TWI714699B - Encoder - Google Patents

Abstract

The present invention provides a technique for appropriately reflecting the offset in an encoder using MR elements to improve accuracy. The 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 obtains the A-phase signal and the B-phase signal from the MR element 10 via the ADC 21 to calculate the angular position of the magnet 50. The offset control unit 23 calculates the Lissajous waveform based on the A-phase signal and the B-phase signal, and uses three consecutive points from the specific candidate points that are divided into the circular Lissajous waveform, etc., to obtain two points between two points. Calculate the vertical bisector with the intersection point as the offset.

Description

Encoder

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

As a device for detecting the displacement or the absolute value of the displacement, a magnetic encoder is known. For example, as a magnetic encoder, there is one that rotates a two-pole disk-shaped magnet that is magnetized into NS, and uses MR (Magnetic Random, magnetoresistive) elements to detect changes in the magnetic field to obtain Sin The signal and Cos signal undergo AD (Analog/Digital) conversion and capture to the microcomputer to detect the absolute value of the rotation position. In this kind of magnetic encoder, for example, if the phase of the arctangent signal is used 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, the so-called Lissajous waveform. If it is assumed that the Sin signal and the Cos signal are ideal signals without noise, etc., they become a circle without center shift or distortion. However, there is actually a circle whose center is offset due to the deviation of the sensor, that is, the distance from the intersection of the Y coordinate and the X coordinate to the circumference of the Lissajous waveform is different. Therefore, when the encoder is shipped from the factory, offset correction is usually performed in advance. Furthermore, there is also a technique that considers the difference between the offset adjustment environment at the time of shipment (initial) and the actual use environment, especially the use environment with different temperature environments, and adjusts the offset error (for example, refer to Patent Document 1 ). [Prior Art Document] [Patent Document] [Patent Document 1] Japanese Patent Laid-Open No. 2010-78340 However, in the technique of calculating the offset from 2 points of intersection with the Y axis and 2 points of intersection with the X axis, In applications where there is only a small rotation angle of movement, there is a limit to the offset calculation, and a technology that can improve accuracy even under such conditions is sought. The present invention was completed in view of the above-mentioned situation, and its object is to appropriately reflect the offset in an encoder using MR elements to improve accuracy.

The encoder of the present invention is provided with: a magnet, which is magnetized into two poles of NS; and a magnetic sensor, which is arranged so as to face the above-mentioned magnet, and outputs a phase A signal and a phase B signal with a phase difference of π/2 Rotation amount calculation unit, which calculates the amount of rotation based on the A-phase signal and the B-phase signal; and an offset control unit, which based on the A-phase signal and the B-phase signal, forms Lissajous on a quadrature coordinate system And calculate the offset between the A-phase signal and the B-phase signal based on the above-mentioned Lissajous waveform; and the offset control unit is divided into a specific number based on the circle represented by the above-mentioned Lissajous waveform. Detect the offset at the intersection of the vertical bisector of the two sides formed by 3 consecutive points among the candidate points. Here, the so-called A-phase signal and B-phase signal having a phase difference of π/2 refer to, for example, Sin signal and Cos signal. Compared with the case where the offset is calculated by the 2 points of intersection with the Y axis and the 2 points of intersection with the X axis as before, the offset can be detected even with a small rotation angle. Therefore, it can be used even in applications with only small rotation angles. Alternatively, when the Lissajous waveform is deformed, the offset control unit may correct it to become an ideal circle and calculate the offset based on the three consecutive points. Even when the shape of the Lissajous waveform is deformed, a more accurate offset can be calculated. In addition, it is also possible that the three consecutive points include at least one intersection point between any one of the orthogonal coordinate systems and the Lissajous waveform. Generally speaking, the Lissajous waveform deforms less at the intersection with the axes 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 faster. Alternatively, the above-mentioned continuous 3 points are the intersection points of any one axis of the above-mentioned orthogonal coordinate system and the above-mentioned Lissajous waveform. By taking all 3 points as the intersection with the axis, and choosing 3 points from the position where the distortion of the Lissajous waveform is less, no distortion correction is needed at all 3 points, so the offset can be calculated faster. Alternatively, the detection of the intersection with the aforementioned coordinate axis is calculated based on the combination of the value when either the aforementioned A-phase signal or the aforementioned B-phase signal becomes zero and the value of the other. It is not possible to perform maximum or minimum detection, but use a simple method to detect the intersection with the axis to calculate the offset. It is also possible that the offset control unit smoothes the offset calculated last time and the offset newly calculated when determining the offset applied to calculate the rotation amount. The result is smoothed (filtered) due to the application of the latest offset plus the weighted value of the previous offset when calculating the above-mentioned rotation amount, even if there are changes in the ambient temperature, the device temperature rise during use, etc. Appropriate offset can be detected following these changes, and by filtering, an unchangeable offset can be formed. Alternatively, when the offset control unit determines the offset applied to calculate the rotation amount, it directly uses the offset detected at the first three points, and the offset detected sequentially afterwards is weighted Make it reflect the offset detected at the first 3 points above. The offset can be quickly calculated immediately after the encoder is rotated, and as described above, it can be calculated as an offset without fluctuation. According to the present invention, in an encoder using an MR element, the offset can be appropriately reflected to improve accuracy.

