Patent ID: 8896811

Claim:
A method for positioning a first stage with respect to a reference object, the first stage moveable relative to a second stage, the second stage moveable with respect to a frame in a moving direction using a main actuator arranged between the second stage and the frame for applying a force to the second stage with respect to the frame in the moving direction, the first stage being moveable in the moving direction between a first and a second position relative to the second stage, the method comprising: positioning the first stage with respect to the reference object at or near a desired position using a passive force system that is activated by positioning the second stage relative to the frame with the main actuator, wherein the passive force system is arranged between the first stage and the second stage, the passive force system comprising at least two magnet systems, each magnet system being configured to apply a force in the moving direction to the first stage with respect to the second stage in a non-contact manner, the forces resulting in a resultant force applied to the first stage in the moving direction by the passive force system, wherein a magnitude and/or a direction of the resultant force depends on the position of the first stage relative to the second stage, and wherein the first stage has a zero-force position between the first and second position in which the resultant force has a zero magnitude.