Displacement measuring apparatus and method

摘要: Displacement measuring apparatus comprises a light source (10), lens (12), and index grating (14), reflective scale (16), three photodetectors (18) at positions corresponding to the zero order positive negative first images of (10). The (14) has castellated surface profile with mark/space ratio (a/b, FIG. 3) castellation height (h, chosen so that see wavefronts having phase separation 120. electrical signals from are used sense magnitude direction movement reading head carrying components (10, 12, 14 18) respect (16).