Hereinafter, a mode for implementing the invention (hereinafter referred to as an "embodiment") will be described with reference to the drawings. Fig. 1 is a conceptual diagram of the hardware configuration of an encoder 1 for performing offset correction of the embodiment of the present invention. Fig. 2 is a functional block diagram of the encoder 1, which mainly focuses on the function of offset correction. The encoder 1 has an MR element 10 and a control unit 20 whose output signal changes in conjunction with the rotation of a rotating body. In this embodiment, as a rotating body, a disk-shaped magnet 50 magnetized into a pair of S pole and N pole magnetic poles is used. It is fixed to the frame of the motor device, etc., and the magnet 50 is used in a state of being connected to the rotating output shaft 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 has an A-phase magnetoresistance pattern and a B-phase magnetoresistance pattern with a phase difference of 90° with respect to the phase of the magnet 50, and outputs an A-phase signal and Phase B signal. Furthermore, in the figure, although only the MR element 10 is shown as one of the constituent elements of the A-phase sensor and the B-phase sensor, in addition to this, for example, a rectifier circuit and a low-pass filter may be used. Various electrical elements, such as an amplifier, a differential amplifier, and a driver for supplying excitation current to the MR element 10, calculate the output of the A-phase sensor and the B-phase sensor. The control unit 20 is formed of various electrical elements such as MPU (Microprocessor Unit), ROM (Read Only Memory), RAM (Random Access Memory), etc., and is functionally equipped with 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 obtains and digitizes the analog signal output from the MR element 10 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 (A-phase signal, B-phase signal) from the MR element 10. 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 deformation correction data storage unit 26. The offset calculation unit 24 calculates the offset between the A-phase signal and the B-phase signal, and provides the angular position calculation processing to the angle calculation unit 22. The specific calculation sequence of the offset will be described below with reference to Figures 4 and 5, but in simple terms, three consecutive points are selected from the candidate points that are divided into the circular Lissajous waveform, and then two points are obtained. The vertical bisector between two consecutive points is calculated as the offset. The value obtained by the initial offset calculation process after the encoder 1 is activated is directly used in the angle calculation unit 22. The offset obtained later is used in the angle calculation unit 22 after smoothing from the initial offset. In this way, the latest offset is reflected as soon as possible when starting, and the offset without change can be used later. Furthermore, how to perform weighting and smoothing can be appropriately selected according to the purpose. The offset data storage unit 25 holds the offset data. Here, the offset value at the time of shipment and the offset value calculated after the actual use state are memorized and used for the above-mentioned smoothing process. The deformation correction data storage unit 26 holds data used for deformation correction when deformation occurs in the Lissajous waveform. There are cases where the analog signal (A-phase signal and B-phase signal) acquired by the ADC 21 is deformed due to the MR element 10 and its accompanying amplifiers, drivers, etc. In addition, among the causes of deformation, there is also a problem in the shape of the magnet 50 and the MR element 10, that is, the main cause of geometry. The magnet 50 is formed in a disc shape, and each is extremely semicircular. From the semicircular area to the semicircular area, the magnetic flux lines are not completely consistent and present a circular distribution. In addition, the magnetic flux applied to each segment of the bridge circuit formed in the MR element 10 slightly differs depending on the location. As a result, the Lissajous waveform is deformed. This kind of deformation generally changes uniformly due to temperature characteristics, so the correction value for normalization is memorized in advance and applied when making Lissajous waveforms, so that a round shape without deformation (or very small deformation) can be obtained. Furthermore, in this embodiment, as described below, when calculating the offset, since a specific candidate point is determined in advance, the amount of data actually held and the amount of calculation required for deformation correction are small. Fig. 3 is a diagram for explaining the offset calculation method applied in this embodiment. Here, three consecutive