Analysis of knee-ankle orthosis modelling: An inverse dynamics approach using adaptive coupled oscillator

Abstract

In this paper, an inverse dynamics approach by means of adaptive coupled oscillators is used in the modelling and control of a lower limb orthosis applied at the knee and ankle joint level. This design is aimed at providing assistance and rehabilitative measures to humans with lower limb disorders and as such presents a platform for which their mobility performance can be improved. Adaptive oscillators are known to have the capability of learning high level parameters of sinusoidal, quasi-sinusoidal or non-sinusoidal signals (amplitude, frequency and offset). However, the later signal (non-sinusoidal) considered in this paper requires a number of oscillators in parallel to replicate the moving joint regarding filtering via adaptive oscillator. The dynamic model for the knee and ankle are considered to take the form of a damped pendulum model connected by two revolute joints. This maps the input torque of both joints (knee and ankle) to their output trajectories, hence integrating the different forces at the joint level of the different joints. The coupling effect is achieved by the use of coupled Adaptive Frequency Oscillator (AFO) for the estimation of the joint trajectories. Tracking performance for the knee-ankle orthosis is studied for non-sinusoidal reference trajectories, having a global coupling between the joints. The results obtained using SCILAB show a good performance of the controller trajectory tracking capabilities even in the presence of external disturbances.