JP2014157069A - Position detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a position detector capable of more accurate position detection.SOLUTION: The position detector includes: a multiplier 7 which calculates A(n) and B(n) as values to be integrated, on the basis of digital signals α(n) and β(n) obtained by A/D conversion of a two-phase analog signal obtained from a position detection sensor 2; an LPF 8 which calculates amplitudes a2 and b2 of secondary higher harmonics by performing second-order low pass filter processing on the output from the multiplier 7; a speed converter 10 which calculates a speed from position data; a storage 9 in which the amplitudes a2 and b2 of secondary higher harmonics are stored only for a period after the lapse of a time proportional to a time constant of the LPF after the calculated time becomes constant, till a time when the speed is changed; a higher harmonic reduction unit 5 which reduces secondary higher harmonic components of the digital signals α(n) and β(n) in accordance with the amplitudes a2 and b2 of the secondary higher harmonics stored in the storage 9; and a position data calculation unit 3 which calculates position data θ from the corrected digital signals.

Description

  The present invention relates to a reduction in harmonic components of an encoder signal such as a rotary encoder that detects a rotation angle of a rotating body such as a motor or a linear encoder that detects displacement of a linear stage or the like.

  A position detection device that reduces the harmonic component of the two-phase signal of the conventional position detection sensor acquires two or more position data calculated by the position data calculation unit based on the two-phase signal, and obtains the third harmonic. There is one that calculates a third harmonic amplitude to be superimposed on each input signal in a wave amplitude calculator (see, for example, Patent Document 1). Hereinafter, a position detection device that reduces the harmonic component of the two-phase signal of the conventional position detection sensor will be described with reference to FIG. In FIG. 3, 1 is an A / D converter that converts two-phase periodic analog signals Sa and Sb obtained from the position detection sensor 2 into digital signals α and β, and 3 is position data calculation that calculates position data. And 4, a harmonic amplitude calculating unit for detecting the third harmonic amplitudes a3 and b3, and a harmonic reducing unit for correcting the two-phase digital signal based on the third harmonic amplitude information. Reference numeral 6 denotes a calculation unit, which includes a position data calculation unit 3, a harmonic amplitude calculation unit 4, and a harmonic reduction unit 5.

  Next, the harmonic amplitude calculation operation in the conventional example will be described. FIG. 4 is a signal waveform diagram for explaining the calculation principle of the harmonic amplitude in the conventional example, and shows the relationship between the fundamental wave and the third harmonic included in the sensor signal. (A) shows the relationship between the fundamental wave and the third harmonic in the A phase signal, and (B) shows the relationship between the fundamental wave and the third harmonic in the B phase signal.

When the third harmonic is superimposed on the sensor signals Sa (cos signal) and Sb (sin signal), the fundamental wave and the third harmonic have a phase relationship as shown in FIG. The digital signals α and β are expressed by the following equations when the amplitude of the fundamental wave is a1, b1, and the amplitude of the third harmonic is a3, b3. However, (theta) is a position.
α = a1 · cos θ + a3 · cos 3θ
β = b1 · sin θ−b3 · sin 3θ

The position data calculation unit 3 calculates position data θ (n) from a two-phase digital signal using an arc tangent calculation (tan ⁻¹ ).

The harmonic amplitude calculation unit 4 calculates position data θ (n) for two or more positions in the A-phase and B-phase digital signals, and digital data α (n) and β (n ) To get. The digital data α (n) and β (n) are expressed by the following equation using the position data θ (n).
a1 · cos (θ (n)) + a3 · cos (3 · θ (n)) = α (n)
b1 · sin (θ (n)) − b3 · sin (3 · θ (n)) = β (n)

  The unknowns in the A phase relational expression are a1 and a3, the B phase relational expression is b1 and b3, and there are two unknowns in both the A phase relational expression and the B phase relational expression. If acquired, a1, a3 and b1, b3 can be obtained.

Third-order harmonic amplitudes a3, b3 from digital data α (n), β (n) and position data θ (n) from two points of data α1, β1, θ1, α2, β2, θ2 at an arbitrary position. Is used, the following equation is used.
a3 = (α1 · cos (θ2) −α2 · cos (θ1)) / (cos (3 · θ1) · cos (θ2) −cos (3 · θ2) · cos (θ1))
b3 = (β1 · sin (θ2) −β2 · sin (θ1)) / (sin (3 · θ2) · sin (θ1) −sin (3 · θ1) · sin (θ2))

Next, the operation of reducing harmonic components will be described. The harmonic reduction unit 5 uses the A phase third harmonic amplitude a3 and the B phase third harmonic amplitude b3 calculated by the harmonic amplitude calculation unit 4 to convert a two-phase digital signal by the following calculation. to correct.
α ′ (n) = α (n) −a3 · cos (3 · θ ′)
β ′ (n) = β (n) + b3 · sin (3 · θ ′)
However, α (n) and β (n) are digital signals of the sensor signals Sa and Sb before correction, and θ ′ is the previous value of the position data θ calculated by the position data calculation unit 3. As described above, in this embodiment, the third harmonic distortion superimposed on the sensor signal can be detected and the distortion can be removed, so that the position data can be calculated with high accuracy.

