JP2017009335A - Displacement measurement device, displacement measurement signal processing device and displacement measurement signal processing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a displacement measurement device capable of curbing measurement errors and a displacement measurement signal processing device and a displacement measurement signal processing method used in the displacement measurement device.SOLUTION: A displacement measurement device comprises: a light source; a first diffraction grating; a second diffraction grating; a detection section 50; and an operation section 40. The second diffraction grating is arranged along a path of a light beam from the light source in a manner as to face the first diffracting grating and can move relative to the first diffraction grating. The detection section 50 has a plurality of light receiving sections 51 which receive light emitted from the second diffracting grating. The operation section 40 has: a selection section 41 which selects, among a plurality of signal values obtained from the plurality of light receiving sections 51, one signal value larger than a minimum signal value and equal to or less than a maximum signal value; and a displacement operation section 43 which calculates a displacement amount due to relative movement between the first diffracting grating and the second diffracting grating on the basis of the selected signal value.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a displacement measurement device, a displacement measurement signal processing device, and a displacement measurement signal processing method that use interference light.

  Patent Document 1 discloses a displacement measuring apparatus that measures the displacement of relative movement of two diffraction gratings by detecting interference light between diffracted lights generated by relative movement of two opposing diffraction gratings. ing. Specifically, the interference light includes −1st order diffracted light generated from the second diffraction grating when + 1st order diffracted light from the first diffraction grating is incident on the second diffraction grating, and − The n-th order diffracted light enters the second diffraction grating and is generated by interference with the + n-order diffracted light generated from the second diffraction grating (see, for example, paragraphs [0028] to [0031] of Patent Document 1). ).

  Patent Document 2 discloses an optical displacement measuring instrument capable of measuring the surface of a measurement object having, for example, an inclined surface or a curved surface. In this displacement measuring device, a light detection unit having the following structure is used. The light detection unit includes one circular light receiving element arranged at the center and a plurality of (16) light receiving elements arranged in a ring shape along the outer periphery of the one light receiving element. Prepare. The focal position detection circuit receives a signal obtained by the light detection unit and calculates a focusing error signal. Specifically, the focal position detection circuit calculates the sum of signals from three adjacent light receiving elements among the fan-shaped light receiving elements over the entire circumference, and the maximum value of the calculated sums. Select. The focus position detection circuit can obtain a pinhole signal by the pseudo pinhole method by performing a predetermined calculation based on this maximum value, and based on the pinhole signal, a focus error signal for focusing control can be obtained. (See, for example, paragraphs [0027] and [0029] of Patent Document 1).

Japanese Unexamined Patent Publication No. 2015-021890 JP 2009-300264

  In general, in a displacement measuring device using an optical element (for example, a diffraction grating or a photodetector), an optical axis misalignment may occur due to an assembly error of the optical element at the time of manufacturing the device. The signal waveform actually obtained by the photodetector is disturbed from the signal waveform to be obtained. This causes a measurement error. Alternatively, for example, in an apparatus that uses interference light of diffracted light by a diffraction grating, interference light of higher-order diffracted light is generated, and noise due to this is added to the detection signal.

  An object of the present invention is to provide a displacement measurement device capable of suppressing the occurrence of measurement errors, a displacement measurement signal processing device used in the displacement measurement device, and a displacement measurement signal processing method.

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 detection unit, and a calculation unit.
Light from the light source is incident on the first diffraction grating.
The second diffraction grating is disposed to face the first diffraction grating along the path of the light beam from the light source, and is provided so as to be relatively movable with respect to the first diffraction grating.
The detection unit includes a plurality of light receiving units that receive light emitted from the second diffraction grating.
The calculation unit selects any one of a plurality of signal values obtained from the plurality of light receiving units from a value greater than a minimum value and less than a maximum value, and based on the selected value, The amount of displacement due to relative movement is calculated.

  The detection unit includes a plurality of light receiving units, and the plurality of light receiving units are configured to receive one light. Therefore, since the calculation unit can select a value other than the minimum value, a signal value having a lot of disturbances and noises can be excluded from the calculation of the displacement amount, so that occurrence of a measurement error can be suppressed.

The calculation unit may select the maximum value.
That is, since the calculation unit selects a signal with the least disturbance and noise, the generation of measurement errors can be suppressed.

The plurality of light receiving units may have an equal area.
Thereby, the calculating part can raise the calculation efficiency for selecting the optimal value (one other than the minimum value among the signals obtained by a plurality of light receiving parts).

  Either one of the first diffraction grating and the second diffraction grating may be configured to generate two or more lights having different phases due to the relative movement. The detection unit may include a plurality of sets of light receiving units in which the plurality of light receiving units are a set of light receiving units.

  The overall width of the plurality of light receiving portions in the relative movement direction is not less than 1/3 of the light flux width of one light emitted from the second diffraction grating in the relative movement direction, and the 1 It may be set to a value smaller than the beam width of one light.

