High speed nano-scale positioning using a piezoelectric tube actuator with active shunt control

Piezoelectric tube scanners are the actuators of choice in scanning probe microscopy. These nanopositioners exhibit a dominant first resonant mode that is excited due to harmonics of the input scan signal. This introduces errors in the scan obtained. The presence of this resonant mode limits the upper bound of a triangular scan rate to around 1/100th of the first mechanical resonance frequency. Passive and active shunts have shown to damp this resonant mode substantially and improve scan performance. Sensorless active shunts optimised using H-2 and H-infinity techniques, is designed. These shunts reduce the amplitude of the first resonant peak of a prototype tube nanopositioner by 24 dB. A triangle wave input is used to test the improvement in scan performance due to the damping achieved by these active shunts. Analysis shows that damping the resonant mode in such fashion reduces the scan error by five times.