An apparatus for converting pressure, exerted by a pressurizing substance between a pressure source and a pressure sink, into increments of displacement, each increment having a length S, said apparatus comprising:
- a housing including a wall having four grooves defined in spaced relationship to each other on an interior surface of said wall and said wall further having four holes defined therethrough so that each hole extends from a respective one of the grooves to an exterior surface of said wall, said grooves and holes thereby defining four ports of said housing, each of said grooves being 0.5 S wide and being spaced from each adjacent groove on centers spaced 1.0 S;
- and
- a double-acting piston disposed for movement in said housing in response to the pressurizing substance, said piston including:
- a side wall having an inner surface and an outer surface and further having a first plurality of apertures and a second plurality of apertures defined in said side wall so that each of said apertures extends from the inner surface to the outer surface, each of said apertures having a diameter of 1.5 S with each aperture of said first plurality of apertures being spaced on a center separated a distance of 4.0 S from a center of each adjacent aperture of said first plurality of apertures and with each aperture of said second plurality of apertures being spaced on a center separated a distance of 4.0 S from a center of each adjacent aperture of said second plurality of apertures, said first plurality of apertures including a first aperture and a second aperture and said second plurality of apertures including a third aperture, wherein:
- said third aperture is defined in said side wall so that said third aperture registers with a first one of said ports when said first aperture registers with a second one of said ports and further so that said third aperture registers with said second one of said ports when said first aperture overshoots in a first direction said second one of said ports;
- and
- said second aperture is defined in said side wall so that said second aperture registers with said first one of said ports when said first aperture overshoots in said first direction said second one of said ports, said first, second and third apertures thereby providing feedback means for precisely positioning said piston relative to said housing;
- a first end wall closing a first portion of a first end of said side wall and leaving a second portion of said first end open;
- a second end wall closing a first portion of a second end of said side wall and leaving a second portion of said second end open;
- and
- a central wall extending from said first end wall to said second end wall and from a first region of the inner surface of said side wall to a second region of the inner surface of said side wall so that a first chamber extending from the first end wall to the open portion of the second end of said side wall and a second chamber extending from said second end wall to the open portion of the first end of said side wall are formed, wherein said first plurality of apertures communicates with said first chamber and wherein said second plurality of apertures communicates with said second chamber.