Patent ID: 7468589

Claim:
A lithographic apparatus, comprising: an illumination system configured to condition a radiation beam; a patterning support constructed to hold a patterning device, the patterning device being capable of imparting the radiation beam with a pattern in its cross-section to form a patterned radiation beam; a substrate support constructed to hold a substrate; a projection system configured to project the patterned radiation beam onto a target portion of the substrate; and a positioning system to position the patterning support, the substrate support, or both, the positioning system comprising a motor with a stator and a mover that is coupled to one of the patterning support and the substrate support, and an associated motor control system having a controller configured to provide an output to control a current applied to the motor, wherein the motor control system is configured to: (a) determine a controller output that is adapted to compensate for a weight of the mover and associated support; (b) determine a deviation of the output obtained under (a) from an output that is adapted to compensate a gravity force acting on the mover and associated support; (c) correct the current applied to the motor based on the deviation obtained under (b), and (d) compare in (b) the deviation with a threshold value, the motor control system being configured such that, if the deviation exceeds the threshold value, (c) is not performed.