Assessment of Influence of Sample Averaging on Accuracy of Point Coordinates Measurement Performed Using Laser Tracking Systems

Abstract

Laser Tracking systems are commonly used in all branches of industry, which requires accurate large-scale measurements for instance aviation, space and shipbuilding industries. Laser Trackers belong to the group of non-Cartesian Coordinate Measuring Systems. Determination of the measured point coordinates involves the measurements of distance using laser beam and two angles recorded by horizontal and vertical encoders. Additionally, the environmental conditions are monitored and used for compensation of measured distance. The coordinates of single measured point are estimated using the results obtained from a series of samples taken in a short time period. The average value obtained from a sample is given as a result; additionally, the dispersion parameters are calculated which can be used to evaluate the probing process. This paper presents the research procedure which allows assessing the influence of chosen dispersion parameter related to the sample averaging on accuracy of the measurements performed with laser tracking devices. The procedure involves standard elements measurements during which the points with similar level of RMS parameter are used for the calculation of the measurement result. Such approach allows simulating the increasing dispersion of points taken into account during sample probing. The results presented in the article can be helpful to the operators of laser tracking systems to assess the influence of the probing process on the measurement accuracy.

Method for Accuracy Assessment of the Length Measurement Unit of Laser Tracking Systems

“…Several facilities around the world are engaged in research on methods of assessing accuracy in large-scale coordinate metrology. These include the University of North Carolina, where the general concept of laser tracking system is given by Lau et al in [2] as well as its application in industrial robot accuracy assessment, while in [3], Morse focuses on the dynamic errors of laser trackers which occur during measurements of a moving target; the National Physical Laboratory, where, in [4], the methodology of obtaining a geometrical model of tracker errors is presented by Hughes et al, which is based on measurements of a target set in predefined positions from different tracker locations, while [5] describes practical aspects of trackers calibration; the University of Zaragoza, including method for the optimization of tracker location during machine tool verification, which is presented by Aguado et al in [6], and a technique for forecasting the optimal distribution of trackers during multilateration measurements is shown by the same team in [7]; the Cracow University of Technology, where Gruza et al in [8] discuss the influence of point averaging which occurs during laser tracker measurements on the measurement uncertainty, while in [9], a tracker is treated as a reference instrument for checking the accuracy of large-scale optical measuring systems and others. Moreover, there are valuable scientific papers that fully or partially present the discussed issues together with the results of the research carried out.…”