Modeling and Closed Loop Control of Contraction in a Pneumatic Artificial Muscle

Pneumatic Artificial Muscles (PAMs) are remarkable for their simplicity, light weight, high stroke, and high force. PAMs are used extensively in robotics applications where actuator bandwidth requirements are relatively low (e.g., < 1 Hz) compared to aerospace applications where higher bandwidth is needed (e.g., as high as 30 Hz in rotor vibration control). Because PAMs couple large stroke with high specific actuation force, adapting PAMs to aerospace applications may provide a substantial gain in performance over conventional hydraulic and pneumatic actuators. This study develops a semi-empirical, nonlinear, pneumo-mechanical analysis of the time histories of pressure, force, and displacement, which is validated using experimental response data from a single PAM working against a spring and mass. A linear proportional + integral + derivative (PID) controller was then tuned analytically to achieve command following of sinusoids. Frequency responses are obtained via both simulation and experiment, and the ability to track relatively high frequency control inputs is demonstrated for periodic motions up to 24 Hz.