MOIRE PATTERNS OF 2 DIFFERENT ELONGATED CIRCULAR GRATINGS FOR THE FINE VISUAL MEASUREMENT OF LINEAR DISPLACEMENTS

An elongated circular grating having the shape of an athletic track wa s proposed to determine both the moving displacement and its direction within an accuracy of ten times that of conventional circular grating s. The properties of moire fringes from two complementary elongated ci rcular gratings were investigated for fine visual measurement of linea r displacements. Moire patterns formed by superposition of two differe nt elongated circular gratings were demonstrated to provide a simple f ringe-counting method for determining both the relative linear displac ement and its direction within the accuracy of 1/10 pitch of the grati ng. The measurement of the refractive indices of C6H12 and CCl4 and th e thermal expansion coefficient of aluminium, using elongated circular gratings, are presented. (C) 1998 Elsevier Science B.V. All rights re served.