Multiple position digital actuator

A multiposition actuator for changing a N-bit digital word into N physical positions of an actuator element comprising:

• N-1 telescoped open ended cylinders mounted in an open ended bore with the open ends of said cylinders disposed toward the closed end of said bore and an end cap closing the open end of said bore;
• said actuator element including an elongated body passing through an aperture in the closed end of said bore and having a flange being a double acting piston disposed within the innermost cylinder;
• said actuator element, cylinders and end cap forming N piston cylinder combinations wherein the piston area of each successive piston increases from the innermost combination to the outermost combination, and wherein the flange piston area disposed toward the closed end of the bore is less than the flange piston area for the innermost cylinder;
• each of said combinations operable to move said actuator element independently of the other combinations through a distance controlled by an expandable chamber disposed between the cylinder and piston of each combination, each distance being related to the other distances by powers of the numeral 2;
• N pilot solenoids, each associated with an expandable chamber and operable to control means for communicating a source pressure to a corresponding chamber and the source pressure from a corresponding chamber to a reference pressure and each associated with one of the bits of said digital input and actuated by one of the states of said bit;
• a bias chamber defined by the open ends of said cylinders and the closed end of said bore;
• means for communicating said source pressure to said bias chamber such that movement of the expandable chambers is accomplished by the force difference between the pistons because of the source and reference pressures acting over the differing piston areas.