Camera automatic focus system of on-line fatigue crack propagation monitor based on VI technology

WANG Jian-miao， GAO Hong-li， CHEN Bei
（Key Laboratory of E & M， Ministry of Education & Zhejiang Province，
Zhejiang University of Technology， Hangzhou 310014， China）

Abstract： In order to improve the efficiency and accuracy of the fatigue cracks on-line detection，a camera automatic focus system of the on-line fatigue crack propagation test based on visual identity（VI） technology was supplied. The system included CCD cameras，lenses，camera PTZ，NI-PCI motion control card，a lighting system，image acquisition card，computer and installation of the image  processing software and PC motion control software. In accordance with the camera movement requirements during the image acquisition，the motion control structure was designed，the technology of automatic focus that based on image processing developed by LabVIEW platform was carefully studied，and the key focused was put on the research of the choice of the clear figure evaluation function and the design of the optimum algorithms. The software and hardware of the system were debugged. The experimental results show that this system achieves the expected function demand and accurate request.
Key words： visual identity（VI） system； camera automatic focus system； on-line monitor； fatigue crack propagation