The Magnetic Fields Modeling And Signal Processing Of Seam Tracking Sensor Based On ACFM Technology

As welding forming technology permeate to various areas of the mechanical manufacturing, development and application of new type welding automation technology will play huge role of national economy,and seam tracking technology is the important aspect of welding automation research.The narrow interval I type butt weld which comman used in engineering usual lack of stable and effective method of tracking, combined with the high frequency alternating magnetic fields measurements (ACFM) technology in use at Non-destructive testing fields, designing and developing a new electromagnetic sensor based on the principle of ACFM applied to seam tracking.In this paper,through the modeling of sensor,s space magnetic fields,focusing on that research the internal relationship between welding line position and magnetic field distortion signal which cause by welding line;and according to the magnetic fields signal characteristic of low SNR and the requirement of welding environment design signal processing circuit to pick up accurately required signal,meanwhile simulate part of the circuit to optimization. The main research content as follows:(1) Analyzed the basic theory and feasibility of ACFM seam tracking sensor. Analyzed the basic principle and working process of ACFM technology, and established the simplified mathematical model of space magnetic fields, completed the three-dimensional space each direction induction strength theory calculation; Study the magnetic fields distribution rule of each point in the same horizontal plane along welding line direction,get the location information of weld starting and terminal point; Study the magnetic fields distribution rule within a certain region along welding line vertical direction, get the direction and amplitude information of weld deviation, fitting for distribution curve with numerical analysis method, calculate the approximate function relationship between the magnetic field strength and weld location; finally designed work flowchart about seam tracking sensor to collect magnetic fields distortion signal.(2) Designed signal processing circuit based on differential amplifier,50Hz power frequency trap and high order no drift low pass filtering, and simulated using MATLAB/simulink; according to analog trap is unable to filter out the residual power frequency harmonics,designed the whole coefficient much stopband band-stop digital filter that with the characteristic of high stopband selectivity and low signal distortion degree; according to complex welding environment and real-time demanded of tracking system,ask for the filter have high stability and response speed,offer the theory of reset filter pole to improve filter quality, seek optimal filtering performance; designed a kind of orthogonal lock-in amplifier circuit to finish DC form output of magnetic fields distortion signal amplitude and phase information simultaneously, improve the accuracy of seam tracking sensor.(3) To proving the correct and effective of signal processing circuit with experiment,and on this basis measuring the induced voltage signal which can indicate magnetic fields distortion information,to proving magnetic fields distribution rule within a certain region along welding line vertical direction; and designed extracting square root circuit to obtain welding line location information.