  The overall width of the plurality of light receiving portions in the direction orthogonal to the relative movement direction is 1 / (light beam width of one light emitted from the second diffraction grating in the direction orthogonal to the relative movement direction). It may be set to a value not less than 5 and smaller than the luminous flux width of the one light.

  In these inventions, the “light flux width” is, for example, a light flux (or one of them) generated as a result of passing through an optical element arranged at the front stage of the first diffraction grating or the rear stage of the second diffraction grating. ) Is the maximum width.

  One of the grating structures of the first diffraction grating and the second diffraction grating has two or more grating pattern regions having a predetermined grating line pitch, and the lattice line arrangement of these grating pattern regions is the relative You may comprise so that each predetermined distance may shift | deviate in a moving direction.

  For example, the relative movement direction of the first diffraction grating and the second diffraction grating is a direction orthogonal to the direction in which the first diffraction grating and the second diffraction grating are separated from each other along the path of the light beam from the light source. May be.

  Alternatively, the relative movement direction of the first diffraction grating and the second diffraction grating may be a direction in which the first diffraction grating and the second diffraction grating are separated from each other along the path of light from the light source.

When n is a natural number of 1 or more, any one of the first diffraction grating and the second diffraction grating is
Of the pair of diffraction gratings, + n-order diffracted light from the first diffraction grating is incident on the second diffraction grating and generated from the second diffraction grating, and -n-order diffracted light from the first diffraction grating is the first-order diffracted light. It may be configured to emit interference light with + n-order diffracted light that enters the second diffraction grating and is generated from the second diffraction grating. Alternatively, any one of the diffraction grating pairs may follow a path of + n-order diffracted light or −n-order diffracted light generated from any one of the first diffraction grating and the second diffraction grating. You may be comprised so that the interference light of a set of diffracted light may be radiate | emitted.

A displacement measuring apparatus according to another aspect of the present invention includes a light source, a first diffraction grating, a second diffraction grating, and a detection unit.
Light from the light source is incident on the first diffraction grating.
The second diffraction grating is disposed so as to face the first diffraction grating along a path of a light beam from the light source, is provided to be relatively movable with the first diffraction grating, and has a different phase due to the relative movement. Two or more lights are emitted.
The detection unit includes a plurality of sets of light receiving units that receive the light emitted from the second diffraction grating, and the plurality of light receiving units are set as a set of light receiving units.

  A displacement measurement signal processing apparatus according to an aspect of the present invention is a signal processing apparatus of the displacement measurement apparatus described above. The displacement measurement signal processing device includes the calculation unit described above.

A displacement measurement signal processing method according to an aspect of the present invention is a signal processing method by the above-described signal processing device. The displacement measurement signal processing method includes selecting any one of a plurality of signal values respectively obtained from a plurality of light receiving units of the detection unit, which is greater than a minimum value and equal to or less than a maximum value. .
Based on the selected value, the displacement amount due to the relative movement is calculated.

  As mentioned above, according to this invention, generation | occurrence | production of a measurement error can be suppressed.

FIG. 1 is a diagram showing a basic optical system configuration of a displacement measuring apparatus according to a first embodiment of the present invention. FIG. 2 shows the configuration of the detection unit and the calculation unit. FIG. 3 schematically shows one of the grating structures of the diffraction grating pair according to the second embodiment of the present invention. FIG. 4A shows a plurality of sets of light receiving units of the detection unit according to the present embodiment. FIG. 4B shows a photograph showing three-phase actual interference light emitted from the diffraction grating pair and a plurality of sets of light receiving units shown in FIG. 4A in an overlapping manner. FIG. 5A shows an ideal three-phase signal obtained by the detection unit. FIG. 5B shows a three-phase signal actually obtained for each light receiving unit. FIG. 6 is a block diagram illustrating a configuration of the calculation unit according to the present embodiment. 7A and 7B show a light receiving unit for detecting three-phase interference light of the detection unit according to the comparative example. FIG. 8 is data showing comparisons of fluctuation amounts based on the signals of the detection unit according to the second embodiment, the detection unit according to Comparative Example 1, and the detection unit according to Comparative Example 2 (FIG. 7B). . 9A to 9D respectively show various modifications of the set of light receiving units in the detection unit.

  1. First embodiment

  1) Configuration of the optical system of the displacement measuring device

  FIG. 1 is a diagram showing a basic optical system configuration of a displacement measuring apparatus according to a first embodiment of the present invention.

  The displacement measurement device 100 includes a light source 12, a collimator lens 14, a diffraction grating pair 20, a detection unit 50, and a calculation unit 40 that functions as a displacement measurement signal processing device.

  The light source 12 is an LD (Laser Diode) or an LED (Light Emitting Diode), and is driven by a driver (not shown). The detection unit 50 is configured by a photodiode or the like.

  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.

  The diffraction grating pair 20 is composed of, for example, a transmission type first diffraction grating 21 and second diffraction grating 22. Light from the light source 12 and the collimator lens 14 enters the first diffraction grating 21 and emits diffracted light. The first diffraction grating 21 and the second diffraction grating 22 are disposed so as to face each other along the light paths 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 will be described later, it is relatively movable in a predetermined direction.

