Inspection Path Planning For Free-form Surfaces Using CMM

With the rapid development of modern manufacturing industry,the inspection accuracy of free-form surface parts is increasing day by day,the traditional manual inspection accuracy and efficiency,in the era of ultra precision manufacturing,is gradually showing deficiencies.A coordinate measuring machine(CMM)with the advantage of strong versatility,high precision,large measuring range,high efficiency,easy process control,becoming an important instrument for precision measurement of free-form surface parts,is particularly important to enhance the quality of mechanical part processing.This thesis focuses on the selection of sampling parameters of CMM,the adaptive arrangement of measuring points,and the large scale measurement points path optimization,which reduces the inspection error of CMM,improves the free-form surface inspection efficiency and reliability.The major contributions of this work include:1.The research background,significance,research status and development trend of free-form surfaces inspection are discussed.According to the deficiency of free-form surfaces of CMM inspection technique at present,this thesis puts forward the research contents,i.e.path planning of inspection.2.The influences of several sampling parameters of the CMM on the inspection errors of the parts are studied,and the optimal values of sampling intervals and ball diameters are obtained by using the inspection method of CMM.Firstly,the influences of the above two parameters on the measurement results are analyzed.Secondly,the inspection process of CMM and the statistical analysis of experimental data are introduced.Thirdly,taking the bicubic B-spline surface part as the research object,the experiment was carried out to obtain the normal errors of some measuring points.Finally,the experimental results were statistically analyzed to determine the optimal sampling parameters.3.In order to solve free-form surface measurement points layout problem,the adaptive measuring points distribution of improved chord method and adaptive shape feature are used.Firstly,the mathematical model of free-form surface is established,which provides the mathematical basis for parametric modeling of the surfaces.Secondly,the improved chord method is studied that combines step measuring point layout simple and high precision of chord method;the adaptive shape feature method is studied meanwhile by using the sampling algorithm of surface shape function,and ensures the adaptive distribution of measurement points.Finally,several surfaces were designed,adaptive points distribution maps were obtained,and the data of the measurement points were verified by CMM.4.In order to improve the efficiency of inspection of complex parts,the path optimization problem of measuring points of free-form surfaces is studied.Firstly,the composition of free-form surface inspection path is analyzed,and the objective function of path optimization is determined.Secondly,the tabu search algorithm,genetic algorithm and ant colony algorithm for solving the traveling salesman problem are modified,so that the above three algorithms can be applied to path optimization of the measurement points of free surfaces.Thirdly,a number of parametric surfaces were taken as examples,and the measured points were optimized by computer,and the distance and the time consuming of each algorithm were obtained.Finally,the actual CMM inspection experiments were carried out.