EXPERIMENTAL CHARACTERIZATION AND MODELING OF A UNIT SOFT AIR BLADDER

The goal of this study was to understand the behavior of a single soft air bladder constructed from nylon-coated thermoplastic polyurethane (TPU) using a CNC heat-sealing device. More specifically, the aim was to examine how load-bearing ability and internal pressures of the bladder can vary as a function of applied compressive displacement and initial inflation pressure. Additionally, the study explored how various parameters such as geometry (size, shape) and fabrication method (3-sided vs. 4-sided seal, and location of the air fitting on the bladder) would affect the ability to withstand large external loads and internal pressures. A series of force-displacement compressive experiments using an Instron machine suggest that larger initial inflation pressures can withstand larger forces and induce larger internal pressures. Additionally, the bladder’s size and shape affect its behavior. Circular bladders of the same characteristic dimension can withstand smaller forces and internal pressures when compared to square bladders. Furthermore, smaller-sized bladders can withstand smaller forces and internal pressures as compared to large bladders. A simple analytical model for circular bladders was also developed to predict bladder inflation height as a function of the initial inflation pressure and the externally applied load. The model was validated against the experimental results. Based on these results, a set of design guidelines are proposed that help engineers design bladder actuators for various soft-robotics applications to meet the application requirements.