order light traveling straight through the first diffraction grating with the second diffracted light. Next, the interference light is detected. This displacement measuring device measures a change in the distance between the first and second diffraction gratings, that is, a displacement to be measured based on a change in the amount of light due to the brightness of the interference light detected by the optical sensor (for example, patent document). 1 specification paragraphs [0020], [0023], [0027], see FIGS.

  The photoelectric encoder described in Patent Document 2 includes two diffraction gratings and a moving grating. Six light beams (21a, 21b, 22a, 22b, 23a, 23b) generated by being diffracted by two diffraction gratings are incident on the moving grating, and light beams in three different directions are emitted from the moving grating 5. Are received by three light receiving elements, respectively. Based on the output signals of these light receiving elements, the encoder processing circuit calculates the phase information of the interference light intensity, so that the displacement of the moving grating in the x and z directions and the displacement of the pitch angle that is the inclination around the y axis are reduced. Information is obtained (see, for example, paragraphs [0008] to [0014] in FIG. 1 of Patent Document 2).

International Publication No. 2011/043354 Pamphlet JP 2005-326232 A

  In the photoelectric encoder of Patent Document 2, since the linear displacement and the angular displacement around the axis are measured as described above, the number of optical components is increased and it is difficult to reduce the size.

  An object of the present invention is to provide a displacement measuring device and a displacement measuring method capable of measuring a displacement in a predetermined direction without using many optical components.

In order to achieve the above object, a displacement measuring apparatus according to an aspect of the present invention includes a light source, a first diffraction grating, a second diffraction grating, a first optical sensor, and a second optical sensor.
The first and second diffraction gratings are disposed along the path of the light beam from the light source, are movable relative to each other, and generate diffracted light.
The first optical sensor has a path of + n-order diffracted light (n is a natural number equal to or greater than 1) by the first diffraction grating among diffracted lights generated by the first diffraction grating and the second diffraction grating. Detect the interference light of a set of diffracted light along.
The second optical sensor includes a set of diffracted light along a path of −n-order diffracted light by the first diffraction grating among diffracted lights generated by the first diffraction grating and the second diffraction grating. Interfering light is detected.

A displacement measurement method according to an aspect of the present invention is a first diffraction grating that is arranged along a path of a light beam from a light source, is relatively movable, has a grating line in the same direction, and generates diffracted light. And a method of measuring displacement using the second diffraction grating.
Among the diffracted lights generated by the first diffraction grating and the second diffraction grating, interference of a set of diffracted lights along the path of + n-order diffracted light (n is a natural number of 1 or more) by the first diffraction grating. Light is detected by the first photosensor.
Among the diffracted lights generated by the first diffraction grating and the second diffraction grating, the interference light of a set of diffracted lights along the path of −n-order diffracted light by the first diffraction grating is a second optical sensor. Is detected.
Then, based on the signals obtained by the first optical sensor and the second optical sensor, relative rotation of the first and second diffraction gratings about an axis along the direction of the grating line. Angular displacement is calculated.

FIG. 1 is a diagram schematically showing a configuration of a basic optical system of a displacement measuring apparatus according to the first embodiment of the present invention. FIG. 2 shows a state of the diffraction grating pair in which no tilt is generated. FIG. 3 shows a state of the diffraction grating pair in which tilt has occurred. FIG. 4 shows both positive and negative order side interference light in a diffraction grating pair in which no tilt occurs. FIG. 5 shows both positive and negative order interference light in a diffraction grating pair in which no tilt occurs. FIG. 6 is an actual measurement graph showing the relationship between the amount of tilt between the diffraction gratings and the difference in signal intensity obtained between the first and second PDs. FIG. 7 is a diagram showing an optical system of a displacement measuring apparatus according to the second embodiment of the present invention. FIG. 8 is a graph schematically showing the relationship between the relative displacement in the z direction of the diffraction grating pair and the signal detected by the first PD. FIG. 9 shows a change in the amount of light detected in the light receiving region of the first PD when the linear region is used as the detection region in the graph of FIG. FIG. 10 shows a change in the interference light incident on the light receiving region of the first PD according to the tilt amount between the diffraction gratings. FIG. 11 shows a flowchart of basic tilt correction processing. FIG. 12 is a perspective view showing an adjustment mechanism for adjusting the tilt. 13 is a plan view of the adjustment mechanism shown in FIG. FIG. 14 shows a drive mechanism according to another embodiment. FIG. 15 is a diagram for explaining another tilt correction method. FIG. 16 is a flowchart showing processing according to another tilt correction method. FIG. 17 is a cross-sectional view showing the configuration of the displacement measuring device and showing the optical system shown in FIGS. 1 and 7 and a housing for housing the optical system. FIG. 18 shows a state where the displacement measuring device is attached to a structure such as a frame as a measurement object.

