JP6668082B2 - Encoder - Google Patents

Description

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

  2. Description of the Related Art A magnetic encoder is known as a device for detecting a displacement amount and an absolute value of a displacement of an object. For example, as a magnetic encoder, a disk-shaped magnet magnetized in two poles of NS is rotated, a change in the magnetic field is detected by an MR element, and the obtained Sin signal and Cos signal are AD-converted to a microcomputer. There is one that detects the absolute value of the capture and rotation position.

  In such a magnetic encoder, for example, a so-called Lissajous waveform is obtained by plotting the Sin signal as a Y coordinate in a rectangular coordinate system and the Cos signal as an X coordinate in a rectangular coordinate system using the phase of the arc tangent signal as a parameter. Assuming that the Sin signal and the Cos signal are ideal signals without noise or the like, the Lissajous waveform is a circular shape without center shift and distortion. However, in practice, the distance from the center of the circle, that is, the intersection of the Y coordinate and the X coordinate, to the circumference of the Lissajous waveform may be different due to variations in the sensors. Therefore, when an encoder is shipped from a factory, it is general to apply offset correction in advance. Further, there is a technique of adjusting an offset error in consideration of a difference between an offset adjustment environment at the time of shipment (initial stage) and an actual use environment, particularly a use environment having a different temperature environment (for example, see Patent Document 1).

JP 2010-78340 A

  By the way, in the technique of calculating an offset based on two points of intersection with the Y axis and two points of intersection with the X axis, there is a limit to offset calculation in an application where only a small rotation angle is moved. Therefore, a technique capable of improving the accuracy has been demanded.

  The present invention has been made in view of the above circumstances, and has as its object to improve accuracy by appropriately reflecting an offset in an encoder using an MR element.

An encoder according to the present invention includes a magnet magnetized to two poles of NS, and a magnetic sensor arranged to face the magnet and outputting 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 forms a Lissajous waveform on a rectangular coordinate system based on the A-phase signal and the B-phase signal; An offset between the A-phase signal and the B-phase signal is calculated based on the Lissajous waveform, and the offset is calculated for the A-phase signal and the B-phase signal when the rotation amount is calculated by the rotation amount calculation unit. And an offset control unit that performs correction by an amount corresponding to a predetermined number of candidate points equally divided into a predetermined number on a circumference represented by the Lissajous waveform. Two sides formed Performed a plurality of times an operation of detecting the offset from the intersection of the perpendicular bisectors at different times, the when determining the offset to be applied to calculate the rotation amount, the detected offset is used as the first three-point The offsets sequentially detected thereafter are weighted and reflected on the offsets detected at the first three points .
Here, the A-phase signal and the B-phase signal having a phase difference of π / 2 indicate, for example, a Sin signal and a Cos signal. The offset can be detected even at a small rotation angle, as compared with the case where the offset is calculated based on two points of intersection with the Y axis and two points of intersection with the X axis as in the related art. Therefore, it can be used even in an application that moves only a small rotation angle. At this time, the offset can be calculated quickly immediately after the rotation of the encode, and can be calculated as a non-fluttering offset as described above.

The offset control unit may calculate the offset from the three consecutive points by correcting the Lissajous waveform so that the Lissajous waveform has an ideal circle.
Even when the circular shape of the Lissajous waveform has distortion, a more accurate offset can be calculated.

In addition, the three consecutive points may include at least one intersection of any one of the coordinate axes of the rectangular coordinate system and the Lissajous waveform.
In general, the Lissajous waveform has little distortion at the intersection with the axes (X axis, Y axis) of the rectangular coordinate system. Therefore, by including the intersection with the axis, it is not necessary to correct the intersection with the axis in the distortion correction, and the offset can be calculated more quickly.

The three consecutive points may be intersections between any of the coordinate axes of the rectangular coordinate system and the Lissajous waveform.
By setting all three points as intersections with the axis, three points are selected from positions where the distortion of the Lissajous waveform is small. Therefore, distortion correction is not required for all three points, and the offset can be calculated more quickly.

