Restrictions on Measurement of Roughness of Textile Fabrics by Laser Triangulation: A Phenomenological Approach

Abstract

Laser triangulation method is one of the methods used for contactless measurement of roughness of textile fabrics. Method is based on measurement of distance between the sensor and the object by imaging the light scattered from the surface. However, experimental results, especially for high values of roughness, show a strong dependence to duration of exposure time to laser pulses. Use of very short exposure times and long exposures times causes appearance on the surface of the scanned textile of pixels with Active peak heights. The number of Active peaks increases with decrease of exposure time down to 0.1 ms, and increases with increase of exposure time up to 100 ms. Appearance of Active peaks leads to nonrealistic increase of roughness of the surface both for short exposure times and long exposure times reaching a minimum somewhere in the region of medium exposure times, 1 to 2 ms. The above effect suggests a careful analysis of experimental data and, also, becomes an important restriction to the method. In this paper we attempt to make a phenomenological approach to the mechanisms leading to these effects. We suppose that effect is related both to scattering properties of scanned surface and to physical parameters of CCD sensors. The first factor becomes more important in the region of long exposure times, while second factor becomes more important in the region of short exposure times.