JP2014025871A - Encoder output signal correction apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an encoder output signal correction apparatus which can efficiently detect a correction value of a two-phase sinusoidal wave outputted by an encoder by suppressing a change with respect to fluctuation of a signal.SOLUTION: An encoder output signal correction apparatus has detection means for detecting correction values of an off-set error included in a Lissajous waveform formed by a two-phase sinusoidal wave signal, an amplitude error, and a phase error of the two-phase sinusoidal wave signal. The detection means evenly divides a phase angle of the Lissajous waveform formed by the two-phase sinusoidal wave signal after correction into N (N is an integral number equal to 8 or larger). Moreover, the detection means obtains a change of the sinusoidal wave form represented by a radius of the Lissajous waveform every phase angle and according to an amplitude and a phase of the change, detects a changed portion of the correction value of the off-set error included in the Lissajous waveform, a changed portion of the correction value of the amplitude error, and a changes portion of the correction value of the phase error.

Description

  The present invention relates to an encoder output signal correction device that corrects a two-phase sinusoidal signal of an encoder that detects position, angle, velocity, angular velocity, and the like.

  Since there is a processing limit on the interval of the grating formed on the encoder scale, in order to measure an interval finer than the scale grating, the spatial period of the phase change of the sinusoidal signal output from the encoder is further subdivided and interpolated. There is a need. For this reason, various interpolation circuits are conventionally used. An interpolation circuit by digital processing is, for example, an A / D converter that samples A and B phase sinusoidal signals output from an encoder with different 90 ° phases and converts them into digital data, and this A / D converter. And a memory storing a lookup table for obtaining the phase angle data PH of each sample point based on the digital data DA and DB obtained by the above. The lookup table is created based on PH = ATAN (DB / DA) using an arctangent function (ATAN).

  The A and B phase sine wave signals output from the encoder are not usually perfect sine waves, and generally represent an elliptical Lissajous waveform when expressed in orthogonal coordinates. When the amplitudes of the A and B phase sinusoidal signal voltages are different, the Lissajous waveform becomes an ellipse, and the Lissajous waveform becomes a circle or ellipse waveform deviated from the origin due to the offset error of each signal voltage. Also, if there is a phase error, the major and minor axes of the ellipse will not be parallel to the coordinate axis. Since the interpolation circuit is made on the assumption that the A and B phase sine wave signals are sine waves, the deviation from the ideal sine wave adversely affects the interpolation accuracy. For this reason, for example, Patent Document 1 proposes an apparatus for correcting an offset error, an amplitude error, and a phase error in A and B phase sinusoidal signals.

  In the apparatus described in Patent Document 1, correction values are based on eight intersections of each line of X = 0, Y = 0, Y = X, and Y = −X of the XY coordinates on which the Lissajous waveform is plotted and the Lissajous waveform. Is calculated. However, in such a correction value calculation method, when the feed speed of the detection head is large, the sampling position does not coincide with the data acquisition position, and data is often missed. If data cannot be acquired, the correction value is updated. Can not do it. That is, with the method of Patent Document 1, there are few opportunities for updating correction values, and dynamic correction cannot be performed efficiently. In addition, the correction value obtained by the method of Patent Document 1 changes greatly with respect to signal fluctuations caused by noise, scale defects, and the like.

JP2006-112862

  It is an object of the present invention to provide an encoder output signal correction apparatus that can acquire a correction value of a two-phase sine wave output from an encoder efficiently and while suppressing a change with respect to signal fluctuation.

  The encoder output signal correction apparatus according to the present invention corrects a phase-shifted two-phase sinusoidal signal output from the encoder. The encoder output signal correction apparatus includes a detection unit and a correction unit. The detecting means detects a correction value of an offset error, an amplitude error, and a phase error of the two-phase sine wave signal included in the Lissajous waveform formed by the two-phase sine wave signal. The correction unit corrects the two-phase sinusoidal signal with correction values of the offset error, amplitude error, and phase error detected by the detection unit. The detection means equally divides the phase angle of the Lissajous waveform formed by the two-phase sinusoidal signal after correction by the correction means into N (N is an integer of 8 or more). Further, the detection means obtains a sinusoidal change represented by the radius of the Lissajous waveform for each phase angle, and corrects the amplitude error by the change in the offset error correction value included in the Lissajous waveform from the amplitude and phase of this change. A change in the value and a change in the correction value of the phase error are detected. Then, the detection means dynamically updates the correction values by accumulating the detected changes in the correction values to obtain new correction values.

