Modélisation thermomécanique et commande d'actionneurs en alliages à mémoire de forme pour la microrobotique.

摘要

A lot of application require the use of small size robots in order to perform tasks in enclosed or inacessible environments for human, such as in pipe inspection or manipulation of objects of small dimensions. The transition from robotics to microrobotics by reducing the size of the existing components has shown its limits : for instance, conventional technologic processes which do not allow a sufficient level of miniaturisation or conventional actuation principles for which mechanical work becomes too weak. These limits require to develop technologies and actuation principles able to generate strokes ans to transmit efforts compatible with the considered scales. In order to fulfil to the need of microactuation, materials such as piezoelectric, magnetostrictive or some shape memory alloys and polymers describe as "active materials", seem to be full of promise because of their characteristics compatible with required forces and movements and miniaturisation possibilities. As for us, we are particularly interested in shpe memory alloys noted SMA, which under certain thermomechanical conditions can transform supplied thermal energy to mechanical work. In this way, they can return strains of about 6 at 8 %, and generate quite important efforts when they are heated. <br />So in order to design, to size and to control such microactuators at the top of their performances, it is at first necessary to collect some knowledge and data about these materials. This constitutes the aim of our research, which is divided in two main parts. The first one is to obtain a predictive dynamic model of the thermomechanical behaviour of SMA. This model is based on the approach developed by Leclercq and Lexcellent. In order to validate this model, appropriate thermomechanical tests habe been made with a view to identify the "material parameters" and simulation have been conducted, for which results are compared with the ones of corresponding tests. The second part of the research is dedicated to the study of SMA actuators. At first, we have taken an interest in characteristics of these microactuators in term of available stroke, energy density, efficiency and bandwidth. In a second time, to treat the problems of motion and effort control of SMA microactuators, we exploit non linear control techniques for dynamic systems, linear with respect to control input, using in particular the Lie derivatives. From a non linear state representation of the system, it is possible with an algebric transformation operating on the states to convert the dynamic behaviour of a non linear system to a partially or totally linear dynamic behaviour and so to control the performances of the system in closed loop.