  The displacement measuring device mainly includes a diffraction grating pair, a first optical sensor, and a second optical sensor, and a predetermined direction is obtained by arithmetic processing based on signals obtained by the first and second optical sensors. Can be measured. That is, the displacement can be measured with a small number of optical components, and the apparatus can be miniaturized.

  The displacement measuring device has axes along the direction of the respective grating lines of the first diffraction grating and the second diffraction grating based on the signals obtained by the first optical sensor and the second optical sensor. A processing unit that calculates an angular displacement of the relative rotation of the surrounding first and second diffraction gratings may be further included. When this displacement measuring device is attached to a measurement object, it is possible to detect an angular displacement around the axis of the measurement object, that is, a tilt amount.

  The processing unit may calculate the angular displacement based on a difference value between signals obtained by the first and second optical sensors. Since there is a correlation between the angular displacement that is the measurement target and the difference between the detected values, the angular displacement can be obtained by obtaining this difference.

  The processing unit detects a displacement in a direction along the optical axis of the first and second diffraction gratings based on a signal obtained by any one of the first and second optical sensors. May be. Accordingly, the displacement measuring device can detect both the displacement in the direction along the optical axis between the diffraction gratings and the tilt amount.

  The processing unit may execute processing for correcting the angular displacement. When measuring the displacement in the direction along the optical axis between the diffraction gratings, the measurement accuracy of the displacement in the direction along the optical axis between the diffraction gratings can be improved by correcting the tilt of the diffraction grating.

  For example, the processing unit may determine whether or not the calculated angular displacement exceeds a threshold value, and may execute processing for correcting the angular displacement when the angular displacement exceeds the threshold value. The processing unit may execute a process of correcting the angular displacement when a difference between the detection values exceeds a threshold value.

  The displacement measuring device may further include an adjustment mechanism that rotates the first or second diffraction grating in the direction of the angular displacement. The processing unit may control the adjustment mechanism based on the calculated angular displacement. The tilt of the two diffraction gratings can be corrected by operating the adjustment mechanism.

  The first optical sensor includes + 1st order diffracted light of the second diffraction grating generated by incidence of 0th order light generated from the first diffraction grating to the second diffraction grating, and the first optical sensor. The + 1st order diffracted light generated from the diffraction grating may enter the second diffraction grating, and interference light with the 0th order light generated from the second diffraction grating may be detected. In addition, the second optical sensor includes the -1st order diffracted light of the second diffraction grating generated when the 0th order light generated from the first diffraction grating enters the second diffraction grating, and The −1st order diffracted light generated from the first diffraction grating may enter the second diffraction grating, and interference light with the 0th order light generated from the second diffraction grating may be detected.

  By using 0th-order light and ± 1st-order diffracted light with a large amount of light, a voltage signal as large as possible can be obtained by the first and second photosensors, and measurement accuracy can be improved.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  1. First embodiment

(1) Basic Configuration of Displacement Measuring Device FIG. 1 is a diagram schematically showing a basic optical system configuration of a displacement measuring device according to the first embodiment of the present invention.

  The displacement measuring apparatus 100 includes a light source 12, a collimator lens 14, a diffraction grating pair 20, a first PD (Photo Detector) 31 as a photosensor, and a second PD32.

  The light source 12 is an LD (Laser Diode) or an LED (Light Emitting Diode), and is driven by a driver (not shown).

  The collimator lens 14 turns the light emitted from the light source 12 into parallel light 15. At least the light source 12 and the collimator lens 14 constitute an optical system that generates parallel light.

  Light from the light source 12 and the collimator lens 14 enters the diffraction grating pair 20 and emits diffracted light. The diffraction grating pair 20 includes a first diffraction grating 21 and a second diffraction grating 22. The first diffraction grating 21 and the second diffraction grating 22 are arranged so as to face each other along the paths of the light beams from the light source 12 and the collimator lens 14, here along the optical axes of the light source 12 and the collimator lens 14. As described later, it is relatively movable in a predetermined direction.

  The first diffraction grating 21 converts the incident parallel light 15 into 0-order light, straight-ahead light 30, + n-order diffracted light (n is a natural number greater than or equal to 1; the same applies hereinafter) 23, and −n-order diffracted light 24 Divide and advance. In the present embodiment, + 1st order diffracted light is used as the diffracted light 23, and −1st order diffracted light is used as the diffracted light 24.

  In the figure, the order of the diffracted light generated on one side in the x direction with respect to the straight light 30 that is the zeroth order light is + n order, and the order of the diffracted light generated on the other side in the x direction is -n order For convenience, the description content is unified.

