Angle detectors and position measuring devices

Abstract

To provide an angle detector and a position measuring device that can perform precise angle detection while eliminating high-order errors and can be miniaturized.SOLUTION: An angle detector includes: a rotary scale having a scale pattern in which multiple patterns are arranged along a circumferential direction and are formed; and multiple detection heads for reading the pattern from each scale pattern. The multiple detection heads are installed while being shifted along a circumferential direction of the rotary scale and are installed while being shifted in a radial direction of the rotary scale.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present case relates to an angle detector and a position measuring device. [Background technology]

[0002] Conventionally, various proposals have been made to detect high-order errors in angle detectors such as rotary encoders in order to detect angles with high accuracy (see, for example, Patent Documents 1 and 2). In Patent Documents 1 and 2, multiple detection heads are arranged on the same circumference with a circumferential offset, thereby enabling detection of high-order errors in the angle detector. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-262518 [Patent Document 2] Japanese Patent Application Laid-Open No. 2006-98392 Summary of the Invention [Problem to be solved by the invention]

[0004] Recently, angle detectors are being required to not only have high-precision angle detection performance but also to be miniaturized. However, when trying to miniaturize the angle detectors disclosed in Patent Document 1 and Patent Document 2, the detector heads are arranged closely together, which may cause interference between the detector heads. For this reason, there is a limit to how miniaturized the angle detectors disclosed in Patent Document 1 and Patent Document 2 can be, and there is room for improvement in this regard.

[0005] In one aspect, the present invention aims to provide an angle detector and a position measuring device that can be miniaturized while enabling high-precision angle detection with high-order errors removed. [Means for solving the problem]

[0006] In one aspect, the angle detector comprises a rotary scale having a scale pattern formed by arranging a plurality of patterns along a circumferential direction, and a plurality of detection heads each reading a pattern from the scale pattern, the plurality of detection heads being offset along the circumferential direction of the rotary scale and also offset in the radial direction of the rotary scale.

[0007] In the above angle detector, the multiple detection heads can include a reference detection head and an nth-order error component detection head installed at a position rotated (360° / 2n) relative to a reference position where the reference detection head is installed, where the reference position is defined as 0°.

[0008] In the angle detector, the plurality of detection heads may be installed at intervals that are equal to N along the circumferential direction around the entire circumference of the scale pattern.

[0009] Furthermore, in the above angle detector, the rotary scale may have a plurality of patterns arranged along a circumferential direction, and may have a plurality of tracks each of which is provided offset in a radial direction, and the plurality of detection heads may be installed corresponding to the plurality of tracks.

[0010] Furthermore, in the angle detector, the plurality of tracks may include a first track and a second track provided circumferentially inward of the first track, and the plurality of detection heads may be arranged such that circumferentially adjacent detection heads are allocated to the first track and the second track.

[0011] Furthermore, in the angle detector, the patterns may each extend radially along a radial direction of the rotary scale.

[0012] In one aspect, a position measuring device comprises a rotary scale having a scale pattern formed by arranging a plurality of patterns along a circumferential direction, and a plurality of detection heads each reading a pattern from the scale pattern, wherein the plurality of detection heads are shifted along the circumferential direction of the rotary scale and also have angle detectors installed shifted in the radial direction of the rotary scale, and a calculation unit that calculates a measurement error based on the angle detection values ​​of the plurality of detection heads.

[0013] In the above-described position measuring device, the plurality of detection heads may include a reference detection head and an nth-order error component detection head installed at a position rotated (360° / 2n) relative to a reference position where the reference detection head is installed, where the reference position is set to 0°, and the calculation unit may obtain a calculated value of the nth-order error component based on the angle detection value detected by the nth-order error component detection head, and subtract the calculated value from the angle detection value detected by the reference detection head to obtain a corrected detection value.

[0014] Furthermore, in the above-described position measuring device, the plurality of detection heads may be installed at N equal intervals along the circumferential direction of the entire circumference of the scale pattern, and the calculation unit may calculate an average value of the angle detection values ​​detected by each of the N detection heads and use the average value as a corrected detection value.

