Patent GB-937859-A (GB)
Title: Linear actuator
IPC: F15B11/12
Filed: 1962-03-27
Abstract: 937,859. Fluid pressure apparatus. CADILLAC GAGE CO. March 27, 1962 [March 27, 1961], No. 11580/62. Class 69 (2). A linear actuator comprises a stationary reference element 18, Fig. 2, a movable reference element 94, a plurality of longitudinally expansible stages 26, 27 ... 36, 37 slidably disposed within a common housing 10 between the stationary and movable reference elements, means for limiting the longitudinal extension of each of the expansible stages, means linking each expansible stage to the next consecutive expansible stage whereby the total displacement of the movable reference element in relation to the stationary reference element is the sum of the individual extensions of the expansible stages. The actuator may be used in a data processing, digital computer, machine tool or other automation system to convert the digital representation of a binary number into an analogue equivalent. The stationary reference element consists of a cap 18 at one end of a bore 16 in the housing 10, the other end of the bore having a bush 100 for guiding the cylinder portion 36 of the endmost expansible stage, a piston 37 of that stage abutting the movable reference element in the form of a shaft 94 which is connected to a member to be positioned. Each of the expansible stages is substantially identical with the exception of the stage 36, 37 and consists of a cylinder 26, 28, 30, 32, 34 and piston 27, 29, 31, 33, 35. The pistons are slidable in bores in the cylinders and the lengths of their strokes are limited by bushes 46 secured to the ends of the cylinders. The chambers 64 in the cylinders are connected by ports 63 and chambers 68 to passages 71, 73, 75, 77, 79, 81 leading to control valves 70, 72, 74, 76, 78, 80. The valves can be selectively actuated to supply fluid pressure to their respective piston and cylinders, the movement of each successive piston to the right, as viewed in Fig. 2, relative to the preceding piston, being twice the movement of the preceding piston. By selective actuation of the stages in the embodiment described having six piston-andcylinder assemblies, the output shaft can be moved to any one of sixty-four positions. The piston 36 of the end expansible stage has a shoulder 122 subjected to fluid pressure so as to bias the stages to their retracted positions. In another embodiment, each expansible stage consists of a sleeve 228, 244, 254, 260, 266, 272, 278, Fig. 5, slidable on a tubular member 212, 242, 252, 258, 264, 270, 276, the movement of the sleeves being limited by stops 227, 246, 256, 262, 268, 274, 280 and arranged so that the movement of each successive sleeve to the right relative to the preceding sleeve is twice that of the preceding sleeve. Fluid pressure supplied selectively to chambers 231, 250, 253, 259, 265, 271, 277 moves the final sleeve 278 and a member 296 abutting the sleeve and connected to an output shaft 308 to any one of 128 positions. The member 296 has an annular face 305 subjected to pressure in a chamber 298, the flow to and from the chamber passing through a restriction in an interchangeable device 312 to control the speed of movement of the shaft. In a further embodiment, each expansible stage consists of a piston 420, 422, 424, 426, 428, 430, 432, Fig. 7. All the pistons, other than the piston 432, have L-shaped projections extending from each face and interengaged with the projection extending from the face of the adjacent piston. The projection on the lefthand of piston 420 interengages an L-shaped projection 414 on a stationary end cap 404 and the projection extending from the right-hand face of the piston 430 interengages an L-shaped projection 436 on the left-hand face of the piston 432, the right-hand face of which is connected to an output rod 450 and has an annular face 466 subjected to fluid pressure to bias the pistons to a retracted position. The chambers between the pistons can be selectively supplied with fluid pressure from valves 472, 474, 476, 478, 480, 482, 484 to selectively move their associated pistons to the right against the biasing force a distance determined by abutment of the L-shaped projections, each successive piston to the right being capable of moving relative to the preceding piston twice the movement of that piston. In other embodiments, a coil spring provides the biasing force and the shaft is stationary and the housing movable. The output shaft of one actuator may be connected to the housing of a second actuator or two actuators may be placed back-to-back in a common housing with output shafts movable through both ends of the housing.