JP6420630B2 - 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 a first diffraction grating and diffracted light (for example 1 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.

International Publication No. 2011/043354 Pamphlet

  Since the displacement measuring device described in Patent Document 1 employs an incremental method, there is a problem that an absolute position or a zero point cannot be detected.

  In view of the circumstances as described above, an object of the present invention is to provide a displacement measuring device and a displacement measuring method capable of detecting an absolute position in a measuring device using optical interference.

In order to achieve the above object, a displacement measuring apparatus according to an aspect of the present invention includes a light source, a diffraction grating pair, a first detector, a second detector, a relative displacement calculator, and an absolute position calculator. It comprises.
The diffraction grating pair is composed of a first optical element and a second optical element, is relatively movable, is provided to face along the path of a light beam, and the light emitted from the light source is the diffraction grating pair. Is incident on.
The first detection unit detects interference light caused by diffracted light respectively emitted from the first optical element and the second optical element.
The second detection unit detects non-interfering light emitted from the diffraction grating pair.
The relative displacement calculation unit is configured to detect the first optical element and the second optical element in the arrangement direction of the lattice lines of the first optical element and the second optical element based on the signal obtained by the first detection unit. Calculate the relative displacement.
The absolute position calculator calculates an absolute position of the other of the first optical element and the second optical element with respect to one of the first optical element and the second optical element in the arrangement direction of the lattice lines based on the signal obtained by the second detector. .
In this displacement measuring apparatus, the relative displacement of the diffraction grating pair is detected based on the interference light signal detected by the first detection unit, and the absolute position is determined based on the non-interference light signal detected by the second detection unit. Can be detected.

The first detector includes a −n-order diffracted light generated from the second optical element when + n-order diffracted light from the first optical element is incident on the second optical element, and a −n-order diffracted light from the first optical element. May enter the second optical element and detect interference light with + n-order diffracted light generated from the second optical element. However, n is a natural number of 1 or more.
As a result, interference light can be formed, and the relative displacement calculator can calculate the relative displacement of the first and second optical elements with high accuracy.

The second detection unit may detect + (n + 1) -order diffracted light generated from the second optical element when + n-order diffracted light from the first optical element is incident on the second optical element.
Accordingly, non-interfering light can be generated from the diffraction grating pair, and the second detection unit can be disposed at a position away from the first detection unit.

The second detection unit may include a first detection region and a second detection region arranged in a direction in which the non-interfering light moves due to relative movement of the first optical element and the second optical element. Further, the absolute position calculation unit may calculate the absolute position based on signals obtained in the first detection area and the second detection area, respectively.
Since two signals are obtained by providing the two detection areas in this way, the absolute position calculation unit can calculate the absolute position with high accuracy based on the two signals.

The absolute position calculation unit may calculate the absolute position based on a difference between signals obtained in the first detection area and the second detection area.
By calculating the difference, the measurement accuracy can be maintained without being affected by a decrease in the output value of the signal due to aging or aging of the second detection unit.

The edge of the light receiving region of the second detection unit is not orthogonal to the moving direction in which the non-interfering light moves due to the relative movement of the first optical element and the second optical element, and is different from the moving direction. A specific edge provided along the edge may be included.
Thereby, the change of the light reception amount of the non-interference light obtained by the 2nd detection part for every relative unit displacement of the 1st optical element and the 2nd optical element can be enlarged. As a result, the resolution of absolute position measurement can be increased.

  The second detection unit may include a light shielding region, and the specific edge of the light receiving region may be a boundary line with the light shielding region.

  The edges of the light receiving areas of both the first detection area and the second detection area are not orthogonal to the moving direction in which the non-interfering light moves due to the relative movement of the first optical element and the second optical element, and The specific edge provided so that the direction different from the said movement direction may be included may be included.

  The first detection area and the second detection area may each have a light shielding area, and the specific edge of the light receiving area may be a boundary line with the light shielding area.

  Either one of the first optical element and the second optical element includes a diffraction grating region and a non-diffraction grating region, and the second detection unit transmits light that has passed through the non-diffraction grating region. You may detect as the said non-interference light.

