Effect of System Parameters on Phase Error of Focus-Free Digital Fringe Projection Profilometry System

Digital Fringe projection profilometry (DFPP) is a noncontact, fast, accurate and flexible technique for 3D measurements. Phase calculation is an important step that affects the accuracy of measurements. in phase calculation, the critical source of error is phase error due to nonlinear gamma effect of the system. This paper introduces an experimental investigation of the nonlinear gamma effect of DFPP system as well as the effect of system parameters, such as fringe intensity, fringe period, surface distance from the camera and projector and finally the ambient illumination, on phase error and consequently system measurements. Fringe patterns are generated using Matlab 2018a and projected by digital laser projector. The deformed patterns are captured using colored CCD camera. Phase shifting technique is used to calculate phase map. The system shows a linear response in the intensity range (50-220) and has small phase error without any compensation for nonlinear gamma effect. The phase error of the system slightly increases with increasing fringe period and the surface distance from the camera and projector, while it is nearly constant with ambient illumination changes from dark to median level and shows a bigger change if the ambient is completely illuminated. In the worst conditions the phase error does not accedes 0.0387 rad without any compensation for nonlinear gamma effect, make the system a useful tool for 3D measurements in different working fields.