The Research On Measuring Method And System Of Resistance Spot Welding Electrode Misalignment

Resistance spot welding is widely used in many industrial production fields due to its advantages of high efficiency,economy and environmental protection.Weld quality in resistance spot welding is greatly affected by the misalignment of the upper and lower electrodes and the displacement of the electrodes.At present,the methods of measuring the misalignment of electrodes and the displacement of electrodes in industrial production are mainly human eye observation or hand-held measuring tools,which are low in efficiency,accuracy and safety.This paper presents a system of measuring electrodes neutralization and electrode displacement monitoring with two industrial CCD cameras.Using image acquisition and image processing to measure the electrode misalignment and the displacement of electrodes can greatly improve the detecting accuracy and efficiency.And the remote operation can also ensure the safety of the measurer to a greater extent.The misalignment of electrodes can be measured by using two CCD cameras capture images of the upper and lower electrode caps at two vertical angles.According to the position of the maximum gray level in the horizontal direction,the left and right edge points of the image are determined.The boundary lines of the electrode cap are fitted by the least square method.The axis of the electrode cap is calculated by using the left and right boundary lines of the image.Then the spatial distance and spatial angle of two electrodes axis are calculated by using the two equations of arch axis.One CCD camera is used continuously shooting test piece which moves with electrode in the process of electrode pressure for measuring the displacement of electrodes.The test piece is set between the upper and lower electrode and stuck on the lower electrode.The process of the movement of test piece is recorded by the camera under electrode pressure.It can record the moving process of test piece at the marked position effectively,so as to determine the electrode deflection and fixing compensation amount.Contrast experiment results of this measuring system and Faro measuring system show that the system can quickly and accurately measure the resistance spot welding electrode misalignment.The space displacement precision can reach 0.05 mm and the space angle precision can reach 0.3°.It can solve the problem of measuring electrode parameters in industrial production and provide the necessary basic data for adjusting the electrode to neutral.It can real-time monitor the displacement of electrode during the process of welding.The displacement precision can reach 0.1mm.The electrodes can be compensated for fixing compensation precisely.It has a great significance for research to improve the quality of welding.