A displacement measurement method according to an aspect of the present invention is a displacement measurement method using a displacement measurement device including a light source, a diffraction grating pair, and a detection unit.
The diffraction grating pair is composed of a first optical element and a second optical element, is relatively movable, is provided to face along the path of a light beam, and the light emitted from the light source is the diffraction grating pair. Is incident on.
The detection unit detects light emitted from the diffraction grating pair.
Interference light by the diffracted light respectively emitted from the first optical element and the second optical element is detected by the first detection unit among the detection units.
Non-interference light emitted from the diffraction grating pair is detected by a second detection unit among the detection units.
Based on the signal obtained by the first detection unit, the relative displacement of the first optical element and the second optical element in the arrangement direction of the lattice lines of the first optical element and the second optical element is calculated.
Based on the signal obtained by the second detection unit, the absolute position of the other of the first optical element and the second optical element in the arrangement direction of the lattice lines is calculated.

  According to the above invention, an absolute position can be detected in displacement measurement using optical interference.

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 the detection areas of the first PD and the second PD constituting the second detection unit. FIG. 3 is a diagram for explaining an example of the mechanical movement of the displacement measuring device. FIG. 4 is a graph showing the relationship between the relative displacement of the diffraction grating pair in the x direction and the voltage signal obtained by the first detection unit. FIG. 5A is a graph showing a signal obtained by the second detection unit. FIG. 5B shows a simulation result of the graph shown in FIG. 5A. FIG. 6 is a block diagram illustrating a functional configuration of the arithmetic circuit. FIGS. 7A to 7C show examples of detection regions of the first PD and the second PD constituting the second detection unit according to the second embodiment of the present invention. 8A and 8B show detection areas according to still another example of the first PD and the second PD constituting the second detection unit according to the second embodiment of the present invention. FIG. 9 shows a part of the configuration of the displacement measuring apparatus according to the third embodiment of the present invention. FIG. 10 shows a main part of a diffraction grating pair according to still another embodiment.

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

1. First Embodiment (1) Configuration of Displacement Measuring Device FIG. 1 is a diagram schematically showing a basic optical system configuration of a displacement measuring device according to a 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 detection unit 31, a second detection unit 32, and an arithmetic circuit 40.

  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, for example, a transmissive first optical element 21 and a second optical element 22. Each of the first optical element 21 and the second optical element 22 is a diffraction grating element. The first optical element 21 and the second optical element 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.

  The first optical element 21 includes the 0th-order light 30a that goes straight on the optical axis of the diffraction grating pair 20 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 optical element 22 emits the 0th-order light 30a emitted from the first optical element 21 and incident on the second optical element 22 as 0th-order light 30b that travels straight on the optical axis. For convenience of explanation, hereinafter, when referring to the diffracted light of both the 0th-order light 30a and the 0th-order light 30b, it is referred to as “0th-order light 30”. The second optical element 22 generates -n-order diffracted light 23b of + n-order diffracted light 23a incident thereon, and generates + n-order diffracted light 25b of -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 first detection unit 31 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. Accordingly, the first detection unit 31 that detects the interference light 27 is disposed on the optical axis of the diffraction grating pair 20. The first detection unit 31 is typically composed of one PD (photodiode).

  The light on the optical axis includes the 0th-order light 30, and the first detection unit 31 receives the 0th-order light 30 in addition to the interference light 27. However, since the zero-order light 30 is not necessary for displacement measurement, the displacement measuring apparatus 100 reduces the influence of the zero-order light 30 by specific means. Another means is to keep the distance between the diffraction grating pair 20 at a predetermined distance, for example.

The predetermined distance is an optical path difference between the three light beams of the 0th-order light 30, the diffracted light (23a, 23b), and the diffracted light (25a, 25b).
(2a + 1) λ / 4 (a is an integer of 0 or more)
It is the distance which satisfies. A substantial optical path difference does not occur in the diffracted light (23a, 23b) and the diffracted light (25a, 25b). Therefore, the optical path difference between the 0th-order light 30 and the diffracted light (23a, 23b) or the diffracted light (25a, 25b) should substantially satisfy the above expression.

