encoder

Abstract

To provide an encoder that can suppress accuracy deterioration even when a scale rotates with respect to a receiving unit with a shaft orthogonal to a receiving surface as a rotating shaft, and is arranged inclining therewith.SOLUTION: An encoder 1 includes: a scale 2; and a detection head 3. The detection head 3 is provided with: a light source (transmitting unit) 4; and a light-receiving unit (receiving unit) 5 that has a light-receiving surface (receiving surface) 50, converts light received at the light-receiving surface 50 into two-phase differential detection signals and outputs the detection signal. The light-receiving surface 50 has: element arrays 71 - 74 provided with a plurality of light-receiving elements (receiving elements) 500, and is provided with an element array group 7 having the element arrays 71 - 74 juxtaposed in four arrays along an orthogonal direction. A plurality of element arrays 71 - 74 in the element array group 7 are disposed in a position where a sum of a distance in the orthogonal direction from a reference position to positive phase signal element arrays 71 and 72 and a distance in the orthogonal direction from the reference position to reverse phase signal element arrays 73 and 74 is equal as to all phases of two phases.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to an encoder.

Background Art

[0002] Conventionally, an encoder including a plate-shaped scale having graduations formed at a predetermined period along a measurement direction, and a detection head provided so as to be relatively movable with respect to the scale along the measurement direction is known. For example, the detection head of the optical encoder (encoder) of Patent Document 1 has a light source (transmission unit) that irradiates light (measurement signal) toward the scale, and a light receiving surface (reception surface) that receives the light from the light source through the scale. The light received at the light receiving surface is converted into a detection signal that changes corresponding to the period of the graduations according to the relative movement between the scale and the detection head, and is output after being converted into differential detection signals of at least two phases having different phases by a light receiving unit (reception unit).

[0003] The light receiving surface of the light receiving unit has an element array including a plurality of light receiving elements (reception elements) arranged along the measurement direction at a period corresponding to the graduations, and includes an element array group in which the plurality of element arrays are arranged side by side along an orthogonal direction orthogonal to the measurement direction. In such an optical encoder, the light irradiated from the light source becomes a plurality of diffracted lights through the graduations. The plurality of diffracted lights generate interference fringes having the same period as the graduations. The light receiving unit receives the 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 from the detection signal.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Figure 10 is a schematic diagram showing the light receiving unit 9, signal input units 600a and 600b, and calculation means 800 in a conventional encoder 100. The light-receiving unit 9 outputs detection signals for two phases with different phases, A phase and B phase. The detection signals for A phase and B phase are differential signals. As shown in Figure 10, the light-receiving surface 90 of the light-receiving unit 9 is provided with a group of element arrays 700 in which multiple element arrays 710 to 740 are arranged in parallel in an orthogonal direction perpendicular to the measurement direction. The multiple element arrays 710 to 740 are, in order from +Y (top of the paper) to the -Y side (bottom of the paper), the first element array 710, the second element array 720, the third element array 730, and the fourth element array 740.

[0006] The first element array 710 outputs the A-phase signal, which is the positive-sequence signal of the A-phase. The second element array 720 outputs the B-phase signal, which is the positive-sequence signal of the B-phase. The third element array 730 outputs the AB-phase signal, which is the negative-sequence signal of the A-phase. The fourth element array 740 outputs the BB-phase signal, which is the negative-sequence signal of the B-phase. Here, the positive-sequence signal is the positive-sequence signal in the differential detection signal used to detect the relative displacement. The negative-sequence signal is the detection signal with the opposite phase to the positive-sequence signal in the differential detection signal. Ideally, the paired positive-sequence and negative-sequence signals are a signal pair with a phase difference of 180°. In the diagrams in the following explanation, the A-phase signal is referred to as "A-phase," the AB-phase signal as "AB-phase," the B-phase signal as "B-phase," and the BB-phase signal as "BB-phase."

[0007] Furthermore, the encoder 100 includes a first signal input unit 600a and a second signal input unit 600b that take the detection signals (i.e., a pair of positive-phase signals and negative-phase signals) output from the light receiving unit 9 as differential signal inputs, and a calculation means 800 that calculates the relative movement amount between the scale 2 (see Figure 11) and the detection head 300 based on the signals output from the two signal input units 600a and 600b. The two signal input units 600a and 600b each include a positive-phase signal input unit 610a and 610b, which receive a positive-phase signal as a detection signal from the light receiving unit 9, and a negative-phase signal input unit 620a and 620b, which receive a negative-phase signal.

[0008] At the first signal input section 600a, an A-phase signal is input from the first element array 710 of the light receiving section 9 to the positive-phase signal input section 610a, and an AB-phase signal is input from the third element array 730 to the negative-phase signal input section 620a. The first signal input section 600a then outputs the difference A-phase signal (i.e., A-phase signal - AB-phase signal), which is the difference between the A-phase signal and the AB-phase signal, to the calculation means 800. At the second signal input section 600b, a B-phase signal is input from the second element array 720 of the light receiving section 9 to the positive-phase signal input section 610b, and a BB-phase signal is input from the fourth element array 740 to the negative-phase signal input section 620b. The second signal input section 600b then outputs the difference B-phase signal (i.e., B-phase signal - BB-phase signal), which is the difference between the B-phase signal and the BB-phase signal, to the calculation means 800. In Figure 10, for the inputs from multiple element arrays 710 to 740 to the two signal input sections 600a and 600b, the positive-phase signal is shown with a solid line, and the negative-phase signal is shown with a dashed line.

[0009] Figure 11 is a top view showing a conventional encoder 100 in which the scale 2 is positioned relative to the light receiving unit 9 at an inclination angle θ=0. Figure 12 is a top view showing a conventional encoder 100 in which the scale 2 is positioned relative to the light receiving unit 9 at an inclination angle θ≠0. Specifically, Figures 11 and 12 are top views of the light receiving unit 9 as seen from the scale 2 side.

[0010] As shown in Figure 11, it is preferable that the encoder 100 is positioned with the scale 2 rotating around an axis perpendicular to the light-receiving surface 90 as its axis of rotation, without being tilted, and with a tilt angle θ=0. In this case, the encoder 100 does not experience the problems related to tilted interference fringes and the amount of shift in the detection signal that will be described later. However, as shown in Figure 12, during the manufacturing process, such as assembly, the scale 2 may be rotated around an axis perpendicular to the light-receiving surface 90 relative to the light-receiving part 9, and positioned at an inclination angle θ≠0. In this case, the following effects occur.

[0011] When the scale rotates around an axis perpendicular to the light-receiving surface relative to the light-receiving unit 9 and is positioned at an angle θ≠0 with respect to the direction perpendicular to the measurement direction (Y direction), the interference fringes generated on the light-receiving surface 90 of the light-receiving unit 9 are also generated at an angle θ≠0 in accordance with the rotation of the scale. When the light-receiving unit 9 receives interference fringes at an angle θ≠0, the phase of the detection signals input to the signal input units 600a and 600b from multiple element rows 710 to 740 arranged in parallel in the Y direction also shifts in accordance with the rotation at an angle θ≠0. Each element row 710 to 740 has a different phase shift amount for the detection signal detected by the light-receiving element (not shown) due to the difference in position in the Y direction. Therefore, the two signals based on the detection signals input to the two signal input units 600a and 600b also shift, affecting the calculation result (relative shift amount).

[0012] Figure 13 is a graph showing the fluctuation of the differential signal based on two phases in a conventional encoder 100. Specifically, in Figure 13, the vertical axis represents the output voltages of the two signal inputs 600a and 600b, and the horizontal axis represents the relative displacement of the detection head 300 with respect to the scale 2. Figure 14 is a graph showing the Lissajous signal calculated from the differential signal based on two phases in a conventional encoder 100. Specifically, in Figure 14, the vertical axis represents the difference B-phase signal, and the horizontal axis represents the difference A-phase signal. In Figures 13 and 14, the graph when the scale is positioned at an angle θ≠0 relative to the light receiving unit 9 is shown with a solid line, and the graph when the scale is positioned at an angle θ=0 relative to the light receiving unit 9 is shown with a dashed line.

[0013] When the scale is positioned relative to the light-receiving unit 9 at an angle θ≠0, as shown in Figure 13, the output voltage decreases and shifts in the direction of the diagonally downward right arrow and the diagonally upward left arrow, compared to the fluctuation when scale 2 (see Figure 11) is positioned at an angle θ=0, as shown by the dashed line. Furthermore, as shown in Figure 14, the Lissajous signal becomes smaller and its shape becomes elliptical compared to the Lissajous signal when scale 2 is positioned at an angle θ=0, as shown by the dashed line. The calculation means 800 performs calculations based on this deformed Lissajous signal and outputs the relative displacement as a calculation result. Therefore, when the scale is positioned at an angle θ≠0 relative to the light-receiving unit 9, there is a problem that the accuracy of the encoder 100 deteriorates.

