Theses and dissertations

Study, fabrication characterization and Control
of a piezoelectric microgripper

“ Micromanipulation” is being increasingly important in a number of domains like microparts assembling (microgear, optical microlens, hybrid microcomponents,...) or manipulation of biological elements for medicine or biotechnology (micro-organismes, cells,...). The work presented in this thesis leads us to achieve a new two-fingered microgripper, each finger being able to move independently from the other in two orthogonal directions. The microgripper has therefore four degrees of freedom and is able to grip, hold, tilt and release submillimetric-sized objects. The functionning principle of one finger is based on a piezoelectric beam with local electrodes, called ``duo-bimorph'', for which a static modelling has been established. Such a microgripper presents a stroke of open/close motion and up/down motion of, respectively, 320 µm and 400 µm for ±100 V as well as blocking forces of 55 mN in gripping (open/close) and 10 mN in insertion (up/down) for 100 V. This thesis reports several expérimentations like the potential assembling of a watch microgear, the manipulation of cubic objects (300 µm square) under a binocular and the manipulation of quasi-spherical objects (200 µm in diameter) under a scanning electron microscope. In order to control this kind of microgripper, and more generally piezoelectric actuators, a new control method is proposed, thus allowing a fine positioning in open loop of the actuator displacement. It is based on the juxtaposition of a constant charge control and a constant voltage control. The hysteresis is thus reduced to a factor of ten.

Keywords: micromanipulation, microgripper, piezoelectric, bimorph, control, hysteresis.

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