JP2008304305A - Method and apparatus for detecting amplitude of sinusoidal wave - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To sample A/D-converted values, to obtain values approximated to the true maximum value and minimum value of a sinusoidal wave after local maximum values and local minimum values are selected from the samples, and accurately detect an amplitude of the sinusoidal wave. <P>SOLUTION: In an apparatus 14 for detecting the amplitude of the sinusoidal wave, the sinusoidal wave is A/D-converted for a constant sampling period at an arbitrary frequency. The tentative maximum value or minimum value is extracted from digital data of the sampled sinusoidal wave. The maximum or minimum data passes through a low pass filter. A correction coefficient A is determined and obtained based on the frequency and the sampling period of the sinusoidal wave. The tentative maximum value or the minimum value is corrected by multiplying an output from the low pass filter by the correction coefficient A. The amplitude of the sinusoidal wave is detected. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a sine wave amplitude detection device, and in particular, processes a sine wave signal output from a position detector for detecting an angle and a position, and digitally samples and extracts maximum and minimum value data. The present invention relates to a discrete signal processing technique that corrects and makes it possible to accurately detect the amplitude value of a sine wave.

  In a machine tool, various signal processing techniques are performed in a control technique for detecting a position and an angle of a moving body using a position detector such as a rotary encoder and a linear scale. Usually, an output signal of an encoder or a linear scale is an analog signal approximated to a sine wave, and it is necessary to perform signal processing by performing analog-digital conversion and converting it into a digital signal that represents a quantity linearly.

  As a sine wave signal processing technique performed before and after this type of analog-digital conversion, for example, an offset error, an amplitude error, a phase error, a third harmonic component, etc. included in a two-phase sine wave signal output from an encoder There is a signal correction device that removes (Patent Document 1). This patent document 1 is a signal correction technique for removing an offset or distortion contained in a sine wave signal to obtain an ideal sine wave.

  In the case of position detection by an encoder, the output sine wave is subjected to analog-digital conversion, and then signal processing for obtaining the amplitude of the original sine wave is performed. In the conventional method, after sampling at a fixed period, the maximum or minimum value data is selected by comparing the sampled data, and these data are regarded as the maximum and minimum values of the original sine wave. That's it.

FIG. 4 shows a maximum value and a minimum value in data obtained by analog-digital conversion of a sine wave. In FIG. 4, the maximum value and minimum value data can be obtained by comparing the magnitudes of the data while sampling the data at the sampling period ts.
JP 2006-112862 A

  Thus, when the maximum value and the minimum value are selected from the data obtained by sampling by analog-digital conversion, an error is included in the direction in which the absolute value is always smaller than the true maximum value and minimum value of the sine wave.

  FIG. 4 shows a sine wave whose maximum value and minimum value are close to the true maximum value and minimum value of the sine wave when the maximum value and the minimum value are selected from the data obtained by sampling. The error that occurs between the maximum and minimum values sampled from an analog sine wave and the true maximum and minimum values is correlated with the frequency of the sine wave and the sampling period. If the frequency is the same, the error tends to increase as the sampling period increases. As shown in FIG. 5, if the sampling period is the same, the error tends to increase as the frequency of the sine wave increases.

  Furthermore, the cause of the error is that the period of the sine wave and the sampling timing are not necessarily synchronized. Even if the frequency of the sine wave is constant, sampling is not always possible at a fixed position. For this reason, variations inevitably occur in the maximum value and the minimum value selected from the sampled data. This variation can be stabilized to some extent by passing the selected data through a low-pass filter, but even in that case, the absolute value is still smaller than the true maximum and minimum values of the sine wave. It does not change to the problem of including errors.

  Therefore, the object of the present invention is to solve the problems of the prior art, sample the analog-digital converted value, select the maximum value and the minimum value from them, and then set the period of the sine wave and the sampling period. A sine wave amplitude detection device capable of accurately detecting the amplitude of a sine wave by obtaining a value as close as possible to the true maximum and minimum values of the sine wave by correcting with a corresponding correction coefficient. It is to provide.

  In order to achieve the above object, the present invention is an apparatus for detecting an amplitude of an analog sine wave having an arbitrary frequency after analog-to-digital conversion at a constant sampling period, and detecting the amplitude of the sine wave. Means for extracting a provisional maximum value or minimum value from the digital data, a low-pass filter to which the data of the maximum value or minimum value is input, and means for detecting the frequency of the sine wave from the digital data of the sine wave A correction coefficient generator for generating a correction coefficient A determined based on the frequency and sampling period of the sine wave, and data of a maximum value or a minimum value by multiplying the output of the low-pass filter by the correction coefficient A And correcting means for outputting amplitude data of a sine wave.

