Research On The Design And Optimal Configuration Of Indexing Joint For AACMM

The Articulated Arm Coordinate Measuring Machine(AACMM)with the advantages of low manufacturing cost,large measurement range,good flexibility and easy to carry,has been successfully applied in the field of three-dimensional measurement.However,due to the multi-joint tandem open-chain structure,various errors accumulate step by step,resulting in a large deviation of the probe position.Summarizing domestic and international researches,it can be found that it is difficult to effectively improve the measurement accuracy of the AACMM by relying on parameter calibration.Therefore,an indexing joint structure for the AACMM has been designed in this thesis.The structure is based on a rotating joint,combing with an indexing structure.Through the method of index positioning calibration,this structure not only can reduce the accuracy requirements and hardware cost of the angle encoder,but also can output high-precision angle value of the limited position of the joint,at the expense of some measurement space and flexibility.The main research work of this paper includes:Firstly,the kinematics model of the AACMM has been established,and the correctness of the model has been verified by simulation.The main error sources and error types have been analyzed systematically according to the structure characteristics.Secondly,a kind of indexing joint structure for the AACMM has been designed.Using this joint to replace part of the rotating joint can improve the measurement accuracy on the premise of realizing the measurement function of the AACMM.The working principle and error types of indexing joints has been introduced,and the effects of repeated positioning errors and coaxiality errors on the accuracy of the measuring machine have been specifically analyzed,which are meaningful for the construction and assembly of the structure.Thirdly,the error model has been established to analyze the influence of each joint angle error on the precision of the AACMM.The Monte Carlo method and the service ball method have been used to compare and analyze the measurement space and flexibility of the indexing joint before and after the measuring machine.Based on the simulation analysis of the above three performance indexes,the feasibility and effectiveness of the indexing joint structure for the accuracy improvement of the measuring machine have been verified theoretically,and the optimal configuration of the joints has been determined.Lastly,photoelectric autocollimator and metal polyhedral prism have been used to build the experimental platform to determine the repeated positioning error of the indexing joint structure.An experimental scheme of joint locking self-calibration has been designed to verify the influence of joint angle error on measurement accuracy and the results can provide experimental basis for the optimal joint configuration of the AACMM.