Importance

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Abstract

A permanent magnet linear motor, optionally built into a bed of a machine tool, employs a combination of bearings and air load-relief pads to support static and dynamic loads. A static preload, exerted by magnetic attraction between permanent magnets and magnetic iron in the armature of the linear motor, provides a static preload to the combination of bearings and air load-relief pads. Air pressure to the air load-relief pad is controlled to a value less than that capable of supporting the entire load applied thereto whereby a reduced, but non-zero, load is carried by the bearings. A dynamic system employs measurement and/or prediction of the bearing loads to modulate air pressures applied to related air load-relief pads, whereby the components of total load supported by the bearings is maintained substantially constant. In one embodiment of the invention, an air bearing is formed between facing surfaces of the motor armature and its plurality of permanent magnets, without using auxiliary contact bearings. In a further embodiment, one or both of the movable and stationary elements of the linear motor are flat plates.

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First Claim