Spot welding is one of the most important welding procedures. Robots are used to perform the welding operation in dangerous and high temperature environment. This technology is to a large extent used in automotive industry to join plates. Specifically, in this work the joining of two plates of a car door is studied for the purpose of making it possible to decrease folded size and thereby materials used and as a result reduce weight of the product. There are many factors adding to uncertainty from the physical world such as noise of the welding machine, weld process or the signals, which all add up related to tolerances in control of the welding process The task of the research in this study is to control spot welding process in order to reduce tolerances and the plate folded size. A sensor system was developed and is described in this report. Universal methods based on laser scanner and cameras are introduced and the advantages and disadvantages of these are discussed. An optimized method based on universal methods with a strategy to meet the timing demands is developed. Experiments are performed to test the methods with ABB robot. The whole sensor system including the communication is built up and the algorithms are executed by programs.     The accuracy of the camera based method is tested in experiments. The result is promising and indicate feasible methods and strategy to locate the spot welding location during operation and thereby make it possible to achieve better welding quality with minimized increasing in cycle time.     Future work should be directed towards to choose a proper laser scanner and to create better mathematical model for the strategy in order to implement this in a real production environment.