Dominant resonant mode damping of a piezoelectric tube nanopositioner using optimal sensorless shunts

Piezoelectric tube scanners are used in most commercial scanning probe microscopes, to provide precise motion to the scanning tip. Due to their mechanical construction, they have a relatively low-frequency first resonant mode. This mode gets excited due to environmental noise and introduces errors in the scan obtained. In precision scanning applications, this limits the upper bound of a triangular scan rate to around 1/100th the first mechanical resonance frequency. Feedback control techniques and shunt damping methods have shown promising results in damping this resonant mode and improving scan performance. Most of these techniques need a sensor, which in turn adds complexity to the overall system. With this motivation, passive sensorless shunt damping has been investigated and documented. In this work, we design active sensorless shunts, optimized using H₂ and Hinfin techniques. These shunts damp the modal amplitude of the first resonant peak by almost 24 dB. A triangle raster pattern used to test the scan accuracy shows significant improvement due to the damping achieved by these active shunts.