A Novel Concept and Proof of Magnetostrictive Motor

Electric motors have commonly been used to generate rotational motion, but provide inadequate torque, demand excessive power and are bulky in general. These disadvantages motivated development of a new type of rotary motor. All magnetostrictive motors that have been reported in the literature have utilized two or more linear magnetostrictive actuators to generate rotational motion for either inchworm or resonant types. Thus, this study presents a novel proof-of-concept of a magnetostrictive motor using a single Terfenol-D rod. The operational concept is based on the Wiedemann effect, that is, the twisting of a Terfenol-D rod due to magnetostriction when longitudinal and circumferential magnetic fields are applied simultaneously. To prove the concept, several ways to twist the Terfenol-D rod are suggested and subjected to simulation. Among them, the way with the best simulated results is adopted. A prototype is made and subjected to the experiments. A sawtooth-like driving signal with an input current from 0.5 to 1 A is applied to the magnetostrictive motor for the experiments. From the first experiments, it is observed that the rotational speed of the ball becomes higher with a lighter ball. The maximum rotation speed reaches up to 60 rpm with the lightest ball. The torque at this speed is calculated as 6.6 N·m. From the second experiments, it is observed that the ratio between the toroidal and solenoid currents causes the change of rotational direction of the rotor.