  In the first diffraction grating 21, the incident parallel light 15 travels straight on the optical axis of the diffraction grating pair 20, and the 0th order light 30a and the + nth order diffracted light (n is a natural number of 1 or more, and so on). 23a and -n-order diffracted light 25a are divided and advanced.

  The second diffraction grating 22 emits the 0th-order light 30a emitted from the first diffraction grating 21 and incident on the second diffraction grating 22 as 0th-order light 30b that travels straight on the optical axis. Further, the second diffraction grating 22 generates a -n-order diffracted light 23b of the + n-order diffracted light 23a incident thereon, and generates a + n-order diffracted light 25b of the -n-order diffracted light 25a incident thereon.

  For convenience of explanation, in FIG. 1, the order of diffracted light generated from one light beam and bent to the right side of the one light beam is positive. Further, the order of the diffracted light that is bent to the left of the one light beam is negative.

  The −nth order diffracted light 23b and the + nth order diffracted light 25b interfere with each other, thereby generating interference light 27. The detection unit 50 is disposed at a position where the interference light 27 is mainly detected. Specifically, the −nth order diffracted light 23b and the + nth order diffracted light 25b travel in a direction along the optical axis of the diffraction grating pair 20 (z direction in FIG. 1), and the interference light 27 is generated at a position including the optical axis. To do. Therefore, the detection unit 50 that detects the interference light 27 is disposed on the optical axis of the diffraction grating pair 20.

  As will be described later, the zero-order light 30 is also included in the light on the optical axis, and this zero-order light 30 is also included, but this zero-order light 30 is removed by another means or The amount of light is reduced.

  In the present embodiment, ± 1st order diffracted light is typically used as ± nth order diffracted light. However, if the light interferes with each other on the optical axis of the diffraction grating pair 20, ± 2nd order and subsequent diffracted light is used. It may be used. In practice, there are many diffracted lights other than those shown in FIG. 1, but they are not shown for ease of explanation.

  The diffracted lights of both the + nth order diffracted light 23a and the nth order diffracted light 23b are hereinafter referred to as the first diffracted light 23 as necessary. Further, the diffracted light of both the −nth order diffracted light 25a and the + nth order diffracted light 25b is hereinafter referred to as the second diffracted light 25 as necessary. In addition, the 0th-order light of both the 0th-order lights 30a and 30b is hereinafter referred to as 0th-order light 30.

  The first diffraction grating 21 and the second diffraction grating 22 have substantially the same shape and the same size. For example, the diffraction grating 21 (and 22) has 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 1 to 10 μm (for example, 4.8 μm), and the groove depth is 200 to 800 μm (for example, 473 μm). Of course, it is not restricted to these values.

  The displacement measuring apparatus 100 according to the present embodiment uses a relative displacement (displacement amount) Δx of the diffraction grating pair in the x direction as the arrangement direction of the grating lines 21a and 22a as a measurement target. The measurable range is, for example, a displacement on the order of submicrometer to micrometer.

  In this specification, two axes orthogonal to the z direction are defined as x and y axes. As described above, the direction along the grating lines 21a and 22a of each diffraction grating is the y direction, and the arrangement direction of the grating lines 21a and 22a is the x direction.

  The light source 12, the collimator lens 14, and the first diffraction grating 21 are integrally held by a holder (not shown), and the second diffraction grating 22 and the detection unit 50 are integrally held by another holder (not shown). These holders are movable in the x direction.

  The calculation unit 40 calculates the displacement Δx by performing calculation processing described later based on the signal obtained by the detection unit 50. The arithmetic unit 40 mainly includes hardware such as an MPU (Micro Processing Unit), a RAM (Random Access Memory), and a ROM (Read Only Memory). The calculation unit 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. In addition, the arithmetic unit 40 may be configured by a plurality of physically separated chip packages, elements, and the like.

  2) Configuration of detection unit and calculation unit of displacement measuring device

  FIG. 2 shows the configuration of the detection unit 50 and the calculation unit 40. The detection unit 50 includes a plurality of light receiving units 51 and includes, for example, three light receiving units 51. A circle C indicated by a broken line surrounding the detection unit 50 indicates a cross-sectional outline of an incident light beam (for example, a light beam of interference light to be detected). The cross-sectional outer shape of the light beam indicates a beam shape shaped by, for example, a collimator lens 14 (or an aperture (not shown)).

  Each of the light receiving parts 51 has the same shape and the same area. The shape of the light receiving unit 51 is, for example, a rectangle. The light receiving parts 51 are arranged side by side in the x direction, which is the relative movement direction of the diffraction grating pair, for example. The light receiving unit 51 may be arranged side by side in the y direction, which is a direction orthogonal to the relative movement direction. The area, arrangement, and shape of the light receiving portions 51 are appropriately designed so that each light receiving portion 51 can receive a light amount as uniform as possible.

