Fringe projection profilometry for 3D measurement of objects with different depth of fields

Fringe projection profilometry (FPP) was widely used in defect detection, reverse engineering, computer vision and other fields due to its non-contact and high measurement accuracy. However, traditional FPP can only obtain the 3D profile of the measured object within limited depth of field in a single measurement, and can not achieve accurate measurement of multiple measured objects with different depth simultaneously. A mirror-assisted FPP system was constructed by adding two mirrors and two prisms on the basis of traditional FPP system in this paper. The proposed method can transform the measured objects in different depth of field ranges to the same depth of field range, so as to achieve high-precision measurement of the 3D profiles of multiple measured objects in different depth of field ranges. The effect of depth of field on 3D profile measurement results was verified using a standard six-step gypsum model. Meanwhile, the profiles of two standard table tennis within different depth of field ranges were measured using the traditional FPP system and the proposed FPP system. The table tennis radius as error results were obtained from the measured profile. The relative errors of the focused and the unfocused table tennis measured by the traditional FPP were 2.9% and 34.3%, respectively. And the corresponding measured errors by proposed mirror-assisted FPP were 2.7% and 5.3%, respectively. The results show that the proposed method can compensate the errors caused by the depth of field, and verifies the feasibility of the proposed method in 3D measurement with different depth of field ranges.