Simulation and experimental analysis of a portable powered ankle-foot orthosis control

A portable powered ankle-foot orthosis (PPAFO) was previously developed using off-the-shelf pneumatic components to explore new opportunities for fluid power in human assist devices. The untethered pneumatically powered ankle-foot orthosis provides both motion control and torque assistance at the ankle via a binary, event-based control scheme that uses solenoid valves. While stable, the binary actuation of the solenoid valves that results from this approach limits the overall performance of the system. This paper addresses the limitations of the current system using a modeling approach for both hardware and control design. Hardware and control configurations were first evaluated using simulations of the modeled PPAFO and shank-foot system during a simplified functional gait task: assistive propulsive torque during stance. These simulations demonstrated that the introduction of a proportional valve and new control architecture resulted in PPAFO performance improvements during the task. These results were then confirmed experimentally with the PPAFO attached to a physical model of a shank and foot.