Patent GB-981924-A (GB)
Title: Improvements in or relating to servo-systems
IPC: H02M7/525
Filed: 1962-11-12
Abstract: 981,924. Automatic control systems. CYBERMECA S. A. Nov.12, 1962 [Nov. 13, 1961; Oct. 30,1962], No. 42682/62. Heading G3R. [Also in Divisions H2 and H3] In an arrangement wherein a switch unit connecting a load to a D.C. source is switched on by a first set of impulses and off by a second set, the selection of "on" or "off" pulses is determined by the value of a control voltage which depends on the difference between a voltage representative of the load and a reference voltage. Figs. 1 and 2. Fig. 1 relates to the supply of current through silicon controlled rectifiers D1, D2, D3 to windings M1, M2, M3 of a polyphase motor from a D.C. source S, though these windings might be primary windings of a transformer in an inverter. The voltages across the windings are compared with reference voltages A1,A2,A3 of a low power alternator and controlled to follow these voltages (Fig. 4, not shown). The star points N of the windings are connected together completing a circuit through the courses A, R1, R11 M, N so that the voltage EE1 across R10 is proportional to the difference voltage. Similar voltages EE2, EE3 are obtained for the other phases whose control is identical and is not therefore further considered. A pulse generator G of higher frequency than the alternator and common to the three phases supplies oppositely phased square waves G1, G2 to a directional selector unit K1 which provides either a set of pulses through K11 or a set of pulses through K12 depending on the sign of EE1. K12 supplies pulses EA1 to fire rectifier D1 and pulses EA11 to fire rectifier D11 to charge a capacitor C10 from a source S1. K11 provides pulses ES1 to fire rectifier D10 allowing capacitor C10 to discharge through D1 and stop this conducting. Fig. 2 shows in detail the units G and K1. Unit G comprises a unijunction transistor oscillator O feeding a bi-stable transistor circuit Ti, T2 to provide square waves G1, G2. These are differentiated and shaped by transistors T11,T12 to provide two trains of pulses 180 degrees phased displaced from one another. These pulses are fed to the collectors of transistors XS1, XA1 respectively which drive output transistors TS1, TA1 to produce outputs ES1, EA1, EA11. When the voltage EE1 is negative a transistor TE is blocked and a line X has a low voltage so that transistor XS1 conducts providing pulses ES1. Also a transistor T11 conducts blocking transistor XA1 and stopping pulses EAT, EA11. When EE1 changes sign, transistor TE conducts and opposite states pertain along the line so that only the pulses EA1, EA11 are produced. Modifications for the extinction of rectifiers D1,D2,D3 are disclosed in which (Fig. 5, not shown) source S1 and rectifier C10 are connected directly across C10, and (Fig. 6, not shown) the supply S plus an additional source is used to charge capacitor C10. Fig. 7. This discloses a motor control circuit in which the motor M is controlled in dependence on a pedal operated rheostat Rh. The motor is supplied from a D.C. source B through a rectifier DA and a resistor SH. The rectifier is fired by pulses EA and extinguished by pulses ES (by means of a shut off circuit comprising rectifier DS and capacitor CS). The choice of these pulses being dependent on the value of a control voltage UC which is applied to a Schmidt bi-stable unit. The output UC is derived from an amplifier transistor TA fed from a comparison transistor TE which effectively compares the "actual" current through the motor with a "desired" value set by the rheostat Rh. A voltage dependent on the "actual" value is derived across the resistor SH and is fed to the emitter of the transistor TE whilst a voltage UD dependent on Rh is fed to the base. To obtain the voltage UD a voltage BZ derived from a potential divider ZZRZ across the supply is connected across resistor 54 and diodes d1, d2 providing a voltage U of fixed value. This is applied across the series connection of Rh and resistor 52 so that the voltage UD across 52 is dependent on the setting of Rh. A feedback loop including the transistor TR is provided to reduce the sensitivity of the transistor TE to the voltage U1. A recovery diode DR is provided to enable current to continue flowing through the motor when the main rectifier DA is cut off.