Safe and compliant guidance by a powered knee exoskeleton for robot-assisted rehabilitation of gait

In the research field of robot-assisted gait rehabilitation the focus grows on the improvement of
physical human-robot interaction (pHRI) by means of high performance actuator technologies and
dedicated control strategies. In this context we propose a combination of lightweight, intrinsically
compliant, high torque actuators (Pleated Pneumatic Artificial Muscles) with safe and adaptable
guidance along a target trajectory by means of Proxy-based Sliding Mode Control. We developed
a powered knee exoskeleton (KNEXO) to evaluate these concepts. In addition to the trajectory-
based controller a torque controller was implemented in view of minimizing the interaction during
unassisted walking. First, various treadmill walking experiments were performed with unimpaired
subjects wearing KNEXO to evaluate the performance of the proposed controllers. Test results
confirm the ability of KNEXO to display low actuator torques in unassisted mode and to provide
safe, adaptable guidance in assisted mode. Subsequently, a multiple sclerosis patient participated in
a series of pilot experiments. Provided some patient-specific controller tuning KNEXO was found
to effectively support and compliantly guide the subject's knee.