A Knee–Ankle–Foot Orthosis to Assist the Sound Limb of Transfemoral Amputees

B. Sanz-Morère, M. Fantozzi, A. Parri, F. Giovacchini, A. Baldoni, M. Cempini , S. Crea, Member, IEEE, Lefeber, Member, IEEE,...
A Knee–Ankle–Foot Orthosis to Assist the Sound Limb of Transfemoral Amputees
  1. B. Sanz-Morère, M. Fantozzi, A. Parri, F. Giovacchini, A. Baldoni, M. Cempini , S. Crea, Member, IEEE, Lefeber, Member, IEEE, and N. Vitiello, Member, IEEE

Abstract: As a consequence of limb loss, trans-femoral amputees exert 60% additional knee extension torque and 50% more plantar flexion torque in the healthy limb compared to nonamputees. In this paper, we developed an active knee–ankle–foot orthosis (KAFO) designed to assist the healthy leg of transfemoral amputees in activities of daily living, such as walking, ascending/descending stairs, and transitioning from sit-to-stand with adequate range of motion, speed, and peak torque. Our KAFO was designed to exceed the performance of similar assistive devices reported in literature in terms of: 1) portability; 2) power; 3) compliance; and 4) versatility. It is based on onedegree- of-freedom active series-elastic actuators in both the knee and ankle, with an additional passive degree of freedom at the ankle level to allow natural inversion/eversion. The knee module consists of a worm-gear surrounded by two pre-compressed springs. The ankle actuator relies on a mechanically adjustable compliance system combined with a 4-bar linkage transmission. The actuators were designed to optimize the torque output at the joints while fulfilling low-power requirements. This novel KAFO is controlled with a three-layer structure. The optimized low level, based on a closed-loop torque controller, has adequate performances for the targeted application. The device is also shown to fulfill the three pre-defined functional requirements for all locomotion modes.

 

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