Deflection Characteristics of Split Electrode Inplane Bending Piezoelectric Actuators With Varying Width

Abstract

The cantilever split-morph, a new type of piezoelectric actuator, have been designed for dual-stage head positioning servo system of high density hard disk drives. In this actuator configuration, a PZT ceramic plate, with one end mechanically clamped and the other free, was poled along its thickness and divided into two symmetric parts along length by splitting electrodes. Driving voltages are preferably so arranged that they make one of the two parts expand by the “31”action while the other part, i.e., the symmetric part, contracts. This will result in a bending motion of the actuator along the direction of its width. The driving voltage-tip displacement characteristics of the actuator have been investigated by theoretical analysis, finite element modeling and experiment. Theoretical analysis indicated that the electric field induced stress is much smaller than stretch strength of piezoelectric ceramic. Tip displacement measured by Michelson interferometer is a little larger than the calculated result. This is mainly due to the increase of piezoelectric coefficient d31 at high driving field. Tip displacement of 1 to 2μm can be achieved at 20 to 50V driving voltage for the split-morph whose size is similar to that of the existing suspension. As to 25 kTPI (track per inch) high track density hard disk drives, this actuating stroke can cover at least one track width and meet the primary requirements of dual-stage head positioning servo system for displacement of the secondary actuator.