The detection of the intersection with the coordinate axis may be calculated from a combination of a value when one of the A-phase signal and the B-phase signal becomes zero and a value on the other side.
It is possible to detect the intersection with the axis and calculate the offset by a simple method without detecting the maximum value or the minimum value.

When determining the offset to be applied to calculate the rotation amount, the offset control unit may smooth the previously calculated offset and the latest calculated offset before use.
By applying a value obtained by adding a weighted value to the previous offset to the latest offset and filtering (filtering) the applied offset when calculating the rotation amount, it is possible to reduce environmental temperature changes, device temperature rise during use, and the like. Even if there is a change, an appropriate offset can be detected following the change, and an offset that does not flutter can be obtained by applying a filter.

  According to the present invention, in an encoder using an MR element, an offset can be appropriately reflected and accuracy can be improved.

FIG. 2 is an image diagram of a hardware configuration of an encoder according to the embodiment. FIG. 2 is a functional block diagram of an encoder according to the embodiment. FIG. 4 is a diagram for describing an offset calculation method according to the embodiment. FIG. 4 is a diagram illustrating a relationship between a Lissajous waveform and candidate points according to the embodiment. 9 is a flowchart illustrating an outline of an offset calculation process according to the embodiment.

  Hereinafter, embodiments for carrying out the invention (hereinafter, referred to as “embodiments”) will be described with reference to the drawings.

  FIG. 1 is an image diagram of a hardware configuration of an encoder 1 that performs offset value correction according to an embodiment of the present invention. FIG. 2 is a functional block diagram of the encoder 1 and mainly shows a function of offset correction.

  The encoder 1 has an MR element 10 whose output signal changes in conjunction with the rotation of the rotating body, and a control unit 20. In the present embodiment, a disk-shaped magnet 50 in which a pair of S poles and N poles are magnetized in a pair is used as the rotating body. The magnet 50 is used while being fixed to a frame or the like of the motor device and connected 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 are output from the MR element 10 to 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 the phase of the magnet 50, and corresponds to the rotation of the magnet 50. To output an A-phase signal and a B-phase signal.

  Although only the MR element 10 which is a component of the A-phase sensor and the B-phase sensor is shown in the drawing, other than that, for example, an exciting current is supplied to a rectifier circuit, a low-pass filter, a differential amplifier, and the MR element 10. The output of the A-phase sensor and the B-phase sensor is calculated by various electric elements such as a driver to be supplied.

  The control unit 20 is formed of various electric elements such as an MPU, a ROM, and a RAM, and functionally includes an A / D conversion unit 21 (hereinafter, referred to as “ADC 21”) and an angle calculation unit 22. And an offset control unit 23.

  The ADC 21 acquires the analog signal output from the MR element 10, digitizes the analog signal, and outputs the digitized signal to the angle calculator 22 and the offset controller 23. The angle calculator 22 calculates the angular position of the magnet 50 based on the outputs (A-phase signal and 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 calculating unit 22 obtains an 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 provides the result to the angle position calculation processing of the angle calculation unit 22. A specific procedure for calculating the offset will be described later with reference to FIGS. 4 and 5. However, in brief, three consecutive points are selected from predetermined candidate points obtained by equally dividing the circular Lissajous waveform, and further continuous points are selected. Two perpendicular bisectors between two points are obtained, and the intersection is calculated as an offset. The value obtained in the first offset calculation process after the activation of the encoder 1 is used by the angle calculation unit 22 as it is. The offset obtained thereafter is used by the angle calculation unit 22 after being smoothed with the first offset. As a result, the latest offset can be reflected as soon as possible at the time of startup, and thereafter, an offset that does not flutter can be used. In addition, what kind of weighting and smoothing can be appropriately selected depending on the purpose.

  The offset data storage unit 25 holds offset data. Here, the value of the offset calculated after the actual use state is stored together with the value of the offset at the time of shipment, and used for the above-described smoothing process.

