M.Sc Thesis


M.Sc StudentRan Gabai
SubjectResonance Tracking Method - Application to a Squeeze-Film
Object Levitation Device
DepartmentDepartment of Mechanical Engineering
Supervisor Full Professors Bucher Izhak


Abstract

Nonlinear vibrating systems having time and state dependent dynamics pose a challenge in terms of identification and actuations. In this work an algorithm to track the optimal excitation frequency of a squeeze-film levitation device is presented. This nonlinear device uses large-amplitude and high-frequency vibrations that squeeze an air-layer periodically to create an average pressure capable of levitating flat objects. Successful operation of this non-contacting levitation device requires the injection of sufficiently large amplitude of vibration at a sufficiently high frequency. Due to power limitations; this device must be operated in a vicinity of a resonance frequency. A difficulty arises since the resonance frequency of the mentioned device depends upon the thermo-dynamical state of the fluid. Thermal heating and change of the humidity level in the squeeze film or changes in the external load, may shift the system's resonance frequencies during operation.

In this work, a resonance tracking method that is sufficiently simple to be performed in real-time, while being able to track the resonance frequency variations and modify the excitation frequency, was developed. The algorithm involves an on-line model estimation procedure making use of a frequency dither such that a sufficient amount of information can be extracted. The optimal momentary excitation frequency is deduced from a performances index based on the estimated model. The algorithm is analyzed statistically and its tracking capabilities are demonstrated via simulative and experimental results.