[0014] The object of the present invention is to provide an encoder that can suppress accuracy degradation even if the scale is rotated and tilted relative to the receiving unit, with the axis of rotation being perpendicular to the axis of rotation of the receiving surface. [Means for solving the problem]

[0015] The encoder of the present invention comprises a plate-shaped scale having a scale formed at a predetermined period along the measurement direction, and a detection head provided so as to be movable relative to the scale along the measurement direction. The detection head includes a transmitting unit that transmits a measurement signal toward the scale, and a receiving surface that receives the measurement signal from the transmitting unit via the scale, and a receiving unit that converts the measurement signal received on the receiving surface into a differential detection signal of at least two phases with different phases, which changes in accordance with the period of the scale according to the relative movement between the scale and the detection head, and outputs it. The receiving surface has an element array comprising a plurality of receiving elements arranged along the measurement direction at a period corresponding to the scale, and includes an element array group comprising at least four rows of the plurality of element arrays arranged in parallel along an orthogonal direction perpendicular to the measurement direction. The plurality of element arrays each comprises a positive-phase signal element array that outputs a positive-phase signal and an inverse-phase signal element array that outputs an inverse-phase signal for each of at least two phases. The at least two phases are arranged offset along the measurement direction by a predetermined phase difference. Multiple element arrays within an element array group are positioned such that the sum of the orthogonal distance from the reference position to the positive-sequence signal element array and the orthogonal distance from the reference position to the negative-sequence signal element array is equal for all phases of at least two phases. The reference position refers to a predetermined position on the receiving surface.

[0016] According to the present invention, the multiple element arrays within the element array are positioned such that the sum of the orthogonal distance from the reference position to the positive-phase signal element array and the orthogonal distance from the reference position to the negative-phase signal element array is equal for all phases of at least two phases. This cancels out the phase difference of the differential signal caused by the scale being rotated and tilted relative to the receiving unit around an axis perpendicular to the receiving surface. Therefore, even if the encoder is positioned with the scale rotated and tilted relative to the receiving unit around an axis perpendicular to the receiving surface, accuracy degradation can be suppressed.

[0017] In this case, it is preferable that the positive-phase signal element array is half of the arrays of elements in the array group and is positioned on one side of the center line extending in the measurement direction at the center of the arrays of elements arranged in orthogonal directions on the receiving surface. It is also preferable that the negative-phase signal element array is half of the arrays of elements in the array group and is positioned on the other side of the center line extending in the measurement direction at the center of the arrays of elements arranged in orthogonal directions on the receiving surface.

[0018] With this configuration, the positive-sequence signal element array is positioned on one side of the center line extending in the measurement direction at the center of the plurality of element arrays arranged in orthogonal directions on the receiving surface, and the negative-sequence signal element array is positioned on the other side of the center line extending in the measurement direction at the center of the plurality of element arrays arranged in orthogonal directions on the receiving surface, thereby simplifying the design and suppressing a decrease in the amplitude of the differential signal.

[0019] In this case, it is preferable that the element array group comprises a first element array group and a second element array group which is arranged adjacent to the first element array group in a direction orthogonal to the receiving surface and has multiple element arrays arranged in a different configuration from the multiple element arrays in the first element array group. Furthermore, it is preferable that the positive-phase signal element array of the first element array group is half of the multiple element arrays in the first element array group and is arranged on one side of the center line extending in the measurement direction at the center of the multiple element arrays arranged in a direction orthogonal to the first element array group, and is arranged in a predetermined reference order from one end in the orthogonal direction toward the center in the first element array group. Here, the "predetermined reference order" is, for example, if the two phases consist of two phases, A phase and B phase, the order may be A phase, then B phase. Preferably, the inverse-phase signal element array of the first element array group is half of the multiple element arrays in the first element array group, and is positioned in the center of the multiple element arrays arranged orthogonally in the first element array group, on the other side of the center line extending in the measurement direction, and is arranged in a predetermined reference order from the other end in the orthogonal direction toward the center in the first element array group. Furthermore, preferably, the positive-phase signal element array of the second element array group is half of the multiple element arrays in the second element array group, and is positioned in the center of the multiple element arrays arranged orthogonally in the second element array group, on the one side of the center line extending in the measurement direction, and is arranged in the reverse order of the predetermined reference order from one end in the orthogonal direction toward the center in the second element array group (in the above example, the order of B phase, A phase). The inverse-phase signal element array of the second element array group is preferably half of the multiple element arrays within the second element array group, positioned in the center of the multiple element arrays arranged orthogonally in the second element array group, on the other side of the center line extending in the measurement direction, and arranged in the second element array group in reverse order from the other end in the orthogonal direction toward the center, compared to a predetermined reference order.

[0020] With this configuration, while suppressing the reduction in the amplitude of the differential signal based on the detection signal from the receiver, it is possible to efficiently cancel out the phase difference of the differential signal caused by the scale rotating and tilting relative to the receiver around an axis orthogonal to the receiving surface, compared to a configuration without the first and second element arrays.

[0021] At this time, it is preferable that a plurality of element row groups are arranged along the orthogonal direction on the reception surface.

[0022] According to such a configuration, it is possible to equalize the distribution of the measurement signal via the scale transmitted to the reception surface. For example, when the encoder is optical and the transmission unit is a light source, it is possible to equalize the light distribution of the light irradiated on the light reception surface as the reception surface via the scale.

[0023] At this time, the detection head has a light source as a transmission unit that irradiates light as a measurement signal toward the scale, and a light reception surface as a reception surface that receives the light from the light source via the scale, and the light received at the light reception surface is converted into a detection signal that changes corresponding to the period of the scale in accordance with the relative movement between the scale and the detection head, and is output as a differential detection signal of at least two phases with different phases, and a light reception unit as a reception unit. The light reception surface has an element row including a plurality of light reception elements as reception elements arranged along the measurement direction at a period corresponding to the scale, and is preferably an optical encoder including an element row group in which a plurality of element rows are arranged in parallel at least in four rows along the orthogonal direction.

[0024] According to such a configuration, even if the scale is arranged to rotate and tilt with the axis orthogonal to the reception surface (light reception surface) as the rotation axis with respect to the reception unit (light reception unit) when the encoder is an optical encoder, it is possible to suppress deterioration of the accuracy.

[0025] At this time, the encoder preferably includes a plate-shaped grating plate having a plurality of gratings formed along the measurement direction at a period corresponding to the scale. The grating plate is preferably arranged between the scale and the light reception unit. The light reception unit preferably receives the light via the grating plate.

[0026] With this configuration, even if, for example, only a photodetector larger than the desired size can be used, by placing a grid plate on top of the photodetector, interference fringes approximately the same as those generated by a photodetector of the desired size can be produced. [Brief explanation of the drawing]

[0027] [Figure 1] Perspective view showing an encoder according to the first embodiment. [Figure 2] Plan view showing the light receiving section of the encoder. [Figure 3] A schematic diagram showing the light receiving unit, signal input unit, and calculation means of the encoder. [Figure 4] A graph showing the fluctuation of the detection signal in the encoder. [Figure 5] A graph showing the fluctuation of the differential signal based on the two phases in the encoder. [Figure 6] A graph showing the Lissajous signal calculated from the differential signal based on the two phases in the encoder. [Figure 7] Plan view showing the light receiving section in the encoder according to the second embodiment. [Figure 8] A schematic diagram showing the light receiving unit, signal input unit, and calculation means of the encoder. [Figure 9] A graph showing the fluctuation of the detection signal in the encoder. [Figure 10] A schematic diagram showing the light receiving unit, signal input unit, and calculation means in a conventional encoder. [Figure 11] A top view showing a conventional encoder where the scale is positioned at an inclination angle θ=0 relative to the light receiving section. [Figure 12] A top view showing a conventional encoder where the scale is positioned relative to the light receiving section at an inclination angle θ≠0. [Figure 13] A graph showing the variation of differential signals based on two phases in a conventional encoder. [Figure 14] A graph showing the Lissajous signal calculated from a two-phase differential signal in a conventional encoder. [Modes for carrying out the invention]

[0028] [First Embodiment] Hereinafter, a first embodiment of the present invention will be described with reference to Figures 1 to 5. Figure 1 is a perspective view showing the encoder 1 according to the first embodiment. As shown in Figure 1, the encoder 1 is an optical linear encoder comprising a plate-shaped scale 2 formed along the measurement direction, the X direction, and a detection head 3 that is movable relative to the scale 2 along the X direction. In the following description and in each drawing, the measurement direction and longitudinal direction of the scale 2 is referred to as the X direction, the short direction of the scale 2 is referred to as the Y direction, and the height direction perpendicular to the X and Y directions is referred to as the Z direction.