  The first optical element 21 and the second optical element 22 are diffraction grating elements having substantially the same shape and the same size. For example, each optical element 21 (and 22) has a plurality of lattice lines 21a (and 22a) which are grooves along the y direction orthogonal to the z direction in FIG. The pitch P of the grid lines 21a of the first optical element 21 and the pitch P of the grid lines 22a of the second optical element 21 are formed substantially the same. As an example of the structure 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 uses the relative displacement Δx of the diffraction grating pair 20 in the x direction, which is 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. In the x-axis, the right direction is positive (+) and the left direction is negative (-) in FIG.

  The second detection unit 32 typically includes a first PD 32A and a second PD 32B as two PDs arranged in the x direction. The first PD 32A has a first detection region on a surface on which light is incident, and the second PD 32B has a second detection region on a surface on which light is incident. FIG. 2 shows the detection areas of the first PD 32A and the second PD 32B. These detection areas have, for example, a generally rectangular shape.

  As shown in FIG. 1, −n-order diffracted light emitted from the first optical element 21 is incident on the second optical element 22, and further − (n + 1) -order diffracted light is detected from the second optical element 22. n is a natural number of 1 or more

  In the present embodiment, typically, the first detection unit 31 includes the + 1st order diffracted light 23a emitted from the first optical element 21, the 1st order diffracted light 23b emitted from the second optical element 22, and the first Interference light 27 with the −1st order diffracted light 25a emitted from the first optical element 21 and the + 1st order diffracted light 25b emitted from the second optical element 22 is detected.

  Also, typically, the second detection unit 32 can receive the −1st order diffracted light 25 a emitted from the first optical element 21 and the −1st order diffracted light 25 c emitted from the second optical element 22. Is arranged. The -1st order diffracted light 25a and the -1st order diffracted light 25c are non-interfering lights that do not interfere with other light.

  As described above, the first detection unit 31 and the second detection unit 32 handle light having a level of ± 1st order diffracted light, but diffracted light of ± 2nd order or later 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.

  Strictly speaking, not all of the beams constituting the −1st order diffracted light 25c are non-interfering light, and there is an optical region where interference occurs at a low light intensity level. However, it does not affect the technology because it is a low level light intensity.

  Returning to the description of FIG. At the reference position, the center C of the light beam of the non-interfering light that is the −1st order diffracted light 25c generated from the diffraction grating pair 20 is substantially coincident with the center between the detection regions of the first PD 32A and the second PD 32B. The first PD 32A and the second PD 32B are arranged. The reference position is a home position of the displacement measuring apparatus 100. From the viewpoint of ease of explanation, this reference position is defined as a position where the displacement (Δx shown in FIG. 1) of the first optical element 21 and the second optical element 22 is 0 for convenience. A state where the diffraction grating pair 20 is at the reference position is defined as a state where the displacement Δx is zero (a state where the diffraction grating pair 20 is at the zero point in the absolute position).

  When the first optical element 21 and the second optical element 22 are relatively displaced in the x direction, as shown in FIG. 2, the beam of the non-interfering light 25c is broken by a broken line from the center position between the first PD 32A and the second PD 32B. As shown, it moves in either positive or negative direction on the x-axis. Depending on the relative movement direction of the first optical element 21 and the second optical element 22, the positive and negative directions on the x-axis along which the beam of the non-interference light 25c moves are different. The first PD 32A and the second PD 32B are arranged in the direction in which the non-interfering light 25c moves due to the relative movement of the first optical element 21 and the second optical element 22 (in this embodiment, the x direction).

  FIG. 3 is a diagram for explaining an example of the mechanical movement of the displacement measuring apparatus 100 configured as described above. The light source 12, the collimator lens 14, and the first optical element 21 are integrally supported by a housing (or frame) 51. The second optical element 22, the first detection unit 31, and the second detection unit 32 are integrally supported by a housing (or frame) 52. The casings 51 and 52 are configured to be relatively movable in the x direction by a slide mechanism (not shown) (for example, a slide shaft). The casings 51 and 52 are configured to return to the reference position by a spring force of a spring (not shown) (for example, a leaf spring).