  The calculation unit 40 includes a selection unit 41 and a displacement amount calculation unit 43. The selection unit 41 selects any one of the signal values (a plurality of signal values) of the voltage corresponding to the light amount obtained by the light receiving unit 51 that is greater than the minimum value and less than or equal to the maximum value. Configured as follows. The displacement amount calculation unit 43 is configured to calculate a displacement amount Δx due to the relative movement of the diffraction grating pair based on the selected value. The selection unit 41 preferably selects the maximum value.

  3) Operation of the displacement measuring device

  The light from the light source 12 enters the diffraction grating pair 20, and the interference light 27 is emitted from the diffraction grating pair 20 as described above. The interference light 27 generates interference fringes on the detection unit 50. Due to the relative movement of the diffraction grating pair in the x direction, the light and dark states of the interference fringes periodically change. The detecting unit 50 detects a change in the amount of light according to the change in the bright and dark state of the interference fringes, and the calculating unit 40 measures the displacement amount Δx based on this change.

  As described above, the selection unit 41 according to the present embodiment changes the three signals obtained by the three light receiving units 51 that change momentarily by the relative movement of the first diffraction grating 21 and the second diffraction grating pair 22. Select the maximum value. And the displacement amount calculating part 43 measures a displacement amount based on the maximum value.

  As a calculation method of the displacement amount Δx by the displacement amount calculation unit 43 after selecting the maximum value, the method disclosed in Patent Document 1 may be used. For example, the change in the amount of light due to the change in the light / dark state of the interference fringes is detected by the detection unit 50 as a periodic signal, for example, a sine wave signal. For example, the displacement amount calculation unit 43 can count the wave number of the sine wave signal to convert the count value into a displacement amount and output it.

  Alternatively, the displacement amount calculation unit 43 may calculate the displacement amount by a phase division method. That is, the displacement amount calculation unit 43 can measure the displacement amount by generating a pulse having a cycle sufficiently shorter than the signal cycle based on the signal obtained by the detection unit 50 and counting the number of pulses. it can.

  The displacement amount calculation unit 43 is not limited to the above method, and can measure the displacement amount by other known calculation methods.

  Next, the reason for selecting, for example, the maximum value other than the minimum value among the signals obtained by the respective light receiving units 51 will be described. Note that the circuit for selecting the maximum value may be configured by an analog circuit in which a plurality of comparators are combined, or the above-described digital circuit such as a CPU or DSP may execute the maximum value selection process. Good.

  Each signal obtained by each light receiving unit 51 is ideally a signal having the same phase and the same amplitude. The closer the obtained signal (the amplitude thereof) is to the maximum value, the more ideal the signal. As long as an ideal signal can be obtained, the number of detection units 50 may not be divided into a plurality of light receiving units 51.

  However, when the displacement measuring apparatus 100 is manufactured, signal disturbance or noise occurs due to an assembly error of the light source 12, the diffraction grating pair 20, and / or the detection unit 50, or due to generation of interference light of high-order diffracted light. There is a case. In this case, a relative shift occurs in the phase and amplitude of the signal from each light receiving unit 51, and an ideal signal cannot be obtained. Alternatively, there may be a case where a measurement error occurs due to deterioration (aging) of the displacement measuring apparatus 100 over time.

  Therefore, the calculation unit 40 according to the present embodiment can sample the signal value closest to the ideal signal, for example, by selecting the maximum value among the signals obtained by the respective light receiving units 51, for example. it can. Thereby, a measurement error can be suppressed.

  2. Second embodiment

  2.1) Displacement measuring device

  Next, a displacement measuring apparatus according to the second embodiment of the present invention will be described. In the following description, elements that are substantially the same as elements and functions included in the displacement measuring device according to the embodiment shown in FIG. 1 and the like are denoted by the same reference numerals, and the description thereof is simplified or omitted. The difference will be mainly described.

  In the displacement measuring apparatus according to the present embodiment, the differences from the first embodiment are mainly the configurations of the diffraction grating pair and the detection unit. FIG. 3 is a diagram schematically showing the grating structure of one of the diffraction gratings 70 of the first diffraction grating on the light source side and the second diffraction grating pair on the detection unit side. .

  The grating structure of the diffraction grating 70 is configured to generate two or more interference lights having different phases by relative movement of the diffraction grating pair. Specifically, the lattice structure shown in FIG. 3 has three lattice pattern regions 72U, 72V, and 72W configured to generate three-phase interference light.

  The arrangement of grating lines (grooves) 73 arranged in the x direction, which is the relative movement direction of the diffraction grating pair, is configured to be shifted by a predetermined distance in the relative movement direction. The grid line arrangement according to the example shown in FIG. 3 is configured to shift by 1/3 pitch of the grid line pitch P, that is, by 120 °. As a result, the diffraction grating on the detection unit side (hereinafter referred to as the second diffraction grating for convenience of description) generates interference light having a phase shifted by 120 °. The grid line width (groove width) and the pitch P are substantially the same in the grid pattern regions 72U, 72V, and 72W.

