GB804835A - Improvements in or relating to control means for electrically power operated machines - Google Patents

Abstract

804,835. Transmitting mechanical power; electromagnetic clutches and brakes. IGRANIC ELECTRIC CO., Ltd. June 8, 1955 [June 9, 1954], No. 16448/55. Classes 35 and 38 (4). The ram of a press 10 is driven downwardly from its upper normal position by operating controller 23 to energize motor 22 which is coupled to shaft 20 and flywheel 21. Simultaneous operation of two push-buttons causes a clutch coil 19a to be connected to generator 25 and a separate excitation circuit to be closed for the field winding 25b of the generator, so that driving torque is transmitted from shaft 20 to shaft 11 which is free to rotate since brake coil 14 is energized. The initial degree of coupling is at a maximum value determined by the adjustment of resistor 30, but, after a time delay, resistor 32 is connected in series with field winding 25b to reduce the degree of coupling between the shafts. Just before the press ram reaches the bottom of its stroke and comes into contact with the work, a limit switch closes to effect the energization of field winding 36b whereby generator 36 energizes brake coil 17a to decelerate the ram as it approaches the work. Further limit switches are subsequently opened to de-energize the field winding 25b and then to energize it reversely, thus rapidly forcing the dissipation of the magnetic field produced by the winding. Accordingly, the driving torque coupling between shafts 20 and 11 is quickly reduced to zero as braking torque is applied to shaft 11. When the voltage of generator 25 is reduced to zero and starts to develop in the reverse direction, the reverse energizing connections of the field winding 25b are discontinued. Further limit switch operation results in disconnection of the field winding 36b and in its reverse excitation to de-energize brake coil 17a and to remove quickly the braking torque on shaft 11. The field-forcing de-energization of the brake coil is interrupted before any appreciable reverse excitation of the coil occurs. Subsequent operation involves the reconnection of field winding 25b with resistor 31 in circuit so that the clutch coil 19a is energized to a reduced degree for re-coupling the shafts 20 and 11. The resistor 31 is then removed from the circuit of the field winding 25b to afford increase of the energization of clutch coil 19a and consequent increase of the driving torque on shaft 11 so that the speed at which the ram moves toward its upper normal position is increased. The push buttons must be released before another cycle of operations can be initiated. As the press reaches its upper position, clutch coil 19a is de-energized by forcing generator field winding 25b, brake coil 17a is energized, and coil 14 is de-energized to set the friction brake. After a time delay period, forced de-energization of the brake coil 17a takes place. The clutch-brake 16 may be replaced by separate clutches and magnetic brakes.