Multi-layer electromagnetic spring with tunable negative stiffness for semi-active vibration isolation

•Improving low-frequency vibration isolation performance by breaking the lower limit of tunable stiffness.•Design procedure for configuring MES to realize negative stiffness on a larger area and with a wider tunable range.•Modeling and testing of tunable HSLDS isolator to verify the online tunability.•Accuracy and resolution improvement of lidar modeling owing to vibration attenuation. Semi-active systems have demonstrated excellent performance in vibration isolation, However, the tunable range of conventional variable stiffness elements is limited by the mount stiffness required to support a load. To improve the performance of low-frequency vibration isolation, a novel compact and contactless multi-layer electromagnetic spring (MES) with tunable negative stiffness is proposed in this paper. The negative stiffness is generated by the electromagnetic force between the coils and the magnets and can be tuned online by controlling the current. Based on a stiffness analysis model, a design procedure for configuring the MES is presented to expand the region where the stiffness is negative and to increase its tunable range. As a result, with only one type of magnet and coil, various negative stiffness elements with different stiffness characteristics can be manufactured, thereby reducing costs. To verify the dynamic behavior of the MES, a tunable high-static-low-dynamic stiffness (HSLDS) vibration isolator based on the MES was modeled and evaluated by applying it to a lidar. The experimental results demonstrate the following: the MES tuned the isolator online and broadened the isolation frequency band such that the isolator attenuated the vibration of the lidar, and it significantly improved the lidar modeling performance.