Multi-stable Structural Elements

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This dissertation considers a number of concepts for discretely stable structural elements. All of the concepts can be manufactured entirely out of non metallic components and have no sliding parts.

A review of current manipulator designs, possible actuation technologies and the expected requirements of discretely stable structural elements is made. Discretely stable structural elements are found to have possible applications in serpentine manipulators and variable geometry trusses.

Two concepts for discrete rotation elements suitable for serpentine manipulators are presented. One is based on hoops of five non-linear springs, whilst the other is based on a modification of an existing rolling hinge design. An analysis predicting the maximum stresses developed in this modified hinge is presented.

Four concepts for linear bistable elements are also presented, along with analytical and experimental results for the behaviour of each. Three of these are based on non-linear springs, whilst the fourth is based on inverting pairs of shallow arches. Out of the four, the most promising were found to be a design based on a four bar linkage with tape springs connecting opposing corners, and a design based on shallow arches.

Prototypes of the latter concept were developed, with research presented on possible variations in design and manufacturing technologies, as well as the material behaviour of nylon 6/66.

A variable geometry truss incorporating thirty variable length elements was designed and built after research into the most suitable truss architectures had been completed. This truss is shown to behave much as predicted by analytical tools, and serves to demonstrate the possibilities offered by the use of discretely stable structural elements.