  ADVANTAGE OF THE INVENTION According to this invention, the encoder output signal correction apparatus which can detect the correction value of the two-phase sine wave output from an encoder efficiently, suppressing the change with respect to the fluctuation | variation of a signal can be provided.

1 is a block diagram showing a basic configuration of an encoder output signal correction apparatus 10 according to an embodiment of the present invention. It is a flowchart which shows the process of the correction apparatus. It is a figure which shows an example of the Lissajous waveform observed. 3 is a flowchart showing details of offset correction, amplitude correction, and phase correction of FIG. 2. It is a figure which shows a Lissajous waveform and the change of phase angle (theta) and the diameter R. FIG. It is a figure which shows a Lissajous waveform and the change of phase angle (theta) and the diameter R. FIG. It is a figure which shows a Lissajous waveform and the change of phase angle (theta) and the diameter R. FIG. It is a figure which shows a Lissajous waveform and the change of phase angle (theta) and the diameter R. FIG. It is a figure which shows a Lissajous waveform and the change of phase angle (theta) and the diameter R. FIG.

  Next, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a block diagram showing a basic configuration of an encoder output signal correction apparatus 10 according to an embodiment of the present invention. The encoder output signal correction apparatus 10 includes A / D converters 20 and 21, an offset / amplitude / phase correction unit 30, an offset / amplitude / phase detection unit 31, and an R-θ conversion unit 40. The signals A0 and B0 are corrected.

  The detection principle of the encoder 50 is not questioned, but is, for example, a photoelectric type or a magnetic type. The A-phase sinusoidal signal and the B-phase sinusoidal signals A0 and B0 output from the encoder 50 usually include an offset error, an amplitude error, a phase error, and the like.

  The signals A 0 and B 0 are sampled at predetermined frequencies by the A / D converters 20 and 21, converted into digital signals A 1 and B 1, and input to the offset / amplitude / phase correction unit 30. The offset / amplitude / phase correction unit 30 corrects the offset, amplitude, and phase of the digital signals A1 and B1 based on the correction values calculated by the offset / amplitude / phase detection unit 31 and outputs output signals A4 and B4. To do.

  The output signals A4 and B4 are sinusoidal output signals whose amplitude, phase, and offset are corrected. The R-θ conversion unit 40 appropriately performs interpolation processing from the output signals A4 and B4 to generate a Lissajous waveform, and calculates a radius R for each phase angle θ of the Lissajous waveform. The offset / amplitude / phase detector 31 stores the radius R for each phase angle θ output from the R-θ converter 40 in an internal R-θ register 31a, and based on this R-θ register 31a The correction value in the amplitude / phase correction unit 30 is calculated.

  Next, details of correction processing using the encoder output signal correction apparatus 10 will be described with reference to FIG. FIG. 2 is a flowchart showing the correction process.

  The A-phase sine wave signal and the B-phase sine wave signals A0 and B0 output from the encoder 50 are first AD converted (S11) to become digital A-phase sine wave signals and B-phase sine wave signals A1 and B1. The signals A1 and B1 can be expressed as the following formula 1.

Here, a ₀ and b ₀ are offset errors of the A phase and the B phase, a ₁ and b ₁ are amplitude errors of the A phase and the B phase, φ ₁ is a phase error of the B phase with respect to the A phase, and u = 2πx / λ , X represents displacement, and λ represents signal pitch. Among these errors, the offset error, amplitude error, and phase error are offset correction processing step (S12) and amplitude correction processing step (S13) executed by the offset / amplitude / phase correction unit 30 and the offset / amplitude / phase detection unit 31, respectively. ) And phase correction processing step (S14). Finally, the phase angle θ is obtained by the R-θ converter 40 using the two-phase sinusoidal signals A4 and B4 from which the error has been removed.

  In this embodiment, dynamic correction using a recurrence formula is performed in each of the correction processing steps (S12 to S14) described above.

