| X-ray Micro-CT systems are widely used in petroleum geology,material science,biology,microelectronics,measurement and other research areas,as its nondestructive detection of samples and micrometer measuring accuracy.For the past few years,CT is also used in measurement field.However,its measurement accuracy is affected by many factors,such as geometric parameters,mechanical motion errors,environment,scanning parameters and so on.Among these,geometric parameters will directly affect all the reconstruction.What’s more,the measurement ability of CT system also needs to be evaluated.Aiming at making CT systems have measurement ability,basing on Micro-CT with dual-detector which is developed at Tianjin University,authors analysed the influence of geometric paraments,motion errors on measurement accuracy;meanwhile,different calibrators are designed and machined to calibrate probe errors and length measuring errors.Main achievements of this research work are listed as follows:1.Analyze the errors which affect CT measuemnt accuracy.According to CT imaging principle,simulate its projection process,and reconstruct 3D image.Basing on the principle of single variable,changing different geometric parameters and rotation errors,analyze the effects of different errors on measurement accuracy.Results show that,it is necessary to calibrate geometric parameters,and radial-runout and axial-runout of the rotation stage.2.Analyze rotation errors of the precision rotation stage.Mathematical model is built to calibrate rotation errors.Meanwhile,the mathematical model is revised taking the reality into account.The model is performed by off-line and on-line experiments.It is shown that,the calibration method can reduce rotation errors from 4.5μm to less than 1.5μm.What’s more,the resolution of the system is also enhanced.3.Analyze calibration methods of geometric parameters of the flat detector.Propose a math model to estimate geometric parameters of the system by using a two-plat-ball phantom.Design a position adjusting mechanism to adjust the location of the flat detector.Also,the math model is performed by experiments.4.Analyze calibration methods of geometric parameters of the CCD-coupled detector.Propose a math model to estimate geometric parameters of the system by microball.Also,the math model is performed by experiments.5.Design and machine four different calibrators to calibrate the dual-detector CT system.All the calibrators are measured and calibrated by F25 or metrological SEM.Finally,scan all the calibrators by CT system. |
