Optical noncontact method to detect amplitude defects of polymeric objects

Abstract

Light sources used in many applications usually need to be covered to prevent mechanical damage and external harmful effects. Such a cover is ordinarily a transparent object made from polymer or glass. During its manufacture, various decorative defects may occur on the surface and/or in the volume of the object. These defects do not significantly affect the function of the object but do affect its visual aspect. Therefore, this paper presents an optical noncontact method to detect amplitude defects on polymeric or glass transparent objects that is suitable for industrial applications. The method uses light with a low degree of spatial and temporal coherence to prevent unwanted interference phenomena originating, e.g., from an orange peel effect of the surface coating. The image created by the tested object (light cover lens) using the presented method is then analysed to find possible amplitude defects. The main idea of the image processing technique is based on the knowledge that amplitude defects influence the intensity of light passing through the tested object. The resolution of the used approach is high because it can detect defects with an area of less than a square millimetre.

Keywords

• Amplitude defect
• Polymeric non-planar transparent objects
• Image processing
• Defect inspection
• Incandescent lamp