GB1523599A - Electric motor control circuits - Google Patents

Abstract

1523599 Control of DC motors STILL GmbH 14 Oct 1975 [17 Oct 1974] 41927/75 Heading H2J A D.C. series motor 20, 21 is controlled by a thyristor 14 passing current pulses from a battery in accordance with the setting of a controller 1 (e.g. a potentiometer or magneticfield-responsive resistor) connected through resistors 2, 3 and an amplifier 5 to a voltage/ frequency converter 9, the direction of rotation being set by contacts 24-27 whose control coils 16, 17 are supplied through a direction change-over switch 13, transistor 12 and resistor 11, the latter controlling a transistor 10 in a circuit including capacitor 4, diode 6 and inverter 7 so that, with switch 13 in one or other position, current through resistor 11 turns on transistor 10 to maintain capacitor 4 charged and allow the signal from controller 1 to pass to converter 9, the transistor 10 turning off when switch 13 opens in the course of changing over, whereby the capacitor 4 discharges through members 6, 7 to cause the signal to converter 9 to be reduced to zero with consequent substantial reduction or cessation of the motor current before opening of whichever contacts 24, 25 or 26, 27 are closed. To ensure closure of the open contacts 24, 25 or 26, 27 before reappearance of the signal to converter 9, the transistor 12 is controlled by the controller signal via a comparator 8 and an AND gate 18, the transistor 12 being initially non- conductive when switch 13 has changed over but being switched on when a predetermined voltage has built up between members 1, 2 (despite the continued discharge of capacitor 4), the consequent flow of current through resistor 11 switching on transistor 10 to cause the controller signalto be reapplied to converter 9, after a delay produced by the charging of capacitor 4. Gate 18 may receive other signals, for example one from a thermal switch responsive to motor temperature, to make the closing of contacts 24, 25 or 26, 27 dependent on other conditions.