Lower-limb amputation affects the ambulation ability and quality of life of about 600,000 individuals in the United States alone1. Individuals with transfemoral amputation typically walk slower, expend more energy, and have a higher risk of falls than able-bodied individuals2. Ambulation activities such as climbing ramps or stairs or standing up from a seated position are much more difficult than for able-bodied persons. Advances in prosthetic technologies are needed to improve the ambulation ability of above-knee amputees.
Passive knee prostheses are lightweight, robust, and quiet, but can only perform activities with dissipative dynamics. Powered prostheses3 overcome this limitation by motorizing the prosthetic joints throughout the entire day, thus enabling the achievement of more activities. However, the prosthesis actuator must then accommodate a wide range of speed and torque to support the various activities, plus provide power over the course of the entire day. Consequently, powered prostheses provide the ability to perform more tasks at the expense of substantial weight, noise, and battery life, which in turn affect their acceptability and clinical viability.
To address these shortcomings, we propose a hybrid actuation design for prosthetic knees. The proposed hybrid actuation system uses a motor, transmission, and control only for those activities requiring net-positive mechanical energy, such as climbing on stairs and ramps or performing sit-to-stand transfers. For non-positive mechanical energy tasks, such as standing and walking, the motor and transmission are mechanically disconnected, and passive knee components are used alone, thus achieving improved joint dynamics, and avoiding any electrical energy consumption.
