This invention relates to a system and method for detecting a break or leak in an industrial optical fiber transmitting high power laser energy.
Flexible laser beam delivery through a single optical fiber at power levels sufficient for manufacturing processes such as drilling, cutting, welding, heat treating and laser surfacing has been demonstrated and is disclosed in commonly assigned patents and copending applications. A laser beam generated by a solid-state total-internal-reflection face-pumped laser or any other high power laser which is operated in pulsed mode, and has a wavelength in the near infrared or visible spectrum, is focused onto the fiber core. More than 400 watts of average laser power have been transmitted through a thin optical fiber for material processing. The integration of a laser to a robot with a fiber optic system increases the flexibility of a laser processing workstation. With the technical advances in high power laser transmission through optical fibers, and the concepts of Flexible Manufacturing Cells/Workstations using lasers coming closer to reality, there is a need to provide a failsafe interlock system to detect breaks in fiber conduits. The occurrence of a leak or break in the fiber conduit will shut the laser system down thus preventing any serious damage or injury to personnel and equipment. If the fiber link is routed through walls and ceilings after an installation, the potential for a fire hazard exists, and thus a fiber break and leak detection system is required for a safe installation.
The use of a laser transmission sensor as an integral part of the output module manipulated by a robot is described in the inventor's copending application Ser. No. 660,837, filed Oct. 15, 1984, now U.S. Pat. No. 4,673,795, "Integrated Robotic Laser Material Processing and Imaging System". If the laser beam is turned on but its presence is not immediately sensed by the photodiode, a break is indicated and the interlock arrangement turns off the laser. This invention is directed to a complete leak and break detection system for any robotic/laser/fiber configured cell or workstation. Other prior art approaches are given, for instance, in U.S. Pat. Nos. 4,311,142 and 4,476,512. These have disadvantages such as placing sensors on the fiber itself, which are costly especially on long fibers, slow response to heat changes if the fiber fails, loss of output power due to monitoring, and EMI problems in a factory environment.