The use of backscatter radiation from the laser process providing process feedback and pro-active laser safety control

In this paper we report the development of a multi-spectral sensor for real-time monitoring of the laser welding process which is also used within a proactive laser safety protection system. The system is based on the gathering of different optical spectra generated by the laser welding process and examining the correlation of enhanced output from different spectral lines and comparing that with x-ray data of the weld. Identification of the peak emitting spectral lines then enables back to the specific output to be fed to a laser safety management system to form the basis of a proactive control strategy to detect the development of a beam delivery failure in real time. Such a proactive safety approach has significant technical advantages with regard to compact localised guarding systems which only need to provide protection from the laser during the shutdown response time of the management system. Here we seek to investigate the potential benefits and cost savings of active sensing of the beam to reduce the unnecessary burden of excessive guarding as well as providing a meaningful laser welding process control system. Usually optical radiation hazards are removed using local guarding so as to prevent accidental exposure to the direct or scattered optical radiation. If a fault occurs between the laser aperture, the necessary beam delivery and the irradiated component i.e. the process then an errant beam can give rise to hazardous levels of laser beam radiation. A passive guard control system requires the laser system being closed so that the laser cannot burn through the housing under fault conditions for the designed protection time. This approach can in some instances be highly restrictive. An alternative is to incorporate sensors onto the surface of the protective guard so that in a fault condition the incident laser radiation is detected and the laser stopped. However failure of this detection system would require the guarding to still be adequate to provide the full level of protection as defined by the passive guarding requirements. Here we wish to clearly define the next level of protection as being proactive control which is different from an active guard which only operates when an errant beam condition is occurring and the guard is providing the protection whilst the active element attempts to shut the system down. Hence the proactive approach can avoid the need for a hazardous situation to exist.