6. Research of Under-Sampling Technique for Digital Image Correlation in Vibration Measurement

In the field of vibration test including modal analysis, the completion of a traditional test requires many devices and takes several days due to its complex process. The development of digital image technology makes the application of the image sensor to complete vibration test and modal test possible, which is known for collecting a large amount of data within several hours. This paper developed a new testing method that targeting at operating deflecting shape vibration test based on stereo vision. Normally, it is required that the image sensor can be triggered at a very high frequency to oversample a high frequency vibration. With the application of undersampling technology, the method proposed in this paper breaks through this limitation and the camera can be triggered at less than 3 Hz to analyze structure that vibrates at more than 30 Hz. Furthermore, a timestamp-based optimization method is proposed and developed to address Jitter problem in the process of undersampling. More than two hundred test results validate the accuracy and reliability of this new method, which can satisfy the needs of operating deflecting shape modal analysis.