Abstract
An electromagnetic micromotor based upon a friction drive features relatively high torque at low speeds without reduction gears. In this paper, we have redesigned the motor structure to reduce the thickness below 3 mm and examined its basic characteristics. The motor has a single-phase, two-pole axial gap structure. The stator is a thin excitation coil with a ferrite core. The rotor consists of a NdFeB magnet, 5 mm in diameter and 1 mm in thickness, with three inclined elastic legs, and is magnetically fixed on the stator. When an alternating current is applied to the coil, the rotor oscillates axially according to the change in the attractive force and hops on the stator. Thus the axial oscillation of the rotor is converted into the rotary movement through the friction of the legs. We constructed the motors using a commercial NdFeB magnet and a surface-modified one. As a result, the torque of the motor using the surface-modified NdFeB magnet was much larger than that of the commercial motor. The maximum starting torque obtained here reached approximately 0.11 mNm, which is several times as large as those of commercial DC motors of this volume.
