Research On Seam Tracking System Based On The Variable-area-styled Electric Eddy Current Sensor

With the development of our modern society, the automation and intellectualization ofwielding becomes necessary. The automatic tracking of welded joint is a key problem whilethe sensor technology is crucial to realize the tracking. This article focuses on the researchinto the principles behind inductance and capacitance detection, giving a brief introduction tothe physical property of eddy current sensors, based on which the author designs avariable-area-styled electric eddy current sensor capable of detecting the change of area andfeatured by simple structure, high control precision, non-mechanical shock, and long servicelife. Besides, this article throws light upon how to realize the butt joint of slabs and theautomatic tracking of lap weld, and overcome the problem of misalignment by using thissensor to detect the change of area.The author first brings up a scheme--the capacitance-and-inductance-basedcomposite-bridge-styled sensor of tracking welded joint: briefly introducing the principlesbehind inductance and capacitance detection, making an analysis of the sensor’s mathematicalmodel, building the Simulink based on the mathematical model, performing the simulatedanalysis of the sensor’s influence factors, and finally doing a test on inductance andcapacitance detection respectively. The test verified that it is quite difficult to apply thisscheme to realize the automatic tracking of welded joint. But in the exploring process, theauthor strengthened his understanding of inductance detection, so based on this, the authorputs forward another scheme—the variable-area-styled electric eddy current sensor based onthe principles of eddy current sensor.Then based on the principles of eddy current sensor, the author analyzes thevariable-area-styled electric eddy current sensor in detail, gains its mathematical modelthrough making a simplified calculation of the equivalent circuit of the sensor, and gains ageneral understanding of the relationship between the sensor’s output signals and everyinfluence factor through applying Simulink of MATLAB to make the simulated analysis, thuslaying a theoretical foundation for subsequent data processing.Given that the main factors influencing the sensor’s output signals include the area andthe distance, through combining the previous theoretical analysis, the author brings up a newdata processing method—separation of variable. By making the separation of variable uponthe two sensors’ output signals, the author acquires the one-to-one relation between adependent variable and an independent variable (area). And the change of area reflects thedeviation of the welding torch’s position. Then the experimental data are used to make backsubstitution to verify its accuracy. Finally to optimize the previous algorithm of separation of variable achieves one well-adapted algorithm with better effect.At last, according to the requirement of the system, the author designs systematichardware circuit. Based on that, the author designs the corresponding software and finishesdesigning and manufacturing the welded joint’s tracking system based on thevariable-area-styled eddy current transducer, and applies this system to do the test on the buttjoint of slabs and the tracking of lap weld. The experimental results verify the feasibility ofthe method of automatically tracking the welded joint brought up in this article.