Encoder

Abstract

This encoder comprises: a rotary disk which has formed thereon a magnetically detectable coded pattern; an array-type magnetic sensor which is formed by arranging a plurality of magnetic sensor elements in an array so as to detect the coded pattern on the rotary disk; an AD converter which perform AD conversion on the output of the array-type magnetic sensor; and a position calculation unit for determining the position of the rotary disk on the basis of information related to the position of the rotary disk obtained by reading the coded pattern in accordance with the output of the AD converter, and on the basis of a calculation result performed on the position of one pattern in the coded pattern with accuracy finer than the array pitch of the plurality of magnetic sensor elements in accordance with the output of the AD converter.

Description

Encoder

[0001] The present disclosure relates to encoders.

[0002] Encoders are sensors used in combination with, for example, robot joint axes or servo motors to detect the position (angle) of such measurement objects. Known types of encoders include incremental encoders and absolute encoders. An incremental encoder outputs incremental signals (A-phase and B-phase signals) that indicate an increase or decrease in the rotational position of the target axis. An absolute encoder outputs absolute position information (angle information) of the target axis.

[0003] For example, an absolute encoder acquires the absolute position (angle information) of a rotating disk by optically reading the code of an absolute track formed on the rotating disk. Also known is an encoder that forms an absolute pattern on the rotating disk by magnetizing it and magnetically reads the absolute pattern (see Patent Document 1).

[0004] Japanese Patent Application Laid-Open No. 2017-215301

[0005] Encoders are required to have high reliability and stability, as well as high accuracy and high resolution. Optical encoders such as those described above have the disadvantage of being susceptible to dust because they optically read patterns. To achieve high accuracy and high resolution, encoders are known that have an incremental track alongside an absolute track and optically read this, but even in this case, the optical system still has the disadvantage of being susceptible to dust. A configuration that magnetically reads patterns formed on a rotating disk can be one way to overcome the disadvantage of optical encoders being susceptible to dust. There is a demand for an encoder that can achieve high accuracy and high resolution even when using a configuration that magnetically reads patterns.

[0006] One aspect of the present disclosure is an encoder comprising: a rotating disk on which a magnetically detectable coding pattern is formed; an array-type magnetic sensor formed by arranging a plurality of magnetic sensor elements in an array so as to detect the coding pattern of the rotating disk; an AD converter that performs AD conversion of the output of the array-type magnetic sensor; and a position calculation unit that determines the position of the rotating disk based on information regarding the position of the rotating disk obtained by reading the coding pattern based on the output of the AD converter, and a result of calculating the position of one pattern in the coding pattern with an accuracy finer than the arrangement pitch of the plurality of magnetic sensor elements based on the output of the AD converter.

[0007] These and other objects, features and advantages of the present invention will become more apparent from the detailed description of exemplary embodiments of the invention illustrated in the accompanying drawings.

[0008] 1 is a diagram illustrating an example of a 4-bit M sequence. FIG. 2 is a schematic diagram of a 4-bit M sequence formed on a single track on a rotating disk. FIG. 3 is a diagram for explaining reading of a 4-bit M sequence on a rotating disk by a sensor. FIG. 4 is a diagram illustrating the configuration of a rotating disk in an encoder according to a first embodiment. FIG. 5 is a side view of an encoder according to a first embodiment. FIG. 6 is a front view of an encoder according to a first embodiment. FIG. 7 is a diagram illustrating a correspondence relationship between an 8-bit M sequence pattern, an array-type magnetic sensor, and a detected waveform. FIG. 8 is a diagram illustrating the configuration of a detection circuit of an encoder according to a first embodiment. FIG. 9 is a diagram for explaining sub-pixel processing by centroid calculation. FIG. 10 is a diagram for explaining sub-pixel processing by edge detection. FIG. 11 is a schematic diagram of a rotating disk in an encoder according to a second embodiment. FIG. 12 is a side view of an encoder according to a second embodiment. FIG. 13 is a front view of an encoder according to a second embodiment. FIG. 14 is a diagram for explaining a first example of magnetization in the second embodiment. FIG. 15 is a diagram for explaining a first example of magnetization in the second embodiment. FIG. 16 is a diagram for explaining a second example of magnetization in the second embodiment. FIG. 17 is a diagram for explaining a second example of magnetization in the second embodiment. FIG. 10 is a diagram illustrating a configuration of a detection circuit of an encoder according to a second embodiment.

[0009] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In the drawings, like components or functional parts are designated by like reference numerals. The scale of these drawings has been changed appropriately to facilitate understanding. Furthermore, the embodiment shown in the drawings is one example for implementing the present invention, and the present invention is not limited to the illustrated embodiment.

[0010] An encoder according to an embodiment of the present disclosure detects the position (angle) of a rotating disk by reading, with an array-type magnetic sensor, an encoding pattern formed on the rotating disk that can be magnetically detected. In the embodiment described below, the encoding pattern is assumed to be an absolute pattern, and an example will be described in which an M-sequence code, which is a pseudo-random code, is used as the absolute pattern. The M-sequence is an abbreviation for Maximum Length Shift Register Sequence, and is a sequence with the longest period among code sequences generated by a certain number of shift register stages or delay elements.

