Study On Thermal Error Modelling And Compensation Of Articulated Arm Coordinate Measuring Machines

The articulated arm coordinate measuring machine is a new kind of multiple degrees of freedom nonorthogonal coordinate measuring device.Because of its high flexibility and good portability,it is widely used in aerospace,machinery manufacturing,auto ship areas’ industrial field on-line inspection and quality control.The thermal error caused by the change of ambient temperature in industrial field is an important factor affecting the precision of articulated arm coordinate measuring Machine.In this paper,a general articulated arm coordinate measuring machine with six degrees of freedom is taken as the research object.Based on the kinematics modeling and finite element analysis,the thermal deformation law of the kinematics parameters of the articulated arm coordinate measuring machine is obtained,and the thermal error compensation model is established.An experimental platform for thermal error compensation of articulated arm coordinate measuring machine was built,and the thermal error compensation model was verified experimentally.The kinematics model of articulated arm coordinate measuring machine is established by D-H(Denaveit-Hartenberg)method,and the correctness of the model is verified by means of graphics and numerical simulation.The factors affecting the measuring accuracy of articulated arm coordinate measuring machine are analyzed,and the corresponding error model is established.The three-dimensional model of the articulated arm coordinate measuring machine was established,and the finite element analysis was carried out to obtain the thermal deformation regulation of each joint,,the variation regulation of probe error and measurement poses under different temperatures.The corresponding relationship between the kinematic parameter errors and temperature changes was established,and a virtual coordinate measurement method was proposed.By extracting the coordinates of the surface nodes after thermal analysis for fitting,the kinematic parameters after thermal deformation were measured by coordinate measurement software.Through analysis,it is found that the temperature change has little effect on the single point repeatability accuracy of articulated arm coordinate measuring machine,but has a significant effect on the measurement accuracy of the spatial distance.Based on the results of numerical analysis,the relationship between the length parameters of each joint and temperature was fitted by BP neural network,and the corresponding thermal error compensation model was established.Through the different positions of the space points,the inverse kinematics is used to solve the joint angle and put it into the compensation model for simulation verification at the corresponding temperature.The results show that the spatial distance measurement error is greatly reduced after the thermal error compensation,and the repetition accuracy of the single point is basically unchanged,which effectively improves the measurement accuracy of the articulated arm coordinate measuring machine.The calibration device is designed and the thermal error compensation experimental platform is built for experimental research.Based on the kinematics parameter identification method,the calibration experiments were carried out at the reference temperature.After calibration of the articulated arm coordinate measuring machine,the repeatability accuracy of the single point cone measurement and the measurement accuracy of the spatial distance measurement were greatly improved compared with that before the calibration.The experiment was carried out in the working temperature range.The results show that the thermal error compensation model established in this paper can improve the spatial distance accuracy of articulated the arm coordinate measuring machine greatly,which effectively reduces the influence of thermal error on its accuracy,and improves its stability.