JP2005326232A - Photoelectric encoder - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a photoelectric encoder with a high operational stability capable of measurement of triaxial directions of the moving grating with a small size and at an economical price. <P>SOLUTION: The six light beams 21a, 21b, 22a, 22b, 23a, 23b generated by the light beam 3 incident diffracted by the diffraction gratings 4A, 4B enter the moving grating 5. These light beams are diffracted by the moving grating 5 respectively, the light beams 21b, and 23b are emitted almost in the same direction and detected by the light receiving element A, the light beams 21a, 22b are emitted almost in the same direction and detected by the light receiving element B, and the light beams 22a, 23a are emitted almost in the same direction and detected by the light receiving element C. Based on the output signal of the light receiving elements A, B, and C, the operation for the phase information etc. of the intensity of the interference light is performed by the encoder processing circuit 7, and based on the phase information, the x-axis movement information, z-axis movement information on the moving grating 5 and pitch angle variation information can be acquired. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a photoelectric encoder that optically generates a movement signal and uses these photoelectric conversion signals as displacement information.

  Conventionally, there has been known a position detection device that can detect a moving direction and a gap direction of a moving scale by using a beat signal of optical heterodyne interference (see, for example, Patent Document 1). In this position detection device, the light of the frequency f1 and the light of the frequency f2 included in the laser emission light are separated, and these lights are incident on the moving scale at an incident angle at which ± first-order diffracted light is generated. Then, ± 1st order diffracted light emitted in the normal direction of the moving grating is caused to interfere to generate a beat signal, and movement information of the moving scale is put on this signal phase difference.

  On the other hand, in the measurement in the gap direction, if light of frequency f2 is incident on the moving scale at an angle at which the third-order diffracted light is generated, the + 1st-order diffracted light of frequency f1 and the -1st-order diffracted light of f2 interfere to generate a beat signal To do. Since the beat signal includes movement information of the movement scale and gap information, the gap information is obtained by subtracting (or adding) the movement information from the phase information obtained here.

Japanese Patent Publication No. 6-63739

  However, in the above-described conventional apparatus, a lateral Zeeman laser or the like is used as a light source, so that the apparatus becomes large and expensive. In addition, since a large number of polarizing elements and mirrors are required in the middle of the optical path, there is a possibility that the optical path becomes very long and the apparatus becomes unstable. Furthermore, in the conventional apparatus, only information in the biaxial direction of the moving scale and the gap direction can be obtained.

According to a first aspect of the present invention, a photoelectric encoder includes: a light source; an optical system that generates at least first, second, and third light fluxes traveling in different directions from the light of the light source; and the first, second, and third And a first diffraction grating that generates a plurality of diffracted lights including zeroth order light for each of the first, second, and third light fluxes, and (a) the first light flux generated from the first light flux. A first interference light is generated by any one of the plurality of diffracted lights and one of the other diffracted lights generated by the first diffraction grating, and (b) a plurality of diffractions generated from the second light flux. The second interference light is generated by any one of the lights and one of the other diffracted lights generated by the first diffraction grating, and (c) any of the plurality of diffracted lights generated from the third light flux. One and another of the diffracted lights generated by the first diffraction grating generate a third interference light. The second diffraction grating, the first detection unit for detecting the first interference light, the second detection unit for detecting the second interference light, and the third detection for detecting the third interference light. And a calculation unit that performs calculation based on phase information calculated from detection results of the first to third detection units, and one of the first and second diffraction gratings is fixed to a movable object In the moving grid, the calculation unit calculates a displacement in a moving direction of the moving grid and a displacement in a direction perpendicular to the moving grid.
A photoelectric encoder according to a first aspect of the present invention includes a light source, and an optical system that generates first, second, third, fourth, fifth, and sixth light fluxes traveling in different directions from the light of the light source, The first to sixth so that the incident angle average values of the first and second light beams, the incident angle average values of the third and fourth light beams, and the incident angle average values of the fifth and sixth light beams are different. And a first diffraction grating for generating a plurality of diffracted lights including zeroth order light for each of the first to sixth light beams, and (a) a plurality of light beams generated from the first light flux. The first interference light is generated by any one of the diffracted light and any one of the plurality of diffracted lights generated from the second light beam, and (b) the plurality of diffracted lights generated from the third light beam. And any one of a plurality of diffracted lights generated from the fourth light flux. (C) the third interference light beam is generated by any one of the plurality of diffracted light beams generated from the fifth light beam and one of the plurality of diffracted light beams generated from the sixth light beam. A second diffraction grating that generates interference light; a first detection unit that detects first interference light; a second detection unit that detects second interference light; and third interference light. A third detection unit; and a calculation unit that performs calculation based on phase information calculated from detection results of the first to third detection units, wherein one of the first and second diffraction gratings is a movable object. The calculation unit calculates a displacement in a moving direction of the moving grid and a displacement in a direction perpendicular to the moving grid.

