Patent GB-699810-A (GB)
Title: Improvements relating to safety guards for power presses
IPC: F16P3/04
Filed: 1950-10-10
Abstract: 699,810. Machinery guards. BRITISH THOMSON-HOUSTON CO., Ltd., and RAYNER, F. J. H. Oct. 8, 1951 [Oct. 10, 1950], No. 24722/50. Class 80 (iv). In a press wherein a guard must be closed manually before the press can be started, the guard then being automatically locked by a detent until the tool is very close to the work, when the detent is released and the guard is opened while the press completes its stroke, the press is driven through a friction clutch which is engaged by fluid pressure under the control both of a pedal-operated valve and of a solenoid-operated valve associated with electric switches operated by the guard and press mechanisms. As shown, the tool 6 of a bending brake is reciprocated by eccentrics on a shaft 7 which is clutched to an electric motor on admission of compressed air to a cylinder 8 through a pedaloperated valve 8a and a solenoid-operated valve 21. The shaft 7 is permanently braked so that its rotation ceases as soon as the clutch is disengaged. A vertically-slidable perforated guard 9, which may be slotted to accommodate partially bent work, is connected by links of adjustable length to levers which are mounted on a shaft 17 and are counter-weighted to bias the guard upwardly to an open position. When the guard has been pulled down a spring-loaded detent 51, Fig. 4, engages a notched sector 50 on the shaft 17 and locks the guard closed. A two-position switch 25 is operated by the detent 51, while two similar switches 26, 27 (only 26 being visible in Fig. 4) are operated by a lever 59 controlled by a cam 62 on the shaft 7, the cam 62 having a nose which engages a roller on the lever 59 and is aligned with the nose 56 of a further cam 55, this further cam having a tail 57 and co-operating with the detent 51 as described below. The switches 25, 26, 27, Fig. 3, control indicator lamps 37, 38 and a rectifier for a solenoid 31 operating the valve 21. Each switch has a movable arm and two fixed contacts 29, 30 and alternating current is supplied at 33. At the beginning of an operating cycle contacts 30 are engaged, thereby illuminating lamp 38. As the guard is closed and automatically locked the switch 25 is released and its contact 29 is engaged, thereby extinguishing lamp 38, illuminating lamp 37 and energizing the solenoid 31. The operator can now engage the clutch by actuating the valve 8a. When the tool is so close to the work that there is no danger of fingers being caught, the cam 62 operates the switches 26, 27 to maintain the energisation of the solenoid while the cam 55 engages a roller on the detent 51, thereby unlocking the guard and operating the switch 25 to re-engage its contact 30. A cam groove 20 on the shaft 7 then engages a roller 19 which is linked to the shaft 17 so that the guard is positively raised while the bending operation takes place and the tool rises until the tail 64 of the cam 62 releases the lever 59, thereby releasing the switches 26, 27, de-energising the solenoid 31 and closing the valve 21 so that the clutch is disengaged and the machine is stopped by the permanentlyengaged brake. A gate closing the' rear of the machine may be interconnected with a switch 49 to prevent operation of the press unless the gate is closed. Each of the two adjustable links carrying the guard includes a member having right and left hand threads so that rotation thereof adjusts the length of the link, and the two members are geared together and rotated by a detachable handle, Fig. 1 (not shown), removal of which locks the members in the adjusted position.