[0029] The detection head 3 comprises a transmitting unit 4 that transmits a measurement signal toward the scale 2, and a receiving unit 5 that converts the received measurement signal into a detection signal and outputs it. In this embodiment, the transmitting unit 4 acts as a light source 4 and irradiates light toward the scale 2 as a measurement signal. The receiving unit 5 acts as a light receiving unit 5 and converts the received light into a detection signal and outputs it. The detection head 3 is provided so as to be able to move back and forth in the X direction relative to the scale 2 together with the light source 4 and the light receiving unit 5. The linear encoder acquires 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.

[0030] Scale 2 is formed in the shape of a plate made of glass or the like. One surface of Scale 2 is provided with a scale 20 formed along the X direction at a predetermined period g. The scale 20 is a grid of holes formed in Scale 2. Note that the scale 20 may also be formed by coating the scale plate with a grid-like film that does not transmit light, for example. Light source 4 irradiates parallel light toward one surface of scale 2. Light source 4 uses an LED (Light Emitting Diode). Note that light source 4 is not limited to an LED; any light source that can generate interference fringes in the light receiving unit 5, such as a semiconductor laser or helium-neon laser, may be used. In Figure 1, the optical path of the light emitted from light source 4 is indicated by an arrow.

[0031] The light-receiving unit 5 is positioned parallel to the XY plane, which is the surface of the scale 2. The light-receiving unit 5 has a light-receiving surface 50 that receives light from the light source 4 via the scale 2. The light-receiving unit 5 receives light through the scale 2 and detects a detection signal from the interference fringes generated by that light. In this embodiment, the interference fringes are generated on the light-receiving surface 50 on the light-receiving unit 5 along the Y direction, which is the short side of the scale 2. A PDA (Photo Diode Array) is used in the light-receiving unit 5. A PDA is a detector that has the property of being able to measure multiple interference fringes at once. Note that the light-receiving unit 5 is not limited to a PDA; any detector such as a CCD (Charge-Coupled Device) may be used.

[0032] Figure 2 is a plan view showing the light receiving unit 5 in the encoder 1. The details of the light-receiving unit 5 will be described below. The light receiving unit 5 outputs a detection signal that changes in accordance with the period of the scale 20 (see Figure 1) in response to the relative movement between the scale 2 (see Figure 1) and the detection head 3, based on the light received by the light receiving surface 50. The detection signal includes detection signals for two phases with different phases (i.e., phase A and phase B), and each phase detection signal is a differential signal. In this embodiment, the detection signal includes the A-phase signal, which is the positive-phase signal of phase A; the AB-phase signal, which is the negative-phase signal of phase A; the B-phase signal, which is the positive-phase signal of phase B; and the BB-phase signal, which is the negative-phase signal of phase B.

[0033] As shown in Figure 2, the light-receiving surface 50 has element rows 71 to 74. Each element row 71 to 74 comprises multiple light-receiving elements 500 arranged along the measurement direction (X direction) at a period corresponding to the scale 20. The multiple element rows 71 to 74 are arranged side by side along an orthogonal direction (Y direction) perpendicular to the measurement direction. Furthermore, the light-receiving surface 50 includes an element array group 7, where four rows of multiple element arrays 71 to 74 are grouped together. The element array group 7 has at least four even-numbered element arrays 71 to 74. Multiple element array groups 7 are arranged along the Y direction on the light-receiving surface 50.

[0034] Figure 3 is a schematic diagram showing the light receiving unit 5, signal input units 6a and 6b, and calculation means 8 in the encoder 1. As shown in Figure 3, the element array group 7 comprises, in order from the +Y side (top of the page) to the -Y side (bottom of the page), a first element array 71, a second element array 72, a third element array 73, and a fourth element array 74. The multiple element arrays 71 to 74 are arranged along the Y direction at a predetermined pitch P. For each of the two phases, the multiple element arrays 71 to 74 include a positive phase signal element array (first element array 71, second element array 72) that outputs a positive phase signal, and a negative phase signal element array (third element array 73, fourth element array 74) that outputs an inverse phase signal.

[0035] The first element array 71 outputs the A-phase signal, which is the positive-phase signal of the A-phase. The second element array 72 outputs the B-phase signal, which is the positive-phase signal of the B-phase. The third element array 73 outputs the BB-phase signal, which is the negative-phase signal of the B-phase. The fourth element array 74 outputs the AB-phase signal, which is the negative-phase signal of the A-phase. Therefore, the first element array 71 and the second element array 72 correspond to the positive-phase signal element arrays in this invention. Also, the third element array 73 and the fourth element array 74 correspond to the negative-phase signal element arrays in this invention.

[0036] Furthermore, the multiple element rows 71 to 74 are arranged with a predetermined phase difference shifted along the X direction. Specifically, with respect to the A-phase signal, the B-phase signal is positioned with a phase difference of 90°, the AB-phase signal with a phase difference of 180°, and the BB-phase signal with a phase difference of 270°. Therefore, the second element row 72 is positioned with a phase difference of 90° relative to the first element row 71, the third element row 73 with a phase difference of 270° relative to the first element row 71, and the fourth element row 74 with a phase difference of 180° relative to the first element row 71, all shifted along the X direction.

[0037] The first and second element rows 71 and 72, which are positive-phase signal element rows, constitute half (2 rows) of the multiple (4 rows) of element rows 71-74 in the element row group 7. The first and second element rows 71 and 72 are positioned on one side (+Y side) of the center line extending in the X direction at the center of the element rows arranged in the Y direction on the light-receiving surface 50. The center line is shown as the X-axis in Figure 3. The third and fourth element rows 73 and 74, which are negative-phase signal element rows, also constitute half (2 rows) of the multiple (4 rows) of element rows 71-74 in the element row group 7. The third and fourth element rows 73 and 74 are positioned on the other side (-Y side) of the center line.

[0038] Furthermore, the encoder 1 includes a first signal input unit 6a and a second signal input unit 6b that use the detection signal output from the light receiving unit 5 as the input for a differential signal, and a calculation means 8 that calculates the relative movement amount between the scale (see Figure 1) and the detection head 3 based on the differential signals output from the two signal input units 6a and 6b.

[0039] The two signal input units 6a and 6b include positive-phase signal input units 61a and 61b, which receive a positive-phase signal as a detection signal from the light receiving unit 5, and negative-phase signal input units 62a and 62b, which receive a negative-phase signal. At the first signal input unit 6a, the A-phase signal is input from the first element array 71 of the light receiving unit 5 to the positive-phase signal input unit 61a, and the AB-phase signal is input from the fourth element array 74 to the negative-phase signal input unit 62a. The first signal input unit 6a then outputs the difference A-phase signal (i.e., A-phase signal - AB-phase signal), which is the difference between the A-phase signal and the AB-phase signal, to the calculation means 8. In the second signal input section 6b, a B-phase signal is input from the second element row 72 of the light receiving section 5 to the positive-phase signal input section 61b, and a BB-phase signal is input from the third element row 73 to the negative-phase signal input section 62b. The second signal input section 6b then outputs the difference B-phase signal (i.e., B-phase signal - BB-phase signal), which is the difference between the B-phase signal and the BB-phase signal, to the calculation means 8. In the diagrams in the following explanation, for inputs from multiple element rows 71 to 74 to the two signal input sections 6a and 6b, the positive-phase signal is shown with a solid line, and the negative-phase signal is shown with a dashed line.

[0040] Here, as mentioned above, it is preferable that the encoder 1 has the scale 2 positioned at an inclination angle θ=0 relative to the light receiving unit 5 (see Figure 11). This is because positioning the scale 2 at an inclination angle θ=0 allows for the generation of ideal interference fringes on the light receiving surface 50 during measurement, thereby obtaining stable measurement results. However, even if the scale 2 is positioned at an inclination angle θ≠0 relative to the light receiving unit 5 (see Figure 12), the encoder 1 can be made less susceptible to this influence. The principle by which the configuration of the light receiving unit 5 can make it less susceptible to the influence of the scale 2 being positioned at an inclination angle θ≠0 relative to the light receiving unit 5 will be explained below.

