Design and Fabrication of an Electric-Field Induction Motor

Abstract

This thesis explores a meso-scale micro-actuator of rotational motion based on electric induction. This electric induction motor (EIM) has a cylindrical geometry with a radial air gap between the stator and the rotor. A significant novelty is that the motor does not contain metal, but is rather manufactured using only 3D printed plastic and injected conducting epoxy. It therefore has the potential to have very little mass, and hence exhibit high torque and power to mass ratios. A traveling potential wave applied to electrodes on the cylindrical stator surface induces and attracts charges on the rotor surface to provide torque. An electric model is developed to predict the average torque of the motor when driven with an ideal sinusoidal potential wave. Using this model, a motor is designed with volume and power comparable to a mesoscale dielectric elastomer actuator, a state-of-the-art technology for micro-actuators. Harmonic decomposition is applied to a realistic drive potential to reveal major harmonics that contribute to the potential wave. The ideal model is then applied to each harmonic, yielding a more realistic estimate of the motor performance given the design parameters. A prototype motor and high-voltage variable-frequency drive circuit are fabricated to confirm the theory. With limited manufacturing capabilities, the motor has an uncertain air-gap separation and rotor surface conductivity, which must be experimentally estimated. Due to manufacturing difficulties with the bearing system and the rotor surface conductivity, the prototype was not functional. The thesis speculates as to the failure mechanism, and solidifies the understanding of the challenges surrounding the cylindrical EIM. Two critical areas of future research are identified: bearing development suitable for very small air gaps, and rotor surface conductor management. If these challenges can be met, then the analysis of this thesis indicates that torque densities approaching 1 mNm/ml are possible.