Patent ID: 8903156
Filing Date: 2014-12-02
Classification: G03F,H01L

Abstract:
1. A method of updating calibration data of a first position detection system adapted to determine the position of an object, the first position detection system comprising a target and a sensor, the target or the sensor being mounted on the object, and the calibration data comprising a coefficient relating an apparent measured position of the object to an actual position of the object, the coefficient being used to convert the apparent measured position to the actual position to correct an error in the first position detection system and to enable determination of the actual position of the object from the apparent measured position of the object, the method comprising: determining the position of the object using a second position detection system that is independent of the first position detection system; calculating a difference between the position detected by the second position detection system and a position of the object determined by the first position detection system; and updating the coefficient of the respective apparent measured position of the object by the first position detection system using the calculated difference on the assumption that the position determined by the second position detection system is the actual position of the object, wherein measurements made to determine the positions of the object used to calculate the difference are made during periods of normal use of the object.