[0041] Multiple element rows 71 to 74 within the element row group 7 are positioned such that the sum of the distance in the +Y direction from the reference position to the positive-phase signal element row (first element row 71, second element row 72) and the distance in the -Y direction from the reference position to the negative-phase signal element row (third element row 73, fourth element row 74) is equal for all phases. Here, the reference position refers to a predetermined position on the light-receiving surface 50, and in this embodiment, the X-axis in the figure is used as the reference position. The first element row 71 is located at a distance of +3P / 2 in the +Y direction from the reference position. The second element row 72 is located at a distance of +P / 2 in the +Y direction from the reference position. The third element row 73 is located at a distance of -P / 2 in the -Y direction from the reference position. The fourth element row 74 is located at a distance of -3P / 2 in the -Y direction from the reference position.

[0042] Similarly, in the conventional encoder 100 shown in Figure 10, the first element row 710 is located at a distance of +3P / 2 in the +Y direction from the reference position. The second element row 720 is located at a distance of +P / 2 in the +Y direction from the reference position. The third element row 730 is located at a distance of -P / 2 in the -Y direction from the reference position. The fourth element row 740 is located at a distance of -3P / 2 in the -Y direction from the reference position. The sum of the distances to the reference position between the first element row 710, which outputs the A-phase signal and is the input for the differential A-phase signal, and the third element row 730, which outputs the AB-phase signal, is given by equation (1). Also, the sum of the distances to the reference position between the second element row 720, which outputs the B-phase signal and is the input for the differential B-phase signal, and the fourth element row 740, which outputs the BB-phase signal, is given by equation (2).

[0043] (+3P / 2)+(-P / 2)=+P ···(1) (+P / 2)+(-3P / 2)=-P ···(2)

[0044] As shown in equations (1) and (2), in the conventional encoder 100, the sum of the distance in the +Y direction from the reference position to the positive-phase signal element array (first element array 710, second element array 720) and the distance in the -Y direction from the reference position to the negative-phase signal element array (third element array 730, fourth element array 740) is located at different positions for the differential A-phase signal and the differential B-phase signal.

[0045] In contrast, in the encoder 1 shown in Figure 3, the sum of the distances to the reference position between the first element row 71, which outputs the A-phase signal and is the input for the differential A-phase signal, and the fourth element row 74, which outputs the AB-phase signal, is given by equation (3). Also, the sum of the distances to the reference position between the second element row 72, which outputs the B-phase signal and the third element row 73, which outputs the BB-phase signal and is the input for the differential B-phase signal, is given by equation (4).

[0046] (+3P / 2)+(-3P / 2)=0 ···(3) (+P / 2)+(-P / 2)=0 ···(4)

[0047] As shown in equations (3) and (4), in encoder 1, the sum of the distance in the +Y direction from the reference position to the positive-phase signal element array (first element array 71, second element array 72) and the distance in the -Y direction from the reference position to the negative-phase signal element array (third element array 73, fourth element array 74) is equal for the difference A-phase signal and the difference B-phase signal. With multiple element arrays 71 to 74 arranged in this way, if the scale 2 (see Figure 1) rotates around an axis perpendicular to the light-receiving surface 50 with respect to the measurement direction (X-direction) and is tilted at an angle θ≠0 in the direction perpendicular to the measurement direction (Y-direction), the following effects can be obtained.

[0048] As shown in Figure 12, in a conventional encoder 100, when the scale 2 is tilted at an angle θ, interference fringes are generated that include a phase difference originating from the tilt angle θ of the scale, as shown in equation (5) for the differential A-phase signal and equation (6) for the differential B-phase signal. When the light receiving unit 9 receives these interference fringes, the phase of the detection signals input to the signal input units 600a and 600b from the multiple element rows 710 to 740 arranged in parallel in the Y direction also shifts. Because the amount of phase shift of the detection signals detected by the light receiving elements differs for each element row 710 to 740 due to the difference in their positions in the Y direction, the two differential signals also shift, affecting the calculation result (relative shift amount).

[0049] (-3P / 2×θ)+(P / 2×θ)=-P·θ ···(5) (-P / 2×θ)+(3P / 2×θ)=+P·θ ···(6)

[0050] In contrast, as shown in Figure 3, even if the scale 2 (see Figure 1) is tilted at an angle θ in the encoder 1, the shift amounts of the two differential signals originating from the tilt angle θ of the scale 2 cancel each other out, as shown in equation (7) for the differential A-phase signal and equation (8) for the differential B-phase signal.

[0051] (-3P / 2×θ)+(3P / 2×θ)=0 ···(7) (-P / 2×θ)+(P / 2×θ)=0 ···(8)

[0052] Figure 4 is a graph showing the fluctuation of the detection signal in encoder 1. Specifically, in Figure 4, the vertical axis represents the output voltage and the horizontal axis represents the displacement. Figure 5 is a graph showing the fluctuation of the differential signal based on the two phases in encoder 1. Specifically, in Figure 5, the vertical axis represents the output voltage of the two signal inputs 6a and 6b, and the horizontal axis represents the relative displacement of the detection head 3 with respect to scale 2. Figure 6 is a graph showing the Lissajous signal calculated from the differential signal based on the two phases in encoder 1. Specifically, in Figure 6, the vertical axis represents the difference B phase signal and the horizontal axis represents the difference A phase signal. Note that in Figures 4, 5, and 6, the graph when scale 2 (see Figure 1) is positioned at an angle θ≠0 relative to the light receiving unit 5 is shown with a solid line, and the graph when scale 2 is positioned at an angle θ=0 relative to the light receiving unit 5 is shown with a dashed line. The following describes the fluctuations in the detection signal output from the light receiving unit 5 to the signal input units 6a and 6b, and the fluctuations in the difference A-phase signal and difference B-phase signal output from the signal input units 6a and 6b to the calculation means 8.

[0053] As shown in Figure 4, when the scale 2 (see Figure 1) is positioned relative to the light-receiving unit 5 at an inclination angle θ≠0, the phase A signal input from the first element row 71 is shifted by -3P / 2×θ compared to when the scale 2 is positioned at an inclination angle θ=0. The phase B signal input from the second element row 72 is also shifted by -P / 2×θ. The phase BB signal input from the third element row 73 is shifted by +P / 2×θ. The phase AB signal input from the fourth element row 74 is shifted by +3P / 2×θ.

[0054] In this state, the signal input section 6a (see Figure 3) that outputs the differential A-phase signal receives an A-phase signal from the first element row 71 with a phase shift of -3P / 2 × θ at the positive-phase signal input section 61a (see Figure 3), and an AB-phase signal from the fourth element row 74 with a phase shift of +3P / 2 × θ at the negative-phase signal input section 62a. Then, during the conversion process to the differential A-phase signal, the calculation in equation (7) is performed, and the phase difference between the A-phase signal and the AB-phase signal is canceled out, resulting in zero phase difference in the differential A-phase signal. Furthermore, the signal input section 6b (see Figure 3) that outputs the differential B-phase signal receives a B-phase signal from the second element row 72 with a phase shift of -P / 2 × θ to the positive-phase signal input section 61b (see Figure 3), and a BB-phase signal from the third element row 73 with a phase shift of +P / 2 × θ to the negative-phase signal input section 62b. Then, during the conversion process to the differential B-phase signal, the calculation in equation (8) is performed, canceling out the phase difference between the B-phase signal and the BB-phase signal, so that the phase difference in the differential B-phase signal becomes zero.

[0055] The phase difference in the differential A-phase signal and the phase difference in the differential B-phase signal are both zero and therefore the same. As a result, the phase difference between the differential A-phase signal and the differential B-phase signal remains unchanged when the inclination angle θ of scale 2 is 0 and when the inclination angle θ of scale 2 is ≠ 0, and the interference fringes generated on the light-receiving surface 50 approximate the interference fringes generated when the inclination angle θ of scale 2 is 0.

[0056] Therefore, as shown in Figure 5, the differential A-phase signal and differential B-phase signal output from the two signal inputs 6a and 6b (see Figure 3) are output to the calculation means 8 as differential A-phase signal and differential B-phase signal that maintain the phase difference at θ=0 (i.e., a 90° phase difference), although the output voltage is smaller compared to when the inclination angle θ=0 on scale 2 (see Figure 1). As shown in Figure 6, the Lissajous signal calculated by the calculation means 8 based on the difference A-phase signal and difference B-phase signal output from the two signal input units 6a and 6b has a smaller amplitude and is an elliptical Lissajous signal with a high degree of flattening compared to the case where scale 2 is positioned at an inclination angle θ=0. However, compared to the Lissajous signal in the conventional encoder 100 shown in Figure 14, it is a Lissajous signal that is closer to a perfect circle. As a result, even if the encoder 1 is positioned at an angle and rotates around an axis perpendicular to the light-receiving surface 50, the encoder 1 can suppress accuracy degradation.