  Further, in a position detection device that reduces the second harmonic component of the two-phase signal of the conventional position detection sensor, the radius R is calculated from the two-phase signal, and the radius R is fast Fourier transformed to obtain the two-phase signal. There is one that calculates the second harmonic component of (see, for example, Patent Document 2).

Hereinafter, this position detection apparatus will be described with reference to FIGS. When the position detection sensor rotates once, the two-phase signal moves for one cycle, and this range is defined as the wavelength λ. The radius calculator 18 is a numerical value R (R = (α (n) ² + β (n) ² ) ^1/2 indicating the square root of the sum of values obtained by squaring the two-phase signals α (n) and β (n). ² ) is output. The FFT processing unit 19 samples the signal R every 1/32 · λ from the previous change in the position signal θ ′, and performs fast Fourier transform on the 32-point signal R every time the position detection sensor moves by λ. The FFT processing unit 19 outputs a numerical value a2 obtained by dividing the cosine component of the third order component by the square of the zeroth order component and a numerical value b2 obtained by dividing the sine component of the third order component by the square of the zeroth order component.

  It is known that the half value of the cosine component of the third order component and the half value of the sine component of the third order component are substantially equal to the amount of the second harmonic contained in the numerical value α (n) and the numerical value β (n). It has been. The zeroth-order component is the average amplitude of the numerical values α (n) and β (n) when moved by λ and is approximately equal to the amplitudes a1 and b1 of the two-phase signal. From the above, the numerical values a2 and b2 are the same as the numerical values obtained by dividing the number of the second harmonics contained in the numerical values α (n) and β (n) by the square of the amplitudes a1 and b1. The movement amount detector 20 outputs a storage command SET to the storage device 31 every time the position detection sensor moves by λ from the change of the position signal θ ′. The storage device 31 stores numerical values a2 and b2 each time a storage command SET is input. Numerical values a <b> 2 and b <b> 2 stored in the storage device 31 are input to the harmonic reduction unit 5.

  The harmonic reduction unit 5 outputs numerical values DCB2 and DSB2 corresponding to the second harmonics synchronized with the signals α (n) and β (n) by square calculation of the numerical values α (n) and β (n), respectively. . Multipliers 35 and 45 multiply the numerical values a2 and b2 stored in the storage unit 31 respectively, and adjust the amplitudes to numerical values DC2 and DS2 that are substantially equal to the second harmonic contained in the signals α (n) and β (n). The In the subtractors 36 and 46, the numerical values DC2 and DS2 are removed from the numerical values α (n) and β (n), respectively, and are output as numerical values α ′ (n) and β ′ (n). The numerical values α (n) and β (n) are converted into highly precise position data θ of the position detection sensor by the position data calculation unit 3.

JP 2008-304249 A JP 2010-156554 A

  In the conventional example of Patent Document 1, the signal of the position detection sensor includes the second harmonic, and the position detection error caused by this and the position detection error caused by the change due to temperature are high. There is a problem that the detection of an accurate position is hindered. In the prior art, the third harmonic can be detected and reduced, but this second harmonic cannot be detected and reduced.

  In the method of detecting the second harmonic from the radius R described in Patent Document 2, this corresponds to the radius R for every position change of 1 / n 2 within the wavelength λ pitch in order to perform Fourier analysis. The value must be calculated. Therefore, there is a problem that an offset component cannot be extracted because Fourier analysis cannot be performed at a speed at which the position changes by more than λ corresponding to 2 to the nth power per A / D sample period.

  In order to solve the above problem, the position detection apparatus of the present invention is a periodic A-phase and B-phase two-phase sinusoidal analog signal obtained from the sensor signal detection unit in accordance with the positions of two relatively displaced objects. Are converted into digital signals, position data is calculated from the digital signals, and a position detection device that obtains the position of the object from the position data performs operations for inputting the digital signals and extracting second harmonics. A multiplier for performing, a low-pass filter for calculating the amplitude of the second harmonic of the digital signal by inputting the output of the multiplier and performing a second-order low-pass filter processing, and a speed converter for calculating the velocity from the position data After the speed becomes constant, after waiting for a time proportional to the time constant of the low-pass filter, the memory valid signal is turned ON. Harmonic setting means for turning off the signal, a memory for storing the amplitude of the second harmonic, which is the output of the low-pass filter, only when the memory valid signal is ON, and the secondary stored in the memory A harmonic reduction unit that reduces a second harmonic component of the digital signal in accordance with an amplitude of the harmonic, and position data is calculated from the digital signal in which the second harmonic component is reduced.

