Simultaneous damping and tracking control of a normal-stressed electromagnetic actuated nano-positioning stage

Abstract

Normal-stressed electromagnetic actuated (NSEA) nano-positioning stage has become more and more promising in various fields due to its high actuation force density and large motion range. However, the intrinsic hysteresis of the actuator and the lightly-damped resonance of the mechanism hinder the stage for the high-accuracy and high-speed applications. To handle these two problems, the damping and tracking controllers are commonly adopted, as the inner and outer loops, respectively, to design a dual-loop controller. However, the existing sequential design approach limits the achievable performance of the controller. This paper proposes a simultaneous optimization approach for a dual-loop controller with the inner loop positive acceleration, velocity, and position feedback (PAVPF) damping controller and the outer loop proportional-integral (PI) tracking controller. The objective is to obtain a flat closed-loop frequency response with a large control bandwidth, and the parameters of the inner and outer loops are tuned simultaneously. Both the damping ratio and stiffness of the vibration mode are improved, and the obtained ± 3 dB control bandwidth exceeds the first resonant frequency of the open-loop system. Experiments are carried out on a custom designed NSEA nano-positioning stage. The tested bandwidth of the simultaneously optimized system agrees well with the theoretical one, and is 188.9% higher than that of the sequentially designed system. Step response tests, triangular wave tracking tests, and hysteresis reduction tests also demonstrate the effectiveness and advancement of the proposed approach.