Control of multi-dimensional drives with variable pole pitch

The planar motor and the spherical motor presented in this paper possess three degrees of freedom in motion. For this type of motor, special drive components and new control algorithms have to be developed because the machine operates with a variable pole pitch. The implemented control uses nonlinear force characteristics to control force and torque. It is proven that position control can be very accurate, despite the fact that the calculated and measured force characteristics contain uncertainties and errors. Simulations and experiments show that the spherical motor offers a high force and torque generation capability combined with a very precise position control. A planar motor based on the same working principle was built first to test the components and control strategies.