Soft Pneumatic Actuators with Controllable Stiffness by Bio-Inspired Lattice Chambers and Fused Deposition Modeling 3D Printing

This article shows how changing 3D printing parameters and using bio-inspired lattice chambers can engineer soft pneumatic actuators (SPAs) with different behaviors in terms of controlling tip deflection and tip force using the same input air pressure. Fused deposition modeling (FDM) is employed to 3D print soft pneumatic actuators using varioShore thermoplastic polyurethane (TPU) materials with a foaming agent. The effects of material flow and nozzle temperature parameters on the material properties and stiffness are investigated. Auxetic, columns, face-centered cubic, honeycomb, isotruss, oct vertex centroid, and square honeycomb lattices are designed to study actuators' behaviors under the same input pressure. Finite-element simulations based on the nonlinear hyper-elastic constitutive model are carried out to precisely predict the behavior, deformation, and tip force of the actuators. A closed-loop pneumatic system and sensors are developed to control the actuators. Results show that lattice designs can control the bending angle and generated force of actuators. Also, the lattices increase the ultimate strength by controlling the contact area inside the chambers. They demonstrate variable stiffness behaviors and deflections under the same pressure between 100 and 500 kPa. The proposed actuators could be instrumental in designing wearable hand rehabilitative devices that assist customized finger and wrist flexion-extension.