In a preferred aspect, when the sensor signal detection order is n and the digital signal is α (n), β (n), the multiplier is A (n) = α (n) ³ /0.75. , B (n) = β (n) ³ /0.75 is calculated, and second harmonic extraction values A (n) and B (n) are output.

  A position where high-accuracy position detection is possible by detecting and reducing the second harmonic even if the second harmonic of the signal of the position detection sensor or the second harmonic of this signal changes due to temperature, etc. A detection device can be realized. In addition, it is possible to identify the second harmonic with high accuracy even in the case of a rotational speed at which the position changes by more than λ corresponding to 2 n power per sample period of the AD converter. Accordingly, it is possible to accurately identify the temporal change of the second harmonic even at high speed, remove the accuracy deterioration component, and greatly improve the interpolation accuracy. As a result, both high accuracy and high speed of the position detection device can be achieved.

It is a block diagram which shows the structure of the position detection apparatus which is embodiment of this invention. It is a signal waveform diagram for demonstrating the calculation principle of the harmonic amplitude in embodiment of this invention. It is a block diagram which shows the structure of the conventional position detection apparatus. It is a signal waveform diagram for demonstrating the calculation principle of the harmonic amplitude in a prior art example. It is a block diagram which shows the structure of the other conventional position detection apparatus. It is a detailed block diagram of the harmonic reduction part of the position detection apparatus of FIG.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows an embodiment of the position detection apparatus of the present invention. FIG. 1 is a block diagram corresponding to FIG. 3, and components having the same functions as those in FIG. The multiplier 7 and the low-pass filter (LPF) 8 function as calculation means for calculating the amplitude of the second harmonic. Digital signals α (n) and β (n) are input to the multiplier 7. In order to extract the second harmonic, the multiplier 7 performs the following calculation and outputs A (n) and B (n) to the low-pass filter. A (n) and B (n) are integrated values integrated by the low-pass filter. However, n is a natural number and shows the order of sensor signal detection. Further, the integrand value is a value in which only the amplitude 2a of the second harmonic remains when integrated.
A (n) = α (n) ³ /0.75
B (n) = β (n) ³ /0.75

From here, how the equations for obtaining A (n) and B (n) were derived will be described. The gain of the A phase signal α (n) is adjusted so that the amplitude is 1. In this case, if the second harmonic component is a2 and the position is θ (n), the third power of the A-phase signal α (n) is α (n) ³ = (cos (θ (n)) + a2 · cos ( 2 · θ (n))) ³
= Cos (θ (n)) ³
+ 3 · a2 · cos (θ (n)) ² · cos (2 · θ (n))
+ 3 · a2 ² · cos (θ (n)) · cos (2 · θ (n)) ²
+ A2 ³ · cos (2 · θ (n)) ³
It becomes.

When rotating at high speed, each term passes through a low-pass filter, that is, when integrated, [cos (θ (n)) ³ ] of the first term and [3 · a2 ² · cos (θ (n)) of the third term ) · Cos (2 · θ (n)) ² ] is zero. Further, since a2 is generally as small as several percent or less, when it is raised to the third power, [a2 ³ · cos (2 · θ (n)) ³ ] of the fourth term can be approximated to zero. Of the remaining second term [3 · a2 · cos (θ (n)) ² · cos (2 · θ (n))], [3 · cos (θ (n)) ² · cos (2 · θ The integrated value of the portion (n))] is 0.75. Therefore, when α (n) 3 / 0.75 is passed through the low-pass filter, the amplitude component a2 of the second harmonic is obtained. Since the B phase signal β (n) is only 90 ° out of phase with the A phase signal, it can be calculated in the same manner. Since this calculation does not use the previous position θ ′, the calculation error is small even at high speed.

This calculation can also be obtained as follows. Even in this case, if A (n) and B (n) are integrated, the amplitude value a2 of the second harmonic is obtained.
A (n) = α (n) · COS (2 · θ ′) · 2
B (n) = β (n) · COS (2 · θ ′ + π) · 2

