Magnetic encoder

Abstract

This technology enables the reduction of angular errors and signal delays in magnetic encoders. [Solution] A magnetic encoder having a magnet, a magnetic detection unit, and a control unit, wherein the control unit 30 includes a coordinate transformation unit 330 that converts a measured three-phase sinusoidal signal into a measured two-phase sinusoidal signal, an observer 340 that estimates a two-phase sinusoidal signal from the measured two-phase sinusoidal signal, and a rotation angle calculation unit 350 that calculates the mechanical angle from the two-phase sinusoidal signal estimate. The observer 340 obtains an estimation error by multiplying the difference between the previously estimated two-phase sinusoidal signal temporarily stored in its internal buffer unit 342 and the measured two-phase sinusoidal signal by a predetermined observer gain, and performs feedback control using this estimation error.

Description

[Technical Field]

[0001] This invention relates to a magnetic encoder. [Background technology]

[0002] Conventionally, as a device for detecting the angle of a rotating body such as a motor, magnetic encoders that utilize magnetoresistance (MR) elements or Hall elements are known, as shown in, for example, Patent Document 1.

[0003] Conventional magnetic encoders, for example as shown in the schematic diagram in Figure 8, configure a magnetic detection unit 20 with three magnetic sensors 211, 212, and 213 arranged at 120° intervals, and detect a three-phase sinusoidal signal (Φ U ,Φ V ,Φ W ) is obtained, and this three-phase sinusoidal signal is used to obtain the mechanical angle (θ) of the rotating body. m This detects )

[0004] However, it is unavoidable that noise components will be generated due to variations in the characteristics of the magnetic sensor, assembly errors, temperature changes, etc., and these noise components affect the mechanical angle (θ). m This was the cause of the error.

[0005] Therefore, as shown in the functional block diagram in Figure 9, for example, a filter section is provided to perform low-pass filtering on the three-phase sinusoidal wave signals output from each magnetic sensor, and the mechanical angle (θ) obtained by calculation. m It was known that noise could be reduced by applying two low-pass filtering processes, consisting of a low-pass filtering process on the first and second frequencies, but this method is usually ineffective at reducing noise below a few kHz.

[0006] This is because a signal delay occurs due to the low-pass filter process, and the mechanical angle (θ) after filtering is mfiltThis is because a delay occurs (see Figure 10). Setting the cutoff frequency low to a few kHz or less increases the noise reduction effect, but this also increases the delay, making it difficult to accurately detect the position of the rotating body and affecting controllability. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2018-132359 [Overview of the project] [Problems that the invention aims to solve]

[0008] The present invention aims to reduce angular errors and signal delays in a magnetic encoder. [Means for solving the problem]

[0009] The present invention, made to solve the above problems, is a magnetic encoder for detecting the mechanical angle of a rotating body relative to a stationary body, comprising: a magnet provided on one of the stationary body and the rotating body; a magnetic detection unit provided on the other of the stationary body and the rotating body, which detects changes in the magnetic field from the magnet and outputs a measured three-phase sinusoidal wave signal; and a control unit that calculates the mechanical angle using the measured three-phase sinusoidal wave signal. The control unit comprises a coordinate transformation unit that converts the measured three-phase sinusoidal wave signal into a measured two-phase sinusoidal wave signal; an observer that estimates a two-phase sinusoidal wave signal from the measured two-phase sinusoidal wave signal; and a rotation angle calculation unit that calculates the mechanical angle from the two-phase sinusoidal wave signal estimate. The observer obtains an estimation error by multiplying the difference between the previously estimated two-phase sinusoidal wave signal temporarily stored in its internal buffer unit and the measured two-phase sinusoidal wave signal by a predetermined observer gain, and performs feedback control using the estimation error. [Effects of the Invention]

[0010] According to the present invention, it is possible to reduce angular errors and signal delays in a magnetic encoder. [Brief explanation of the drawing]

