Theoretical and Experimental Loss and Efficiency Studies of a Magnetic Lead Screw

This paper investigates mechanical and magnetic losses in a magnetic lead screw (MLS). The MLS converts a low-speed high-force linear motion of a translator into a high-speed low-torque rotational motion of a rotor through helically shaped magnets. Initial tests performed with a novel 17-kN demonstrator and a simplified motor model showed an efficiency of only 80% at low load; however, it was expected that the efficiency should be above 95%. For understanding and future optimization, a detailed study of the loss in the MLS is presented with the aim of identifying and segregating various loss components that was not accounted for in previous results. This is done through theoretical loss calculations and various experiments. It is concluded that the linear guide is the dominating loss component in the MLS demonstrator, whereas the losses in the axial thrust bearing is not as dominant as expected; furthermore, an efficiency above 94% was measured.