[0011] First, the generation of the M-sequence and the principle of detecting the absolute position of the rotating disk when the M-sequence code is used for the rotating disk will be described.

[0012] Figure 1 shows the generator polynomial X ４ +X １ = 0 (where + is an exclusive OR). Using this generating polynomial, a 4-bit M sequence is obtained by the following procedure: (1) A 4-bit string (X ４ , X ３ , X ２ , X １ ) is set to all 1s (number 0 in Figure 1). (2) The result of the generator polynomial (generated value) is obtained. (3) The result is added to the beginning of the 4-bit string, and the upper 4 bits of the resulting bit string are shifted to the right to become the value of the next stage (number 1 in Figure 1). (4) By repeating the above steps (2) and (3), 2 ４ -1 = 15 different data types are generated. (5) To make the number of data a multiple of 2, all-0 data, which is not generated by the generating polynomial, is inserted into number 12 to obtain 16 different data types.

[0013] FIG. 2 is a schematic diagram showing the M sequence generated by steps (1) to (5) above, formed on a single track on a rotating disk. The rotating disk 21 shown in FIG. 2 has an M sequence absolute track 22 formed on its outer periphery. A sensor 23 is disposed relative to the rotating disk 21 as shown in FIG. 3. In the state shown on the left side of FIG. 3, the sensor 23 reads data "1111," and the position (angle) of the rotating disk 21 is obtained by obtaining the angle associated with the data "1111" from a table or the like. Here, it is assumed that the M sequence code and the angle of the rotating disk 21 are associated as shown in FIG. 1. In this case, it is determined from the data "1111" that the angle of the rotating disk 21 is 360 degrees (0 degrees). When the rotating disk 21 rotates as shown on the right side of FIG. 3, the data obtained by the sensor 23 indicates "1110," and therefore, it is possible to determine from the table that the position (angle) of the rotating disk 21 is 337.5 degrees.

[0014] The above is the principle of obtaining the absolute position of a rotating disk using an absolute track. In this embodiment, an M-series absolute track is formed on the rotating disk as a magnetically detectable pattern, and the code of the absolute track is read by an array magnetic sensor. This configuration makes it possible to overcome the disadvantage of optical encoders, which are susceptible to dust. Furthermore, as will be explained in detail below, the encoder according to this embodiment is configured to be able to output position information with an accuracy equivalent to sub-pixel accuracy when each magnetic sensor element of the array magnetic sensor corresponds to one pixel of an optical sensor, thereby achieving position detection with high accuracy and high resolution.

[0015] Two examples of the encoder according to this embodiment will be described below. The first example is a configuration example in which the rotary disk is made of a magnetic material and a pattern of 1s or 0s is formed by cutting out slits. The second example is a configuration example in which the pattern of 1s or 0s is formed by magnetizing the rotary disk.

[0016] First Embodiment FIG. 4 shows the configuration of the rotating disk 121 in the encoder 101 (see FIG. 5) according to the first embodiment. The rotating disk 121 is made of a magnetic material such as metal. A single M-sequence track 122 is formed on the outer periphery of the rotating disk 121. In FIG. 4, an enlarged view of the M-sequence track in the portion enclosed by the dashed rectangle is shown on the right side. As shown in the figure, the patterns "1" and "0" of the M-sequence track 122 are formed by cutting out slits in the outer periphery of the rotating disk 121. In this embodiment, the circumferential width of the slits 122a for the pattern "1" is made wider than the circumferential width of the slits 122b for the pattern "0", thereby enabling the patterns "1" and "0" to be distinguished when detected by a magnetic sensor. For convenience of explanation, the enlarged view on the right side of FIG. 4 shows that the 8-bit pattern of the slits in this portion is "11110101". As shown in the figure, each slit is rectangular, and is formed so that its geometric center is equidistantly spaced in the circumferential direction of the rotary disk 121 .

[0017] In this embodiment, the M sequence code is an 8-bit code. When an 8-bit M sequence code is used, the absolute position (angle) of the rotating disk 121 can be detected with a resolution of 256 levels. Note that the 8-bit M sequence code is an example, and an M sequence code with another number of bits may also be used.

[0018] 5A and 5B show a schematic configuration of an encoder 101 according to the first embodiment. FIG. 5A is a side view of the encoder 101 when the rotating disk 121 is viewed from the side. FIG. 5B is a front view of the encoder 101 when viewed from the direction of arrow A in FIG. 5A. A rotating shaft 121a of the rotating disk 121 is connected to the rotating shaft of a detection target (such as a servo motor). A printed circuit board 130 is disposed so as to face the surface of the rotating disk 121. An array-type magnetic sensor 140 is mounted on a surface 130a of the printed circuit board 130 facing the rotating disk, in a portion facing the outer periphery (M-sequence track 122) of the rotating disk 121. A permanent magnet (hereinafter referred to as "magnet") 150 is mounted on a surface 130b of the printed circuit board 130 opposite the rotating disk, in a portion facing the array-type magnetic sensor 140.

