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Theses, Masters


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Publication Details

Successfully submitted for the award of Master of Philosophy (M.Phil) to the Dublin Institute of Technology 2001.


With the ever decreasing tolerances in modern manufacturing processes it has become more important to define surface topography measurements quickly and accurately. Though contact methods, using the stylus probe, have been used for a long time more optical techniques are being brought into the market place. The advantages in using optical methods is obvious; no contact with the surface eliminates damage due to a probing tip and also the surface may be scanned in a matter of seconds. Optical techniques also have the advantage that a full field of view may be acquired, unlike point measurement where the surface must be scanned many times to build up a 3 dimensional view of the surface. This thesis is concerned with the work carried out in the design and construction of a portable low cost-non contact profiler that is based on the analysis of interference fringe patterns produced by a Michelson interferometric setup. One system has been designed with the incorporation of two LabVIEW programs, with one program having the capability of profiling discontinuous smooth surfaces and the other having the capability of profiling smooth continuous surfaces. The algorithm used for profiling discontinuous smooth surfaces is based on the degree of mutual coherence that exists between two interacting beams. It analyses the visibility of the interference fringes to obtain a 3 dimensional profile of the surface. The second algorithm is based on phase shifting interferometry and uses a minimum of four intensity frames to calculate the relative phase difference of the two interfering beams. By calculating the phase difference of the two beams in the interferometer it is possible to extract the surface height of the sample. The profiler has a field of view of 3mm2, a lateral or spatial resolution of approximately 4 um with a vertical resolution between 5nm and o.06 um depending on the algorithm being used to acquire a profile. The design process and algorithms will be explained in greater detail in the proceeding chapters, also the limitations and advantages of the system will be discussed.



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