A3-D Shape Measurement System Based On Phase-shifting Method

The three-dimensional shape characteristics of object is the one of the mostimportant and fundamental characteristics of objects, which is also the basis forcomparing, recoding and replicating objects. Therefore, the measurement ofthree-dimensional shape of object has important significance. Three-dimensional shapemeasurement has wide and important application in real life and industrial production,such as reverse engineering, quality monitoring in industrial production, visual systemof robots, criminal detection and biomedicine. There are many ways to achievethree-dimensional shape measurement, however, as compared to other methods, opticalmeasurement method has the advantages including high accuracy, non-contact, full-field,and liable to achieve automation.Through projecting sinusoidal grating, this paper adopts4-step phase-shiftingmethod to acquire the height of object. Firstly, phase principal value shall be acquiredvia the basic principle of4-step phase-shifting method, i.e. the phase value wrappedamong [-π,+π]. Then, after analyzing and comparing different phase unwrappingmethods, quality guide the non-continuous path was adopted to obtain the right andcontinuous phase value. Finally, the height of each point in the object was obtained bythree-dimensional reconstruction. Moreover, objects of different shapes were measured,and the measured relative error and error area were analyzed. As the pictures collectedby only one CCD camera may exist shadow area, resulting in that the three-dimensionaldata obtained by measuring the objects with rapid surface height change is not complete.Therefore, double CCD cameras were adopted to collect pictures for disposing the errorarea. Moreover, as per the characteristics of face mask,180omosaic method wasadopted basing on the facial characteristics. This mosaic method was carried out tothree-dimensional data measured from different visual angles, thus the influence ofshadow area to height measurement was finally effectively avoided. Furthermore, thetransition of mosaic area was smooth and natural.On the basis of analyzing theory, and considering the measurement accuracy andpractical condition, three-dimensional shape measurement system based onphase-shifting method was designed.And it was achieved via experiment and MATLABprogramming. Moreover, three-dimensional measurement was carried out to differentobjects, and experiment was carried out to the system. The experiment result showed that this three-dimensional shape measurement system designed by this paper iseffective and feasible, and good experiment result is obtained.