Piezoactive motor based on independent stator modules

A piezoactive motor having an actuating shaft and a stator which is equipped with one or more stator modules designed, by vibrating, to cause relative movement of a driven part over a large travel by means of driving means by friction, said stator modules, by deforming, in addition enabling fine positioning of the driven part, each stator module comprising at least:

• one pair of colinearly arranged piezoactive actuators electrically excited so as to deform and produce small longitudinal movements,
• a mechanical coupling element to which the movements of the two actuators are applied, said element being formed by a ring shaped as a shell and made of a deformable flexible material, surrounding each pair of actuators by fixing at two opposite points, wherein:
• each stator module is independent from the others, is free to vibrate, and is only fixed to other parts by flexible links performing decoupling in vibration,
• each stator module comprises in addition a central countermass playing the role of inertia, inserted without clearance inside the shell between the piezoactive actuators and the shell,
• first means of deformation, in translation, are active when said piezoactive actuators are deformed longitudinally in opposition and produce a tangential movement of peaks of the shell relatively to the countermass,
• second means of deformation in flexion are active when said piezoactive actuators are deformed longitudinally in the same way and produce a flexion of the shell resulting in a normal movement of the peaks, the countermass remaining immobile in the centre,
• the mass ratio between the countermass and the shell is chosen so that in vibration in translation, the longitudinal deformations of the internal actuators generate a movement of the shell, of non-negligible amplitude with respect to that of the countermass,
• a combination of said first and second means is obtained when said piezoactive actuators are deformed longitudinally at the same frequency with a mechanical phase difference different from 0.degree. or 180.degree., and produce a closed trajectory of the peaks usable to cause relative movement of the driven part by friction.