Test sieves with dense grid structure are widely used in many fields, accurate gird size calibration is rather critical for success of grading analysis and test sieving. But traditional calibration methods suffer from the disadvantages of low measurement efficiency and shortage of sampling number of grids which could lead to quality judgment risk. Here, a fast and precise test sieve inspection method is presented. Firstly, a coaxial imaging system with low and high optical magnification probe is designed to capture the grid images of the test sieve. Then, a scaling ratio between low and high magnification probes can be obtained by the corresponding grids in captured images. With this, all grid dimensions in low magnification image can be obtained by measuring few corresponding grids in high magnification image with high accuracy. Finally, by scanning the stage of the tri-axis platform of the measuring apparatus, whole surface of the test sieve can be quickly inspected. Experiment results show that the proposed method can measure the test sieves with higher efficiency compare to traditional methods, which can measure 0.15 million grids (gird size 0.1mm) within only 60 seconds, and it can measure grid size range from 20μm to 5mm precisely. In a word, the presented method can calibrate the grid size of test sieve automatically with high efficiency and accuracy. By which, surface evaluation based on statistical method can be effectively implemented, and the quality judgment will be more reasonable.
A method for real-time three-dimensional (3D) imaging based on Hilbert transform is proposed. Based on the properties
of Hilbert transform and De Bruijn sequence, we design an encoding technique based on color fringe patterns to realize
3-D reconstruction of the phase distribution and range images. The calculation of phase map is implemented by using
two sinusoidal fringe patterns with phase shifting 0 and π / 2 each other. Two phase-shifted fringe patterns are assigned
to the red and blue channel of a color pattern, respectively. The phase unwrapping is accomplished with aid of the De
Bruijn sequence pattern stored in the green channel. The experiment results show that the proposed method can not only
acquire 3D data in real-time and one-shot fashion, but also obtain high-resolution and high-density range image data
without any error propagation.