TW201727199A - Encoder appropriately reflecting an offset and improving accuracy in an encoder using an MR element - Google Patents

Abstract

This invention provides a technique for appropriately reflecting an offset in order to improve accuracy in an encoder using an MR element. An encoder includes an MR element 10 and a control unit 20. The control unit 20 includes an ADC 21, an angle calculation unit 22, and an offset control unit 23. The angle calculation unit 22 acquires the A-phase signal and the B-phase signal from the MR element 10 via the ADC 21, and calculates the angular position of a magnet 50. The offset control unit 23 calculates a Lissajous waveform according to the A-phase signal and the B-phase signal, and also calculates, by using three consecutive points from predetermined candidate points obtained by equally dividing a circular Lissajous waveform, two vertical dividing lines between two points, wherein the intersection is calculated as an offset.

Description

Encoder

The present invention relates to an encoder, for example, to a magnetic encoder for calculating a rotation angle obtained based on a magnetic sensor output of an A-phase signal and a B-phase signal having a phase difference of π/2.

As a means for detecting the absolute value of the displacement amount or displacement of the object to be detected, a magnetic encoder is known. For example, as a magnetic encoder, a disk-shaped magnet magnetized to have two poles of NS is rotated, and a magnetic field change is detected by an MR (Magnetic Random) element, and the obtained Sin is obtained. The signal and Cos signal are converted into AD (Analog/Digital) and captured to the microcomputer to detect the absolute value of the rotational position. In such a magnetic encoder, for example, if the phase of the arctangent signal is taken as a parameter, the Sin signal is used as the Y coordinate of the orthogonal coordinate system, and the Cos signal is drawn as the X coordinate of the orthogonal coordinate system, so that the so-called Lisa is like a wave. If the Sin signal and the Cos signal are assumed to be ideal signals without noise or the like, they become circular without center offset or deformation. However, there is actually a circle which is center-shifted due to the deviation of the sensor or the like, that is, a distance from the intersection of the Y coordinate and the X coordinate to the circumference of the Lissajous waveform. Therefore, when the encoder is shipped from the factory, the offset correction is usually performed in advance. Further, there is a technique in which the offset error is adjusted in consideration of the difference in the environment in which the offset adjustment environment at the time of shipment (initial) differs from the actual use environment, particularly the temperature environment (for example, refer to Patent Document 1) ). [Prior Art Document] [Patent Document 1] Japanese Patent Laid-Open Publication No. 2010-78340, however, in the technique of calculating the offset by two points of intersection with the Y-axis and two points of intersection with the X-axis, In the case where only a small rotation angle is used, there is a limit in the offset calculation, and a technique for improving the accuracy even in such a situation can be achieved. The present invention has been made in view of the above circumstances, and an object thereof is to improve accuracy by appropriately reflecting an offset in an encoder using an MR element.

