Browse Prior Art Database

Hybrid System for Measurement or Control of Velocity

IP.com Disclosure Number: IPCOM000090079D
Original Publication Date: 1969-Jan-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 3 page(s) / 33K

Publishing Venue

IBM

Related People

Akins, VE: AUTHOR [+3]

Abstract

The instantaneous velocity of a motor is measured by counting the number of pulses produced by an oscillator during the time span between two tachometer pulses and using the later tachometer pulse for transferring the count into a storage register and for beginning a new accumulation of oscillator pulses. The storage register output can be used to indicate motor speed through a D-to-A converter to control motor speed through a feedback arrangement, or the like.

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Hybrid System for Measurement or Control of Velocity

The instantaneous velocity of a motor is measured by counting the number of pulses produced by an oscillator during the time span between two tachometer pulses and using the later tachometer pulse for transferring the count into a storage register and for beginning a new accumulation of oscillator pulses. The storage register output can be used to indicate motor speed through a D-to-A converter to control motor speed through a feedback arrangement, or the like.

The output from a digital tachometer associated with a motor is coupled through a squaring circuit to terminal 11. Timing logic 23 is activated by the rising edge of each pulse at 11 to provide shift gate 24 for transferring the contents of counter 27 through shift register 28 into storage register 29. Then reset gate 25 causes 27 to be cleared or to be preset to a specified start number. Count gate output 26 allows pulses from oscillator 31 to be counted by 27 via gate 30. The rise of the next sequential tachometer pulse drops 26, inhibiting 30, and begins a new sequence of transfer, reset, and count. The complete transfer and reset cycle is kept small in time relative to the ratio of 31 to 26 in order to minimize error of transfer time. For example, if 200 cycles from 31 occur during one cycle at 26 at desired velocity and the transfer-reset cycle is equal to one cycle from 31, then the absolute error introduced is 0.5% at that velocity.

Polarization of the final count by direction gates 32 and 38 permits the error signal to add algebraically to the reference signal 33 such that the output from D- to-A converter 36 is a voltage representative of true velocity. Initializing 27 with a residual count permits 27 to be completely filled by 31 and recycle to a low-order count before 30 is degated. By using this technique, units 28, 29, 32, 36, and 38 can be relatively small and yet have a fairly wide count range for very fine control of velocity. To increase the fineness of control, a higher frequency oscillator ca...