Evaluation of contact surface configuration with a scanning laser microscope

Arc discharge between contact electrodes brings material transfer and erosion, which sometimes cause serious contact failure. To achieve better reliability and longer life of electromechanical components, characteristics of material transfer and arc erosion of each contact material under different load conditions have to be studied. However, no effective methods for gathering numerical 3D information on contact surfaces have been available. In this paper, the theory and system of a scanning laser microscope is explained, which is confirmed to be useful equipment for this purpose. A confocal optical system and a focus scan memory of the equipment enable us to measure depth of craters and height of pips on contact surfaces in a short time without damaging specimens. By processing the measured data with an image-data processing software, 3D images of contact surfaces are displayed and volume of craters and pips is easily calculated. Relay contact surfaces operated in a capacitive load circuit are numerically evaluated with the scanning laser microscope. The 3D data such as height, depth and volume of craters and pips are measured and material transfer rate per unit arc energy is calculated. The results are shown to confirm how useful the equipment is for investigation of electrical contacts.