GB843394A - Remote positional control for hydraulic presses - Google Patents

Abstract

843,394. Fluid-pressure servomotor-control systems. LOEWY ENGINEERING CO. Ltd. Sept. 19, 1957 [Sept. 29, 1956], No. 29801/56. Class 135. An hydraulic servomotor system for the remote control of a forging press 10 having a crosshead 11 movable with respect to the press base 12 by an hydraulic ram under the control of a main control valve 20, comprises a servo valve 21 controlling the supply and exhaust of pressure liquid to and from cylinders 25, 25a to actuate a pair of opposed pistons 24, 24a in one or other direction which through a rocker or cam-shaft 22 raises and lowers valve elements of the main control valve. The servo valve 21 comprises a valve piston 105, 106 connected by a rod 26 to a shaft 71 mounting a sprocket 70 of remote control mechanism 40 and a follow-up sleeve 104 connected by linkage 27 to the shaft 22. The sprocket engages a pair of endless chains 55, 61 which when moving at the same rate rotate the sprocket without raising or lowering the rod 26 so that the servo valve is inoperative. The chain 62 is movable between stops 47, 47a, adjustable to correspond to the desired length of the stroke of the crosshead 11, by a manually-operable handle 65 whilst the chain 55 is moved by the crosshead 11 by means of a further endless chain 52 and sprockets 53, 54. To operate the press, the operator moves the handle 65 downwards along with the chain 62 and, since the chain 55 is at this time stationary, the sprocket 70 moves downwards besides rotating, and actuates the servo valve 21 and through it, the pistons 24, 24a, the main control valve 20 and the crosshead 11. The crosshead moving downwards then moves the chains 52, 55, and the downward movement of the sprocket 70 becomes a differential of the movement of the handle 65 and the crosshead 11. When the crosshead moves at a speed corresponding to that of the handle 65, downward movement of the sprocket 70 ceases so that the positions of the servo-valve and the main control valve are unchanged and the hydraulic pressure to the ram cylinder remains the same. A pointer 57 indicates the actual position of the crosshead and a pointer on the handle 65 the desired position of the crosshead. To limit the speed at which the operator may operate the press a device 90 controlled by a centrifugal governor 91, or a dashpot is connected to a sprocket 64 on the chain 62. An auxiliary hand control 80 to operate the servo valve 21, is provided. The mechanical differential mechanism constituted by the sprockets and chains may be replaced by an electrical differential which includes potentiometers whose movable elements are connected to a handle operable by the operator and the crosshead, and a Wheatstone bridge or other balance circuit.