[0057] According to this first embodiment, the following actions and effects can be achieved. (1) Multiple element rows 71 to 74 within the element row group 7 are positioned such that the sum of the distance from the reference position to the positive-phase signal element row (first element row 71, second element row 72) in the orthogonal direction (+Y direction) and the distance from the reference position to the negative-phase signal element row (third element row 73, fourth element row 74) in the orthogonal direction (-Y direction) is equal for the differential A-phase signal and the differential B-phase signal. This allows the phase difference of the differential signal caused by the scale 2 being rotated and tilted relative to the light-receiving unit 5 around an axis orthogonal to the light-receiving surface 50 to be canceled out. Therefore, the encoder 1 can suppress accuracy degradation even if the scale 2 is rotated and tilted relative to the light-receiving unit 5 around an axis orthogonal to the light-receiving surface 50 to be the axis of rotation. (2) The positive-phase signal element arrays (first element array 71, second element array 72) are positioned on the +Y side with respect to the center line in the middle of the arrays of elements arranged in the Y direction on the light-receiving surface 50, and the negative-phase signal element arrays (third element array 73, fourth element array 74) are positioned on the -Y side with respect to the center line. This makes the design easier and suppresses the reduction in the amplitude of the differential signal. (3) Multiple element arrays 7 are arranged along the Y direction on the light-receiving surface 50, which makes it possible to equalize the light distribution caused by light irradiated onto the light-receiving surface 50 via the scale 2.

[0058] [Second Embodiment] A second embodiment of the present invention will be described below with reference to Figures 7 to 9. In the following description, parts that have already been described will be denoted by the same reference numerals and their descriptions will be omitted.

[0059] Figure 7 is a plan view showing the light receiving unit 5A in the encoder 1A according to the second embodiment. In the first embodiment described above, in the element array group 7, the first element array 71 inputs the A-phase signal to the positive-phase signal input unit 61, the second element array 72 inputs the B-phase signal to the positive-phase signal input unit 61, the third element array 73 inputs the BB-phase signal to the negative-phase signal input unit 62, and the fourth element array 74 inputs the AB-phase signal to the negative-phase signal input unit 62. In the second embodiment, as shown in Figure 7, the light-receiving surface 50A differs from the first embodiment in that it comprises a first element array 7 similar to the element array 7 in the first embodiment, and a second element array 7A arranged adjacent to the first element array 7 in the Y direction, which is orthogonal to the first element array 7 on the light-receiving surface 50A.

[0060] The following describes the details of the light-receiving unit 5A. The element array comprises a first element array 7 and a second element array 7A arranged adjacent to the first element array 7 in the orthogonal direction (Y direction) on the light-receiving surface 50. The second element array group 7A has at least four even-numbered element arrays 75-78 arranged differently from the arrays 71-74 in the first element array group 7. The arrays 75-78 are arranged side by side along an orthogonal direction (Y direction) perpendicular to the measurement direction.

[0061] In the first embodiment, multiple element arrays 7 were arranged along the Y direction on the light-receiving surface 50. In the second embodiment, the first element array group 7 and the second element array group 7A are combined into a pair of element array groups 7,7A, and this pair of element array groups 7,7A is arranged in multiple sets along the Y direction on the light-receiving surface 50A, which is different from the first embodiment. Specifically, the first element array 7 and the second element array 7A are arranged alternately and repeatedly along the Y direction on the light-receiving surface 50A.

[0062] Figure 8 is a schematic diagram showing the light receiving unit 5A, signal input units 6a and 6b, and calculation means 8 in encoder 1A. As shown in Figure 8, the second element array group 7A comprises, in order from the +Y side (top of the page) to the -Y side (bottom of the page), a fifth element array 75, a sixth element array 76, a seventh element array 77, and an eighth element array 78. The multiple element arrays 75 to 78 are arranged along the Y direction at a predetermined pitch P.

[0063] Each of the element arrays 75-78 comprises, for each of the two phases, a positive-phase signal element array (fifth element array 75, sixth element array 76) that outputs a positive-phase signal, and a negative-phase signal element array (seventh element array 77, eighth element array 78) that outputs an negative-phase signal. Furthermore, multiple element rows 75 to 78 are arranged with a predetermined phase difference along the X direction. Specifically, the sixth element row 76 is 90° in phase with respect to the fifth element row 75, the seventh element row 77 is 270° in phase with respect to the fifth element row 75, and the eighth element row 78 is 180° in phase with respect to the fifth element row 75, all arranged with a phase difference along the X direction.

[0064] The fifth element array 75 outputs a B-phase signal, which is the positive-phase signal of phase B. The sixth element array 76 outputs an A-phase signal, which is the positive-phase signal of phase A. The seventh element array 77 outputs an AB-phase signal, which is the negative-phase signal of phase A. The eighth element array 78 outputs a BB-phase signal, which is the negative-phase signal of phase B. Therefore, the fifth element array 75 and the sixth element array 76 correspond to the positive-phase signal element arrays in this invention. Also, the seventh element array 77 and the eighth element array 78 correspond to the negative-phase signal element arrays in this invention.

[0065] In the first element array group 7, the positive-phase signal element arrays (first element array 71, second element array 72) are half (2 arrays) of the multiple (4 arrays) of element arrays 71-74 within the first element array group 7. The positive-phase signal element arrays (first element array 71, second element array 72) are positioned on the +Y side with respect to the center line in the first element array group 7, which is arranged in parallel in the Y direction. Furthermore, the positive-phase signal element arrays (first element array 71, second element array 72) are arranged in the first element array group 7 in a predetermined reference order from one end (top of the page) in the Y direction toward the center (downward on the page). In this embodiment, the "predetermined reference order of the positive-phase signal element arrays" is the order of A phase, then B phase.

[0066] Furthermore, in the second element array group 7A, the positive-phase signal element arrays (fifth element array 75, sixth element array 76) constitute half (2 arrays) of the multiple (4 arrays) of element arrays 75-78 within the second element array group 7A. The positive-phase signal element arrays (fifth element array 75, sixth element array 76) are positioned on the +Y side with respect to the center line in the second element array group 7A, which is arranged in parallel in the Y direction. In addition, the positive-phase signal element arrays (fifth element array 75, sixth element array 76) are arranged in the second element array group 7A in the reverse order of a predetermined reference order, moving from one end (top of the paper) in the Y direction towards the center (downward on the paper).

[0067] Specifically, the "predetermined reference order of the positive-phase signal element array" is set to the order of A-phase, then B-phase. Therefore, the "reverse order of the predetermined reference order of the positive-phase signal element array" is the order of B-phase, then A-phase. Consequently, if the positive-phase signal element array of the first element array group 7 is arranged from one end in the Y direction (top of the page) toward the center (downward on the page) in the order of the first element array 71 that outputs the A-phase signal, then the second element array 72 that outputs the B-phase signal, then the positive-phase signal element array of the second element array group 7A is arranged from one end in the Y direction (top of the page) toward the center (downward on the page) in the order of the fifth element array 75 that outputs the B-phase signal, then the sixth element array 76 that outputs the A-phase signal, so that the order in which the two phases are arranged is reversed.

[0068] In the first element array group 7, the inverse-phase signal element arrays (third element array 73, fourth element array 74) are half (2 arrays) of the multiple element arrays 71-74 within the first element array group 7 (4 arrays). The inverse-phase signal element arrays (third element array 73, fourth element array 74) are positioned on the -Y side with respect to the center line in the first element array group 7, which is arranged in parallel in the Y direction. Furthermore, the inverse-phase signal element arrays (third element array 73, fourth element array 74) are arranged in the first element array group 7 from the other end in the Y direction (bottom of the page) toward the center (upward on the page) in a predetermined reference order. In this embodiment, the "predetermined reference order of the inverse-phase signal element arrays" is the order of AB phase, BB phase.

[0069] Furthermore, in the second element array group 7A, the inverse-phase signal element arrays (7th element array 77, 8th element array 78) constitute half (2 arrays) of the multiple (4 arrays) of element arrays 75-78 within the second element array group 7A. The inverse-phase signal element arrays (7th element array 77, 8th element array 78) are positioned on the -Y side with respect to the center line in the center of the element arrays in the second element array group 7A, which are arranged in parallel in the Y direction. In addition, the inverse-phase signal element arrays (7th element array 77, 8th element array 78) are arranged in the second element array group 7A in the reverse order of a predetermined reference order, moving from the other end in the Y direction (bottom of the page) towards the center (upward on the page).

