Mar 11, 2008
Control scheme fixes resonance problem
Piezoelectric stack actuated nanopositioning systems are a popular choice for scanning applications, but their construction can sometimes introduce a low-frequency resonance peak that limits tracking bandwidth. To get round this, researchers have devised a control scheme that boosts the platform's bandwidth by more than 1 kHz and allows operation at much higher speeds.
"Ultimately, our goal is to perform atomic force microscopy at video frame rates so that we can study dynamic samples," Reza Moheimani of the University of Newcastle, Australia, told nanotechweb.org. "In the immediate future we'll be using our technique to rapidly generate accurate topographical maps up to 100 × 100 µm."
As Moheimani points out, there's no shortage of applications for their enhanced nanopositioning devices. "The robust tracking performance delivered by our feedback–feed-forward technique makes the stages suitable for nanolithography, wafer integrity testing and nanomachining," he added. "Other uses include ultra-high-precision laser cutting and pointing."
The team's algorithm involves damping an inversion-based feed-forward model of the system with a polynomial-based controller to reduce the sensitivity of the system to changes in resonance frequency.
"We've shown that closed-loop techniques, which combine damping and integral action can significantly increase tracking speeds while using feedback-based damping and inversion-based feed-forward can give extremely fast positioning speeds without sacrificing the positioning accuracy," said Moheimani. "Having worked with closed-loop nanopositioning strategies for some time, it was quite a surprise to note that the use of integral action alone, which significantly limits the achievable tracking speed, is still the prevalent practice in commercially available models."
The researchers presented their results in Nanotechnology.
About the author
James Tyrrell is editor of nanotechweb.org.