Capacitive sensor calibration method and apparatus for opposing electro-magnetic actuators

Abstract

In a stage assembly, for instance a fine stage using a pair of push-pull electro-magnetic actuators to move the stage back and forth along an axis, there is typically a sensor to determine the actual stage location. This sensor's home position must correspond to the actual stage position where the two opposed actuators are observed to exert forces of the same magnitude but opposing directions on this stage. Since the actuators depend on the sensor reading to exert their forces correctly, misalignment of the home position will decrease system performance. The calibration of this sensor is accomplished using actual system feedback signals, which are the currents drawn by the two opposed actuators, during run time conditions. The sensor is considered calibrated (meaning a virtual “null” position) when each of the two opposed actuators draws the same amount of current. If this is not the case a feedback process calibrates the sensor.

Dependencies are inferred from the claim text.