Moire patterns of two different elongated circular gratings for the fine visual measurement of linear displacements

摘要

An elongated circular grating having the shape of an athletic track was proposed to determine both the moving displacement and its direction within an accuracy of ten times that of conventional circular gratings. The properties of moire fringes from two complementary elongated circular gratings were investigated for fine visual measurement of linear displacements. Moire patterns formed by superposition of two different elongated circular gratings were demonstrated to provide a simple fringe-counting method for determining both the relative linear displacement and its direction within the accuracy of 1/10 pitch of the grating. The measurement of the refractive indices of C_(6)H_(12) and CCl_(4) and the thermal expansion coefficient of aluminium, using elongated circular gratings, are presented.