Research And Development Of Automatic Extraction System For Weld Trajectory In Space Surfaces

Automatic welding of surface work-piece welds has always been a difficult point in industrial automation.especially for irregularly curved work-piece.With the appearance of various complicate shape work-piece,there is an increasing demand for automatic welding of irregular surface work-piece in the industry.The key to automatic welding lies in the accurate extraction of the weld trajectory,and the irregular curved surface work-piece are difficult to extract due to the difficulty of positioning fixture design.Nowadays most production lines still use a manual welds extract,which is a time consuming and high cost work.Some advanced production lines use laser scanners and teaching robots to weld irregularly curved work-piece,but this method need to design the special fixtures with higher precision.Therefore,an efficient and accurate extraction system for weld trajectory is particularly important.This paper designs and implements an automatic weld trajectory extraction system,the major research contents are as follows:1.Using a single-line laser scanner which named "SmartRay",optical ruler,two-phase stepper motor and other equipment to build a hardware platform to scan the work-piece,realize the single axis motion control and data acquisition for scanners.2.For the CAD model point cloud and real point cloud of work-piece with irregular surface,a fast rough alignment algorithm base of PCA is proposed to quickly estimate the approximate position of the weld in the CAD work-piece relative to the actual work-piece.3.The data volume of the scanning point cloud is usually in the range of hundreds of thousands to millions,but the actual welds only occupy a small part of them.In order to reduce the extraction range of the weld,the feature point extraction needs to be performed first.In this paper,the features of the scanning point cloud are extracted by data reduction by the features of the laser line.4.Based on the ICP and libnabo algorithm,the coarsely-registered CAD weld spot cloud and the physical feature point cloud are accurately registered and the weld position in the feature point cloud is acquired.Combined with the solid body point cloud,the extracted weld seam is modified and compensated.5.Based on the MFC framework under the Windows system,combined with the open source point cloud library PCL,an integrated interactive interface that is easy to operate is designed.Users can select different parameters or registration options for online and offline welds extraction,and check the weld extraction result.Using the solution proposed in this paper can reduce a lot of man-made operations during the weld extraction,and without the design of a dedicated positioning fixture.Experiments show that the proposed algorithm is feasible and efficient for the welds extraction of irregular surface,and it is better than the similar algorithms.The software system can automatically extract the welds for irregular surface work-piece in a short time,and the components of the hardware system can be easily obtained and changed,which can save a lot of manpower and material resources.