BRIEF DESCRIPTION OF THE DRAWINGS
These and other objects and features of the present invention will become clearer from the following description of the preferred embodiments given with reference to the attached drawings, wherein:
FIG. 1 is a schematic block diagram showing a conventional amplitude calculation apparatus of an output signal of an encoder;
FIG. 2 is a schematic block diagram showing an amplitude calculation apparatus of an output signal of an encoder according to a first embodiment of the present invention;
FIG. 3 is a view showing a theoretical resurge waveform in a first embodiment of the present invention;
FIG. 4 is a view showing the relationship between an angle θ of a resurge waveform and coefficients α and β according to a first embodiment of the present invention;
FIG. 5 is a graph for explaining the effect obtained by the first embodiment;
FIG. 6 is a flow chart of a program for running the operation of the first embodiment on a computer;
FIGS. 7A to 7D are views explaining conversion of angles θ of second to fourth quadrants of a resurge waveform to an angle θ′ of a first quadrant according to the polarity of the A-value and B-value according to the second embodiment of the present invention; and
FIG. 8 is a flow chart of a program for running the operation of the second embodiment on a computer.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Below, embodiments of the present invention will be explained.
First Embodiment
FIG. 2 is a schematic block diagram showing an amplitude calculation apparatus of an output signal of an encoder according to a first embodiment of the present invention. In the figure, the A/D converters 21, 22 and angle detection circuit 23 are the same as the A/D converters 11, 12 and angle detection circuit 13 shown in FIG. 1.
According to the first embodiment of the present invention, the R′ calculation circuit 24 for calculating the radius R′ of the resurge waveform is connected to the outputs of the A/D converters 21, 22 and angle detection circuit 23.
FIG. 3 is a view showing the theoretical resurge waveform normalized to the radius R=1 in the first embodiment of the present invention. In the figure, the abscissa indicates the A-value, while the ordinate indicates the B-value. Both the A-value and B-value are in units of voltage, that is, volts. If the A-phase signal and the B-phase signal are complete sine waves and have a phase difference of 90°, a true circular theoretical resurge waveform is obtained as illustrated, but when the waveform of one or more of the phases is not a complete sine wave but is a quasi sine wave or when the phase difference between the A-phase and B-phase is off from 90°, it is learned that the resurge waveform is not a true circle, but an ellipse.
FIG. 4 is a table showing the relationship of the angle θ of the resurge waveform and the coefficients α and β according to a first embodiment of the present invention. In the first embodiment, both the A-value and B-value are assumed to be digital signals expressed by 5 bits, the 2π angle is divided into 32 1/16π areas, and the coefficients α and β are made predetermined 4-bit numbers for each angle area. The predetermined 4-bit numbers are set so as to make αA+βB approximate the radius R of the theoretical resurge waveform shown in FIG. 3.
Specifically, when angle area is 0≦θ<π/16, the resurge radius R′ is mainly determined by the A-value. The effect of the B-value is the smallest, so α is set to 20 and β is set to 2−4 in advance. At the next angle area π/16≦θ<2π/16, the effect of the A-value is slightly reduced and the effect of the B-value is slightly increased, so α is set to 2−1+2−2+2−3+2−4 and β is set to 2−2+2−3. Below, in the same way, the coefficients α and β in each angle area are set as illustrated. In the final angle area of the first quadrant, that is, 7π/16≦θ<8π/16, it is learned that the resurge radius R′ is mainly determined by the B-value and the effect of the A-value is the smallest, so α is set to 2−4 and β is set to 20 in advance. Further, at the final angle area of the fourth quadrant, 31π/16≦θ<32π/16, it is learned that the resurge radius R′ is mainly determined by the A-value and the effect of the B-value is the smallest, so α is set to 20 and β is set to 2−4.
The relationship of θ and α and β shown in FIG. 4 is only an example. In general, it is sufficient to set the coefficients α and β in advance by binary numbers of numbers of bits smaller than the number of bits of the A-value and B-value. By using the binary numbers, the processing at the digital calculation circuit, that is, the R′ calculation circuit, becomes easy. However, the coefficients α and β are not limited to binary numbers. Any expression is possible if setting them so that αA+βB approximates the radius R of the theoretical resurge waveform.
FIG. 5 is a graph for explaining the effects obtained according to the above first embodiment. The figure shows that the resurge radius R′=αA+βB in the case where the A-phase sine wave and B-phase sine wave are ideal sine waves and the phases differ by 90°. As shown in the figure, the resurge radius R′ calculated by the first embodiment is not dependent on the angle θ and remains at the substantially constant value of 1.0.
FIG. 6 is a flow chart of a program for making a computer perform the operation of the first embodiment. In the figure, at step 61, the program samples, at the same timing, an A-phase sine wave signal or a signal resembling the A-phase sine wave signal and a B-phase sine wave signal or a signal resembling the B-phase sine wave signal differing in phase by exactly a predetermined angle and thereby acquires an A/D converted value A of the A-phase sine wave signal or a signal resembling the A-phase sine wave signal and an A/D converted value B of the B-phase sine wave signal or a signal resembling the B-phase sine wave signal.
