Reducing pitch error of a linear motion system actuated by a permanent magnet open face linear motor

When using iron-core open face linear motors, the magnetic attraction between the forcer and the magnet track is about 5–7 times higher than the maximum motor force. The magnetic attraction can be used in a motor-preloaded-bearing concept, e.g. to preload aerostatic or hydrostatic bearings. Based on this concept a high-precision grinding tool machine that moves on aerostatic bearings has been successfully introduced. However, the attraction force also creates an inherent pitch moment and resulting position dependent, periodic pitch error motion due to finite bearing stiffness. A method to model and reduce the resulting pitch error is presented. In experiments the overall pitch was reduced by a factor of 3.