Rotational deviation detecting method and system using a periodic pattern

摘要

A deviation detecting system for detecting a rotational deviation of an object, includes a pattern formed on the object and having a periodicity, a light source for providing light, a detecting device for projecting the light from the light source onto the pattern and for detecting at least two diffraction lights from the pattern with a predetermined detection plane, and a determining device for determining a rotational deviation of the object with respect to a predetermined axis, on the basis of the positions of incidence of the diffraction lights upon the detection plane as detected through the detection by the detecting device.