  The arithmetic circuit 40 performs a predetermined arithmetic processing based on the respective signals (voltage signals corresponding to the amount of received light) S1, S2A, S2B obtained by the first detection unit 31 and the second detection unit 32, so that the relative It is configured to calculate the displacement Δx and the absolute position. Specifically, the arithmetic circuit 40 calculates the displacement Δx based on the signal S1 obtained by the first detector 31, and based on the signals S2A and S2B obtained by the second detector 32, the absolute position, that is, zero. Calculate the position from the point.

(2) Displacement Measurement Principle by Displacement Measuring Device (a) Signal Obtained by First Detection Unit FIG. 4 shows the relative displacement (μm) in the x direction of the diffraction grating pair 20 and the first detection unit 31. It is a graph which shows the relationship with the voltage signal obtained. In this example, the pitch of the grating lines 21a and 22a of the diffraction grating pair 20 is, for example, 3.3 μm, and the center wavelength of the light from the light source 12 is 850 nm.

  As can be seen from this graph, the first detector 31 outputs a waveform signal having periodicity for each pitch P of the lattice lines 21a and 22a. That is, for each pitch P, the first detection unit 31 obtains a light amount with a period of light and dark sets of the grid lines as one cycle. The waveform signal having periodicity is typically a sin waveform signal.

(B) Signal Obtained by Second Detection Unit As shown in FIG. 2, from the position of the non-interfering light 25c beam corresponding to the reference position (the beam position indicated by hatching in FIG. 2) to the right of the non-interfering light beam As the amount of movement increases, the amount of light received by the second PD 32B increases and the amount of light received by the first PD 32A decreases. Conversely, as the amount of non-interfering light beam moving leftward from the non-interfering light beam position corresponding to the reference position increases, the amount of light received by the second PD 32B decreases and the amount of light received by the first PD 32A increases.

  FIG. 5A is a graph showing a signal obtained by the second detection unit 32. The horizontal axis represents the relative displacement (Δx) of the diffraction grating pair 20. The relative movement direction of the first optical element 21 and the second optical element 22 was defined with the right direction on the horizontal axis being positive (+) and the left direction being negative (-). The vertical axis represents the amount of received light. The solid line indicates the amount of light received by the first PD 32A, and the broken line indicates the amount of light received by the second PD 32B. As described above, the second detection unit 32 can obtain a light reception amount symmetrical in the x direction around the zero point corresponding to the reference position of the diffraction grating pair 20. FIG. 5B shows a simulation result of the graph shown in FIG. 5A.

(C) Arithmetic Circuit FIG. 6 is a block diagram showing a functional configuration of the arithmetic circuit 40. The arithmetic circuit 40 includes an A / D converter 41 and a relative displacement calculation unit 42.

  The A / D converter 41 converts the analog waveform signal S1 output from the first detection unit 31 into a digital value. The A / D converter 41 is configured to count the number of waves of the input signal, for example, by counting the frequency of the waveform signal, and to output this count value.

  The relative displacement calculator 42 is configured to calculate the relative displacement based on the count value. As described above, one wave number (one count value) corresponds to the pitch P of the lattice lines 21a and 22a. Therefore, the relative displacement calculator 42 can calculate the relative displacement of the diffraction grating pair 20 by multiplying the count value by the fixed pitch P.

  The relative displacement Δx is the displacement of the diffraction grating pair 20 measured for the first time when the power is turned on. Therefore, when the diffraction grating pair 20 is not at the reference position at the moment of turning on the power, the relative displacement Δx indicates the displacement from the position at the moment of turning on the power, and does not indicate the displacement from the reference position.

  The arithmetic circuit 40 includes a difference calculation unit 43, an A / D converter 44, an absolute position calculation unit 45, a data storage unit 46, and a displacement calculation unit 47.

  The difference calculation unit 43 is configured to calculate a difference between the analog waveform signal S2A output from the first PD 32A in the second detection unit 32 and the analog waveform signal S2B output from the second PD 32B. The difference calculation unit 43 is typically configured by a differential amplifier.

  The A / D converter 44 converts the analog signal output from the difference calculation unit 43 into a digital value.

  The arrangement of the difference calculation unit 43 and the A / D converter 44 may be reversed. In this case, the waveform signals S2A and S2B are AD-converted, and the difference between the two obtained signal values is calculated by the difference calculation unit 43. In this case, the difference sending unit is configured by a circuit capable of digital processing.

