Computed-torque method for the control of a 2 DOF orthosis actuated through pneumatic artificial muscles: a specific case for the rehabilitation of the lower limb

TL;DR

This paper introduces a computed-torque control model for a 2 DOF lower limb orthosis actuated by pneumatic muscles, including system characterization, modeling, and validation for rehabilitation applications.

Contribution

It presents a novel control approach based on computed-torque method tailored for pneumatic muscle-actuated orthoses, with detailed system modeling and validation.

Findings

Successful control of the orthosis demonstrated in validation tests.

Effective modeling of pneumatic muscles using polynomial fit functions.

Enhanced understanding of pneumatic muscle dynamics for rehabilitation devices.

Abstract

In this paper we give a new control model based on the so called computed-torque method for the control of a 2 degrees of freedom orthosis for the rehabilitation of the lower limb, the AIRGAIT exoskeleton's leg orthosis. The actuation of the AIRGAIT is made through self-made pneumatic muscles. For this reason this work starts with the static and dynamic characterization of our pneumatic muscles. The followed approach is based on the analytical description of the system. For this, we describe the pneumatic muscles behaviour with an easy-invertible polynomial fit function in order to model its non-linear trend. We give a geometrical model of the mechanical system to compute the length between the attachments of the pneumatic muscles to the structure for every angles assumed by the two joints. We evaluate through Newton-Euler equation the couples at the joints for each values of the angles. At last we show some validation tests in order to characterize the functioning of the proposed control model on the actuation of the orthosis.