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Double parallel-joint coordinate measuring machine (CMM) is a new type of coordinate measuring devices. The accuracy of double parallel-joints CMM can reach or closely reach to the accuracy level of traditional CMM in the industrial site. The measuring principle of double parallel-joint CMM at first is described in this paper. By using Denavit-Hartenberg analysis arithmetic, the ideal mathematical model and error model of double parallel-joints CMM is established. Due to the particularity of this type of measuring machine, the additional items Rot(y, s_i) is introduced to solve the problem that the D-H model is not consistent with the conditions of "small error model", and the simon-pure error model is established on that basis. The feasibility of the ideal mathematical model is verified by graphical method. By using M-function of MTALAB, the impact of the error of each parameter to the system measurement errors can be figured out, and the impact rule is summed up. The study in this thesis lays solid foundations for the accuracy design of the double parallel-joint CMM .The tasks accomplished in this thesis will be provided as a solid base for developing double parallel-joint CMM with our own intellectual property and accuracy higher than, cost lower than existing imported CMM. |
