Fluid pressure operable servo positioner

Claim 1

Servo positioner apparatus for selectively positioning a mechanical member in a desired position until a change is effected, said servo positioner apparatus comprising: (a) a double acting piston device including a power piston connected to the mechanical member and alternatively subjectable on opposite sides to operating fluid pressure for effecting operation of the mechanical member to respective pluralities of different positions in opposite directions from a normal central position, depending upon which of said opposite sides is subjected to said operating fluid pressure and the degree thereof; (b) control valve means having a cut-off position in which a supply communication, via which operating fluid pressure may be supplied to said power piston, is closed, and being operable, in response to a variable control fluid pressure, to one of a plurality of supply positions in which said supply communication is open for supplying said operating fluid pressure to said power piston at a degree commensurate with the degree of said control fluid pressure; (c) force balancing means including: (i) a spring disposed at one side of said power piston for exerting a biasing force on and urging the power piston toward its said normal central position in opposition to the operating pressure acting thereon, said power piston and the mechanical member assuming one of said plurality of different positions upon attainment of a balanced state between the opposing forces of said spring and said operating pressure acting on the power piston, and (ii) a cam member connected to and positionally movable with said power piston and having a cam surface of predetermined contour operatively engaging said control valve means, said cam surface being operable to one of a plurality of cam positions relative to the control valve means, such cam position corresponding to said one of said plurality of different positions of the mechanical member, for exerting a counter force on said valve means in opposition to said control fluid pressure to produce a balanced state therebetween and in which said control valve means is maintained in said one of said plurality of supply positions; (d) respective delivery pipes connecting to said opposite sides of said power piston; and (e) a changeover valve device interposed between said delivery pipes and said control valve means, (f) said changeover valve device normally biased to a first position in which one of said delivery pipes is communicated with the control valve means for effecting supply of operating pressure to one of said opposite sides of the power piston, and being operable responsively to actuating fluid pressure to a second position in which said one of said delivery pipes is cut off from said control valve means and the other is communicated therewith for effecting supply of operating pressure to the other of said opposite sides of the power piston.