Encoder

Abstract

An encoder is provided that can suppress the degradation of accuracy even if the scale is set in an inclined manner relative to a receiving unit by rotating around an axis orthogonal to a receiving surface. The encoder 1 includes a scale 2 and a detection head 3. The detection head 3 includes a light source (transmitting unit) 4 and a light receiving unit (receiving unit) 5. The light receiving unit includes a light receiving surface 50, and converts the light received at the light receiving surface 50 into a differential detection signal having two phases and outputs it. The light receiving surface 50 includes an element array group 7, which includes four element arrays 71-74 arranged in parallel along an orthogonal direction, each array including a plurality of light receiving elements (receiving elements) 500. The plurality of element arrays 71-74 in the element array group 7 are arranged at a position where the sum of (i) the distance from a reference position to a positive phase signal element array 71, 72 in the orthogonal direction and (ii) the distance from a reference position to a negative phase signal element array 73, 74 in the orthogonal direction is the same for all phases of at least two phases.

Description

Technical Field

[0001] The present invention relates to encoders. Background Art

[0002] The conventionally known encoder is provided with a plate-shaped scale having scales formed at a predetermined period along the measuring direction, and a detection head movably arranged relative to the scale along the measuring direction. For example, the detection head of the optical encoder (encoder) in Patent Document 1 is provided with a light source (emitting unit) radiating light (measurement signal) to the scale and a light receiving unit (receiving unit) having a light receiving surface (receiving surface) receiving light from the light source via the scale. The light receiving unit converts the light received on the light receiving surface into a detection signal, which changes in response to the relative movement between the scale and the detection head and corresponds to the period of the scale, and outputs such a detection signal. The detection signal is a differential detection signal having at least two different phases.

[0003] The light receiving surface of the light receiving unit includes an element array group, which includes a plurality of element arrays arranged in parallel along an orthogonal direction orthogonal to the measuring direction, and each element array includes a plurality of light receiving elements (receiving elements), which are arranged along the measuring direction at a period corresponding to the period of the scale. In this optical encoder, the light radiated from the light source is converted into a plurality of diffraction lines via the scale. The plurality of diffraction lines generate interference fringes having the same period as the scale period. The light receiving unit receives these interference fringes, and the detection head detects a detection signal for detecting the relative movement amount between the scale and the detection head from the interference fringes received by the light receiving unit. The optical encoder calculates the relative movement amount between the scale and the detection head based on the detection signal.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent document 1: Japanese Unexamined Patent Application Publication No. 2019-012064. Summary of the invention

[0007] Problems to be solved by the present invention

[0008] Fig.10 is a schematic diagram showing the light receiving unit 9 , the signal input units 600 a , 600 b , and the calculation device 800 in the conventional encoder 100 .

[0009] The light receiving unit 9 outputs a detection signal having an A-phase and a B-phase, which are two different phases. Each of the A-phase detection signal and the B-phase detection signal is a differential signal. Fig.10As shown, the light receiving surface 90 of the light receiving unit 9 is provided with an element array group 700, wherein a plurality of element arrays 710-740 are arranged in parallel along an orthogonal direction orthogonal to the measuring direction. The plurality of element arrays 710-740 include a first element array 710, a second element array 720, a third element array 730, and a fourth element array 740 in the order from the +Y side (top in the paper plane) to the -Y side (bottom in the paper plane).

[0010] The first element array 710 outputs an A-phase signal which is a positive phase signal of the A-phase, the second element array 720 outputs a B-phase signal which is a positive phase signal of the B-phase, the third element array 730 outputs an AB-phase signal which is a negative phase signal of the A-phase, and the fourth element array 740 outputs a BB-phase signal which is a negative phase signal of the B-phase.

[0011] Here, the positive phase signal refers to the positive phase signal of the differential detection signal for detecting the relative movement amount. The negative phase signal refers to the negative phase detection signal paired with the positive phase signal of the differential detection signal. The paired positive phase signal and negative phase signal are a pair of signals whose phases are ideally shifted by 180 degrees. In the drawings described below, the A-phase signal will be represented by "A-phase", the AB-phase signal will be represented by "AB-phase", the B-phase signal will be represented by "B-phase", and the BB-phase signal will be represented by "BB-phase".

[0012] The encoder 100 is further provided with: a first signal input unit 600a and a second signal input unit 600b, to which the detection signal (i.e., a pair of positive phase signal and negative phase signal) output from the light receiving unit 9 is input as a differential signal; and a calculation device 800, which calculates the scale 2 (see Fig.11 ) and the relative movement between the detection head 300.

[0013] Each of the two signal input units 600a, 600b is provided with a positive phase signal input unit 610a, 610b and a negative phase signal input unit 620a, 620b, the positive phase signal being input into the positive phase signal input unit 610a, 610b as a detection signal from the light receiving unit 9, and the negative phase signal being input into the negative phase signal input unit 620a, 620b as a detection signal from the light receiving unit 9.

[0014] For the first signal input unit 600a, the A-phase signal is input to the positive phase signal input unit 610a from the first element array 710 of the light receiving unit 9, and the AB-phase signal is input to the negative phase signal input unit 620a from the third element array 730. The first signal input unit 600a then outputs a differential A-phase signal to the computing device 800, which is the difference between the A-phase signal and the AB-phase signal (i.e., the A-phase signal minus the AB-phase signal).

[0015] For the second signal input unit 600b, the B-phase signal is input to the positive phase signal input unit 610b from the second element array 720 of the optical receiving unit 9, and the BB-phase signal is input to the negative phase signal input unit 620b from the fourth element array 740. The second signal input unit 600b then outputs a differential B-phase signal to the computing device 800, which is the difference between the B-phase signal and the BB-phase signal (i.e., the B-phase signal minus the BB-phase signal). Fig.10 In FIG. 1 , regarding the input from the plurality of element arrays 710 - 740 to the two signal input units 600 a , 600 b , the positive phase signal is represented by a solid line, and the negative phase signal is represented by a dotted line.

[0016] Fig.11 1 is a top view showing a state in which the scale 2 is disposed at an inclination angle θ=0 with respect to the light receiving unit 9 in the conventional encoder 100 . Fig.12 is a top view showing a state in which the scale 2 is set at an inclination angle θ≠0 relative to the light receiving unit 9 in the conventional encoder 100. More specifically, Fig.11 and 12 2 is a top view in which the light receiving unit 9 is seen from the scale 2 side.

[0017] like Fig.11 As shown, in the encoder 100, the scale 2 is preferably set at an inclination angle θ=0 relative to the light receiving unit 9, and the scale 2 is not set in an inclined manner by rotating around an axis (i.e., a rotation axis) orthogonal to the light receiving surface 90. At this time, the problem (to be described below) regarding the shift amount of the inclined interference fringes and / or the detection signal will not occur in the encoder 100.

[0018] However, if Fig.12 As shown, in a manufacturing process such as assembly, the scale 2 can be disposed at an inclination angle θ≠0 relative to the light receiving unit 9 by rotating about a rotation axis orthogonal to the light receiving surface 90. In this case, the following effects occur.

[0019] If the scale is set in an inclined manner with an inclination angle θ≠0 relative to the light receiving unit 9, especially with respect to the direction (Y direction) orthogonal to the measuring direction, by rotating around a rotation axis orthogonal to the light receiving surface, the interference fringes generated in the light receiving surface 90 of the light receiving unit 9 are also generated at an inclination angle θ≠0 according to the rotation of the scale. When the light receiving unit 9 receives the interference fringes at an inclination angle θ≠0, the phase of the detection signal input to the signal input unit 600a, 600b from the multiple element arrays 710-740 arranged in parallel in the Y direction is also shifted according to the rotation of the inclination angle θ≠0. The phase shift amount of the detection signal detected at the light receiving element (not shown) varies due to the positional difference of the respective element arrays 710-740 in the Y direction. Therefore, the two signals based on the detection signals input to the two signal input units 600a, 600b will also be shifted, and the calculation result (relative movement amount) will be affected.

[0020] Fig.13 is a graph showing the variation of the differential signal based on two phases in the conventional encoder 100. More specifically, Fig.13 In the graph, the vertical axis represents the output voltage of the two signal input units 600 a and 600 b , and the horizontal axis represents the relative displacement of the detection head 300 relative to the scale 2 . Fig.14 is a graph showing a Lissajous signal calculated based on a differential signal of two phases in the conventional encoder 100. More specifically, Fig.14 In , the vertical axis represents the differential B-phase signal, and the horizontal axis represents the differential A-phase signal. Fig.13 and 14 In FIG. 1 , a graph when the scale is disposed at an inclination angle θ≠0 relative to the light receiving unit 9 is indicated by a solid line, and a graph when the scale is disposed at an inclination angle θ=0 relative to the light receiving unit 9 is indicated by a dotted line.

[0021] If the scale is set at an inclination angle θ≠0 relative to the light receiving unit 9, as Fig.13 As shown, when compared with the change shown by the dotted line, when the scale 2 is set at an inclination angle θ = 0 (see Fig.11 ), the change moves in the direction of the arrow pointing to the southeast of the paper plane and the direction of the arrow pointing to the northwest of the paper plane, and the output voltage decreases. In addition, if Fig.14 As shown in FIG. 1 , when the scale 2 is set at an inclination angle θ=0, the Lissajous signal is smaller than the Lissajous signal indicated by the dotted line, and its shape becomes an ellipse. The calculation device 800 performs calculation based on the deformed Lissajous signal and outputs the relative movement amount as a calculation result. Therefore, there is a problem that if the scale is set in an inclined manner with respect to the light receiving unit 9 at an inclination angle θ≠0, the accuracy of the encoder 100 will deteriorate.

