Tachometer system
First Claim
1. A tachometer system for supplying a control signal indicative of positional and/or speed errors of a rotatable element comprising, a tachometer coupled to the rotatable element, the tachometer having a plurality of marks arranged in a closed track, a detector responsive to said marks for supplying n tacho-pulses per revolution of the rotatable element, and a correction circuit for supplying n correction signals in synchronism with the tacho-pulses so as to compensate for control-signal deviations caused by positional errors of the marks, the correction circuit comprising, a memory device with n memory locations, a write system for storing n phase error signals in said n memory locations in synchronism with the tacho-pulses, the phase error signals being obtained by phase comparison of the tacho-pulses with a reference signal while the tachometer is driven at approximately a constant speed, and a read system for reading said n phase error signals from the memory device in synchronism with the tacho-pulses so as to obtain the n correction signals.
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Accused Products
Abstract
A tachometer system for supplying a control signal indicative of positional and/or speed errors of a rotatable element comprises a tachometer on which marks are arranged in a closed track and a detector responsive thereto to produce n tacho-pulses per revolution of the tachometer. The tachometer system further comprises a memory device with n locations in which n correction signals are stored. The correction signals are obtained by driving the tachometer at an accurately constant speed, measuring the phase difference between the tacho-pulses and the reference signal, and storing the phase-error signals related to the consecutive tacho-pulses in separate locations of the memory device. When the tachometer system is used in a servo control loop these correction signals are used to correct the phase-error signals then measured, yielding a correction in respect of the deviations in these phase-error signals owing to positional tolerances of the marks on the tachometer.
47 Citations
12 Claims
- 1. A tachometer system for supplying a control signal indicative of positional and/or speed errors of a rotatable element comprising, a tachometer coupled to the rotatable element, the tachometer having a plurality of marks arranged in a closed track, a detector responsive to said marks for supplying n tacho-pulses per revolution of the rotatable element, and a correction circuit for supplying n correction signals in synchronism with the tacho-pulses so as to compensate for control-signal deviations caused by positional errors of the marks, the correction circuit comprising, a memory device with n memory locations, a write system for storing n phase error signals in said n memory locations in synchronism with the tacho-pulses, the phase error signals being obtained by phase comparison of the tacho-pulses with a reference signal while the tachometer is driven at approximately a constant speed, and a read system for reading said n phase error signals from the memory device in synchronism with the tacho-pulses so as to obtain the n correction signals.
- 6. A control system for a rotatable element comprising, a tachometer coupled to the rotatable element and including a plurality of n marks arranged in a closed track for deriving n pulse signals per revolution of the rotatable element, a reference frequency source providing a reference signal indicative of a desired rotation of the rotatable element, comparision means connected to compare the output of the reference frequency source with the output of the tachometer in sychronism with said pulse signals to produce at its output corresponding phase error signals, or addressable memory device having n unique memory locations corresponding individually with the n marks in the closed track of said tachometer, means for storing n phase error signals in said n memory locations in sychronism with the tachometer pulse signals by means of an open-loop method of initally comparing the tachometer pulse signals with said reference signals with the tachometer driven at approximately constant speed so as to yield said n phase error signals which are independent of the speed of the rotatable element, a read system sychronized with the tachometer for reading out said n phase error signals stored in the memory device in sychronism with the tachometer pulse signals to derive n correction signals corresponding to said n marks, means for subtractively combining the phase error signals supplied by the comparison means with the correction signals supplied by the memory device to produce a control signal, and a control device responsive to said control signal for driving the rotatable element.
- 8. An error compensation system for an apparatus that controls a rotatable element comprising, a tachometer adapted to be coupled to the rotatable element and including a plurality of indicia arranged in a closed track for deriving n pulse signals per revolution of the rotatable element, a memory device having n separate memory locations corresponding to said n pulse signals, respectively, means for storing n phase error correction signals in said n memory locations in synchronism with the tachometer pulse signals by means of an open-loop method of comparing the phase of the tachometer pulse signals with a reference signal and with the tachometer driven at a constant speed independent of the tachometer indicia thereby the derive said n phase error correction signals in the memory device, and means for reading out said n phase error correction signals stored in the memory device in synchronism with said tachometer pulse signals so as to derive n correction signals per revolution of the rotatable element.
- 11. An error compensation system for an apparatus that controls a rotatable element comprising, a tachometer adapted to be coupled to the rotatable element and including a plurality of indicia arranged in a closed track for deriving n pulse signals per revolution of the rotatable element, a memory device having n separate memory locations corresponding to said n pulse signals, respectively, means for storing n phase error correction signals in said n memory locations in synchronism with the tachometer pulse signals including means for comparing the phase of the tachometer pulse signals with a reference signal over a measuring period that encompasses a plurality of revolutions of the rotatable element and means for deriving the approximate average value over said measuring period of each of the phase error correction signals corresponding to the indicia in the tachometer track, a read system for reading out of the memory device said n phase error correction signals in synchronism with the tachometer pulse signals, a control device for driving the rotatable element and connected in a control-loop circuit that includes the tachometer and the phase comparing means, and the control-loop circuit includes means for limiting the control-loop circuit bandwidth during the measuring period so as to limit the upper frequency of signals passed by the control-loop circuit to a frequency value related to the speed of the rotatable element.
Specification