Quasistatic piezomotor using resonant structures dedicated to electroactive lubrication effect

In the field of piezoelectric motors, which are characterized by a double energy conversion, ensured by the frictional forces, piezoelectric structures can be classified according to different families, resonant, quasistatic, inertial, for the most well known. This article deals specifically with quasistatic actuators, which operate with elementary movements generated by multilayer piezo-ceramics. Due to an air gap of about 10 to 20 μm, thermal expansion of the different parts of the motor are able to affect the efficiency of the piezomotor. The idea developed in the context of this paper is to exploit the electroactive lubrication phenomenon to limit the effect of friction in the return phase of reciprocation of the actuator. Then, the rotor/stator contact is assumed by springs, and the necessary declutching function is realized by the introduction of mechanical vibrations. A first part of the article is dedicated to the theoretical conditions of the electroactive lubrication effect. The proposed model requires the consideration of different friction coefficients (static, dynamic, apparent), the normal and tangential stiffness of the mechanical contact in order to maximize the electroactive lubrication phenomenon to reduce the parasitic friction torque. In this context, the characteristics of the resonant piezoelectric actuator implemented for the declutching function, such as amplitudes and excitation frequencies, contact geometry have to be specified. A prototype has been realized in order to validate the operating principle of this structure and then characterized.