  The second diffraction grating 22 emits the straight light 30 emitted from the first diffraction grating 21 and made incident on the second diffraction grating 22, further the straight light 30, the + n-order diffracted light 25, and the −n-order diffracted light 26. It is divided and progressed. In the present embodiment, + 1st order diffracted light is used as the diffracted light 25, and −1st order diffracted light is used as the diffracted light 26.

  The second diffraction grating 22 also generates zero-order light that causes the ± first-order diffracted lights 23 and 24 emitted from the first diffraction grating 21 to travel in the same direction. Here, for convenience of explanation, the first-order diffracted light 23 (or 24) of the first diffraction grating 21 and the 0th-order light of the second diffraction grating 22 along the path thereof are collectively combined into the first-order diffracted light 23 (or 24). It expresses. Further, after passing through the first diffraction grating 21 and the second diffraction grating 22, the 0th order light traveling in the same direction as the parallel light 15 is collectively expressed as a straight traveling light 30.

The configurations of the diffracted beams 23 to 26 are listed below (see FIG. 4).
Diffraction light 23: + 1st order diffracted light of diffraction grating 21 and 0th order light of diffraction grating 22 Diffraction light 24: -1st order diffracted light of diffraction grating 21 and 0th order light of diffraction grating 22 Diffraction light 25: 0th order light of diffraction grating 21 And + 1st order diffracted light from diffraction grating 22 Diffracted light 26: 0th order light from diffraction grating 21 and −1st order diffracted light from diffraction grating 22

  Of each diffracted light generated by the first diffraction grating 21 and the second diffraction grating 22, at least one set of diffracted light along the path of the + 1st order diffracted light 23 (-1st order diffracted light 24) by the first diffraction grating 21. Interfering light is generated from the diffraction grating pair 20.

  Specifically, the + 1st-order diffracted light 23 by the first diffraction grating 21 interferes with the + 1st-order diffracted light 25 generated when the straight traveling light 30 enters the second diffraction grating 22 to generate interference light 27. Further, the -1st order diffracted light 24 from the first diffraction grating 21 interferes with the -1st order diffracted light 26 generated when the straight traveling light 30 enters the second diffraction grating 22 to generate interference light 28. The first PD 31 detects the interference light 27 on the positive order side, and the second PD 32 detects the interference light 28 on the negative order side.

  In this embodiment, 0th-order light and ± 1st-order diffracted light are used, but displacement may be measured using other predetermined orders of diffracted light. In practice, there are many diffracted lights other than those shown in FIG. 1, but the illustration is omitted to facilitate the following description. The same applies to the description of other embodiments and later described later.

  The first diffraction grating 21 and the second diffraction grating 22 have substantially the same shape and the same size. For example, these diffraction gratings 21 and 22 have a plurality of grating lines 21a and 22a, which are grooves along the y direction orthogonal to the z direction in FIG. The pitch P of the grating lines 21a of the first diffraction grating 21 and the pitch P of the grating lines 22a of the second diffraction grating 21 are formed substantially the same. As an example of the lattice lines 21a and 22a, the pitch P is 3.3 μm and the groove depth is 473 μm. Of course, it is not restricted to these values.

  The displacement measuring apparatus 100 according to the present embodiment calculates the angular displacement Δθ of the relative rotation of the first diffraction grating 21 and the second diffraction grating 22 around the y axis that is an axis along the grating lines 21a and 22a. Measured. That is, the amount of tilt between the first diffraction grating 21 and the second diffraction grating 22 is a measurement target.

  The arithmetic circuit 40 calculates a tilt Δθ by performing a predetermined arithmetic processing based on signals obtained by the first PD 31 and the second PD 32. In this case, the arithmetic circuit 40 functions as a processing unit. The arithmetic circuit 40 mainly includes hardware such as an MPU (Micro Processing Unit), a RAM (Random Access Memory), and a ROM (Read Only Memory). The arithmetic circuit 40 may include a PLD (Programmable Logic Device) such as an FPGA (Field Programmable Gate Array) in addition to or instead of the MPU, or a DSP (Digital Signal Processor), ASIC (Application Specific Integrated Circuit) or the like may be provided. The arithmetic circuit 40 may be configured by a plurality of physically separated chip packages or elements.

  As will be described later, the light source 12, the collimator lens 14, the diffraction grating pair 20, the first PD 31 and the second PD 32 are capable of supporting these parts such as a frame and the parts such as a frame. Are held together by means. These frames or housings have a part for holding them so that the first diffraction grating 21 and the second diffraction grating 22 can move relatively, and this part is more rigid than the other parts. It is set low.

