GB1185830A - Improvements relating to Braking Systems for Power Presses and like Machines - Google Patents

Abstract

1,185,830. Metal working presses; press brakes; safety devices. BROUGHTON ENG. Ltd. 6 Dec., 1967 [6 Dec., 1966], No. 54576/66. Headings B3E, B3H and B3W. [Also in Division F2] A power press or like machine whose tool is actuated by a crank, eccentric or cam, has a primary braking system and a secondary braking system which is operative only if the primary system fails to stop the tool in a predetermined distance. The press may be a power press, shears or a press brake fitted with mechanical guards or preferably with a photoelectric safety system and whose crankshaft 12 carries a brake drum 11 co-operating with a brake band 13 formed by two parts 13a, 13b pivoted together at 14. The brake is actuated through a toggle link 16 by a bell crank lever 17 connected to the piston-rod 21 of a pneumatic or hydraulic cylinder 20 forming the primary braking system. The brake is applied by a spring 22, Fig. 5, acting on the piston 21a, assisted if required by pressure fluid admitted through port 81. To release the brake, pressure fluid is admitted to the opposite side of the piston through port 82. The secondary braking system comprises a rotary cam 25 acting on a leg 23 of lever 17 and which is driven through a toothed clutch (30) and shaft (29), Fig. 2 (not shown), from the crank-shaft 12. The clutch (30) is normally held in engagement by a spring (32) but is released by a lever 38 actuated by a diaphragm 41 in a fluid cylinder 39. A delay mechanism for the secondary braking system comprises a disc 64 driven from the crank-shaft, co-operating with a brake shoe 63 carried by a piston-rod 56 in a fluid cylinder 54 pivoted at (55), Fig. 3 (not shown), to a base-plate (50). The fluid cylinders 20, 54, 39 are supplied with fluid through solenoid actuated change-over valves 83, 88. Alternatively the valves may be operated pneumatically or hydraulically or by mechanical linkages. In operation, a switch 102 actuated by opening of the safety guard or by interruption of a light beam to the photo-cell, energizes solenoid valve 83 causing primary cylinder 20 to apply the brake 13. Simultaneously fluid is admitted to cylinder 54 to press brake shoe 63 into engagement with the rotary disc 64. The pivotal mounting of cylinder 64 causes the shoe to move circumferentially with the disc until the shoe engages a switch 76 which energizes solenoid valve 88. This admits fluid into cylinder 39 to engage the clutch (30) whereby the cam 25 is rotated to augment the braking pressure. The switch 76 is movable around the circumference of the disc 64 to vary the time delay before the secondary braking system operates. Instead of the brake shoe 63 and disc 64, a clutch or a differential gear mechanism may be used whose output element drives the cam 25 to energize the secondary braking system. The invention facilitates inching movement of the upper press tool. The brake is released by operation of the press control pedal. The primary braking system may be mechanically linked with the main press clutch.