Study On A Reconfigurable Articulated Arm Coordinate Measuring Machine

The articulated arm coordinate measuring machine (AACMM) is a new type of non-cartesian measuring system. Compared with traditional orthogonal coordinate measuring machine it has many advantages such as simple structure, compact size, light weight, large measuring volume, high flexibility, low cost and easy to be used in industrial field. Recently AACMMs have been widely applied in mould design, reverse engineering, quality inspection online, equipment assembly and maintenance and so on. However, the accuracy of AACMMs is much lower than traditional orthogonal coordinate measuring machines, because they are serial mechanisms with many joints and freedoms, the parameter errors transmitting to measuring probe will be accumulated and amplified, on the other hand, the measuring volume of AACMMs is usually much bigger than size of measured parts, therefore it will cause the accuracy loss. So how to improve the accuracy of AACMMs become the focus and hotspot of the research work on AACMMs.In this thesis, a reconfigurable articulated arm coordinate measuring machine is presented, through an operation of changing measuring volume or decreasing degrees of freedom (DOF) of machine, the new type of machine can meet the requirements of high accuracy as well as high resolution by making the measuring volume fitting to the sizes of measured objects. Around this train of thought, the thesis carries out the theoretical analysis, simulation study and experimental validation.In the first chapter, the background and the significance of articulated arm coordinate measuring machines are introduced, and then the disadvantages of AACMMs in the market are analyzed. Finally the main framework of the dissertation is presented.In the second chapter, the work principle of the reconfigurable articulated arm coordinate measuring machine is explained, the advantages of the reconfigurable articulated arm coordinate measuring machine are discussed, then the mathematical model and the error model of the reconfigurable articulated arm coordinate measuring machine are established.In the third chapter, the mechanical structure of the reconfigurable articulated arm coordinate measuring machine are presented in detailed.In the fourth chapter, a data acquisition system based on Field Programable Gate Array (FPGA) is designed, which can collect signals of 6 channel circular grating angle sensors,1 channel temperature value, and 3 operation buttons input and communicate with PC based on protocol of RS-232C.In the fifth chapter, the error simulation and experimental research are carried out. Based on the error model of the reconfigurable articulated arm coordinate measuring machine, the error simulation is carried out with the software of Matlab; finally a validation experiment is carried out with a commercial AACMM product.In the sixth chapter, the research work is summarized and the futural work is proposed.