  The present invention is also a method for detecting an amplitude of an sine wave having an arbitrary frequency at a constant sampling period after analog-to-digital conversion of the analog sine wave having an arbitrary frequency at a constant sampling period. Analog-to-digital conversion, the provisional maximum value or minimum value is extracted from the sampled sine wave digital data, the maximum value or minimum value data is passed through a low-pass filter, and the frequency and sampling period of the sine wave are set. A correction coefficient A determined based on the above is obtained, and the provisional maximum value or minimum value data is corrected by multiplying the output of the low-pass filter by the correction coefficient A, and the amplitude of the sine wave is detected. Is.

In the present invention, the correction coefficient A is expressed as follows: sine wave digital data sampling period is ts and sine wave period is T.

Is given by.

  According to the present invention, the analog-digital converted value is sampled, and after selecting the maximum value and the minimum value from the sample, the relationship between the selected temporary maximum value and minimum value and the true maximum value and minimum value is determined. By correcting with the derived correction coefficient, it is possible to realize discrete signal processing that obtains a value close to the true maximum value and minimum value of the sine wave and detects the amplitude of the sine wave with high precision.

Hereinafter, an embodiment of a sine wave amplitude detection device according to the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a block diagram showing a configuration of an embodiment in which the present invention is applied to a technique for discretely processing a sine wave signal from a position detector. In FIG. 1, reference numeral 10 indicates a position detector such as an encoder or a linear scale, and reference numeral 12 indicates an analog-digital-converted sine wave output from the position detector 10 at a constant sampling period. A digital converter is shown (hereinafter abbreviated as A / D converter). Reference numeral 14 indicates the entire amplitude detection apparatus.

  The position detector 10 detects the position of a moving body such as a table in a machine tool. The position detector 10 outputs an analog sine wave having a constant frequency. Here, it is assumed that the sine wave is an ideal sine wave having no offset or distortion by being processed by a known signal processing technique.

  In FIG. 1, sampling data output from the A / D converter 12 is introduced into a maximum value / minimum value detection unit 16. The maximum value / minimum value detection unit 16 outputs the detected maximum value data to the first low-pass filter 18, and the minimum value data is output to the second low-pass filter 20.

  On the other hand, the frequency detection unit 22 detects the frequency of the sine wave by measuring the sign change interval of the sampling data given from the A / D converter 12 and outputs it to the correction coefficient generation unit 24. The correction coefficient generator 24 generates a correction coefficient A based on the frequency of the sine wave and the sampling period.

  The maximum value correction unit 25 outputs the maximum value of the sine wave obtained by multiplying the data that has passed through the first low-pass filter 18 by the correction coefficient A. Similarly, the minimum value correction unit 26 multiplies the data that has passed through the second low-pass filter 20 by the correction coefficient A and outputs the minimum value of the sine wave.

  The above is an outline of the configuration of the amplitude detection device 14, and next, specific functions of each component will be described.

  The detection of the maximum value in the maximum value / minimum value detection unit 16 is the same as described in the section of the prior art, and the maximum value or the minimum value is determined by comparing the data sampled by the A / D converter 12. Are selected and detected as the maximum and minimum values. As described above, the maximum value and the minimum value detected at this time are not true maximum values and minimum values but include errors.

Here, the relationship between the sampling period ts in the A / D converter 12 and the true maximum value will be described (the same applies to the true minimum value).
When the largest data among digital data obtained by sampling an analog sine wave at a constant sampling period ts is set as a provisional maximum value, the true maximum value is determined before and after the provisional maximum value is sampled. Appears in the middle of sampling time. If so, the time interval between the time when the provisional maximum value data is sampled and the time when the true maximum value is expressed is 0 (s) at the minimum and ts (s) at the maximum.

  Next, assuming that the sine wave repeats the cycle many times and a large number of maximum value data is detected, the relationship of the maximum value data based on the true maximum value is considered. At this time, as shown in FIG. 2, the maximum value data represented by white dots is a range of time intervals of ± ts / 2 (s) centered on the time of the true maximum value represented by black dots. Exists within. Since the sine wave and the sampling period are asynchronous, the distribution is considered to be stochastically uniform.

Next, the meaning of the process of passing such maximum value data through the first low-pass filter 18 will be considered.
As described above, the provisional maximum value data is data that exists in a stochastic uniform distribution within a time interval of ± ts / 2 (s) around the time of the true maximum value. Moreover, since the true maximum value itself does not fluctuate with a predetermined value, the output data of the first low-pass filter 18 is expected to show a certain value.

  Assuming that the frequency of the sine wave, the true maximum value of the sine wave, and the sampling frequency are constant values, the output data of the first low-pass filter 18 is ± ts / It can be regarded as the average value Vlp of the data that can exist probabilistically in the time interval of 2 (s). Although not shown in the block diagram of FIG. 1, the measured sine wave cycle is not desired to change rapidly, so a value stabilized by passing the detected frequency data through a low-pass filter is adopted. It is preferable.

