Dynamic Analysis of Lower Limb Exoskeleton Motion and Control Using Differential Transform Method

Abstract

In this study, the nonlinear dynamic analysis of the motion and control of the lower limb exoskeleton using differential transform method is presented. Devices for medical processes are continuously undergoing improvement such as enhancing and assisting automatic therapies with flexible and configurable programs for treating people with partial disability in lower limbs as applied in lower-limb exoskeleton. The configurable programs in this exoskeleton can be applied to observe and control the motion of the exoskeleton for effective physiotherapy and reduced rehabilitation time for patients with such disability. Hence, a two degree of freedom nonlinear dynamic model for the motion and control of the lower limb exoskeletons was developed for two links. The nonlinear dynamic models are solved by applying the differential transform method (DTM) and verified with the forth order Runge-Kutta numerical method (RK4). The effects of the applied torque on the two links are investigated and it is observed that Link 1 has large negative deflection amplitude that drives link 2 towards the opposite positive direction. An increase in the applied torque resulted in increase in the amplitude of the system for all initial condition considered. This in turns increases the nonlinear dynamic behavior of link 2 due to its lower mass value. The speed of both links dampens out over the history due to the presence of damping term. At equilibrium, both links are in phase and have the same amplitude over the time history. This study provides an analytical tool for observing and controlling the motions of the lower limb exoskeleton and for improving the designs of the medical device.