The Heun group has trusted in the CLOOS welding technology for decades. With this robot system the company welds ladders for underground engineering. The system consists of two stations which are identical at both sides. Thus the employee on one side can remove the welded components and reload the system whilst the welding process takes place at the other station. The system produces a wide range of different types of ladders. So the ladder width and the number of rungs vary considerably. Therefore, the robot is also fitted with a gas nozzle sensor which uses electromechanical sensing technology to determine the start and end of the weld seam. The programmed welding distance is corrected correspondingly. The system also adapts the welding process automatically to the type of ladder. Thus, only one program is required for the robot system which facilitates the operation significantly.