[0011] [Figure 1] A diagram showing the overall configuration of an example embodiment of the magnetic encoder according to the present invention. [Figure 2] A schematic diagram showing the arrangement of the magnetic detection unit and output signal in the embodiment shown in Figure 1. [Figure 3] A functional block diagram showing the control unit in the embodiment shown in Figure 1. [Figure 4] A flowchart showing the processing performed by the observer and rotation angle calculation unit in the embodiment shown in Figure 1. [Figure 5] This diagram shows the flowchart in Figure 4 replaced with a calculation formula. [Figure 6] A graph showing the operating waveform in the embodiment shown in Figure 1. [Figure 7] A diagram showing the overall configuration of an example of a conventional magnetic encoder. [Figure 8] Figure 7 is a schematic diagram showing the arrangement of the magnetic detection unit and output signal in a conventional example. [Figure 9] Figure 7 shows a functional block diagram illustrating the control unit in a conventional example. [Figure 10] Figure 7 shows a graph illustrating the operating waveform in a conventional example. [Modes for carrying out the invention]

[0012] Embodiments of the present invention will be described below with reference to the drawings.

[0013] <Conventional Example> First, a conventional magnetic encoder will be explained with reference to Figures 7 and 8. This magnetic encoder 2 uses a three-phase sinusoidal signal detected by the magnetic detection unit 20 to determine the mechanical angle (θ) of the rotating body. m) is for detection. The magnetic detection unit 20 in the magnetic encoder 2 detects the change in the magnetic field of the rotating magnet 10 by three magnetic sensors 21, 22, and 23 arranged at intervals of 120° in the mechanical angle in the circumferential direction around the axis of the rotating body, and outputs three-phase sine wave signals (Φ U , Φ V , Φ W ) of U-phase, V-phase, and W-phase. Generally, it outputs such signals.

[0014] As the magnetic sensor, a Hall sensor using a Hall element or an MR sensor using a magnetoresistive element (MR element) is typical. In this specification, a magnetic encoder of a conventional example will be described in which a Hall sensor is used as the magnetic sensor and three Hall sensors are arranged on the outer peripheral side of a two-pole magnet magnetized in the radial direction.

[0015] FIG. 9 is a functional block diagram showing the control unit 30 in the magnetic encoder 2 of the conventional example. The magnetic encoder 2 has a first filter unit 320, a coordinate conversion unit 330, a rotation angle calculation unit 350, and a second filter unit 360 in a control unit 30 composed of electronic components such as an IC or a microcomputer. The first filter unit 320 and the second filter unit 360 perform low-pass filter processing, and for example, a soft filter implemented by a program as shown in the following calculation formula can be used.

[0016]

Equation

[0017] When three-phase sine wave signals (Φ U , Φ V , Φ W ) of U-phase, V-phase, and W-phase are output from the magnetic detection unit 20 to the control unit 30, the first filter unit 320 performs low-pass filter processing to obtain three-phase sine wave signals after filtering (Φ Ufilt , Φ Vfilt , Φ Wfilt ), and then, two-phase sine wave signals (Φ α , Φ βConvert to (alpha-beta conversion).

[0018]

number

[0019] Two-phase sine wave signal (Φ α ,Φ β Once the θ is obtained, calculate the arctangent using the following formula to determine the mechanical angle of the rotating body (θ). m ) obtain.

[0020]

number

[0021] Mechanical angle (θ m Once the desired result is obtained, the second filter section 360 performs low-pass filtering to remove noise and smooth the signal, and the filtered mechanical angle (θ) is then processed. mfilt ) and the mechanical angle after this filter (θ mfilt The mechanical angle of the rotating body is output as θ. Therefore, in the conventional example described above, as shown in Figure 6, the mechanical angle (θ m The machine angle (θ) after the second low-pass filter processing is performed after calculation. mfilt This causes a signal delay. And because the signal delay becomes larger, it is difficult to reduce noise below a few kHz.

