Electricity: measuring and testing – Electrical speed measuring – Including speed analog electrical signal generator
Patent
1991-10-02
1993-11-09
Snow, Walter E.
Electricity: measuring and testing
Electrical speed measuring
Including speed analog electrical signal generator
364565, G01P 346, G01P 352
Patent
active
052606503
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates generally to methods and apparatus for generating a voltage proportional to the rotational-speed with a resolver, and more specifically to such a method and apparatus whereby the sign of the rotational-speed-proportional voltage corresponds to the direction of rotation of the resolver, whereby two path-dependent or angle-dependent amplitude-modulated (AM) sinusoidal voltages in phase quadrature can be tapped at the two resolver outputs, and whereby the sinusoidal voltages have amplitudes that can be modulated as a function of the rotor position or the angle of rotation.
Brushless feed and main spindle drives are being used to an increasing degree for machine-tool drives. The measurement of speed and rotor position is likewise supposed to take place without brushes. For this purpose, one uses optical and magnetic incremental encoders, three-phase tachometers and resolvers, also called synchro-generators. To provide high positioning accuracy (position servo loop), the secondary speed control loop of a control and regulating unit associated with a feed and/or main spindle drive must have high rotational-speed resolution. Optical incremental encoders are already capable of acquiring the lowest detectable rotational-speed of<0.01 min.sup.-1. For example, this type of incremental encoder produces 1,000 to 20,000 sine/cosine periods for each mechanical revolution. As an example, using an appropriate multiplication circuit one can then attain a positional resolution of 60 million positions per mechanical revolution. When a digital automatic speed control with a sampling time of 1 msec. is used, the rotational-speed is calculated from the difference between two rotor positions relative to the sampling time, whereby a rotational-speed of 0.01 min.sup.-1 can be acquired with the indicated sampling time and resolution.
The periodical "Elektronik Industrie" [Electronics Industry] 12--1985, p. 50 to 54, discloses a resolver/digital converter, which generates a digital angular value from the two resolver voltages by means of a tracking process. A phase-sensitive demodulator, an integrator and a voltage-controlled oscillator form a closed loop, in which the analog input angle is continually compared to the digital analog value. The resolution amounts to 16 bits per revolution and the angle information can be queried directly from a microprocessor. The resolver voltages are processed in the microvolt range through the application of a 16-bit digital-to-analog converter.
DE 32 18 101 C2 discloses an evaluation unit for a digital incremental encoder, in which two path-dependent or angle-dependent sinusoidal voltages in phase quadrature having identical amplitudes and periods can be tapped at the encoder outputs. These sinusoidal voltages can be converted into a number of pulses proportional to the path or angle covered. In addition, a voltage derived from a sinusoidal voltage can be converted into a digital value. Linear path-dependent or angle-dependent segments of the sinusoidal voltages in the area of the zero crossings are joined together electrically to form a periodic delta voltage, whose fundamental frequency is an integral multiple of the frequency of a sinusoidal voltage. The amplitude of the generated delta voltage has a linear correlation to the position within every eighth period of the encoder. By means of analog-to-digital conversion and linkage to comparator signals, which select the correct eighth periods, the subdivision of the encoder periods is facilitated.
A resolver is used in place of an optical encoder to detect rotational-speed and rotor position because the resolver is more cost-effective and sturdy, has a smaller unit volume and can be used in higher temperature ranges. However, the basic information of the resolver is several orders of magnitude lower than that of an optical encoder, and therefore must be analyzed using a costly evaluation circuit. These evaluation circuits usually contain expensive 16-bit analog-to-digital or digital-to-analog
REFERENCES:
patent: 4225931 (1980-09-01), Schwefel
Elektronik Industrie, Dec. 1985 (Heidelberg) Manfred Karcher: "R/D-Wandler im Vergleich zu Winkelcodierern und Tachogeneratoren", pp. 50, 52, 54.
Donat Albrecht
Schwesig Gunter
Siemens Aktiengesellschaft
Snow Walter E.
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