The LPF 8 performs secondary low-pass filter processing on the outputs A (n) and B (n) of the multiplier by the following calculation.
A1 (n) = A1 (n-1) + (A (n) -A1 (n-1)) / k
B1 (n) = B1 (n-1) + (B (n) -B1 (n-1)) / k
A2 (n) = A2 (n-1) + (A1 (n) -A2 (n-1)) / k
B2 (n) = B2 (n-1) + (B1 (n) -B2 (n-1)) / k

  k is a constant that determines the time constant of the low-pass filter, A1 (n) and B1 (n) are calculated values of the first low-pass filter, and A2 (n) and B2 (n) are calculated values of the second low-pass filter. . By performing such calculation, the amplitudes A2 (n) and B2 (n) of the second harmonics of the digital signals α (n) and β (n) can be obtained. The speed converter 10 calculates the speed V from the previous position θ ′ and the previously stored position. After the speed V becomes constant, the harmonic setting means 11 waits for a time proportional to the time constant k of the LPF 8 and then turns on the storage valid signal S. At this time, the calculated values A2 (n) and B2 (n) of the low-pass filter have already converged to become constant values a2 and b2. Further, when the speed V changes, the storage valid signal S is turned OFF. The storage unit 9 updates the stored second harmonic amplitudes A2 (n) and B2 (n), which are the outputs of the LPF 8 and converged to a constant value, as a2 and b2 only when the storage valid signal is ON. To do.

Next, the operation of reducing harmonic components will be described. The harmonic reduction unit 5 corrects the two-phase digital signal by the following calculation using the A-phase second-order harmonic amplitude a2 and the B-phase second-order harmonic amplitude b2 of the storage unit 9.
α ′ (n) = α (n) −a2 · cos (2 · θ)
= Α (n) −a2 · (cos θ ² · 2-1)
Here, since α (n) = cos θ + a2 · cos (2 · θ), cos θ = α (n) −a2 · cos (2 · θ), which is [a2 · cos (2 · θ) compared to α (n). ] Is sufficiently small, so that cos θ≈α (n), and if this is substituted, α ′ (n) = α (n) −a2 · (α (n) ² · 2-1)
It becomes. Similarly,
β ′ (n) = β (n) −b2 · (β (n) ² · 2-1)
It becomes.

This calculation can also be obtained as follows.
α ′ (n) = α (n) −a2 · COS (2 · θ ′)
β ′ (n) = β (n) −b2 · COS (2 · θ ′ + π)
However, α (n) and β (n) are digital signals of the sensor signals Sa and Sb before reduction, and θ ′ is the previous value of the position data θ calculated by the position data calculation unit 3.

  FIG. 2 is a signal waveform diagram for explaining the calculation principle of the harmonic amplitude in this embodiment, and shows the relationship between the fundamental wave and the second harmonic contained in the sensor signal. (A) shows the relationship between the fundamental wave and the second harmonic in the A phase signal, and (B) shows the relationship between the fundamental wave and the second harmonic in the B phase signal. The reason why the phase component is not required in the detection and reduction of the second harmonic component is that the phase relationship between the fundamental wave and the second harmonic component is fixed as shown in FIG. 2 due to the symmetry of the position detection sensor. Because it is.

  With this configuration, even if the second harmonic of the signal of the position detection sensor or the second harmonic of the signal changes due to temperature or the like, the second harmonic component can be detected and reduced. Accurate position detection is possible.

  1 A / D converter, 2 position detection sensor, 3 position data calculation unit, 4 harmonic amplitude calculation unit, 5 harmonic reduction unit, 6 calculation unit, 7, 35, 45 multiplier, 8 low-pass filter, 9, 31 , 33, 43 Memory, 10 Speed converter, 11 Harmonic setting means, 18 Radius calculator, 19 FFT processor, 20 Movement detector, 32, 42 Squarer, 34, 44, 36, 46 Subtractor.

Claims (2)

The A-phase and B-phase two-phase sinusoidal analog signals obtained from the sensor signal detector according to the positions of the two objects that are relatively displaced are converted into digital signals, respectively, and position data is obtained from the digital signals. In the position detection device that calculates and obtains the position of the object from the position data,
A multiplier for inputting the digital signal and performing an operation for extracting a second harmonic;
A low-pass filter that inputs the output of the multiplier and performs second-order low-pass filter processing to calculate the amplitude of the second-order harmonic of the digital signal;
A speed converter for calculating a speed from the position data;
After the speed becomes constant, after waiting for a time proportional to the time constant of the low-pass filter, the storage valid signal is turned ON, and when the speed changes, the harmonic setting means for turning the storage valid signal OFF,
A memory that stores the amplitude of the second harmonic that is the output of the low-pass filter only when the memory valid signal is ON;
A harmonic reduction unit that reduces the second harmonic component of the digital signal in accordance with the amplitude of the second harmonic stored in the memory;
A position detection apparatus for reducing harmonics, wherein position data is calculated from the digital signal in which the second harmonic component is reduced. When the sensor signal detection order is n and the digital signal is α (n), β (n),
The multiplier is
A (n) = α (n) ³ /0.75
B (n) = β (n) ³ /0.75
And the second harmonic extraction values A (n) and B (n) are output.
The position detection device for reducing the second harmonic component according to claim 1.

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