A nut-type ultrasonic motor and its application in the focus system

This article reports a screw-driven polyhedron linear ultrasonic motor （USM） of nut-type. It is comprised of a stator, which is a threaded metal nut bonded with piezoelectric plates on its external surface, and a rotor with external threads, which engage with the internal threads of the stator. A traveling wave in the plane is stimulated on the stator when harmonic electric signals are applied to the piezoelectric plates. The traveling wave drives the rotor to rotate, and the threads transform the rotation into a linear motion. The lens can be fixed in the rotor and realize the integrated design of the auto focus system. This structure can omit retarder and directly drive to obtain a high accuracy of positioning, and it is shockproof. A mini AF cellular phone module （8.5 mm×8.5 mm×5.9 mm） driven by this motor was made and an image resolution of 3-5 MP was obtained in the module prototypes of the cellular phone.