[0022] An object of the present invention is to provide an encoder capable of suppressing deterioration in accuracy even if a scale is disposed in an inclined manner relative to a receiving unit by rotating about an axis (ie, a rotation axis) orthogonal to a receiving surface.

[0023] Means of solving the problem

[0024] The encoder of the present invention comprises: a plate-shaped scale having scales formed at a predetermined period along a measuring direction; and a detection head movably arranged along the measuring direction relative to the scale. The detection head comprises: a transmitting unit, which transmits a measuring signal to the scale; and a receiving unit, which comprises a receiving surface, which receives the measuring signal from the transmitting unit via the scale. The receiving unit converts the measuring signal received on the receiving surface into a differential detection signal having at least two different phases, and outputs the detection signal. In response to the relative movement between the scale and the detection head, the detection signal changes corresponding to the scale period. The receiving surface comprises: an element array group, which comprises a plurality of element arrays arranged in parallel along an orthogonal direction orthogonal to the measuring direction. The plurality of element arrays comprises at least four element arrays. Each element array comprises a plurality of receiving elements arranged along the measuring direction, and the period thereof corresponds to the period of the scale. For each of the at least two phases, the plurality of element arrays comprises: a positive phase signal element array outputting a positive phase signal; and a negative phase signal element array outputting a negative phase signal. The at least two phases are arranged in a shifted manner with a predetermined phase difference along the measuring direction. The plurality of element arrays in the element array group are arranged at positions where the sum of the following two distances is the same for all phases in at least two phases: (i) the distance from a reference position to the positive phase signal element array in an orthogonal direction; and (ii) the distance from the reference position to the negative phase signal element array in an orthogonal direction. The reference position refers to a predetermined position on the receiving surface.

[0025] According to such an invention, a plurality of element arrays in an element array group are arranged at positions at which the sum of the following two distances is the same for all phases in the at least two phases: (i) the distance from a reference position to the positive phase signal element array in an orthogonal direction; and (ii) the distance from a reference position to the negative phase signal element array in an orthogonal direction. This enables the shift in the phase difference between differential signals caused by a scale arranged in an inclined manner relative to a receiving unit by rotating around an axis (i.e., the rotation axis) orthogonal to the receiving surface to be offset. Therefore, even when the scale is arranged in an inclined manner relative to the receiving unit by rotating around an axis (i.e., the rotation axis) orthogonal to the receiving surface, the encoder can suppress degradation in accuracy.

[0026] In this case, the positive phase signal element array preferably occupies half of the multiple element arrays in the element array group and is arranged on one side of the receiving surface relative to a center line extending along the measuring direction at the center of the multiple element arrays arranged in parallel in orthogonal directions. In addition, the negative phase signal element array preferably occupies half of the multiple element arrays in the element array group and is arranged on the other side of the receiving surface relative to a center line extending along the measuring direction at the center of the multiple element arrays arranged in parallel in orthogonal directions.

[0027] According to this configuration, the positive phase signal element array is arranged on one side of the receiving surface relative to the center line at the center of the element array arranged in parallel in the orthogonal direction, and the negative phase signal element array is arranged on the other side of the receiving surface relative to the center line at the center of the element array arranged in parallel in the orthogonal direction. This enables the design to be simplified and the reduction in the amplitude of the differential signal to be suppressed.

[0028] In this case, the element array group preferably includes: a first element array group; and a second element array group. The second element array group is adjacent to the first element array group in an orthogonal direction in the receiving surface and is arranged in parallel, and the second element array group includes a plurality of element arrays arranged differently from the plurality of element arrays in the first element array group. Preferably, the positive phase signal element array in the first element array group occupies half of the plurality of element arrays in the first element array group, is arranged on one side relative to the center line, and is arranged in an order used as a predetermined reference from one end in the orthogonal direction toward the center in the first element array group, wherein the center line extends along the measuring direction at the center of the plurality of element arrays, and the plurality of element arrays are arranged in parallel in the orthogonal direction in the first element array group. Here, the "order used as a predetermined reference" can be defined as, for example, the order of A-phase and then B-phase, if the two phases consist of A-phase and B-phase. Preferably, the negative phase signal element array in the first element array group occupies half of the multiple element arrays in the first element array group, is arranged on the other side relative to the center line, and is arranged in an order used as a predetermined reference from the other end in the orthogonal direction toward the center of the first element array group, wherein the center line extends along the measuring direction at the center of the multiple element arrays, and the multiple element arrays are arranged in parallel in the orthogonal direction in the first element array group. Preferably, the positive phase signal element array in the second element array group occupies half of the multiple element arrays in the second element array group, is arranged on one side relative to the center line, and is arranged in an order opposite to the order used as a predetermined reference (in the above example, in the order of B-phase and then A-phase) from one end in the orthogonal direction toward the center of the second element array group, wherein the center line extends along the measuring direction at the center of the multiple element arrays, and the multiple element arrays are arranged in parallel in the orthogonal direction in the second element array group. Preferably, the negative phase signal element array of the second element array group occupies half of the multiple element arrays in the second element array group, is arranged on the other side relative to the center line, and is arranged in the second element array group from the other end in the orthogonal direction toward the center in an order opposite to the order used as a predetermined reference, wherein the center line extends along the measuring direction at the center of the multiple element arrays, and the multiple element arrays are arranged in parallel in the orthogonal direction in the second element array group.

[0029] According to this configuration, while suppressing the reduction in the amplitude of the differential signal based on the detection signal from the receiving unit, the shift in the phase difference between the differential signals caused by the scale being set in an inclined manner relative to the receiving unit by rotating around an axis (i.e., the rotation axis) orthogonal to the receiving surface can be more effectively offset compared to the case where the first element array group and the second element array group are not set.

[0030] In this case, preferably, a plurality of element array groups are arranged along orthogonal directions in the receiving surface.

[0031] This configuration makes the distribution of the measurement signal emitted onto the receiving surface via the scale uniform.For example, if the encoder is of an optical type and the emitting unit is a light source, the light distribution of the light radiated onto the light receiving surface via the scale can be uniform.

[0032] In this case, the detection head includes: a light source used as an emitting unit, which radiates light used as a measurement signal to the scale; and a light receiving unit used as a receiving unit, the light receiving unit including a light receiving surface used as a receiving surface for receiving light from the light source via the scale. The light receiving unit converts the light received at the light receiving surface into a differential detection signal having at least two different phases, and outputs the detection signal. In response to the relative movement between the scale and the detection head, the detection signal changes corresponding to the scale period. Preferably, the light receiving surface includes: an element array group, which includes a plurality of element arrays arranged in parallel along an orthogonal direction orthogonal to the measuring direction. The plurality of element arrays include at least four element arrays. Each element array includes a plurality of light receiving elements used as receiving elements, and these light receiving elements are arranged along the measuring direction with a period corresponding to the scale period.

[0033] If the encoder is an optical encoder, this configuration makes it possible to suppress degradation of the encoder's accuracy even if the scale is set in an inclined manner relative to the receiving unit (light receiving unit) by rotating about an axis (i.e., a rotation axis) orthogonal to the receiving surface (light receiving surface).

[0034] In this case, the encoder preferably includes a plate-like grid plate having a plurality of grids formed along the measuring direction, the period of the grids corresponding to the period of the scale. The grid plate is preferably arranged between the scale and the light receiving unit. The light receiving unit preferably receives light that has passed through the grid plate.

[0035] For example, even if only a light receiving element having a size larger than a desired size can be used, this configuration can generate interference fringes almost similar to those generated by a light receiving element having a desired size by providing a grid plate on the light receiving element. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 is a perspective view showing an encoder according to the first embodiment.

[0037] Figure 2 is a plan view showing a light receiving unit in the above-mentioned encoder.

[0038] Figure 3 is a schematic diagram showing a light receiving unit, a signal input unit, and a calculation device in the above-mentioned encoder.

[0039] Figure 4 is a graph showing changes in the detection signal in the above encoder.

[0040] Figure 5 is a graph showing changes in a differential signal based on two phases in the above encoder.

[0041] Figure 6 is a graph showing a Lissajous signal calculated from a differential signal based on two phases in the above-mentioned encoder.

[0042] Figure 7 is a plan view showing a light receiving unit in an encoder according to a second embodiment.

[0043] Figure 8 is a schematic diagram showing a light receiving unit, a signal input unit, and a calculation device in the above-mentioned encoder.

[0044] Fig. 9 is a graph showing changes in the detection signal in the above encoder.

[0045] Fig.10 is a schematic diagram showing a light receiving unit, a signal input unit, and a calculation device in a conventional encoder.

[0046] Fig.11 : is a top view showing a state in which a scale is disposed at an inclination angle θ=0 with respect to a light receiving unit in a conventional encoder.

[0047] Fig.12 : is a top view showing a state in which a scale is disposed at an inclination angle θ≠0 with respect to a light receiving unit in a conventional encoder.

[0048] Fig.13 is a graph showing changes in a differential signal based on two phases in a conventional encoder.

[0049] Fig.14 is a graph showing a Lissajous signal calculated from a differential signal based on two phases in a conventional encoder. DETAILED DESCRIPTION

[0050] First embodiment

[0051] The following will refer to Figures 1 to 5 A first embodiment of the present invention is described.

[0052] Figure 1 is a perspective view showing an encoder 1 according to the first embodiment.

