Research On Evaluation Method Of Accuracy Of Laser Tracker

With the development of modern precision engineering and industrial measurement,the measurement accuracy of spatial coordinates is put forward.The traditional measuring instruments and measurement methods have been difficult to meet the requirements in terms of precision.Laser tracker with high accuracy angle and distance measurement function is quickly applied to point coordinate measurements(angular accuracy is sub-second,ranging accuracy is micron),and is widely used in precision engineering and industrial measurement.The nominal accuracy of the laser tracker is given by the instrument manufacturer according to the machining and after the test under certain experimental conditions,only for its performance.The measurement environment,instrument status and operator's difference will have an impact on the actual measurement accuracy of the laser tracker.Therefore,it is necessary to evaluate the accuracy of the laser tracker.A series of precision evaluation methods are designed to reflect the real measurement of the instrument by indirect means Accuracy,and according to the experimental results put forward some effective methods to weaken the error.Firstly,the paper introduces the development history and current situation of laser tracker,and lists several kinds of laser trackers and their parameters in the market.According to the basic structure of the laser tracker,the measurement principle is described,and the difference between the principle of laser interferometry and the IFM of laser interferometer and ADM laser absolute range finder is introduced in detail.According to the principle of polar coordinate measurement,the error formula of the point measurement of the laser tracker is deduced by the law of error propagation,which is based on the principle of polar coordinate measurement.The measurement accuracy of the laser tracker is evaluated by designing the following experiment by measuring the standard length as a true value using a long track and a laser interferometer in a metrology room:(1)It is proved that the machining error of part of the shaft can be weakened by double-sided measurement,which can reduce the error of measuring angle by repeating the fixed point of different height by laser tracker.It is found that the distance error increases with the increase of the incident angle.Therefore,it is necessary to ensure that the target ball and the instrument are in positive relation to the measurement and reduce the measurement of the incident angle.(2)The angle of rotation of the laser tracker is very small,and the error of the angle is minimized.The accuracy of the Leica AT901-LR laser tracker is evaluated by the linear regression model.With the distance less than 20 meters,it is shown that3?m + 0.7?m/m.The accuracy of the instrument is 17?m more than 20 meters.Using the Logistic Regression Model to get the accuracy of the ranging expression:y(x)=18.4/1+4.867e-0.2018x By verifying that the expression obtained by the logistic regression model can more accurately show the accuracy of the instrument in the measurement conditions By using the distance measurement error,the indirect adjustment model Accuracy of the corners,the results in line with the full range of instrument angle measurement accuracy of 15?m +6?m/m.It is proved that the angle error is the main source of the measurement error of the laser tracker,which is the best choice for the position of the instrument.(3)It is proved that the dynamic measurement accuracy of the laser tracker decreases with the increase of the measurement distance,and there is no correlation with the measurement frequency by measuring the rotation trajectory of the rotating club Ball Bar at different distance and measurement frequency.In order to measure the straightness of the cylindrical guide by measuring the circular cross section,the influence of the precision of the sampling point,the number of sampling points and the position of the distribution on the fitting result is analyzed by the least square circular curve fitting model.The number of circular cross-section sampling points in the 15 to 20 and distributed in the 3/4 range for the best choice.