A computer controlled hydraulic resistance device for apparatus such as a prosthetic knee for above knee amputees, includes a two stage pilot operated solenoid valve connected to control the flow of hydraulic fluid to and from a hydraulic actuator which applies resistance to the prosthetic knee or other...http://www.google.com/patents/US6113642?utm_source=gb-gplus-sharePatent US6113642 - Computer controlled hydraulic resistance device for a prosthesis and other apparatus
