A real-time ultrasound based system for controlling robotic weld quality by monitoring the weld pool is presented. The weld penetration depth is one of the most important geometric parameters that define the weld quality, hence remains a key control quantity. The sensing system is based on using laser phased array technique to generate focused and steered ultrasound, and an Electro-Magnetic Acoustic Transducer (EMAT) as a receiver. Both ultrasound generation by the laser and reception by EMAT are non-contact, which eliminates the need for a couplant medium. Hence, they are capable of operating at high temperatures involved in the welding process. The ultrasound generated by the laser phased array propagates through the weld pool and is picked up by the EMAT receiver. A signal processing algorithm based on cross-correlation technique has been developed to estimate the Time-of-Flight (ToF) of the ultrasound. The relationship between the ToF and the penetration depth of the weld has been established both experimentally and numerically. The analytical relationship between the ToF and the penetration depth, which is obtained by ray-tracing algorithm and geometric analysis, matches well to the experimental measurements.
展开▼
