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Miniature hydraulics for a mechatronic lower limb prosthesis

In Germany alone, 10,000 to 12,000 transfemoral amputations occur every year. Persistent rehabilitation efforts and advanced medical devices like prosthetic knee joints are crucial to reintegrating amputees into daily life successfully. Modern knee joints represent a highly integrated mechatronic system including special kinematics, a lightweight design, various sensors, microprocessors and complex algorithms to control a damping system in the context of the given situation. A knee joint is a passive system and normally has no actuator for an active movement. To enable a natural gait pattern, dampers decelerate the swinging speed of the prosthesis depending on the walking speed and situation. The invention of a novel knee joint called VarioKnie provides two kinematics a monocentric and a polycentric one. Both kinematics have diametrical advantages and the user can choose the preferred setting through an electromechanical switching unit. With this knee joint in mind, a special hydraulic damper is developed to support both kinematics. Requirements and technical data are provided in the present paper. State of art are microprocessor-controlled knee joints with only one kinematic and either a hydraulic, a pneumatic, or a rheological damper.