Active Bearing Force Reduction in Non-Commutated Linear Actuators

Planar linear magnetic actuators are used in a wide range of industrial applications. Permanent magnet movers in particular allow high axial thrust forces, which result in considerable destabilizing stiffness in the direction perpendicular to the direction of motion. These forces, which can reduce bearing lifetime significantly, must therefore be stabilized with linear bearings. This paper introduces an integrated active bearing-force compensation concept that minimizes the forces acting on the mechanical bearings. The potential and limits of bearing force compensation are analyzed based on a short-stroke linear actuator with an E-shaped stator. Further the extent to which bearing forces can be compensated for even with simple actuator layouts is described. Particularly in linear oscillating drives, such compensation can (i) significantly reduce wear and thus improve lifetime and (ii) reduce the size of mechanical bearings. Measurements of a prototype system confirm the simulated results.