Therefore, when an average value of the maximum value data is obtained by dividing the time interval of ± ts / 2 (s) infinitely around the true maximum value of the sine wave, it can be expressed by Expression (1).

  Here, the average value is Vlp, the true maximum value is P, the sine wave period is T, and the sampling period is ts.

Solving this for the true maximum value P,

It becomes.

Next, when equation (2) is transformed into equation (3),

This equation (3) means that the true maximum value can be obtained by multiplying the average value Vlp by the correction coefficient A. In this case, the correction coefficient A can be calculated by the equation (4).

Here, FIG. 3 is a graph showing a result of calculating the correction coefficient A from the frequency of the sine wave when the sampling period ts = 1 (μs).
As the position detector 10, for example, it is assumed that a rotary encoder capable of generating a sine wave of 512 cycles per round is used. When the rotation speed is 10,000 rpm, the frequency of the rotary encoder is 85.333 kHz. The correction count generation unit 24 may calculate the correction coefficient A in this case from Equation 4, or store a data table like the graph of FIG. 3 for each sampling period in advance, and the sampling period and frequency at that time The correction coefficient A may be generated by reading the correction coefficient A corresponding to the above from the table.

  Next, using the correction coefficient A thus obtained, the maximum value correction unit 25 performs correction by multiplying the temporary maximum value that has passed through the first low-pass filter 18 by the correction coefficient A. Thereby, it is corrected to a value that is as close as possible to the true maximum value of the sine wave, and this value is detected as the amplitude of the sine wave. This detection data is output to the numerical control device of the machine tool.

  As described above, the correction coefficient A determined from the equation (4) is corrected to the provisional maximum value that has passed through the first low-pass filter 18 by the correction coefficient A, so that the amplitude of the sine wave is as much as possible. High-precision detection close to the value of can be realized.

  The sine wave amplitude detection device according to the present invention has been described with the preferred embodiment. However, the present invention discretely processes a sine wave signal obtained by digitally sampling the signal from the position detector. In the embodiment, the function realizing means constituting the present invention can be realized by a software program, an LSI logic circuit such as ASIC or FPGA, or the like.

The block diagram which shows the structure of the amplitude detection apparatus of the sine wave by one Embodiment of this invention. The figure which shows the relationship between the temporary maximum value taken out from the data sampled by analog-digital conversion, and a true maximum value. The graph which shows the specific example of a correction coefficient. The figure which shows the relationship between the sample data which carried out analog-digital conversion in the conventional signal processing which detects the amplitude of a sine wave, and a sine wave. The figure which shows the correlation from which the error of the taken-out maximum value and a true maximum value changes with high and low in conventional signal processing.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Position detector 12 A / D converter 14 Amplitude detector 16 Maximum value / minimum value detector 18 First low-pass filter 20 Second low-pass filter 22 Frequency detector 24 Correction coefficient generator 25 Maximum value corrector 26 Minimum value correction unit

Claims (5)

An apparatus for detecting an amplitude of an analog sine wave having an arbitrary frequency after analog-to-digital conversion at a constant sampling period,
Means for extracting a provisional maximum value or minimum value from sampled sine wave digital data;
A low-pass filter to which the data of the maximum value or the minimum value is input;
Means for detecting the frequency of the sine wave from the digital data of the sine wave;
A correction coefficient generator for generating a correction coefficient A determined based on the frequency of the sine wave and the sampling period;
Correction means for correcting the data of the maximum value or the minimum value by multiplying the output of the low-pass filter by the correction coefficient A, and outputting amplitude data of a sine wave;
A sine wave amplitude detecting device comprising: The correction coefficient A is expressed as follows: sine wave digital data sampling period is ts and sine wave period is T.

The amplitude detector for a sine wave according to claim 1, wherein   The sine wave amplitude detection device according to claim 1, wherein the analog sine wave is an output of a detector that detects a position or an angle of a moving body of a machine tool. A method of detecting an amplitude of an analog sine wave of an arbitrary frequency after analog-to-digital conversion at a constant sampling period,
Analog-to-digital conversion of a sine wave of any frequency at a fixed sampling period
Take the temporary maximum or minimum value from the sampled sine wave digital data,
Passing the maximum or minimum value data through a low-pass filter;
A correction coefficient A determined based on the frequency of the sine wave and the sampling period is obtained, and the provisional maximum value or minimum value data is corrected by multiplying the output of the low-pass filter by the correction coefficient A. A method for detecting an amplitude of a sine wave, wherein the amplitude is detected. The correction coefficient A is expressed as follows: sine wave digital data sampling period is ts and sine wave period is T.

4. The method of detecting amplitude of a sine wave according to claim 3, wherein:

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