A three-degree-of-freedom short-stroke lorentz-force-driven planar motor using a halbach permanent-magnet array with unequal thickness

This paper presents a three-degree-of-freedom (3-DOF) Lorentz-force-driven planar motor for a nanopositioning system. The short-stroke planar motor consists of three Lorentz-force-driven units equally spaced by 120 $^{\circ} $ around the mass center. To increase the force and decrease the force variation with horizontal displacement, a Halbach permanent-magnet array with unequal thickness is used. First, the basic structure and 3-DOF kinematics of the planar motor are introduced. Second, the magnetic field and force expressions are derived based on the charge model and the image method. Third, four typical Lorentz-force-driven units are compared in the aspect of magnetic field, force, force density, and force variation within the effective stroke. Fourth, a suitable cooling structure is designed for the planar motor. Finally, a prototype of the planar motor is constructed and tested. The measured values are in good agreement with results from analysis and finite element model.