Research On Efficient Combined Measurement Method Based On Laser Tracker And Structured Light Scanner

The space missions represented by deep space exploration and space station have an urgent demand for super large spacecraft capsule.As the key component,the large spacecraft capsule can provide the supporting structure for a series of key loads outside the capsule.Therefore,the manufacturing accuracy of the capsule load bracket will directly affect the service performance of the spacecraft.In order to ensure the machining accuracy of the bracket,it is necessary to accurately measure the mounting profile and position characteristics of the large size spacecraft capsule bracket in the whole capsule state.However,due to the large size of large spacecraft,large number of load brackets,complex geometry structure and cross scale distribution,it is very difficult to achieve high precision,high efficiency and high reliability measurement of load support mounting surface.This paper presents a combined and efficient measurement method based on the long-distance global control of laser tracker and the short-range surface scanning of structured light scanner.In order to solve the problems of large coordinate transformation error between global and local cross-scale data,low automation and low measurement efficiency of multi-type equipment combination measurement,and difficult extraction of 3D point cloud features,the key technology of "laser tracking & local scanning" combination measurement is studied,and the combination measurement system is built,which realizes the measurement of large-scale feature geometry.The main research contents of this paper include :1.According to the characteristics of the system composition and the accuracy requirements for the measurement,it is proposed the calibration algorithm for the measurement system,which is based on dual quaternion hand-eye calibration and combined with ICP point cloud registration and Proctor analysis.This method can solve the high precision calibration for the scanner external parameters and the rough hand-eye calibration between laser tracker and robot arm,meanwhile reducing the cost and improving the efficiency on the premise of high measurement accuracy.Finally,through the experimental verification,the high-precision stitching of multi view measurement data is realized.The measurement exactness of the system is better than 35 μm within the range of 300 mm.2.In order to solve the problem of feature extraction and feature fitting of scanning object,firstly,according to the material and size of the measured object,the exposure parameter range and shooting angle range are determined by experimental method;secondly,according to the measurement requirements and the characteristics of the measurement target,two feature extraction algorithms based on image processing and three-dimensional point cloud segmentation are proposed by referring to the two data formats of two-dimensional depth image and three-dimensional point cloud output from the scanner,so as to realize the segmentation and extraction of the features such as target ball,bracket surface of interest and the smalldiameter unthreaded hole.In addition,it is proposed the geometric feature fitting algorithm for spherical surface and planar surface.3.In order to meet the needs of measurement automation,improve measurement efficiency and facilitate personnel operation,it is necessary to develop corresponding software integrated measurement system.Therefore,the software of automatic measurement system is developed in Windows 10 operating system,based on.Net framework 4.7.2 framework and using C # language and WINFORM interface framework.The software integrates multithreading,device SDK,Halcon machine vision library,Ethernet communication,JSON and unity3 d technologies,and finally realizes multiple functions such as device control,data acquisition,data management,point cloud image processing,algorithm integration,image display and 3D twin of measurement system.In addition,on the basis of the hand-eye calibration model between the tracker and the robot arm,the software uses Unity3 D Engine to build the three-dimensional twin model of the system,and realizes the optical path accessibility prediction of the laser target ball.