Process modeling, simulation, and paint thickness measurement for robotic spray painting

An algorithm and a computer program are developed for modeling of the spray painting process, simulation of robotic spray painting, and off-line programming of industrial robots for painting of curved surfaces. The computer program enables the user to determine the painting strategies, parameters, and paths which will give the desired paint thickness. Surface models of the parts that are to be painted are obtained by using a computer-assisted design (CAS) software. Models of relatively simple surfaces are formed by using the surface generation tools of the CAD software. For parts with more complex surfaces, point data related to the part is collected by using a laser scanner, and this data is used to form the CAD model of the part surface. The surface is then divided into small. triangular elements and centroid coordinates, and unit normals of the elements are determined. Surface data together with the spray distance, painting velocity, and paint flow rate flux are used for simulation of the process and paint thickness analysis. Paint flow rate flux is determined experimentally by using different spray gun settings and painting parameters. During the experiments flat surfaces are painted by using a single painting stroke of the gun. Then, paint thickness measurements are made on the surfaces. It is observed that besides the technical specifications of the spray gun, air and paint nozzles, and paint needle, basic settings like paint tank pressure, spray air pressure, and gun needle-valve position affect paint cone angle and paint flow rate, which finally characterize the spray painting process. For that reason, settings and parameters should be changed and the painting process should be simulated until an acceptable paint thickness distribution is obtained for the part that is going to be painted. The robot program is then generated in the robot's programming language. Paint thickness distribution on the painted surface is determined by measuring the thicknesses using the robot and the CAD model of the part surface. The thicknesses are at the centroids of the surface elements. A measurement probe of the coating thickness measurement gauge is attached to the wrist of the robot by using a feedback/safety adapter designed and manufactured for this purpose, (C) 2000 John Wiley & Sons, Inc