  (2) Tilt detection principle between diffraction gratings

  FIG. 2 shows a state of the diffraction grating pair 20 in which no tilt is generated. Here, of the positive and negative order diffracted light, only the positive order side is shown. The desired distance between the diffraction gratings 21 and 22 is D, and the diffraction angle of the diffracted light 23 generated by the first diffraction grating 21 is θ.

  As shown in FIG. 2, the optical path lengths from the diffracted light 23 and the straight traveling light 30 emitted from the first diffraction grating 21 to the second diffraction grating 22 are A and B, respectively. The optical path difference B-A can be expressed by the following equation (1).

  When this optical path difference B-A satisfies mλ (λ is the wavelength of light), the interference light 27 is intensified, and when it satisfies m (1 + 1/2) λ, it is weakened.

  The derivation method of the above formula (1) is as follows.

  FIG. 3 shows a state of the diffraction grating pair 20 in which tilt has occurred. In such a state where the tilt is generated, the optical path difference B1-A is expressed by the following equation (2).

  3 shows a triangle formed by the line A, the line B1, and the second diffraction grating 22 in FIG. The method for deriving the above formula (2) is as follows.

  FIG. 4 shows both positive and negative order side interference lights 27 and 28 in the diffraction grating pair 20 in which no tilt occurs. When no tilt occurs, the optical path on the positive order side and the optical path on the negative order side are symmetrically arranged with respect to the optical axis in the z direction in FIG. 4, and the optical path difference B-A and the optical path difference on the negative order side B′-A ′ represents the same value. At this time, B−A (= B′−A ′) is expressed as Expression (1). Therefore, at this time, the light amounts of the interference lights 27 and 28 detected by the first PD 31 and the second PD 32 are substantially the same.

  However, as shown in FIG. 5, when tilt occurs between the diffraction gratings 21 and 22, the optical path difference B1-A on the positive order side is expressed by the following equation (2), and the optical path difference on the negative order side. B1′−A ′ is expressed by the following equation (3), and the positive order side and the negative order side have different values.

  Therefore, in this case, the detection values of the first PD 31 and the second PD 32 are different.

  FIG. 6 is an actual measurement graph showing the relationship between the amount of tilt between the diffraction gratings 21 and 22 and the difference in signal intensity obtained between the first PD 31 and the second PD 32. This difference in signal intensity is equivalent to the lightness difference or light quantity of each interference light 27 and 28 in the light receiving area of each PD 31 and 32.

  The wavelength of the light from the light source 12 was 633 nm, and the diffraction angle in the diffraction grating pair 20 was 11 deg. The brightness difference on the vertical axis is normalized and the unit is dimensionless. As can be seen from this graph, the brightness difference becomes more significant as the tilt amount increases. The arithmetic circuit 40 can output a tilt amount corresponding to the calculated brightness difference by storing the relationship of FIG.

  As described above, in this embodiment, the diffraction grating pair 20, the first PD 31, and the second PD 32 are provided, and the angle around the y axis is calculated by calculating the difference value between the signals obtained by the PD 31 and 32. Displacement can be measured. That is, the displacement can be measured with a small number of optical components, and the displacement measuring apparatus 100 can be downsized.

  In the present embodiment, by using the 0th-order light and the 1st-order diffracted light with a large amount of light, as large a voltage signal as possible can be obtained by the PDs 31 and 32, and the measurement accuracy can be improved.

  2. Second embodiment

(1) Basic Concept FIG. 7 is a diagram showing an optical system of a displacement measuring apparatus according to the second embodiment of the present invention. The configuration of the optical component in the displacement measuring device according to the present embodiment is substantially the same as the configuration of the displacement measuring device 100 according to the first embodiment. The difference is the processing by the arithmetic circuit 40. As shown in FIG. 7, the arithmetic circuit 40 has a relative relationship between the diffraction gratings 21 and 22 based on a signal obtained from any one of the first PD 31 and the second PD 32, here the first PD 31. The displacement Δz in the z direction is calculated.

(2) Detection principle of displacement in z direction Referring to FIG. 1, for example, when the second diffraction grating 22 is displaced in the z direction with respect to the first diffraction grating 21, each path of the diffracted light 23 and 25 ( Optical path) difference occurs. Therefore, interference fringes are generated by the interference light 27 between the diffracted light 23 by the first diffraction grating 21 and the diffracted light 25 by the second diffraction grating 22. The first PD 31 detects a change in the amount of interference fringes.

