Automatic CO2 laser beam delivery system based on self-tracking transmitting and receiving units

摘要

Abstract: This development is in the framework of the activity carried out to establish welding techniques applicable in radioactive environment to the vacuum vessel of the ITER fusion reactor. An automatic welding equipment will consist of three functional blocks: carrier, end-effector and beam delivery system. A trolley is driven along the walls of the component to be welded in order to position a welding head close to the operating zone. Accurate approach to the final position is demanded to an intelligent end-effector capable of on-line processing and monitoring. To be integrated on- board of the carrier but not directly belonging to the operating head is the power beam delivery system. In the case of CO$-2$/ laser beams a special active beam delivery system based on units capable of automatic alignment and of mutual tracking is required. The work described in this paper demonstrates the feasibility and effectiveness of such a system based on self controlled units capable of deflecting the beam from a fixed station to a moving operating head, thus realizing a sort of transmitting/receiving device applied to a free propagating beam. One of the units, the receiver, set on the carrier, is automatically aligned with a twin static unit, the transmitter, which is fed directly by the laser source. Each unit is a two degrees of freedom rotatory head, capable of covering nearly the whole solid angle. This system is equipped with sensors, suitable to provide high precision alignment of the power beam into the final focusing head with adequate stability. The experimental set-up tested makes use of a power level of 6 kW. The distance transmitter-receiver is in a range 2 - 10 m, and trials are performed on 5 - 10 AISI 316 L stainless steel at a welding speed up to 2 m/min. Results are consistent with expectations. As the welding head is moved, the alignment error detected by the self-tracking units is immediately recovered within small tolerances. Sharp corners are matched with higher accuracy than required by heavy section welding. This system for beam delivery is completely innovative and of relevant interest for application to components of large dimension, approached from inside in a standard configuration not different from that used with conventional techniques.!0