Patent GB-628299-A (GB)
Title: Improvements in or relating to dynamic braking for electrically driven machines
IPC: H02P5/46
Filed: 1947-05-27
Abstract: 628,299. Control of motors. HARVEY, V. P., POWELL G. F. W., and MOLINS MACHINE CO., Ltd. May 27, 1947, No. 14085. [Class 38(iii)] A control system for an electric motor for driving a machine which is adapted to be stopped by. dynamic braking comprises a switch-oper. ating lever or the like movable from a stopping-position to a running-position and back again and adapted in its first movement to complete a circuit through the coil of a contactor, .contact bars whereof close and connect the motor to the supply, said contactor comprising a contact bar which also closes when the contactor is energized and provides a further circuit for the contactor coil, means (e.g., a rotatable member) moving in timed rela. tionship with the driven part of the machine adapted to break said further circuit once per cycle of movement of said means, whereby, on return of the switch-operating lever to the stopping-position, the first contactor circuit is broken, and the further contactor circuit is thereafter broken by said means, so that the contactor bars move back to their original position and the motor-driving current ceases, said movement also closing a circuit to cause dynamic braking. With the switch-arm S1 in the position shown, the closure of a main switch MS energizes a relay A/2 to close contacts A1 and A2. When switch-arms S1 and S3 engage contacts 2 and 5 respectively, a transformer T is energized and rectified current is supplied to stator windings W1 and W2 of an A.C. motor, and, at the same time, a contactor D/4 is closed to supply alternating-current to the motor stator windings. The motor starts at a moderate speed due to the braking-effect of the D.C. excitation of the stator windings. When switch-arms S1 and S3 engage contacts 3 and 6 respectively, a relay B/2 is energized to disconnect the transformer T. Simultaneously, a holding-circuit, independent of the contact A2, for the relay D/4 is closed through contacts D1 and a timing-switch TS, and a relay C/2 is energized to close contacts C1 and C2. Upon return of the switch-arms S1 and S3 to the " off " position, the relay B/2 is maintained energized by a condenser K1 so that direct-current braking is not immediately applied. The energization of the relay D/4 is now dependent upon the switch TS and the contact B2. The switch TS is coupled to a conveyer or like machine driven by the motor and it opens when the machine is in a desired predetermined position. When the switch TS opens, the relay D/4 is de-energized and the alternating-current excitation of the motor stator windings is disconnected. A normally-open contact NCC of the relay D/4 is closed and the transformer T is energized, to supply the motor stator windings with direct-current, and the relay C/2 is maintained energized by the condenser K2. The machine may be inched by oscillating a switch-arm S2 between contacts 2 and 3. A switch WD is automatically adapted to stop the machine upon opening of the switch TS, in the event, for example, of a failure in the supply of work-pieces. A switch CD immediately stops the machine when a mechanical clutch breaks due to overload. In a modification, the machine is driven by a direct-current shunt motor which, upon opening of the timing-switch, has its armature open-circuited, and then shortcircuited with the shunt field excitation maintained. Specification 615,946 is referred to.