Method and apparatus for absolute moire distance measurements using a

Abstract

Method and apparatus are disclosed for providing absolute Moire distance measurements of a diffusely reflective surface from a reference position. More particularly, a first grating is located, formed, or printed on the diffusely reflective surface. An image of the first grating is formed on a second grating or detector array by imaging means for generating a Moire pattern that is detected by a detector means. At the reference position of the diffusely reflective surface relative to the imaging means, the periods of the image of the first grating and the second grating match. Movement of the diffusely reflective surface from the reference position in a direction normal thereto, produces a spatially varying intensity pattern at the detector means which results from the shifting and magnification mismatch between the pattern of the image of the first grating and the pattern of the second grating. Measuring the amount of magnification differences between the two patterns provides information related to the instantaneous absolute distance of the diffusely reflective surface from the reference position. Various methods are disclosed for using the information from the detector means for determining the absolute distance measurements.