  FIG. 8 is a graph schematically showing the relationship between the relative displacement in the z direction of the diffraction grating pair 20 and the signal (voltage value) detected by the first PD 31. In FIG. 8, as described later, both the case where the tilt between the diffraction grating pairs 20 does not occur (shown by a solid line) and the case where a predetermined tilt occurs (shown by a broken line) are shown. As described above, the detection signal of the first PD 31 draws a sine curve in accordance with the repeated bright and dark interference fringes. This sine curve corresponds to the displacement in the z direction to be measured. The arithmetic circuit 40 can obtain a signal intensity corresponding to a displacement in a predetermined range in the z direction by using, for example, a substantially linear region corresponding to a half wavelength among the light amount change of the sine curve of the interference fringes.

  FIG. 9 shows a change in the amount of light (or brightness) detected in the light receiving region of the first PD 31 when the linear region is used as a detection region. In this way, light having uniform brightness enters the entire light receiving region of the first PD 31, and the brightness changes for each distance between the diffraction gratings in the z direction.

  The first PD 31 outputs a current corresponding to a change in light amount due to the interference fringes of the interference light 27 to the arithmetic circuit 40 as an output signal. The arithmetic circuit 40 converts the current output from the first PD 31 into a voltage corresponding to the change in the light amount. Thereby, the arithmetic circuit 40 can output the displacement between the diffraction gratings in the z direction with high accuracy.

(3) Influence on Measurement Accuracy due to Generation of Tilt FIG. 10 shows a change in the interference light 27 incident on the light receiving region of the first PD 31 according to the tilt amount Δθ between the diffraction gratings 21 and 22 (see FIG. 1). Indicates. As the tilt amount increases, the generation of interference fringes becomes more prominent and the number of interference fringes increases. In the leftmost diagram of FIG. 10, no tilt is generated, and the first PD 31 can receive the interference light 27 with a uniform light amount as described above, whereby the diffraction grating 21 in the z direction and The measurement accuracy of the displacement between 22 can be kept constant. However, for example, as shown in the two diagrams on the right side of FIG. 10, when a tilt of a predetermined amount or more occurs, the amount of light received in the light receiving area of the first PD 31 is not stable, and the displacement between the diffraction gratings 21 and 22 in the z direction is not stable. Measurement accuracy decreases.

  FIG. 8 is a graph explaining this. The amplitude of the detection signal is maximized in a state where no tilt occurs between the diffraction gratings 21 and 22. As can be seen from the graph shown in FIG. 8, when a predetermined amount of tilt occurs, the first PD 31 outputs a voltage value different from the voltage value corresponding to the actual displacement amount, and the detection accuracy decreases. To do. In addition, when the tilt is generated, the amplitude of the signal is reduced, so that the range of the linear region that can be used as the detection region is narrowed.

  Therefore, the displacement measuring apparatus according to the present embodiment corrects the tilt as follows in order to reduce the error in the detected value due to the tilt amount.

(4) Correction of Tilt FIG. 11 shows a flowchart of basic tilt correction processing. When the power source of the displacement measuring device is turned on (step 101), the interference light 27 and 28 are received by the first PD 31 and the second PD 32, respectively, and the arithmetic circuit 40 obtains their voltage values ( Step 102). The arithmetic circuit 40 calculates those difference values (step 103) and determines whether or not the difference values are equal to or less than a threshold value T (see FIG. 6) (step 104). If the difference value is equal to or less than the threshold value T, the arithmetic circuit 40 measures the displacement in the z direction assuming that the tilt amount is within the allowable range (step 107).

  On the other hand, if the difference value exceeds the threshold value T in the determination process of step 104, the arithmetic circuit 40 stores the tilt amount in the memory (step 105) and executes a process for correcting the tilt amount (step 105). Step 106). A specific tilt correction method will be described below.

(A) Tilt correction method 1
FIG. 12 is a perspective view showing an adjustment mechanism that adjusts the tilt by driving any one of the first diffraction grating 21 and the second diffraction grating 22 in the diffraction grating pair 20. FIG. 13 is a plan view thereof. In the example of these drawings, the first diffraction grating 21 is fixed, and the second diffraction grating 22 is driven by the adjusting mechanism 60.

  The adjustment mechanism 60 includes a rotating body 63 that supports the second diffraction grating 22 and a drive unit 65 that rotates the rotating body 63 about the y-axis. The rotating body 63 has, for example, a semi-cylindrical shape including a flat portion 63b. The second diffraction grating 22 is attached and fixed to the flat surface portion 63 b of the rotating body 63. The rotating body 63 has a drive shaft 64 provided along the y-axis direction, and the drive shaft 64 is driven by the drive unit 65. The drive shaft 64 is formed in a gear shape, for example.

