Patent GB-559148-A (GB)
Title: Improvements in or relating to work holding devices for machine tools
IPC: B23Q3/08
Filed: 1942-07-30
Abstract: 559,148. Hydraulic machines. WICKMAN, Ltd., A. C., AUTOMOTIVE PRODUCTS CO., Ltd., CORNELIUS, J. R., and CLENCH. E. C. S. July 30, 1942, No. 10684. [Class 69 (ii)] [Also in Group XXII] In a hydraulic work-clamping device for machine-tools particularly for milling machines operating on long work-pieces such as aircraft wing spars, the clamps are actuated by one or more hydraulic motor units associated with a safety device operated by the pressure fluid and including power cut-out or warning means which are operated when the clamping pressure falls below a safe minimum value. In one form three clamps 16 are actuated by hydraulic motors 10 ... 12 having return springs 18 which withdraw the clamps when hydraulic pressure is released. The system is supplied by a constantdelivery variable-pressure pump 19 delivering through a safety byepass valve 24 to a handoperated valve 27 controlled by a knob 29. In the position shown pressure fluid passes to the clamping-motors and also to a cylinder 36 the piston of which moves against a spring 38 and operates a switch 41 in the circuit of a warning lamp 42. If the pressure in the clamping cylinders becomes dangerously low the spring is effective to move the switch to the " on " position to light the warning lamp. To release the clamps the valve 27 is moved to the left thus connecting the clamping cylinders to the return line 26 and cutting off the pressure supply. In a modification, Fig. 2, a small hydraulic accumulator 45 is included between the pump 19 which is of constant-pressure variable-delivery type, and the valve 23. The safety device comprises a bellows 48 controlling a switch 35a in the circuit of a solenoid 49 by which the starter of the machinedriving motor is operated so that the machine can only be started when there is adequate pressure in the clamping cylinders. In another modification, Fig. 3, two sets of clamps, viz., side clamps 10s ... 12s and top clamps 10t ... 12t are controlled by valves 23s, 23t respectively. Either or both sets of clamps may be rendered operative by a selector valve 69 controlling the flow to a pair of safety units 34s, 34t operating a pair of switches 41s, 41t both of which are in circuit with the solenoid 49. In the selector position " B " shown both sets of clamps may be brought into operation by moving valves 23s, 23t to admit pressure fluid to the lines 32s, 32t. When clamping pressure is sufficient both switches are maintained in the " on " position so that solenoid 49 can be energized while if the pressure falls both switches move to " off " positions. If as when only the side clamps are required the selector arm is moved to the " S " position and valve 23t moved to the shut-off position pressure fluid flows from port 66s to both the ports 72s, 72t and the two safety devices still remain operative. If however the valve 23t is inadvertently moved to admit fluid to line 32t this fluid will flow through ports 66t, 73t to the bottom of cylinder 35t so that on account of the greater area of piston portion 55 the piston will move upwardly and move switch 41t to "off position and de-energize the solenoid 49. A similar action occurs if only the top clamps 10t ... 12t are required. In other modifications the safety device may operate a belt fork or automatic stop devices for the machine. Specification 452,317, [Group XXII], is referred to.