An Improved Calibration Method of Grating Projection Measurement System

In the traditional fringe projection profilometry system, the projector and the camera light center are both spatially virtual points. The spatial position relationships specified in the model are not easy to obtain, leading to inaccurate system parameters and affecting measurement accuracy. This paper proposes a method for solving the system parameters of the fringe projection profilometry system, and the spatial position of the camera and projector can be adjusted in accordance with the obtained calibration parameters. The steps are as follows: First, in accordance with the conversion relationship of the coordinate system in the calibration process, the calculation formula of the vertical distance from the camera light center to the reference plane and the calculation formula of the distance between the projector and the camera light center are given respectively. Secondly, according to the projector calibration principle, the position of the projector light axis perpendicular to the reference plane is gained by comparing the parallel relationship between the reference plane coordinate system and the projector coordinate system’s Z-axis. Then, in order to fulfill the position restriction that the line between the projector light center and the camera light center must be parallel to the reference plane, the camera’s spatial location is adjusted so that the vertical distance between it and the reference plane tends to that between the projector light center and the reference plane. And finally, the three-dimensional (3D) reconstruction of the target object can be finished using the phase height model’s system parameters once the aforementioned position limitations are put into practice. Experimental results demonstrate that the method improves the measurement accuracy, and verifies that it is effective and available in 3D shape measurement.