This paper presents a new method for pattern recognition of 3-dimensional objects. Three dimensional objects are recognized by means of a moire contour difference technique. The technique utilizes the projection of a grating upon the object. The grating is perturbed according to the topography of the object surface; thus the perturbed grating acts as information carrier about the surface topography. The image of a master part which has been illuminated with a projected grating is stored in a negative photographic transparency, and it is used as a transmission filter when inspecting other parts. The transmitted image contains the correlation information of the part under inspection with the master part. If the two parts are identical, an autocorrelation occurs which results in a minimum level of light transmitted. If the inspected part is different from the reference part, a cross-correlation occurs which results in the presence of moire fringes and causes more light to be transmitted. Missing parts are detected by identifying the presence of moire fringes or simply detection of the level of the transmitted light and decision can be made automatically. The feasibility of the method was verified by a laboratory demonstration.
Joseph Der Hovanesian,
Yau Yan Hung,
"Three-Dimensional Shape Recognition By Moire Correlation", Proc. SPIE 0360, Robotics and Industrial Inspection, (23 May 1983); doi: 10.1117/12.934087; https://doi.org/10.1117/12.934087