Precision Position Control Techniques Using Moire Signals

Precision position control techniqes using moire signals have been investigated. First. the calculated results of the moire signals are compared with the experimental results. Good agreements were obtained between these results. Secondly, two position control techniques using moire signals have been investigated under the same experimental conditions. One is a differential moire technique using two grating pairs. The signals obtained by the grating pairs are out of phase 180 each other. In this technique, a differential moire signal between the two moire signals is used as the control signal. In-phase noises in the moire signals are cancelled and the S/N ratio of the signal is improved. Therefore, high positioning accuracy is obtained by this technique. The other is a modified moire technique. In this technique, only one grating pair is used. An inverted moire signal is calculated by a computer from the experimentally obtained moire signal. The positioning accuracies and S/N ratios are compared between these two techniques. The accuracy and the S/N ratio for the differential moire technique were better than those of the modified moire technique. However, the system using later technique is simpler in construction.