Based On The Narrow Gap Welding Capacitance Sensor And Tracking Method Research

With the application of sensor technology in industrial production,capacitive sensor has been widely applied in fields including two-phase flow,material medium reconstruction analysis and high-precision measurement based on its features of compact structure,sensitive precision,non-contact measurement and strong adaptability.The technical background of narrow clearance automation welding system and capacitive sensor were researched in this paper in the first place.According to the characteristics of narrow gap welding and FEF sensor technology,this paper constructed a cylindrical FEF capacitive sensor for narrow clearance automation welding,and further designed the basic structure of cylindrical FEF capacitive sensor.Meanwhile,the measuring principle of cylindrical FEF capacitive sensor in narrow gap welding was expounded,and its feasibility in narrow gap weld detection was analyzed as well.Then the simplified mathematical model of cylindrical capacitance sensing in narrow clearance automation welding was established based on the general theory of electromagnetic field and Possion equation.This paper also constructed the finite element model of capacitive sensor installed in the welding nozzle,was set up the characteristics of capacitance sensor electric field distribution in the narrow gap welding process.Electric field distribution,sensitivity and penetration depth of sensors were studied by simulating the narrow clearance automation welding capacitive sensors under different structural parameters.The variation tendency of capacitance was observed via the transverse and longitudinal migration of sensor in the narrow gap welding process.The capacitor electrode and shield structure was optimized.In this model,the capacitance-distance curve is nonlinearly mapped,and the relationship between the capacitance value and the position of the narrow gap is deduced.The simulation results show that it is completely feasible for the appliance of cylindrical adjacent capacitive sensor in the narrow gap automatic welding system.Besides,this paper proposed the amplifying circuit and filter circuit measuring the size of capacitance value against the fact of capacitive sensor’s current drawbacks including its low self-capacitance,spurious nature and oversized parasitic capacitance.And we use the AD7745 dual-channel 12-bit capacitance-to-digital converter(CDC)to collect the signal value.The chip measured two sets of capacitance values through the host computer software and PC side control,with that the chip draws out the weld offset signal by operation.Several experimental platforms for measuring capacitance were built.Finally,this paper made comparisons between the simulating results and the experimental result.The experimental results were processed through spectral analysis,and then compared with the ANSYS analytical results after wavelet filtering,which came to an almost consistent variation tendency.The external interference clutter,such as temperature and welding splash,is excluded,and the spatial location information of the welding torch was extracted from the filtered signal’s non-linear mapping and mathematical operation.Moreover,the image result and the narrow gap welding is basically consistent via the reconstruction of the welding surface.The experimental results further demonstrate that the cylindrical adjacent capacitive sensor can perfectly match the narrow gap seam tracking system.