Force Ripple Attenuation of 6-DOF Direct Drive Permanent Magnet Planar Levitating Synchronous Motors

A novel direct drive 6-degree-of-freedom (DOF) planar levitating synchronous motor has been developed that is comprised of multiple 1-D magnet arrays attached to a moving stage and multiple stationary 1-D coils built as a printed circuit board (https://www.youtube.com/watch?v=-r4Tv7GbB8o). Together these make up a set of four 2-DOF Lorentz force motors that actuate the moving stage in 6-DOF over a large planar range. This motor topology allows scalability with minimal increase in controller and drive complexity as well as direct drive actuation of a single mover body without intervening bearing elements, making it ideal for a variety of industrial automation and manufacturing applications. For high performance applications that require rapid high-precision motion, a linear, position independent force characteristic is desired to minimize the controller effort and reduce the intrinsic force disturbances, which adversely affect positioning accuracy. In the presented planar levitating synchronous motor, the primary source of force disturbance is the interaction between higher order spatial harmonics of the magnetic field of the mover and the commutated excitation current in the stationary coils. This paper presents analysis and experiment results of a novel method of reducing force ripple associated with permanent magnet planar levitating synchronous motors through the design of appropriately split and spaced magnet arrays. This method internally cancels out specific force harmonics within each 2-DOF motor, without adding controller complexity or resorting to higher order magnet arrays. Experimental results demonstrate force ripple reduction from 1.1% without magnet array splitting to 0.12% with magnet array splitting.