Research On Test Accuracy Of Dynamometer Considering The Differences Of Sensitive Units

In research of high-end equipment,accurate measurement of vector force determines the multi-device control coordination and force adaptability,which is essential for real-time control of working conditions and process adjustment.Calibration,as an important part of test,determines sensitivity coefficient of test,and directly affects accuracy of test.In calibration,the mapping relationships between force input and output at different action points are different.If the mapping relationship obtained by single loading point calibration is applied to offset force calibration,there will be a large error,which brings a great challenge to improve the test accuracy.To improve the test accuracy of the dynamometer,taking piezoelectric dynamometer in four-sensor square layout as an example,the paper researches the establishment of assembly error model for the piezoelectric three-component sensitive unit,the offset calibration algorithm of the dynamometer,the calibration of dynamometer with variable span,the optimization of layout and other aspects.Taking cross-talk of piezoelectric three-component sensitive unit caused by displacement and angle assembly error of sensor into consideration,a theoretical model of assembly error of three-component sensitive unit is established,and theory of cross-talk caused by assembly error of sensor is proposed.Through finite element analysis and deformation measurement experiments,three-dimension stiffness of relevant components is calculated.To achieve that the cross-talk of three-component sensitive unit is less than 3%,the assembly tolerance range is proposed by the theoretical model of assembly error combined with stiffness of relevant components.The piezoelectric three-component sensitive units are assembled which meet the assembly tolerance range,and the calibration experiment is performed to obtain static performance.The rationality of the assembly tolerance range is verified,and the reliability of the theoretical model is proved.The four three-component sensitive units are used to form the piezoelectric dynamometer.To solve the problem that offset loading forces of four-sensor piezoelectric dynamometer are difficult to be accurately calibrated,the multi-loading points force calibration experiments of dynamometer in three directions are performed.The calibration results are analyzed,and the difference of sensors' sensitivities is the main reason affecting the calibration accuracy of offset loading points.Applying six-dimension force test model combined three-axis sensitivities difference of four three-component sensitive units,a calibration algorithm based on the sensitivities difference of three-component sensitive units is proposed.The calibration results of dynamometer are calculated applying this method,which improves the test accuracy of offset vector force.The influence of the arrangement span of four piezoelectric three-component sensitive units on the output of dynamometer is researched.The multi-loading point calibration experiments with variable span of dynamometer are carried out.The results show that the output difference in the area of dynamometer is reduced as the increase of the span on the premise that the dynamometer has sufficient rigidity.The assembly error theoretical model of the dynamometer is established,and the output fluctuation caused by the assembly error of the sensitive units is obtained.The optimal layout theory of the four-point dynamometer is proposed,and the optimal layout scheme of the four piezoelectric three-component sensitive units is determined,and the comparative arrangement experiment is set for verification.The results show that the test accuracy of the optimal layout scheme is higher than that of the comparative arrangement,which proves the reliability of optimized layout theory.The optimal layout theory reduces the output fluctuation in the area of dynamometer,and improves the test performance of dynamometer.