Design and Analysis of a Variable Stiffness Mechanism

The design and analysis of a mechanism with variable stiffness is examined. The mechanism, which is a simple arrangement of two springs, a lever arm and a pivot bar, has an effective stiffness that is a rational function of the horizontal position d of the pivot. The external pure force acting on the system is constrained to always remain vertical. The effective stiffness is varied by changing d while keeping the point of application of the external load constant. The expression for the effective stiffness is derived. A reverse analysis is also carried out on the mechanism. Special design cases are considered. The dynamic equation of the system is derived and used to deduce the natural frequency of the mechanism from which some insights were gained on the dynamic behavior of the mechanism.