Electricity: measuring and testing – Electrical speed measuring – Including speed-related frequency generator
Patent
1982-12-13
1985-12-24
Krawczewicz, Stanley T.
Electricity: measuring and testing
Electrical speed measuring
Including speed-related frequency generator
324161, 324163, G01P 346
Patent
active
045609276
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a speed detecting apparatus, and more particularly to a speed detecting apparatus capable of detecting speeds ranging from low to high speeds with high accuracy.
DC and AC motors are controlled using data on the actual speeds of the motors fed back in a feedback loop. For example, in an AC motor control system in which the AC motor is driven by primary three-phase current commands generated by digital processing, the speed difference .DELTA.v between a commanded speed and an actual speed, and the actual speed n are supplied as inputs, and digital processing is carried out on the basis of .DELTA.v and n to determine the frequency and amplitude of the primary three-phase current commands. For example driving the spindle in a machine tool with an AC motor requires that the spindle be rotatable in a wide range of from low to high speeds. For accurate control, the speeds of rotation, both low and high, should be detected with precision.
According to a conventional speed detecting system, two-phase signals PA and PB which are .pi./2 out of phase with each other and have a frequency f proportional to the speed of rotation of the motor are generated, then the two-phase signals PA, PB are converter by a quadrupling circuit into signals having a frequency of 4f. Finally, a voltage (actual-speed voltage TSA) proportional to the speed of rotation is produced as an output of a frequency-to-voltage converter which serves to generate a voltage in proportion to the frequency 4f. With the prior system, however, as the pulse frequency becomes lower, the output voltage value from the frequency-to-voltage converter goes out of proportion to the frequency and is rapidly reduced. For this reason, the known system has not been suitable for the detection of speeds of AC motors which rotate at extremely low speeds.
SUMMARY OF THE INVENTION
With the foregoing in view, it is an object of the present invention to provide a speed detecting apparatus capable of precisely detecting the speed of rotation of a motor in a range of from low to high speed.
According to the present invention, there is disclosed a speed detecting apparatus having a detector for generating two sine-wave signals which are .pi./2 out of phase with each other and have a frequency proportional to the speed of rotation of a motor so that output voltages can be produced which depend on the speed of rotation of the motor through the use of the two sine-wave signals, thus detecting the speed. The speed detecting apparatus of the invention includes a frequency-to-voltage converter for converting the frequency of the sine-wave signals into a voltage and an inverter circuit for inverting the phases of the two-phase sine-wave signals to produce output signals. A synchronous rectifier circuit is supplied with the sine-wave signals directly or via a differentiating circuit to rectify the supplied signals in synchronism and combine them. A detector circuit detects whether the speed of rotation of the motor is greater or smaller than a predetermined value and generates switching signals. Analog switches deliver the output voltage produced by the frequency-to-voltage converter at high speeds and the output voltage produced by the synchronous rectifier circuit at low speeds in response to the switching signals from the detector circuit. With the present invention, the output voltage V.sub.H from the frequency-to-voltage converter and the output voltage V.sub.L from the synchronous rectifier circuit are selectively issued as an actual-speed voltage TSA depending on the speed of motor. This allows the actual-speed voltage TSA to be proportional to the number n of RPM in a range of low to high speeds so that the speed of motor can be detected precisely.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram of the present invention;
FIG. 2 is a diagram showing various signal waveforms;
FIG. 3 is a circuit diagram of a frequency-to-voltage converter;
FIG. 4 is a circuit diagram of a synchronous rectifier circui
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Hirome Itoh: "Know How for Application of Optical Device"-Sharp Co.
Fujioka Yoshiki
Ishida Hiroshi
Ota Naoto
Fanuc Ltd.
Krawczewicz Stanley T.
Solis Jose M.
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