[0019] As shown in FIG. 5B , the array-type magnetic sensor 140 has a configuration in which a plurality of magnetic sensor elements 141 are arranged in an array substantially parallel to the circumferential direction of the rotating disk 121. Note that in FIG. 5B , to avoid complication, only one magnetic sensor element is denoted by the reference numeral 141. As shown in FIG. 5B , the array-type magnetic sensor 140 has a width D corresponding to the width of 8 bits of the M-sequence (the width of 8 slits) in a direction substantially parallel to the circumferential direction of the rotating disk 121 (the horizontal direction in FIG. 5B ). The number of magnetic sensor elements included in the array-type magnetic sensor 140 (i.e., the number of magnetic sensor elements 141 arranged substantially parallel to the circumferential direction of the rotating disk 121) is, for example, 256 or 512, but a different number of magnetic sensor elements may also be arranged. Hereinafter, it is assumed that the number of magnetic sensor elements 141 included in the array-type magnetic sensor 140 is 256.

[0020] The array-type magnetic sensor 140 configured as described above can be considered as a sensor that magnetically images a coded pattern when compared to the configuration of an optical sensor in which multiple pixels are arranged in an array. In this case, each magnetic sensor element 141 corresponds to a pixel of the optical sensor.

[0021] Similarly, the magnet 150 may have a width substantially equal to the width D or slightly larger than the width D in a direction substantially parallel to the circumferential direction of the rotating disk 121 (the horizontal direction in FIG. 5B ). The magnet 150 is arranged so that the magnetic poles are oriented substantially perpendicular to the surface of the rotating disk 121.

[0022] Fig. 6 is a diagram schematically showing the correspondence relationship between an 8-bit M sequence pattern, the array magnetic sensor 140 (256 magnetic sensor elements 141), and the detection waveform acquired by the array magnetic sensor 140. Here, the symbol R represents the width of an area equivalent to one slit in the M sequence track 122. Note that Fig. 6 is intended to conceptually show the correspondence relationship between the 8-bit M sequence pattern and the array magnetic sensor 140, and does not show the actual strict arrangement relationship. Reading of the M sequence pattern from the rotating disk 121 will be described with reference to Figs. 5B and 6.

[0023] As shown in FIG. 5B , the magnet 150 has its magnetic poles oriented perpendicular to the surface of the rotating disk 121. The array magnetic sensor 140 is disposed between the rotating disk 121 and the magnet 150. The rotating disk 121 is formed of a magnetic material, and the magnetic material is hollowed out in the areas corresponding to the patterns "1" and "0." In this case, magnetic flux from the magnet 150 is generated toward the magnetic material of the rotating disk 121. Therefore, the magnetic flux density between the magnet 150 and the rotating disk 121 (i.e., the magnetic flux density detected by the array magnetic sensor 140) is low directly below the slits of the rotating disk 121 and high directly below the areas where the magnetic material is present (i.e., areas without slits). Therefore, the array magnetic sensor 140 can detect the presence or absence of a pattern based on the magnitude of the detected magnetism. Furthermore, the width of the slits formed on the rotating disk 121 is formed so that the slit width of the pattern "1" is larger than the slit width of the pattern "0." Therefore, it is possible to distinguish between pattern "1" and pattern "0" based on the difference in width of the area where the magnetism detected by the array-type magnetic sensor 140 is reduced.

[0024] Each magnetic sensor element 141 may be a magnetic sensor of a type that detects the magnitude of magnetism (such as a magnetic sensor using a Hall element), or may be a magnetic sensor of a type that detects the vector of magnetism (such as a TMR (Tunnel Magneto-Resistance Effect) sensor). When a magnetic sensor of a type that detects the vector of magnetism is used as the magnetic sensor element 141, it is preferable to arrange the magnetic sensor so that its detection sensitivity is in a direction along the orientation of the magnetic pole of the magnet 150, i.e., in a direction perpendicular to the surface of the rotating disk 121.

[0025] Using the above measurement principle, as conceptually shown in FIG. 6 , an 8-bit M-sequence code "11110101" can be detected by an array of 256 magnetic sensor elements in the array magnetic sensor 140, thereby obtaining a detected waveform 145 as shown in the bottom row of FIG. 6 . If the array magnetic sensor 140 has 256 magnetic sensor elements 141, the number of magnetic sensor elements required to detect one pattern ("0" or "1") is 32. The detected waveform 145 is an example of a case in which the detection circuit is configured so that the height of the waveform increases as the detected magnetic field decreases. Therefore, the detected waveform 145 has a peak-shaped waveform with an upward projection at the portion where the slit (i.e., pattern "1" or pattern "0") exists. The width of the peak-shaped waveform corresponding to each slit is wide for pattern "1" and narrow for pattern "1." Therefore, by detecting the difference in the width of the peak-shaped waveform, it is possible to distinguish between pattern "1" and pattern "0."