  The drive unit 65 includes, for example, a stepping motor 62 and a screw unit 66 connected thereto. For example, like the worm gear, the screw portion 66 is engaged with the drive shaft 64, and the rotating body 63 can rotate around the y-axis by the rotation of the screw portion 66.

  The adjustment mechanism 60 is provided with a wall member 68 having a V-groove-shaped wall surface 68a. As shown in FIG. 13, the side surface portion 63a formed in a cylindrical surface shape of the rotating body 63 is in contact with the wall surface 68a at two locations. As described above, the rotating body 63 is supported by the V-groove shaped wall surface 68a, so that the rotating body 63 can be stably rotated while being in contact with the wall surface 68a. Therefore, the movement of the second diffraction grating 22 other than the direction along the z axis and the direction other than the direction around the y axis can be reliably restricted. The movement of the diffraction grating pair 20 in the z direction is ensured by, for example, a structure of a casing described later.

  The rotating body 63 and the wall member 68 are provided with passages 63c and 68c through which at least a part of the interference lights 27 and 28 (see FIGS. 1 and 7) emitted from the diffraction grating pair 20 pass. Yes. These passages 63 c and 68 c are formed through the rotating body 63 and the wall member 68.

  In step 106, the arithmetic circuit 40 generates a control signal for driving the drive unit 65 of the adjustment mechanism 60 based on the difference value obtained in step 103 shown in FIG. A driver (not shown) of the driving unit 65 generates a driving signal based on the control signal output from the arithmetic circuit 40 so that the driving unit 65 outputs the driving amount of the rotating body 63 corresponding to the difference value. Specifically, the driving amount of the rotating body 63 is a driving amount such that the generated tilt amount is equal to or less than the threshold value T.

  As described above, the tilt is corrected by the adjusting mechanism 60, the influence on the z-direction displacement detection is reduced, and the measurement accuracy of the z-direction displacement is improved.

  FIG. 14 shows an adjustment mechanism according to another embodiment. The adjustment mechanism 70 includes, for example, a piezoelectric actuator 67 supported by a support 69 as a drive unit. The piezoelectric actuator 67 is in contact with the drive shaft 61 of the rotating body 63. When the piezoelectric actuator 67 moves in the direction of the arrow, the power is transmitted to the drive shaft 61, and the rotating body 63 rotates.

  As an adjustment mechanism, it is not restricted to the form shown in FIGS. For example, there may be no member such as the rotating body 63, the second diffraction grating 22 may be provided with a rotating shaft, and the rotating shaft may be driven. A diffraction grating having such a fine structure can be realized by MEMS (Micro Electro Mechanical Systems) technology.

(B) Tilt correction method 2
It is not restricted to the form using the said adjustment mechanism, The arithmetic circuit 40 may correct | amend a tilt with software. FIG. 16 is a flowchart showing this correction processing. For example, as shown in FIG. 8, the arithmetic circuit 40 stores the relationship between the detection signal S of the first PD 31 and the amount of displacement in a state where no tilt has occurred (step 200). This step 200 may be performed at the device design stage or manufacturing stage. Steps 201 to 205 are the same as steps 101 to 105 described above.

  In step 206, the arithmetic circuit 40, as shown in FIG. 15, with respect to the detection signal, as shown by the broken line of the first PD 31, the detection signal S ′ of the displacement amount in the z direction when the tilt is occurring, Processing to replace the stored detection signal S is performed. That is, the arithmetic circuit 40 performs a process of compensating for an error in the displacement amount detected in the z direction by the tilt amount exceeding the allowable range (step 206). For example, the replacement process may be performed on the detection values for the half wavelength region to be used.

  Specifically, for example, at the design stage or manufacturing stage of the apparatus, the arithmetic circuit 40 may store in advance a difference value between the levels of the detection signal S and the detection signal S ′ according to the tilt amount. As a result, in step 206, the arithmetic circuit 40 refers to the table indicating the relationship between the stored tilt amount and the level difference value according to the tilt amount stored in step 205, and outputs a signal from the detection signal S ′. Substitution processing for S can be performed.

  The arithmetic circuit 40 outputs the stored displacement amount corresponding to the detected value after the replacement as described above as an actual displacement amount (step 207).

  Note that the tilt correction methods 1 and 2 may be processing performed after shipment of the product as the displacement measuring device, or processing performed before product shipment (manufacturing stage), The process performed in both of these may be sufficient.

  The displacement measuring apparatus according to the present embodiment uses the displacement Δz in the z direction between the diffraction gratings 21 and 22 as a measurement object. In addition to this Δz, the tilt amount Δθ is used as a measurement object as in the first embodiment. Also good.

