טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentShadmi Idan
SubjectDesign, Experiments and Stiffness Identification of an
Acoustically Levitated Bearing System and
a Development of a Nonlinear Amplifier
Concept
DepartmentDepartment of Mechanical Engineering
Supervisor Professor Izhak Bucher
Full Thesis textFull thesis text - English Version


Abstract

In this thesis an active acoustic bearing, which employs near-field acoustic levitation, capable of holding a sliding part ‘in the air’ with no mechanical contact is presented. By creating sufficiently large high frequency vibrations, a thin layer of air generates an elevated pressure, capable of supporting a levitated structure is formed (Minikes et al 2003).

This application enables an axial translation for light weighted objects (up to several Kg and potentially more) parallel to the air-gap which find use in clean room applications. This device virtually eliminates sliding friction and contamination at the expanse of being less stiff than a ball-bearing. This stiffness of the air-layer was experimentally estimated on a manufactured model with good success.

Furthermore, a high precision of movement can be obtained with no friction error. Other non-contact bearings, such as an air or magnet bearings, contaminate the room by inserting an outer air or magnetic force on the sliding object.

First, the acoustic levitation phenomena will be elaborated. Later, a proof of concept for the above system is presented. which consist of design, manufacturing and an experimental identification of key parameters.

In order to enhance the ability to produce acoustic levitation, an improved mechanical amplifier, utilizing parametrically excited electromechanical device, is put forward in this thesis. The new amplifier is presented as a dual actuated beam driven by both a bending moment and an axial force, operating at different frequencies - primary and 2:1 parametric excitations of the beam first mode shape respectively. These actuations are phase shifted with respect to each other and this shift is studied in this research. The simulated model presents an amplification of a small displacement at its ends to a larger one at its center.

The beam 's lateral motion PDE is discretized by the Galerkin approach and the solution is separated into temporal and spatial solutions. A frequency response solution is achieved by assessing the spatial solution by the first mode eigen-function and multiple time-scales on the temporal solution. The frequency response is validated by a numerical solution of the discretized PDE. Validation attempt of the analytic modal via Ansys finite elements software model will be presented.

The vibrating beam offers a large amplifying ratio due to its geometry and excitations. This ratio is bounded by the beam nonlinear stiffness, which grows as the beam bends. This latter variation in time in the system parameter makes the parametric excitation possible.
The amplifier amplifying ratio and applied power is investigated in the finite elements model.

In conclusion, this research is a gateway to an efficient and is suitable for specific applications air bearing. The research is introducing a novel concept of a mechanical amplifier to improve the performance of the bearing.