Characterization of Active/Passive Pneumatic Actuators for Assistive Devices

Assistive devices have been developed for power augmentation and task-oriented assistance such as loaded walking. The effective joint dynamics of the user can be altered using a wearable system, providing assistance when a task is performed. The authors have investigated an Active/Passive Pneumatic Actuator (AP2A) for an assistive device, which has a simple structure and responds as a passive nonlinear spring with controllable stiffness. This paper introduces a novel controller for the AP2 A and validates the performance through experiments. The developed controller is found to stabilize at the desired stiffness response within 1 second, confirming the ability of the AP2 A to act as an adjustable passive nonlinear spring.