[0053] like Figure 1As shown, the encoder 1 is an optical linear encoder provided with a plate-like scale 2 formed along the X direction as a measuring direction, and a detection head 3 movably provided along the X direction relative to the scale 2. In the following description and the respective drawings, the measuring direction, i.e., the longitudinal direction of the scale 2 will be referred to as the X direction, the lateral direction of the scale 2 will be referred to as the Y direction, and the height direction orthogonal to the X direction and the Y direction will be referred to as the Z direction.

[0054] The detection head 3 is provided with a transmitting unit 4 that sends a measurement signal to the scale 2 and a receiving unit 5 that converts the received measurement signal into a detection signal and outputs it. In the present embodiment, the light source 4 used as the transmitting unit 4 radiates light used as a measurement signal to the scale 2, and the light receiving unit 5 used as the receiving unit 5 converts the received light into a detection signal and outputs it. The detection head 3 is integrally provided with the light source 4 and the light receiving unit 5, and can be moved forward or backward in the X direction relative to the scale 2. The linear encoder obtains position information from the relative movement amount between the scale 2 and the detection head 3 by moving the detection head 3 along the scale 2.

[0055] The scale 2 is formed in a plate shape from a material such as glass. One side of the scale 2 is provided with scales 20 formed at a predetermined period g along the X direction. The scales 20 are specifically grid-like holes formed in the scale 2. Instead of the grid-like holes, the scales 20 may also be formed by applying a material such as a light-proof film formed in a grid shape to a scale plate, for example.

[0056] The light source 4 radiates parallel light above the scale 2. A light emitting diode (LED) is used for the light source 4. However, the light source 4 is not limited to the LED, and any light source such as a semiconductor laser, a helium-neon laser may be used as long as it can cause interference fringes to be generated in the light receiving unit 5. The optical path of the light radiated from the light source 4 is Figure 1 Indicated by arrows.

[0057] The light receiving unit 5 is arranged in parallel to an XY plane corresponding to a plate plane of the scale 2. The light receiving unit 5 includes a light receiving surface 50 serving as a surface for receiving light from the light source 4 through the scale 2.

[0058] The light receiving unit 5 receives the light that has passed through the scale 2 and detects a detection signal from the interference fringes generated by the light. In the present embodiment, interference fringes are generated at the light receiving surface 50 on the light receiving unit 5 along the Y direction, which is the lateral direction of the scale 2. A photodiode array (PDA) is used for the light receiving unit 5. The PDA is a detector having a characteristic that allows a plurality of interference fringes to be measured simultaneously. However, the light receiving unit 5 is not limited to the PDA, and any detector, such as a charge coupled device (CCD), may be used.

[0059] Figure 2 is a plan view showing the light receiving unit 5 in the encoder 1 .

[0060] The light receiving unit 5 will be described in detail below.

[0061] The light receiving unit 5 responds to the scale 2 (see Figure 1 ) and the relative movement between the detection head 3, the output corresponds to the scale 20 (see Figure 1 ). The detection signal includes a detection signal having two different phases (i.e., A-phase and B-phase). The detection signal of each phase is a differential signal. In the present embodiment, the detection signal includes an A-phase signal as a positive phase signal of the A-phase, an AB-phase signal as a negative phase signal of the A-phase, a B-phase signal as a positive phase signal of the B-phase, and a BB-phase signal as a negative phase signal of the B-phase.

[0062] like Figure 2 As shown, the light receiving surface 50 includes a plurality of element arrays 71-74. Each element array 71-74 is provided with a plurality of light receiving elements 500, which are used as a plurality of receiving elements arranged along the measuring direction (X direction) at a period corresponding to the period of the scale 20. The plurality of element arrays 71-74 are arranged in parallel along a direction (Y direction) orthogonal to the measuring direction.

[0063] The light receiving surface 50 is also provided with an element array group 7 that groups four arrays (i.e., element arrays 71-74) into a single group. The element array group 7 includes at least four element arrays 71-74, and any even number of element arrays 71-74. A plurality of element array groups 7 are arranged in the light receiving surface 50 along the Y direction.

[0064] Figure 3 is a schematic diagram showing the light receiving unit 5 , the signal input units 6 a , 6 b , and the calculation device 8 in the encoder 1 .

[0065] like Figure 3 As shown, the element array group 7 includes a first element array 71, a second element array 72, a third element array 73 and a fourth element array 74, which are arranged in sequence from the +Y side (the top in the paper plane) to the -Y side (the bottom in the paper plane). The plurality of element arrays 71-74 are arranged along the Y direction at a predetermined pitch P. For each of the two phases, the plurality of element arrays 71-74 include a positive phase signal element array (the first element array 71 and the second element array 72) that outputs a positive phase signal and a negative phase signal element array (the third element array 73 and the fourth element array 74) that outputs a negative phase signal.

[0066] The first element array 71 outputs an A-phase signal as a positive phase signal of the A-phase, the second element array 72 outputs a B-phase signal as a positive phase signal of the B-phase, the third element array 73 outputs a BB-phase signal as a negative phase signal of the B-phase, and the fourth element array 74 outputs an AB-phase signal as a negative phase signal of the B-phase. Therefore, the first element array 71 and the second element array 72 correspond to the positive phase signal element array in the present invention, and the third element array 73 and the fourth element array 74 correspond to the negative phase signal element array in the present invention.

[0067] In addition, a plurality of element arrays 71-74 are arranged in a shifted manner along the X direction with a predetermined phase difference. More specifically, when the A-phase signal is taken as a reference, the B-phase signal is arranged to have a phase difference of 90 degrees, the AB-phase signal is arranged to have a phase difference of 180 degrees, and the BB-phase signal is arranged to have a phase difference of 270 degrees. Therefore, the second element array 72 is arranged in a shifted manner along the X direction with a 90-degree phase difference relative to the first element array 71, the third element array 73 is arranged in a shifted manner along the X direction with a 270-degree phase difference relative to the first element array 71, and the fourth element array 74 is arranged in a shifted manner along the X direction with a 180-degree phase difference relative to the first element array 71.

[0068] The first element array 71 and the second element array 72 as the positive phase signal element arrays occupy half (i.e., two arrays) of the plurality of (i.e., four) element arrays 71-74 in the element array group 7. The first element array 71 and the second element array 72 are arranged on one side (i.e., +Y side) of the light receiving surface 50 with respect to the center line extending in the X direction at the center of the element arrays arranged in a parallel manner in the Y direction. The center line is Figure 3 The third element array 73 and the fourth element array 74, which are negative phase signal element arrays, occupy half (i.e., two arrays) of the plurality of (i.e., four) element arrays 71-74 in the element array group 7. The third element array 73 and the fourth element array 74 are arranged on the other side (i.e., -Y side) of the light receiving surface 50 relative to the center line.

[0069] The encoder 1 is further provided with: a first signal input unit 6a and a second signal input unit 6b, into which the detection signal output from the light receiving unit 5 is input as a differential signal; and a calculation device 8, which calculates the scale (see Figure 1 ) and the relative movement between the detection head 3.

[0070] Each of the two signal input units 6a, 6b is provided with a positive phase signal input unit 61a, 61b and a negative phase signal input unit 62a, 62b, and the positive phase signal is input into the positive phase signal input unit 61a, 61b as a detection signal from the light receiving unit 5, and the negative phase signal is input into the negative phase signal input unit 62a, 62b as a detection signal from the light receiving unit 5.

[0071] For the first signal input unit 6a, the A-phase signal is input to the positive phase signal input unit 61a from the first element array 71 of the light receiving unit 5, and the AB-phase signal is input to the negative phase signal input unit 62a from the fourth element array 74. Then, the first signal input unit 6a outputs a differential A-phase signal to the calculation device 8, which is the difference between the A-phase signal and the AB-phase signal (i.e., the A-phase signal minus the AB-phase signal).

[0072] For the second signal input unit 6b, the B-phase signal is input from the second element array 72 of the light receiving unit 5 to the positive phase signal input unit 61b, and the BB-phase signal is input from the third element array 73 to the negative phase signal input unit 62b. Then, the second signal input unit 6b outputs a differential B-phase signal to the calculation device 8, which is the difference between the B-phase signal and the BB-phase signal (i.e., the B-phase signal minus the BB-phase signal). In the drawings described below, with respect to the input from the plurality of element arrays 71-74 to the two signal input units 6a, 6b, the positive phase signal is represented by a solid line, and the negative phase signal is represented by a dotted line.

[0073] Now, as described above, in the encoder 1, the scale 2 is preferably disposed at an inclination angle θ=0 relative to the light receiving unit 5 (see Fig.11 ). This is because, when the scale 2 is set at an inclination angle θ=0, ideal interference fringes can be generated on the light receiving surface 50 when measuring, and a stable measurement result can be obtained. However, even if the scale 2 is set at an inclination angle θ≠0 relative to the light receiving unit 5 (see Fig.12 ), the encoder 1 can also be made less affected by this situation. Hereinafter, such a principle will be described, by which the encoder 1 can be made less affected by this situation by the configuration of the light receiving unit 5 even if the scale 2 is set at an inclination angle θ≠0 relative to the light receiving unit 5.

[0074] The multiple element arrays 71-74 in the element array group 7 are arranged at some positions at which, for all phases, the sum of the following two distances is the same: (i) the distance from the reference position to the positive phase signal element array (the first element array 71 or the second element array 72) in the +Y direction; and (ii) the distance from the reference position to the negative phase signal element array (the third element array 73 or the fourth element array 74) in the -Y direction.

[0075] Here, the reference position refers to a predetermined position on the light receiving surface 50 , and in the present embodiment, a description will be provided by taking the X axis in the drawing as the reference position.

