Adopting phase-shifting technique in moire topography provides many advantages in measuring complex surface profiles with varying reflectance. However, still the so- called 2(pi) -ambiguity problem remains, which limits the maximum measurable step height difference between two neighboring sample points to be less than half the equivalent wavelength of moire fringes. To cope with the problem in this investigation, a two-wavelength scheme of projection moire topography is proposed along with necessary hardware design considerations. Test results prove that the proposed scheme is capable of finding absolute fringe orders automatically, so that the 2(pi) -ambiguity problem can be effectively overcome so as to treat large step discontinuities in measured surfaces.
We present a method of projection moire specially devised for the three-dimensional inspection of printed circuit boards. This method incorporates phase-shifting technique in analyzing moire fringes so as to achieve a fine resolution of 1 micron in height measurement. Further a synchronous grating translation scheme enhances the lateral measuring resolution by inherently removing the original pattern of the reference grating in resulting moire fringes. Finally we discuss the advantages of the proposed method using several measurement results performed on the various types of solder paste silk-screened on printed circuit boards.
An industrial application of phase-shifting shadow moire interferometry for automatic 3D inspection of fine objects is presented. A line grating is used to generate shadow type moire fringes whose relative phases are readily determined by implementing the principle of phase shifting so that the surface height of the object can be measured. A special phase-measuring algorithm, named the A-bucket algorithm, is used which can precisely computes the relative phases even though there exists a significant level of errors in phase shifting due to miscalibration and external vibration. Finally, several experimental cases are discussed to demonstrate that a measuring accuracy in the order of 0.001 mm can practically be achieved.
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