[0015] Furthermore, in the above position measuring device, the rotary scale may have a plurality of patterns arranged along a circumferential direction, and may include a plurality of tracks each of which is provided offset in a radial direction, and the plurality of detection heads may be installed corresponding to the plurality of tracks.

[0016] In addition, in the above-described position measuring device, the plurality of tracks may include a first track and a second track provided circumferentially inward of the first track, and the plurality of detection heads may be installed such that circumferentially adjacent detection heads are allocated to the first track and the second track.

[0017] Furthermore, in the position measuring device, the patterns may each extend radially along the radial direction of the rotary scale. [Effects of the Invention]

[0018] It is possible to provide an angle detector and a position measuring device that can be miniaturized while enabling highly accurate angle detection with high-order errors removed. [Brief explanation of the drawings]

[0019] [Figure 1] FIG. 1 is a schematic diagram showing a schematic configuration of an angle detector according to the first embodiment. [Figure 2] FIG. 2 is a block diagram illustrating the configuration of the position detection device according to the first embodiment. [Figure 3] FIG. 3 is a graph showing an example of the difference tn between the angle detection value of the reference detection head and the angle detection value detected by the nth-order error component detection head in the first embodiment, and the transition of the shift value obtained by shifting the difference tn by X degrees in the circumferential direction. [Figure 4] FIG. 4 is a graph showing the trends of the difference t3 (=sn(0°)) between the angle detection value of the reference detection head and the angle detection value detected by the third-order error component detection head in the first embodiment, the shift value sn(120°) obtained by shifting the difference t3 by 120° in the circumferential direction, and the shift value sn(240°) obtained by shifting the difference t3 by 240° in the circumferential direction. [Figure 5] FIG. 5 is a graph illustrating the third-order error component in the first embodiment. [Figure 6] FIG. 6 is a schematic diagram showing a schematic configuration of an angle detector according to the second embodiment. [Figure 7] FIG. 7 is a schematic diagram showing a schematic configuration of an angle detector according to the third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0020] Hereinafter, embodiments will be described with reference to the drawings.

[0021] (First embodiment) First, an angle detector 1 according to a first embodiment and a position detection device 1000 equipped with this angle detector 1 will be described with reference to FIGS. 1 to 5. FIG. 1 is a schematic diagram illustrating the overall configuration of the angle detector 1 according to the first embodiment. FIG. 2 is a block diagram illustrating the configuration of the position detection device 1000 according to the first embodiment. FIG. 3 is a graph illustrating an example of the difference tn between the angle detection value of the reference detection head 5 and the angle detection value detected by the nth-order error component detection head, and the transition of a shift value obtained by shifting the difference tn by X degrees in the circumferential direction in the first embodiment. FIG. 4 is a graph illustrating the transition of the difference t3 (= sn(0°)) between the angle detection value of the reference detection head 5 and the angle detection value detected by the third-order error component detection head 8 in the first embodiment, the shift value sn(120°) obtained by shifting the difference t3 by 120 degrees in the circumferential direction, and the shift value sn(240°) obtained by shifting the difference t3 by 240 degrees in the circumferential direction in the first embodiment. FIG. 5 is a graph illustrating a third-order error component in the first embodiment.

[0022] Referring to FIG. 1, the angle detector 1 of the first embodiment forms an electromagnetic induction type rotary encoder. The angle detector 1 includes a rotary scale 2, a reference detection head 5, a first-order error component detection head 6, a second-order error component detection head 7, a third-order error component detection head 8, a fourth-order error component detection head 9, and an eighth-order error component detection head 10. Referring to FIG. 2, the position detection device 1000 includes a calculation unit 11. The reference detection head 5, the first-order error component detection head 6, the second-order error component detection head 7, the third-order error component detection head 8, the fourth-order error component detection head 9, and the eighth-order error component detection head 10 are electrically connected to the calculation unit 11. Detection signals are input from these detection heads to the calculation unit 11. The angle detector 1 may also be a photoelectric encoder.

[0023] The angle detector 1 of the first embodiment performs highly accurate angle detection by subtracting high-order error components based on the angle detection values ​​detected by each of the nth-order error component detection heads 6 to 10 from the angle detection value detected by the reference detection head 5.