[0076] The first element array 71 is located at a distance of +3P / 2 from the reference position in the +Y direction, the second element array 72 is located at a distance of +P / 2 from the reference position in the +Y direction, the third element array 73 is located at a distance of -P / 2 from the reference position in the -Y direction, and the fourth element array 74 is located at a distance of -3P / 2 from the reference position in the -Y direction.

[0077] Similarly, in Fig.10 In the conventional encoder 100 shown, the first element array 710 is located at a distance of +3P / 2 from a reference position in the +Y direction, the second element array 720 is located at a distance of +P / 2 from a reference position in the +Y direction, the third element array 730 is located at a distance of -P / 2 from a reference position in the -Y direction, and the fourth element array 740 is located at a distance of -3P / 2 from a reference position in the -Y direction.

[0078] The following equation (1) shows the sum of the following distances: (i) the distance between the first element array 710 outputting the A-phase signal and the reference position; and (ii) the distance between the third element array 730 outputting the AB-phase signal and the reference position. The A-phase signal and the AB-phase signal serve as inputs for generating a differential A-phase signal. The following equation (2) shows the sum of the following distances: (i) the distance between the second element array 720 outputting the B-phase signal and the reference position; and (ii) the distance between the fourth element array 740 outputting the BB-phase signal and the reference position. The B-phase signal and the BB-phase signal serve as inputs for generating a differential B-phase signal.

[0079] (+3P / 2) + (-P / 2) = +P (1)

[0080] (+P / 2) + (-3P / 2) = -P (2)

[0081] As shown in equations (1) and (2), in the conventional encoder 100, the element array is arranged at the following positions, where, for the differential A-phase signal and the differential B-phase signal, the sum of the following distances is different: (i) the distance from the reference position to the positive phase signal element array (the first element array 710 or the second element array 720) in the +Y direction, and (ii) the distance from the reference position to the negative phase signal element array (the third element array 730 or the fourth element array 740) in the -Y direction.

[0082] In contrast, Figure 3 In the encoder 1 shown, the following equation (3) shows the sum of the following distances: (i) the distance between the first element array 71 outputting the A-phase signal and the reference position; and (ii) the distance between the fourth element array 74 outputting the AB-phase signal and the reference position. The A-phase signal and the AB-phase signal serve as inputs for generating a differential A-phase signal. The following equation (4) shows the sum of the following distances: (i) the distance between the second element array 72 outputting the B-phase signal and the reference position; and (ii) the distance between the third element array 73 outputting the BB-phase signal and the reference position. The B-phase signal and the BB-phase signal serve as inputs for generating a differential B-phase signal.

[0083] (+3P / 2) + (-3P / 2) = 0 (3)

[0084] (+P / 2) + (-P / 2) = 0 (4)

[0085] As shown in equations (3) and (4), in encoder 1, the element arrays are arranged at positions where, for the differential A-phase signal and the differential B-phase signal, the sum of the following distances is the same: (i) the distance from the reference position to the positive phase signal element array (the first element array 71 or the second element array 72) in the +Y direction, and (ii) the distance from the reference position to the negative phase signal element array (the third element array 73 or the fourth element array 74) in the -Y direction. If scale 2 (see Figure 1 ) is arranged in an inclined manner with an inclination angle θ≠0 relative to the light receiving unit 5 (especially relative to the direction (Y direction) orthogonal to the measuring direction (X direction)) by rotating around an axis (i.e., the rotation axis) orthogonal to the light receiving surface 50, then this arrangement of multiple element arrays 71-74 allows the following effects to be obtained.

[0086] If in Fig.12In the conventional encoder 100 shown, the scale 2 is set in an inclined manner at an inclination angle θ, and interference fringes including a phase difference caused by the inclination angle θ of the scale are generated, as shown in equation (5) about the differential A-phase signal and equation (6) about the differential B-phase signal. When the light receiving unit 9 receives these interference fringes, the phase of the detection signal input to the signal input unit 600a, 600b from the multiple element arrays 710-740 arranged in parallel in the Y direction is also shifted. The phase shift amount of the detection signal detected at the light receiving element in each element array 710-740 varies according to their position difference in the Y direction. Therefore, the two differential signals are also shifted, and the calculation result (relative movement amount) is affected.

[0087] (-3P / 2 × θ) + (P / 2 × θ) = -P·θ (5)

[0088] (-P / 2 × θ) + (3P / 2 × θ) = +P·θ (6)

[0089] In contrast, Figure 3 As shown, even if the scale 2 (see Figure 1 ) is set in an inclined manner at an inclination angle θ in encoder 1, and the shift amounts of the two differential signals generated by the inclination angle θ of scale 2 are offset, as shown in equation (7) about the differential A-phase signal and equation (8) about the differential B-phase signal.

[0090] (-3P / 2 × θ) + (3P / 2 × θ) = 0 (7)

[0091] (-P / 2 × θ) + (P / 2 × θ) = 0 (8)

[0092] Figure 4 is a graph showing changes in the detection signal in the encoder 1. More specifically, Figure 4 In the figure, the vertical axis represents the output voltage and the horizontal axis represents the displacement. Figure 5 is a graph showing changes in a differential signal based on two phases in the encoder 1. More specifically, Figure 5 In FIG. 1 , the vertical axis represents the output voltage of the two signal input units 6 a and 6 b , and the horizontal axis represents the relative displacement of the detection head 3 with respect to the scale 2 . Figure 6 is a graph showing a Lissajous signal calculated from a differential signal of two phases in the encoder 1. More specifically, Figure 6 In , the vertical axis represents the differential B-phase signal, and the horizontal axis represents the differential A-phase signal. Figure 4 , 5 and 6, when scale 2 (see Figure 1 ) is represented by a solid line when the scale 2 is set at an inclination angle θ≠0 relative to the light receiving unit 5, and a dotted line when the scale 2 is set at an inclination angle θ=0 relative to the light receiving unit 5.

[0093] Hereinafter, changes in the detection signal output from the light receiving unit 5 to the signal input units 6a, 6b and changes in the differential A-phase signal and the differential B-phase signal output from the signal input units 6a, 6b to the calculation device 8 will be described.

[0094] like Figure 4 As shown, if ruler 2 (see Figure 1 ) is set at an inclination angle θ≠0 relative to the light receiving unit 5, then compared with the case where the scale 2 is set at an inclination angle θ=0, the phase shift (phase shift) of the A-phase signal input from the first element array 71 is -3P / 2×θ. The phase shift of the B-phase signal input from the second element array 72 is -P / 2×θ. The phase shift of the BB-phase signal input from the third element array 73 is +P / 2×θ. The phase shift of the AB-phase signal input from the fourth element array 74 is +3P / 2×θ.

[0095] In this case, for the signal input unit 6a (see Figure 3 ), the A-phase signal with a phase shift of -3P / 2×θ is input from the first element array 71 to the positive phase signal input unit 61a (see Figure 3 ), and the AB-phase signal having a phase shift of +3P / 2×θ is input to the negative phase signal input unit 62a from the fourth element array 74. Then, the calculation of equation (7) is performed in the process of conversion into a differential A-phase signal, and the phase shift between the A-phase signal and the AB-phase signal is canceled, so that the phase shift in the differential A-phase signal becomes zero.

[0096] In addition, for the signal input unit 6b (see Figure 3 ), the B-phase signal with a phase shift of -P / 2×θ is input from the second element array 72 to the positive phase signal input unit 61b (see Figure 3 ), and the B-phase signal having a phase shift of +P / 2×θ is input to the negative phase signal input unit 62b from the third element array 73. Then, the calculation of equation (8) is performed in the process of conversion into a differential B-phase signal, and the phase shift between the B-phase signal and the BB-phase signal is canceled, so that the phase shift in the differential B-phase signal becomes zero.

[0097] The phase shift of the differential A-phase signal and the phase shift of the differential B-phase signal both become zero and are therefore identical. Therefore, between the case where the scale 2 is at an inclination angle θ=0 and the case where the scale 2 is at an inclination angle θ≠0, the phase difference between the differential A-phase signal and the differential B-phase signal remains unchanged, and the interference fringes generated in the light receiving surface 50 are also similar to the interference fringes generated when the scale 2 is at an inclination angle θ=0.

[0098] Therefore, if Figure 5 As shown, although with scale 2 (see Figure 1 ) is at an inclination angle θ = 0, compared to the case where the two signal input units 6a, 6b (see Figure 3 ) output voltages of the differential A-phase signal and the differential B-phase signal outputted by the calculation device 8 are reduced, but the differential A-phase signal and the differential B-phase signal are outputted to the calculation device 8 while maintaining the phase difference when the tilt angle θ=0 (i.e., a phase difference of 90 degrees).

[0099] In addition, if Figure 6 As shown in FIG. 1 , although the Lissajous signal calculated at the calculation device 8 based on the differential A-phase signal and the differential B-phase signal output from the two signal input units 6a, 6b becomes an elliptical Lissajous signal whose amplitude is reduced and whose flattening is higher than that in the case where the scale 2 is set at the inclination angle θ=0, Fig.14 Compared with the Lissajous signal in the conventional encoder 100 shown, a Lissajous signal close to a perfect circle is obtained.

[0100] Therefore, even if the scale 2 is disposed in an inclined manner relative to the light receiving unit 5 by rotating about an axis (ie, a rotation axis) orthogonal to the light receiving surface 50 , the encoder 1 can suppress degradation in accuracy.

