GB1445972A - Motor control apparatus - Google Patents

Abstract

1445972 Automatic control systems PRINTED MOTORS Ltd 21 June 1973 [21 March 1972] 13243/72 Heading G3R [Also in Division H2] A control system as shown in Fig. 1 and generally similar to that described in Fig. 4 as modified by Figs. 6 and 7 of Specification 1416681, is provided with a tachogenerator 31 coupled to or integral with the low inertia motor 30 and supplying a speed signal to the input of amplifier 20, whereby the droop of the speed-load characteristic is limited. The negative feedback effect of the speed signal on the error signal at input terminal 21 is explained for error signals just outside the dead band defined by stages 27, 28, Figs. 2 and 3 (not shown). These stages receive the output of a variable gain stage 24, 25 and produce pulses at a rate and of polarity respectively determined by the magnitude and polarity of the error signal. The pulses are provided by a reference oscillator 33 consisting of an amplifier (50) with feedback through a variable resistor (55) and a phase shifting network, the amplitude and frequency of the amplifier output being adjustable by a potentiometer (51) which varies the proportion of the non-linear effect of diodes (52, 53), Fig. 5 (not shown). The oscillator produces a square wave output of unity mark/space ratio. The control system of Fig. 1 is described in detail, Figs. 4, 7 and 8 (not shown). Regulation may be improved by passing the signal from tachogenerator 31 through a parallel R.C. circuit (71, 72) to the input of amplifier 20, which is shunted by a capacitor (73) in this case to compensate for the loss of gain in the amplifier, Fig. 10 (not shown). In another modification of amplifier 20 to protect against malfunction caused by transient inputs thereto, limiting diodes (85, 86) are reverseparallel-connected across its input and its feedback circuit consists of a resistor in parallel with the series combination of a capacitor (81) and reverseparallel-connected limiting diodes (82, 83), Fig. 11 (not shown). The output pulses from oscillator 33 may be modified to comprises two waveforms phase displaced by 180 degrees, to prevent maloperation of the motor power stage, Fig. 4 (not shown) when a sudden change in polarity of the error signal tries to produce a corresponding sudden reversal of the motor. The feedback circuit of amplifier 20 may comprise the series combination of a resistor and capacitor, Fig. 14 (not shown). Uni-directional drive of the motor may be provided by using only two thyristors with a modified firing circuit, Fig. 15 (not shown).