US Patent 7525643 Lithographic apparatus, and mechanism

A lithographic apparatus has a mechanism with a movable element, at least partially made from a magnetizable material. The movable element is movable between a first position and a second position. A pretensioner exerts a pretension force on the movable element urging it to the first position. A permanent magnet produces a magnetic field exerting a force on the movable element urging it to the second position. A coil produces, when energized in a first direction, a magnetic field exerting a force on the movable element urging it to the second position. The combined magnetic field of the magnet and the coil exerts a force on the movable element which is higher than the pretension force.