Lateral Pleated Pneumatic Artificial Muscles: High-Contraction and Extended High-Force Range Actuators for Soft Robotics

Soft actuators have shown strong potential in wearable devices, mobile robotics, and manipulators. This article presents a soft actuator driven by positive pressure, termed lateral pleated pneumatic artificial muscles (LPPAM). LPPAMs incorporate tensile belts to convert the expansion of laterally placed pleats into linear contraction, achieving a high contraction ratio of 0.581 (theoretically up to 0.611) and an extended force range. In particular, the output force remains above 80% of the maximum in 86.01% of the contraction range, indicating excellent force consistency. A key feature of LPPAMs is their one-sided directional expansion, where inflation occurs primarily on one side of the tensile belts, minimising interference in wearable applications. The study validates a predictive model and analyses how design parameters affect performance. Extended configurations are also explored, including symmetric and serial arrangements. Side-stacked serial LPPAMs retain the directional expansion advantage and are used in a lightweight elbow flexion assistive exosuit. Preliminary experimental results demonstrate a significant reduction in muscle activation for users, highlighting the potential of LPPAMs in soft wearable applications.