For steel flexures, complex geometries are required to reach high support stiffness and limit axis drift over large ranges of motion. These complex flexures are expensive, difficult to manufacture, and hard to clean. This limits their usability in for instance industrial applications.&nbsp;Instead of using steel, this paper presents a method of using polymers to design short wire flexures with high support stiffness over large ranges of motion. Due to the large amount of allowed strain in polymers, the thickness of the flexure can be increased significantly. For the 3D printable Thermoplastic Polyurethane (TPU) used in this paper, the flexure diameter could be increased by a factor of 110 with respect to steel. Even though the material stiffness of polymers is substantially lower than that of steel, the larger diameter results in a support stiffness increase. This leads to the counterintuitive result that by using a polymer instead of steel, the support stiffness increases by a factor 7800 at 70 degrees deflection.The short wire flexure exhibits a considerable axis drift when subjected to such large rotation angles. Instead of mitigating this axis drift, the strategy in this paper is to model it using a new method named the arc method. This method is based on the fact that a wire flexure forms a circular arc when subjected to a pure moment. Due to the high support stiffness of the polymer wire flexures, deformations due to force components are small and the assumption of a circular arc can be made. The model is compared to pre-existing pseudo-rigid body models (PRBM), finite element methods (FEM) and experiments, showing at least a factor 10 lower error than the PRBM models over a range of 70 degrees deflection to each side.&nbsp;

Modelling the Axis Drift of Short Wire Flexures and Increasing Their Support Stiffness Using Polymers

Paper Proceedings: https://asmedigitalcollection.asme.org/IDETC-CIE/IDETC-CIE2021/volume/85369

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