US Patent 7779747 Actuator and method for producing mechanical motion

A system for producing mechanical motion is provided. The system includes an actuator having a first end, a second end, and a radially expandable bladder assembly extending therebetween, and a source of pressurized fluid external to said actuator. The bladder assembly further includes an inner cavity. In addition, a substantially fixed-volume reservoir positioned within the cavity is provided, wherein the bladder assembly is configured to expand in a radial direction and contract in an axial direction when a volume of fluid is introduced from the reservoir into the inner cavity.