A wide-range variable stiffness mechanism for semi-active vibration systems

This paper presents the design and experiment of a variable stiffness mechanism (VSM) for semi-active vibration systems. Compared with vibration isolators or absorbers with constant stiffness elements, the use of a variable stiffness element can adapt to the variation in disturbance frequency or load. The idea of the proposed VSM is to adjust the symmetric rotation of two parallel connected springs. The output force-to-displacement curve can exhibit zero to very large stiffness depending on the rotation amount of the springs. Infinite stiffness is further achieved by using mechanical stoppers to constrain the displacements of the springs. To reduce the VSM size and complexity, specifically designed planar springs are proposed to replace commercially available coil springs. Force and stiffness analyses are presented to design a VSM with the largest stiffness variation. The effects of various parameters on the stiffness variation are discussed. Finally, a prototype and its associated experiments are presented to demonstrate the vibration absorption performance against various disturbance frequencies.