Measurement Strategies Analysis And Uncertainty Evaluation With Coordinate Measuring Machine

As a high precision measuring instrument of geometrical quantities, CMM iswidely used in modern industrial production and scientific research. However, due tothe complexity of error and diversity of measurement task, to evaluate the uncertaintyof its measurement result properly is very difficult and becomes an urgent problem inthe application of CMM. Based on the new generation of Geometrical ProductSpecification and Verification, this paper focused on measurement strategies analysis,studied several methods of uncertainty evaluation for task-oriented measurement withCMM.In the paper, firstly, the definition of task-oriented measurement uncertainty isexplained, the souces that may cause uncertainty during the measurement of CMMare analysed. The definition and scope of measurement strategy of CMM are speciallydiscussed, and the effects of measurement strategy factors on the uncertainty ofmeasurement results are studied.According to the measurement systems analysis, the method for determining theuncertainty components of task-oriented measurement with CMM is proposed, whichis based on quantum property factors. And on this basis, three typical measurementstrategyies of CMM are studied: conventional measuring method, compensationmeasuring method and alternative measuring method. The conditions, principles andprocedures of each measurement strategy are described in detail, error transferrelations and the uncertainty evaluation index during the measurement are analysised,the corresponding measurement uncertainty evaluation models are established.Meanwhile, based on the LabVIEW development platform, an uncertaintyevaluation software for CMM operators is writed. By using this software, which hasthe functions of data processing, preservation and printing of the measuring reports,etc, uncertainty of measurement with typical strategis can be evaluated.Finally, the experiment study for CMM uncertainty evaluation are carried out. Inthe measurement of diameter of workpiece, three different measurement strategies areapplicated. For each strategy, the detection schemes to assess uncertainty componentsare designed. The uncertainty model is used to obtain estimates and uncertainties ofmeasured parameter. Experimental results show that while applying differentmeasurement strategies, the uncertainty of measurement results differs greatly. To select measurement strategy reasonablely, which can reduce the uncertainty ofmeasurement effectively, has a great significance for improving the quality ofmeasurement result in the application of CMM.