Coil-Reinforced Flat Tube Actuators for Robotic Applications

Soft pneumatic actuators (SPAs) are widely used in robotic applications due to their inherent compliance and outstanding mechanical performance. However, a tradeoff between load capacity and deformation capacity is required when selecting material hardness for SPAs. Too hard material usually results in limited deformation, such as small extension, bending, and twisting, while too soft a material decreases robustness. This study introduces coil-reinforced flat tube actuators (CFTAs) that exhibit excellent flexibility and high load capacity by braiding flat tubes in coil springs. By adjusting the braiding pattern of the flat tube, the CFTAs can realize extending, in-plane bending, and out-of-plane helical bending motions. In addition, analytical models are proposed to predict the deformation behavior of the CFTAs and verified by experiments. The bending type CFTA deforms with an excellent curvature (0.516 mm⁻¹) under 160 kPa input pressure, five times larger than the reported SPAs on the same scale. The CFTAs show high design flexibility by programming the flat tube pattern and using multiple coiled springs for wide application scenarios. Based on the CFTAs, this study shows wearable upper limb robots, a soft entanglement gripper, and a rob-climbing robot. CFTAs provide design insight for applications requiring dexterous and versatile deformations.