Mechanism and Bias Considerations for Design of a Bi-Directional Artificial Muscle Actuator

Pneumatic artificial muscles (PAMs), or McKibben actuators, have received considerable attention for robotic manipulators and in aerospace applications due to their similarity to natural muscles. Like natural muscles, PAMs are a purely contractile actuator, so that, in order to produce bidirectional or rotational motion, they must be arranged in an agonist/antagonist pair, which inherently limits the deflection of the system due to the high parasitic stiffness of the antagonistic PAM. This study presents two methods for increasing the performance of an antagonistic PAM system by decreasing the passive parasitic moment, rather than increasing the active moment. The first involves selection of the kinematic mechanism geometry, and the second involves the introduction of bias into the system, both in terms of PAM contraction, and passive (antagonistic) PAM pressure. It was found with the proper selection of design parameters, including mechanism geometry, PAM geometry, and bias conditions, that an ideal actuator configuration can be found that maximizes deflection for a given arbitrary loading. When comparing a baseline design to an improved design for a simplified case, a nearly 50% increase in maximum deflection was predicted simply by optimizing mechanism geometry and bias contraction.