Electromagnetic nanopositioner

Abstract

This thesis presents the analysis, design, and control of a new class of magnetic nanopositioner. Applications for this class of positioner include sample positioning for scanning microscopy and interferometry, nanofabrication, vibration cancellation, biological cell tracking/positioning, and beam focusing/steering. The nanometer-resolution positioning required in these applications is often provided using piezoelectric ceramic actuators. The drawbacks to using piezoelectric actuators include high hysteretic heating, lightly damped structural resonances, the need for preload on the actuator stack, as well as the requirement for a high voltage amplifier. This thesis demonstrates an electromagnetically driven nanopositioner that is suspended on rubber bearings as a promising, low cost alternative to the piezoelectric nanopositioners. Several key features of the electromagnetic nanopositioner are the flux-steering actuator that applies a force linear in both coil current and displacement, replacement of the conventional metal flexures with rubber bearings, as well as power and sense electronics that can be easily integrated into a compact package. A prototype of this class of nanopositioner with 100,pm of travel and a maximum force output of 460 N was built and tested.

(cont.) A closed-loop bandwidth of 580 Hz was obtained using capacitance distance sensor feedback. The feasibility and procedure for casting rubber bearings was investigated. Several room-temperature vulcanizing (RTV) rubbers were considered for low volume, in-lab production of test specimens. A compression specimen was cast from a two-part RTV silicone rubber that was found to be suitable. A compression fixture that was previously used to test bonded rubber pads was modified to accept the cast rubber bearings. The cast rubber bearing was found to have the predicted DC stiffness and the stiffness increased with frequency as expected. Casting of rubber bearings was demonstrated as a feasible method for putting rubber bearings into devices such as nanopositioners.