in an actuator device for hard disks a suspension element carries a slider that is subject to undesired vibrations which give rise to rotations of the slider with respect to a nominal position . an electrostatically controlled position - control structure is arranged between the suspension and the slider and is controlled in an active way so as to generate torsions of the platform that counter the undesired rotations . the position - control structure comprises a platform of conductive material and control electrodes arranged underneath the platform . the platform is connected to a load - bearing structure by spring elements that enable movements of roll and pitch . four control electrodes are arranged according to the quadrants of a square and can be selectively biased for generating electrical forces acting on the platform .