[0101] According to the first embodiment, the following effects can be achieved:

[0102] (1) The plurality of element arrays 71-74 in the element array group 7 are arranged at positions in which, for the differential A-phase signal and the differential B-phase signal, the sum of the following distances is the same: (i) the distance from the reference position to the positive phase signal element array (the first element array 71 or the second element array 72) in the orthogonal direction (+Y direction), and (ii) the distance from the reference position to the negative phase signal element array (the third element array 73 or the fourth element array 74) in the orthogonal direction (-Y direction). This enables the shift in the phase difference between the differential signals caused by the scale 2 being set in an inclined manner relative to the light receiving unit 5 by rotating around an axis (i.e., the rotation axis) orthogonal to the light receiving surface 50 to be offset. Therefore, even if the scale 2 is set in an inclined manner relative to the light receiving unit 5 by rotating around an axis (i.e., the rotation axis) orthogonal to the light receiving surface 50, the encoder 1 can suppress the degradation of accuracy;

[0103] (2) The positive phase signal element array (the first element array 71 and the second element array 72) is arranged on the +Y side in the light receiving surface 50 with respect to the center line at the center of the element arrays arranged in a parallel manner in the Y direction, and the negative phase signal element array (the third element array 73 and the fourth element array 74) is arranged on the -Y side in the light receiving surface 50 with respect to the center line. This enables the design to be simplified and enables reduction in the amplitude of the differential signal to be suppressed; and

[0104] (3) The plurality of element array groups 7 are arranged in the light receiving surface 50 along the Y direction. This makes the light distribution of the light radiated onto the light receiving surface 50 via the scale 2 uniform.

[0105] Second embodiment

[0106] The following will refer to Figures 7 to 9 A second embodiment of the present invention is described. In the following description, the same reference numerals will be given to parts that have already been described, and their description will be omitted.

[0107] Figure 7 : is a plan view showing a light receiving unit 5A in an encoder 1A according to the second embodiment.

[0108] In the above-mentioned first embodiment, in the element array group 7, the first element array 71 inputs the A-phase signal into the positive phase signal input unit 61, the second element array 72 inputs the B-phase signal into the positive phase signal input unit 61, the third element array 73 inputs the BB-phase signal into the negative phase signal input unit 62, and the fourth element array 74 inputs the AB-phase signal into the negative phase signal input unit 62.

[0109] like Figure 7As shown, the difference between the second embodiment and the above-mentioned first embodiment is that the light receiving surface 50A is provided with a first element array group 7 similar to the first element array group in the first embodiment, and a second element array group 7A is adjacent to the first element array group 7 in the Y direction which is an orthogonal direction in the light receiving surface 50A and is arranged in a parallel manner.

[0110] The light receiving unit 5A will be described in detail below.

[0111] The element array groups include a first element array group 7 and a second element array group 7A which is adjacent to the first element array group 7 in the Y direction (orthogonal direction) in the light receiving surface 50 and is disposed in a parallel manner.

[0112] The second element array group 7A includes a plurality of element arrays 75-78 arranged in a manner different from the plurality of element arrays 71-74 in the first element array group 7, i.e., at least four element arrays and an even number of element arrays. The plurality of element arrays 75-78 are arranged in parallel along an orthogonal direction (Y direction) orthogonal to the measuring direction.

[0113] Now, in the above-described first embodiment, the plurality of element array groups 7 are arranged in the light receiving surface 50 along the Y direction.

[0114] The second embodiment is different from the above-described first embodiment in that the first element array group 7 and the second element array group 7A are grouped into one group, and a plurality of element array groups 7, 7A are arranged in the light receiving surface 50A along the Y direction. More specifically, the first element array 7 and the second element array 7A are arranged in the light receiving surface 50A along the Y direction in an alternating and repeated manner.

[0115] Figure 8 is a schematic diagram showing the light receiving unit 5A, the signal input units 6 a , 6 b , and the calculation device 8 in the encoder 1A.

[0116] like Figure 8 As shown, the second element array group 7A includes a fifth element array 75, a sixth element array 76, a seventh element array 77 and an eighth element array 78, which are arranged in the above order from the +Y side (top in the paper plane) to the -Y side (bottom in the paper plane). A plurality of element arrays 75-78 are arranged at a predetermined pitch P along the Y direction.

[0117] For each of the two phases, the multiple element arrays 75-78 include a positive phase signal element array (the fifth element array 75 and the sixth element array 76) that outputs a positive phase signal and a negative phase signal element array (the seventh element array 77 and the eighth element array 78) that outputs a negative phase signal.

[0118] In addition, a plurality of element arrays 75-78 are arranged in a shifted manner along the X direction with a predetermined phase difference. More specifically, the sixth element array 76 is arranged in a shifted manner along the X direction with a 90-degree phase difference relative to the fifth element array 75, the seventh element array 77 is arranged in a shifted manner along the X direction with a 270-degree phase difference relative to the fifth element array 75, and the eighth element array 78 is arranged in a shifted manner along the X direction with a 180-degree phase difference relative to the fifth element array 75.

[0119] The fifth element array 75 outputs a B-phase signal as a positive phase signal of the B-phase, the sixth element array 76 outputs an A-phase signal as a positive phase signal of the A-phase, the seventh element array 77 outputs an AB-phase signal as a negative phase signal of the A-phase, and the eighth element array 78 outputs a BB-phase signal as a negative phase signal of the B-phase. Therefore, the fifth element array 75 and the sixth element array 76 correspond to the positive phase signal element array in the present invention, and the seventh element array 77 and the eighth element array 78 correspond to the negative phase signal element array in the present invention.

[0120] In the first element array group 7, the positive phase signal element array (the first element array 71 and the second element array 72) occupy half (i.e., two arrays) of the multiple (i.e., four) element arrays 71-74 in the first element array group 7. The positive phase signal element array (the first element array 71 and the second element array 72) are arranged on the +Y side relative to the center line at the center of the element array in the first element array group 7 arranged in a parallel manner in the Y direction. In addition, the positive phase signal element array (the first element array 71 and the second element array 72) are arranged in an order serving as a predetermined reference (predetermined reference) from one end in the Y direction (the top of the first element array group 7 in the paper plane) toward the center in the first element array group 7 (the downward direction in the paper plane). In the present embodiment, the "order as a predetermined reference for the positive phase signal element array" is defined as the order of A-phase and B-phase.

[0121] In addition, in the second element array group 7A, the positive phase signal element array (the fifth element array 75 and the sixth element array 76) occupies half (i.e., two arrays) of the multiple (i.e., four) element arrays 75-78 in the second element array group 7A. The positive phase signal element array (the fifth element array 75 and the sixth element array 76) is arranged on the +Y side relative to the center line at the center of the element array in the second element array group 7A arranged in a parallel manner in the Y direction. In addition, the positive phase signal element array (the fifth element array 75 and the sixth element array 76) is arranged from one end in the Y direction (the top of the second element array group 7A in the paper plane) toward the center in the second element array group 7A (the downward direction in the paper plane) in the opposite order to the order used as the predetermined reference.

[0122] More specifically, since "the order as a predetermined reference for the positive phase signal element array" is defined as the order of A-phase and then B-phase, "the order opposite to the order of the predetermined reference for the positive phase signal element array" is defined as the order of B-phase and then A-phase. Therefore, if the positive phase signal element arrays in the first element array group 7 are arranged from one end in the Y direction (the top of the first element array group 7 in the paper plane) toward the center (the downward direction in the paper plane) in the order of a first element array 71 that outputs an A-phase signal and then a second element array 72 that outputs a B-phase signal, the positive phase signal element arrays in the second element array group 7A are arranged from one end in the Y direction (the top of the second element array group 7A in the paper plane) toward the center (the downward direction in the paper plane) in the order of a fifth element array 75 that outputs a B-phase signal and then a sixth element array 76 that outputs an A-phase signal, and the positive phase signal element arrays are arranged so that the two phases are arranged in an order opposite to each other.

[0123] In the first element array group 7, the negative phase signal element array (the third element array 73 and the fourth element array 74) occupies half (i.e., two arrays) of the multiple (i.e., four) element arrays 71-74 in the first element array group 7. The negative phase signal element array (the third element array 73 and the fourth element array 74) is arranged on the -Y side relative to the center line at the center of the element array in the first element array group 7 arranged in a parallel manner in the Y direction. In addition, the negative phase signal element array (the third element array 73 and the fourth element array 74) is arranged in an order serving as a predetermined reference from the other end in the Y direction (the bottom of the first element array group 7 in the paper plane) toward the center in the first element array group 7 (the upward direction in the paper plane). In the present embodiment, the "order serving as a predetermined reference for the negative phase signal element array" is defined as the order of AB-phase and then BB-phase.

[0124] In addition, in the second element array group 7A, the negative phase signal element array (the seventh element array 77 and the eighth element array 78) occupies half (i.e., two arrays) of the multiple (i.e., four) element arrays 75-78 in the second element array group 7A. The negative phase signal element array (the seventh element array 77 and the eighth element array 78) is arranged on the -Y side relative to the center line at the center of the element array in the second element array group 7A arranged in parallel in the Y direction. In addition, the negative phase signal element array (the seventh element array 77 and the eighth element array 78) is arranged from the other end in the Y direction (the bottom of the second element array group 7A in the paper plane) toward the center in the second element array group 7A (the upward direction in the paper plane) in an order opposite to the order used as a predetermined reference.

[0125] More specifically, since "the order as a predetermined reference for the negative phase signal element array" is defined as the order of AB-phase and then BB-phase, "the reverse order of the order as a predetermined reference for the negative phase signal element array" is defined as the order of BB-phase and then AB-phase. Therefore, if the negative phase signal element arrays in the first element array group 7 are arranged from the other end in the Y direction (the bottom of the first element array group 7 in the paper plane) toward the center (the upward direction in the paper plane) in the order of the fourth element array 74 that outputs the AB-phase signal and then the third element array 73 that outputs the BB-phase signal, the negative phase signal element arrays in the second element array group 7A are arranged from the other end in the Y direction (the bottom of the second element array group 7A in the paper plane) toward the center (the upward direction in the paper plane) in the order of the eighth element array 78 that outputs the BB-phase signal and then the seventh element array 77 that outputs the AB-phase signal, and the negative phase signal element arrays are arranged so that the two phases are arranged in an order opposite to each other.

