| The Articulated Arm Coordinate Measuring Machine(AACMM)is widely used in the field of geometry measurement because of its advantages such as large measuring space,simple operation,easy to carry and convenient for field measurement.However,due to the series open chain structure,the probe error is amplified step by step.Kinematic calibration is one of the important means to improve the measurement accuracy.This paper focuses on how to improve the global measurement accuracy of AACMM by the mean of calibration.The main work includes the following aspects:Firstly,the mathematical model of AACMM was constructed.The principle of coordinate transformation between joints was analyzed and the kinematics model of AACMM was established.The error sources that affect the measuring accuracy of the measuring machine were analyzed to determine the relationship between the error sources and kinematic parameters.The probe position error model and the total differential error model were established.Finally,the accuracy of the error model was verified by numerical method.Secondly,the global measurement space of the AACMM was solved,and the influence of parameter coupling error of the single point measurement error and plane measurement error of the measuring machine was analyzed.The kinematic inverse solution method was used to calculate the attitude of single point measurement,and the scatter diagram of parameter coupling error was drawn,so as to determine the relevant parameters that affecte the measurement accuracy of the AACMM.The influence rule of joint angular error on plane measurement of coordinate measuring machine was summarized,and the best measuring area was selected to guide the field operation.Then,the influence of single point calibration and length reference calibration on the spatial accuracy of the measuring machine was studied.In order to improve the global space measurement accuracy of the AACMM,the influence of single point calibration and length reference calibration on the space measurement accuracy was compared and analyzed.This paper presents a global calibration method based on the length benchmark,which greatly improves the global measurement accuracy of the measuring machine.Finally,the experimental system was set up for the experimental study of the global calibration method.The precision of global space measurement was compared between the single point calibration method and the global calibration method.The experimental results show that the proposed global calibration method improves the global space measurement accuracy of the AACMM and can guide the practical operation and field use. |