  According to the present invention, it is possible to provide a small-sized and inexpensive photoelectric encoder that can measure the displacement of the moving grating in the three-axis directions and has a very small number of optical components.

Hereinafter, the best mode for carrying out the present invention will be described with reference to the drawings.
-First embodiment-
FIG. 1 is a diagram showing a first embodiment of a photoelectric encoder according to the present invention, and shows a main configuration of the encoder. The encoder according to the present embodiment includes a light source 1, a collimating lens 2, diffraction gratings 4A and 4B functioning as beam splitting elements, a moving grating fixed to a position measurement object 5, and light receiving elements A and B that detect interference light. , C and an encoder processing circuit 6. In the present embodiment, the grating pitches of the diffraction gratings 4A and 4B and the moving grating 5 are all set to p.

  In the encoder shown in FIG. 1, the movement information of the moving grid 5 in the x direction and the z direction and the change in the pitch angle, which is the inclination around the y axis, are detected, and the x position, z position, and Measure the pitch angle. The encoder processing circuit 8 may be provided on the encoder side, or may be included in an actuator control circuit controlled based on an encoder output signal.

  The light emitted from the light source 1 is converted into parallel light by the collimating lens 2. As the light source 1, a laser light source, a light emitting diode (LED), or the like is used. The light beam 3 converted into parallel light by the collimator lens 2 is incident on the diffraction grating 4A which is the first light beam splitting element. The light beam 3 is subjected to 0th order and ± 1st order diffraction by the diffraction grating 4A to generate three light beams 21, 22, and 23. The light beam 21 has an angle a1, the light beam 21 has an angle 0, and the light beam 23 has an angle −a1. Emitted. These light beams 21, 22, and 23 further enter the diffraction grating 4B, which is the second light beam splitting element, and are divided into two light beams by the diffraction grating 4B.

  The light beam 21 is subjected to + 1st order diffraction and + 2nd order diffraction by the diffraction grating 4B, and the light beam 21a subjected to + 1st order diffraction is emitted at an angle 0, and the light beam 21b subjected to + 2nd order diffraction is emitted in the angle -a1 direction. . The light beam 22 undergoes ± first-order diffraction at the diffraction grating 4B, and the light beam 22a is emitted in the direction of the angle −a1 and the light beam 22b is emitted in the direction of the angle + a1. The light beam 23 is subjected to −1st order diffraction and −2nd order diffraction by the diffraction grating 4B, and the light beam 23a subjected to −1st order diffraction is emitted at an angle 0, and the light beam 23b subjected to −2nd order diffraction is emitted at an angle a1. Is done. Here, with respect to the incident angle and the outgoing angle, the clockwise direction from the perpendicular is the plus direction.

  These six light beams 21a, 21b, 22a, 22b, 23a, and 23b are diffracted by the moving grating 5, respectively. Incident on A. Further, the light beam 21a subjected to the −1st order diffraction and the light beam 22b which is the 0th order diffracted light enter the light receiving element B at an angle a1. Further, the light beam 22a which is 0th-order diffracted light and the light beam 23a which has received the −1st-order diffraction are incident on the light receiving element C at an angle −a1.

