Variable Recruitment Testing of Pneumatic Artificial Muscles for Robotic Manipulators

This paper investigates the orderly recruitment of pneumatic artificial muscles for efficient torque production in a robotic manipulator. Pneumatic artificial muscles (PAMs) are arranged in a parallel bundle, and independently-controlled “motor units” are employed to imitate the structure and function of human skeletal muscle. Simulated cycling tests are conducted on a model of the robotic manipulator to quantify the benefits of variable recruitment, and experimental testing is performed to validate the simulated predictions. Results reveal a distinct relationship between recruitment and system efficiency. Key factors influencing the value of a variable recruitment strategy include nonlinear PAM bladder elasticity, pneumatic losses, and dissipative forces in the robotic joint. Recruitment guidelines are proposed to maximize efficiency over a range of payload masses. The potential challenges associated with maintaining smooth motion control during discrete transitions in recruitment are also identified and discussed.