Development and evaluation of passive assist device with biomimetic knee joint

Abstract

Movement of knee joints include rolling and sliding. To assist the standing movement, we developed two types of passive assist devices with bio-inspired knee joints (BKJ); movable-shaft passive device with BKJ (MSP-BKJ), and single-shaft passive device with BKJ (SSP-BKJ). The MSP-BKJ composed of a fixed noncircular gear, a circular gear, and torsion springs. The SSP-BKJ, in contrast, composed only of an ellipsoidal cam, and torsion springs. The motion of the rotational shaft of the MSP-BKJ was designed to mimics the motion of human joints, in contrast, the rotational shaft of the SSP-BKJ does not move. In order to compare their performances on the supporting effect and burden on the skins, we evaluated the electromyogram (EMG) of lower limbs and shear stress between users’ skin and two types of the assist devices. Shear-force sensitive sheet (SSS) was used to assess the shear stresses on the skin. Although, the EMGs did not show significant differences, the shear stress in the case with the MSP-BKJ was significantly lower than that with the SSP-BKJ.