[0022] <This invention> Figure 1 is a schematic diagram showing the overall configuration of an example embodiment of the magnetic encoder 1 according to the present invention. This magnetic encoder 1 controls the mechanical angle (θ) of a rotating body, such as the rotor of a synchronous motor. m It is used to detect the mechanical angle (θ) of the rotating body. The magnetic encoder 1 uses the three-phase sinusoidal signal detected by the magnetic detection unit 20 arranged around the magnet 10 to control the control unit 30, which then determines the mechanical angle (θ) of the rotating body. m ) detects.

[0023] Figure 2 is a schematic diagram showing the arrangement and output signals of the magnetic detection unit 20 in the magnetic encoder 1. As shown in Figure 2, the magnetic detection unit 20 consists of six magnetic sensors 21, 22, 23, 24, 25, and 26 arranged on the outer circumference of a radially magnetized two-pole magnet. In this embodiment, Hall sensors using Hall elements are used as magnetic sensors.

[0024] Similar to conventional examples, three magnetic sensors 21, 22, and 23, arranged circumferentially around the axis of the rotating body at mechanical angle intervals of 120°, detect changes in the magnetic field of the rotating magnet and generate a three-phase sinusoidal signal (Φ) of U-phase, V-phase, and W-phase. U ,Φ V ,Φ W ) will be output.

[0025] Then, the three magnetic sensors 24, 25, and 26, positioned axially symmetric to the magnetic sensors 21, 22, and 23, detect the change in the magnetic field of the rotating magnet and generate a three-phase sinusoidal signal (Φ) with U-phase, V-phase, and W-phase components that are inverse phase with the U-phase, V-phase, and W-phase three-phase sinusoidal signal. -U ,Φ -V ,Φ -W ) will be output.

[0026] In other words, the magnetic sensor consists of three sets, A to C, where each set comprises two of the aforementioned magnetic sensors positioned axially symmetrically with respect to the rotation axis of the rotating body. A: U phase (Φ U ) and -U phase (Φ -U A pair of magnetic sensors, 21 and 24, that output a measured three-phase sinusoidal signal. B: V phase (Φ V ) and -V phase (Φ -V A pair of magnetic sensors, 22 and 25, that output a measured three-phase sinusoidal signal. C: W phase (Φ W ) and -W phase (Φ -W A pair of magnetic sensors, 23 and 26, that output a measured three-phase sinusoidal signal.

[0027] Therefore, the following equation (1) gives the three-phase sinusoidal signal (Φ) of the U-phase, V-phase, and W-phase.U ,Φ V ,Φ W ) and the inversely phased -U, -V, and -W phases of a three-phase sinusoidal signal (Φ -U ,Φ -V ,Φ -W By calculating the difference between (Φ), common-mode noise is removed, and the measured three-phase sinusoidal signal after noise removal (Φ) is obtained. US ,Φ VS ,Φ WS ) can be obtained.

[0028]

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[0029] Figure 3 is a functional block diagram showing the control unit 30 in the magnetic encoder 1. The magnetic encoder 1 has a control unit 30, which is composed of electronic components such as an IC or microcontroller, and includes a common-mode noise removal unit 310, a filter unit 320, a coordinate transformation unit 330, an observer 340, and a rotation angle calculation unit 350.

[0030] The common-mode noise reduction unit 310 calculates the measured three-phase sinusoidal signals (Φ) of the U-phase, V-phase, and W-phase output from the magnetic detection unit 20 using the above formula (1). U ,Φ V ,Φ W ) and the measured three-phase sinusoidal signals of the -U, -V, and -W phases which are in opposite phase (Φ -U ,Φ -V ,Φ -W ) The difference is calculated to obtain the measured three-phase sinusoidal signal (Φ) after noise reduction. US ,Φ VS ,Φ WS Outputs ).

