This invention relates to hydraulically driven actuators and more particularly to such an actuator which may be centered and locked at a predetermined position.
It has long been desired to lock a hydraulic actuator in a predetermined position with the position being determined by the particular application in which the hydraulic actuator is being utilized. Such actuators are specifically used in the aerospace industry for positioning of various parts of aerospace vehicles including the control surfaces thereof. It is, however, to be understood that the present invention is not limited to such an application.
Typical locking devices for hydraulic actuators of the prior art include such structures as a pin or tongue which is inserted through a slot provided in the piston rod of the hydraulic actuator, an eccentric ring positioned around the actuator piston rod which, upon rotation, grips the rod to preclude movement, a latching dog which engages threads or grooves in the piston rod, a U-shaped member which is disposed within opposed grooves on the actuator piston rod, a reduced diameter portion of the piston rod which engages stops positioned at spaced apart positions, or the like.
The best prior art known to applicants is shown in the following U.S. Pat. Nos.:
______________________________________ 2,213,264 J. E. Wall September 3, 1940 2,329,743 M. B. Cameron September 21, 1943 2,369,513 V. F. Zahodiakin February 13, 1945 2,512,150 V. E. Geren June 20, 1950 2,598,560 B. F. Kenyon May 27, 1952 2,684,770 G. S. Park July 27, 1954 2,750,994 R. B. Howell, Jr. June 19, 1956 2,861,549 C. A. Gardener November 25, 1958 3,157,194 R. D. Stolte November 17, 1964 3,168,759 J. P. Johannigman February 9, 1965 3,177,976 P. D. Wenzel April 13, 1965 3,283,596 J. O. Roeser November 8, 1966 3,416,390 R. D. Houk December 17, 1968 3,572,161 H. V. Lichtenberger March 23, 1971 et al 3,834,198 M. Wiczer September 10, 1974 3,834,282 S. Kongelbeck September 10, 1974 4,073,345 M. E. Miller February 14, 1978 ______________________________________
In all instances, the particular apparatus as disclosed works well for the application intended. However, none of the structures shown in the prior art known to applicants positions the hydraulic actuator at a predetermined variable desired position and locks it in place irrespective of the position of the actuator at the time the command signal is received to position the actuator at the predetermined position and lock it in that position.