[0024] It should be noted that the actual dimensions of the reference detection head 5, first-order error component detection head 6, second-order error component detection head 7, third-order error component detection head 8, fourth-order error component detection head 9, and eighth-order error component detection head 10 depicted in Fig. 1 are not shown. In other words, Fig. 1 shows the positional relationship of these detection heads to the rotary scale 2 and the positional relationship between the detection heads, but does not accurately represent the distance between each detection head, the dimensions of each detection head, or the dimensions of the rotary scale 2.

[0025] The rotary scale 2 is a disk-shaped member that is attached to an object (not shown) whose angle is to be detected, with its rotation axis and center of rotation C aligned. The rotary scale 2 has a first track 3 and a second track 4. The first track 3 has a scale pattern 3a including multiple patterns 3a1 arranged along the circumferential direction of the rotary scale 2. The second track 4 has a scale pattern 4a including multiple patterns 4a1 arranged along the circumferential direction of the rotary scale 2. Both the first track 3 and the second track 4 are circular, but the diameter of the first track 3 is larger than the diameter of the second track 4. In other words, the second track 4 is arranged circumferentially inward of the first track 3, so that the first track 3 and the second track 4 are radially offset from each other. Note that while FIG. 1 illustrates the relative positions of the first track 3 and the second track 4, it does not accurately represent the distance between them.

[0026] 1, when the position of θ=0° is taken as the reference position, the reference detection head 5 is installed in alignment with this reference position. The reference detection head 5 is installed at θ=0° and aligned with the first track 3.

[0027] The first-order error component detection heads 6 to eighth-order error component detection heads 10 are installed at positions rotated by (360° / 2n), where n represents the order of the error component. The reference detection head 5 and the first-order error component detection heads 6 to eighth-order error component detection heads 10 are installed such that adjacent detection heads in the circumferential direction are allocated to the first track 3 and the second track 4.

[0028] The first-order error component detection head 6 is installed at θ=180° and aligned with the second track 4. The second-order error component detection head 7 is installed at θ=90° and aligned with the first track 3. The third-order error component detection head 8 is installed at θ=60° and aligned with the second track 4. The fourth-order error component detection head 9 is installed at θ=45° and aligned with the first track 3. The eighth-order error component detection head 10 is installed at θ=22.5° and aligned with the second track 4.

[0029] The eighth-order error component detection head 10 is positioned in alignment with the second track 4 because the reference detection head 5, which is circumferentially adjacent to the eighth-order error component detection head 10, is positioned on the first track 3. The fourth-order error component detection head 9 is positioned in alignment with the first track 3 because the eighth-order error component detection head 10, which is circumferentially adjacent to the fourth-order error component detection head 9, is positioned on the second track 4. The third-order error component detection head 8 is positioned in alignment with the second track 4 because the fourth-order error component detection head 9, which is circumferentially adjacent to the third-order error component detection head 8, is positioned on the first track 3. The second-order error component detection head 7 is positioned in alignment with the first track 3 because the third-order error component detection head 8, which is circumferentially adjacent to the second-order error component detection head 7, is positioned on the second track 4. The first-order error component detection head 6 is positioned in alignment with the second track 4 because the second-order error component detection head 7, which is circumferentially adjacent to the first-order error component detection head 6, is positioned on the first track 3.

[0030] In this way, by distributing and arranging circumferentially adjacent detection heads on the first track 3 and the second track 4, interference between the detection heads can be avoided. In other words, the detection heads can be installed close to each other, allowing the angle detector 1 to be made more compact. In particular, five detection heads are installed between θ=60° and θ=90°. If these detection heads were installed on a single circumference, the circumferential distance required for installation would be long, making it difficult to make the angle detector 1 more compact. In contrast, by arranging the detection heads with a radial offset as in the first embodiment, interference between the detection heads can be avoided.

[0031] Here, an example of an angle detection method using the position detection device 1000 of the first embodiment will be described. First, the principle of the angle detection method in the first embodiment will be described. This principle is consistent with the processing performed by the angle detector disclosed in Japanese Patent Application Laid-Open No. 2003-262518. To detect an angle using the position detection device 1000, first, (1) an angle detection value is acquired in advance for each nth-order error component detection head, and each higher-order error component is calculated based on this. Then, (2) these higher-order error components are subtracted from the angle detection value acquired by the reference detection head 5. Below, the angle detection method will be described in accordance with this principle. Note that calculations such as subtraction are performed by the calculation unit 11.