[0031] The filter section 320 filters the measured three-phase sinusoidal signal (Φ) after noise removal. US ,Φ VS ,Φ WS ) is subjected to a low-pass filter and the measured three-phase sinusoidal signal (Φ USfilt ,Φ VSfilt ,Φ WSfilt) This low-pass filter process removes noise components caused by circuit board wiring, temperature changes, etc. This low-pass filter process can use a soft filter implemented in a program, for example, similar to the conventional magnetic encoder 2. However, for example, the measured three-phase sinusoidal signal after noise removal (Φ US ,Φ VS ,Φ WS If the noise component can be sufficiently removed, this low-pass filtering process may be omitted.

[0032] The coordinate transformation unit 330 uses the following formula (2) to calculate the filtered measured three-phase sinusoidal signal (Φ USfilt ,Φ VSfilt ,Φ WSfilt ) is a measured two-phase sinusoidal signal of α-phase and β-phase (Φ αS ,Φ βS Convert to (alpha-beta conversion).

[0033]

number

[0034] Observer 340 is a sinusoidal observer and consists of an estimation unit 341 and a buffer unit 342. Observer 340 receives a measured two-phase sinusoidal signal (Φ αS ,Φ βS ) From this, the estimated value of the two-phase sinusoidal signal (Φ αOB ,Φ βOB This is an estimate of ).

[0035] The buffer unit 342 calculates the estimated two-phase sinusoidal signal value output from the estimation unit 341 from the previous estimated two-phase sinusoidal signal value (Φ αOB_pre ,Φ βOB_pre Stored temporarily as (Φ). Previous two-phase sinusoidal signal estimate (Φ αOB_pre ,Φ βOB_pre ) is input again to the estimation unit 331.

[0036] The principle of a sine wave observer is explained below.

[0037] <Measured two-phase sine wave signal (Φ αS , Φ βS ) deformation> First, when constructing the observer 340, solve the differential equation for the parameter to be estimated. In the present invention, the estimated values of the two-phase sine wave signal (Φ αOB , Φ βOB ) are used as the parameters to be estimated.

[0038] When the measured two-phase sine wave signal (Φ αS , Φ βS ) is expressed by trigonometric functions, it becomes as shown in the following formula (3).

[0039]

Equation

[0040] Assuming that the angular error (Δθ) is sufficiently smaller than the measured two-phase sine wave signal (Φ αS , Φ βS ), the above formula (3) is transformed into the following formula (4) by the addition theorem formula.

[0041]

Equation

[0042] Furthermore, the angular error (Δθ) is expressed as the product of the mechanical angular velocity (ω m ) and the operation processing period (T s ) as shown in the following formula (5).

[0043]

Equation

[0044] When substituting formula (5) into formula (4), it is transformed into the following formula (6).

[0045]

Equation

[0046] <Differentiation of the measured two-phase sine wave signal (Φ αS , Φ βS ), and calculation of the mechanical angular velocity (ω m )> The differential values (dΦ αS , dΦ βS ) of the measured two-phase sine wave signal are expressed by the following formula (7) assuming that the angular error (Δθ) is sufficiently small.

[0047]

Equation

[0048] The mechanical angular velocity (ω m ) satisfies the relationship shown in the following formula (8).

[0049]

Equation

[0050] The relationship shown in formula (8) is derived as shown in the following formula (9).

[0051]

Equation

[0052] By referring to formula (7) and transforming formula (8), the mechanical angular velocity (ω m ) can be expressed as shown in the following formula (10).

[0053]

Equation

[0054] <Construction of the observer> An observer (sine wave observer) for calculating the error between the measured value and the estimated value (estimation error) and performing feedback control using the estimation error is constructed.

[0055] The estimation error (e ΦTα , eΦTβ ) is a measured two-phase sinusoidal signal (Φ αS ,Φ βS ) from which the previously estimated two-phase sinusoidal signal (Φ) was temporarily stored in the buffer section 342 αOB_pre ,Φ βOB_pre The difference after subtracting the observer gain (K Φ Multiplying by ), it is expressed as shown in the following formula (11).