  As will be described later, the 0th-order diffracted lights 22a and 22b emitted from the moving grating 5 are not affected by the movement of the moving grating 5, and the light beams 21a, 21b, 23a and 23b subjected to ± 1st-order diffraction are obtained from the moving grating 5. The phase shifts under the influence of movement. The light receiving element A is disposed at a position where the interference light of the light beams 21b and 23b is detected, the light receiving element B is disposed at a position where the interference light of the light beams 21a and 22b is detected, and the light receiving element C is the light beams 22a and 23a. The interference light is disposed at a position where it is detected.

  In FIG. 1, only the central axis of the light beam is shown for the light beams after the light beams 21, 22, and 23. Thus, in this embodiment, three different types of interference light are detected by the light receiving elements A, B, and C, respectively. The light reception signals output from the respective light receiving elements A, B, and C are input to the encoder processing circuit 6, and the encoder processing circuit 6 performs calculations such as phase information of interference light intensity described later.

<Description of principle>
As described above, in the encoder of the present invention, the two light beams 11 and 12 are incident on the moving grating 5, and the interference light obtained with respect to each of the light beams 11 and 12 is detected by the light receiving elements A and B, respectively. The movement in the x direction (movement direction) and the movement in the z direction are detected. At that time, the measurement is performed based on the movement information of the moving grating using the Doppler shift of the light scattered by the moving grating. Therefore, before describing the measurement method in the encoder of FIG. 1, the principle of laser Doppler shift will be described with reference to the principle diagram of FIG.

FIG. 2 is a diagram for explaining the Doppler shift, and 100 is an object to be measured. First, consider a case where the object to be measured 100 is moving in the x-axis plus direction by the velocity vector V _X. The Doppler shift f _DX of the light (wave vector K _S ) in which light of the wave vector K _O is incident on the measured object 100 at an angle α and scattered in the angle β direction is calculated as follows. Here, as shown in FIG. 2, a case where the vectors V _X , K _O , and K _S are in the same plane (xz plane) is considered, and the angles α and β represent angles formed with the z axis.

At this time, the Doppler shift f _DX is expressed by the following equation (1). In the equation (1), the first equation on the right side is an inner product equation of the vector (K _S −K _O ) and the vector V _X, and the second and third equations on the right side are specifically calculated inner products. Here, the angle θ represents an angle formed by the vector (K _S −K _O ) and the x axis. K represents the wave number which is an absolute value of the wave number vectors K _O and K _S , and the value is 2π / λ. v _X is the absolute value of the vector _{V X.}
2πf _DX = (K _S −K _O ) · V _X
= | K _S -K _O | × | V _X | × cos θ
= [2k cos (α / 2−β / 2)] × v _X cos θ (1)

Here, when the angle θ in FIG. 2 is expressed by the angles α and β, the following equation (2) is obtained. Therefore, the equation (1) can be transformed as the equation (3).
θ = π / 2− (α / 2 + β / 2) (2)
2πf _DX = 2 kv _X cos (α / 2−β / 2) × cos [π / 2− (α / 2 + β / 2)]
= Kv _X x [sin (α) + sin (β)] (3)

Next, consider a case where the measured object 100 is moving in the z-axis plus direction with a velocity vector V _Z (| V _Z | = v _Z ). In this case as well, the Doppler shift f _DZ of the scattered light is obtained by calculating in the same manner as in the case of the velocity vector V _X , which is expressed by the following equation (4).
2πf _DZ = [2k cos (α / 2−β / 2)] × v _Z cos (π / 2−θ)
= 2kv _Z cos (α / 2−β / 2) × cos (α / 2 + β / 2)
= Kv _Z x [cos (α) + cos (β)] (4)

