Error Analysis And Compensation Research Of Articulated Arm Coordinate Measuring Machines

With the rapid development of advanced manufacturing technology, coordinate measuring machines (CMMs) are hugely needed in more and more applications and the requirements of CMMs are on the increase. The application of traditional orthogonal coordinate measuring machine is being restricted in more and more conditions, such as outdoor measurement, task on production line, detection in small space, large-size measurement and so on. The demand of non-orthogonal articulated arm coordinate measuring machine (AACMM) grows increasely because of its light weight, small size, easy operation, portability, large-size measurement and low cost. Compared with the traditional coordinate measuring machine, the wide application of AACMM is restricted due to its low measuring accuracy. Based on the development of AACMM, the key factors which affect the accuracy of AACMM were discussed, including mechanical design, joint angle error, structural parameter error, mechanical deformation, thermal deformation and experimental research.Firstly, the main mechanical structure and equilibrious mechanism were designed. Based on its mechanical structure, a kinematics model of AACMM was established by D-H method. With the kinematics model, error sources of AACMM were discussed and classified.The relationship of joint angle error and measuring accuracy of AACMM was analysed and a conclusion of demand on joint angle precision was derived. And then, the detailed analysis of off-center and gradient installing of circle grating of AACMM was made, and their mathematical models were obtained. Installing technique to minish off-center error and error compensation method were applied to ensure the measuring precision of joint angles.The research on structure parameter error of AACMM was done and the principle of structure parameter identification was clearly presented. Following the finite element and intensity analysis of the mechanical structure of AACMM, an error compensation method of structural bending deformation was introduced.The thermal deformation of the machine was also analysed and the compensation method by a on-line temperature measuring system was presented.The experiments on joint angle error compensation with two high precision measuring devices—CMM and photoelectric autocollimator were introduced in the experimental part of the thesis. It found out that the installing error of experimental equipments would cause angle measuring error. A method of using least-squares method to identify eccentricity parameters of AACMM was described. Applying the parameter identified to compensate the joint angle error, the joint angle precision of AACMM was improved. And parameter identification experiment was designed to validate the structure parameter error compensation method.Finally, conclusions were summarized and the futural work was pointed out.