[0026] 7 shows the configuration of a detection circuit for reading out the output of the array-type magnetic sensor 140 and detecting the absolute value of the rotating disk 121. The detection circuit includes a readout circuit 131, an AD converter 132, and a position calculation unit 133. The position calculation unit 133 includes a subpixel processing unit 134. The readout circuit 131 is a circuit for outputting the magnetic strength detected by each magnetic sensor element 141 as a voltage. For example, if the magnetic sensor element 141 is a type of sensor whose resistance value changes depending on the magnetic strength, the readout circuit 131 has a circuit configuration for outputting a voltage whose magnitude depends on the resistance value of the magnetic sensor element 141. The readout circuit 131 reads out the output from the magnetic sensor element array arranged in the array-type magnetic sensor 140 and outputs it to the AD converter 132.

[0027] Analog signals representing the individual detection results of the magnetic sensor elements 141 are provided from the readout circuit 131 to the AD converter 132 and converted into digital values. The number of quantization bits of the AD converter 132 is, for example, 12 bits. In this case, the amplitude of the analog signal (detected magnetic value) is converted into a 12-bit digital value. Note that the number of quantization bits of the AD converter 132, 12, is an example, and the AD converter 132 may have another number of quantization bits.

[0028] The position calculation unit 133 calculates the absolute position of the rotating disk 121 based on the detection values ​​of each magnetic sensor element 141 output from the AD converter 132. The position calculation unit 133 recognizes the M-sequence pattern by distinguishing between patterns "1" and "0" from waveform data representing an 8-bit M-sequence pattern detected by the array magnetic sensor 140. The position calculation unit 133 then references a table previously stored in a storage unit that associates 8-bit M-sequence codes with absolute positions (angles) of the rotating disk, and obtains the absolute position (angle) of the rotating disk 121 corresponding to the read M-sequence pattern. In other words, the position calculation unit 133 obtains the absolute position of the rotating disk 121 by decoding the M-sequence pattern. The absolute position of the rotating disk 121 recognized at this stage is an absolute position with a resolution of 8 bits (256 levels).

[0029] The subpixel processing unit 134 of the position calculation unit 133 executes processing for detecting the position (angle) of the rotating disk 121 with subpixel accuracy when the magnetic sensor element rows arranged in the array magnetic sensor 140 correspond to the pixels in the optical sensor (this processing will be referred to as subpixel processing in this specification). The subpixel processing is processing for calculating the absolute position (angle) of the rotating disk 121 with higher accuracy (subpixel accuracy) than the array pitch (pixel pitch) of the magnetic sensor elements of the array magnetic sensor 140. As a result, the position calculation unit 133 can ultimately output the absolute position (angle) of the rotating disk 121 calculated with subpixel accuracy.

[0030] The following describes the sub-pixel processing performed by the sub-pixel processing unit 134. The sub-pixel processing unit 134 can perform sub-pixel processing by centroid calculation or sub-pixel processing by edge detection.

[0031] FIG. 8 is a diagram illustrating subpixel processing using centroid calculation. In subpixel processing using centroid calculation, the position of each slit is determined more precisely by the centroid calculation. The top row of FIG. 8 shows one slit (pattern PT is "1" or "0"), and the middle row of FIG. 8 shows a magnetic sensor element array corresponding to one slit. As described above, if the total number of magnetic sensor elements 141 in the array-type magnetic sensor 140 is 256, the number of magnetic sensor elements corresponding to one slit will be 32. The bottom row of FIG. 8 shows the AD-converted value (reference numeral 151) of the waveform detected by the magnetic sensor element array in the middle row of FIG. 8 for the pattern PT (slit) in the top row of FIG. 8. The waveform in the bottom row of FIG. 8 corresponds to one of the mountain-shaped waveforms in the detected waveform 145 in the bottom row of FIG. 6. The individual digital values ​​in the bottom row of FIG. 8 are values ​​obtained by 12-bit quantization of the output of each magnetic sensor element by the AD converter 132. The symbol Q in the bottom row of FIG. 8 indicates the range of digital values ​​represented by quantization. Please note that Figure 8 conceptually shows the correspondence between one slit, a magnetic sensor element row corresponding to one slit, and detection values ​​in order to explain subpixel processing, and does not show the actual strict arrangement relationship.

[0032] Using the digital values ​​obtained as shown in the bottom row of Fig. 8, the center of gravity position of the slit in the top row of Fig. 8 is calculated, and the result is set as the position of the slit with sub-pixel accuracy. The x-axis corresponds to the arrangement direction of the magnetic sensor elements 141 as shown in the figure, and the position of each magnetic sensor element 141 is x, the detected value at position x is I(x), and the 0th moment is m ０ , the first moment is m １ Then, the center of gravity C can be determined by the following equations (1) and (2): In equation (1), p is 0 for the zeroth moment and 1 for the first moment.

