Vibration and Tracking Control of a Flexure-Guided Nanopositioner Using a Piezoelectric Strain Sensor

This paper presents a novel sensing technique which uses a piezoelectric strain sensor for damping and accurate tracking of a nanopositioning stage. Piezoelectric elements have been used effectively as sensors for vibration control of smart structures. However, complications arise when one uses a piezoelectric strain sensor in a feedback loop for tracking. This is due to the high-pass characteristic of the piezoelectric strain voltage at low frequencies which tends to destabilize a closedloop tracking system. Here, we overcome this problem by using a low-frequency bypass technique which replaces the low frequency signal with an estimate based on the open-loop system. Once the high-pass characteristic is accounted for, an analog Integral Resonant Control (IRC) and an integral tracking controller were implemented. The resultant tracking bandwidth of the closedloop system was measured to be 1.86 kHz. To evaluate the closedloop tracking performance of the nanopositioning stage, it was forced to track triangular waveforms at 40 Hz and 78 Hz. The closed-loop system shows significant improvement where the nonlinearity of the system is effectively reduced.