Patent GB-1157757-A (GB)
Title: Improvements in or relating to Controls for Electric Brakes
IPC: F16D65/28
Filed: 1967-12-21
Abstract: 1,157,757. Electromagnetic brake circuits. WARNER ELECTRIC BRAKE & CLUTCH CO. 21 Dec., 1967 [16 Jan., 1967], No. 57999/67. Heading F2E. [Also in Divisions D1 and H3] A control circuit for an electromagnetic brake comprises a capacitor which is charged while the power supply is connected, and means responsive to disappearance of the supply voltage to allow the charge on the capacitor to connect a source of stored potential to the brake winding for rapid application of the brake. The circuit is described in connection with a system (Fig. 1, not shown), where a 3-phase A.C. supply operates a motor to drive a load and also provides D.C. supplies for the control circuit. A load can be connected either to the motor via an electromagnetic clutch or to a stationary part via an electromagnetic brake. If the supply fails, or if the circuit-breakers are tripped manually or by an overload, the circuit of the invention brings the load rapidly to rest, if desired in a predetermined position, e.g. so that the shuttle of a loom will stop in its box. In Fig. 3, the 10V and 100V batteries shown are actually rectified D.C. sources obtained from the A.C. supply via thermal overload circuitbreakers (Fig. 1, not shown), and the switch S3 represents operation of these or the main circuitbreakers or a failure of the A.C. supply. The brake winding BW and the clutch winding CW are energized by thyristors 46 and 40 respectively, with a commutating capacitor 50, these thyristors being turned on by momentary closure of switches S2 and S1 respectively. Capacitors 52 and 51 provide a higher voltage source for rapid build-up of current through the windings. Control circuit.-Means are provided for discharging a stored potential through the brake winding BW when the power supply ceases, the stored potential being that on capacitor 52 (as shown) or on an extra component. Transistor 64 is normally conducting and (assuming S4 or TS1 is closed, see below) will hold the gate of thyristor 46 near earth potential. If the supply voltage fails, capacitor 68 discharges through the clutch winding CW and thyristor 40, the resulting current through resistor 69 turning off transistor 64. Also, capacitor 60 discharges through resistors 65 and 49, the potential across the latter firing thyristor 46, allowing capacitor 52 to discharge through the brake winding BW to bring the load to a rapid halt. (Resistor 49 may be omitted.) In a modification (Figs. 4 and 5, not shown) a PNP transistor is used and and resistor 65 is between the collector of the transistor and earth. In this case the transistor is normally cut off by a positive base bias which disappears when the supply voltage ceases; conduction of the transistor by the capacitor voltage allows the capacitor discharge current to fire the thyristor. Stopping a load in a predetermined position.- The passage of the driven shaft through a particular angular position # 1  is signalled by a transistor triggered by a magnetic pick-up or (as in Fig. 2) by a cam 80 tripping a switch TS. This switch has contacts TS between the transistor 64 and thyristor 46 so that the latter will not receive a firing pulse until the contacts close. The position # 1  is chosen so that after actuation of the brake winding the shaft will come to rest in the desired position # 2 .