  The data storage unit 46 stores look-up table data that associates the difference value with the amount of movement due to the relative movement of the diffraction grating pair 20 (the amount of movement from the zero point corresponding to the reference position). In the present embodiment, when the difference value is 0, it is assumed that the diffraction grating pair 20 is at the reference position. This table data is created based on the data shown in FIGS. 5A and 5B when the displacement measuring apparatus 100 is designed or manufactured, and is stored in the data storage unit 46.

  The absolute position calculation unit 45 refers to the table data, extracts the absolute position corresponding to the difference value actually calculated by the difference calculation unit 43, and outputs this.

  The absolute position calculation unit 45 may not store the look-up table method, and may store an arithmetic expression for obtaining the absolute position, which is created based on FIGS. 5A and 5B, for example. In this case, the absolute position calculation unit 45 can calculate the absolute position based on the actually calculated difference value using the arithmetic expression.

  The displacement calculator 47 is configured to calculate an absolute displacement based on the relative displacement obtained by the relative displacement calculator 42 and the absolute position obtained by the absolute position calculator 45. Specifically, the displacement calculation unit 47 obtains the absolute position calculated by the absolute position calculation unit 45, and outputs the absolute displacement by adding the relative displacement calculated by the relative displacement calculation unit 42 to the absolute position. can do.

  5A and 5B, the absolute position calculation unit 45 determines which side the current position is from the reference position from the polarity (positive or negative) of the difference value obtained by the difference calculation unit 43. can do.

  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 composed of a plurality of physically separated chip packages or elements. A part of the arithmetic circuit 40 may be configured by an analog circuit (for example, the above-described differential amplifier).

(3) Summary As described above, in the displacement measuring apparatus 100 according to the present embodiment, the relative displacement of the diffraction grating pair is detected based on the interference light signal S1 detected by the first detection unit 31, and the second detection unit. Based on the non-interfering light signals S2A and S2B detected at 32, the absolute position can be detected. Therefore, absolute displacement can be detected.

  As a result of detecting the absolute displacement, even when the power of the displacement measuring device 100 is turned off, the displacement measuring device 100 starts to operate and detects the absolute position when the power is turned on next time. Absolute displacement can be measured. Therefore, when the displacement measuring apparatus 100 is not used, the power consumption can be reduced by turning off the power.

  In the present embodiment, the second detection unit 32 has the first PD 32A and the second PD 32B, that is, two detection regions, and the difference calculation unit 43 calculates the difference between these signals to calculate the absolute position. Therefore, highly accurate measurement is possible as compared with the case where the absolute position is calculated in one detection region. Specifically, even if the output values of the PDs 32A and 32B fluctuate due to, for example, aging or aging of the two PDs 32A and 32B, the influence of the fluctuations on the measured values is reduced.

2. Second Embodiment Next, a displacement measuring apparatus according to a second embodiment of the present invention will be described. In the following description, elements that are substantially the same as members and functions included in the displacement measuring apparatus 100 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 explanation will focus on the different points.

  FIGS. 7A to 7C and FIGS. 8A and 8B show detection areas of the first PD and the second PD constituting the second detection unit according to the second embodiment.

  The second detection unit illustrated in FIG. 7A includes a light shielding region 84 in each rectangular detection region of the first PD 82A and the second PD 82B. That is, the detection area has a light receiving area 83 and a light shielding area 84. The light shielding region 84 has, for example, a triangular shape. The light shielding regions 84 of the first PD 32A and the second PD 32B are arranged so as to be rotationally symmetric with respect to the center (see FIG. 2) of the beam of the non-interference light 25c corresponding to the reference position.

  In a higher concept, the edge of the light receiving region 83 among these detection regions is not orthogonal to the moving direction (left and right direction in the figure) in which the non-interfering light beam moves due to the relative movement of the diffraction grating pair 20, and The specific edge 85 provided along the direction different from a moving direction is included. In the present embodiment, the specific edge 85 is an edge along the oblique side of the isosceles light shielding region 84, and is an edge corresponding to the boundary line between the light receiving region 83 and the light shielding region 84.

