ResearchFields

Advanced Control of Nanopositioning Systems

The demand for flexure-based, piezoelectric stack-actuated nanopositioning stages in nano-precision applications, such as nanolithography, scanning probe microscopy and nanometrology is increasing due to their capability of providing high mechanical bandwidth, large motion range and low cross-coupling between the axes. In the field of cell biology, high bandwidth nanopositioning stages are required to monitor some biological processes that evolve at fast pace. To increase the bandwidth of nanopositioning stages, various approaches have been investigated particularly by improving the mechanical design and by implementing various control algorithms on the systems.

In this project, a fast XY nanopositioning stage is designed to have its first dominant mode at 2.5 kHz (see Fig. 1). Cross-coupling between the two axes is kept to -35 dB, low enough to utilize SISO control strategies for tracking. Finite-element-analysis (FEA) is used during the design process to analyze the mechanical resonance frequencies, travel range and cross-coupling between the X and Y axes of the stage. Non-linearities such as hysteresis are present in such stages. These effects, which exist due to the use of piezoelectric stacks for actuation, are minimized using charge actuation. The Integral Resonant Control (IRC) method is applied in conjunction with feedforward inversion technique to achieve high-speed and accurate scanning performances. The IRC scheme is a simple yet well-performing technique which adds substantial damping to resonant modes of the system without exciting the high frequency dynamics. Together with the feedforward technique, accurate high-speed scans up to 400 Hz were achieved.

Fig. 1
Left: Experimental setup of the XY nanopositioning stage. Capacitive sensors are used to measure the displacement of the stage.
Right: FEA simulations of the nanopositioning stage in the X axis. Simulated first resonant mode appears at 2.5 kHz.