Patrick Delobelle

Active damping of a micro-cantilever piezo-composite beam

Thick PZT films are of major interest in the actuation of mechanical structures. One of the promising fields deals with active damping. Since it is a dynamic application, hard-PZT type of screen-printed films are suited to this kind of use. Nevertheless, the drop in dielectric, ferroelectric and piezoelectric properties induced by the fabrication process is a serious constraint and it needs to be evaluated. The first section of this paper will present the mechanical system used for the experimental investigations. These investigations look to quantify the electromechanical properties of the films once the deposition process is achieved. The experimental observations highlighting the efficiency of hard-PZT thick films in active damping despite the drop in the electromechanical properties will then be considered. The control strategy used in the experiments can be called pseudo-direct-velocity feedback. Then the constitutive relations of the composites will be needed to derive the roots locus analysis by means of finite element modelling on one hand and through the roots of the partial derivative equations on the other hand. The unconditional stability of the uncollocated system will be demonstrated and its typical asymptotic behavior when the gain tends towards infinity will be explained.

Active damping with piezoelectric MEMS devices

Thick PZT films are of major interest in the actuation of mechanical structures. One of the promising fields deals with active damping. Piezoelectric actuators have proved to be effective control devices for active stabilization of structural vibrations and are now used in a wide range of engineering applications. Piezo materials can be integrated in various structural components as distributed sensors or actuators. In this context, Micro-Electro-Mechanical Systems appear very attractive in improving the mechanical efficiency of structural active control. These systems can be distributed on a structure and are very powerful since it induces a very high level of stress density. They can effectively present a good opportunity in a large class of problem. The studied micro controlling system is a micro beam totally covered by a piezoelectric, PZT, film. This sample system can be considered as a suspension element being able to support very light and sensitive systems like frequency generator or MEMS sensors. We first describe modeling and the experimental updating methods used to characterize piezoelectric behavior. Secondly, we show the observations highlighting the efficiency of hard-PZT thick films in active damping of sensitive devices by using pseudo direct velocity feedback.