The Chain-Link Actuator: Exploiting the Bending Stiffness of McKibben Artificial Muscles to Achieve Larger Contraction Ratios

McKibben artificial muscles, comprised of an expandable bladder wrapped in a double-helix-braided sheath, have the ability to generate forces without restricting motion to occur exclusively along the direction of actuation. This makes them attractive for a variety of applications including soft, wearable, and biomimetic robots. Despite their advantages, the theoretical maximum contraction ratio of McKibben muscles is only 36.3%, which restricts the range of motion of the systems they actuate. This work introduces a novel ‘chain-link actuator’ that exploits the bending stiffness of McKibben muscles to achieve contraction ratios of more than 50%. A static model that captures the relationship between pressure, displacement, and force is presented and validated on several real chain-link actuator systems.