points are used from the candidate points equally divided on the circular Lissajous waveform, and the offset is calculated based on the intersection of the vertical bisectors of the two sides formed by the consecutive three points. Here, as 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 of the side 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 of the side with the third point P3 (X3, Y3) and the second intersection point Pm2 (Xm2, Ym2) of the side are obtained by the following formula. Xm1=(X1+X2)/2 Ym1=(Y1+Y2)/2 Xm2=(X2+X3)/2 Ym2=(Y2+Y3)/2 The vertical bisector through the first intersection point Pm1(Xm1, Ym1) The intersection point P0 (X0, Y0) between L1 and the vertical bisector L2 passing through the second intersection point Pm2 (Xm2, Ym2) is obtained by the following formula. The value of the intersection point P0 (X0, Y0) becomes the newly calculated offset. X0=(Nr1×Ys2－Nr2×Ys1)/(Nr1－Nr2) Y0=(Ys2－Ys1)/(Nr1－Nr2) Among them, Nr1 (the slope of L1), Nr2 (the slope of L2), Ys1, Ys2 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 Figure 4(a) shows an example of dividing the Lissajous waveform into 4 equal parts, and Fig. 4(b) shows that Fig. 4(a) is further divided into equal parts and the Lissajous waveform is divided into 8 equal parts. example. As shown in Fig. 4(a), suppose that the Lissajous waveform is divided into 4 equal parts, and the four intersection points (P1 to P4) of the X-axis and the Y-axis become candidate points. Here, similarly to FIG. 3, the intersection point P0 that becomes the offset is calculated using the first to third points P1 to P3. Generally speaking, there is less deformation at the intersection of the Lissajous waveform and the axis (on the X axis or the Y axis), so the value obtained as the offset of the intersection point P0 (X0, Y0) is very accurate. From other viewpoints, even if no deformation correction is performed, the offset can be obtained with sufficient accuracy. In addition, since the magnet 50 rotates once to output two periods of Sin signal and Cos signal, in the circular Lissajous waveform, the center angle can be 180 degrees, that is, the rotation of the magnet 50 is 90 degrees (180 degrees/ 2) To detect the offset, that is, to quickly perform the offset calculation process. Furthermore, in Figure 4(b), the third point P3 to the fifth point P5 of the eight candidate points (P1 to P8) that are further equally divided to divide the Lissajous waveform into 8 equal positions are calculated as Offset point P0. When selecting consecutive 3 points from 8 equally divided candidate points, it must include 1 point or 2 points on the X-axis or Y-axis. In addition, points other than the points on the axis have a slope of ±45 degrees with respect to the origin, which corresponds to the intersection of the A-phase signal and the B-phase signal. Since this position has a large deformation, the value corrected for the deformation is used. As a result, the value obtained as the offset of the intersection point P0 (X0, Y0) is very accurate. In this case, in the circular Lissajous waveform, the deviation can be detected with the center 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 only rotates slightly, the offset can be calculated appropriately, and the detection accuracy of the encoder 1 can be improved. Next, the outline of the procedure for calculating the offset will be explained using the flowchart of FIG. 5. The control unit 20 obtains 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 obtains the Lissajous waveform based on the A-phase signal and the B-phase signal (S12). At this time, the deformation correction described above is performed by referring to the deformation correction data storage unit 26 as necessary. Then, the offset calculation unit 24 identifies three consecutive points from the specified candidate points (S14), obtains the vertical bisector of the two sides obtained by connecting the two consecutive points, and calculates the intersection of the two points (S16), Determine the latest offset (S18). If the latest offset is determined, the offset calculation unit 24 determines whether it is the first offset calculation after the encoder 1 is activated (S20). If it is the calculation of the initial offset (Y (Yes) in 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 it is not the calculation of the initial offset (N (No) in S20), the offset calculation section 24 uses the latest offset and the offset calculated in the past recorded in the offset data storage section 25 for smoothing processing (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 based on the embodiment, but the embodiment is an example, and the industry should understand that there may be various variations in the combination of the various constituent elements, and these variations are also within the scope of the present invention.