  According to the configuration of the second detection unit, it is possible to increase the change in the amount of received non-interference light obtained by the second detection unit for each relative unit displacement of the diffraction grating pair 20. As a result, the resolution of absolute position measurement can be increased.

  Moreover, according to the structure of this 2nd detection part, there also exist the following merit. For example, even if the non-interfering light beam moves in one direction of the positive direction and the negative direction and is received by only one detection area among the detection areas of the first PD 32A and the second PD 32B, the non-interference light A change in the amount of received light due to the movement of the beam can be detected. Thereby, the detection range of the received light signal, that is, the measurement range of the absolute position can be expanded.

  FIG. 7B shows a detection region of the second detection unit according to a modification of the second detection unit shown in FIG. 7A. In the second detection unit, the two light shielding regions 84 are not rotationally symmetric but are arranged symmetrically with respect to a line passing through the center of the non-interfering light beam corresponding to the reference position. The effect by this 2nd detection part is the same as that of what was shown to FIG. 7A.

  FIG. 7C shows a second detection unit according to still another modification. In the second detection unit, two light shielding regions 84 are arranged in the y direction (see FIG. 1) in one detection region, and a total of four light shielding regions 84 are provided in the two detection regions. The shape of one light shielding region 84 is a triangle, similar to that shown in FIGS. 7A and 7B. In this embodiment, two specific edges 85 are provided in one detection area.

  According to this embodiment, the change in the amount of received non-interfering light obtained by the second detection unit for each relative unit displacement of the diffraction grating pair 20 is the same as that of the second detection unit shown in FIGS. In comparison, it can be made even larger.

  FIG. 8A shows a second detection unit according to still another modification. The first PD 132A and the second PD 132B of the second detection unit according to this example include a light receiving region 83 having a specific shape. The light receiving region 83 has, for example, a trapezoid. The edge of the light receiving region 83 is not orthogonal to the moving direction in which the beam of the non-interfering light 25c moves due to the relative movement of the diffraction grating pair 20, and is along a direction different from the moving direction, as in the above embodiment. Specific edge 85 provided. More specifically, the light receiving area 83 has a shape of an area excluding the light shielding area 84 in the detection area shown in FIG. 7B. Even with the second detector having such a structure, the same effect as that of the second detector shown in FIG. 7B can be obtained.

  Or you may provide PD which has the light reception area | region 83 except the light shielding area | region 84 among the detection areas shown to FIG. 7C like the 2nd detection part shown to FIG. 8B.

  As described above, the specific edge 85 of the light receiving region 83 of the second detection unit illustrated in FIGS. 7 and 8 is linear, but may be curved. In this case, the curve may have a shape such that the received light amount obtained by the curve is obtained as a straight line as shown in FIG. 5A.

3. Third Embodiment FIG. 9 shows a part of the configuration of a displacement measuring apparatus according to a third embodiment of the present invention. The diffraction grating pair 70 of this displacement measuring device is composed of a first optical element 21 and a second optical element 72. One of the first optical element 21 and the second optical element 72, here, the second optical element 72 on the rear stage side has a form including a diffraction grating region 72a and a non-diffraction grating region 72b. . The non-diffraction grating region 72b is, for example, a region that is formed in a flat plate shape and does not include a groove. For example, the first optical element 21 may be the same as the first optical element 21 in the first embodiment.

  The first detection unit 31 detects the interference light 27 emitted from the diffraction grating pair 70 as in the first embodiment.

  The second detector 32 detects the non-interference light 75 emitted from the diffraction grating pair 70. The non-interfering light 75 is light that is incident on the second optical element 72 and has passed through the non-diffraction grating region 72b from the -n-order diffracted light emitted from the first optical element 21. In the present embodiment, −1st order diffracted light or −2nd order diffracted light is used as the −nth order diffracted light passing through the non-diffraction grating region 72b.

  The first detection unit 31, the second detection unit 32, an arithmetic circuit (not shown), and other configurations can adopt the same configurations as those in the first and second embodiments.

  As described above, non-interfering light can also be generated by providing a non-diffraction grating region in one of the optical elements constituting the diffraction grating pair. Thereby, the same effect as the first and second embodiments can be obtained.

