Design of an energy-efficient active knee prosthesis through comparison of optimized kinematic chains including elastic actuator and variable transmission concepts
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- Background: Individuals with transfemoral amputation face diverse mobility deficiencies. Knee prostheses stand out as rehabilitation devices capable of improving the quality of life for amputees. While passive designs remain the most commonly used, a growing number of active devices are emerging. Active prostheses hold potential to restore users' freedom of movement through their versatility in common lower limb tasks. However, their development must address critical challenges, such as ensuring sufficient autonomy and remaining lightweight, despite the embedded motor and battery. Objectives: The aim is to design a lightweight active knee prosthesis with high energetic efficiency by comparing different kinematic chains from motor to knee joint in terms of motor energy consumption and peak power. Simulation: The kinematic chains are grouped into two families of solutions: elastic actuators and variable transmissions. Optimizations are conducted on the simulation models of these different kinematic chains for walking exclusively and for walking and stairs ascent combined. Three small electrical motors are considered as candidate to actuate the prosthesis, with particular attention paid to their mechanical and thermal limitations. Results: The double parallel elastic actuator (2PEA) and the clutchable series elastic actuator (CSEA) stand out in the first solutions category. The 2PEA excels in terms of walking energy consumption but is less efficient for stairs ascent. The CSEA provides inferior but more consistent results for various lower limb tasks. Similarly, two variable transmissions stand out from the optimizations: the 2-stage planetary gear (2PG) and the Utah bionic leg mechanism, both allowing the use of the smaller candidate motor to drive the kinematic chain. As the beneficial effects of the two approaches are distinct, combining them proves advantageous. After evaluating the 4 possible combinations, the CSEA-2PG combination is chosen. A draft mechanism for implementing this combination is proposed.