1‧‧‧Encoder 10‧‧‧MR element 20‧‧‧Control part 21‧‧‧ADC (AD conversion part) 22‧‧‧Angle calculation part 23‧‧‧Offset control part 24‧‧‧Offset calculation Section 25‧‧‧Offset data memory unit 26‧‧‧Data memory unit for deformation correction 50‧‧‧Magnet L1‧‧‧Vertical bisector L2‧‧‧Vertical bisector P0‧‧‧Intersection point P1～P8‧‧‧ Candidate point Pm1‧‧‧The first intersection Pm2‧‧‧The second intersection

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

10‧‧‧MR element

20‧‧‧Control Department

21‧‧‧ADC (AD conversion section)

22‧‧‧Angle calculation section

23‧‧‧Offset Control Unit

24‧‧‧Offset calculation section

25‧‧‧Offset data memory

26‧‧‧Data memory for deformation correction

Claims (12)

An encoder, characterized by comprising: a magnet, which is magnetized into two poles of NS; a magnetic sensor, which is arranged to face the above-mentioned magnet, and outputs a phase A signal with a phase difference of π/2, and B-phase signal; a rotation amount calculation unit that calculates the rotation amount based on the A-phase signal and the B-phase signal; and an offset control unit that is formed on a quadrature coordinate system based on the A-phase signal and the B-phase signal Lissajous waveform, and calculate the offset between the A-phase signal and the B-phase signal based on the Lissajous waveform; and the offset control unit is based on the Lissajous waveform on the circumference represented by the waveform. Divide into the intersection of the vertical bisectors of the two sides formed by 3 consecutive points among the specified number of candidate points to detect the offset. Such as the encoder of claim 1, wherein the offset control unit corrects to become an ideal circle when the circle shown by the Lissajous waveform is deformed, and calculates the offset based on the three consecutive points . Such as the encoder of claim 2, wherein the above-mentioned three consecutive points include at least one intersection point of any one axis of the above-mentioned orthogonal coordinate system and the above-mentioned Lissajous waveform. Such as the encoder of claim 3, wherein the above-mentioned continuous 3 points are the intersection points of any one axis of the above-mentioned orthogonal coordinate system and the above-mentioned Lissajous waveform. Such as the encoder of claim 3, wherein the detection of the intersection with the aforementioned coordinate axis is calculated based on the combination of the value when either the aforementioned A-phase signal or the aforementioned B-phase signal becomes zero and the value of the other. Such as the encoder of any one of claims 1 to 5, wherein when the offset control unit determines the offset applied to calculate the rotation amount, it smoothes the offset calculated last time and the offset calculated newly use. Such as the encoder of claim 6, wherein the offset control unit directly uses the offset detected at the first 3 points when determining the offset applied to calculate the rotation amount, and then the offset detected sequentially Then, after weighting, the offset detected at the first 3 points is reflected. Such as the encoder of claim 1, wherein the three consecutive points include at least one intersection point of any one of the orthogonal coordinate systems and the Lissajous waveform. Such as the encoder of claim 8, wherein the above-mentioned continuous 3 points are the intersection points of any one axis of the above-mentioned orthogonal coordinate system and the above-mentioned Lissajous waveform. Such as the encoder of claim 8, wherein the detection of the intersection with the aforementioned coordinate axis is calculated based on the combination of the value when either the aforementioned A-phase signal or the aforementioned B-phase signal becomes zero and the value of the other. Such as the encoder of any one of claims 8 to 10, wherein when the offset control section determines the offset applied to calculate the rotation amount, it smoothes the offset calculated last time and the offset calculated newly use. Such as the encoder of claim 11, wherein the offset control unit directly uses the offset detected at the first 3 points when determining the offset applied to calculate the rotation amount, and then the offset detected sequentially Then, after weighting, the offset detected at the first 3 points is reflected.

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