A Novel Sandwich Design for Improved Out-of-Plane Stiffness in Double Parallelogram Flexure Mechanism

Abstract

This paper proposes a novel sandwich design for improved out-of-plane stiffness in the Double Parallelogram Flexure Mechanism (DPFM). In DPFMs and flexure mechanisms comprising DPFMs, low in-plane stiffness along the motion direction helps improve the range of motion and reduces the actuation effort. On the other hand, high out-of-plane stiffness is essential to support large payloads and minimize out-of-plane parasitic motions. Achieving both of these design objectives simultaneously is challenging in DPFMs due to the inherent tradeoff between the in-plane and out-of-plane mechanics. The novel sandwich DPFM design proposed in this paper achieves a significant improvement in the out-of-plane bearing stiffness without affecting the in-plane motion-direction stiffness, thereby overcoming the tradeoff between the out-of-plane and in-plane stiffness values. Analytical models are presented for the out-of-plane and in-plane stiffness of the sandwich DPFM, which match very closely with Finite Element Analysis (FEA) predictions. The superior performance of the sandwich DPFM is demonstrated and several design insights are presented using the analytical stiffness models.