[0033]

[0034]

[0035] The center of gravity C calculated by the above equations (1) and (2) provides position information with sub-pixel accuracy, i.e., position information with higher accuracy than the accuracy of one pixel when the magnetic sensor element array corresponds to the pixel array in the optical sensor. By combining the position information read from the M-sequence pattern with the position information of each slit with sub-pixel accuracy calculated by the center of gravity calculation, it is possible to obtain an absolute value (angle) of the rotary disk 121 with sub-pixel accuracy. For example, when the absolute position (angle) detected with 256 levels of resolution using the detected 8-bit pattern is θ, and the angle corresponding to the deviation Δx of the slit position (center of gravity C) calculated by the center of gravity calculation from the reference position is α, the final absolute position (angle) can be calculated as θ + α.

[0036] Next, we will explain subpixel processing using edge detection, one of the functions of the subpixel processing unit 134. FIG. 9 is a diagram for explaining the calculation of slit positions using edge detection. The upper part of FIG. 9 represents the magnitude of the detection value detected by the magnetic sensor element array in a portion corresponding to one slit (region R) using shading. In this case, shading distribution 152 corresponds to one mountain-shaped portion in the detection waveform 145 of FIG. 6. In the upper part of FIG. 9, the darker the shading, the higher the height of the detection waveform. The subpixel processing unit 134 performs edge detection by differentiating the shading information (detection waveform) shown in the upper part of FIG. 9. As shown in the lower part of FIG. 9, the x-axis is assigned along the arrangement direction of the magnetic sensor element array. The subpixel processing unit 134 calculates a differential value I' of the detection value I(x) represented by the shading distribution 152. Waveform 153 in the lower part of FIG. 9 represents the differential value I'. Note that, for convenience, the absolute value of the differential value I' is represented as waveform 153. As a result of the differentiation operation, two peaks pk1 and pk2 are obtained in the portion where the detected value changes.

[0037] The subpixel processing unit 134 determines the center position C1 of the two peaks pk1 and pk2 as the position of the slit. The position C1 obtained by such calculation provides position information with subpixel accuracy, i.e., position information with higher accuracy than the single-pixel accuracy obtained when the magnetic sensor element array corresponds to the pixel array of the optical sensor. The position information read from the M-sequence pattern and the subpixel-accurate position information of each slit obtained by edge detection can be combined to obtain an absolute value (angle) of the rotating disk 121 with subpixel accuracy. For example, when the absolute position (angle) detected with 256 levels of resolution using the detected 8-bit pattern is θ, and the angle corresponding to the deviation Δx of the slit position (position C1) calculated by edge detection from the reference position is α, the final absolute position (angle) can be calculated as θ + α.

[0038] As described above, the position calculation unit 133 according to this embodiment is configured to read the encoded pattern on the rotating disk 121 magnetically, thereby eliminating the disadvantage of optical encoders, which are susceptible to dust, and is also able to provide highly accurate and high-resolution detection results through sub-pixel processing.

[0039] Second Example Fig. 10 shows a schematic diagram of a rotating disk 221 in an encoder 102 (see Fig. 11A) according to a second example. A single M-sequence track 222 is formed on the outer periphery of the rotating disk 221. In this example, a magnetic pattern is formed by magnetizing the surface of the rotating disk 221. The rotating disk 221 may be manufactured by, for example, forming a magnetic film on a resin disk substrate by vacuum deposition or sputtering.

[0040] 11A and 11B show a schematic configuration of an encoder 102 according to the second embodiment. FIG. 11A is a side view of the encoder 102 when the rotating disk 221 is viewed from the side. FIG. 11B is a front view of the encoder 102 when viewed from the direction of arrow A in FIG. 11A. A rotating shaft 221a of the rotating disk 221 is connected to the rotating shaft of a detection target (such as a servo motor). A printed circuit board 130 is disposed so as to face the surface of the rotating disk 221. An array-type magnetic sensor 240 is mounted on the rotating disk-side surface 130a of the printed circuit board 130 in a portion facing the outer periphery (M sequence track 222) of the rotating disk 221.

[0041] The array magnetic sensor 240 according to the second embodiment has a configuration similar to that of the array magnetic sensor 140 according to the first embodiment. In the array magnetic sensor 240, magnetic sensor elements 241 are arranged substantially parallel to the circumferential direction of the rotating disk 221. Note that in FIG. 11B, to avoid complexity, only one magnetic sensor element is denoted by the reference numeral 241. The array magnetic sensor 240 has a width D corresponding to the width of 8 bits of the M sequence. The number of magnetic sensor elements included in the array magnetic sensor 240 is, for example, 256, but a different number of magnetic sensor elements may be arranged. In the following, it is assumed that the number of magnetic sensor elements included in the array magnetic sensor 240 is 256.

[0042] When a magnetization pattern is formed on the surface of the rotating disk 221 as in this embodiment, the magnetic flux density is high directly below the magnetized region on the surface of the rotating disk, and is low directly below the portion of the surface of the rotating disk outside the magnetized region. Therefore, the magnetization pattern can be detected by the magnetic sensor element array of the array-type magnetic sensor 240.