The encoder of the present invention includes: a magnet magnetized to have two poles of NS; and a magnetic sensor configured to face the magnet to output an A-phase signal and a B-phase signal having a phase difference of π/2 a rotation amount calculation unit that calculates a rotation amount based on the A-phase signal and the B-phase signal, and an offset control unit that forms a Lissajous system on the orthogonal coordinate system based on the A-phase signal and the B-phase signal a waveform, and calculating an offset between the A-phase signal and the B-phase signal based on the Lissajous waveform; and the offset control unit is equally divided into a specific number according to a circle represented by the Lissajous waveform The offset is detected by the intersection of the vertical bisectors of the two sides formed by three consecutive points among the candidate points. Here, the A-phase signal and the B-phase signal having a phase difference of π/2 are, for example, Sin signals and Cos signals. The offset can be detected even with a small rotation angle as compared with the case where the offset is calculated by the two points of the intersection with the Y-axis and the two points of the intersection with the X-axis as before. Therefore, it can be used even in applications where only a small rotation angle is active. Alternatively, when the Lissajous waveform is deformed, the offset control unit may perform correction so as to become an ideal circle, and calculate the offset based on the three consecutive points. Even in the case where the shape of the circle represented by the Lissajous figure is deformed, a more accurate offset can be calculated. Moreover, the continuous three points may include at least one coordinate axis of one of the orthogonal coordinate systems and an intersection of the Lissajous waveform. In general, the Lissajous waveform has less distortion at the intersection with the axis of the orthogonal coordinate system (X-axis, Y-axis). Therefore, by including the intersection with the axis, it is not necessary to correct the intersection with the axis in the deformation correction, and the offset can be calculated more quickly. Alternatively, the three consecutive points may be the intersection of any coordinate axis of the orthogonal coordinate system and the Lissajous waveform. By using all three points as the intersection with the axis, three points are selected from the position where the deformation of the Lissajous waveform is small, so that no deformation correction is required for all three points, so the offset can be calculated more quickly. Alternatively, the detection of the intersection with the coordinate axis may be calculated based on a combination of the value of the A phase signal or the B phase signal becoming zero and the value of the other. The maximum value detection or the minimum value detection can be performed, and the intersection with the axis can be detected by a simple method to calculate the offset. When the offset control unit determines to apply the offset to calculate the amount of rotation, the offset control unit may use the offset calculated from the previous calculation and the latest calculated offset. When the amount of rotation is calculated, the smoothing (filtering) is performed by adding the value obtained by weighting the latest offset to the previous offset, and even if there is a change in the ambient temperature or a rise in the temperature of the device during use, Appropriate offsets can be detected following these changes, and by filtering, an unvariable offset can be formed. The offset control unit may directly use the offset detected at the first three points when determining the offset applied to calculate the rotation amount, and the offset detected in the subsequent steps may be weighted. It is reflected as the offset detected at the first three points mentioned above. The offset can be quickly calculated immediately after the encoder is rotated, and as described above, can be calculated as an offset without variation. According to the present invention, in an encoder using an MR element, the offset can be appropriately reflected to improve the accuracy.

