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Utilizing the large piezoelectric coefficients and high dielectric constants of ferroelectric thin films, it is possible to microfabricate ultrasonic motors on silicon substrates. This talk will describe our efforts in this area. By using ferroelectric thin films of lead zirconate titanate (PZT), a two-order of magnitude improvement over bulk ceramic materials is obtained in breakdown strength. This characteristic, in combination with high dielectric permittivities, leads to a three-order of magnitude improvement over electrostatic micromotors in terms of energy densities.
We have fabricated resonant structures on one micron thick silicon nitride membranes which are able to spin two-millimeter diameter rotors which are placed down on top. Stator-rotor interaction is achieved through frictional coupling and an inherent geardown creates motors which run at low speeds with high torques.
I will also discuss experiments with 8 mm diameter ultrasonic motors fabricated from bulk ceramic PZT and an analysis of the contact mechanics at the rotor-stator interface where the overall efficiency of the motor is critically determined. Models of line contact, Hertzian contact and linear spring contact for Coulomb and viscous friction have been derived and simulations will be presented which predict speed-torque curves, efficiencies and overall output power for various conditions of operating voltage and normal force.
Work in progress on a new laser-etching technique for piezoelectric ultrasonic micromotors offers promise for simplifying the fabrication steps and developing more practical motors. We plan to incorporate these actuators into small robots and create truly integrated intelligent machines. Presently, we are developing small palm-sized autonomous robots, using conventional electromagnetic motors, with onboard computers and 18 sensors which can crawl through tubes, pick up small objects and cooperate on tasks. Later, ultrasonic motors will be retrofit as they become available, enabling miniaturization. I will show videotapes of these machines in a robotic ant colony and as intestine crawlers for telepresence surgery.
Host: Michael Erdmann, me@cs, 8-7883; Appts: Cleah Schlueter, cleah@cs, 8-7884.