Design and performance of an optical sensor for the measurement of surface roughness and waviness

We developed a novel sensing equipment for the measurement of roughness and waviness of rolls during grinding. The sensors can operate on different materials, in harsh conditions, and measurements can be performed on-line, in a non-contact fashion. The sensing equipment makes use of a commercial triangulation sensor, suitably integrated with an additional optical head. The triangulator produces two signals, respectively proportional to the distance from the target surface and to the intensity of the scattered light. The optical head consists of two photodiodes placed in the proximity of the excitation beam and produces a signal proportional to the intensity of the light scattered at smaller angle. The distance signal is used to extract the waviness information, whereas its combination with the intensity of the light scattered both at large and small angles is necessary to derive the roughness information. The resulting sensor is able to measure waviness and roughness in the spatial wavelength ranges of 1 mm divided by 100 mm and 0.1 mm divided by 1 mm respectively; with height range of the defects equal to 200 nm divided by 5 micrometer. The measurement uncertainty is less than 2.5% and the linearity is 1% of the measuring range.