Evaluation of surface smoothness using a light-sectioning shadow scanner

Abstract

A new type of sensor for rapid three-dimensional evaluation of surface geometrical properties is presented. Light emitted with a fixed small angle to the surface plane by a projector is directed into the measured surface. A curtain installed in the light path close to the surface creates a shadow on the measured surface. The shape of the border between bright (highly lit area) and dark (shadow area) is a profile section of the surface. The camera installed over the measured surface captures an image of the border and a digital signal processor using image analysis techniques digitizes the profile section. The shadow scanner method evaluated here could be used for rapid and accurate scans of surfaces of various porous materials, particularly wood, veneer, paper, fiberboards, leaves, and similar materials in both laboratory and industrial applications. The simplicity of the sensor is an advantage because it makes the system easy to maintain, resistant to breakage, and inexpensive. Its straightforward nature and high accuracy enables the method to be utilized for on-line measurement, and therefore it is suitable for industrial application.