  The distortion correction data storage unit 26 holds data for performing distortion correction when distortion occurs in the Lissajous waveform. The analog signal (A-phase signal and B-phase signal) acquired by the ADC 21 may be distorted by the MR element 10 and an amplifier, a driver, and the like attached thereto. The distortion is caused by a problem in the shape of the magnet 50 and the MR element 10, that is, a geometrical factor. The magnet 50 is formed in a disk shape, and each pole has a semi-circular shape, so that the magnetic flux lines are distributed from semi-circular region to semi-circular region with not being completely uniform but having roundness. Further, the magnetic flux applied to each segment of the bridge circuit formed on the MR element 10 slightly differs depending on the location. These cause distortion in the Lissajous waveform.

  Since such distortion generally varies uniformly depending on temperature characteristics, a correction value for normalization is stored in advance and applied when a Lissajous waveform is created, so that distortion is eliminated (or (Very small) circles can be obtained. In the present embodiment, as will be described later, when calculating an offset, a predetermined candidate point is determined in advance, so that the amount of data to be actually held and the amount of calculation necessary for distortion correction are small.

  FIG. 3 is a diagram for explaining an offset calculation method applied in the present embodiment. Here, three consecutive points from the equally divided candidate points on the circular Lissajous waveform are used, and an offset is calculated from the intersection of the perpendicular bisectors of two sides formed from the three consecutive points. .

Here, the three consecutive points are a first point P1 (X1, Y1), a second point P2 (X2, Y2), and a third point P3 (X3, Y3). A first intersection Pm1 (Xm1, Ym1) between the first point P1 (X1, Y1) and a second point P2 (X2, Y2), and a second intersection P2 (X2, Y2) and a third point P3 (X3, Y3). The second intersection Pm2 (Xm2, Ym2) is obtained by the following equation.
Xm1 = (X1 + X2) / 2
Ym1 = (Y1 + Y2) / 2
Xm2 = (X2 + X3) / 2
Ym2 = (Y2 + Y3) / 2

The intersection P0 (X0, Y0) of the perpendicular bisector L1 of the first intersection Pm1 (Xm1, Ym1) and the perpendicular bisector L2 of the second intersection Pm2 (Xm2, Ym2) is obtained by the following equation. . The value of this intersection P0 (X0, Y0) is the newly calculated offset.
X0 = (Nr1 × Ys2-Nr2 × Ys1) / (Nr1-Nr2)
Y0 = (Ys2-Ys1) / (Nr1-Nr2)
Here, Nr1 (slope of L1), Nr2 (slope of L2), Ys1 and Ys2 are represented by the following equations.
Nr1 =-(X2-X1) / (Y2-Y1)
Nr2 =-(X3-X2) / (Y3-Y2)
Ys1 = Ym1-Nr1 × Xm1
Ys2 = Ym2-Nr2 × Xm2

  4A and 4B are diagrams showing the relationship between the Lissajous waveform and the candidate points. FIG. 4A shows an example in which the waveform is divided into four equal parts, and FIG. 4B shows a case in which FIG. An example is shown.

  As shown in FIG. 4A, it is assumed that the Lissajous waveform is divided into four equal parts, and four intersections (P1 to P4) with the X axis and the Y axis are candidate points. Here, similarly to FIG. 3, the intersection P0 serving as an offset is calculated using the first to third points P1 to P3. In general, at the intersection between the Lissajous waveform and the axis (on the X-axis or the Y-axis), the value of the offset of the obtained intersection P0 (X0, Y0) becomes very accurate because distortion is small. From another viewpoint, an offset can be obtained with sufficient accuracy without performing distortion correction. In the case of a circular Lissajous waveform, an offset can be detected at a central angle of 180 degrees, that is, 90 degrees (180 degrees / 2) when the magnet 50 is rotated. That is, a quick offset calculation process can be performed.