[0032] First, we will explain how to obtain the nth-order high-order error component. To obtain the nth-order high-order error component, we calculate the difference tn between the angle detection value obtained by the reference detection head 5 installed at an angle θ = 0° and the angle detection value obtained by the nth-order error component detection heads 6 to 10 installed at an angle θ = 360° / 2. Here, if the angle detection value detected by the detection head installed at angle θ is expressed as GS(θ), the angle detection value detected by the reference detection head 5 will be expressed as GS(0°). Similarly, the angle detection value detected by the nth-order error component detection head will be expressed as GS(360° / 2n).

number

[0033] Then, the difference tn represented by Equation (1) is obtained over one cycle. Here, a value obtained by shifting the difference tn by an angle of X° from θ = 0° is defined as a shift value sn(X°). An example of the shift value sn(X°) is represented as a graph shown in FIG. 3.

[0034] The sum of the shift values sn(X°) defined in this way becomes the total value Gn of the nth-order error component. That is, the total value Gn can be obtained by the following Equation (2).

Equation

[0035] By calculating the total value Gn for each nth-order error component using Equation (2) and subtracting them from the angle detection value obtained by the reference detection head 5, highly accurate angle detection with higher-order errors removed can be performed. In Equation (2), k is an integer satisfying 0 ≦ k < n.

[0036] Here, to show an example of calculating the nth-order higher-order error component, the calculation of G3, that is, the total value of the third-order error component when n = 3, will be described.

[0037] To calculate the total value G3 of the third-order error component, first, the difference t3 is calculated using the following Equation (3). The difference t3 is the difference between the angle detection value GS(0°) of the reference detection head 5 installed at the position of θ = 0° and the angle detection value GS(60°) of the third-order error component detection head 8 installed at the position of θ = 60°. θ = 60° is obtained by substituting n = 3 into (360° / 2n).

Equation

[0038] Next, the difference t3 expressed by equation (3) is calculated over one cycle. Here, the shift value sn(0°) obtained by shifting the difference t3 by 0°, the shift value sn(120°) obtained by shifting the difference t3 by 120°, and the shift value sn(240°) obtained by shifting the difference t3 by 240° are calculated. The shift value sn(0°) is the value when k=0 in equation (2), the shift value sn(120°) is the value when k=1 in equation (2), and the shift value sn(240°) is the value when k=2 in equation (2). Note that the shift value sn(0°) is the value when the difference t3 is not shifted at all, and is therefore the difference t3 itself.

[0039] The shift values ​​sn(0°), sn(120°), and sn(240°) can be plotted as shown in the graph in Fig. 4. By summing these shift values ​​using equation (4), the total value G3 of the third-order error components plotted in the graph in Fig. 5 can be obtained.

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[0040] The n-th order error components other than the third order error components can also be calculated in a similar manner. The calculation unit 11 subtracts each of the total values ​​Gn calculated in this manner from the angle detection value acquired by the reference detection head 5 to obtain the final detected angle value.

[0041] The angle detector 1 of the first embodiment is capable of highly accurate angle detection with high-order errors removed, since multiple detection heads are arranged at offset positions along the circumferential direction of the rotary scale 2. Furthermore, since multiple detection heads are arranged at offset positions in the radial direction of the rotary scale 2, the angle detector 1 can be made smaller.

[0042] The angle detector 1 of the first embodiment includes a reference detection head 5 and an n-th order error component detection head installed at a position rotated (360° / 2n) from the reference position where the reference detection head 5 is located, where 0° is defined. This enables highly accurate angle detection with high-order errors removed.

[0043] According to the angle detector 1 of the first embodiment, the rotary scale 2 has multiple tracks arranged with a radial offset, and multiple detection heads are arranged corresponding to the multiple tracks, so that the angle detector 1 can be made smaller.

[0044] Furthermore, the angle detector 1 of the first embodiment has a first track 3 and a second track 4 provided circumferentially inward of the first track 3, and circumferentially adjacent detection heads are allocated to the first track 3 and the second track 4. This makes it possible to avoid interference between the detection heads and to reduce the size of the angle detector 1.

