Nonlinear compensator design for active sliders to suppress head-disk spacing modulation in hard disk drives

As the slider´s flying height (FH) continues to reduce in hard disk drives, the flying height modulation (FHM) due to disk morphology and interface instability caused by highly nonlinear attractive forces becomes significant. Based on the concept that the FH of a portion of the slider that carries the read/write element can be adjusted by a piezoelectric actuator located between the slider and suspension and that the FH can be measured by the use of the magnetic readback signal, a new 3-DOF analytic model and an observer-based nonlinear compensator are proposed to achieve ultralow FH with minimum modulation under short-range attractive forces. Numerical simulations show that the FHM due to disk waviness is effectively controlled and reduced.