Hereinafter, a mode for carrying out the invention (hereinafter referred to as "embodiment") will be described with reference to the drawings. Fig. 1 is a conceptual diagram showing the hardware configuration of an encoder 1 for performing offset value correction according to an embodiment of the present invention. Fig. 2 is a functional block diagram of the encoder 1, mainly focusing on the function of the offset correction. The encoder 1 has an MR element 10 and a control unit 20 that output a signal change in conjunction with the rotation of the rotating body. In the present embodiment, as the rotating body, a disk-shaped magnet 50 magnetized into a pair of S poles and N pole magnetic poles is used. It is fixed to a frame or the like of the motor device, and the magnet 50 is used in a state of being coupled to a rotation output shaft or the like of the motor device. In the encoder 1, a Cos signal (A-phase signal) and a Sin signal (B-phase signal) having a phase difference of π/2 from each other are output from the MR element 10 toward the control unit 20. More specifically, the MR element 10 includes an A-phase magnetoresistive pattern and a B-phase magnetoresistive pattern having a phase difference of 90° with respect to each other in phase with the magnet 50, and outputs an A-phase signal corresponding to the rotation of the magnet 50 and Phase B signal. Further, in the drawings, only the MR element 10 which is one of the components of the A-phase sensor and the B-phase sensor is illustrated, but other than this, for example, a rectification circuit or a low-pass filter may be used. Various electrical components such as a comparator, a differential amplifier amplifier, and a driver that supplies an excitation current to the MR element 10 perform calculation processing on the outputs of the A-phase sensor and the B-phase sensor. The control unit 20 is formed of, for example, an MPU (Microprocessor Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), and the like, and has a function A/. D (Analog/Digital) conversion unit 21 (hereinafter referred to as "ADC 21"), angle calculation unit 22, and offset control unit 23. The ADC 21 acquires the analog signal output from the MR element 10 and digitizes it, and outputs it to the angle calculation unit 22 and the offset control unit 23. The angle calculation unit 22 calculates the angular position of the magnet 50 based on the output from the MR element 10 (A phase signal, B phase signal). The offset control unit 23 has a function of calculating a Lissajous waveform and an offset correction function. When calculating the angular position of the magnet 50, the angle calculation unit 22 acquires the offset from the offset control unit 23, and calculates an appropriate angular position. The offset control unit 23 includes an offset calculation unit 24, an offset data storage unit 25, and a distortion correction data storage unit 26. The offset calculation unit 24 calculates the offset between the A-phase signal and the B-phase signal, and supplies the calculation to the angular position of the angle calculation unit 22. The calculation procedure of the specific offset will be described below with reference to FIGS. 4 and 5, but in short, two consecutive points are selected from the candidate points of the circular Lissajous waveform, etc., and two are obtained. The vertical bisector between two consecutive points is calculated as the offset. The value obtained by the first offset calculation process after the encoder 1 is started is directly used in the angle calculation unit 22. The offset obtained later is used for the angle calculation unit 22 after smoothing with the initial offset. In this way, the latest offset is reflected as early as possible at startup, and the unchanging offset can be used later. Furthermore, how to perform weighting and smoothing can be appropriately selected depending on the purpose. The offset data storage unit 25 holds the offset data. Here, the value of the offset at the time of shipment and the value of the offset calculated after the actual use state are used for the above-described smoothing processing. The distortion correction data storage unit 26 holds data for performing deformation correction when the Lissajous waveform is deformed. There is a case where the analog signal (A phase signal and B phase signal) acquired by the ADC 21 is deformed by the MR element 10 and its accompanying amplifier, driver, and the like. Further, among the causes of the deformation, there are also problems in the shape of the magnet 50 and the MR element 10, that is, the main cause of geometry. The magnets 50 are formed in a disk shape, each of which is extremely semicircular, and has a circular distribution from the semicircular region to the semicircular region. Further, the magnetic flux applied to each section of the bridge circuit formed in the MR element 10 is slightly different depending on the location. Thus, Lissajous deforms like a waveform. Such deformation generally varies uniformly due to temperature characteristics, so the correction value for normalization is memorized in advance and applied when a Lissajous waveform is produced, whereby a circular shape without deformation (or very small deformation) can be obtained. Further, in the present embodiment, as described below, when the offset is calculated, since the specific candidate point is determined in advance, the amount of data actually required to be held and the amount of calculation required for the distortion correction may be small. Fig. 3 is a view for explaining an offset calculation method applied in the embodiment. Here, three consecutive