[0043] In the second embodiment, two examples of how to form magnetized patterns on the rotating disk surface will be described. The first example of magnetization is a configuration example in which the width of the magnetized region is changed to distinguish between patterns "0" and "1". The second example of magnetization is a configuration example in which the direction of magnetization is changed to distinguish between patterns "0" and "1".

[0044] A first example of magnetization will be described with reference to FIGS. 12A, 12B, and 12C. In each of FIGS. 12A, 12B, and 12C, the top row shows the magnetization direction of a two-bit magnetization pattern, the middle row shows a magnetic sensor element row of a two-bit region of the array-type magnetic sensor 240, and the bottom row shows a read waveform 251 resulting from reading the magnetization pattern in the top row with the magnetic sensor element row in the middle row. As in the first example, the symbol R indicates the width of a one-bit region in the M sequence track 222. As shown in FIGS. 12A, 12B, and 12C, in this example, the magnetization direction of the pattern is set along the circumferential direction of the rotating disk (to the right in the drawings), and the circumferential width of the magnetized region of magnetization pattern "1" is made larger than the circumferential width of pattern "0."

[0045] With this configuration, as shown in the bottom rows of Figures 12A, 12B, and 12C, pattern "1" can be detected as a waveform with relatively wide peaks, and pattern "0" can be detected as a waveform with relatively narrow peaks. In this embodiment, the readout circuit 131 (see Figure 14) is configured to generate an output in which the height of the waveform increases in areas with strong magnetism. As shown in Figure 12A, when pattern "00" is read, the readout waveform 251 is a waveform with two relatively narrow peaks. As shown in Figure 12B, when pattern "11" is read, the readout waveform 251 is a waveform with two relatively wide peaks. As shown in Figure 12C, when pattern "10" is read, the readout waveform 251 is a waveform with a relatively wide peak and a relatively narrow peak.

[0046] The configuration of the detection circuit in the second embodiment is shown in Fig. 14. As in the first embodiment, the basic configuration of the detection circuit comprises a read circuit 131 that reads the output of the magnetic sensor element 241, an AD converter 132 that performs AD conversion of the output from the read circuit 131, and a position calculation unit 133 that calculates the absolute position of the rotating disk based on the output of the AD converter 132. The position calculation unit 133 includes a subpixel processing unit 134 for determining the absolute position with subpixel accuracy.

[0047] When the first example of magnetization in the second embodiment is adopted, each magnetic sensor element 241 may be a magnetic sensor of a type that detects the magnitude of magnetism (such as a magnetic sensor using a Hall element), or may be a magnetic sensor of a type that detects the vector of magnetism (such as a TMR sensor). However, when using a magnetic sensor that detects the vector of magnetism, it is preferable to arrange the magnetic sensor so that it has sensitivity in the magnetization direction (the circumferential direction of the rotating disk).

[0048] In the first example of magnetization, similarly to the first embodiment, the position calculation unit 133 calculates the absolute position (angle) of the rotating disk 221 with a resolution of 256 based on the results of reading an 8-bit M-sequence pattern. Furthermore, the subpixel processing unit 134 calculates the position of a 1-bit magnetization pattern with subpixel accuracy. The subpixel processing unit 134 can calculate a more accurate position of the magnetization pattern by a calculation method using a center of gravity or edge detection. The bottom rows of each of Figures 12A, 12B, and 12C show the state in which the center of gravity C is obtained by a center of gravity calculation for the detected waveform of each magnetization pattern.

[0049] In the first example relating to magnetization, as in the first embodiment, the absolute position in 256 steps obtained by reading the 8-bit M-sequence pattern and the position information of each magnetization pattern obtained by the center of gravity calculation or edge detection technique with sub-pixel accuracy can be combined to obtain the absolute value (angle) of the rotating disk 221 with sub-pixel accuracy.

[0050] Next, a second example of magnetization (a configuration example in which a pattern "0" and a pattern "1" are distinguished by changing the direction of magnetization) will be described with reference to FIGS. 13A, 13B, and 13C. In each of FIGS. 13A, 13B, and 13C, the top row shows the magnetization state of a two-bit magnetization pattern, the middle row shows a magnetic sensor element row of a two-bit region of the array-type magnetic sensor 240, and the bottom row shows a read waveform 251 resulting from reading the magnetization pattern in the top row with the magnetic sensor element row in the middle row. As in the first embodiment, the symbol R indicates the width of a one-bit region in the M sequence track 222. As shown in FIGS. 13A, 13B, and 13C, in this example, the magnetization direction of the pattern is set to be along the circumferential direction of the rotating disk, and the magnetization direction of the pattern "1" is set to be opposite to the magnetization direction of the pattern "0."

[0051] When the second example regarding magnetization is adopted, each magnetic sensor element 241 is a magnetic sensor (such as a TMR sensor) that detects magnetic vectors, and each magnetic sensor element 241 is arranged so as to have sensitivity in the circumferential direction of the rotating disk. In this case, the direction of magnetism (vector) detected in the magnetization pattern "1" is opposite to the direction of magnetism (vector) detected in the magnetization pattern "0", so it is possible to distinguish between the magnetization pattern "1" and the magnetization pattern "0" based on the output of the magnetic sensor element 241.

