Dual-stage nanopositioner augmented with feedforward control

Abstract

A piezoelectric walking stage is retrofitted with a secondary stage for precisely tracking ramp position references. Fine motion control of the secondary stage shuttle is achieved using a voice coil actuator to correct for small, periodic deviations in position produced by the walking motion of the piezoelectric drive modules. The shuttle position tracking error is more than an order of magnitude smaller than the walking stage error for velocities less than 1.0 mm/s, however, the shuttle error remains dominated by harmonics of the walking stage stepping frequency. A feedforward controller using a modulated-demodulated implementation is designed to augment the high-bandwidth (300 Hz) shuttle controller to reject three dominant disturbance modes. When the system is tracking a 1.0 mm/s position ramp reference, the modulated-demodulated controller reduces the RMS shuttle position error from 44 to 21 nm. The reported system is under development to meet the scanning requirements of spaceborne Fourier Transform spectrometers.