Equations (3) and (4) show the relationship between the frequency shift amount and the moving speed. When these sides are multiplied by time Δt, they are expressed by the following equations (5) and (6). The relationship between the positional changes Δx and Δz of the measured object 100 and the phase changes φ _X and φ _Z can be obtained. When the object to be measured 100 is moving in both the x and z directions, the sum of φ _X and φ _Z is the phase shift amount φ of the scattered light, which is expressed as in equation (7). The
φ _X = kΔx × [sin (α) + sin (β)] (5)
_{φ Z = kΔz × [cos (} α) + cos (β)] ... (6)
φ = kΔx × [sin (α) + sin (β)] + kΔz × [cos (α) + cos (β)] (7)

Here, consider a case where the object 100 to be measured is a diffraction grating having a pitch p. The first light beam enters the diffraction grating at an incident angle α1, and n-order diffracted light is emitted in the direction of the outgoing angle β. The second light beam is incident on the diffraction grating at an incident angle α2, and m-order diffracted light is emitted in the same emission angle β direction. The phase shift amounts φ1 and φ2 of each diffracted light are calculated using the equation (7) and are given by the following equations (8) and (9).
φ1 = kΔx × [sin (α1) + sin (β)] + kΔz × [cos (α1) + cos (β)] (8)
φ2 = kΔx × [sin (α2) + sin (β)] + kΔz × [cos (α2) + cos (β)] (9)

When the light beam having the phase shift amount φ1 and the light beam having the phase shift amount φ2 emitted in the direction of the emission angle β interfere with each other, the phase information ψ of the interference light is expressed by the following equation (10). Since ψ is the phase term of the cos function, the phase information is obtained as absolute value information.
ψ = φ1-φ2
= KΔx · [sin (α1) + sin (β)] + kΔz · [cos (α1) + cos (β)]
−kΔx · [sin (α2) + sin (β)] − kΔz · [cos (α2) + cos (β)]
= KΔx × [sin (α1) −sin (α2)] + kΔz × [cos (α1) −cos (α2)] (10)

Here, since the pitch of the grating is p, the relationship of the following equation (11) is established between the incident angle α1 and the output angle β of the n-th order diffracted light, and between the incident angle α2 and the output angle β of the m-order diffracted light. Satisfies the relationship (diffraction condition) of the following equation (12). Then, when Expressions (11) and (12) are substituted into Expression (10), Expression (13) is obtained as phase information ψ.
sin (α1) + sin (β) = nλ / p (11)
sin (α2) + sin (β) = mλ / p (12)
ψ = kΔx × [sin (α1) −sin (α2)] + kΔz × [cos (α1) −cos (α2)]
= 2π (n−m) Δx / p + kΔz × [cos (α1) −cos (α2)] (13)

<< Explanation of measurement method in encoder >>
In the encoder of the present embodiment shown in FIG. 1, based on the principle as described above, specifically, by using the phase information obtained by the equations (10) and (13), the x direction of the moving grating 5 is obtained. , Z-direction movement information and pitch angle fluctuation information are detected.

(Light receiving element A)
First, the interference light intensity of the light receiving element A will be described. As described above, the light beam 21b incident on the moving grating 5 at the angle −a1 undergoes −1st order diffraction and is incident on the light receiving element A at the angle 0, and the light beam 23b incident on the moving grating 5 at the angle a1 is + 1st order diffraction. Is incident on the light receiving element A at an angle of zero. At this time, the following equation (14) is established between the incident angle a1 and the grating pitch p.
sin (a1) = λ / p (14)

Then, when φ1 in the above equation (10) is the phase shift amount of the light beam 23b and φ2 is the phase shift amount of the light beam 21b, the following equation (15) obtained by substituting -a1 for α1 to α1 Then, phase information ψ _A of the interference intensity between the light beam 21b and the light beam 23b generated in the light receiving element A is calculated. Note that the equation was transformed using equation (14).
ψ _A = kΔx × [sin (a1) −sin (−a1)] + kΔz × [cos (a1) −cos (−a1)]
= 2kΔx × sin (a1)
= 4πΔx / p (15)

