Anisotropic Rigid Load-Bearing Threshold Design of Tendon-Constrained Inflatables

Abstract Tendon-constrained inflatables (TCIs), composed of inflatable bladder and internal tendons, provide rigid load-bearing (RLB) with high stiffness up to predefined thresholds based on the input pressure and tendon configuration. At loads above these thresholds, select tendons become slack and enable deformation. Engineered arrangements of tendons in spatial configurations enable customizable anisotropic RLB thresholds in six dimensions. This customizability is useful for applications that require complex load thresholds like mobility aids that need to provide specific rigidity thresholds in different directions before deforming to act as safety mechanisms. However, the design of the anisotropic RLB thresholds is challenging because the RLB thresholds in different directions are coupled and trade-off with other design factors like package size, number of tendons, and input pressure. This article presents a comprehensive model-based design optimization of spatial TCI's six-dimensional anisotropic RLB thresholds including discussion of various design objectives, parameters, and load requirements. A design process including visualizations of the normalized RLB region and a two-step optimization scheme is developed to guide the negotiation of the large and complex design space of TCIs. A case study on a wheelchair headrest interface is presented using the design process to provide rigid support during rest and motion when viewing sideways under user-specific head loads while minimizing pressure. The established scientific foundation supports the design of customizable, six-dimensional RLB TCI for complex load requirements.