4). Other Various Embodiments The present invention is not limited to the above-described embodiments, and other various embodiments can be realized.

  In each of the above embodiments, as the non-interfering light received by the second detectors 32, 82, and 132, -n-order diffracted light and-(n + 1) -order diffracted light generated on the negative side in the x direction are used. Of course, + n order diffracted light and + (n + 1) order diffracted light generated on the positive side in the x direction may be used.

  The 2nd detection part 32 concerning the above-mentioned embodiment was constituted by the 1st PD32A and the 2nd PD32B. However, the second detection unit may be configured by one PD that is not physically separated, and the one PD may have two detection regions.

  In the second detection units 32, 82, and 132 according to the above-described embodiment, the difference between the signals obtained by the first PD and the second PD is calculated. However, instead of calculating the difference, as a second detection unit, one PD (for example, one detection region) detects non-interfering light, and the arithmetic circuit is based on the signal obtained by the one detection region, An absolute position can also be calculated. In this case, the one PD may be arranged at one of the positions of the first PD 32A and the second PD 32B shown in FIG. In this case, the one PD may have the light shielding region described in the second embodiment.

  The arithmetic circuit 40 according to the above embodiment calculates the difference between the signals obtained by the first PD and the second PD of the second detectors 32, 82, and 132. However, instead of calculating the difference, the absolute position may be calculated by another algorithm using two signal values.

  The arrangement of the optical elements shown in FIG. 1 and the like may be any arrangement as long as the desired function can be exhibited. For example, a mirror may be provided in the middle of the light path, and the path may be bent. In addition, for example, the first PD and the second PD of the second detection units 32, 82, and 132 are not necessarily arranged in the x direction. For example, an optical element such as a mirror is interposed in the middle of the optical path. The arrangement direction may be a direction other than the x direction. In short, the arrangement of the first PD and the second PD may be in the direction in which the non-interfering light moves due to the relative movement of each optical element constituting the diffraction grating pair.

  In the above embodiment, the signal of the interference light 27 detected by the first detection unit 31 is a signal of only one phase. However, the displacement measuring apparatus may include, for example, a diffraction grating pair that generates a plurality of phases of interference light having different phases, and a first detection unit that has a plurality of detection regions for each of these interference lights. For example, as shown in FIG. 10, any one of the two optical elements constituting the diffraction grating pair may have a plurality of diffraction grating regions that are divided.

  In FIG. 10, three diffraction grating regions 122A, 122B, and 122C are provided in the y direction. In each of the regions 122A, 122B, and 122C, lattice lines 123 are provided that are shifted from each other by a predetermined distance along the measurement target direction (x direction). In each diffraction grating region 122A, 122B, 122C, the pitch of the grating lines 123 is the same. The deviation of the predetermined distance is set to be shorter than 1 pitch, for example, if the diffraction grating region is divided into n, it is set to be shorter than 1 / n of 1 pitch.

  When the diffraction grating region is divided into three parts, three-phase interference light is generated from the diffraction grating regions 122A, 122B, and 122C, respectively, so that the first detector can receive these interference light independently. It has three detection areas where each signal can be generated. In this case, the arrangement direction of the detection regions of the first detection unit is also set to the y direction, similarly to the arrangement direction of the diffraction grating regions 122A, 122B, and 122C of the optical element.

  As described above, since a plurality of phase signals are obtained from the first detection unit, displacement can be measured with a resolution shorter than one pitch. Also, the arithmetic circuit can determine the direction of displacement (in the figure, the positive or negative direction of the x direction) by obtaining a signal of a plurality of phases. Of course, it is not limited to three phases, and may be two phases or four or more phases.

