KEYWORDS: 3D image processing, Cameras, Digital image correlation, Calibration, 3D image reconstruction, 3D metrology, Speckle pattern, Digital electronics, Digital electronic circuits, Distortion
There is an urgent demand for high-accuracy, real-time three-dimensional (3-D) shape measurements in industrial production as an ideal tool for quality control. Based on 3-D digital image correlation (3D-DIC), in this study, we measured micro-stair-steps of solder paste and printed circuits on circuit boards. The 3-D shapes of the circuit boards were successfully reconstructed, and the shapes of both solder paste and printed circuits were identified with high accuracy. To evaluate the performance of the 3D-DIC method, a stylus profiler was used to conduct shape measurements for printed circuit boards (PCBs), and comparisons were made between the results of 3D-DIC and the stylus profiler. The experimental results demonstrate that: (1) printed circuits with a length of several tens of microns can be measured with an accuracy of 3 μm using 3D-DIC in a field of view of 14 × 12 mm2; (2) the time required for 3-D reconstruction was less than 1 s for a 500 × 500 image with a grid step of 3 and a subset size of 19 on a consumer-grade computer (i7 4790k CPU, 16 GB of memory), thus meeting the requirements of online and real-time shape measurements of PCBs; and (3) for printed circuit measurements, the subset size chosen should be close to or slightly larger than the width of the printed circuit.
A novel calibration method that uses a planar object to determine the relative position and orientation between the CCD camera and the projector is developed. In this method the planar object is placed at different positions and orientations in the structured light system, the projector projects grids images on the plane, and the CCD camera takes images of the grids on the object. Using the fact that the object is planar we can recover the relative position and orientation between the CCD camera and the projector. An error model is also set up to correct the aberration of the light projector. Preliminary experiments suggest that this novel calibration method is flexible and is applicable to many shape measurement tasks.
A method to measure the 3D movement and attitude of a moving object based on the theory of optical measurement is introduced. In order to measure the 3D movement and attitude of a moving object, the method uses cameras to take image sequences of the moving object and extracts the information of the moving object in the images. The extracted information mainly consists of the object edges and the cooperative man-made marks, such as ellipses, lines, angles and the ratio of length over width etc., instead of points in traditional methods.
A new method using cameras as transducers to measure the bridge displacement and vibration is developed. The method and corresponding system have the advantages of non-contact, high accuracy. Also it can dynamically measure the displacement and then derive the vibration parameters of the bridge. The accuracy of the optical measurement system can reach to 0.017mm.
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