Error Analysis and Compensation of 3D Coordinate Measuring System by Watching an Image of Object

The portable three-dimensional coordinate measuring system by watching an image of object, which consists of a light probe, a CCD camera and a laptop computer, can be widely applied in most coordinate measuring fields especially on the industrial spots. On the basis of PnP and spatial analytical geometry theory, the system´s mathematical model is established. And the analytical equations of the measured point´s coordinates are derived by using the system´s mathematical model and the restrict condition that several light sources and the probe stylus are aligned according to certain rules. The effectiveness of the mathematical model is confirmed by stimulation experiments. However, the price of the system will surge up too high to accept while the top performance hardware in practice, such as CCD camera, image captured card and etc, have to be applied in the system to obtain the high axis-oriented measurement precision, which it is unavoidable for the measurement system using a single camera. With the help of the point-shaped light sources on the light probe the inner and outer parameters of camera are first calibrated, and then the whole measurement system is set up by use of redundancy technique now. When the two sub-systems eliminate the axis-oriented error each other, which is inherent and disastrous for measurement in the single camera system, the high precision measurement is obtained by the system. The result of experiment compared to that from coordinate measurement machine (CMM) indicates that system accuracy is better than 0.15 mm with the distance of 2 m, which shows a reliable repeatability and stableness.