Research On Laser Scanning Multi-parameter Detection System For Friction Stir Welding

In order to meet the increasing requirements for the control accuracy and reliability of the welding process,this paper developed a multi-parameter detection system based on the principle of laser ranging for friction stir welding.The system uses laser displacement sensor to obtain the three-dimensional topography of the workpiece surface near the welding tool,and gets welding parameters such as the tool tilt angle,tool plunge depth and the deviation of welding direction.This system is benefit to achieve a stable and accurate welding process,and has important practical significance for adaptive parameter control of friction stir welding process.A multi-parameter detection system for robot friction stir welding was established.The system is mainly composed of following hardwares: servo motor,transmission components,laser displacement sensor,industrial personal computer,data acquisition card and so on.The working principle is as follows: the laser displacement sensor rotates around the welding tool at a proper speed,and gets the changes of surface morphology on the workpiece in the area near the welding tool.At the same time,the two-dimensional position information of the detection point can be acquired through the pulse information recorded by the encoder on the servo motor.The industrial personal computer uesd to obtain the three-dimensional coordinates of the detection point by processing the measured value of the laser displacement sensor and the pulse value of the encoder.A welding parameter detection algorithm for laser scanning friction stir welding multi-parameter detection system was developed.Using detection points datas in a detective period to fitting the plane equation.Based on the vertical distance from the detection point to the workpiece plane,the detection points belonging to the workpiece surface,the welded area and the weld seam area are separated.The detection points on the workpiece surface are used to repeatedly iterate multiple times to fit the plane equation of the workpiece.The angle between the normal vector of the workpiece and the z-axis of the sensor coordinate system is the tool tilt angle.The distance from the detection point of the welded area to the workpiece plane is the tool plunge depth.The distance between the projection point of the weld position on the workpiece surface and the advancing direction of the welding tool is the deviation of the weld.The calibration method of friction stir welding multi-parameter detection system is studied.The purpose of the sensor coordinate system calibration is to obtain the three-dimensional coordinates of the detection point from collected datas.The process is as follows: design a calibration plate with grooves of equal distance and equal width,and extract the mutation points at the groove based on the laser measurement.Use the mutation points to calulate the relationship between the measurement value and the detection radius.Adjust the distance between the calibration plate and laser displacement sensor,and get different detection point datas to calculate the angle between the laser measured value and the z-axis of the sensor coordinate system.The calibration purpose of the sensor coordinate system and the robot tool coordinate system is to determine the three-dimensional coordinates of the detection point data in the physical world.It mainly involves TCP(Tool Center Point)calibration and TCF(Tool Center Frame)calibration,respectively determining the the relative position and posture of the sensor coordinates in the tool coordinate system.Performance test of the friction stir welding multi-parameter detection system.Welding parameters are extracted by adaptive threshold and multiple iterative plane fitting methods,and the accuracy of the algorithm for extracting each welding parameter is verified.The results show that the welding parameter extraction accuracy has reached the system design index and meets the real-time monitoring welding process.