[0126] That is, in the first element array group 7, the plurality of element arrays 71-74 are arranged from the +Y side to the -Y side so that their output detection signals are in the order used as a predetermined reference, that is, in the order of A-phase signal, B-phase signal, BB-phase signal and AB-phase signal. In the second element array group 7A, the plurality of element arrays 75-78 are arranged from the +Y side to the -Y side so that the order of their output detection signals is opposite to the order used as a predetermined reference, that is, in the order of B-phase signal, A-phase signal, AB-phase signal and BB-phase signal.

[0127] With regard to the two signal input units 6a, 6b, for the first signal input unit 6a, the A-phase signal is input to the positive phase signal input unit 61a from the first element array 71 and the sixth element array 76 in the light receiving unit 5, and the AB-phase signal is input to the negative phase signal input unit 62a from the fourth element array 74 and the seventh element array 77. Then, the first signal input unit 6a outputs a differential A-phase signal to the calculation device 8, which is the difference between the A-phase signal and the AB-phase signal (i.e., the A-phase signal minus the AB-phase signal).

[0128] For the second signal input unit 6b, the B-phase signal is input to the positive phase signal input unit 61b from the second element array 72 and the fifth element array 75 in the light receiving unit 5, and the BB-phase signal is input to the negative phase signal input unit 62b from the third element array 73 and the eighth element array 78. Then, the second signal input unit 6b outputs a differential B-phase signal to the calculation device 8, which is the difference between the B-phase signal and the BB-phase signal (i.e., the B-phase signal minus the BB-phase signal).

[0129] The multiple element arrays 71-78 in the first element array group 7 and the second element array 7A are arranged in such positions that, for all phases of two phases (i.e., A-phase and B-phase), the sum of the following distances is the same: (i) the distance in the Y direction from the reference position to the positive phase signal element array (the first element array 71, the second element array 72, the fifth element array 75 or the sixth element array 76); and (ii) the distance in the Y direction from the reference position to the negative phase signal element array (the third element array 73, the fourth element array 74, the seventh element array 77 or the eighth element array 78).

[0130] The first element array 71 is located at a distance of +7P / 2 from the reference position in the +Y direction, the second element array 72 is located at a distance of +5P / 2 from the reference position in the +Y direction, the third element array 73 is located at a distance of +3P / 2 from the reference position in the +Y direction, the fourth element array 74 is located at a distance of +P / 2 from the reference position in the +Y direction, the fifth element array 75 is located at a distance of -P / 2 from the reference position in the -Y direction, the sixth element array 76 is located at a distance of -3P / 2 from the reference position in the -Y direction, the seventh element array 77 is located at a distance of -5P / 2 from the reference position in the -Y direction, and the eighth element array 78 is located at a distance of -7P / 2 from the reference position in the -Y direction.

[0131] In the encoder 1A, the sum of the following distances is represented by the following equation (9): (i) the distance between the first element array 71 outputting the A-phase signal and the reference position; (ii) the distance between the sixth element array 76 outputting the A-phase signal and the reference position; (iii) the distance between the fourth element array 74 outputting the AB-phase signal and the reference position; and (iv) the distance between the seventh element array 77 outputting the AB-phase signal and the reference position. The A-phase signal and the AB-phase signal serve as inputs for generating a differential A-phase signal. The sum of the following distances is represented by the following equation (10): (i) the distance between the second element array 72 outputting the B-phase signal and the reference position; (ii) the distance between the fifth element array 75 outputting the B-phase signal and the reference position; (iii) the distance between the third element array 73 outputting the BB-phase signal and the reference position; and (iv) the distance between the eighth element array 78 outputting the BB-phase signal and the reference position. The B-phase signal and the BB-phase signal serve as inputs for generating a differential B-phase signal.

[0132] (+7P / 2) + (-3P / 2) + (+P / 2) + (-5P / 2) = 0 (9)

[0133] (+5P / 2) + (-P / 2) + (+3P / 2) + (-7P / 2) = 0 (10)

[0134] As shown in equations (9) and (10), in encoder 1A, the element arrays are arranged in positions where, for the differential A-phase signal and the differential B-phase signal, the sum of the following distances is the same: (i) the distance in the Y direction from the reference position to the positive phase signal element array (the first element array 71, the second element array 72, the fifth element array 75, or the sixth element array 76); and (ii) the distance in the Y direction from the reference position to the negative phase signal element array (the third element array 73, the fourth element array 74, the seventh element array 77, or the eighth element array 78). If scale 2 (see Figure 1 ) is arranged in an inclined manner with an inclination angle θ≠0 relative to the light receiving unit 5A (especially relative to the direction (Y direction) orthogonal to the measuring direction (X direction)) by rotating around an axis (i.e., the rotation axis) orthogonal to the light receiving surface 50A. Such an arrangement of the multiple element arrays 71-78 allows the following effects to be obtained.

[0135] In the encoder 1A, even if the scale 2 (see Figure 1) is set in an inclined manner at an inclination angle θ, and the shift amounts of the two differential signals generated by the inclination angle θ of the scale 2 are offset, as shown in equation (11) regarding the differential A-phase signal and equation (12) regarding the differential B-phase signal.

[0136] (-7P / 2 × θ) + (-P / 2 × θ) + (3P / 2 × θ) + (5P / 2 × θ) = 0 (11)

[0137] (-5P / 2 × θ) + (-3P / 2 × θ) + (P / 2 × θ) + (7P / 2 × θ) = 0 (12)

[0138] Fig. 9 is a graph showing changes in the detection signal in the encoder 1A. More specifically, Fig. 9 In the figure, the vertical axis represents the output voltage and the horizontal axis represents the displacement. Fig. 9 In the case of scale 2 (see Figure 1 ) is represented by a solid line when the scale 2 is set at an inclination angle θ≠0 relative to the light receiving unit 5A, and a dotted line when the scale 2 is set at an inclination angle θ=0 relative to the light receiving unit 5A.

[0139] Hereinafter, changes in the detection signal output from the light receiving unit 5A to the signal input units 6a, 6b and changes in the differential A-phase signal and the differential B-phase signal output from the signal input units 6a, 6b to the calculation device 8 will be described.

[0140] like Fig. 9 As shown, if ruler 2 (see Figure 1 ) is set at an inclination angle θ≠0 relative to the light receiving unit 5A, then compared with the case where the scale 2 is set at an inclination angle θ=0, the phase shift of the A-phase signal input from the first element array 71 is -7P / 2×θ. The phase shift of the B-phase signal input from the second element array 72 is -5P / 2×θ. The phase shift of the BB-phase signal input from the third element array 73 is -3P / 2×θ. The phase shift of the AB-phase signal input from the fourth element array 74 is -P / 2×θ. The phase shift of the B-phase signal input from the fifth element array 75 is +P / 2×θ. The phase shift of the A-phase signal input from the sixth element array 76 is +3P / 2×θ. The phase shift of the AB-phase signal input from the seventh element array 77 is +5P / 2×θ. The phase shift of the BB-phase signal input from the eighth element array 78 is +7P / 2×θ.

[0141] In this case, for the signal input unit 6a (see Figure 8), the A-phase signal with a phase shift of -7P / 2×θ is input from the first element array 71 to the positive phase signal input unit 61a (see Figure 8 ), and the A-phase signal with a +3P / 2×θ phase shift is input to the positive phase signal input unit 61a from the sixth element array 76, and the AB-phase signal with a -P / 2×θ phase shift is input to the negative phase signal input unit 62a from the fourth element array 74, and the AB-phase signal with a +5P / 2×θ phase shift is input to the negative phase signal input unit 62a from the seventh element array 77. Then, the calculation of equation (11) is performed in the process of conversion into a differential A-phase signal, and the phase shift between the A-phase signal and the AB-phase signal is canceled, so that the phase shift in the differential A-phase signal becomes zero.

[0142] In addition, for the signal input unit 6b (see Figure 8 ), the B-phase signal with a phase shift of -5P / 2×θ is input from the second element array 72 to the positive phase signal input unit 61b (see Figure 8 ), and a B-phase signal with a +P / 2×θ phase shift is input from the fifth element array 75 to the positive phase signal input unit 61b, and a BB-phase signal with a -3P / 2×θ phase shift is input from the third element array 73 to the negative phase signal input unit 62b, and a BB-phase signal with a +7P / 2×θ phase shift is input from the eighth element array 78 to the negative phase signal input unit 62b. Then, the calculation of equation (12) is performed in the process of conversion into a differential B-phase signal, and the phase shift between the B-phase signal and the BB-phase signal is canceled, so that the phase shift in the differential B-phase signal becomes zero.

[0143] The phase shift of the differential A-phase signal and the phase shift of the differential B-phase signal both become zero and are therefore identical. Therefore, between the case where the scale 2 is at an inclination angle θ=0 and the case where the scale 2 is at an inclination angle θ≠0, the phase difference between the differential A-phase signal and the differential B-phase signal remains unchanged, and the interference fringes generated in the light receiving surface 50A are also similar to the interference fringes generated when the scale 2 is at an inclination angle θ=0.

