Research On Calibration Technology For Large Target Surface Of Visual Testing System

The test accuracy of vertical large area target measurement system is influenced by the optical lens distortion, geometry accuracy, lighting conditions, linear CCD noise and many other factors. These factors are often used calibration to get. The traditional calibration methods were respectively conducted to factors by laboratory calibration. These factors have no certain independence, there are high correlation between these factors. The traditional separate calibration method is not reflects the real condition of system for vertical large area target measurement system. Therefore, doing research on the calibration of large target surface visual testing system is rather important.This paper research on calibration of the large area target linear CCD intersection measuring system, firstly built the model for the linear CCD intersected vertical target testing system. then simulated and analyzed the measurement accuracy of the system. This paper came up with a calibration method of on entire system parameters calibration which used the linear CCD camera lens distortion rectification function model. Secondly, taking into account how the sampling points distribution on the target surface and the surface fitting principle, many traditional fitting methods were analyzed, we built surface fitting calibration method that is based on the moving least, It is also analyzed the impact of these factors on the calibration accuracy by choosing a surface fitting supporting domain and weight function fitting. Compared different fitting model and a curved surface fitting model of a suitable for large target surface visual testing system was yielded. Curved surface function relation that between the actual coordinates and their imaging points is obtained by curved surface fitting, and then using a method of inversion to derivation the relation which realized the calibration of the testing system.As the result shows, the calibration method based on entire system parameters calibration for the static and known target is able to control the measurement error under5cm, the other calibration method based on the moving least squares surface fitting able to control the measurement error under3cm.Through the large target surface visual testing system calibration technology research can provide the same kind of visual testing system a more simple and effective calibration method.