| dc.description.abstract | This study developed an automatic hole positioning and measurement system based on the
shape-from-focus technique, solving the problem of mechanical arms′ inability to accurately
align sapphire glass holes with the measurement field of view, thus achieving fully automated
measurement. The system captures images at different focus positions, uses focus value
algorithms for 3D shape reconstruction of holes, and measures hole geometry non-contactly.
The system comprises hardware and software components. Hardware includes a CCD
camera, industrial lens, low distortion macro lens, microscope lens, illumination device, and
motorized translation stages, forming a high-precision imaging and positioning system.
Software uses Python for image analysis and 3D reconstruction, while C++ controls hardware
for automated positioning. The workflow consists of automatic coarse and fine hole positioning
and 3D shape reconstruction.
Automatic hole positioning includes coarse and fine positioning. Coarse positioning
quickly moves the hole into the 2.5x microscope lens field of view using X and Y-axis
motorized stages. Fine positioning further optimizes the hole position, aligning it with the 20x
microscope lens field center. Experiments show 100% success rates for both coarse and fine
positioning, with a maximum distance of only 8 μm between the hole center and field center.
During 3D shape reconstruction, the system controls a motorized lift platform to capture
hole images at 1 μm intervals. Focus value algorithms analyze each image, calculating pixel
focus values and identifying the image position with the maximum value, determining the
relative positions of the hole entrance and exit for 3D shape reconstruction.
The study compared Roberts, Prewitt, Laplacian, Sobel, and Scharr focus value algorithms.
Results show the Scharr algorithm has the smallest relative error, maximum 1%, compared to
commercial shape analysis laser microscope measurements, outperforming other algorithms.
For system performance verification, the 20x objective measurement range is 425 μm *
III
355 μm, with lateral resolution of 0.871 μm and vertical resolution of 0.8 μm. Repeatability
experiments show 100% positioning success rate, with 1% and 1.4% errors in hole diameter
and depth, respectively. Measurement limit experiments confirm accurate 3D model
construction for hole wall angles less than 80 degrees, with 1.25% error. | en_US |