[0070] Specifically, the "predetermined reference order of the inverse phase signal element array" is set to the order of AB phase, then BB phase. Therefore, the "reverse order of the predetermined reference order of the inverse phase signal element array" is the order of BB phase, then AB phase. Consequently, if the inverse phase signal element array of the first element array group 7 is arranged from the other end in the Y direction (bottom of the page) toward the center (upward on the page) in the order of the fourth element array 74 that outputs the AB phase signal, then the third element array 73 that outputs the BB phase signal, then the inverse phase signal element array of the second element array group 7A is arranged from the other end in the Y direction (bottom of the page) toward the center (upward on the page) in the order of the eighth element array 78 that outputs the BB phase signal, then the seventh element array 77 that outputs the AB phase signal, so that the order in which the two phases are arranged is reversed.

[0071] In other words, in the first element array group 7, the multiple element arrays 71 to 74 are arranged from the +Y side to the -Y side such that the detection signals they output are in the order of A phase signal, B phase signal, BB phase signal, and AB phase signal, which is a predetermined reference order. Then, in the second element array group 7A, the multiple element arrays 75 to 78 are arranged from the +Y side to the -Y side such that the detection signals they output are in the order of B phase signal, A phase signal, AB phase signal, and BB phase signal, which is the reverse of the predetermined reference order.

[0072] In the two signal input sections 6a and 6b, the first signal input section 6a receives an A-phase signal from the first element row 71 and the sixth element row 76 of the light receiving section 5 to the positive-phase signal input section 61a, and an AB-phase signal from the fourth element row 74 and the seventh element row 77 to the negative-phase signal input section 62a. The first signal input section 6a then outputs the difference A-phase signal (i.e., A-phase signal - AB-phase signal), which is the difference between the A-phase signal and the AB-phase signal, to the calculation means 8. In the second signal input section 6b, the B-phase signal is input to the positive-phase signal input section 61b from the second element row 72 and the fifth element row 75 of the light receiving section 5, and the BB-phase signal is input to the negative-phase signal input section 62b from the third element row 73 and the eighth element row 78. The second signal input section 6b then outputs the difference B-phase signal (i.e., B-phase signal - BB-phase signal), which is the difference between the B-phase signal and the BB-phase signal, to the calculation means 8.

[0073] Multiple element rows 71 to 78 within the first element row group 7 and the second element row 7A are positioned such that the sum of the distance in the Y direction from the reference position to the positive-phase signal element row (first element row 71, second element row 72, fifth element row 75, sixth element row 76) and the distance in the Y direction from the reference position to the negative-phase signal element row (third element row 73, fourth element row 74, seventh element row 77, eighth element row 78) is equal for all phases of the two phases.

[0074] The first element row 71 is located at a distance of +7P / 2 in the +Y direction from the reference position. The second element row 72 is located at a distance of +5P / 2 in the +Y direction from the reference position. The third element row 73 is located at a distance of +3P / 2 in the +Y direction from the reference position. The fourth element row 74 is located at a distance of +P / 2 in the +Y direction from the reference position. The fifth element row 75 is located at a distance of -P / 2 in the -Y direction from the reference position. The sixth element row 76 is located at a distance of -3P / 2 in the -Y direction from the reference position. The seventh element row 77 is located at a distance of -5P / 2 in the -Y direction from the reference position. The eighth element row 78 is located at a distance of -7P / 2 in the -Y direction from the reference position.

[0075] In encoder 1A, the sum of the distances to the reference position of the first element row 71 and the sixth element row 76, which output the A-phase signal and are input to the differential A-phase signal, and the fourth element row 74 and the seventh element row 77, which output the AB-phase signal, is given by equation (9). Also, the sum of the distances to the reference position of the second element row 72 and the fifth element row 75, which output the B-phase signal and are input to the differential B-phase signal, and the third element row 73 and the eighth element row 78, which output the BB-phase signal, is given by equation (10).

[0076] (+7P / 2)+(-3P / 2)+(+P / 2)+(-5P / 2)=0 ···(9) (+5P / 2)+(-P / 2)+(+3P / 2)+(-7P / 2)=0...(10)

[0077] As shown in equations (9) and (10), in encoder 1A, the sum of the distance in the Y direction from the reference position to the positive-phase signal element array (first element array 71, second element array 72, fifth element array 75, sixth element array 76) and the distance in the Y direction from the reference position to the negative-phase signal element array (third element array 73, fourth element array 74, seventh element array 77, eighth element array 78) is equal for the difference A-phase signal and the difference B-phase signal. With multiple element arrays 71 to 78 arranged in this way, if the scale 2 (see Figure 1) rotates around an axis perpendicular to the light-receiving surface 50A with respect to the light-receiving surface 5A and is tilted at an angle θ≠0 with respect to the direction perpendicular to the measurement direction (X-direction) (Y-direction), the following effects can be obtained.

[0078] Even if the scale 2 (see Figure 1) in encoder 1A is tilted at an angle θ, the shift amounts of the two differential signals originating from the tilt angle θ of scale 2 cancel each other out, as shown in equation (11) for the differential A-phase signal and equation (12) for the differential B-phase signal.

[0079] (-7P / 2×θ)+(-P / 2×θ)+(3P / 2×θ)+(5P / 2×θ)=0 (11) (-5P / 2×θ)+(-3P / 2×θ)+(P / 2×θ)+(7P / 2×θ)=0 (12)

[0080] Figure 9 is a graph showing the fluctuation of the detection signal in encoder 1A. Specifically, in Figure 9, the vertical axis represents the output voltage and the horizontal axis represents the displacement. In Figure 9, the graph when scale 2 (see Figure 1) is positioned relative to the light receiving unit 5A at an angle θ≠0 is shown as a solid line, and the graph when scale 2 is positioned relative to the light receiving unit 5A at an angle θ=0 is shown as a dashed line. The following describes the fluctuations in the detection signal output from the light receiving unit 5A to the signal input units 6a and 6b, and the fluctuations in the difference A-phase signal and difference B-phase signal output from the signal input units 6a and 6b to the calculation means 8.

[0081] As shown in Figure 9, when the scale 2 (see Figure 1) is positioned relative to the light-receiving unit 5A at an inclination angle θ≠0, the phase of the A-phase signal input from the first element row 71 is shifted by -7P / 2×θ compared to when the scale 2 is positioned at an inclination angle θ=0. Also, the phase of the B-phase signal input from the second element row 72 is shifted by -5P / 2×θ. The phase of the BB-phase signal input from the third element row 73 is shifted by -3P / 2×θ. The phase of the AB-phase signal input from the fourth element row 74 is shifted by -P / 2×θ. The phase of the B-phase signal input from the fifth element row 75 is shifted by +P / 2×θ. The phase of the A-phase signal input from the sixth element row 76 is shifted by +3P / 2×θ. The phase of the AB-phase signal input from the seventh element row 77 is shifted by +5P / 2×θ. The BB phase signal input from the 8th element array 78 is shifted in phase by +7P / 2 × θ.

[0082] In this state, the signal input section 6a (see Figure 8) that outputs the differential A-phase signal receives the A-phase signal from the first element row 71 with a phase shift of -7P / 2×θ and the A-phase signal from the sixth element row 76 with a phase shift of +3P / 2×θ from the first element row 71 to the positive-phase signal input section 61a (see Figure 8), and the AB-phase signal from the fourth element row 74 with a phase shift of -P / 2×θ and the AB-phase signal from the seventh element row 77 with a phase shift of +5P / 2×θ from the fourth element row 74 to the negative-phase signal input section 62a. Then, during the conversion process to the differential A-phase signal, the calculation in equation (11) is performed, and the phase difference between the A-phase signal and the AB-phase signal is canceled out, resulting in zero phase difference in the differential A-phase signal.

[0083] Furthermore, the signal input section 6b (see Figure 8) that outputs the differential B-phase signal receives a B-phase signal from the second element row 72 with a phase shift of -5P / 2×θ and a B-phase signal from the fifth element row 75 with a phase shift of +P / 2×θ from the second element row 72 to the positive-phase signal input section 61b (see Figure 8), and a BB-phase signal from the third element row 73 with a phase shift of -3P / 2×θ and a BB-phase signal from the eighth element row 78 with a phase shift of +7P / 2×θ from the third element row 73 to the negative-phase signal input section 62b. Then, during the conversion process to the differential B-phase signal, the calculation in equation (12) is performed, and the phase difference between the B-phase signal and the BB-phase signal is canceled out, resulting in zero phase difference in the differential B-phase signal.

