Finite Element Modeling of Pneumatic Bending Actuators for Inflated-Beam Robots

Inflated-beam soft robots, such as tip-everting vine robots, can control their curvature by contracting one side of the beam using pneumatic actuation. In this work, a general finite element modeling approach is developed and applied to characterize bending of inflated-beam soft robots. The model is tested on four types of pneumatic actuators used in these robots (series, compression, embedded, and fabric pneumatic artificial muscles) and can be extended to other designs. Actuators rely on two types of bending mechanisms: geometry-based contraction and material-based contraction. Geometry-based contraction implies shape-change of the muscles from a flat to an inflated shortened configuration that causes buckling of the inflated beam. Material-based contraction relies on material anisotropy to produce a contraction effect. The model depicts both mechanisms and accommodates for the complex and highly nonlinear effects of buckling and anisotropy. Simulation results are verified experimentally for each actuator type at three working pressures (10, 20, and 30 kPa). Geometry-based contraction achieves the largest deformation at accuracy values of 92.1% and higher once the buckling pattern is established, and 80.7% and higher for lower pressures due to the stress singularities occurring with buckling formation. Material-based contraction achieves smaller bending angles but is at least 96.7% accurate. The models are freely available online, and can thus be used by others to design inflated-beam robots, such as tip-everting vine robots. Labor and material waste can be reduced with this tool by optimizing designs that use knowledge of material properties and stress to distributions to enable bending and manage stress peaks.