Motion Planning Of Lower Limb Exoskeleton With Passive Ankle For Paraplegics

In this paper, a motion planning method is proposed for a lower limb exoskeleton with passive ankle. Walking motion is divided into two phases: loading phase and swing phase. Via-points are assigned at different postures, and angles of each via-point are solved analytically. Then these angles are interpolated by a third order spline for generating joint trajectories, and they can be adjusted by given step length and foot clearance. Exoskeletons for paraplegics usually have passive ankle to reduce system weight, but passive ankle drops down the foot in swing phase, thus hip and knee joints need larger flexion to lift the swing toe compared with healthy individuals. This work proposes a design that drives the ankle joint with a cable for dorsiflexion in swing phase. Simulation results show that the swing toe can be lifted higher with this design, and it is promising that the maximum hip and knee flexion can be reduced so as to achieve better energy efficiency.