A High Precision and Fast Alignment Method Based on Binocular Vision

Abstract

Alignment tasks for precision electronics manufacturing require high accuracy and low time consumption. However, in the current industrial environment, multiple servo alignment operations are often required to achieve the desired accuracy targets, which is time-consuming. In this paper, a high precision, fast alignment method based on binocular vision is proposed, which allows the accurate movement of the workpiece to the target position in only one alignment operation, without the need for a standard calibration board. Firstly, a calibration method of the telecentric lens camera is proposed based on an improved nonlinear damped least-squares method to establish the relationship between the image coordinate system and the local world coordinate system in the binocular vision system. Secondly, in order to transform the coordinates from the local world coordinate system to a unified coordinate system with the platform’s rotation center as the origin, an angle constraint-based rotation center calibration method is proposed. Thirdly, a two-stage feature point detection method based on shape matching is proposed to detect the feature points of the workpiece. Based on these, the position and pose of the workpiece are obtained. Then the alignment commands are calculated based on the current and the target position and pose of the workpiece, enabling the accurate alignment to be accomplished in one operation. Finally, taking the mobile phone’s cover glass alignment task as an example, a series of calibration and alignment experiments were carried out. The experiments and results show that the alignment errors are within ± 0.020 mm and the time taken to calculate alignment commands is less than 20 ms, which demonstrates the effectiveness of the proposed method.