Date of Award

Summer 1998

Document Type

Dissertation

Degree Name

Doctor of Engineering (DEng)

Department

Mechanical Engineering

First Advisor

William Jordan

Abstract

The most common means of electrically activated actuation is the electromagnetic motor. All electromagnetic motors have a low output to weight ratio and low energy efficiency. The motor's weight is due to the coils and magnets used to generate propulsion. The energy loss is mainly the result of Joule heating that is inherent with any current driven device. An electrostatic motor offers the potential of significantly less weight and higher energy efficiency. This lower weight characteristic is due to the epoxide material used to construct the major components of its propulsion unit. Greater efficiency results from the reduced Joule heating since it is propelled by voltage induced charging which requires only small current pulses.

Electrostatic motors have not been successful in the past because the fabrication methods for producing very small electrodes in light-weight materials were not available. As the methods for construction of the ultra-fine electrodes necessary for sufficient torque became common, another problem arose due to the presumption of arbitrary values for the design parameters. Since methods for manufacturing microstructures are now commercially available, the remaining challenge is to systematically vary the fabrication parameters to discover the best possible design of an electrostatic motor that could possibly deliver the same torque as an electromagnetic motor but has less weight and uses less energy to perform the same amount of work.

Using the COULOMB program for the numerical analysis of the electrostatically induced torque between the motor's electrodes, a design optimization process has been established. By following this method for a fixed set of fabrication parameters, the electrode pattern that produces the highest torque or greatest work per revolution can be found. An example is given to show that when the design parameters are chosen randomly, the resulting electrode pattern generates torque that is less than half the optimum value. By evaluating the combined effect of stacking the flat stator-rotor pairs into the housing of an electromagnetic motor, the total predicted output torque from an optimized electrostatic motor is shown to match that delivered by the electromagnetic motor selected for comparison. Thus, an optimized rotary electrostatically driven actuator has the potential to replace the electromagnetic motor as the preferred means of electrically induced motion.

Download

Share

COinS