A switched stiffness approach for structural vibration control: theory and real-time implementation

A simple semi-active structural vibration control based on switching the system equivalent stiffness between two distinct values is proposed. When the system is moving away from its equilibrium state, the stiffness of the system is set to the higher value, and when it returns to its equilibrium, it is set to the lower value. Termed here “switched stiffness”, this vibration control method leads to change in the stored potential energy, which results in reduced total energy of the system. The switched stiffness can be typically implemented using a bi-stiffness spring setting, with the resulting relay-type control logic based on the position and velocity feedback. Unavailability of velocity sensors makes it difficult to implement this simple control logic. Although, numerical differentiation of the position signal can be utilized to acquire the velocity, but intervention of noise and the resulting signal phase-lag due to the filters used may degrade the vibration suppression performance. Hence, a novel output feedback variable structure observer, robust in nature, is used to estimate the required velocity signal. A single degree of freedom setup is considered to experimentally implement the switched stiffness concept proposed here. Simulations and experimental results demonstrate the effectiveness of the vibration suppression method proposed here.