Closed-loop identification of an unstable electromagnetic isolator under floor vibration

This paper studies closed-loop identification of the Permanent Magnetic (PM) force produced by an unstable contactless Electro-Magnetic Isolator (EMI) designed for passive gravity compensation of heavy payload. According to the criterions of high force density and minimized stiffness, the EMI magnetic topology parameters can be optimized based on theoretically calculated PM force. To validate this design method, the PM force has to be measured accurately. One solution is closed-loop identification of the unstable suspension system formed by a rigid payload suspended by a single EMI. The two objects that can be directly identified are the passive force (the sum of the PM force and gravity force) and the payload mass. The PM force can be calculated by the passive force minus the gravity force. To guarantee the closed-loop stability and floor vibration suppression with unknown plant parameters, the generalized frequency-shaped sliding surface control approach can be applied. An iterative method is proposed to directly estimate the payload mass. To evaluate the proposed methods, the identification of the passive force and the payload mass is simulated using a 1-DOF model taken from a candidate design of the EMI. The results show that the estimation errors for both objects are reasonably small. The mass identification has improved performance by iterative estimations.