points are used for the candidate points equally divided on the waveform of the circular Lissajous figure, and the offset is calculated from the intersection of the vertical bisectors of the two sides formed by the three consecutive points. Here, as the three consecutive points, the first point P1 (X1, Y1), the second point P2 (X2, Y2), and the third point P3 (X3, Y3) are set. The vertical bisector connecting the first point P1 (X1, Y1) and the second point P2 (X2, Y2) and the first intersection Pm1 (Xm1, Ym1) of the side, and the second point P2 (X2, Y2) The vertical bisector with the side of the third point P3 (X3, Y3) and the second intersection Pm2 (Xm2, Ym2) of the side are obtained by the following equation. Xm1=(X1+X2)/2 Ym1=(Y1+Y2)/2 Xm2=(X2+X3)/2 Ym2=(Y2+Y3)/2 Vertical bisector passing through the first intersection Pm1(Xm1, Ym1) L1 is obtained by the following equation by the intersection P0 (X0, Y0) passing through the vertical bisector L2 of the second intersection Pm2 (Xm2, Ym2). The value of the intersection P0 (X0, Y0) becomes the newly calculated offset. X0=(Nr1×Ys2-Nr2×Ys1)/(Nr1-Nr2) Y0=(Ys2-Ys1)/(Nr1-Nr2) where Nr1 (slope of L1), Nr2 (slope of L2), Ys1, Ys2 are set For the following formula. Nr1=-(X2-X1)/(Y2-Y1) Nr2=-(X3-X2)/(Y3-Y2) Ys1=Ym1-Nr1×Xm1 Ys2=Ym2-Nr2×Xm2 Figure 4 shows the Lissajous waveform Fig. 4(a) shows an example in which the Lissajous waveform is equally divided, and Fig. 4(b) shows that Fig. 4(a) is further divided and the Lissajous waveform 8 is equally divided. example. As shown in FIG. 4(a), it is assumed that the Lissajous waveform 4 is equally divided, and four intersections (P1 to P4) of the X-axis and the Y-axis are candidates. Here, similarly to FIG. 3, the intersection point P0 which becomes an offset is computed using the 1st - 3rd point P1 - P3. In general, the deformation of the Lissajous waveform and the axis (on the X-axis or the Y-axis) is less, so the value obtained as the offset of the intersection P0 (X0, Y0) is very accurate. From other points of view, the offset can be obtained with sufficient accuracy even without deformation correction. Further, since the Sin signal and the Cos signal are output for two cycles by the rotation of the magnet 50, the circular Lissajous waveform can be rotated at a central angle of 180 degrees, that is, the rotation of the magnet 50 is 90 degrees (180 degrees / 2) The offset is detected, that is, the calculation processing of the offset can be performed quickly. Further, in FIG. 4(b), the third point P3 to the fifth point P5 among the eight candidate points (P1 to P8) at the position where the Lissajous waveform 8 is equally divided are calculated using the equal division. The intersection point of the offset P0. In the case of selecting 3 consecutive points from the candidate points of 8 equal parts, it is necessary to include points on the X-axis or the Y-axis of 1 or 2 points. Further, the point other than the point on the axis has a slope of ±45 degrees with respect to the origin, corresponding to the intersection of the A-phase signal and the B-phase signal. Since the position is large in deformation, the value corrected for the deformation is used. As a result, the obtained value of the offset as the intersection point P0 (X0, Y0) is very accurate. In this case, in the circular Lissajous waveform, the offset can be detected at a central angle of 90 degrees, that is, the rotation of the magnet 50 is 45 degrees. Therefore, even when the magnet 50 is attached to a device that rotates only slightly, the offset can be appropriately calculated, and the detection accuracy of the encoder 1 can be improved. Next, an outline of the calculation procedure of the offset will be described using the flowchart of FIG. 5. The control unit 20 acquires the A-phase signal and the B-phase signal output from the MR element 10 (S10). The acquired A-phase signal and B-phase signal are output to the angle calculation unit 22 and the offset control unit 23. The offset calculation unit 24 acquires a Lissajous waveform based on the A-phase signal and the B-phase signal (S12). At this time, the above-described deformation correction is performed by referring to the deformation correction data storage unit 26 as necessary. Then, the offset calculation unit 24 specifies three consecutive points from the specific candidate points (S14), and obtains two vertical bisectors of the sides obtained by connecting two consecutive points, and calculates the intersection point of the points (S16). Determine the latest offset (S18). When the latest offset is determined, the offset calculation unit 24 determines whether or not the first offset is calculated after the encoder 1 is started (S20). When the first offset is calculated (Y of S20), the offset calculation unit 24 notifies the angle calculation unit 22 of the latest offset (S22). After the notification, the calculated offset is stored in the offset data storage unit 25 (S24). If the initial offset is not calculated (N of S20), the offset calculation unit 24 performs smoothing processing using the latest offset and the offset calculated in the past in the offset data storage unit 25 (S26). The smoothed offset is notified to the angle calculation unit 22 (S28). After the notification, the calculated offset is stored in the offset data storage unit 25 (S24). The present invention has been described with reference to the embodiments. However, the embodiment is exemplified, and it should be understood that the various combinations of the constituent elements and the like may be variously modified, and such modifications are also within the scope of the present invention.

