Abstract
A real-time method is developed for measuring 3-dimensional profiles from fringe patterns generated by moiré-topography or a deformed grating method. This paper presents theoretically relationship between object shapes and phases of fringes. It also describes the construction of an experimental system which uses a Digital Phase-Locked Loop (DPLL) circuit. Furthermore, experimental results that confirm the DPLL circuit's performance are reported. In the system, a video-camera scans the fringe patterns across the array of fringe stripes. The video signal has a sine-wave form. The low frequency component of the wave is eliminated by a high-pass filter and its output is digitized by an A/D converter. The phase restoration of the digital signal is performed by the DPLL circuit. The obtained phase signal is proportional to relative distance between the camera and the object. Then the phase signal is converted into analog signal by a D/A converter and the results are displayed as gray-level images on a CRT monitor and also as perspective diagrams on an oscilloscope. An exact profile of the object can be obtained at the video-rate with this method.
