Evaluation of an External Axis for Tool Manipulation in Robotized Laser Beam Welding

Sammanfattning: Laser beam welding applications are widely used in the industry. However, laser beam welding applications have a very small position tolerance to an offset. In this project, the offset is defined as the distance between the point, which the laser tool welds, and the point which laser tool should weld the weld joint. In other words, the offset is the position error in a welding application. To perform successful welding, the laser beam must hit the exact coordinate of the weld joints to weld the parts together. For dealing with these inaccuracy issues, tool manipulation systems can be used. In this project, an external axis is used for the precise manipulation of the laser beam welding tool as a complement to robotic nominal movement. Input data to the external axis system is obtained from an image from a vision system of the work pieces which need to be welded. Tool manipulation systems are used to manipulate tools to ensure certain position accuracy during any application. The tool manipulation system in this project has two main parts; a seam tracking system (outside this project) and an external axis system. The seam tracking system gives an on-line measurement of the offset, and that there is a feedback loop with a controller, which gives the system information about how much to manipulate the external axis module to the external axis system. The seam tracking system consists of two main parts; a camera and the seam tracking image processing program. In the seam tracking system, a camera takes images of the work pieces which shall be welded. Then the seam tracking program calculates the offset by image processing. This estimated offset is the input for the external axis system. The external axis system has three main parts; the external axis program, input-output module and the external axis module. The external axis program is the system which controls the input-output module for manipulating the external axis module in this project. The external axis module manipulates the laser beam welding tool by changing the orientation of the tool in order to reduce the offset. This project is about the external axis system. There is a relationship between the offset input and the required manipulation angle of the external axis. In this project, the required manipulation angle is the external axis angle. By using this relationship, the laser beam welding tool can be manipulated to weld in the desired position. The same system can be used in applications which require high position accuracy. The evaluation of the external axis system emphasizes that the accuracy demand of the laser beam welding applications can be satisfied by an external axis system. However, the investigated external axis system behaves in a way that when the offset is larger than it supposed to be, the speed of the TCP movement slows down.