  FIG. 4A shows a set of a plurality of (for example, three) light receiving units 150U, 150V, and 150W of the detection unit 150 according to the present embodiment. FIG. 4B shows a photograph showing three-phase actual interference light emitted from the second diffraction grating in a specific phase state, and a set of the light receiving units 150U, 150V, and 150W shown in FIG. 4A. FIG. The arrangement relationship of each set of light receiving units 150U, 150V, and 150W is designed so that the three sets of light receiving units 150U, 150V, and 150W detect the three-phase interference lights 27U, 27V, and 27W, respectively. ing. The detection unit 150 configured as described above outputs a three-phase sine wave signal (U, V, W) corresponding to different three-phase interference light.

  In addition, a plurality of light receiving units are provided for each region indicated by reference numerals 150U, 150V, or 150W of the detection unit 150. For example, the area indicated by reference numeral 150U has three light receiving parts 51U, the area indicated by reference numeral 150V has three light receiving parts 51V, and the area indicated by reference numeral 150W has three light receiving parts 51W, for a total of nine. Is provided. That is, the detection unit 150 includes a plurality of sets of light receiving units 150U, 150V, and 150W in which the plurality of light receiving units are a set of light receiving units. Hereinafter, the plurality of light receiving parts 51U are referred to as a set of light receiving parts 150U. Similarly, the plurality of light receiving units 51V are referred to as a set of light receiving units 150V, and the plurality of light receiving units 51W are referred to as a set of light receiving units 150W.

  The light receiving portions 51U, 51V, 51W have a rectangular shape that is long in the y direction. The voltage signal (U-phase signal) obtained from the light-receiving unit 51U of the set of light-receiving units 150U is (U1, U2, U3), and the voltage signal (V-phase signal) obtained from the light-receiving unit 51V of the set of light-receiving units 150V. (V1, V2, V3), a voltage signal (W-phase signal) obtained from the light receiving unit 51W of the pair of light receiving units 150W is defined as (W1, W2, W3).

  As described in the description of the first embodiment, in one set of light receiving units 150U, 150V, or 150W, the area, arrangement, and shape of the light receiving units are such that each light receiving unit receives a light amount that is as uniform as possible. It is designed as appropriate so that it can.

  FIG. 5A shows an ideal three-phase signal (U, V, W) obtained by the detection unit 150. Ideally, the amplitude and phase of each signal (U1, U2, U3) match. Similarly, ideally, the amplitude and phase of each signal (V1, V2, V3) match, and the amplitude and phase of each signal (W1, W2, W3) match. However, actually, due to the problem described in the first embodiment, for example, the waveform of each signal is disturbed or the amplitude is not constant.

  FIG. 5B shows three-phase signals (U, V, W) actually obtained by the detection unit. Here, a three-phase signal (a three-phase signal by a general three-phase detection unit) obtained by a detection unit configured by three divided light receiving units is shown. In this way, an ideal three-phase signal waveform cannot be obtained due to the occurrence of disturbance or noise in each signal waveform.

  FIG. 6 is a block diagram illustrating a configuration of the calculation unit 140 according to the present embodiment. Of the three signals (U1, U2, U3) respectively obtained by the light receiving unit 51U, the selection unit 41U selects a maximum value Umax here other than the minimum value, as in the first embodiment. The selection unit 41V selects the maximum value Vmax from the three signals (V1, V2, V3) respectively obtained by the light receiving unit 51V. The selection unit 41W selects the maximum value Wmax from the three signals (W1, W2, W3) respectively obtained by the light receiving unit 51W. The displacement amount calculation unit 43 calculates the displacement amount Δx based on these maximum values (Umax, Vmax, Wmax).

  Note that the calculation method for obtaining the amount of displacement from signals having a plurality of different phases may be the same as in the first embodiment. Alternatively, the technique described with reference to FIG. 13 of Japanese Patent Laid-Open No. 2015-021890 may be applied so that only linear regions of U, V, and W signals are used.

  As shown in FIG. 4A, the preferable value of the overall width (lateral width of a set of light receiving portions) a1 of the plurality of light receiving portions in the x direction is one interference light emitted from the second diffraction grating in the x direction. Is set to a value equal to or greater than 1/4 of the luminous flux width d1 and smaller than the luminous flux width d1. The beam width d1 is indicated by the width of each interference light 27U, 27V, or 27W as shown in FIG. 4B.

  The width a1 is set to be smaller than d1 when the width a1 is the same as the beam width d1, when there is an optical axis shift due to the assembly of the diffraction grating pair and the detection unit 150, and a set of light receiving units 150U, 150V, This is because 150 W includes a region deviating from the luminous flux width d1. The reason why the width a1 is set to a value larger than 1/4 is that if it is smaller than that, the desired detection accuracy and consequently the measurement accuracy cannot be obtained.

  The lower limit value of the width a1 can be set to 1/3, 1/2, 2/3, or the like.