[0056]

number

[0057] As shown in the following equation (12), the mechanical angular velocity (ω) in the above equation (10) m The formula for calculating the cutoff frequency (f ω ) is filtered to obtain the estimated machine angular velocity (ω mOB ) obtain.

[0058]

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[0059] The measured two-phase sinusoidal signal (Φ) in the above formula (6) αS ,Φ βS The formula for calculating (7) and the derivative of the measured two-phase sinusoidal signal (dΦ) αS ,dΦ βS Using the formula (11) above, the estimated error (e ΦTα ,e ΦTβ The following formula (13) provides feedback. The estimated value of the two-phase sinusoidal signal (Φ αOB ,Φ βOB The derivative of the estimated two-phase sinusoidal signal (dΦ) is calculated using the following formula (14): αOB ,dΦ βOB ) is calculated.

[0060]

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[0061]

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[0062] In the above formula (11), the estimation error of the α phase and β phase (e ΦTα ,e ΦTβ When calculating the differential value (dΦ) of the measured two-phase sinusoidal wave signal, the original method is to use the differential value (dΦ) of the measured two-phase sinusoidal wave signal. αS ,dΦ βS ) from the previous estimated two-phase sinusoidal signal (dΦ αOB_pre ,dΦ βOB_pre The difference after subtracting the observer gain (K Φ It is desirable to multiply by ). However, the effect of noise reduction changes depending on the value of this estimation error. Therefore, from the viewpoint of reducing the amount of computation and from the viewpoint of making fitting easier, the above formula (14) is used to multiply the estimation errors (e) of the α phase and β phase obtained in the above formula (11). ΦTα ,e ΦTβ ) Adjustable gain (K dΦ The formula was to multiply by ).

[0063] That is, the adjustment gain (K) in the above formula (14) dΦ ) is a coefficient used to convert the estimation error between the measured two-phase sinusoidal wave signal and the previously estimated two-phase sinusoidal wave signal into the estimation error between the derivative of the measured two-phase sinusoidal wave signal and the derivative of the previously estimated two-phase sinusoidal wave signal. Adjustment gain (K dΦ ) is a number greater than 0 and less than or equal to 1 (0 <K dΦ It is set to ≤1).

[0064] Estimated value of two-phase sinusoidal signal (Φ αOB ,Φ βOB Once the result is obtained, the arctangent is calculated using the following formula (15), and the machine angle (θ) after observer processing of the rotating body is calculated. mOB ) obtain.

[0065]

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[0066] Machine angle (θ) after observer processing of the rotating body mOBOnce the value is obtained, it is used as the mechanical angle of the detected rotating body for various control purposes. For example, if the rotor of a synchronous motor is the rotating body to be detected by the magnetic encoder 1, the mechanical angle (θ) after observer processing will be used. mOB This can be used as the rotor rotation angle for various control purposes. Unlike conventional methods, there is no need to perform low-pass filtering by the second filter unit, so there is no delay in the mechanical angle.

[0067] Also, the derivative of the estimated two-phase sinusoidal signal (dΦ) αOB ,dΦ βOB After calculating the two-phase sinusoidal signal (Φ) in the calculation process, αOB ,Φ βOB ) is the previously estimated two-phase sinusoidal signal (Φ αOB_pre ,Φ βOB_pre It is temporarily stored in buffer section 342 as the previous two-phase sinusoidal signal estimate (Φ αOB_pre ,Φ βOB_pre ) is the estimated error (e) of formula (11). ΦTα ,e ΦTβ This is used in the calculation and feedback control is performed.

[0068] Figure 4 is a flowchart illustrating the processing performed by the observer 340 and the rotation angle calculation unit 350 of the control unit 30. Figure 5 shows the flowchart in Figure 4 replaced with calculation formulas. The numbers in parentheses at the right end of Figure 5 indicate the formulas used in this specification.

