Patent GB-961339-A (GB)
Title: Improvements in or relating to hydraulic drives
Inventor: FIRTH DONALD
IPC: F15B11/18
Filed: 1961-10-05
Abstract: 961,339. Machine tool details. NATIONAL RESEARCH DEVELOPMENT CORPORATION. Jan. 4, 1963 [Oct. 5, 1961], No. 35848/61. Addition to 924,906. Heading B3B. [Also in Divisions F1 and G3] An hydraulic drive for causing relative linear movement between a machine tool table 10 and a bed 13 as described in the parent Specification comprises a first and second set of piston members 19, 18 engaging either side of a rack member 17 secured to the table 10, and a control valve 23 operable to supply hydraulic fluid under pressure to and exhaust hydraulic fluid from the piston members in each set, in a given sequence, whereby the action of the first set of piston members 19 against the action of the second set of piston members 18 causes the relative movement in one direction. The control valve 23 (Fig. 3), comprises a valve member 25 rotatable in a body 24 and having a longitudinal fluid supply passage 28 communicating with an inlet 32, and a longitudinal exhaust passage 29 communicating through an annular groove 31 with an outlet 33 which has a constriction 33a so that exhaust takes place against a back pressure. The upper portion of the valve member (Fig. 5) controls the supply and exhaust through a plurality of pipes 49, each connected to one of the cylinders 21 containing the pistons 19, and the lower portion (Fig. 4) controls the supply and exhaust through a plurality of pipes 38, each connected to one of the cylinders 20 containing the pistons 18. A sleeve 52 provided with openings 51, 53, 54 is fixed in a central bore in the valve member 25 and has a control member 56 therein, rotatable by a servomotor or as shown, by a handle 57. In the position shown the table is locked against movement since the control member 56 prevents fluid from being supplied to or exhausted from the pipes 49 which open out into the segmental recess 43 of the control member 25. When the control member 56 is rotated in a clockwise direction high-pressure fluid passes from the opening 51 to the opening 54 and the segmental recess 43 and thence to the associated cylinders 21 to move the table. A rack 27 secured to the table and movable therewith rotates a pinion 26 and the valve member 25 secured thereto in the same direction as the control member 56 until the original relative positions of the control and valve members is restored and movement stops. Anticlockwise rotation of the control member 56 results in the openings 53, 54 providing communication between the exhaust passage 29 and the pipes 49 connected to the cylinders 21 so that movement of the table takes place in the opposite direction due to the action of those of the second set of pistons 18 which are supplied with pressure fluid through the pipes 38. In a modification the control member 56 is dis pensed with and fluid supplied to the pipes 49 is controlled by an external valve. The table 10 has a pair of taper-section slides 11 running in slideways 12, the upper and lower faces of the slides 11 having shallow recesses 14 supplied with pressure fluid for centralizing the table.