  Next, the correction processing step will be described in detail with reference to FIGS. FIG. 3 shows a Lissajous waveform used in the correction processing step, and FIG. 4 shows a flowchart of the correction processing steps (S12 to S14). First, as shown in FIG. 3, a Lissajous waveform for one round is obtained by performing interpolation processing from the A-phase and B-phase sinusoidal signals A4 and B4. Then, the points on the Lissajous waveform are acquired as sample points Pi (i = 0 to N−1) every 2π / N so that the phase angle of the Lissajous waveform is equally divided into N. Since the Lissajous waveform is divided into N equal parts, the sample point Pi does not need to coincide with the sample points of the A / D converters 20 and 21. N is preferably an integer of 8 or more. The calculation time increases as N increases, but the correction value calculation accuracy improves. FIG. 3 shows an example where N = 32.

  Then, as shown in FIG. 4, changes Δda1 and Δdb1 of offset error correction values in the X-axis and Y-axis directions are obtained from the sample points Pi as follows (S111). In the following equation, the phase angle at each sample point Pi is 2πθi / N (i = 0 to N−1, θi = −0.5 to 0.5), and the phase angle from the origin at each sample point Pi is The diameter is Ri (i = 0 to N−1), and the weight coefficient is wd.

  Δda1 and Δdb1 obtained here are close to the offset errors a0 and b0, but do not completely coincide with each other due to the amplitude error and the phase error. Therefore, this error is gradually converged by repeating the feedback process several times. That is, the correction values da1 and db1 are obtained as the cumulative addition values as follows (S112).

  Then, a correction process for removing the offset error from the signals A1 and B1 is executed by the following equation (S113).

  Similarly to the above, the change Δkab of the correction value of the amplitude error in the Y-axis direction with respect to the amplitude in the X-axis direction from the sample point Pi on the Lissajous waveform is obtained as in the following equation (S121). In the following equation, the phase angle at each sample point Pi is 2πθi / N (i = 0 to N−1, θi = −0.5 to 0.5), and the diameter from the origin at each sample point. Is Ri (i = 0 to N−1), and the weighting coefficient is wk.

  Also in this case, the error is gradually converged by repeating the feedback process several times. That is, the correction value kb1 is obtained as a cumulative integrated value as shown in the following equation (S122). The correction value ka1 is fixed at ka1 = 1.

  Then, correction processing for removing the amplitude error from the signals A2 and B2 is executed according to the following formula (S123).

  Similarly to the above, the change Δkp1 in the correction value of the phase error of the A phase and the B phase is obtained from the sample point Pi on the Lissajous waveform as follows (S131). In the following equation, the phase angle at each sample point Pi is 2πθi / N (i = 0 to N−1, θi = −0.5 to 0.5), and the diameter from the origin at each sample point. Is Ri (i = 0 to N−1) and the weighting coefficient is wkp1.

  Also in this case, the error is gradually converged by repeating the feedback process several times. That is, the correction value kp1 is obtained as an accumulated multiplication value as in the following equation (S132).

  Then, a correction process for removing the phase error from the signals A3 and B3 is executed by the following equation (S133).

  As described above, this embodiment is not based on the sample points of the A / D converters 20 and 21, but based on the sample points Pi detected by dividing the phase angle of the Lissajous waveform into N equal parts (N is an integer of 8 or more). A sinusoidal signal can be corrected. Therefore, according to the present embodiment, the correction value detection / update opportunities are increased as compared with the conventional case, and the correction value can be acquired efficiently. In particular, the present embodiment is effective when the sampling speed is low, the detection head feed speed is high, or the signal pitch period is small. In addition, according to the present embodiment, since the correction value is obtained by adding the sine wave function and the cosine wave function using all the sample points Pi, the scale non-uniformity on the scale and the scale mounting alignment are obtained. And the robustness against partial contamination of the scale can be improved. Further, according to the present embodiment, it is possible to improve robustness against short-time (short distance) signal fluctuations caused by noise or the like.

  Next, referring to FIG. 5 to FIG. 9, the equation (Equation 2) used for calculating the offset error correction value, the equation (Equation 5) used for calculating the amplitude error correction value, and the phase error (Equation 8) used in the calculation of the correction value will be described. 5 to 9 are diagrams showing changes in the Lissajous waveform and the phase angle θ and the diameter R. FIG.

  As shown in FIG. 5, when the Lissajous waveform is an ideal perfect circle and its center overlaps the origin, the diameter R is constant with respect to the change in the phase angle θ. On the other hand, as shown in FIG. 6, when the Lissajous waveform includes an offset error in the X-axis direction, the diameter R changes in a cosine wave shape with respect to the phase angle θ. That is, this change is represented by the following approximate proportional expression.

