A Novel High-Torque Bidirectional Curl Pneumatic Muscle With Stretchable Sheath: Design and Finite Element Method Analysis

This article presents design and modeling of a novel high-torque bidirectional curl pneumatic artificial muscle (BCPAM) consisting of two identical inflatable semielliptic cylindrical chambers in parallel and symmetric arrangement. Each chamber is enclosed by a hyperelastic silicone (polymer) bladder encircled by an anisotropic elastic fabric sheath in circumference and fastened by conical fittings at two ends. The sheath is composed of rubber-blended polyester-knitted fabric (RPF) with high uniaxial nonlinear elasticity to allow longitudinal stretch and restrict radial expansion of the bladder, and is partially reinforced by polyvinyl chloride (PVC)-coated polyester-woven fabric (PPF) with high in-plane strength working as a neutral limit layer for bending deformation of the BCPAM. Based on mesoscopic measurements, tensile tests, and parameter identifications of the utilized materials, we build the finite element method (FEM) model and solve it by explicit dynamic solver with numerical method in Abaqus software to predict the bending angles and actuation torques of the BCPAM under different inflating pressures, verified by experiments. Simulations and experiments show the proposed BCPAM produces large range of motion (±82.7°) and high force output (34.1 Nm) under 400 kPa of inflating pressure. Experiments of cyclic and step actuations show repetition accuracy, response time, and bandwidth frequency of the BCPAM are ±0.98°, 0.78 s, and 1.6 Hz in bending angle, and ±0.03 Nm, 0.50 s, and 6.9 Hz in actuation torque. The proposed BCPAM has potential applications in bionic and rehabilitation robots.