Study On The Kinematic Calibration Method Of Articulated Arm Coordinate Measuring Machines

The orthogonal Coordinate Measuring Machine (CMM) is a precision measuring instrument, which is called "measuring center" with the characteristics of high preci-sion and powerful function. However, requirements for measuring enviroment of the orthogonal CMM is very strict, which makes it difficult to meet the needs of industrial field measurement. With the development of sensor technology, new materials and so on, the Articulated Arm Coordinate Measuring Machine (AACMM) comes into being. The AACMM is a new type of multi-degree of freedom of non-orthogonal coordinate measuring machine, and with the characteristics of small volume, light weight, easy to carry, flexible measuring, low cost and environmental adaptability, there is a enormous development and application prospect for the AACMM. Compared with the orthog-onal CMM, measurement accuracy of the AACMM is relatively low, which has be-come the key issue to limit its application. Calibration is one of the main means to im-prove the measurement accuracy of the AACMM. In this thesis, we focus on the cali-bration technology to improve the measurement accuracy of the AACMM.Firstly, the system composition and structural configuration scheme of the AACMM are studied. The choice of freedom and structural design of the base, rotating joints and linkages is analyzed to improve measurement accuracy and flexibility of the AACMM. Based on the analysis, the selection principles of key components are pro-posed.Secondly, the measuring principle of AACMM is studied. To solve the singularity problem of D-H model, a kinematic modeling method is proposed based on the MCPC (Modified Complete and Parametrically Continuous) model and the homogeneous co-ordinate transformation. The kinematic model and the error model of the AACMM are established, and then they are verified by numerical simulation. The main error sources to influence the measurement accuracy of the AACMM are studied, and the kinematic simulation model is established to draw the measurement errors transfer chars. Ac-cording to the measurement errors transfer charts, the influences of kinematic parame-ters on the measurement accuracy are found. The joint angle error and joint inclination angle deviation will be progressively larger when they are transferred to the measure-ment error, and the linkage length errors will not be enlarged or reduced. These conclu-sions provide a theoretical basis of structural design, component selection and manu-facturing of the AACMM.Thirdly, the kinematic parameter calibration principle of the AACMM is studied, and then a kinematic parameters of MCPC kinematic model is proposed. In this meth-od, a calibration plate is used as the reference standard. Based on the kinematic model, the over determined equations of kinematic parameters as the unknown quantity is es-tablished, and then the results are solved by the least squares method and iterative al-gorithm. In the end, the method is validated, which shows that:(1) the kinematic pa-rameters errors of AACMM can be calculated through several iterations,(2) the posi-tional accuracy of the calibrated probe has been greatly improved,(3) the effects of systematic errors are eliminated.At last, the main work of this thesis is summarized, and the further research sub-jects are proposed.