Patent GB-1476161-A (GB)
Title: Thyristor motor control circuit
IPC: H02H7/08
Filed: 1974-08-08
Abstract: 1476161 Control of D.C. motors RAYMOND CORP 8 Aug 1974 [26 Dec 1973] 34939/74 Heading H2J A control system for a D.C. series motor A, FL driving a lift truck comprises a main thyristor SCR1 and commutating circuit SCR2, SCR3, C1, T1, L1 having a conventional control circuit, by-pass contacts M, forward and reverse contacts Fa, Fb, Ra, Rb, an operatorcontrolled member MS movable firstly to engage contact f or r to actuate appropriate forward or reverse contacts and connect the motor to battery B, secondly to increase the mark/space ratio of the thyristor SCR1 and finally to close contacts M by changeover of contacts a, b from the position shown, and a number of oscillator, time delay and thyristor circuits which provide the following protective actions to prevent energization of or de-energize the motor if members SCR1 and M fail in an open or closed condition :- (1) Starting in reverse or forward mode Closure of member MS to contact f for example fires SCR7, after a delay determined by circuit members C17, PUT4, to energize coil F and actuate the forward contacts, the subsequent cycling of SCR1 stopping further oscillation of circuit C17, PUT4 by current flow through members D45, R64. If SCR1 or contacts M are failed closed when MS is operated, diode D36 conducts to prevent circuit C17, PUT4 firing SCR7. If SCR1 is failed open, SCR7 will be fired and circuit C17, PUT4 will continue to oscillate, but the motor cannot be energized. (2) Control by SCR1 or contacts M. If SCR1 fails closed or is not commutated in a predetermined time, termination occurs of the charge and discharge of a capacitor C20 with the on/off cycling of SCR1, whereby capacitor C20 charges to fire members PUT5 and SCR8 and so turn off SCR7 to de-energize the motor. If switch S2 is closed, the firing of SCR8 grounds C17 to prevent firing of PUT4. To ascertain whether the fault on SCR1 is permanent or transitory, switch S2 or a keyswitch KS is momentarily opened, preferably the former to avoid the interruption of other circuits controlled by the switch KS. Such opening turns off SCR8 and allows members C17, PUT4 to fire SCR7, the coil F and its contacts being operated to restart the motor if the fault was transitory, and being successively operated without restarting the motor if the fault is permanent, due to alternate operation of members C17, PUT4 and SCR8. Such operation provides an audible signal to ensure that switch KS is opened by the operator to shut down the control system. When contacts a, b change over, the contacts M are closed after a time delay determined by circuit VR8, C22, PUT6, which fires SCR9 to energize the coil of contacts M. Switch-on of SCR9 also turns on a transistor Q10 to discharge capacitor C20 and so prevent firing of SCR8, since closure of contacts M corresponds to the "SCR1 failed closed or not commutated" condition. If contacts M do not open when member MS is returned to thyristor control, transistor Q10 is turned off by changeover of contacts a, b and members C20, PUT5 and SCR8 turn off SCR7 as before to deenergize the motor. Contacts M cannot be closed if SCR1 does not turn on or "fails open", since the circuit C17, PUT4 oscillates to periodically ground the capacitor C22 and so prevent PUT6 firing SCR9.