[0052] With this configuration, as shown in the bottom rows of Figures 13A, 13B, and 13C, pattern "0" is detected as a mountain-shaped waveform with a peak in the negative direction, and pattern "1" is detected as a mountain-shaped waveform with a peak in the positive direction. In this embodiment, the readout circuit 131 (see Figure 14) is configured to output the rightward magnetic strength in Figures 13A to 13C as a voltage value in the positive direction, and the leftward magnetic strength in Figures 13A to 13C as a voltage value in the negative direction. As shown in Figure 13A, the readout waveform 251 when pattern "00" is read is a waveform with two peaks in the negative direction. As shown in Figure 13B, the readout waveform 251 when pattern "11" is read is a waveform with two peaks in the positive direction. As shown in Figure 13C, the readout waveform 251 when pattern "10" is read is a waveform with a peak in the positive direction and a peak in the negative direction.

[0053] In the second example related to magnetization, similarly to the first embodiment, the position calculation unit 133 calculates the absolute position (angle) of the rotating disk 221 with a resolution of 256 based on the results of reading an 8-bit M-sequence pattern. Furthermore, the subpixel processing unit 134 calculates the position of a 1-bit magnetization pattern with subpixel accuracy. The subpixel processing unit 134 can calculate a more accurate position of the magnetization pattern by a calculation method using a center of gravity calculation or edge detection. The bottom rows of each of Figures 13A, 13B, and 13C show the state in which the center of gravity C is obtained by a center of gravity calculation for the detected waveform of each magnetization pattern.

[0054] In the second example relating to magnetization, similarly to the first embodiment, the absolute position in 256 steps obtained by reading the 8-bit M-sequence pattern and the position information of each magnetization pattern obtained by the centroid calculation or edge detection technique with sub-pixel accuracy can be combined to obtain the absolute value (angle) of the rotating disk 221 with sub-pixel accuracy.

[0055] In the above embodiment, a pattern equivalent to 1 bit is detected by a plurality of magnetic sensor elements (32 pixels / 1 bit in the above example), and sub-pixel processing is used to read the pattern with sub-pixel accuracy. This achieves high accuracy and high resolution. The number of quantization bits of the AD converter also contributes to high accuracy and high resolution. The number of divisions of the absolute position by the absolute pattern is set to 2. ｎ , the number of magnetic sensor elements per bit is 2 ｋ , the quantization number of the AD converter is 2 ｍ Then, the resolution is 2 ｎ ×2 ｋ ×2 ｍ When the numerical example in the above embodiment (M sequence code=8 bits, number of magnetic sensor elements per bit=32, number of quantization bits of the AD converter=12 bits) is assigned to the calculation of the resolution using this formula, the resolution is 2 ８ ×2 ５ ×2 １２ It can be seen that an extremely high resolution is achieved.

[0056] As described above, according to this embodiment, by using a magnetic encoder, it is possible to realize an encoder that is highly reliable and stable, and is capable of detecting absolute position with high accuracy and high resolution.

[0057] The rotating disks 121 and 221 shown in the above-described embodiment are configuration examples in which a single-track M-sequence pattern is formed as a magnetically readable encoding pattern, but this is merely an example, and the rotating disks according to the present embodiment may have other configurations. For example, in one embodiment, the encoding pattern on the rotating disk may be represented by multiple tracks. In one embodiment, the rotating disk may use a code other than the M-sequence as a code indicating an absolute position.

[0058] The above-described embodiment is an example of a configuration related to a rotary encoder using a rotating disk. However, the configuration of the above-described embodiment, i.e., a configuration in which absolute position is detected using a magnetically readable code and position is detected with sub-pixel accuracy using sub-pixel processing, can also be applied to a linear encoder for detecting position on a straight line.

[0059] At least a part of the detection circuit shown in Figures 7 and 14 (for example, the position calculation unit 133) may be configured by a microcomputer chip in which memories such as ROM, RAM, and non-volatile memory, a processor, and other circuit elements are integrated.

[0060] When the calculation of absolute position and subpixel processing in the detection circuit are realized as a processing procedure (software processing) by a processor, the program can be recorded on various computer-readable recording media (for example, semiconductor memories such as ROM, EEPROM, and flash memory, magnetic recording media, and optical disks such as CD-ROM and DVD-ROM).

[0061] Although the present disclosure has been described in detail, the present disclosure is not limited to the individual embodiments described above. Various additions, substitutions, modifications, partial deletions, etc. are possible in these embodiments without departing from the gist of the present disclosure or the spirit of the present disclosure derived from the content of the claims and their equivalents. These embodiments can also be implemented in combination. For example, in the above-described embodiments, the order of each operation and the order of each process are shown as examples and are not limited to these. The same applies when numerical values ​​or mathematical expressions are used in the description of the above-described embodiments.

