Patent GB-996337-A (GB)
Title: Improvements in or relating to hydraulic servo-mechanisms
IPC: B23Q5/36
Filed: 1962-03-30
Abstract: 996,337. Hydraulic apparatus. PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd. March 30, 1962 [April 4, 1961], No. 12305/62. Heading F1P. [Also in Division B3] An hydraulic servo-mechanism for a machine tool comprises a piston 31 dividing a cylinder 30 into two compartments, at least one of which communicates with an inlet h 1  and outlet h 2  for hydraulic fluid, external control means 50 for regulating the flow through the inlet h 1  and/or the outlet h 2  and means 51, 55 operable upon a variation of the pressure in the compartment to vary the flow of fluid through the inlet and/or the outlet so that the difference in the quantities of fluid supplied to and conducted away from the compartment per unit time is substantially independent of the pressure in the compartment. The inlet and outlet are formed by the spaces between a valve spool 36 and a housing 35 and a further inlet h 3  and outlet h 4  communicate with the second compartment B of the cylinder. The spool is of magnetostrictive material and its length is variable by energization of a coil 50 to vary the areas of the inlets and outlets and move the piston. In the event of a load being applied to the rod of the piston to cause an increase in pressure in compartment A and a decrease in pressure in compartment B, diaphragms 51, 52 are deformed and cause a difference signal from an amplifier 27 to energize a compensating coil 55 which alters the length of the spool so that the areas of the inlet h 3  and outlet h 2  become smaller and the areas of the inlet h 1  and outlet h 4  become larger to minimise the effect of the load on the piston. In another embodiment, one compartment B, Fig. 3, is connected directly to a constant pressure source P o  and the other compartment A is connected by a pipe 68 to an inlet h 1  and an outlet h 2  controlled by a valve spool 63 movable by an electro magnet 64. The spool is secured to a diaphragm 75 forming one side of a chamber C connected by a pipe 71 to the compartment A. Variations in the load EP cause a variation in the pressure in compartment A which is transmitted to the chamber C to move the diaphragm and hence the spool, the movement varying the areas of the inlet and outlet to compensate for the load. In a further embodiment, a spool 88, Fig. 4, controls inlets h 1 , h 3  leading to compartments A, B, respectively, and the pressure in the compartments acts on diaphragms 95, 96 secured to a spool 94 controlling outlets h 2 , h 4 . In another embodiment, the compartment B, Fig. 5, is connected to a constant pressure source 110 and by a passage 101 in the piston to an inlet hi to the compartment A, the latter compartment being connected by an outlet h 2 , the area of which is variable by a spool 104. If the load EP on the rod of the piston increases, the increase in pressure in compartment A deforms a diaphragm 106 so that the area of the inlet h 1  increases to increase the flow into the compartment A and compensate for the increase in load. A known arrangement not controlled by the pressure in the mechanism is described in which each compartment is connected both to a pump and to a tank and a valve controls the flow through both inlets and both outlets.