Abstract
A monoarticular series elastic actuator (SEA) reduces energetic and peak power requirements compared to a direct drive (DD) in active prosthetic ankle-foot design. Simulation studies have shown that similar advantages are possible for the knee joint. The aims of this paper were to investigate the advantages of a monoarticular SEA-driven hip joint and to quantify the energetic benefit of an SEA-driven leg (with monoarticular hip, knee and ankle SEAs), assuming that damping (negative power) is passively achieved. The hip SEA provided minor energetic advantages in walking (up to 29%) compared to the knee and the ankle SEA. Reductions in required peak power were observed only for speeds close to preferred walking speed (18% to 27%). No energetic advantages were found in running, where a DD achieved the best performance when optimizing for energy. Using an SEA at each leg joint in the sagittal plane reduced the positive work by 14% to 39% for walking and by 37% to 75% for running. When using an SEA instead of a DD, the contribution of the three leg joints to doing positive work changed: the knee contributed less and the hip more positive work. For monoarticular SEAs, the ankle joint motor did most of the positive work.
Highlights
Powered prosthetics that actively support the amputee in movement tasks require a great battery capacity
We investigated the amount of reductions in energy and peak power requirements at the hip, knee and ankle for walking and running at various speeds with monoarticular series elastic actuators (SEAs) compared to a direct drive system
Large reductions in peak power and energy requirements were observed at the ankle
Summary
Powered prosthetics that actively support the amputee in movement tasks require a great battery capacity. One way to reduce the motor’s mass is to increase the mechanical efficiency of, e.g., gear boxes or ball screws. Another way to achieve this goal is to reduce motor requirements by introducing elastic structures complementing the motor. Design approaches using springs in series, in parallel or a mixture of both are utilized to exploit elastic recoil and decrease motor peak power requirements. Such bio-inspired solutions mimic the function of muscle fibers (motor), ligaments and tendons (springs). A compromise between design complexity to achieve energy and peak power requirements and system variability must be made
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