[0045] (Second embodiment) Next, an angle detector 50 according to a second embodiment will be described with reference to Fig. 6. Fig. 6 is a schematic diagram showing a general configuration of the angle detector 50 according to the second embodiment.

[0046] 6, the angle detector 50 of the second embodiment forms an electromagnetic induction type rotary encoder. The angle detector 50 includes a rotary scale 2 and first to eighth detection heads 51 to 58. The rotary scale 2 is the same as that employed in the first embodiment, and therefore a detailed description thereof will be omitted here.

[0047] The first detection head 51 to the eighth detection head 58 are provided in place of the reference detection head 5 and the first-order error component detection heads 6 to 8th-order error component detection heads 10 in the first embodiment. Therefore, the first detection head 51 to the eighth detection head 58 are electrically connected to the calculation unit 11 (see FIG. 2), similar to the reference detection head 5 and the first-order error component detection heads 6 to 8th-order error component detection heads 10 in the first embodiment. Detection signals are input from these detection heads to the calculation unit 11. The angle detector 1 may be a photoelectric encoder.

[0048] The first to eighth detection heads 51 to 58 are installed at equal intervals of N=8 along the circumferential direction of the entire circumference of the rotary scale 2. Specifically, the first detection head 51 is installed at a position of θ=0°, the second detection head 52 at a position of θ=45°, the third detection head 53 at a position of θ=90°, and the fourth detection head 54 at a position of θ=135°. The fifth detection head 55 is installed at a position of θ=180°, the sixth detection head 56 at a position of θ=225°, the seventh detection head 57 at a position of θ=270°, and the eighth detection head 58 at a position of θ=315°.

[0049] These first to eighth detection heads 51 to 58 are installed so as to be offset in the radial direction of the rotary scale 2. Specifically, the first to eighth detection heads 51 to 58 are installed so that adjacent detection heads in the circumferential direction are allocated to the first track 3 and the second track 4. In other words, of the first to eighth detection heads 51 to 58, the first detection head 51, the third detection head 53, the fifth detection head 55, and the seventh detection head 57 are installed in accordance with the first track 3. Furthermore, the second detection head 52, the fourth detection head 54, the sixth detection head 56, and the eighth detection head 58 are installed in accordance with the second track 4.

[0050] In this way, interference between the detection heads can be avoided by distributing the circumferentially adjacent detection heads to the first track 3 and the second track 4. In other words, the detection heads can be installed close to each other, which allows the angle detector 50 to be made smaller.

[0051] Here, an example of the relationship between the dimensions of each detector head and the dimensions of the rotary scale 2 will be described. Assume that the dimension of each detector head along the circumferential direction of the rotary scale 2 is approximately 40 mm. Assume also that the diameter of the rotary scale 2 is 60 mm. In this case, since the circumferential length of the rotary scale is 60π mm, if multiple detector heads are to be installed on one circumference, the maximum number of detector heads is four, and it is not possible to install five or more detector heads. In contrast, if multiple detector heads are installed with a radial offset on the rotary scale 2, as in this embodiment, there is room to install five or more detector heads. This extra space for installing the detector heads allows the angle detector 50 to be made smaller.

[0052] In the second embodiment, eight detection heads are installed, but by installing these detection heads while shifting them in the radial direction of the rotary scale 2, it is possible to reduce the size of the angle detector 50 while maintaining the circumferential arrangement of the detection heads. Note that in the angle detector 50 of the second embodiment, N=8, and the detection heads are installed at intervals where 360° (=2π) is equally divided into eight, but the number of equal divisions is not limited to this, and N can be any natural number other than 1.

[0053] In this way, when multiple detection heads are installed at N equal intervals around the entire circumference of the rotary scale 2, angle detection can be performed using the "equal division averaging method." The "equal division averaging method" is a technique used to perform high-precision angle detection using multiple detection heads, and the second embodiment also performs calculations that follow the basic principles of this "equal division averaging method." An example of angle detection in the second embodiment will be described below. In the following description, θ=0° is set as the reference position.

