Researchers at Technical University of Denmark in Lyngby have demonstrated a closed-loop control system for laser welding that maintains even seam widths for materials at variable welding speeds. The technique also can compensate for materials of different thicknesses.The system, which they reported in the February issue of Journal of Laser Applications, uses a photodiode to monitor the root-side emissions from the workpiece and to signal the system controller to adjust the power from the 1.5-kW CO2 welding laser accordingly.The researchers noted that they initially used proportional integral and proportional integral differential regulators in the system but that they found the 5- to 10-s response times to be too slow for the application. The final system compares the root-side emissions with an established reference value and displays a response time of approximately 1 s.