Research On The Key Technology Of Non-contact Measurement Of The Geometrt For Large Diameter Pipeline

In recent years,with the increasing application of large diameter pipelines in water conservancy,petroleum,chemical and other industries,so the quality requirements of the pipeline are also higher and higher.The inner diameter,roundness and straightness of large diameter pipeline are important geometric parameters of pipeline,it is accurately measured is a key element to ensure the processing quality of the pipeline.The measurement method of the inner diameter,roundness and straightness of the large diameter pipeline at present is mainly relying on manual measurement,which is not only inaccurate,but also inefficient.At the same time,such a method affected the production cycle of the pipeline,and reduced the level of automation.Therefore,how to bring about the automatic comprehensive measurement of the inner diameter,roundness and straightness of the large diameter pipeline has become an engineering problem needs to be solved at the moment.In order to solve this problem,designed a pipeline measurement system which can realize the automatic non-contact measurement of the inner diameter,roundness and straightness of the large diameter pipeline.The main research contents of this dissertation are as follows:(1)Introduced the measurement principle and system structure of the pipeline measurement system in detail and the selection of main hardware for measuring system.The data acquisition program of the measurement system is designed with Lab VIEW development platform,and the robot program is designed according to the measurement principle.(2)In order to ensure the measurement accuracy of the system,it was necessary to ensure that the robot end effectors if it could carry the laser displacement sensor along the parallel direction of the pipeline axis into the pipeline.To solve this problem,the adjustment scheme of the robot attitude of the measurement system was put forward.Firstly,made sure that the controlled robot end effectors with a laser displacement sensor was able to be scanned the measured pipe section.Then,the coordinates of the center points of each section were obtained by using least square to conduct ellipse fitting on the scanned cross-section contour.Next,fitted the center point of each section to the spatial line,the axis equation of the pipeline was acquired and further obtained the axis direction vector of the pipeline.Then,the corresponding attitude adjustment was calculated according to the related theory of robot attitude adjustment,and then the host computer fed back the data to the robot.And the robot had adjusted its attitude and it was able to carry a laser displacement sensor to measure along the parallel direction of the pipeline axis.(3)For improved the evaluation accuracy of the roundness and straightness of the pipeline measurement system,the Improved Whale Optimization Algorithm was applied into the error evaluation of circular degree and linearity to against the difficult problem and low accuracy existed in the traditional calculation methods.First,three improvement strategies were proposed for Whale Optimization Algorithm:used the Latin hypercube sampling method to initialize the population,replaced the linear convergence factor in the original algorithm with the nonlinear convergence factor,and introduced the nonlinear weight into Whale Optimization Algorithm.The test results showed that the accuracy,stability and convergence speed of the improved Whale Optimization Algorithm were improved effectively.At last,conducted the experience of applying improved Whale Optimization Algorithm into the error evaluation of roundness and straightness based on the mathematical models of the minimum zone circle method and the minimum zone method and verified this example.The results showed that the algorithm improved the evaluation accuracy and convergence speed,and could be effectively applied to the roundness and straightness error evaluation of pipeline measurement system.(4)Had built an experimental platform of non-contact measurement of pipeline.The inner diameter,roundness and straightness of the measured pipeline were measured and tested by the measurement platform.At the same time,the robot pose adjustment scheme was verified by experiment,and the error source of the pipeline measurement system was analyzed as well.In this dissertation,a pipeline measurement system was designed and it can realize the automatic non-contact measurement for the inner diameter,roundness and straightness of large pipeline.Moreover,a measurement of robot attitude adjustment scheme was proposed to ensure the accuracy of the measurement system.In addition,the improved Whale Optimization Algorithm was applied to the error evaluation of roundness and straightness,which improved the evaluation accuracy of the measurement system.It has been verified by experiments that the measurement accuracy of this system is better than 0.5mm,and the repeatability accuracy is better than 0.25mm.The system has high measurement accuracy and high repeatability accuracy,which can meet the measurement requirements,and has a certain practical application value.