Keywords: pneumatic artificial muscle, shape memory polymer, dual-mode actuation, flexible sensing

This paper presents a dual-mode pneumatic artificial muscle integrated with three circumferentially arranged S-shaped shape memory polymer (SMP) constraints. By selectively heating the SMPs, the actuator achieves reversible switching between axial elongation and multi-directional bending, enabling four distinct deformation modes (3C, 2C1H, 1C2H, and 3H). A thermomechanically coupled, energy-based theoretical framework is developed to model this behavior. The static equilibrium equations are derived from the total potential energy functional—which includes the hyperelastic strain energy of the bladder, the temperature-dependent stiffness of the SMPs, and the work done by pneumatic pressure—using the principle of minimum potential energy. A high-fidelity finite element model employing a sequentially coupled thermo-pneumaticsolid strategy is also established. A prototype was fabricated and systematically tested on a custom platform integrating pneumatic, thermal, and mechanical measurement systems. The results demonstrate good agreement among the theoretical model, finite element simulation, and experimental data, with the majority of relative errors falling below 10%. The experimentally measured maximum bending curvature reaches 0.0174 mm⁻¹, and the maximum axial elongation ratio is about 18.4%. An error analysis identifies residual SMP stiffness, contact friction, and braided sleeve slippage as primary sources of discrepancy. This study provides a systematic theoretical and technical basis for designing, modeling, and controlling multi-modal soft actuators.

Zhengyue Li, Jinchi Li, Chenchao Fang, Jian Sun, Yanju Liu, Jinsong Leng

Dual-mode pneumatic artificial muscle integrating shape memory polymer constraints multiphysics modeling and experimental validation.pdf