Precision position control systems using moire signals

A positioning accuracy of a nanometer has been obtained by a precise positioning system using moire technique. Two precise position control techniques using moire signals have been investigated. One is a differential moire technique using two grating pairs in which the control signal is the differential signal between two moire signals. The other is a technique using one grating pair. The system using the latter technique is simpler in construction. However, in the former technique, since in-phase noises in the moire signals are cancelled and the effect of the drift of the laser intensity on the positioning accuracy is small, higher positioning accuracy is obtained than in the latter technique. The positioning accuracy of /spl plusmn/4 nm was obtained by optimization of the system.