Adaptive Based Assist-As-Needed Control Strategy for Ankle Movement Assistance

Stroke affects a large number of people every year. One consequence is the weakness of ambulatory muscles resulting in a paretic gait. Actuated ankle foot orthoses can be a solution to assist paretic patients to dorsiflex and/or plantar flex their ankle joint during the gait phases. To assist the wearer following a predefined ankle joint desired trajectory, an adaptive active disturbance rejection controller is proposed in this study. The human muscular torque and estimation errors are estimated through a nonlinear disturbance observer based on the estimated model. This estimated torque is compensated within the proposed projection based adaptive controller com- bined to a saturated proportional derivative term. The purposes of using this controller are : i) the no need of prior system’s parameter identification due to the adaptive structure, ii) the assistance-as-needed of the wearer through the rejection term and iii) the avoidance of the actuator saturation by including projection and saturation functions. This controller is tested in real time using an actuated ankle-foot-orthosis (AAFO) in lab environment with three healthy subjects to show its effectiveness.