[0084] The phase difference in the differential A-phase signal and the phase difference in the differential B-phase signal are both zero and therefore the same. As a result, the phase difference between the differential A-phase signal and the differential B-phase signal remains unchanged when the inclination angle θ of scale 2 is 0 and when the inclination angle θ of scale 2 is ≠ 0, and the interference fringes generated on the light-receiving surface 50A approximate the interference fringes generated when the inclination angle θ of scale 2 is 0.

[0085] Therefore, as shown in Figure 5, the differential A-phase signal and differential B-phase signal output from the two signal input units 6a and 6b (see Figure 8) are output to the calculation means 8 as differential A-phase signal and differential B-phase signal that maintain the phase difference at θ=0 (i.e., a 90° phase difference), although the output voltage is smaller compared to when the inclination angle θ=0 on scale 2 (see Figure 1). As shown in Figure 6, the Lissajous signal calculated by the calculation means 8 based on the difference A-phase signal and difference B-phase signal output from the two signal input units 6a and 6b has a smaller amplitude and is an elliptical Lissajous signal with a high degree of flattening compared to the case where the scale 2 is positioned at an inclination angle θ=0. However, it is closer to a perfect circle than the Lissajous signal in the conventional encoder 100 shown in Figure 14. Furthermore, the Lissajous signal in encoder 1A of the second embodiment is even closer to a perfect circle than the Lissajous signal in encoder 1 of the first embodiment. As a result, even if the encoder 1A is positioned at an angle, rotating around an axis perpendicular to the light-receiving surface 50A, the encoder 1A can suppress accuracy degradation.

[0086] In the second embodiment, the same actions and effects as in (1) to (3) in the first embodiment can be achieved, as well as the following actions and effects. (4) While suppressing the reduction in the amplitude of the differential signal based on the detection signal from the light-receiving unit 5A, the phase difference of the differential signal caused by the scale 2 rotating and tilting relative to the light-receiving unit 5A around an axis orthogonal to the light-receiving surface 50A can be efficiently canceled out compared to the case where the first element array 7 and the second element array 7A are not provided.

[0087] [Variations of the Embodiment] Furthermore, the present invention is not limited to the embodiments described above, and any modifications, improvements, etc., that can achieve the objectives of the present invention are included within the scope of the present invention. For example, in each of the above embodiments, the present invention was described in which the encoder 1,1A is a linear encoder, but the type of detector, detection method, etc. are not particularly limited as long as it is an encoder.

[0088] Specifically, in each of the above embodiments, the detection heads 3 and 3A comprise a light source 4 as a transmitting unit that irradiates light as a measurement signal toward the scale 2, and light receiving units 5 and 5A as receiving units having light receiving surfaces 50 and 50A that receive light from the light source 4 via the scale 2. The light receiving surfaces 50 and 50A were optical encoders 1 and 1A having an element array comprising multiple light receiving elements 500. However, the encoder may be an encoder of another detection method, such as a capacitive or electromagnetic induction type, instead of an optical type. In this case, the transmitting unit that transmits the measurement signal, the receiving unit having a receiving surface, and the multiple receiving elements can be any encoder that has similar functions, such as a capacitive or electromagnetic induction type encoder. For example, in an electromagnetic induction type encoder, the transmitting unit transmits a magnetic force corresponding to a measurement signal that excites a coil which is a scale, and the receiving unit has multiple receiving coils corresponding to multiple receiving elements and can receive changes in the magnetic flux of the coils.

[0089] In the embodiments described above, no optical elements or the like were placed between the scale and the light-receiving section, but elements with the following configuration may be placed between them. In other words, the encoder preferably includes a plate-shaped grid plate having multiple grids formed along the measurement direction at a period corresponding to the scale. The grid plate is preferably positioned between the scale and the light-receiving unit. The light-receiving unit preferably receives light through the grid plate. With this configuration, even if, for example, only a photodetector larger than the desired size can be used, by placing a grid plate on top of the photodetector, interference fringes approximately the same as those generated by a photodetector of the desired size can be produced.

[0090] In the second embodiment described above, the first element array group 7 and the second element array group 7A were considered as a pair of element array groups 7,7A, and the first element array 7 and the second element array 7A were arranged alternately and repeatedly along the Y direction on the light-receiving surface 50A. However, it is not necessary to arrange multiple pairs of element array groups 7,7A along the Y direction on the light-receiving surface 50A. For example, instead of arranging the first element array group 7 and the second element array group 7A alternately and repeatedly, multiple pairs may be arranged along the Y direction on the light-receiving surface 50A in any combination. In short, it is sufficient for multiple element array groups to be arranged along the orthogonal direction on the receiving surface.

[0091] In the first embodiment described above, the first element array 71 outputs an A-phase signal, which is a positive-phase signal; the second element array 72 outputs a B-phase signal, which is a positive-phase signal; the third element array 73 outputs a BB-phase signal, which is an inverted-phase signal; and the fourth element array 74 outputs an AB-phase signal, which is an inverted-phase signal. However, the first element array may output an A-phase signal, which is a positive-phase signal; the second element array may output a BB-phase signal, which is an inverted-phase signal; the third element array may output a B-phase signal, which is a positive-phase signal; and the fourth element array may output an AB-phase signal, which is an inverted-phase signal.

[0092] Furthermore, in the second embodiment, in the first element array 7, the first element array 71 output an A-phase signal, which is a positive-phase signal; the second element array 72 output a B-phase signal, which is a positive-phase signal; the third element array 73 output a BB-phase signal, which is an inverted-phase signal; and the fourth element array 74 output an AB-phase signal, which is an inverted-phase signal. In addition, in the second element array 7A, the fifth element array 75 output a B-phase signal, which is a positive-phase signal; the sixth element array 76 output an A-phase signal, which is a positive-phase signal; the seventh element array 77 output an AB-phase signal, which is an inverted-phase signal; and the eighth element array 78 output a BB-phase signal, which is an inverted-phase signal.

[0093] However, in the second group of element arrays, multiple element arrays may output detection signals in other combinations. In short, at least two signal input sections only need to receive detection signals from element arrays positioned such that the sum of the phase difference of the element array inputting a positive-phase signal to the positive-phase signal input section and the phase difference of the element array inputting an inverted-phase signal to the inverted-phase signal input section is equal at each respective signal input section.

[0094] Furthermore, although the X-axis was used as the reference position in each of the above embodiments, the reference position may be any predetermined position on the light-receiving surface. For example, if the reference position for the multiple element rows 71 to 74 in the first embodiment shown in Figure 3 is set to the first element row 71, it will be as follows. The second element row 72 is located at a distance of -P in the -Y direction from the reference position (first element row 71). The third element row 73 is located at a distance of -2P in the -Y direction from the reference position. The fourth element row 74 is located at a distance of -3P in the -Y direction from the reference position. The sum of the distances to the reference position between the first element row 71, which outputs the A-phase signal that is the input to the differential A-phase signal, and the fourth element row 74, which outputs the AB-phase signal, is given by equation (13). Also, the sum of the distances to the reference position between the second element row 72, which outputs the B-phase signal that is the input to the differential B-phase signal, and the third element row 73, which outputs the BB-phase signal, is given by equation (14).

[0095] 0 + (-3P) = -3P ... (13) (-P) + (-2P) = -3P ... (14)

[0096] As shown in equations (13) and (14), the sum of the distance in the Y direction from the reference position (first element row 71) to the positive-phase signal element row (first element row 71, second element row 72) and the distance in the Y direction from the reference position to the negative-phase signal element row (third element row 73, fourth element row 74) is equal for the difference A-phase signal and the difference B-phase signal. Therefore, the reference position can be any predetermined position on the light-receiving surface. In short, multiple element rows within an element row group only need to be positioned such that the sum of the distance in the orthogonal direction from the reference position to the positive-phase signal element row and the distance in the orthogonal direction from the reference position to the negative-phase signal element row is equal for all phases of at least two phases.

[0097] In the embodiments described above, the encoders 1 and 1A output a differential A-phase signal and a differential B-phase signal as differential signals of two phases, but they may output differential signals of multiple phases as long as they are differential signals of at least two phases. Also, in the embodiments described above, the first element array group 7 and the second element array group 7A each had four element arrays, but they may have six or eight arrays.

