High-bandwidth nanopositioning via active control of system resonance

摘要

Typically,the achievable positioning bandwidth for piezo-actuated nanopositioners is severely limited by the first,lightly-damped resonance.To overcome this issue,a variety of open-and closed-loop control techniques that commonly combine damping and tracking actions,have been reported in literature.However,in almost all these cases,the achievable closed-loop bandwidth is still limited by the original open-loop resonant frequency of the respective positioning axis.Shifting this resonance to a higher frequency would undoubtedly result in a wider bandwidth.However,such a shift typically entails a major mechanical redesign of the nanopositioner.The integral resonant control(IRC)has been reported earlier to demonstrate the significant performance enhancement,robustness to parameter uncertainty,gua-ranteed stability and design flexibility it affords.To further exploit the IRC scheme’s capabilities,this paper presents a method of actively shifting the resonant frequency of a nanopositioner’s axis,thereby delivering a wider closed-loop positioning bandwidth when controlled with the IRC scheme.The IRC damping control is augmented with a standard integral tracking controller to improve positioning accuracy.And both damping and tracking control parameters are analytically optimized to result in a Butterworth Filter mimicking pole-placement—maximally flat passband response.Experiments are conducted on a nanopositioner’s axis with an open-loop resonance at 508 Hz.It is shown that by employing the active resonance shifting,the closed-loop positioning bandwidth is increased from 73 to 576 Hz.Consequently,the root-mean-square tracking errors for a 100 Hz triangular trajectory are reduced by 93%.