Kalman Filter-Based Coarse-to-Fine Control for Display Visual Alignment Systems

A coarse-to-fine two-stage control method is investigated for the display visual alignment systems. The proposed visual servo is with hierarchical loops, where the original fine but slow vision loop is necessary for the exact localization of alignment marks while the coarse but fast vision loop of exploiting pruned image data is to compensate for the mask-panel misalignment. The degraded resolution of the reduced images is recovered in terms of the Kalman filter which tracks the mark centroids in near real-time. In order to construct the recursive estimation algorithm, the motion model for the moving alignment marks is determined by solving the forward kinematics of positioning mechanism and the measurements from vision sensors are given by means of the geometric template matching (Kwon and Hwang, “Kinematics, pattern recognition, and motion control of mask-panel alignment system,” Control Eng. Practice, vol. 19, pp. 883–892, 2011). Compared with the conventional alignment methods, this approach enables a fast and fine alignment control. Experimental results are followed to validate the proposed control framework.