Two-sensor-based H ∞ control for nanopositioning in probe storage

The ultra-high storage density in probe-storage devices makes positioning a significant challenge. The probes have to be positioned over the storage medium with nanoscale accuracy. A feedback-control scheme based on a high-precision global-positioning sensor can provide the required accuracy. However, drift and low frequency noise affect the performance over long periods of operation. A novel control architecture based on the H∞ control framework is presented which addresses this problem by using medium-derived positional information along with the global-positioning sensor. This controller has a multiple-input single-output (MISO) structure and uses the best measurement in different frequency regions. Experimental results on a probe-storage device prototype demonstrate the efficacy of this approach.