[0144] Therefore, if Figure 5 As shown, although with scale 2 (see Figure 1 ) is at an inclination angle θ = 0, compared to the case where the two signal input units 6a, 6b (see Figure 3 ) output voltages of the differential A-phase signal and the differential B-phase signal outputted by the calculation device 8 are reduced, but the differential A-phase signal and the differential B-phase signal are outputted to the calculation device 8 while maintaining the phase difference when the tilt angle θ=0 (i.e., a phase difference of 90 degrees).

[0145] In addition, if Figure 6 As shown in FIG. 1 , although the Lissajous signal calculated at the calculation device 8 based on the differential A-phase signal and the differential B-phase signal output from the two signal input units 6a, 6b becomes an elliptical Lissajous signal whose amplitude is reduced and whose flattening is higher than that in the case where the scale 2 is set at the inclination angle θ=0, Fig.14 A Lissajous signal close to a perfect circle is obtained compared with the Lissajous signal in the conventional encoder 100 shown. It should be noted that the Lissajous signal in the encoder 1A of the second embodiment is closer to a perfect circle than the Lissajous signal in the encoder 1 of the first embodiment.

[0146] Therefore, even if the scale 2 is disposed in an inclined manner relative to the light receiving unit 5A by rotating about an axis (ie, a rotation axis) orthogonal to the light receiving surface 50A, the encoder 1A can suppress degradation in accuracy.

[0147] In the second embodiment, in addition to the effects (1) to (3) of the first embodiment described above, the following effects can be achieved:

[0148] (4) While suppressing the reduction in the amplitude of the differential signal based on the detection signal from the light receiving unit 5A, the shift in the phase difference between the differential signals caused by the scale 2 being set in an inclined manner relative to the light receiving unit 5A by rotating around an axis (i.e., the rotation axis) orthogonal to the light receiving surface 50A can be more effectively offset compared to the case where the first element array group 7 and the second element array group 7A are not set.

[0149] Variations of the Embodiments

[0150] It should be noted that the present invention is not limited to the above-described respective embodiments, and changes, modifications, etc. are included in the present invention to the extent that these changes, modifications, etc. can achieve the objects of the present invention.

[0151] For example, in the above-mentioned respective embodiments, the case where the present invention is applied to the encoders 1, 1A which are linear encoders is described; however, any encoder may be used without particular regard to the type of detector, the detection method, etc.

[0152] More specifically, in each of the above-mentioned embodiments, an optical encoder 1, 1A is used, wherein the detection head 3, 3A is provided with: a light source 4 used as a transmitting unit, which radiates light used as a measurement signal to the scale 2; and a light receiving unit 5, 5A used as a receiving unit, which includes a light receiving surface 50, 50A used as a receiving surface, which receives light from the light source 4 via the scale 2, and the light receiving surface 50, 50A is provided with an element array including a plurality of light receiving elements 500 used as receiving elements. Instead of the optical type, the encoder may be other detection types, such as a capacitive type or an inductive type. In this case, the transmitting unit that transmits the measurement signal, the receiving unit including the receiving surface, the plurality of receiving elements, etc. may be any unit / element having similar functions in a capacitive type, an inductive type, etc. encoder. For example, in an inductive type encoder, the transmitting unit may transmit a magnetic force corresponding to the measurement signal for exciting a coil corresponding to the scale, and the receiving unit may include a plurality of receiving coils corresponding to the plurality of receiving elements, and receive changes in the magnetic flux of the coil.

[0153] In the above-described respective embodiments, a component such as an optical member is not provided between the scale and the light receiving unit; however, a member configured as described below may be provided.

[0154] That is, the encoder is preferably provided with a plate-like grid plate having a plurality of grids formed along the measuring direction, the period of the grids corresponding to the period of the scale. The grid plate is preferably provided between the scale and the light receiving unit. The light receiving unit preferably receives light that has passed through the grid plate.

[0155] For example, even if only a light receiving element having a size larger than a desired size can be used, the above configuration can produce interference fringes almost similar to those produced by a light receiving element having a desired size by providing a grid plate above the light receiving element.

[0156] In the above-mentioned second embodiment, the first element array group 7 and the second element array group 7A are grouped into one group, and the first element array 7 and the second element array 7A are arranged in the light receiving surface 50A in an alternating and repeated manner along the Y direction. However, it is not necessary to arrange multiple groups of element array groups 7, 7A along the Y direction in the light receiving surface 50A. For example, instead of arranging the first element array group 7 and the second element array group 7A in an alternating and repeated manner, multiple element array groups may be arranged in any combination along the Y direction in the light receiving surface 50A. In short, it is sufficient if multiple element array groups are arranged along orthogonal directions in the receiving surface.

[0157] In the above-mentioned first embodiment, the first element array 71 outputs the A-phase signal as a positive phase signal, the second element array 72 outputs the B-phase signal as a positive phase signal, the third element array 73 outputs the BB-phase signal as a negative phase signal, and the fourth element array 74 outputs the AB-phase signal as a negative phase signal. However, the first element array may output the A-phase signal as a positive phase signal, the second element array may output the BB-phase signal as a negative phase signal, the third element array may output the B-phase signal as a positive phase signal, and the fourth element array may output the AB-phase signal as a negative phase signal.

[0158] Furthermore, in the above-mentioned second embodiment, in the first element array group 7, the first element array 71 outputs an A-phase signal as a positive phase signal, the second element array 72 outputs a B-phase signal as a positive phase signal, the third element array 73 outputs a BB-phase signal as a negative phase signal, and the fourth element array 74 outputs an AB-phase signal as a negative phase signal. In addition, in the second element array group 7A, the fifth element array 75 outputs a B-phase signal as a positive phase signal, the sixth element array 76 outputs an A-phase signal as a positive phase signal, the seventh element array 77 outputs an AB-phase signal as a negative phase signal, and the eighth element array 78 outputs a BB-phase signal as a negative phase signal.

[0159] However, in the second element array group, the plurality of element arrays may output detection signals in any other combination. In short, it is sufficient if at least two signal input units receive detection signals as input from element arrays arranged at positions where the sum of the following phase differences is the same at each signal input unit: (i) the phase difference of the element array that inputs the positive phase signal to the positive phase signal input unit; and (ii) the phase difference of the element array that inputs the negative phase signal to the negative phase signal input unit.

[0160] In the above-mentioned embodiments, the X-axis is defined as the reference position; however, the reference position may be any position as long as it is a predetermined position on the light receiving surface. For example, in the case where the reference position is defined as the position for Figure 3 In the case of the first element array 71 of the plurality of element arrays 71-74 of the first embodiment shown:

[0161] The second element array 72 will be located at a distance of -P from the reference position (i.e., the first element array 71) in the -Y direction, the third element array 73 will be located at a distance of -2P from the reference position in the -Y direction, and the fourth element array 74 will be located at a distance of -3P from the reference position in the -Y direction.

[0162] The sum of the following distances is expressed as the following equation (13): (i) the distance between the first element array 71 that outputs the A-phase signal and the reference position; and (ii) the distance between the fourth element array 74 that outputs the AB-phase signal and the reference position. The A-phase signal and the AB-phase signal serve as inputs for generating a differential A-phase signal. In addition, the sum of the following distances is expressed as the following equation (14): (i) the distance between the second element array 72 that outputs the B-phase signal and the reference position; and (ii) the sum of the distances between the third element array 73 that outputs the BB-phase signal and the reference position. The B-phase signal and the BB-phase signal serve as inputs for generating a differential B-phase signal.

[0163] 0 + (-3P) = -3P (13)

[0164] (-P) + (-2P) = -3P (14)

[0165] As shown in equations (13) and (14), the element arrays are arranged at positions where, for the differential A-phase signal and the differential B-phase signal, the sum of the following distances is the same: (i) the distance in the Y direction from the reference position (first element array 71) to the positive phase signal element array (first element array 71 or second element array 72); and (ii) the distance in the Y direction from the reference position to the negative phase signal element array (third element array 73 or fourth element array 74). Therefore, any position can be defined as a reference position as long as it is a predetermined position on the light receiving surface. In short, if a plurality of element arrays in an element array group are arranged at positions where, for all phases of at least two phases (i.e., A-phase and B-phase), the sum of the following distances is the same: (i) the distance in the orthogonal direction from the reference position to the positive phase signal element array; and (ii) the distance in the orthogonal direction from the reference position to the negative phase signal element array.

[0166] In the above-mentioned embodiments, the encoder 1, 1A outputs the differential A-phase signal and the differential B-phase signal as differential signals having two phases; however, differential signals having multiple phases may be output as long as they are differential signals having at least two phases. In the above-mentioned embodiments, the first element array group 7 and the second element array group 7A each include four element arrays; however, it may include six arrays or eight arrays.

[0167] For example, if the encoder outputs a differential signal having three phases (A-phase, B-phase, and C-phase), the first element array group and the second element array group each include six element arrays, and such element arrays can be arranged as follows. For example, in a first embodiment, the six element arrays in the element array group can be arranged along an orthogonal direction orthogonal to the measuring direction, so that they output detection signals in the order of A-phase signal, B-phase signal, C-phase signal, CB-phase signal, BB-phase signal, and AB-phase signal. For example, in a second embodiment, the six element arrays in the first element array group can be arranged from one side toward the other side in an orthogonal direction orthogonal to the measuring direction, so that they output detection signals in the order of A-phase signal, B-phase signal, C-phase signal, CB-phase signal, BB-phase signal, and AB-phase signal, and this order is used as a predetermined reference. The six element arrays in the second element array group can be arranged from one side to the other in an orthogonal direction orthogonal to the measuring direction, so that they output detection signals in an order opposite to a predetermined reference, that is, in the order of C-phase signal, B-phase signal, A-phase signal, AB-phase signal, BB-phase signal and CB-phase signal.

