Six degree of freedom quasi-zero stiffness magnetic spring with active control: Theoretical analysis of passive versus active stability for vibration isolation

This paper presents a comparison of passive and active stability analyses of a six degree of freedom (DOF) quasi-zero stiffness magnetic levitation vibration isolation system. The passive rotational stability of the system is varied by changing lever arms, and its effects on the vibration isolation performance and control cost are investigated via static and dynamic simulations. The practicality of the design is also discussed by simulating off-centred load scenarios. It is shown that the vibration isolation bandwidth reduces with increasing passive stiffness when such (passively) stable DOFs are close to being uncontrolled, and that the passively unstable rotational DOF benefits from an optimal control action. In practice, the effect of increasing the passive stability on the isolation performance is insignificant as the controller would typically be designed with a relatively large stability margin to account for uncertainties, thus dominating the closed-loop response. In contrast, the control does benefit from the improved passive stability. The robustness of the designed control system to probable time delay, sensor measurement noise, and actuation error is simulated and verified. Additionally, the importance of taking cross-coupling into consideration when designing a stabilising control through a decentralised control scheme is highlighted. (c) 2021 Elsevier Ltd. All rights reserved.

Automated summary

This paper compares passive and active stability analyses of a six degree of freedom quasi-zero stiffness magnetic levitation vibration isolation system. The study shows that increasing passive stability has a minimal impact on isolation performance, but control benefits from improved passive stability. The designed control system demonstrates robustness to uncertainties with a large stability margin dominating the closed-loop response.