1‧‧‧Encoder
10‧‧‧MR components
20‧‧‧Control Department
21‧‧‧ADC (AD conversion unit)
22‧‧‧Angle calculation unit
23‧‧‧Offset Control Department
24‧‧‧Offset calculation unit
25‧‧‧Offset Data Memory Department
26‧‧‧Data memory department for deformation correction
50‧‧‧ magnet
L1‧‧‧ vertical bisector
L2‧‧‧ vertical bisector
P0‧‧‧ intersection
P1～P8‧‧‧ candidate points
Pm1‧‧‧1st intersection
Pm2‧‧‧2nd intersection

Fig. 1 is a conceptual diagram showing the hardware configuration of an encoder of an embodiment. Figure 2 is a functional block diagram of the encoder of the embodiment. Fig. 3 is a view for explaining a method of calculating an offset in the embodiment. 4(a) and 4(b) are diagrams showing the relationship between the Lissajous waveform and the candidate points in the embodiment. Fig. 5 is a flow chart showing an outline of a procedure for calculating the offset of the embodiment.

10‧‧‧MR components

20‧‧‧Control Department

21‧‧‧ADC (AD conversion unit)

22‧‧‧Angle calculation unit

23‧‧‧Offset Control Department

24‧‧‧Offset calculation unit

25‧‧‧Offset Data Memory Department

26‧‧‧Data memory department for deformation correction

Claims (12)

An encoder comprising: a magnet magnetized to have two poles of NS; a magnetic sensor configured to face the magnet and output an A-phase signal having a phase difference of π/2 and a B-phase signal; a rotation amount calculation unit that calculates a rotation amount based on the A-phase signal and the B-phase signal; and an offset control unit that forms on the orthogonal coordinate system based on the A-phase signal and the B-phase signal Is a waveform, and calculates an offset between the A-phase signal and the B-phase signal based on the Lissajous waveform; and the offset control unit is equally distributed on the circumference represented by the Lissajous waveform The offset is detected by dividing the intersection of the vertical bisectors of the two sides formed by the continuous three points among the specific number of candidate points. The encoder of claim 1, wherein the offset control unit corrects the circular shape of the Lissajous waveform as a perfect circle and calculates the offset based on the consecutive three points. . The encoder of claim 2, wherein said consecutive three points comprise at least one coordinate axis of one of said orthogonal coordinate systems and an intersection of said Lissajous waveform. The encoder of claim 3, wherein the continuous three points are the intersection of any coordinate axis of the orthogonal coordinate system and the Lissajous waveform. The encoder of claim 3, wherein the detection of the intersection with the coordinate axis is calculated based on a combination of the value of the A phase signal or the B phase signal becoming zero and the value of the other. The encoder according to any one of claims 1 to 5, wherein, when the offset control unit determines to apply the offset to calculate the rotation amount, smoothing the previously calculated offset from the newly calculated offset use. The encoder of claim 6, wherein the offset control unit directly uses the offset detected at the first three points when determining the offset applied to calculate the rotation amount, and sequentially detects the offset later. Then, after the weighting, the offset detected by the first three points is reflected. The encoder of claim 1, wherein the consecutive three points comprise at least one coordinate axis of one of the orthogonal coordinate systems and an intersection of the Lissajous waveform. The encoder of claim 8, wherein the continuous three points are the intersection of any coordinate axis of the orthogonal coordinate system and the Lissajous waveform. The encoder of claim 8, wherein the detection of the intersection with the coordinate axis is calculated based on a combination of the value of the A phase signal or the B phase signal becoming zero and the value of the other. The encoder according to any one of claims 8 to 10, wherein, when the offset control unit determines to apply the offset to calculate the amount of rotation, smoothing the offset calculated last time and the latest calculated offset use. The encoder of claim 11, wherein the offset control unit directly uses the offset detected at the first three points when determining the offset applied to calculate the rotation amount, and sequentially detects the offset later. Then, after the weighting, the offset detected by the first three points is reflected.