Coordinate unification method in large scale metrology system based on standard artifact

Aiming at the problem that the measurement error of the reference common points cannot be controlled in the coordinate unification process in field large scale metrology system, a new method is proposed, which uses field traceable standard artifact to replace the traditional method using independent common points. A standard artifact is designed; a coordinate measuring machine with higher precision is used to calibrate the spatial geometric relationships of the target points on the standard artifact, and the geometric relationships are employed for the constraints. In the field applications, the multiple large scale instruments in different stations are used to measure the target points on the standard artifact. The difference between the geometric relationships and the calibrated constraints is calculated, and the difference is compared with the preset error limit to determine whether the measurement results of the common points are effective. The method is analyzed in theory and proved in simulation. A 7 parameter coordinate registration algorithm is proposed and used to conduct spatial coordinate data registration in large scale metrology. The laser tracker, laser radar and 4 standard artifacts were employed to perform field experiment, the experiment results were compared with those of traditional methods; and using the proposed method the coordinate registration error was reduced. In order to further verify the effectiveness of the proposed method, a scale bar with known length was placed in 12 different locations in the measurement space. The mean and standard deviation of the scale bar length were calculated using the 2 group coordinate registration parameters before and after using the standard artifact constraints. The results show that the standard artifact constraint method can greatly improve the coordinate unification accuracy in large scale metrology system.