Control circuits for electromagnetic clutch-brake driving devices

Abstract

Abstract A circuit which does not require mechanical relays is disclosed using silicon-controlled rectifiers (SCR''s) for controlling manually and/or automatically the starting and stopping of a clutch-brake motor having an electromagnetically actuated clutch and brake. Each clutch turnoff brake winding is connected to a source of full wave rectified AC voltage through its own SCR and selective turnoff is effected by capacitor commutation. Momentary overexcitation of both windings is provided by alternative initial discharge therethrough of energy previously stored in respective capacitors. These capacitors are charged through separate individual SCR''s from an AC voltage of a value higher than the normal DC energizing voltage used for continuously exciting the coils. The four SCR''s are turned on in pairs, one SCR of each pair closes a circuit connecting the respective winding to the previously charged capacitor and thereafter to the normal DC energizing bus. Diode gates prevent adverse interaction between the capacitors and the DC bus and provide properly timed energy flow from the DC bus to the winding as soon as the capacitor voltage drops to a value slightly below the bus voltage so that there is no discontinuity in the winding excitation. The trigger pulse which turns on one SCR to energize one winding also turns on the other SCR of the pair, which latter SCR connects the capacitor for charging or storing energy which is later released for initially energizing the other winding. A no-voltage release circuit employs a unijunction transistor (UJT) as a relaxation oscillator connected to a DC supply having a large capacitor. This oscillator provides triggering pulses to the gate of the SCR which controls excitation of the brake winding. Normally, however, with full line voltage, a transistor base-biased to saturation, has its emitter-collector circuit connected across the timing capacitor of the UJT oscillator, thus normally shorting the capacitor and preventing oscillation. Upon failure of line voltage, the transistor turns off due to loss of base bias and the timing capacitor charges from the energy in the large capacitor, and the oscillator supplies a triggering pulse to the SCR for energizing the brake coil. The voltage of the previously charged capacitor now connected to the brake winding will, even in the absence of line voltage, supply a high impulse of energy to the brake coil to bring the load quickly to standstill.

Inventors

• 👤 Henry A Seesselberg

Bibliographic Details