Calibration Of Industrial CT's Geometry Measuring Error

In recent years,industrial CT is becoming more and more popular not only in the nondestructive testing,but also in the geometry measurement,benefiting from its excellent capability of making non-contact,non-destructive measurements of the internal and external structure of work pieces.However,the calibration method of ICT's dimensional measurement ability still can't reach an agreement now,due to its complicated working principle.Some material standards used to calibrate the industrial CT's geometry measuring error are developed.As to the industrial CT's probing error,a kind of ball standard used is developed.The mainbody of the ball standard is a kind of ceramic?Si₃N₄?standard ball,with diameters of 4mm,8mm,15mm,25mm,50mm.The diameter and roundness of standard balls are calibrated by F25 coordinate measuring machine and Talyrond 73 roundness measuring machine separately.As to the industrial CT's length measuring error,a small forest-ball and a ball-plate are developed,which are made by ruby balls fixing on carbon fiber bars and carbon plate separately.These two material standards are calibrated by F25 coordinate measuring machine.The calibrated ball standards are applied to the calibration of industrial CT's probing error.Experiment research is carried out to observe the impact of the industrial CT's settings,sampling strategy and some other factors during the measurement to the probing error.The result indicates that the industrial CT's probing error can be greatly affected by the settings,the size of ball standard,sampling strategy and so on.In this paper,the strategy of sampling 200 points on the episphere is recommended,and to make the calibration result more convinced,a statement about the size and material of the ball,and the industrial CT's settings should be made.The industrial CT's length measuring error can be classified to sphere distance error and plane distance error according to the material standard used during the calibration.Some calibration experiments about the industrial CT's sphere distance error and plane distance error are carried out with different material standards.The experiment result demonstrates that the industrial CT's sphere distance error is much smaller than the plane distance error.The sphere distance error can reflect the intrinsic measuring accuracy of the machine directly,because it's not affected by the material of the standard.However,the plane distance error is greatly affected by the material,and it's more similar to the real measuring situation.These two kinds of errors are suitable for different conditions,so they should be treated differently at different occasions.