Large stroke high off-axis stiffness three degree of freedom spherical flexure joint

Three degree of freedom spherical flexure joints are typically limited to small deflections because of their strong loss of stiffness in support directions when deflected. In this paper, a smartly stacked folded leafspring based large stroke spherical flexure joint is presented which can maintain a high level of support stiffness over a +/- 30 degrees tip-tilt and a +/- 10 degrees pan motion. To enable this large range of motion, two sets of three leafsprings are stacked in series. A large loss of support stiffness over the range of motion due to the underconstrained intermediate body is avoided by assuring that the instant centers of rotation coincide. To mitigate internal dynamics caused by the underconstraints, a design with underconstraint eliminators and a design with eddy current damping are presented. Furthermore, the design of the spherical joint has been optimized which has resulted in a flexure joint design which can achieve a support stiffness of over 200 N/mm and a load capacity of 290 N at the maximum deflection angle. Experimental measurements validate the high level of support stiffness and load capacity over the entire range of motion.