Abstract: A digitally controlled air-over-hydraulic actuator includes a pneumatic cylinder and a hydraulic cylinder each having a separate piston and a common connecting rod. The pneumatic piston applies force to the connecting rod urging movement of the hydraulic piston. Bleeding of oil from one side of the hydraulic piston to the other is controlled by means of digital pulses applied to a digital valve that allows oil on either side of the hydraulic piston to flow to the other. The digital valve includes a moving piston having an oil passage that is momentarily aligned with ports to opposite sides of the hydraulic cylinder. A control system senses the differential pressure between opposite sides of the pneumatic piston to produce pulses that accelerate the digital valve piston past the ports, precisely controlling forced movement of the hydraulic piston.

Abstract: A digital linear actuator includes a plurality of digital actuator cells each connected to the next in sequential fashion. Each of the digital actuator cells contracts or expands a predetermined amount along an expansion/contraction axis when it is actuated by a corresponding digital signal. Each digital actuator cell includes an inner portion containing a medium which expands or contracts in response to a digital signal. The inner portion is disposed within an outer portion that contracts in the direction of the axis in response to expansion of the inner portion, and expands in the direction of the axis in response to contraction of the inner portion. The device is useful in simulating the behavior of a muscle in a prosthetic device. Several embodiments of the invention are disclosed in which an arm can be extended to and retracted from a snake-like configuration. Another embodiment of the invention is disclosed which effectively simulates a shoulder and arm mechanism.