Kiyoshi Itao

Damping characteristics of beam-shaped micro-oscillators

Abstract The damping characteristics of beam-shaped microactuators that oscillate in the transverse direction are analytically evaluated to establish a design method that minimizes energy consumption and increases dynamic performance. The damping force due to airflow is calculated using the Navier-Stokes equation, the accuracy of which is verified by comparing the calculated damping with experimental results. The contributions to the damping due to squeeze force, internal friction, and support loss are calculated by using the Reynolds equation, structural damping theory, and a two-dimensional theory of elasticity, respectively. The final formulae, obtained in simple and closed forms for easy use in the actual design process, are then used to evaluate the relationships between the beam size and the damping ratio of silicon cantilevers, Permalloy cantilevers, and Permalloy spiral springs. Finally, the step response of a Permalloy cantilever is calculated and the relationship between beam size and settling time is determined.

Evaluation of energy dissipation mechanisms in vibrational microactuators

The energy dissipation characteristics of beam-shaped microactuators are analytically evaluated here as a first step in establishing a design method that minimizes their energy consumption. The energy dissipation by airflow force is calculated by using the Navier-Stokes equation and its accuracy is verified by comparing it with experimental results. Additionally, the dissipations due to squeeze force, internal friction, and support loss are respectively calculated by using a Reynolds equation, structural damping theory, and a two-dimensional theory of elasticity. The final formulas, obtained in simple and closed forms so that they can easily be used in the actual design process, are then used to evaluate the relationships between beam size and dissipation ratio for silicon cantilevers, Permalloy cantilevers, and Permalloy spiral springs. Finally,the indicial responses of a Permalloy cantilever is calculated and the relationship between beam size and settling time is clarified.

Design of Ultrasonic Motor for Driving Spherical Surface

This paper presents a new ultrasonic motor, which uses two sets of actuator in order to control the direction of the thrust within the tangential plane at the contact point of the actuator and the rotor. The drive unit consists of four piezoelectric stack actuators arranged in a pyramid shape. Circular vibration at the apex generates a thrust when a rotor is pressed against the apex. The direction of the thrust within the tangent plane of the rotor is controlled by the amplitude and phase differences among the four actuators. This enables a spherical drive if a spherical surfaced rotor is used. Experiments have verified that the direction of the thrust was controllable by the ratio between the two drive signals, as predicted by the theoretical analysis.