Radially Biased Axial Magnetic Bearings/Motors for Precision Rotary-Axial Spindles

Unlike traditional position holding thrust magnetic bearings, electromagnetic actuators can be advantageously used as both an axial bearing and an in-feed motor in precision machine tools that require only millimeter axial stroke. This paper presents the working principle, design, and analysis of radially biased electromagnetic actuators for precision rotary-axial spindle applications. The analysis results indicate that the radially biased actuator design can offer eight times higher load capacity and 16 times higher force-to-power ratio than conventional horseshoe-type thrust bearings. Experimental results from the constructed rotary-axial spindle prototype demonstrate 5000-N load capacity, 340-N/mu m dynamic stiffness, and 1.5-mm axial stroke with 10-nm motion resolution.