Linear Step Motor Based on Magnetic Force Control Using Composite of Magnetostrictive and Piezoelectric Materials

We assemble a composite of giant magnetostrictive material (Terfenol-D) and stack piezoelectric transducer (PZT) actuator, and use it in a linear step motor. Control of the magnetic force exploits the inverse magnetostrictive effect of the Terfenol, in which the composite and a magnetic circuit in combination controls the magnetic force on a movable yoke with the voltage of the PZTs via mechanical stress. The unique feature of this arrangement is zero power consumption needed to maintain a constant magnetic force; once the PZTs have been charged, no current flows in static operation due to the capacitive property. A composite having simple configuration, bonding both Terfenol and PZT to iron yokes, is verified to control the magnetic force over wide variations under appropriate prestress conditions. A linear step motor with four composites as a stator also demonstrates variation of the thrust force and the possibility of motion control. Microstep motion of the mover was achieved using sinusoidal voltage, and zero current was observed with stationary voltage. The principle should be advantageous in high-precision positioning