Rotary-axial spindles for ultra-precision machining

By combining pressurized fluid journal bearings with a novel magnetic thrust bearing, a rotary-axial spindle design is presented to achieve both rotary motion for cutting and mm-range linear motion along the axial direction for feeding. The advantages of such rotary-axial spindles include stiffer structure loops, fewer components, higher accuracy and resolution, and less heat generation. Our first prototype has demonstrated 9000 rpm, 600 N axial load capacity, 100 N/mu m dynamic stiffness, 1 mm axial stroke, and 5 nm resolution. These are significant improvements over aerostatic spindles of comparable size. (C) 2009 CIRP.