(Light receiving element B)
The light beam 21 a incident on the moving grating 5 at an angle 0 undergoes −1st order diffraction, is emitted at an angle a 1, and enters the light receiving element B. On the other hand, the light beam 22b incident on the moving grating 5 at the angle a1 is emitted as the 0th-order diffracted light at the angle a1 and enters the light receiving element B. In this case, φ1 in equation (10) is the phase shift amount of the light beam 22b, and φ2 is the phase shift amount of the light beam 21a. The phase information ψ _B is expressed as shown in the following equation (16) by substituting a1 into α1 and α2 into α2 in equation (10) and transforming using equation (14).
ψ _B = kΔx × [sin (a1) −sin (0)] + kΔz × [cos (a1) −cos (0)]
= KΔx × sin (a1) + kΔz × [cos (a1) −1]
= 2πΔx / p−kΔz × [1-cos (a1)]
= 2πΔx / p−kΔz × [1- {1- (λ / p) ² } ^1/2 ]
≈ 2πΔx / p−πλΔz / p ² (16)

(Light receiving element C)
The light beam 22a incident on the moving grating 5 at the angle −a1 is emitted as the 0th-order diffracted light at the angle −a1 and enters the light receiving element C. On the other hand, the light beam 23 a incident on the moving grating 5 at the angle 0 undergoes + 1st order diffraction, is emitted at the angle −a 1, and enters the light receiving element C. In this case, φ1 in equation (10) is the phase shift amount of the light beam 23a, and φ2 is the phase shift amount of the light beam 22a. Phase information [psi _C, by deforming using Equation (10) Equation (14) by substituting the -a1 the α1 to 0 α2 of, is expressed by the following equation (17).
_{ψ C = kΔx × [sin (} 0) -sin (-a1)] + kΔz × [cos (0) -cos (-a1)]
= KΔx × sin (a1) + kΔz × [1-cos (a1)]
= 2πΔx / p + kΔz × [1- {1- (λ / p) ² } ^1/2 ]
≈ 2πΔx / p + πλΔz / p ² (17)

In this way, phase information ψ _A , ψ _B , ψ _C of the interference light intensity is obtained for each of the light receiving elements A, B, and C. Since the encoder processing circuit 6 in FIG. 1 calculates and outputs the phase angle of the interference signal, after processing the outputs of the light receiving elements A, B, and C, the four arithmetic operations of those signals are performed. The x-axis movement information, the z-axis movement information, and the pitch angle fluctuation information regarding the moving grid 5 can be obtained.
(X-axis movement information)
Δx = pψ _A / 4π
(Z-axis movement information)
Δz = (ψ _C −ψ _B ) p ² / 2πλ

(Pitch angle fluctuation information)
The above-described (ψ _C −ψ _B ) can be considered as an average value of the z-axis movement of the moving grating 5. By the way, when the fluctuation of the pitch angle occurs from the initial state with respect to the moving grating 5, each ψ _B and ψ _C includes z movement information at each beam irradiation position on the moving grating 5, and therefore, equations (18) and (19 ).
ψ _B = 2πΔx / p−πλΔz _B / p ² (18)
ψ _C = 2πΔx / p + πλΔz _C / p ² (19)

Since the irradiation position interval D on the moving grating 5 is known in advance, the change in pitch angle is given by the following equation (20) using the interval D and Δz _B and Δz _C.
Change in pitch angle = tan ⁻¹ [(Δz _C −Δz _B ) / D] (20)
However, Δz _C −Δz _B is given by the following equation (21).
Δz _C −Δz _B = (φ _B + φ _C −φ _A ) p ² / πλ (21)

  These values Δx, Δz and changes in pitch angle represent fluctuation amounts per predetermined time. For example, in the case of repeatedly detecting at predetermined time intervals, they represent fluctuation amounts per time interval. Therefore, the x position, the z position, and the pitch angle of the moving grid 5 can be calculated from the movement information and the reference position acquired in advance. As the reference position, for example, a position when the encoder is turned on is selected.

