טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentZelikov Eido
SubjectModel of contact and wear between high speed moving parts of
piezo-drives
DepartmentDepartment of Mechanical Engineering
Supervisor Dr. Yuri Kligerman
Full Thesis textFull thesis text - English Version


Abstract


Piezoelectric motors are used as a generator of motion of objects in micro- and nanotechnology. The system is based on a ceramic edge coming into contact with a ceramic stage attached to an aluminum table by a double-sided (DS) tape. The cyclic displacement of the edge causes normal and tangential loading and lateral movement of the stage and table.

One of the problems in such systems is the wear at the edge-stage interface, which is a direct result of the fretting motion between the edge and stage. The wear might cause numerous problems like contamination and shorten the life-time of the system.

A numerical model is created to evaluate the wear at the edge-stage interface and to suggest ways to decrease it. Wear is affected by multiple factors like: temperature, geometry and materials. Some of these factors would be checked in order to ensure the reduction of this wear.

            Friction at the interface between the edge and stage was defined using Coulomb's friction law, typical for rough surfaces. 

The wear is evaluated using an energy criterion which correlates with the local dissipated energy due to friction (local frictional work). The local frictional work depends on both the shear stress at the interface and the relative displacement between the edge and stage. Despite the fact that it is difficult to measure these parameters experimentally, using a theoretical model, it is easy to do so. The first criterion is the maximum frictional work. Another wear criterion, which was checked, was the over-all work calculated by integrating the frictional work over the instantaneous contact width.  The advantage of the latter criterion is that it takes into consideration the distribution of the frictional work.

In order to decrease the wear, a parametric analysis was done. The viscous and elastic properties of the DS tape and the elastic modulus of the edge were examined to evaluate their influence on the wear. It was found that small elastic modulus and small viscous parameter reduce the frictional work tremendously. It was also found that when the edge is stiffer, the frictional work increases.

The viscous and elastic properties affect the interaction between the edge and stage causing different relative displacement between them and different shear stress at contact. Therefore, an increase or decrease in these properties would also cause changes in the frictional dissipated energy and wear.

Preliminary experimental results concerning the effect of the radius of curvature of the edge are also presented. A fretting experiment was done in our tribology lab. The results of the experimental study were compared with the results obtained from the numerical model. A good agreement was found between the experimental and theoretical models

            Overall, the numerical model described in this work provides an adequate tool of analysis for the proposed system, predicting its behavior. Evaluating the work dissipated at interface as a result of the friction is our main interest.