Robust Design Optimization of Compliant Constant Force Contacts with Simulated Pin Joints

Abstract

Constant force mechanisms are mechanical devices that provide a near-constant output force over a prescribed deflection range. These mechanisms have proven to be innovative solutions in applications ranging from robot end-effectors to commercial exercise equipment. This paper focuses on the robust design optimization of constant force electrical contacts. Electrical contacts are small in size, manufactured using progressive-die forming, and carry electrical current; as such, any constant force mechanism proposed for use as a contact should not have pin joints. For cases such as these, simulated pin joints are used to achieve the necessary kinematics. These simulated joints, however, are subject to mating/assembly uncertainties that can significantly change the percent constant a mechanism’s output force is. In this paper, the basic constant force contact architecture is presented, followed by the design and optimization model used to characterize the forcedeflection relationships for the contact. This is done for both an ideal simulated pin joint, and for one that is subject to mating uncertainties. The numerical results show that under the ideal conditions, a contact with 98% constant force can be identified, albeit sensitive to mating uncertainty. When the conditions are considered uncertain, and minimizing the effect of uncertainty is included in the optimization problem, a more robust design is found. Monte Carlo simulation is used to confirm the results.