  In the present embodiment, at least four of the six light beams 21 a, 21 b, 22 a, 22 b, 23 a, and 23 b have different moving grating incident angles, and the light beams 21 b and 23 b are incident upon the moving grating 5. It is important that the incident angle average value of the light beams 21a and 22b is different from the average incident angle value of the light beams 22a and 23a. Then, by detecting three different types of interference light by the light receiving elements A, B, and C, the x-axis movement information, the z-axis movement information, and the pitch angle variation information as described above can be obtained.

[Modification 1]
In the above-described embodiment, the transmissive encoder that receives the light beam transmitted through the moving grating 5 by the light receiving elements A, B, and C is configured. However, the present invention is also applied to a reflective encoder as shown in FIG. be able to. In this case, the moving grating 15 is composed of a half mirror so that the transmittance is 50% and the reflectance is 50%. The encoder processing circuit 6 is not shown. The light beams 21 b and 23 b are diffracted and reflected by the moving grating 15 and enter the light receiving element A, the light beams 21 a and 22 b are diffracted and reflected by the moving grating 15 and enter the light receiving element B, and the light beams 22 a and 23 a are diffracted by the moving grating 15. The light is reflected and enters the light receiving element C. Since the phase information and the movement information are calculated in the same manner as in the above-described embodiment, description thereof is omitted here.

[Modification 2]
FIG. 4 is a view showing a second modification of the photoelectric encoder according to the present invention. The encoder processing circuit 6 is not shown. In this modification, the light beam 3 is divided into six light beams 41 to 46 by the diffraction grating 30 which is a light beam splitting element. In the encoder shown in FIG. 4, the grating pitch of the diffraction grating 30 is set to 2 p and the grating pitch of the diffraction grating 31 is set to p / 4 with respect to the grating pitch p of the moving grating 5.

The light beams 42 and 45 are diffracted in the same direction by the moving grating 5 and enter the light receiving element A, and the light beams 41 and 44 are diffracted in the same direction by the moving grating 5 and enter the light receiving element B. Is diffracted in the same direction by the moving grating 5 and enters the light receiving element C. Similarly to the first embodiment, phase information ψ _A , ψ _B and ψ _C of interference intensity is obtained for each of the light receiving elements A, B, and C, and is used to obtain x-axis movement information and z-axis movement information. And pitch angle variation information is calculated. That is, measurement can be performed in the three-axis directions.

  The embodiment described above is an example of the present invention, and the grating pitch and the diffracted light order are not limited to those described above, and the same effect can be obtained as long as the optical system can obtain two types of interference intensities. Can do. Various embodiments other than those described above are possible. For example, although a diffraction grating is used as a light beam splitting element, a prism, a half mirror, or the like may be used. Further, although two diffraction gratings (4A, 4B or 30, 31) are used as the light beam splitting elements, for example, these two kinds of grating grooves may be formed on two mutually parallel surfaces of the glass optical element. .

  The light beams incident on the light beam splitting elements 4A and 30 are parallel light and vertically incident. However, the light beams may not necessarily be parallel light and may not be vertically incident. However, the grating exit angle is not a symmetric equiangular angle when it is not perpendicularly incident. In addition, although the moving grating 5 and the index grating 6 have the same grating pitch p, they need not necessarily be the same pitch. Furthermore, the optical system for obtaining the interference light may be a moiré method or a vernier method having a different grating pitch, and a multi-segment light receiving element may be used for the light receiving elements A and B. 1, 3 and 4, the gratings 4B and 31 may be moving gratings, and the movement amount is calculated by the same calculation.

  Of course, a transverse Zeeman laser or the like can be used as the light source, and a high-resolution encoder can be configured by constructing a heterodyne interferometer. In addition, a 5-degree-of-freedom encoder can be configured by using two sets of the present optical system configuration.