  The photoelectric encoder described in Patent Document 2 measures displacement in two orthogonal axes and angular displacement around one axis, that is, a total of three displacements. For this reason, this photoelectric encoder applies the principle of laser Doppler shift and calculates phase information using three diffraction gratings and three light receiving elements, so the processing circuit needs to perform complicated calculations. is there. On the other hand, the displacement measuring apparatus according to this embodiment includes two diffraction gratings and two optical sensors. When this displacement measuring apparatus measures both displacements of Δz and Δθ as described above, although it is one less than the measurement target of the photoelectric encoder of Patent Document 2, the diffraction grating and the optical sensor are compared with the photoelectric encoder. One by one can be reduced. Therefore, downsizing can be realized.

  In the second embodiment described above, the signal obtained by the first PD 31 was used to detect the displacement in the z direction between the diffraction gratings 21 and 22, but of course the signal obtained by the second PD 32. May be used for this purpose.

  3. Housing that supports the optical components of the displacement measuring device

  FIG. 17 is a cross-sectional view showing the configuration of the above-described displacement measuring apparatus 100 and showing the optical system shown in FIGS. 1 and 7 and a housing 50 that accommodates the optical system.

  The housing 50 has a hole 55 in which the optical path is disposed. The hole 55 includes a first hole 55 a from the light source 12 to the diffraction grating pair 20, a second hole 55 b from the diffraction grating pair 20 to the first PD 31, and a second PD 32 from the diffraction grating pair 20. Up to the third hole 55c. The second hole portion 55b and the third hole portion 55c are formed at angles that allow the interference lights 27 and 28 along the path of the ± nth order, here ± 1st order diffracted light, to pass therethrough.

  Hereinafter, the z-axis along the longitudinal direction of the first hole 55a is referred to as a main axis for convenience. The direction of the main axis is parallel to the optical axis of the diffraction grating pair 20.

  Mounting boards 51 and 52 are mounted on both ends of the housing 50 in the main axis direction, respectively. The light source 12 is mounted on the mounting substrate 51, and the first PD 31 and the second PD 32 are mounted on the mounting substrate 52.

  The housing 50 includes a light source side member 50a, a sensor side member 50b, and a spring portion 50c provided therebetween. The spring portion 50c is formed by providing two cutouts 53 on each of two opposing side surfaces of the casing 50 and providing a slit 54 therein. The diffraction grating pair 20 is held by the housing 50 so as to sandwich the slit 54. Since the casing 50 can be expanded and contracted in the main axis direction and the y-axis by the spring portion 50c, the first diffraction grating 21 and the second diffraction grating 22 can be relatively moved, and the displacement measurement of Δz and Δθ can be performed. It becomes.

  As a material of the housing 50, metal or resin is used. In the case of a metal, for example, stainless steel, aluminum and the like can be mentioned. The light source side member 50a and the sensor side member 50b may be formed of a first material, and the spring portion 50c may be formed of a second material having a Young's modulus lower than that of the first material. In this case, the first material is a metal and the second material is a resin. Of course, different types of metals may be used as the first and second materials, or different types of resins may be used.

  FIG. 18 shows a state in which the displacement measuring apparatus 100 is attached to a structure such as a frame as a measurement object. The structure 150 includes, for example, a housing frame (column or beam), but is not limited thereto, and may be an arbitrary frame. The structure 150 is not limited to a frame, and any object having a relatively high rigidity may be used.

  4). Other embodiments

  The present invention is not limited to the embodiment described above, and other various embodiments can be realized.

  The arithmetic circuit 40 according to the second embodiment determines whether or not the difference between the detection values of the first PD 31 and the second PD 32 exceeds a threshold value, and performs tilt correction based on the determination result. However, the arithmetic circuit 40 may obtain the tilt amount from the difference between the detection values of the PDs 31 and 32, determine whether the tilt amount exceeds a threshold value, and perform tilt correction based on the determination result.

In each of the embodiments described above, an example in which both the PDs 31 and 32 detect the interference light of the 0th order light and the 1st order diffracted light, that is, an example in which the interference light symmetric with respect to the z axis is detected is shown. However, PD 31 and 32 may detect a non-symmetrical interference light with respect to the z-axis. For example. The first PD 31 detects the interference light of the 0th order and the 1st order diffracted light, the second PD 32 detects the interference light of the 2nd order light and the 1st order diffracted light, and so on.

  In the above embodiment, the light emitted from the light source 12 is incident on the collimator lens 14, and the collimator lens 14 generates the parallel light 15. However, the parallel light 15 does not necessarily have to be formed. For example, diffused light or convergent light having a predetermined light orientation angle is generated by a light source or an optical system including the light source, and the diffused light or convergent light is diffracted. It may be incident on the grating pair 20. In this case, the optical axis of the diffraction grating pair 20 is typically configured to coincide with the optical axis of the light source or the optical system, but they may be configured not to coincide with each other.

