THE USE OF CARRIER FREQUENCY-SHIFTING FOR THE ELIMINATION OF PHASE DISCONTINUITIES IN FOURIER-TRANSFORM PROFILOMETRY

This paper presents a novel application of frequency shifting in the Fourier transform fringe analysis technique applied to surface shape measurement In recent years little use has been made of frequency shifting, although it was a feature of the method as originally proposed. The paper shows that if the angle between fringe projection and viewing is small, it is possible to employ a frequency shift to effectively eliminate the occurrence of any wraps in the resulting phase distribution. This is obviously of value in cases where the object to be measured contains several discontinuities which would lead to a highly complex, may be unprocessable, wrapped phase distribution. The technique is presented and analysed, and its effects on measurement resolution discussed. It is illustrated with a measurement made on a populated surface mount technology printed circuit board.