  Furthermore, as described above, in the present invention, movement information is acquired using the principle of laser Doppler shift, so it is possible to construct a laser Doppler velocimeter with five degrees of freedom with this optical system configuration. Note that the present invention is not limited to the above embodiment as long as the characteristics of the present invention are not impaired.

  In the correspondence between the embodiment described above and the elements of the claims, the light beams 21, 22, 23 are the first to third light beams of claim 1, the diffraction gratings 4A, 30 are the optical system, and the diffraction grating. 4B and 31 are the first diffraction grating, the light receiving element A is the first detecting unit, the light receiving element B is the second detecting unit, the light receiving element C is the third detecting unit, and the encoder processing circuit 6 is the arithmetic unit. The moving grating 5 constitutes the second diffraction grating, and the luminous fluxes 41 to 46 constitute the first to sixth luminous fluxes of claim 2, respectively.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows 1st Embodiment of the photoelectric encoder by this invention, and shows the main structures of an encoder. It is a figure explaining the principle of Doppler shift. It is a figure which shows a 1st modification. It is a figure which shows the 2nd modification.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Light source 2 Collimating lens 3, 21, 22, 23, 21a, 21b, 22a, 22b, 23a, 23b, 41-46 Light beam 4A, 4B, 30, 31 Diffraction grating 5 Moving grating 6 Encoder processing circuit A, B, C Light receiving element

Claims (2)

A light source;
An optical system that generates at least first, second, and third light fluxes traveling in different directions from the light of the light source;
A first diffraction grating that receives the first, second, and third light fluxes and generates a plurality of diffracted lights including zero-order light for each of the first, second, and third light fluxes;
(A) generating a first interference light by any one of the plurality of diffracted lights generated from the first light flux and one of the other diffracted lights generated by the first diffraction grating; (B) generating a second interference light by any one of the plurality of diffracted lights generated from the second light flux and one of the other diffracted lights generated by the first diffraction grating; (C) A third interference light is generated by using one of the plurality of diffracted lights generated from the third light flux and one of the other diffracted lights generated by the first diffraction grating. Two diffraction gratings;
A first detector for detecting the first interference light;
A second detection unit for detecting the second interference light;
A third detection unit for detecting the third interference light;
A calculation unit that performs calculation based on phase information calculated from detection results of the first to third detection units,
One of the first and second diffraction gratings is a moving grating fixed to a movable object, and the calculation unit calculates a displacement in a moving direction of the moving grating and a displacement in a direction perpendicular to the moving grating. A photoelectric encoder characterized by that. A light source;
An optical system for generating first, second, third, fourth, fifth and sixth light fluxes traveling in different directions from the light of the light source;
The first and second light beam incident angle average values, the third and fourth light beam incident angle average values, and the fifth and sixth light beam incident angle average values are different from each other. A first diffraction grating on which each of the first to sixth light beams is incident, and each of the first to sixth light beams generates a plurality of diffracted lights including zeroth-order light;
(A) A first interference light is generated by any one of the plurality of diffracted lights generated from the first light flux and one of the plurality of diffracted lights generated from the second light flux. And (b) second interference light by any one of the plurality of diffracted lights generated from the third light flux and one of the plurality of diffracted lights generated from the fourth light flux. (C) the third diffracted light generated from the fifth light flux and the third diffracted light generated from the sixth light flux. A second diffraction grating that generates interference light;
A first detector for detecting the first interference light;
A second detection unit for detecting the second interference light;
A third detection unit for detecting the third interference light;
A calculation unit that performs calculation based on phase information calculated from detection results of the first to third detection units,
One of the first and second diffraction gratings is a moving grating fixed to a movable object, and the calculation unit calculates a displacement in a moving direction of the moving grating and a displacement in a direction perpendicular to the moving grating. A photoelectric encoder characterized by that.

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