Semi-active control of the electromagnetic negative stiffness mechanism in a double-layer vibration isolator

Semi-active vibration isolators have attracted considerable attention due to their high reliability and excellent vibration isolation performance. Most of the existing adjustable stiffness components can only be adjusted in the positive stiffness range. However, the bearing stability requires that the stiffness should not be too low, which limits the vibration isolation frequency band. To extend the isolation frequency band to low frequencies, an electromagnetic negative stiffness mechanism (ENSM) which can be continuously adjusted in the positive and negative stiffness range is proposed, and a semi-active control algorithm is proposed for it. The configuration of the coils and magnets in the ENSM is optimized, and the stiffness adjustable range and energy efficiency are improved. A double-layer vibration isolator with an ENSM in parallel is designed, and its nonlinear dynamic characteristics are analyzed. The suboptimal control method based on linear quadratic regulator (LQR) is introduced into the nonlinear vibration isolator by feedback linearization method. The input current of the ENSM is controlled according to the relative displacement and electromagnetic force model to generate the required control force. The simulation results show that extending the adjustable stiffness to the negative stiffness range can reduce the stiffness adjustment range required for vibration isolation. The vibration test results show that the ENSM can extend the isolation frequency band while maintaining the bearing stability, and the semi-active control of the ENSM can suppress resonance and further improve the vibration isolation performance.