[0062] The following supplementary notes are further provided with respect to the above-described embodiment and modified examples. (Supplementary Note 1) An encoder (101, 102) comprising: a rotating disk (121, 221) on which a magnetically detectable encoded pattern is formed; an array-type magnetic sensor (140, 240) formed by arranging a plurality of magnetic sensor elements in an array so as to detect the encoded pattern of the rotating disk; an AD converter (132) that performs AD conversion of an output of the array-type magnetic sensor; and a position calculation unit (133) that determines the position of the rotating disk based on information about the position of the rotating disk obtained by reading the encoded pattern based on the output of the AD converter and a result of calculating the position of one pattern in the encoded pattern with precision finer than the arrangement pitch of the plurality of magnetic sensor elements based on the output of the AD converter. (Supplementary Note 2) The encoder (101, 102) according to Supplementary Note 1, wherein the position calculation unit (133) determines the position of the one pattern by calculating the center of gravity. (Supplementary Note 3) The encoder (101, 102) according to Supplementary Note 1, wherein the position calculation unit (133) determines the position of the one pattern by edge detection. (Supplementary Note 4) The encoder (101, 102) according to any one of Supplements 1 to 3, wherein the coded pattern represents absolute position information of the rotating disk, and the position calculation unit determines the position of the rotating disk based on absolute position information of the rotating disk with a resolution based on the coded pattern, obtained by reading the coded pattern based on the output of the AD converter, and the calculated position of the one pattern. (Supplementary Note 5) The encoder (101, 102) according to Supplementary Note 4, wherein the coded pattern is a pseudo-random code pattern. (Supplementary Note 6) The encoder (101) according to any one of Supplements 1 to 5, wherein the rotating disk (121) is made of a magnetic material, and the coded pattern is formed as a pattern with a shape cut out of the rotating disk (121). (Supplementary Note 7) The encoder (101) according to Supplementary Note 6, wherein the encoding pattern can distinguish between Pattern 0 and Pattern 1 based on a difference in width in the circumferential direction of the hollowed-out shape of the rotary disk (121).(Supplementary Note 8) The encoder (102) according to any one of Supplementary Notes 1 to 5, wherein the encoding pattern is formed on the rotating disk (221) by magnetization. (Supplementary Note 9) The encoder (102) according to Supplementary Note 8, wherein the encoding pattern is capable of distinguishing between Pattern 0 and Pattern 1 based on a difference in width of magnetization in a predetermined direction of the rotating disk (221). (Supplementary Note 10) The encoder (102) according to Supplementary Note 8, wherein the encoding pattern is capable of distinguishing between Pattern 0 and Pattern 1 based on a difference in direction of magnetization.

[0063] 21 Rotating disk 22 Absolute track 101, 102 Encoder 121, 221 Rotating disk 121a, 221a Rotating shaft 122, 222 M-sequence track 122a, 122b Slit 130 Printed circuit board 131 Readout circuit 132 AD converter 133 Position calculation unit 134 Subpixel processing unit 140, 240 Array type magnetic sensor 141, 241 Magnetic sensor element 150 Magnet

Claims

1. An encoder comprising: a rotating disk on which a magnetically detectable coding pattern is formed; an array-type magnetic sensor formed by arranging a plurality of magnetic sensor elements in an array so as to detect the coding pattern of the rotating disk; an AD converter that performs AD conversion of the output of the array-type magnetic sensor; and a position calculation unit that determines the position of the rotating disk based on information regarding the position of the rotating disk obtained by reading the coding pattern based on the output of the AD converter, and the result of calculating the position of one pattern in the coding pattern with an accuracy finer than the arrangement pitch of the plurality of magnetic sensor elements based on the output of the AD converter.

2. The encoder according to claim 1, wherein the position calculation unit determines the position of the one pattern by calculating the center of gravity.

3. The encoder according to claim 1, wherein the position calculation unit determines the position of the one pattern by edge detection.

4. An encoder as claimed in any one of claims 1 to 3, wherein the coding pattern represents absolute position information of the rotating disk, and the position calculation unit determines the position of the rotating disk based on the absolute position information of the rotating disk at a resolution based on the coding pattern obtained by reading the coding pattern based on the output of the AD converter, and the calculated position of the one pattern.

5. The encoder of claim 4, wherein the coding pattern is a pseudo-random code pattern.

6. An encoder according to any one of claims 1 to 5, wherein the rotary disk is made of a magnetic material, and the encoding pattern is formed as a pattern formed by hollowing out the rotary disk.

7. The encoder according to claim 6, wherein said coded pattern can be distinguished between pattern 0 and pattern 1 by the difference in width of said hollowed-out shape in the circumferential direction of said rotating disk.

8. An encoder according to any one of claims 1 to 5, wherein the encoding pattern is formed on the rotating disk by magnetization.

9. The encoder according to claim 8, wherein said coded pattern can be distinguished between pattern 0 and pattern 1 by the difference in width of magnetization in a predetermined direction of said rotary disk.

10. The encoder according to claim 8, wherein the coding pattern can be distinguished between pattern 0 and pattern 1 by the difference in the direction of magnetization.

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