Nanopositioning: Construction and Analysis of a Piezoelectric Tube Actuator

Abstract

Piezoelectric tubes are commonly used as scanning actuators in nano precision microscopes. They can achieve precision down to sub-nanometer scale, but their vibrational dynamics and nonlinear properties hamper their ability to achieve higher bandwidths. In order to deal with this, further research is needed. This thesis is a first look into the field of piezoelectric tube actuators, intended to lay the groundwork for further research on the subject at NTNU. It details the construction of a laboratory setup for actuation and nanometer displacement measurement of a piezoelectric tube. Needed specifications are found and a mechanical setup is designed. Basic theory on piezoelectricity is presented, along with the setup and equipment used for the thesis. Several experiments are designed and conducted in order to identify the linear dynamics and nonlinear properties of the piezoelectric tube. The results are discussed and related to current literature. This includes the linear frequency responses from applied voltage to displacement of the piezoelectric tube, noise levels and nonlinear properties such as displacement creep and hysteresis. Generally, the results are found to closely match what has been found in similar research, although there are some notable differences, such as a somewhat smaller low frequency gain and a much lower resonant peak frequency of the system. Several possible explanations for these disparities are discussed. Both a capacitive sensor and a piezoelectric strain voltage sensor are utilized for measuring displacement. It is found that the capacitive sensor has a higher noise level but is more accurate at lower frequencies than the strain voltage sensor. The two measurements are then combined into an improved estimate of the displacement of the piezoelectric tube.