Architecturally Programmable Tendon Constrained Inflatables for Advanced Functionalities

Abstract

Inflatable structures have evolved to offer advanced functions such as high rigidity and complex actuated motions. These are achieved by controlling bladder inflation with stiff constraints like plates and fibers. However, the functionalities of inflatable structures are closely tied to their architecture, and existing inflatable architectures couple the bladder and constraints, limiting their capabilities. This dissertation introduces a novel architecture, tendon constrained inflatables (TCIs), with decoupled constraints and bladder that can be architecturally programmed to provide advanced functionalities. A TCI consists of an inflatable bladder with two rigid end caps connected internally by inextensible tendons, such as strings. TCIs can be architecturally programmed by designing their tendon configurations to constrain or allow select pre-defined motions through engaged and disengaged tendons based on external load inputs at a given pressure, without the need for electronic controls or actuators. This allows them to passively provide different magnitudes and directions of three functionalities: (1) rigid load-bearing capacities, (2) multiple segmented motions, and (3) collaborative responses. If an external load is applied on the end cap along engaged tendon directions, the TCI remains rigid up to its rigid load-bearing capacity, defined by the active tendon tension, until one or more tendons disengage, and the TCI assumes the bladder’s stiffness. If a load is applied along the unconstrained directions, the TCI moves along the degrees of freedom defined by the engaged set of tendon constraints. A TCI can have different sets of engaged tendons from slackening tendons and achieve multiple segmented motions. Furthermore, when a load is applied on an array of connected TCIs, they can provide collaborative responses – collaborative and independent motions to external loads based on the engaged or disengaged constraint connection between the TCIs. The goal of this dissertation is to establish the scientific foundation of TCIs through modeling and design methodologies of this novel architecture to provide advanced programmable functionalities. To enable these functionalities, a progression of the three types of TCI architectures is developed: fully constrained TCIs, partially constrained TCIs, and mutually constrained multi-TCIs. The dissertation investigates each TCI constraint variation with respect to architecture, model, design methodologies, and concludes with application case studies utilizing this supporting infrastructure. For each TCI, various architectural features, such as bladders, end caps, types of tendon constraints, and use of engaging and disengaging tendon constraints, are explored to enhance the TCI’s functionalities, setting the architecture foundation. Using differential motion analysis to determine the constraints imposed by a tendon configuration, a 3D kineto-static equilibrium model is derived by application of principle of virtual work to relate tendon configuration to the applied loads on the TCI. This enables the prediction of a tendon configuration’s six-dimensional rigid load-bearing capacities, multiple segmented motions, and collaborative motions in response to external loads. For each TCI constraint variation, model-based design methodologies are developed using interactive visualizations and optimization to finely tune the tendon configuration to control the TCI’s functionalities, while considering package and load requirements. Case studies across various fields were conducted to demonstrate the vast applicability of TCIs and their design methods, including rigid structures for confined or temporary spaces, enhanced mobility aids for daily living, and occupant safety devices for future mobility. TCI architecture is promising for realizing a new variety of structures capable of advanced, programmable functionalities that respond to the external loads from the environment.