[0069] Figure 6 shows the operating waveform of this embodiment. In the conventional operating waveform shown in Figure 10, a delay occurred in the rotation angle (θ) as the rotational speed of the rotating body increased. On the other hand, in the operating waveform of this embodiment shown in Figure 6, noise reduction is possible without delay even at high rotational speeds, and the rotational angle error of the rotating body to be detected can be reduced, which can greatly contribute to improving the controllability of a synchronous motor, for example.

[0070] It should be noted that the embodiments of the present invention are not limited to those having three sets of six magnetic sensors as shown in Figure 2. For example, it is also possible to implement the invention with only three magnetic sensors, similar to the conventional example shown in Figure 8. [Explanation of Symbols]

[0071] 1. Magnetic encoder 10 Magnets 20 Magnetic detection unit 21 Magnetic Sensor 22 Magnetic Sensors 23 Magnetic Sensor 24 Magnetic Sensors 25 Magnetic Sensors 26 Magnetic Sensors 30 Control Unit 310 Common-mode noise rejection section 320 Filter section 330 Coordinate Transformation Unit 340 Observers 341 Estimation Department 342 Buffer section 350 Rotation Angle Calculation Unit

Claims

1. A magnetic encoder for detecting the mechanical angle of a rotating body relative to a stationary body, A magnet provided on one of the fixed body and the rotating body, A magnetic detection unit is provided on the other of the fixed body and the rotating body, which detects changes in the magnetic field from the magnet and outputs a measured three-phase sinusoidal signal. The system includes a control unit that calculates the mechanical angle using the measured three-phase sinusoidal signal, The control unit, A coordinate transformation unit that converts the measured three-phase sinusoidal signal into a measured two-phase sinusoidal signal, An observer that estimates a two-phase sinusoidal signal value from the measured two-phase sinusoidal signal, The system includes a rotation angle calculation unit that calculates the mechanical angle from the estimated two-phase sinusoidal signal, The observer obtains an estimation error by multiplying the difference between the previously estimated two-phase sinusoidal signal value temporarily stored in its internal buffer section and the measured two-phase sinusoidal signal by a predetermined observer gain, and performs feedback control using the estimation error. A magnetic encoder characterized by the following:

2. The magnetic detection unit consists of six magnetic sensors. The magnetic sensor is configured as a set of two magnetic sensors positioned axially symmetrically with respect to the rotation axis of the rotating body, U-phase (Φ Ｕ ) and -U phase (Φ －Ｕ A set that outputs a measured three-phase sinusoidal signal, V phase (Φ Ｖ ) and -V phase (Φ －Ｖ A set that outputs a measured three-phase sinusoidal signal, W phase (Φ Ｗ ) and -W phase (Φ －Ｗ It consists of three sets: one that outputs a measured three-phase sinusoidal signal, and another set that outputs a measured three-phase sinusoidal signal. Each set is arranged at 120° intervals in the circumferential direction. The magnetic encoder according to claim 1, characterized by the features described above.

3. The control unit further comprises a common-mode noise rejection unit, The common-mode noise removal unit calculates the difference between the measured three-phase sine wave signals of the U-phase (Φ Ｕ ), V-phase (Φ Ｖ ), and W-phase (Φ Ｗ ) output by the magnetic sensor and the measured three-phase sine wave signals of the -U-phase (Φ －Ｕ ), -V-phase (Φ －Ｖ ), and -W-phase (Φ －Ｗ ) with opposite phases, and obtains the measured three-phase sine wave signals after noise removal (Φ ＵＳ , Φ ＶＳ , Φ ＷＳ ). The magnetic encoder according to claim 2, characterized by the features described above.

4. The control unit, The mechanical angle obtained by the arctangent calculation of the rotation angle calculation unit is not subjected to low-pass filtering. The magnetic encoder according to claim 1, characterized by the features described above.

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