DIRECT ACTING SERVO CYLINDER

PURPOSE:To improve stop position setting accuracy and duration of life and shorten control time by accommodating an input shaft rotatably in the feedback shaft of a servo valve rotated by the movement of a piston rod, and throttling the return oil flow by the angular deviation between both shafts. CONSTITUTION:A rack 49 is provided at the piston rod 31 of a hydraulic cylinder 32, and the feedback shaft 42 of a servo valve 37 is provided with a pinion gear 48 to be meshed with the feedback shaft 42, and also with first to third ports 57-59 connected to the ports a, b of the hydraulic cylinder 32 and a tank. An input shaft 43 is rotatably fitted into the feedback shaft 42. There are further provided a pressure passage 62 communicated with one of the first and second ports 57, 58 by the relative rotation of both shafts 42, 43, and a return groove 64, gradually changing its opening area, and communicated with the third port 59. Stop position setting accuracy and the duration of life are thereby improved, and control time is shortened.