This paper presents a novel approach of camera calibration under the near-parallel condition based on geometric moments. The near-parallel condition means that the calibration board is near parallel (or parallel) to the imaging plane. A camera calibration model for the near-parallel condition and a calibration board with arranged rectangular features are suggested. Before calibration, feature regions on the image of calibration board are extracted, and centroid and rotation of each feature are detected using geometric moments. These centroids are used for feature points, and meanwhile mean value of rotations is used for the rotation around axis Z. Then, the closed-form solutions to the translations, other two angles and effective focal length are provided by combining Gauss lens model with camera model. Subsequently, principal point is received by radial alignment constraint (RAC), and distortion coefficients are calculated. Finally, all camera parameters are refined by a nonlinear minimization procedure according to the distortion coefficients. Simulations and experiments are performed to verify the proposed camera calibration algorithm. The precision of detecting feature points and calibrating camera parameters are analyzed. The precision of camera calibration results is also evaluated.
In this paper, a calibration method to improve the accuracy of MEMS Wire Bonder is presented. With the requirements
of high accuracy and high speed in wire bonding, vision system has become one of important factors which influence the
precision of MEMS packaging. It can be used as a feedback of control system to fulfill the requirement of accurate
locating. A positioning system using computer vision technology has been designed to obtain high locating accuracy
during wire bonding. The calibration of this system is the assurance to get distorting parameters and the relationship of
all coordinate systems. Usually, Zhang's camera calibration method is widely used to get high accurate camera
calibration results. But this method was only applied in normal imaging system. In this paper, the method is improved to
be applied in micro-imaging system used for MEMS Wire Bonder. Combining the camera pinhole model and the Gauss
lens law, the micro-imaging camera model is established. Certain smaller rotation angles are adopted to get acceptable
calibration results. Simulations and experiments are performed to validate the proposed method with satisfied results.