Research On Measuring Method Of Workpiece Surface Profile Tolerance Based On Point Cloud Reconstruction Technology

With the proposal of Industry 4.0 and Made in China 2025,new challenges have been put forward in all fields of China’s manufacturing industry.As the guarantee of product manufacturing quality,precision measuring is also developing towards a direction of faster,more accurate and more practical.Surface design is more and more widely used in some intelligent electronic products,such as smartphone,watch screen camera edge,etc.,but the processing quality measurement of surface profile tolerance is not as convenient as the measurement of length,width and other dimensions.Therefore,how to measure the surface profile quickly and accurately is an urgent problem to be solved on the production line of precision electronic products..At present,the single point measurement method based on point laser is utilized to measure the surface profile tolerance automatically in the non-standard automatic production field,but the efficiency of point laser is low.To obtain a profile data,it needs to trigger sampling from the beginning to the end.Therefore,although the point laser can be used to measure the profile tolerance,for which it is difficult to meet the requirements of industrial efficiency when measuring multiple positions.While the line laser overcomes the disadvantage of the point laser,which can get thousands of point data at one time.After 3D reconstruction of point cloud data,any position can be measured.Meanwhile,with the rapid development of 3D scanning technology,the accuracy of line laser scanning is also greatly improved.Although line lasers have great advantages in scanning efficiency and accuracy,they also have the following problems:First,the density of the original point cloud data collected by high-precision laser scanning equipment is too large,and excessive data volume will not only waste a lot of computer storage resources,but also greatly reduce the processing speed of subsequent algorithms.Therefore,it is necessary to preprocess the collected original point cloud data;second,due to the limitations of the laser line width and the shape of the workpiece,it is difficult to scan the workpiece completely at one time.If we want to carry out the positioning measurement of multiple positions of objects,it is necessary to study the method of registration of the point cloud data scanned from multiple angles of view(coordinate system)through precise coordinate transformation and unifying them into the same angle of view(coordinate system).The third is to study how to establish a suitable measurement reference coordinate system and the extraction method of the profile for the registered point cloud to facilitate the positioning measurement of the profile tolerance.To solve the above problems,this paper studies a measurement method of surface profile tolerance based on point cloud reconstruction technology.In order to scan the edge of the workpiece completely,this paper first designs a motion control system,which drives the laser and the workpiece through the motor,scans the 8 positions of the workpiece from 8 perspectives through the line laser,after the scanning is completed,the point cloud is simplified by using a variety of point cloud reduction methods,so as to greatly reduce the amount of invalid data and improve the subsequent algorithm processing efficiency.In order to calibrate the rotation and translation relationship among eight viewing angles,a calibration block which is easy to extract the marker points is designed and manufactured.The rotation and translation matrix is determined after extracting the corner points of the calibration block point cloud.This method can greatly improve the efficiency and accuracy of registration.After the point cloud registration is completed,the basic shape of the workpiece can be truly restored.In order to realize the location and measurement of the surface profile tolerance,this paper carries out three-dimensional reconstruction of the point cloud after registration.Firstly,the feature of the point cloud is extracted and the coordinate system is reestablished,and then the measurement is completed by the contour extraction of the model after the local surface reconstruction of the point cloud.Finally,the effectiveness of the point cloud preprocessing,registration and reconstruction measurement methods proposed in this paper is verified by experiments.The experiments show that the measurement efficiency and accuracy meet the industrial measurement requirements.