Optimization and error correction of dual-path fiber point-diffraction interference projection system

The fringe projection testing technology provides a non-contact three-dimensional profile measurement method with large dynamic range for various complex surfaces. In the dual-path point-diffraction interference projection testing system, the system structure parameters could significantly influence the surface testing accuracy. The system structural parameters were optimized based on the geometric model of testing system. In view of the projection angle calibration error in dual-fiber point-diffraction probe, the traditional method based on location of zero-order bright fringe could lead to obvious measurement error, due to the fact that the light intensity of the neighboring-order fringes was too close to distinguish from each other. To address this issue, an iterative correction method based on reference plane was proposed for the projection angel calibration, and it could effectively improve the testing accuracy. To demonstrate the feasibility of the proposed method, an experimental testing system was built to test the samples with various slopes dynamic ranges. The results show that the measurement deviation between the testing system after error correction and high-precision coordinate measuring machine is reduced from 0.418 2 mm to 0.021 1 mm, and the testing accuracy in the order of microns is achieved, providing a feasible way for the high-precision testing of various complex surfaces.