Importance

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Abstract

A positioning table includes a pair of parallel rails defining an axis of motion. A movable assembly including a first linear motor assembly disposed for motion along one of the rails. An outboard linear motor assembly on the other rail is rigidly bridged to the first linear motor assembly for concerted motion therewith. The first linear motor assembly includes a plurality of permanent magnets defining a plane at a predetermined angle to the horizontal and an armature defining a plane at the same angle closely spaced from the permanent magnets. The permanent magnets may be disposed on the movable element of the linear motor assembly or on the first rail. The armature is disposed on the other of the movable element and the first rail. First and second bearings on the movable element of the linear motor assembly, which may be air bearings support loads in the vertical and horizontal directions. The predetermined angle establishes the direction of a magnetic attractive vector between the permanent magnets and the armature. The predetermined angle is adjusted to proportion the total load of the static and dynamic load and the magnetic attractive force to a desired value. The outboard linear motor assembly on the second rail includes a plurality of permanent magnets and a second armature. The outboard linear motor assembly and the second rail may include provision for magnetic attraction at the same predetermined angle as that employed in the first linear motor assembly.

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