Manufacturing and modeling of helix-wrapped pneumatic artificial muscles

Abstract Pneumatic artificial muscles (PAMs) are lightweight, compliant actuators that mimic the contraction mechanism of biological muscles, making them well suited for robotics, prosthetics, and wearable systems. This paper presents the design, fabrication, mathematical modeling, and experimental characterization of a custom PAM tailored for integration in a continuum robot. The actuator consists of a flexible air chamber reinforced with low-angle ( α = 30°) helically wound nylon filaments, which constrain radial expansion and induce axial contraction upon inflation. A geometry-based, constant-volume model was first developed to capture the nonlinear coupling between helix angle, diameter, and length. Experimental testing under varying pressures and external loads confirmed strong, predictable axial contraction and revealed repeatable hysteresis loops characteristic of viscoelasticity and internal friction. The experimental data were used to derive a compact second-order polynomial predictor that demonstrated high accuracy in estimating contraction ratio as a function of pressure and load, suitable for on-board implementation. Taken together, these results validate the proposed helix-wrapped PAM as a low-cost, tunable, and manufacturable actuator that achieves the desired stroke–load trade-offs for continuum robot applications while offering a practical platform for future sensing, durability, and advanced modeling studies.