  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, 70 ... Diffraction grating pair 21 ... 1st optical element 21a, 22a, 123 ... Grating line 22 ... 2nd optical element 25c, 75 ... Non-interference light 27 ... Interference light 31 ... 1st detection part 32 ... 1st 2 detection parts 32A, 132A ... 1st PD
32B, 132B ... 2nd PD
DESCRIPTION OF SYMBOLS 40 ... Arithmetic circuit 42 ... Relative displacement calculation part 43 ... Difference calculation part 45 ... Absolute position calculation part 72 ... Optical element 72b ... Non-diffraction grating area | region 72a ... Diffraction grating area | region 83 ... Light reception area | region 84 ... Light-shielding area 85 ... Specific edge 100 ... Displacement measuring device 122 ... Optical element 122A, 122B, 122C ... Diffraction grating region

Claims (11)

A light source;
A diffraction grating pair configured by the first optical element and the second optical element, relatively movable, provided opposite to each other along the path of the light beam, and on which the light emitted from the light source is incident;
A first detector for detecting interference light caused by diffracted light respectively emitted from the first optical element and the second optical element;
A second detector for detecting non-interfering light emitted from the diffraction grating pair;
Relative displacement for calculating relative displacement of the first optical element and the second optical element in the arrangement direction of the respective lattice lines of the first optical element and the second optical element based on the signal obtained by the first detection unit A calculation unit;
An absolute position calculation unit that calculates the absolute position of the other of the first optical element and the second optical element in the arrangement direction of the respective lattice lines based on the signal obtained by the second detection unit. Displacement measuring device. The displacement measuring apparatus according to claim 1,
The first detection unit, when n is a natural number of 1 or more, + n-order diffracted light generated from the second optical element when + n-order diffracted light from the first optical element is incident on the second optical element; A displacement measuring device that detects interference light with + n-order diffracted light generated from the second optical element when -n-order diffracted light from the first optical element is incident on the second optical element. The displacement measuring device according to claim 1 or 2,
In the case where n is a natural number equal to or greater than 1, the second detection unit generates + (n + 1) -order diffracted light generated from the second optical element when + n-order diffracted light from the first optical element is incident on the second optical element. Displacement measuring device that detects. The displacement measuring device according to any one of claims 1 to 3,
The second detection unit has a first detection region and a second detection region arranged in a direction in which the non-interfering light moves by relative movement of the first optical element and the second optical element,
The absolute position calculation unit calculates the absolute position based on signals obtained in the first detection region and the second detection region, respectively. The displacement measuring device according to claim 4,
The absolute position calculation unit calculates the absolute position based on a difference between signals obtained in the first detection region and the second detection region, respectively. The displacement measuring device according to any one of claims 1 to 3,
The edge of the light receiving region of the second detection unit is not orthogonal to the moving direction in which the non-interfering light moves due to the relative movement of the first optical element and the second optical element, and is different from the moving direction. Displacement measuring device including a specific edge provided along. The displacement measuring device according to claim 6,
The second detection unit includes a light shielding region, and a specific edge of the light receiving region is a boundary line with the light shielding region. It is a displacement measuring device according to claim 4 or 5,
The edges of the light receiving areas of both the first detection area and the second detection area are not orthogonal to the moving direction in which the non-interfering light moves due to the relative movement of the first optical element and the second optical element, and A displacement measuring device including a specific edge provided along a direction different from the moving direction. The displacement measuring device according to claim 8,
The first detection region and the second detection region each have a light shielding region, and a specific edge of the light receiving region is a boundary line with the light shielding region. The displacement measuring apparatus according to claim 1,
Either one of the first optical element and the second optical element includes a diffraction grating region and a non-diffraction grating region,
The second detection unit detects light that has passed through the non-diffraction grating region as the non-interference light. A light source;
A diffraction grating pair configured by the first optical element and the second optical element, relatively movable, provided opposite to each other along the path of the light beam, and on which the light emitted from the light source is incident;
A displacement measuring method by a displacement measuring device comprising a detector for detecting light emitted from the diffraction grating pair,
Interference light caused by diffracted light respectively emitted from the first optical element and the second optical element is detected by the first detection unit among the detection units,
Non-interference light emitted from the diffraction grating pair is detected by a second detection unit among the detection units,
Based on the signal obtained by the first detection unit, the relative displacement of the first optical element and the second optical element in the arrangement direction of each lattice line of the first optical element and the second optical element is calculated,
A displacement measurement method that calculates the absolute position of the other of the first optical element and the second optical element with respect to one of the first optical element and the second optical element in the arrangement direction of the lattice lines based on the signal obtained by the second detection unit.