[0168] In the above-mentioned embodiments, two signal input units 6a, 6b are described; however, the number of signal input units may be increased or decreased according to the number of element arrays and / or the number of signals to be acquired, or even no signal input unit may be provided. In addition, the above-mentioned embodiments are provided with a calculation device 8; however, if, for example, the encoder is connected to an external device and the calculation is performed in such an external device, the calculation device may not be provided.

[0169] Industrial Applicability

[0170] As described above, the present invention can be applied to an encoder.

Claims

1. An encoder, comprising: a plate-like scale having scales formed at a predetermined period along a measuring direction; and a detection head, which is movably arranged along the measuring direction relative to the plate-shaped scale, The detection head comprises: a transmitting unit that transmits a measurement signal to the plate-shaped scale; and a receiving unit, comprising a receiving surface, the receiving surface receiving the measurement signal from the transmitting unit via the plate-shaped scale, the receiving unit converting the measurement signal received at the receiving surface into a differential detection signal having at least two different phases and outputting the detection signal, the detection signal changing in response to the relative movement between the plate-shaped scale and the detection head corresponding to the period of the scale, wherein the receiving surface comprises: An element array group, comprising a plurality of element arrays arranged in parallel along an orthogonal direction orthogonal to the measuring direction, the plurality of element arrays comprising at least four element arrays, each element array comprising a plurality of receiving elements arranged along the measuring direction at a period corresponding to the period of the scale, Wherein, for each phase of the at least two phases, the plurality of element arrays comprises: a positive phase signal element array outputting a positive phase signal; and a negative phase signal element array outputting a negative phase signal, wherein the at least two phases are arranged in a shifted manner with a predetermined phase difference along the measuring direction, wherein the plurality of element arrays in the element array group are arranged at positions where the sum of the following two distances is the same for all phases in the at least two phases: (i) a distance from a reference position to a positive phase signal element array in an orthogonal direction; and (ii) a distance from a reference position to a negative phase signal element array in an orthogonal direction, wherein the positive phase signal element array occupies half of the plurality of element arrays in the element array group and is arranged on one side of the receiving surface relative to a center line, the center line extending along a measuring direction at the center of the plurality of element arrays, the plurality of element arrays being arranged in parallel in an orthogonal direction, and The negative phase signal element array occupies half of the multiple element arrays in the element array group and is arranged on the other side of the receiving surface relative to the center line, wherein the center line extends along the measuring direction at the center of the multiple element arrays, and the multiple element arrays are arranged in parallel in an orthogonal direction.

2. An encoder, comprising: a plate-like scale having scales formed at a predetermined period along a measuring direction; and a detection head, which is movably arranged along the measuring direction relative to the plate-shaped scale, The detection head comprises: a transmitting unit that transmits a measurement signal to the plate-shaped scale; and a receiving unit, comprising a receiving surface, the receiving surface receiving the measurement signal from the transmitting unit via the plate-shaped scale, the receiving unit converting the measurement signal received at the receiving surface into a differential detection signal having at least two different phases and outputting the detection signal, the detection signal changing in response to the relative movement between the plate-shaped scale and the detection head corresponding to the period of the scale, wherein the receiving surface comprises: An element array group, comprising a plurality of element arrays arranged in parallel along an orthogonal direction orthogonal to the measuring direction, the plurality of element arrays comprising at least four element arrays, each element array comprising a plurality of receiving elements arranged along the measuring direction at a period corresponding to the period of the scale, Wherein, for each phase of the at least two phases, the plurality of element arrays comprises: a positive phase signal element array outputting a positive phase signal; and a negative phase signal element array outputting a negative phase signal, wherein the at least two phases are arranged in a shifted manner with a predetermined phase difference along the measuring direction, and wherein the plurality of element arrays in the element array group are arranged at positions where the sum of the following two distances is the same for all phases in the at least two phases: (i) a distance from a reference position to a positive phase signal element array in an orthogonal direction; and (ii) a distance from a reference position to a negative phase signal element array in an orthogonal direction, The element array group includes: a first element array group; and a second element array group, the second element array group being adjacent to the first element array group in an orthogonal direction in the receiving surface and arranged in parallel therewith, the second element array group including a plurality of element arrays arranged differently from the plurality of element arrays in the first element array group, wherein the positive phase signal element array in the first element array group occupies half of the plurality of element arrays in the first element array group, is arranged on one side relative to the center line, and is arranged in an order used as a predetermined reference from one end in the orthogonal direction toward the center in the first element array group, wherein the center line extends along the measuring direction at the center of the plurality of element arrays, and the plurality of element arrays are arranged in parallel in the orthogonal direction in the first element array group, wherein the negative phase signal element array in the first element array group occupies half of the plurality of element arrays in the first element array group, is arranged on the other side relative to the center line, and is arranged in an order used as a predetermined reference from the other end in the orthogonal direction toward the center in the first element array group, wherein the center line extends along the measuring direction at the center of the plurality of element arrays, and the plurality of element arrays are arranged in parallel in the orthogonal direction in the first element array group, wherein the positive phase signal element array in the second element array group occupies half of the plurality of element arrays in the second element array group, is arranged on one side relative to the center line, and is arranged in an order opposite to the order used as a predetermined reference from one end in the orthogonal direction toward the center in the second element array group, wherein the center line extends along the measuring direction at the center of the plurality of element arrays, and the centers of the plurality of element arrays are arranged in parallel in the orthogonal direction in the second element array group, and In which, the negative phase signal element array in the second element array group occupies half of the multiple element arrays in the second element array group, is arranged on the other side relative to the center line, and is arranged from the other end in the orthogonal direction toward the center of the second element array group in an order opposite to the order used as a predetermined reference, wherein the center line extends along the measuring direction at the center of the multiple element arrays, and the multiple element arrays are arranged in parallel in the orthogonal direction in the second element array group.

3. The encoder according to claim 1, A plurality of element array groups are arranged along orthogonal directions in the receiving surface.

4. The encoder according to claim 1, wherein the encoder is an optical encoder, The detection head comprises: a light source serving as a transmitting unit for radiating light serving as a measurement signal toward the plate-shaped scale; and a light receiving unit serving as a receiving unit, the light receiving unit including a light receiving surface serving as a receiving surface, the light receiving surface receiving light from the light source via the plate-shaped scale, the light receiving unit converting the light received at the light receiving surface into a differential detection signal having at least two different phases, and outputting the detection signal, the detection signal changing in response to a relative movement between the plate-shaped scale and the detection head corresponding to a period of the scale, and wherein the light receiving surface comprises: An element array group, comprising a plurality of element arrays arranged in parallel along an orthogonal direction orthogonal to a measuring direction, the plurality of element arrays comprising at least four element arrays, each element array comprising a plurality of light receiving elements used as receiving elements, the plurality of light receiving elements being arranged along the measuring direction at a period corresponding to the period of the scale.

5. The encoder according to claim 4, further comprising a plate-shaped grid plate having a plurality of grids formed along a measuring direction, wherein a period of the plurality of grids corresponds to a period of the scale, wherein the plate-like grid plate is disposed between the plate-like scale and the light receiving unit, and The light receiving unit receives light that has passed through the plate-like grid plate.

6. An optical encoder, comprising: a plate-like scale having scales formed at a predetermined period along a measuring direction; A detection head, which is movably arranged along a measuring direction relative to the plate-shaped scale; and a plate-like grid plate having a plurality of grids formed along a measuring direction, wherein a period of the plurality of grids corresponds to a period of the scale, The detection head comprises: a light source that radiates light serving as a measurement signal toward the plate-like scale; and a light receiving unit including a light receiving surface that receives light from the light source via the plate-shaped scale, the light receiving unit converting the light received at the light receiving surface into a differential detection signal having at least two different phases, and outputting the detection signal, the detection signal varying in response to a relative movement between the plate-shaped scale and the detection head corresponding to a period of the scale, and wherein the light receiving surface comprises: an element array group, comprising a plurality of element arrays arranged in parallel along an orthogonal direction orthogonal to a measuring direction, the plurality of element arrays comprising at least four element arrays, each element array comprising a plurality of light receiving elements arranged along the measuring direction at a period corresponding to a period of the scale, wherein a plurality of element array groups are arranged in orthogonal directions in the light receiving surface, Wherein, for each phase of the at least two phases, the plurality of element arrays comprises: a positive phase signal element array outputting a positive phase signal; and a negative phase signal element array outputting a negative phase signal, wherein the at least two phases are arranged in a shifted manner with a predetermined phase difference along the measuring direction, and wherein the plurality of element arrays in the element array group are arranged at positions where the sum of the following two distances is the same for all phases in the at least two phases: (i) a distance from a reference position to a positive phase signal element array in an orthogonal direction; and (ii) a distance from a reference position to a negative phase signal element array in an orthogonal direction, wherein the plate-shaped grid plate is disposed between the plate-shaped scale and the light receiving unit, wherein the light receiving unit receives light having passed through the plate-like grid plate, wherein the positive phase signal element array occupies half of the plurality of element arrays in the element array group and is arranged on one side of the receiving surface relative to a center line, the center line extending along the measuring direction at the center of the plurality of element arrays, the plurality of element arrays being arranged in parallel in an orthogonal direction, and The negative phase signal element array occupies half of the multiple element arrays in the element array group and is arranged on the other side of the receiving surface relative to the center line, wherein the center line extends along the measuring direction at the center of the multiple element arrays, and the multiple element arrays are arranged in parallel in an orthogonal direction.

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