<title>High-speed two-dimensional fringe analysis using frequency demodulation</title>

Abstract

This paper describes a new high speed 2D fringe analysis technique in the time domain using an electric circuit based on frequency demodulation. A 1D fringe analysis system based on this new technique has already been built, and its performance and characteristics were reported. With that system, a 1D fringe pattern could be processed every 10 msec. The accuracy was better than 1/20 fringe. In this paper, the principle of 1D fringe analysis is expanded to two dimensions. New electric circuits with which to process horizontal (x-) and vertical (z-) directional simultaneously were built. The paper proposes principles for the design of such circuits, which combine two outputs--one for the x- direction and the other for the z-direction. A new 2D fringe analysis system was then built using both analogue and digital processing circuits. Each fringe pattern was treated as an analogue signal synchronized with the CCD clock-pulse in the system. Using this new fringe analysis method, high- speed 2D image-processing can be realized. The system can process fourteen images a second. The characteristics of a laboratory prototype of this fringe analysis system were tested.