[0054] Here, the detection heads installed at positions where 2π is equally divided into N are numbered as k=0, 1, ..., N-1, and the angle detection value of each detection head is expressed as L kThen, the detected angle value M obtained by the equal division averaging method is expressed by the general formula shown in Equation (5). In this embodiment, the first detection head 51 is installed at the reference position of θ=0°, and this first detection head 51 corresponds to the detection head with k=0. The second detection head 52 corresponds to the detection head with k=1, and the corresponding relationships are set in a similar manner for the third detection head 53 and the following detection heads.

number

[0055] By performing calculations using equation (5), highly accurate angle detection can be performed. Here, the reason why highly accurate angle detection can be performed by using equation (5) will be explained by generalizing the angle detection value, etc.

[0056] In general, the detection value H(θ) of the detection head for the position θ relative to the reference position of the rotary encoder is expressed by the following equation (6).

number

[0057] In equation (6), θ is the angular position expressed in the range of 0 to 2π from the reference position, and ε(θ) is the error term. The detection heads placed at positions that divide 2π into N equal parts are numbered k=0, 1, ..., N-1. If θ=0° where the 0th detection head is installed is taken as the reference position, then for the kth detection head, the phase of the error term is shifted by 2πk / N, and the detected value H n,k (θ) is expressed by the following equation (7).

number

[0058] Since a rotary encoder returns to its original position after one rotation, the error term is a closed periodic curve, and is therefore expressed as in equation (8) below.

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[0059] In equation (8), Cn is the amplitude of the nth-order component of the error, and αn is the phase shift of the nth-order component of the error.

[0060] Here, the average value A of the angle detection values ​​of N detection heads N,k Considering (θ), it can be expressed as the following equation (9).

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[0061] Then, by rearranging this equation (9), the following equation (10) is obtained.

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[0062] Furthermore, by substituting equation (8) for ε into equation (10), the following equation (11) is obtained.

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[0063] Here, if j is an arbitrary natural number, the following equations (12) and (13) hold. When n=jN

number

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[0064] Equations (12) and (13) are the average value A of the angle detection values ​​of the equally spaced detection heads. N,k This shows that only errors of multiples of N remain in (θ), and the other components become zero.

[0065] Therefore, when eight detection heads are installed at equal intervals as in the second embodiment, if the equal interval averaging method is used, the remaining error components will be 8th order, 16th order, 24th order, etc. In other words, errors of 1st to 7th order, 9th to 15th order, 17th to 23rd order, etc. can be eliminated, and as a result, angle detection can be performed with high accuracy.

[0066] The angle detector 50 of the second embodiment is capable of highly accurate angle detection with high-order errors removed, since multiple detection heads are arranged at offset positions along the circumferential direction of the rotary scale 2. Furthermore, since multiple detection heads are arranged at offset positions in the radial direction of the rotary scale 2, the angle detector 1 can be made smaller.

[0067] The angle detector 50 of the second embodiment includes a plurality of detection heads that are installed at equal intervals of N along the circumferential direction around the entire circumference of the rotary scale 2. This allows for highly accurate angle detection using the equal interval averaging method.

[0068] According to the angle detector 50 of the second embodiment, the rotary scale 2 has multiple tracks arranged with a radial offset, and multiple detection heads are arranged corresponding to the multiple tracks, so that the angle detector 50 can be made smaller.

[0069] Furthermore, the angle detector 50 of the second embodiment has a first track 3 and a second track 4 provided circumferentially inward of the first track 3, and circumferentially adjacent detection heads are allocated to the first track 3 and the second track 4. This makes it possible to avoid interference between the detection heads and reduce the size of the angle detector 50.

[0070] (Third embodiment) Next, an angle detector 100 according to a third embodiment will be described with reference to Fig. 7. Fig. 7 is a schematic diagram showing a general configuration of the angle detector 100 according to the third embodiment.

[0071] The angle detector 100 of the third embodiment is equipped with a rotary scale 102 instead of the rotary scale 2 equipped in the angle detector 50 of the second embodiment. In other respects, there is no difference from the angle detector 50 of the second embodiment, so the common components are given the same reference numerals in the drawings and detailed description thereof will be omitted.