Next, at step 62, the program finds a phase angle θ at different sampling points of a resurge waveform obtained by plotting the A/D converted value A of the A-phase sine wave signal or a signal resembling the A-phase sine wave signal and the A/D converted value B of the B-phase sine wave signal or a signal resembling the B-phase sine wave signal at the sampling points by the sampling on an X-axis and Y-axis.
Next, at step 63, the program divides the resurge waveform into a predetermined number of angle areas and stores in advance the A-phase coefficient α and B-phase coefficient β corresponding to each of the divided angle areas, in which case, the coefficients being set so αA+βB approximates a radius of a theoretical resurge waveform.
Next, at step 64, the program calculates the radius R′ of the resurge waveform as αA+βB. The thus obtained radius R′ expresses the amplitude of the detection signal of the encoder of the signal.
Second Embodiment
FIG. 7A to FIG. 7D are views explaining conversion of angles θ of second to fourth quadrants of a resurge waveform to an angle θ′ of a first quadrant according to the polarity of the A-value and B-value according to a second embodiment of the present invention. As shown in FIG. 7A, if A≧0, B≧0, the resurge radius is in the first quadrant, so the angle θ=θ′. As shown in FIG. 7B, if A<0, B≧0, the resurge radius is in the second quadrant, so by calculation of θ′=π−θ, θ′ is obtained in the first quadrant. As shown in FIG. 7C, if A<0, B<0, the resurge radius is in the third quadrant, so by calculation of θ′=θ−π, θ′ is obtained in the first quadrant. As shown in FIG. 7D, if A≧0, B<0, the resurge radius is in the fourth quadrant, so by calculation of θ′=−θ, θ′ is obtained in the first quadrant.
α and β corresponding to the thus obtained θ′ are set in advance in the same way as the table of FIG. 4. In that case, since the angles θ′ are restricted to the first quadrant, in the example of FIG. 4, it is enough to use α and β corresponding to the angle area in the scope of the first quadrant from 0≦θ′<π/16 to 7π/16≦θ′<8π/16 and the circuit size can be made smaller than the case of the first embodiment.
However, the A/D converted value A of the A-phase is negative in the second and third quadrants and the A/D converted value B of the B-phase is negative in the third and fourth quadrants, so in actual calculation of the radius R′ of the resurge waveform, the R′ is calculated by the approximation equation R′=α|A|+β|B| from the absolute value of the A/D converted value of the A-phase, the absolute value of the A/D converted value of the B-phase, and the processing ratios α, β.
FIG. 8 is a flow chart of a program for making a computer perform the operation of the second embodiment. In the figure, at step 81, the program samples, at the same timing, an A-phase sine wave signal or a signal resembling the A-phase sine wave signal and a B-phase sine wave signal or a signal resembling the B-phase sine wave signal differing in phase by exactly a predetermined angle and thereby acquires an A/D converted value A of the A-phase sine wave signal or a signal resembling the A-phase sine wave signal and an A/D converted value B of the B-phase sine wave signal or a signal resembling the B-phase sine wave signal.
Next, at step 82, the program finds a phase angle θ at different sampling points of a resurge waveform obtained by plotting the A/D converted value A of the A-phase sine wave signal or a signal resembling the A-phase sine wave signal and the A/D converted value B of the B-phase sine wave signal or a signal resembling the B-phase sine wave signal at the sampling points by the sampling on an X-axis and Y-axis.
Next, at step 83, the program finds a quadrant n of the phase angle θ from the A/D converted value A and a polarity of the A/D converted value B, where,
{(n−1)/2}π≦θ<(n/2)π,
where n is 4 or a smaller natural number and converting the phase angle θ of the quadrant n to a phase angle θ′ of a quadrant 1.
Next, at step 84, the program divides the resurge waveform into a predetermined number of angle areas in the quadrant 1 and presets and stores in advance an A-phase coefficient α and B-phase coefficient β in accordance with the divided angle areas. In that case, the coefficients are set so α|A|+β|B| approximates a radius of a theoretical resurge waveform.
Next, at step 85, the program calculates the radius R′ of the resurge waveform as α|A|+β|B|. The thus obtained radius R′ expresses the amplitude of the detection signal of the encoder of the signal.
In the above embodiments, an example of dividing the angle area into π/16 areas was explained, but the present invention is not limited to this example. It is also possible to set α and β finer to raise the precision of approximation and conversely to set them coarser to enable the circuit size to be further reduced and the processing time to be shortened.
As clear from the above explanation, according to the present invention, just αA and βB are added without calculation of the square or calculation of the square root of the radius of the resurge waveform using an encoder, so it is possible to reduce the circuit size of the encoder and possible to shorten the calculation time in the case of calculation by software.
While the invention has been described with reference to specific embodiments chosen for purpose of illustration, it should be apparent that numerous modifications could be made thereto by those skilled in the art without departing from the basic concept and scope of the invention.
Patent Application
20070297535