  Therefore, if an appropriate weighting factor is multiplied based on the correlation coefficient between R and cos2πθ, the equation of Δda1 in (Equation 2) is obtained.

  As shown in FIG. 7, when the Lissajous waveform includes an offset error in the Y-axis direction, the diameter R changes in a sine wave shape with respect to the phase angle θ. That is, this change is represented by the following approximate proportional expression.

  Therefore, if an appropriate weighting factor is multiplied based on the correlation coefficient between R and sin2πθ, the equation of Δdb1 in (Equation 2) can be obtained.

  As shown in FIG. 8, when the Lissajous waveform includes an amplitude error, the diameter R changes in a cosine wave shape with respect to the phase angle θ. That is, this change is represented by the following approximate proportional expression.

  Therefore, if an appropriate weighting factor is multiplied based on the correlation coefficient between R and cos4πθ, the formula (Equation 5) is obtained.

  As shown in FIG. 9, when the Lissajous waveform includes a phase error, the diameter R changes in a sine wave shape with respect to the phase angle θ. That is, this change is represented by the following approximate proportional expression.

  Therefore, if an appropriate weighting factor is multiplied based on the correlation coefficient between R and sin4πθ, the equation (Equation 8) is obtained.

  Although the embodiments of the invention have been described above, the present invention is not limited to these embodiments, and various modifications and additions can be made without departing from the spirit of the invention. For example, in the above embodiment, correction of amplitude, phase, and the like is executed by a digital circuit, but similar processing may be performed by a DSP, software, or the like.

  DESCRIPTION OF SYMBOLS 10 ... Encoder output signal correction device 20, 21A ... A / D converter, 30 ... Offset / amplitude / phase correction part, 31 ... Offset / amplitude / phase detection part, 40 ... R-theta conversion part, 50 ... Encoder.

Claims (5)

In an encoder output signal correction device that corrects a phase-shifted two-phase sinusoidal signal output from an encoder,
Detecting means for detecting a correction value of an offset error, an amplitude error, and a phase error of the two-phase sine wave signal included in the Lissajous waveform formed by the two-phase sine wave signal;
Correction means for correcting the two-phase sinusoidal signal with correction values of the offset error, the amplitude error, and the phase error detected by the detection means;
The detection means equally divides the phase angle of the Lissajous waveform formed by the two-phase sinusoidal signal after correction by the correction means into N (N is an integer of 8 or more), and the radius of the Lissajous waveform for each phase angle. A change in the correction value of the offset error, a change in the correction value of the amplitude error, and a correction of the phase error included in the Lissajous waveform are obtained from the amplitude and phase of the change. Encoder output signal correction characterized in that the correction value is dynamically updated by detecting a change in the value and accumulating the detected change in the correction value to obtain a new correction value. apparatus. The detecting means changes the correction value of the offset error included in the Lissajous waveform by adding the sine wave function or cosine wave function represented by one radius of the Lissajous waveform for each phase angle. The encoder output signal correction apparatus according to claim 1, wherein a change amount, a change amount of the correction value of the amplitude error, and a change amount of the correction value of the phase error are detected. The phase angle in the Lissajous waveform is 2πθi / N (i = 0 to N−1, θi = −0.5 to 0.5), and the radius of the Lissajous waveform at each phase angle is Ri (i = 0 to N). -1) and the weighting factor is wd,
The detecting means calculates changes Δda1 and Δdb1 of offset error correction values with respect to the X axis and Y axis on which the Lissajous waveform is drawn, using the following equations, respectively.

The encoder output signal correction apparatus according to claim 2, wherein The phase angle in the Lissajous waveform is 2πθi / N (i = 0 to N−1, θi = −0.5 to 0.5), and the radius of the Lissajous waveform at each phase angle is Ri (i = 0 to N). -1) and the weighting factor is wk,
The detecting means calculates a change Δkab of the correction value of the amplitude error of the other sine wave signal with respect to one sine wave signal using the following equation:

The encoder output signal correction apparatus according to claim 2 or 3, The phase angle in the Lissajous waveform is 2πθi / N (i = 0 to N−1, θi = −0.5 to 0.5), and the radius of the Lissajous waveform at each phase angle is Ri (i = 0 to N). -1) and the weighting factor is wkp1,
The detecting means calculates a change Δkp1 in the correction value of the phase error using the following formula:

5. The encoder output signal correction apparatus according to claim 2, wherein the encoder output signal correction apparatus is characterized in that

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