Coded data generation or conversion – Phase or time of phase change
Patent
1997-04-14
1998-07-28
Gaffin, Jeffrey A.
Coded data generation or conversion
Phase or time of phase change
341115, 341600, G01D 5245
Patent
active
057867810
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a method and an apparatus for computing angle data for encoders, and a technique for interpolating detection signals in a detecting device for detecting the positions of a table and motor of a machine tool with an NC apparatus or the like.
BACKGROUND ART
A rotary pulse encoder, which is mounted on a motor shaft or the like, and a linear pulse encoder, which is attached to a worktable or the like, are known as detecting devices for detecting the positions of a table and motor of a machine tool with an NC apparatus, whereby the amount of movement and moving speed of a moving body are detected. Usually, in these pulse encoders, a phase-A signal, a sine-wave signal (Ksin.theta.), and a phase-B signal, a sine-wave signal (Ksin.theta..+-..pi./2) with a phase difference of 90.degree. from the phase-A signal, are generated as the moving body moves, and an interpolation signal is formed from these two sine-wave signals to obtain angle data, whereby the resolutions of positions and speeds are improved.
One such interpolation technique is known, in which sine-wave signals and cosine-wave signals from a signal source are supplied to a converter circuit that is composed of a plurality of resistors and a comparator array.
As another interpolation means, there is a known method in which angle data .theta. are obtained by inputting values a and b, obtained by A/D conversion of phase-A and phase-B sine-wave signals, to arithmetic means 4, as shown in FIG. 14, for computing tan.sup.-1 (a/b). The arithmetic operation of the inverse transform of this tangent is carried out by Taylor development calculation.
Moreover, another proposed interpolation technique is one comprising A/D converters and storage means such as a ROM. FIG. 15 is a block diagram for illustrating a conventional interpolating device using a storage element. In the interpolating device shown in FIG. 15, values a and b obtained by A/D conversion of phase-A and phase-B sine-wave signals are inputted to storage means 8 such as a ROM. The storage means 8 is stored with interpolated angle data, and outputs the angle data .theta. with digital signals from A/D converters 1 and 2 used as addresses.
FIG. 16 is a diagram showing relations between addresses and storage contents of the storage means in the conventional interpolating device provided with the A/D converters and the storage means. In FIG. 16, the axis of absciassa represents X-direction addresses, while the axis of ordinate represents Y-direction addresses. Each address corresponds to the values of sine and cosine waves converted into digital signals by the A/D converters. For example, when each address is represented by 8 bits, the value of each axis is represented by 256 addresses from 0 to 255. The storage contents are stored in positions corresponding to the individual lattices composed of the X- and Y-direction addresses. In FIG. 12, the portions loaded with the storage contents are hatched.
A circle shown in the drawing indicates position data represented by signals A and B, and the position data are fetched by appreciating the storage contents on a circle defined by addresses corresponding to the input signals A and B.
However, in the case where a converter circuit composed of resistors and a comparator array is used in the conventional interpolation technique, for example, the resistors and the comparator array pose problems such as a high cost and a large occupation space. Furthermore, in where tan.sup.-1 (a/b) is to be computed, there is a problem that the Taylor development calculation requires a complicated arithmetic circuit. In the case of an interpolating device provided with the A/D converters and the storage means, its storage contents must be previously loaded corresponding to all the addresses, so that large-capacity storage means is necessary.
DISCLOSURE OF THE INVENTION
The object of the present invention is to provide for an encoder angle data computation method and computation apparatus, capable of solving the aforementioned conv
REFERENCES:
patent: 4723201 (1988-02-01), Tanamachi et al.
patent: 5068777 (1991-11-01), Ito
patent: 5650708 (1997-07-01), Sawada et al.
"A Method of Improving the Resolution and Accuracy of Rotary Encoders Using Code Compensation Technique", Instrumentation and Measurement Technology Conference, Atlanta, May 14-16, 1991, No. Conf. 8, May 14, 1991, Institute of Electrical and Electronics Engineers, pp. 183-184.
Taniguchi Mitsuyuki
Yamaguchi Hiroshi
Fanuc Ltd
Gaffin Jeffrey A.
Jean-Pierre Peguy
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