  As shown in FIG. 4A, a preferable value of the overall maximum width (vertical width of one set of light receiving portions) a2 of the plurality of light receiving portions in the y direction is emitted from the second diffraction grating in the y direction. It is set to a value that is 1/5 or more of the minimum value d2 (see FIG. 4B) of the vertical beam width of each interference light and smaller than d2.

  When the cross-sectional shape of the beam is a circle C, if the vertical width a2 of the light receiving portion is set to be the same as the minimum value d2 of the light beam vertical width, the light receiving portion includes a region deviating from the light beam width as described above. Because it ends up.

  The lower limit of the width b can be set to 1/4, 1/3, 1/2, 2/3, or the like.

  2.2) Comparative example

  The inventor conducted an experiment to compare the detection signal from the detection unit 150 according to the second embodiment with the detection signal from the detection unit according to the comparative example.

  The design values of the detection unit 150 according to this embodiment used in the experiment are as follows.

Length of one light receiving part in the x direction: 25 μm,
Length of one light receiving part in the y direction: 150 μm,
The pitch of each light receiving part within a set of light receiving parts (three light receiving parts): 30 μm
Pitch per pair of light receiving parts: 82μm
Beam diameter (aperture diameter) of the light beam input to the detector 150: 700 μm

  7A and 7B show detectors 160 and 170 according to a comparative example for detecting three-phase interference light. In this comparative example, the grating structure of one of the diffraction grating pairs is the same as that according to the second embodiment shown in FIG.

  The detection unit 160 according to Comparative Example 1 illustrated in FIG. 7A includes three rectangular light receiving units 160U, 160V, and 160W that detect interference light of each phase. The light receiving area of one light receiving unit 160U, 160V, or 160W is substantially the same as the sum of the areas formed by the three light receiving units (for example, 51U) according to this embodiment.

  In the detection unit 170 according to the comparative example 2 illustrated in FIG. 7B, the pair of light receiving units 170U, 170V, and 170W that detect the interference light of each phase are arranged in the y direction orthogonal to the relative movement direction of the diffraction grating pair. Furthermore, it has three light receiving parts 71U, three light receiving parts 71V, and three light receiving parts 71W. The area of one light receiving portion according to Comparative Example 2 was set to be substantially the same as or smaller than the area of one light receiving portion according to this embodiment.

  FIG. 8 shows fluctuations due to disturbances and noises of the signals of the detection unit 150 according to the present embodiment (second embodiment), the detection unit 160 according to comparative example 1, and the detection unit 170 according to comparative example 2. It is the data which compared and showed quantity (deviation) (sigma) (nm). FIG. 8 shows data when there is no optical axis misalignment between the diffraction grating pair and the detection unit, and data when there is. The assembly error is reproduced by intentionally giving "optical axis deviation".

  As examples of the case where there is an optical axis shift, four examples of -40 μm (x axis), +40 μm (x axis), and -40 μm (y axis) +40 μm (y axis) are shown. For example, “-40 μm (x axis)” means that the optical axis of the detection unit (corresponding to the central axis of the detection unit 50) is x with respect to the optical axis of the diffraction grating pair (corresponding to the central axis of the diffraction grating pair). It shows that it is shifted by 40 μm in one direction of the axis.

  As the detected three-phase signal is ideal, σ approaches zero. Specifically, when taking an intersection between a specific slice level (a constant voltage value) of the signal and these three-phase signals, the three-phase signals are shown in FIG. Approaching the ideal state, σ approaches zero. In the present embodiment, the slice level is the sum of three-phase signals (ideally always always zero).

  In FIG. 8, the data of the detection unit 150 and the comparative example 2 according to the present embodiment indicate data based on the maximum values when the maximum values obtained by the respective light receiving units are selected. That is, also in Comparative Example 2, as in the present embodiment, the maximum value Umax is selected from the signals (U1, U2, U3) obtained by the three light receiving units 71U, and the signals obtained by the three light receiving units 71V are selected. The maximum value Vmax is selected from (V1, V2, V3), and the maximum value Wmax is selected from the signals (W1, W2, W3) obtained by the three light receiving units 71W.

  In the detection unit 150 according to the present embodiment, when the fluctuation amount σ of “no optical axis deviation” and “−40 μm (x axis)” are compared, the latter has a smaller fluctuation amount. This is due to causes such as variations in the incident state of interference light for each measurement, and this does not cause a problem.

  As can be seen from FIG. 8, in the detection unit 150 according to the present embodiment, the variation amount σ in the x direction is improved as compared with the detection units 160 and 170 according to Comparative Examples 1 and 2. When there is an optical axis shift in the x direction at the time of assembly, the amount of variation σ increases due to the light receiving unit protruding from the light beam due to the relative movement of the diffraction grating pair. From such a result, the means of selecting the maximum value among the values obtained by the plurality of light receiving units as in the present technology is effective.

  On the other hand, in the y direction, if the light receiving portion is included in the light beam, the large difference in the amount of variation σ between the detection unit 150 according to this embodiment and the detection units 160 and 170 according to Comparative Examples 1 and 2 is Absent.