[0072] The rotary scale 102 has patterns 103 extending radially along its diameter. In other words, the rotary scale 102 has patterns 103 instead of the first track 3 and second track 4 that the rotary scale 2 of the first and second embodiments has.

[0073] The angle detector 100, like the angle detector 50 of the second embodiment, is equipped with first to eighth detection heads 51 to 58 that are installed at equal intervals of N=8 along the circumferential direction of the entire circumference of the rotary scale 102. Therefore, like the angle detector 50, the angle detector 100 can perform angle detection with high precision using the equal interval averaging method. Furthermore, because the first to eighth detection heads 51 to 58 are installed at radially offset positions within the radial range of the rotary scale 102 on which the pattern 103 is provided, the angle detector 100 can be made smaller.

[0074] The angle detector 100 may employ the reference detection head 5 and the first-order error component detection heads 6 to 8th-order error component detection heads 10 in the first embodiment instead of the first detection head 51 to the eighth detection head 58. In this case, highly accurate angle detection can be performed in the same manner as described in the first embodiment.

[0075] Although the embodiments of the present invention have been described in detail above, the present invention is not limited to such specific embodiments, and various modifications and variations are possible within the scope of the gist of the present invention as defined in the claims. [Explanation of symbols]

[0076] 1.50 Angle detector 2, 102 rotary scale 3 Track 1 3a, 4a scale patterns 3a1, 4a1, 103 patterns 4. Track 2 5 Reference detection head 6 First-order error component detection head 7 Second-order error component detection head 8 Third-order error component detection head 9 Fourth-order error component detection head 10 8th-order error component detection head 11 Arithmetic section 51 First detection head 52 Second detection head 53 Third detection head 54 4th detection head 55 5th detection head 56 6th detection head 57 7th detection head 58 8th detection head

Claims

1. a rotary scale having a scale pattern formed by arranging a plurality of patterns in a circumferential direction; a plurality of detection heads each reading the pattern from the scale pattern; the plurality of detection heads are disposed so as to be shifted along the circumferential direction of the rotary scale and so as to be shifted in the radial direction of the rotary scale, an angle detector characterized in that the plurality of detection heads include a reference detection head and an n-th order error component detection head installed at a position rotated by (360° / 2n) relative to a reference position where the reference detection head is installed, where the reference position is defined as 0°.

2. the rotary scale has a plurality of patterns arranged along a circumferential direction, and includes a plurality of tracks provided so as to be offset from one another in a radial direction; 2. The angle detector according to claim 1, wherein the plurality of detection heads are installed corresponding to the plurality of tracks.

3. the plurality of tracks include a first track and a second track provided radially inward of the first track, 3. The angle detector according to claim 2, wherein the plurality of detection heads are arranged such that adjacent detection heads in the circumferential direction are allocated to the first track and the second track.

4. 2. The angle detector according to claim 1, wherein each of the patterns extends radially along a radial direction of the rotary scale.

5. a rotary scale having a scale pattern formed by arranging a plurality of patterns in a circumferential direction; a plurality of detection heads each reading the pattern from the scale pattern; the plurality of detection heads are offset along the circumferential direction of the rotary scale, and angle detectors are installed offset in the radial direction of the rotary scale; and a calculation unit that calculates a measurement error based on angle detection values ​​of the plurality of detection heads, the plurality of detection heads include a reference detection head and an n-th order error component detection head installed at a position rotated by (360° / 2n) relative to a reference position where the reference detection head is installed, where the reference position is defined as 0°; a calculation unit for calculating an nth-order error component based on the angle detection value detected by the nth-order error component detection head, and subtracting the calculated value from the angle detection value detected by the reference detection head to obtain a corrected detection value;

6. the rotary scale has a plurality of patterns arranged along a circumferential direction, and includes a plurality of tracks provided so as to be offset from one another in a radial direction; 6. The position measuring device according to claim 5, wherein the plurality of detection heads are installed corresponding to the plurality of tracks.

7. the plurality of tracks include a first track and a second track provided radially inward of the first track, 7. The position measuring device according to claim 6, wherein the plurality of detection heads are arranged such that adjacent detection heads in the circumferential direction are allocated to the first track and the second track.

8. 6. The position measuring device according to claim 5, wherein each of the patterns extends radially along the radial direction of the rotary scale.

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