  It is also possible to combine at least two feature portions among the feature portions of each embodiment described above.

DESCRIPTION OF SYMBOLS 12 ... Light source 20 ... Diffraction grating pair 21 ... 1st diffraction grating 21a, 22a ... Grating line 22 ... 2nd diffraction grating 22a ... Grating line 23, 25 ... + n-order (+ 1st-order) diffracted light 24, 26 ...- n Next (-1st order) diffracted light 27, 28 ... Interference light 30 ... Straight light 31 ... First PD
32 ... Second PD
DESCRIPTION OF SYMBOLS 40 ... Arithmetic circuit 51, 52 ... Mounting board 54 ... Slit 55 (55a, 55b, 55c) ... Hole 60, 70 ... Adjustment mechanism 65 ... Drive part 67 ... Piezoelectric actuator 100 ... Displacement measuring device

Claims (8)

A light source;
A first diffraction grating and a second diffraction grating, which are arranged along a path of a light beam from the light source, are relatively movable, and each generate diffracted light;
Among the diffracted lights generated by the first diffraction grating and the second diffraction grating, interference of a set of diffracted lights along the path of + n-order diffracted light (n is a natural number of 1 or more) by the first diffraction grating. A first light sensor for detecting light;
A second detector for detecting interference light of a set of diffracted light along a path of -n-order diffracted light by the first diffraction grating out of diffracted light generated by the first diffraction grating and the second diffraction grating; An optical sensor ;
Based on the difference value of the signals obtained by the first optical sensor and the second optical sensor, around the axis along the direction of the respective grating lines of the first diffraction grating and the second diffraction grating, A displacement measuring device comprising: a processing unit that calculates an angular displacement of relative rotation of the first and second diffraction gratings . The displacement measuring apparatus according to claim 1 ,
The processing unit detects displacement in a direction along the optical axis of the first and second diffraction gratings based on a signal obtained by any one of the first and second optical sensors. Displacement measuring device. The displacement measuring device according to claim 2 ,
The processing unit executes a process of correcting the angular displacement. The displacement measuring apparatus according to claim 3 ,
The said process part determines whether the calculated angular displacement exceeds a threshold value, and when the said angular displacement exceeds the said threshold value, the process which correct | amends the said angular displacement is performed. The displacement measuring apparatus according to claim 3,
The said process part performs the process which correct | amends the said angular displacement, when the said difference value exceeds a threshold value The displacement measuring device.

A displacement measuring apparatus according to any one of the claims 3 5,
An adjustment mechanism for rotating the first or second diffraction grating in the direction of the angular displacement;
The processing unit controls the adjustment mechanism based on the calculated angular displacement. The displacement measuring device according to any one of claims 1 to 6 ,
The first optical sensor includes + 1st order diffracted light of the second diffraction grating generated by incidence of 0th order light generated from the first diffraction grating to the second diffraction grating, and the first optical sensor. + 1st order diffracted light generated from the diffraction grating is incident on the second diffraction grating and detects interference light with 0th order light generated from the second diffraction grating;
The second optical sensor includes a −1st order diffracted light of the second diffraction grating generated by incidence of 0th order light generated from the first diffraction grating on the second diffraction grating, and the first optical sensor. Displacement measuring device that detects interference light with zero-order light generated from the second diffraction grating when −1st-order diffracted light generated from the second diffraction grating is incident on the second diffraction grating. The first diffraction grating and the second diffraction grating, which are arranged along the path of the light beam from the light source, are relatively movable, have grating lines in the same direction, and generate diffracted light, respectively, are used to change the displacement. A method of measuring,
Among the diffracted lights generated by the first diffraction grating and the second diffraction grating, interference of a set of diffracted lights along the path of + n-order diffracted light (n is a natural number of 1 or more) by the first diffraction grating. Light is detected by a first light sensor;
Of the diffracted light generated by the first diffraction grating and the second diffraction grating, a pair of diffracted light interference light along the path of -n-order diffracted light by the first diffraction grating is used as a second optical sensor. Detect with
An angular displacement of relative rotation of the first and second diffraction gratings about an axis along the direction of the grating line based on signals obtained by the first optical sensor and the second optical sensor is calculated,
In the calculation of the angular displacement, based on the difference value between the signals obtained by the first optical sensor and the second optical sensor, the respective grating lines of the first diffraction grating and the second diffraction grating are calculated. A displacement measurement method for calculating an angular displacement of a relative rotation of the first and second diffraction gratings about an axis along a direction .