Patent GB-905848-A (GB)
Title: Safety control for mechanical presses or the like machine tools
IPC: F16P3/18
Filed: 1959-01-30
Abstract: 905,848. Controlling clutch-brake combinations ; machinery safety-devices. HERION, E. Jan. 30, 1959 [Feb. 1, 1958], No. 3458/59. Classes 80 (2) and 80 (4). The clutch K, Fig. 1, and brake B of an eccentric press are actuated by compressed air passing through two electromagnetic valves MV1, MV2 arranged as shown so that when the valves are de-energized the clutch and brake are connected to exhaust even if one valve sticks in the operated position, and each valve is linked to a switch EMV1, EMV2 arranged to prevent re-starting of the press and to energize a warning lamp or bell should one of the valves so stick. As shown the valve-operating solenoids' CMV1, CMV2, Fig. 2, are arranged in parallel and controlled by the serially arranged contacts SS1 3-4, SS2 3-4 of two relays SS1, SS2 which are arranged in parallel and energized when a safety switch Z, which must be operated with both hands, is actuated. Fig. 2 shows all relays and switches in their non-operated state. As soon as a main switch S is closed, relay VS is energized so that its contacts VS 15-16 are opened, and contacts VS 1-2 are closed to energize relay TS. This closes hold-on contacts TS 1-2, closes contacts TS 5-6 to energize indicator lamp KL, and closes contacts TS 3-4. Actuation of switch Z, to start the press, deenergizes relay VS to re-close contacts VS 15-16 and energizes relays SS1, SS2 whose contacts 3-4 close to actuate valves MV1, MV2. If the two-handed switch Z is held actuated the press operates until a cam switch TN is opened by the ram shortly before the completion of the return stroke, thus de-energizing relay TS so that its contacts TS 3-4 open and de-energize relays SS1, SS2. The contacts 3-4 of these relays then open to de-energize the valve solenoids CMV1, CMV2 and stop the press at the top of its stroke. Since the relay TS is initially energized through the normally closed contacts of the switches EMV1, EMV2 actuated by the valves, and the normally closed contacts 15-16 of the relays SS1, SS2 it follows that if any of these valves or relays fails to return to its normal position when the press stops then the relay TS cannot be energized, i.e. the press cannot be restarted. Moreover if a valve fails to return, a warning bell Sch is energized through one or other of the normallyclosed contact pairs SS1 19-20, SS2 19-20 of relays SS1, SS2 and through one or other of the normally-open contact pairs of the switches EMV1, EMV2. To provide for automatic operation of the press irrespective of the time for which the twohanded starting switch Z is held closed, the press has two selector switches WSI, WSII and a cam switch EN. For " continuous operation " both switches WSI, WSII are closed so that once the relays SS1, SS2 controlling the valves MV1, MV2 have been energized by actuating and releasing the starting switch Z they are held energized through the two selector switches and by their own hold-on contacts 1-2, irrespective of the movements of cam switches TN and EN. The press is then stopped by pressing button SB. For " single-stroke operation " the selector switch WSI only is closed, so that after actuation and release of the switch Z the relays SS1, SS2 are held energized as before by their own hold-on contacts 1-2 but are de-energized to stop the press at the top of the return stroke by the automatic opening of the cam switch EN.