The Probing Error And Error Of Indication For Size Measurement Of Industrial CT

Probing error and length error are some of the most basic measuring errorof the industrial CT applying in the metrology area. In this paper, the mathematicalmodel of an ideal ball is established, moreover, the influence factor andinterrelationship between the probing error and length error are also discussed.Ball-stick materials standard used for calibrating industrial CT are developed, andthe influence factor to the measuring error is analyst.Firstly, the concepts of probing error and length error are defined according tothe standards and specification at home and abroad. The ideal model of the leastsquare ball is established. Furthermore, the relationship between the relativevariation of the center of least square ball and probing point number on the surface ofthe ball, according to the measuring principle of industrial CT and some physicaltheory. This provides theoretical foundation to the establish of optimum measuringstrategy and the calibration of length error with ball standards.Secondly, some experiments based on the standard ball of Zeiss27ballsstandard, and the validity of the model is proved. According to some experimentresult, an objection is raised about the probing points number of the ball measuringstrategy in the VDI/VDE2630and ISO10360-CT.The ball measuring strategy ofindustrial CT is given as follows according to the model and experiment results: thepreferred probing points number is600-800，and the distribution of the points canrefer to the specification of CMMs.Thirdly, a type of material standard used in industrial CT is developed,including the choice of material, screen of standard balls, manufacture of sticks,assignment of ball-stick, and the holding method of ball-stick standard.At last, the length error distribution in the measuring volume of the industrialCT Metrotom1500is measured and calibrated, according to the developed materialstandard and27balls standard of Zeiss. The influence factors are analyst too.This paper provides some evidence based on theoretical and experimentalresults, to the fact that, benefit from the average effect of the ball, the probing error could make little influence to the determination of sphere center, as long as themeasuring strategy is optimized. So we can get the conclusion that the ball isappropriate to be made of standard used in the calibration of length error. Anotherwork is developing a type of ball-stick standard with traceability successfully, andcalibrating the length error of Metrotom1500. All of this provides some new methodof the research on the industrial CT in metrology application.