Research On Underwater Weld Seam Recognition Of Ultrasonic Phased Array

With the development of underwater welding technology, automatic weld seamtracking system has been popular with researchers at home and abroad. But most ofthe researches still use the methods on land, without considering its inadaptability inwater. Accurate weld seam recognition is the premise of the weld seam tracking.Based on the current ultrasonic sensing weld seam recognition method, this paperproposes choosing ultrasonic phased array probe, instead of traditional ultrasonicprobe, as the sensor in the seam recognition process. Ultrasonic sensors areinsensitive to electromagnetic, arc light and the dark environment. Compared withtraditional ultrasonic probe, ultrasonic phased array has better focusing performanceand wider scanning range. Therefore, ultrasonic phased array can be a morepotential sensor in weld seam recognition.Firstly, the paper gives a brief introduction of the principle of ultrasonic phasedarray beam forming and the calculation method of the time delay. CombinedRayleigh intergration method and Pencil method, the model of acoustic emissionfield of ultrasonic phased array is established. The model of acoustic emission fieldis simulated through Matlab simulation software. By comparing the acousticemission field of ultrasonic phased array and traditional ultrasonic probe, theadvantage of ultrasonic phased array is obvious.Secondly, in order to improve detection resolution, the paper analyzes theinfluence of the parameters of ultrasonic phased array probe to beam directivity.Receiving interval cross scanning mode, which has more scanning lines relatively, ischosen as the scanning mode. According to this scanning mode, the relevant elementstrobe circuit and sequential circuit is designed.Thirdly, the improved algorithm of ultrasonic distance measurement and weldseam recognition is proposed. Accurate distance measurement is the basis ofultrasonic sensing weld seam recognition. In the distance measuring process,choosing digital coding sequence based on m sequence and binary frequency shiftkeying modulation as the excitation signal to remove the external noise interferenceand the mutual interference between the elements.The zero-crossing algorithm isused to capture the transit time. On the basis of roughly divided point sets and theleast-square fitting method, the weld line can be extracted. Accordingly, the positionof weld seam is achieved.Finally, the influence of the environment is taken into account. In theenvironment of seawater, especially in coastal waters, there are a large number ofsilt and other suspended particles. Ultrasonic cavitation and underwater welding work will produce many bubbles, and the seawater itself is also different from purewater. In the light of this special environment, the influence of seawater, suspendedparticles and bubbles on sound propagation is analyzed.