Abstract: A global calibration method based on two planar targets is proposed to solve the problem that the global calibration of multi-sensor vision system depends on the external high-precision measurement equipment. The coordinate frame of one of the vision sensors, called the base vision sensor, is selected as the global coordinate frame. The relative position of two planar targets is fixed according to the relative position between the base vision sensor and the vision sensor to be calibrated. The two planar targets are placed in front of the two sensors several times (at least three times) with no restriction. Each sensor catches the image of the corresponding planar target each time. Using the invariance of the relative positions between the two planar targets, the transformation from the local coordinate frame of the vision sensor to be calibrated to the global coordinate frame can be solved. Maximum likelihood estimation of the transformation matrix is achieved through non-linear optimization algorithm. The global calibration can be realized by means of pair-wise calibration. Experimental results show that the method is easy, flexible and practical in the vision inspection applications.

Key words: Flexibility, Global calibration, Machine vision, Multi-sensor vision system, Two planar targets