Control Algorithm for an Active Ankle-Foot Orthosis (AAFOs): Adaptative Admittance Control

Most of current prostheses and orthoses use physical springs and dampers with various control strategies to replicate the compliant behavior of a normal ankle during the gait. The springs, dampers and the control strategies are usually tuned for a single patient and for a fixed gait speed which does not allow adaptation to another patient or another gait speed. In this work, we propose a control strategy that overcomes those adaptation problems. The algorithm is based on an admittance control and replicates the ankle torque-angle curve to assist level-ground gait. The particularity of this control comes from the fact that the physical spring is replaced by a mechatronic spring. It uses principally force and position sensors in order to replicate the behavior of a physical spring. Thanks to the use of a mechatronic spring, the orthosis and the control strategy can easily be adapted to any individual and can adapt themselves to any gait speed.