Research On Articulated Arm Coordinate Measuring Machine Used In Electric Multiple Units Bogies

The Articulated Arm Coordinate Measuring Machine (AACMM) is a kind of muIti-degree-of-freedom measuring instrument, with the features of portable, universal, wide measuring range. The instrument can meet the measurement demands for different working conditions, and it is convenient to be applied in many industrial fields. At present, the measuring instrument used in EMU bogies has single function. Applying the articulated arm coordinate measuring machine into EMU bogies can solve the problem. Moreover, it can improve the present measurement level and efficiency of the EMU bogies to obtain more useful data. For this purpose, some work has been done below to research the application of AACMM in EMU bogies.Firstly, measurement models of the four, five and six DOFs measuring machine were established based on homogeneous coordinate transformation theory and D-H parameters method and the different link parameters were given. Graphical method and numerical method were used to compare the coordinate positions of measurement points in different poses. The result shows that both the two methods obtain the same coordinate position, and the validity of the measurement models are verified.Secondly, Monte-Carlo method was used to calculate the measuring space of four, five, six DOFs measuring machines. It can be seen that the measuring space are all sphere, and the measuring space of the four and five DOFs measuring machines exist cavity, while the six DOFs measuring machine has no cavity. Finally, the five DOFs measuring machine which was meeting with the machine size of CRH2 EMU bogie was chosen. Then the fixture of AACMM which was fixed on the central of the axle was designed based on the measurement demands, and the baffle of the wheel tread was designed to improve the measurement efficiency.Finally, the five DOFs measuring machine error analysis was done based on the error model, and the effect of system structure deviation on measuring error was analyzed. The result shows that the relationship between the joint angle error and the measuring error is linear, which is the same as the relationship between the link deflection angle error and the measuring error. The effects of the shoulder and elbow pitching joint on measuring errors caused by joint angle error and link deflection angle error are most distinct. The effects of the errors of other parameters on the measuring error are tiny. Moreover, Gauss-Newton method and L-M method used in the calibration of the error parameters were discussed respectively.