  In addition, the form of the comparative example 2 is a form included in the concept of the present invention because the set of light receiving parts 170U (170V or 170W) includes a plurality of light receiving parts 71U (71V or 71W). . In this case, as will be described later, as shown in FIG. 9A, it is desirable that the length of one light receiving portion in the x direction be as long as possible (for example, about the same as the beam width of one interference light).

  3. Third embodiment

  Next, as a third embodiment, various modified examples of a set of light receiving units including a plurality of light receiving units will be described. 9A to 9D each show a set of light receiving units according to these modifications. These modifications according to the present embodiment are applicable to both the first embodiment and the second embodiment.

  3.1) Modification 1

  As shown in FIG. 9A, the set of light receiving units according to Modification 1 includes a plurality of horizontally long light receiving units 52U (52V or 52W) having substantially the same area. The horizontal direction is the relative movement direction (x direction) of the diffraction grating pair. Since the light receiving parts 52U are formed horizontally, each light receiving part 52U is provided so as to cross as many interference fringes as possible. Thereby, each light receiving portion 52U can receive a uniform amount of light, so that the measurement accuracy is improved.

  Although there are three light receiving parts 52U, there may be two, or four or more. The same applies hereinafter.

  3.2) Modification 2

  Modified example 2 shown in FIG. 9B shows an example of a set of light receiving parts which are substantially equal in area but are configured so that the shapes of at least two light receiving parts are different. In this example, the left first light receiving portion 53Ua and the right third light receiving portion 53Uc are disposed so as to surround the center second light receiving portion 53Ub. Further, the first light receiving portion 53Ua and the third light receiving portion 53Uc have a line-symmetric shape with respect to the y axis. For example, the center second light receiving portion 53Ub may be further divided into a plurality of light receiving portions.

  3.3) Modification 3

  As shown in FIG. 9C, the set of light receiving units according to Modification 3 includes a plurality of light receiving units 54U configured substantially in the same area and in a triangular shape. These light receiving parts 54U have the same shape, but are arranged so that, for example, the adjacent light receiving parts 54U have opposite vertical directions.

  3.4) Modification 4

  As illustrated in FIG. 9D, the set of light receiving units according to Modification 4 is configured such that the area of at least one light receiving unit among the plurality of light receiving units is different from the areas of the other light receiving units. In this example, three light receiving portions 54Ua, 54Ub, 54Uc are provided, and the area of the central light receiving portion 54Ub is twice the area of each of the light receiving portions 54Ua 54Uc on both sides thereof. In this case, the calculation unit may perform a calculation by multiplying the signal value obtained by the central light receiving unit 51 by 1/2.

  In the fourth modification, the light receiving portions 54Ua, 54Ub, and 54Uc are triangular, but may be rectangular.

  4). Various other embodiments

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

  Although the displacement measuring apparatus according to the above embodiment is an apparatus that measures linear displacement, the present invention can also be applied to a rotary encoder that measures displacement of a rotation angle.

  In the case of using a rotary encoder, the shape of the light receiving unit may be a rectangle, but may be a triangle or a fan.

  The optical system of the displacement measuring device may have the configuration shown in FIG. 1 of Japanese Patent Laid-Open No. 2015-17943, for example, instead of the configuration example shown in FIG. In this case, any one diffraction grating of the diffraction grating pair emits a set of interference light beams of a diffracted light along the path of the + n-order diffracted light or the −n-order diffracted light generated from any one of the diffraction gratings. That is, the interference light includes the light generated when the + n-order (or -n-order) diffracted light by the first diffraction grating passes through the second diffraction grating as the 0th-order light, and the 0th order through the first diffraction grating. Light transmitted as light is interference light with + n-order (or -n-order) diffracted light generated by being incident on the second diffraction grating. Such a configuration of the displacement measuring apparatus is applicable to the first to third embodiments described above and other embodiments.

  The selection unit according to the embodiment is configured to select the maximum value as a value other than the minimum value. However, when high output spike noise is assumed as the maximum value, a value smaller than the maximum value (for example, a value next to the maximum value) may be selected to exclude the maximum value. Such spike noise can be removed by using a separate filter, but by removing the maximum value, such a separate filter is not required.

  In the above embodiment, the first diffraction grating and the second diffraction grating are provided so as to be relatively movable in the arrangement direction of the grating lines (x direction in FIG. 1). However, as disclosed in Japanese Patent Application Laid-Open No. 2014-102260, they are provided so as to be relatively movable in the direction of separation along the path of the light beam from the light source (z direction in FIG. 1). The structure which calculates the displacement amount of the relative movement may be sufficient.

