Diffractive optical sensor for gloss differences of injection molded plastic products

A diffractive optical element (DOE) based sensor is presented for measurement of gloss differences of injection molded convex or concave plastic products. Increases of local gloss of the samples, and hence local wear of the tool, were observed to correlate linearly with the DOE signal by exploiting a simple image analyzing method. The measurement is based on the utilization of the fully developed speckle pattern, which grain size is much larger than the aperture of the DOE. Corroborative measurements by spectrophotometer and a commercial glossmeter confirmed the reliability of the DOE sensor. It is suggested that robust DOE sensor can be utilized for industrial inspection of non-planar plastic products.