Research And Application Of Three-dimensional Profilometry Based On Fringe Projection

With the development of science and industrial production, there has been a growing needfor three-dimensional profilometry in automated inspection, cultural creativity, biomedicine andheritage etc. And with the proficiency of full field analysis, non-contact and high precision, theprofilometry based on fringe projection has become one of the most important and popularbranches of active optical measurement.A three-dimensional profilometry system based on fringe projection has been built with adigital projector and a CCD camera. Measurement experiments of objects with discontinuoussurface were carried out for studies and the measurement system was optimized based on thelocalization requirements from tea flushes plucking robot. The profilometry algorithm was alsomajorized to adapt to the measurement of various surfaces when raising the complexity ofobject surface in order to ensure the accuracy, enhance the reliability and reduce themeasurement time.At first the phase shifting profilometry (PSP) was selected for further research bycomparing the simulation and experiment results of simple objects. Then, it was found that thenoises, discontinuities and line-like errors were caused by the uncontrollable light intensitywithin the blind spots from projection. A solution was proposed in this paper by using thedifference of light intensity to determine the blind spots, and after detected, the phase valueswould be replaced by the wrapped phase map of reference plane from the same position.A dual-frequency grating profilometry was used to improve the measurement accuracyhere. However it led to some abnormal height values, which were caused by the phaseunwrapping of high-frequency. A processing scheme was made to solve the problem: Spot thepixels with abnormal height values by considering features of height and area distribution;，and then substitute the spots by modified median filtering. Besides, in order to avoid the tediousprocess of original system calibration in fields, a new system calibration method was proposedby measuring multiple calibration blocks to solve the nonlinear system structure parametersreversely, which was more suitable for field applications. Experiments showed that theimproved system was able to measure different types of surfaces to make a better result withhigh accuracy.