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

20 ... Diffraction grating pair 21 ... Diffraction grating (first diffraction grating)
22 ... Diffraction grating (second diffraction grating)
21a, 22a, 73 ... grating lines 23, 25 ... diffracted light 23a, 25b ... + n order diffracted light 23b, 25a ... -n order diffracted light 27, 27U, 27V, 27W ... interference light 40, 140 ... computing units 41, 41U, 41V , 41W ... selection unit 43 ... displacement amount calculation unit 50, 150 ... detection unit 51, 51U, 51V, 51W, 52U, 53Ua, 53Ub, 53Uc, 54U, 55Ua, 55Ub, 55Uc, 71U, 71V, 71W ... light receiving unit 72U , 72V, 72W ... lattice pattern region 100 ... displacement measuring device 150U, 150V, 150W ... a set of light receiving units

Claims (13)

A light source;
A first diffraction grating on which light from the light source is incident;
A second diffraction grating disposed to face the first diffraction grating along a path of a light beam from the light source and provided to be movable relative to the first diffraction grating;
A detection unit having a plurality of light receiving units for receiving light emitted from the second diffraction grating;
A displacement amount due to the relative movement is selected based on the selected value selected from among a plurality of signal values obtained from the plurality of light receiving units, each of which is greater than the minimum value and less than or equal to the maximum value. A displacement measuring device comprising: a computing unit that computes. The displacement measuring apparatus according to claim 1, wherein the calculation unit selects the maximum value. The displacement measuring apparatus according to claim 1, wherein the plurality of light receiving units have an equal area. One of the grating structures of the first diffraction grating and the second diffraction grating is configured to generate two or more lights having different phases due to the relative movement,
The displacement measuring device according to any one of claims 1 to 3, wherein the detection unit includes a plurality of sets of light receiving units in which the plurality of light receiving units are a set of light receiving units. The overall width of the plurality of light receiving portions in the relative movement direction is not less than 1/3 of the light flux width of one light emitted from the second diffraction grating in the relative movement direction, and the 1 The displacement measuring device according to claim 4, wherein the displacement measuring device is set to a value smaller than a beam width of two lights. The overall width of the plurality of light receiving portions in the direction orthogonal to the relative movement direction is 1 / (light beam width of one light emitted from the second diffraction grating in the direction orthogonal to the relative movement direction). The displacement measuring device according to claim 4, wherein the displacement measuring device is set to a value that is 5 or more and smaller than a light flux width of the one light. One of the grating structures of the first diffraction grating and the second diffraction grating has two or more grating pattern regions having a predetermined grating line pitch, and the lattice line arrangement of these grating pattern regions is the relative The displacement measuring device according to any one of claims 1 to 6, wherein the displacement measuring device is configured to be shifted by a predetermined distance in the moving direction. The relative movement direction of the first diffraction grating and the second diffraction grating is a direction orthogonal to a direction in which the first diffraction grating and the second diffraction grating are separated from each other along a path of a light beam from the light source. The displacement measuring device according to any one of 1 to 7. The relative movement direction of the first diffraction grating and the second diffraction grating is a direction in which the first diffraction grating and the second diffraction grating are separated from each other along a path of a light beam from the light source. The displacement measuring apparatus of any one of them. When n is a natural number of 1 or more, any one of the first diffraction grating and the second diffraction grating is
The + n-order diffracted light generated from the second diffraction grating when the + n-order diffracted light from the first diffraction grating is incident on the second diffraction grating and the −n-order diffracted light from the first diffraction grating are incident on the second diffraction grating. Interference light with + n-order diffracted light generated from the second diffraction grating, or
The interference light of a set of diffracted light along the path of + n-order diffracted light or -n-order diffracted light generated from one of the first diffraction grating and the second diffraction grating is emitted. The displacement measuring device according to claim 1. A light source;
A first diffraction grating on which light from the light source is incident;
Two or more lights that are arranged to face the first diffraction grating along the path of the light beam from the light source, are provided so as to be movable relative to the first diffraction grating, and have different phases due to the relative movement. A second diffraction grating;
A displacement measuring apparatus comprising: a detector having a plurality of sets of light receiving units, each receiving the light emitted from the second diffraction grating, wherein the plurality of light receiving units are a set of light receiving units. A light source, a first diffraction grating on which light from the light source is incident, and a light beam from the light source are disposed so as to face the first diffraction grating along the path of the light beam, and are provided so as to be movable relative to the first diffraction grating. A signal processing device of a displacement measuring device comprising the second diffraction grating and a detection unit,
Any one of a plurality of signal values obtained from the plurality of light receiving units that receive the light emitted from the second diffraction grating in the detection unit is greater than the minimum value and equal to or less than the maximum value. A displacement measurement signal processing apparatus comprising: a calculation unit that selects one and calculates a displacement amount due to the relative movement based on the selected value. A light source, a first diffraction grating on which light from the light source is incident, and a light beam from the light source are disposed so as to face the first diffraction grating along the path of the light beam, and are provided so as to be movable relative to the first diffraction grating. A signal processing method by a displacement measuring device comprising the second diffraction grating and a detector,
Any one of a plurality of signal values obtained from the plurality of light receiving units that receive the light emitted from the second diffraction grating in the detection unit is greater than the minimum value and equal to or less than the maximum value. Select
A displacement measurement signal processing method for calculating a displacement amount due to the relative movement based on a selected value.