[0098] For example, when an encoder outputs differential signals for three phases (A phase, B phase, and C phase), the first element array group and the second element array group each have six element arrays, and these element arrays may be arranged as follows. For example, in the first embodiment, the six element arrays in the element array group may be arranged so that the detection signals they output are A phase signal, B phase signal, C phase signal, CB phase signal, BB phase signal, and AB phase signal, along an orthogonal direction perpendicular to the measurement direction. Furthermore, in the second embodiment, for example, the six element rows in the first element row group may be arranged such that the detection signals they output are in a predetermined reference order, from one side in an orthogonal direction perpendicular to the measurement direction to the other side, as A-phase signal, B-phase signal, C-phase signal, CB-phase signal, BB-phase signal, and AB-phase signal. In the second element row group, the six element rows may be arranged such that the detection signals they output are in the reverse order of the predetermined reference order, from one side in an orthogonal direction perpendicular to the measurement direction to the other side, as C-phase signal, B-phase signal, A-phase signal, AB-phase signal, BB-phase signal, and CB-phase signal.

[0099] In the above embodiments, there were two signal input units 6a and 6b, but they may be increased or decreased depending on the number of element arrays or the number of signals to be acquired, or the signal input units may not be provided at all. Also, in the above embodiments, a calculation means 8 was provided, but for example, an encoder may be connected to an external device and the calculation may be performed by that external device, so the calculation means may not be provided. [Industrial applicability]

[0100] As described above, the present invention can be suitably used in encoders. [Explanation of Symbols]

[0101] 1.1A encoder 2 scales 3,3A detection head 4. Light source (transmitter) 5.5A Light receiving unit (receiver) 50, 50A Light-receiving surface (receiving surface) 7,7A element array 71-78 element array 500 light-receiving elements (receiving elements)

Claims

1. An encoder comprising a plate-shaped scale having markings formed at a predetermined period along the measurement direction, and a detection head provided so as to be movable relative to the scale along the measurement direction, The detection head is A transmitting unit that transmits a measurement signal toward the scale, The receiving unit has a receiving surface that receives the measurement signal from the transmitting unit via the scale, and converts the measurement signal received on the receiving surface into a detection signal which changes in accordance with the period of the scale according to the relative movement between the scale and the detection head, and outputs a differential detection signal of at least two phases with different phases. The receiving surface is, The element array comprises a plurality of receiving elements arranged along the measurement direction at a period corresponding to the scale, and the element array group comprises at least four arrays of the plurality of element arrays arranged in parallel along an orthogonal direction perpendicular to the measurement direction. The plurality of element arrays are arranged for each of the at least two phases, A sequence of positive-sequence signal elements that outputs a positive-sequence signal, It comprises a series of inverted phase signal elements that output an inverted phase signal, The at least two phases are arranged to be offset along the measurement direction by a predetermined phase difference. The plurality of element arrays within the group of element arrays are, An encoder characterized in that it is positioned such that the sum of the distance in the orthogonal direction from the reference position to the row of positive-phase signal elements and the distance in the orthogonal direction from the reference position to the row of negative-phase signal elements is equal for all of the at least two phases.

2. In the encoder described in claim 1, The aforementioned positive-sequence signal element array is Half of the plurality of element rows within the element row group are located in the center of the plurality of element rows arranged in the orthogonal direction on the receiving surface, and are positioned on one side with respect to the center line extending in the measurement direction. The aforementioned inverted phase signal element array is An encoder characterized in that it is half of the plurality of element rows within the element row group and is positioned on the other side of the center line extending in the measurement direction at the center of the plurality of element rows arranged in the orthogonal direction on the receiving surface.

3. In the encoder according to claim 1 or claim 2, The aforementioned group of elements is The system comprises a first group of element arrays, and a second group of element arrays arranged adjacent to the first group of element arrays in the orthogonal direction on the receiving surface, and having a plurality of element arrays arranged differently from the plurality of element arrays in the first group of element arrays. The positive-sequence signal element array of the first element array group is, Half of the plurality of element rows in the first element row group, and arranged in the center of the plurality of element rows arranged in the orthogonal direction in the first element row group, on one side with respect to the center line extending in the measurement direction, and arranged in the first element row group in a predetermined reference order from one end in the orthogonal direction toward the center, The inverse-phase signal element array of the first element array group is, Half of the plurality of element rows in the first element row group, and positioned in the center of the plurality of element rows arranged in the orthogonal direction in the first element row group, on the other side of the center line extending in the measurement direction, and arranged in the first element row group in a predetermined reference order from the other end in the orthogonal direction toward the center, The positive-sequence signal element array of the second group of elements is Half of the plurality of element rows in the second element row group, and in the second element row group, positioned in the center of the plurality of element rows arranged in the orthogonal direction, on one side with respect to the center line extending in the measurement direction, and arranged in the second element row group from one end in the orthogonal direction toward the center in the reverse order of the predetermined reference order, The inverse-phase signal element array of the second element array is, An encoder characterized in that half of the plurality of element rows in the second element row group are located in the center of the plurality of element rows arranged in the orthogonal direction in the second element row group, on the other side of the center line extending in the measurement direction, and are arranged in the second element row group in the reverse order of the predetermined reference order from the other end in the orthogonal direction toward the center.

4. In an encoder according to any one of claims 1 to 3, The aforementioned group of elements is Encoders characterized by being arranged in multiples along the orthogonal direction on the receiving surface.

5. In an encoder according to any one of claims 1 to 4, The detection head is A light source, which acts as a transmitter, irradiates light as a measurement signal toward the aforementioned scale, The system includes a light-receiving surface that receives light from the light source via the scale, and a light-receiving unit that converts the light received on the light-receiving surface into a detection signal that changes in accordance with the period of the scale according to the relative movement between the scale and the detection head, and outputs a differential detection signal of at least two phases with different phases. The light-receiving surface is An encoder characterized by having an element array comprising a plurality of light-receiving elements arranged along the measurement direction at a period corresponding to the scale, and a group of element arrays comprising at least four rows of the plurality of element arrays arranged in parallel along an orthogonal direction perpendicular to the measurement direction.

6. In the encoder described in claim 5, The grid plate comprises a plate-shaped grid having multiple grids formed along the measurement direction at a period corresponding to the scale, The aforementioned grid plate is Displaced between the scale and the light-receiving section, The light receiving unit is An encoder characterized by receiving light through the aforementioned grid plate.

7. An encoder comprising: a plate-shaped scale having markings formed at a predetermined period along the measurement direction; a detection head provided so as to be movable relative to the scale along the measurement direction; and a plate-shaped grid plate having a plurality of grids formed along the measurement direction at a period corresponding to the markings, The detection head is A light source that irradiates light as a measurement signal toward the aforementioned scale, The light receiving unit has a light receiving surface that receives the light from the light source via the scale, and converts the light received on the light receiving surface into a detection signal which changes in accordance with the period of the scale according to the relative movement between the scale and the detection head, and outputs a differential detection signal of at least two phases with different phases. The light-receiving surface is The element array comprises a plurality of light-receiving elements arranged along the measurement direction at a period corresponding to the scale, and the element array group comprises at least four arrays of the plurality of element arrays arranged in parallel along an orthogonal direction perpendicular to the measurement direction. The aforementioned group of elements is Multiple such arrangements are provided along the orthogonal direction on the light-receiving surface. The plurality of element arrays are arranged for each of the at least two phases, A sequence of positive-sequence signal elements that outputs a positive-sequence signal, It comprises a series of inverted phase signal elements that output an inverted phase signal, The at least two phases are arranged to be offset along the measurement direction by a predetermined phase difference. The plurality of element arrays within the group of element arrays are, The device is positioned such that the sum of the distance in the orthogonal direction from the reference position to the positive-sequence signal element array and the distance in the orthogonal direction from the reference position to the negative-sequence signal element array is equal for all phases of at least two phases. The aforementioned grid plate is Displaced between the scale and the light-receiving section, The light receiving unit is An optical encoder characterized by receiving light through the aforementioned grid plate.

8. In the encoder described in claim 7, The aforementioned positive-sequence signal element array is Half of the plurality of element rows within the element row group are located in the center of the plurality of element rows arranged in the orthogonal direction on the light-receiving surface, and are positioned on one side with respect to the center line extending in the measurement direction. The aforementioned inverted phase signal element array is An encoder characterized in that half of the plurality of element rows within the element row group are located in the center of the plurality of element rows arranged in the orthogonal direction on the light-receiving surface, and are positioned on the other side with respect to the center line extending in the measurement direction.

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