Study On Error Modeling And Compensation Of The Articulated Arm Coordinate Measuring Machine

Articulated arm coordinate measuring machine is a kind of non-orthogonal precision instrument based on angular measurement.It has the characteristics of simple operation,light weight,strong flexibility,wide application scenarios and large measurement space.It is mainly used in mold design and fixtures,position detection,product quality control,retrograde engineering,etc.It has a great application prospect.The main problem of the articulated arm coordinate measuring machine is the low measurement accuracy.The factors that affect the measurement accuracy can be divided into two categories: dynamic and static factors.The static factor refers to the error of the structural parameters of the measuring machine and the error of the angle encoders,etc.,such as the error of the length of the linkage,the error of the length of the joint,etc.,which can be generally decreased by kinematic calibration.The dynamic factor refers to the changing parameters of the measuring machine during the measuring process,such as measuring force and inertial force.An important method to improve measurement accuracy is to eliminate their influence on measurement accuracy.Firstly,a six-degree-of-freedom articulated coordinate measuring machine is taken as the research object,and a kinematics model based on DH(DenavitHartenberg)method.The kinematics model was verified by numerical simulation.The error model of the articulated arm coordinate measuring machine based on the DH method,and the commonly used kinematics parameter identification method is studied.The least square method was used to simulate and identify the kinematic parameters of the model.Secondly,the influence of gravity and inertial force on the measurement accuracy of the articulated arm coordinate measuring machine was studied.The software of ANASY was used to analyze the force of the articulated arm coordinate measuring machine of different materials,and the influence of inertial force on the deformation of the linkage was studied by experiments.Based on the study of the influence of gravity and inertial force on the measurement accuracy of the articulated arm coordinate measuring machine,an error correction model of the articulated arm coordinate measuring machine based on the cylindrical coordinate system is proposed.Parameters of the model can directly compensate the error of the coordinate value of the end probe.The methods of multiple nonlinear regression and RBF neural network were used to simulate the error correction model to verify the validity of the method and model.Finally,the parameters of the kinematic parameters of the articulated arm coordinate measuring machine are identified through experiments,and the parameters of the kinematic model are compensated.The experimental results show that the single-point reread accuracy is improved from 2.018 mm to 0.054 mm.The length measurement errors of the 300 mm and 500 mm standard gauge blocks are reduced respectively by 35.61% and 32.07%.On the basis of the kinematics parameter identification experiment,the proposed error compensation model is used to carry out parameter identification and error compensation experiments using the method of multiple nonlinear regression and RBF neural network.The single-point repeat accuracy in the error compensation experiment based on multiple nonlinear regression is improved by 22.64%.The length measurement errors of 300 mm and 500 mm standard gauge blocks are reduced respectively by 25.59% and 22.31%.The single point repeat accuracy in the error compensation experiment based on RBF neural network is improved by 24.52%.The length measurement errors of 300 mm and 500 mm standard gauge blocks are reduced respectively by 26.73% and 23.08%.Experimental results verify the effectiveness of the error compensation model and method proposed in this paper.