  In FIG. 4B, among the eight candidate points (P1 to P8) at the eight equally-divided positions, the intersection P0 serving as an offset is calculated using the third point P3 to the fifth point P5. I have. When three consecutive points are selected from the eight equally-divided candidate points, one or two points on the X-axis or the Y-axis are always included. Points other than points on the axis have an inclination of ± 45 degrees with respect to the origin, and correspond to intersections of the A-phase signal and the B-phase signal. At this position, since the distortion is large, a value corrected for the distortion is used. As a result, the resulting value of the offset of the intersection point P0 (X0, Y0) becomes very accurate. In this case, in the circular Lissajous waveform, the offset can be detected at a central angle of 90 degrees, that is, 45 degrees when the magnet 50 is rotated. 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, the outline of the offset calculation process will be described with reference to the flowchart of FIG. 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 calculator 22 and the offset controller 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 distortion correction is performed with reference to the distortion correction data storage unit 26 as necessary. Subsequently, the offset calculation unit 24 specifies three consecutive points from the predetermined candidate points (S14), obtains two perpendicular bisectors of a side that can connect the two consecutive points, and calculates an intersection thereof. Then, the latest offset is determined (S18).

  When the latest offset is determined, the offset calculator 24 determines whether or not the first offset has been calculated since the encoder 1 was started (S20).

  If the first offset is to be calculated (Y in S20), the offset calculator 24 notifies the angle calculator 22 of the latest offset (S22). After the notification, the calculated offset is stored in the offset data storage unit 25.

  If the first offset is not calculated (N in S20), the offset calculating unit 24 performs a smoothing process using the latest offset and the previously calculated offset recorded in the offset data storage unit 25 ( S26), and notifies the angle calculation unit 22 of the smoothed offset (S28). After the notification, the calculated offset is stored in the offset data storage unit 25 (S24).

  Although the present invention has been described based on the embodiments, this embodiment is an exemplification, and various modifications can be made to combinations of the respective components, and such modifications are also included in the present invention. It is well understood by those skilled in the art that they are in the range.

1 encoder 10 MR element 20 control unit 21 ADC (A / D conversion unit)
22 Angle calculation unit 23 Offset control unit 24 Offset calculation unit 25 Offset data storage unit 26 Strain correction data storage unit 50 Magnet

Claims (6)

A magnet magnetized to two poles of NS,
A magnetic sensor disposed to face the magnet and outputting 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;
A Lissajous waveform is formed on a rectangular coordinate system based on the A-phase signal and the B-phase signal, an offset between the A-phase signal and the B-phase signal is calculated based on the Lissajous waveform, and the rotation amount is calculated. An offset control unit that corrects the A-phase signal and the B-phase signal when calculating the rotation amount in the calculation unit by the offset.
With
The offset control unit is configured to determine, from among the candidate points equally divided into a predetermined number on the circumference of the Lissajous waveform, the intersection of the perpendicular bisectors of two sides formed from three consecutive points. Perform the operation of detecting the offset several times at different times,
When determining the offset to be applied to calculate the rotation amount, the offset detected at the first three points is used as it is, and the offsets sequentially detected thereafter are weighted and the offset detected at the first three points is weighted. An encoder characterized in that it is reflected in the encoder.   2. The offset control unit according to claim 1, wherein, when there is a distortion in a circle presented by the Lissajous waveform, the offset control unit calculates the offset from the three consecutive points by performing correction so as to be an ideal circle. 3. Encoder.   The encoder according to claim 1, wherein the three consecutive points include at least one intersection point between any one of the coordinate axes of the rectangular coordinate system and the Lissajous waveform.   The encoder according to any one of claims 1 to 3, wherein the three consecutive points are intersections between any of the coordinate axes of the rectangular coordinate system and the Lissajous waveform.   4. The method according to claim 3, wherein the detection of the intersection with the coordinate axis is performed based on a combination of a value obtained when one of the A-phase signal and the B-phase signal becomes zero and the other value. Or the encoder according to 4.   2. The offset control unit according to claim 1, wherein when determining the offset to be applied to calculate the rotation amount, the offset control unit smoothes and uses a previously calculated offset and a latest calculated offset. 6. The encoder according to any one of items 1 to 5.

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