Zero Torque Compliant Mechanisms Employing Pre-buckled Beams

The concept of a statically balanced mechanism with a single rotational degree-of-freedom is presented. The proposed device achieves static balancing by combining positive stiffness elements and negative stiffness elements within an annular domain. Two designs are discussed. The first is composed of an Archimedean spiral and two pinned-pinned pre-buckled beams. The overall mechanism is modeled via an analytical approach and the element dimensions are optimized. The optimal configuration is then tested through finite element analysis (FEA). A second approach replaces the spiral beam with elastic custom-shaped spline beams. A FEA optimization is performed to determine the shape and size of such spline beams. The behavior of the negators is used as reference for the optimization so as to achieve a complete balancing. A physical prototype of each configuration is machined and tested. The comparison between predicted and acquired data confirmed the efficacy of the design methods.