GB1242130A - Improvements in or relating to pulse operated control devices for series wound direct current electric motors - Google Patents

Abstract

1,242,130. Control of D.C. motors. CONVEYANCER FORK TRUCKS Ltd. 11 March, 1970 [11 Dec., 1968], No. 58781/68. Heading H2J. A D.C. series-motor is supplied with pulses, the motor current flow being maintained during inter-pulse periods, and means are provided for interrupting the current-flow during a part of each inter-pulse period. When a positive feed is applied to switch 4, rectifiers SCR1, SCR2, are switched-on whereby capacitors C1, C3, are charged, while transistor TR1 conducts to charge capacitor C2. When the current through coil 3, field winding 1, armature 2, and rectifier SCR1 reaches a limiting value, the coil 3 responds to change-over the switch 4. Gating signals are removed from rectifiers SCR1, SCR2, and applied to rectifier SCR3, capacitor C1 discharging through rectifier SCR3.to turn-off the rectifier SCR1. The inductive effect of the motor re-charges the capacitor C1 reversely, while capacitor C2 discharges through coil 2, field winding 1, armature 2, resistor R1 and diode D2, and recharges with reversed polarity. The rectifier SCR4 is switched-on, when its gate-potential becomes sufficient, to conduct the motor circulating current. As the circulating current decreases, coil 3 responds to return the switch 4, the gate signal to rectifier SCR3 being removed, and rectifiers SCR1, SCR2, being switched-on again. Rectifier SCR4 is switched-off while capacitor C2 discharges at least in part through components R4, TR1, SCR1, and, at the same time, capacitor C3 is charged through resistor R2. The coil 3 then changes-over the switch 4, any charge on capactor C2 shortening the delay before rectifier SCR4 is switched-on. If the motor current is interrupted when the motor is in the fully-on condition, maximum time delay is imposed before a conducting path is provided for the circualting current. Restoration of the current in the reverse direction through either the armature or the field provides a braking torque. Coil 3 changes over the switch 4, and rectifier SCR4 is turned-on after a delay whereby the motor self-excites until coil 3 responds to a falling current level. Switch 4 returns and braking energy is applied progressively as the firing-delay of rectifier SCR4 decreases. Capacitor C3 is re-charged while the motor is at standstill, to enable restarting to take place at a slow rate. If the motor is being pulsed when reverse-current braking is applied, the capacitor C3 is restored to a fully charged condition to impose maximum delay in firing the rectifier SCR4.