Fringe projection profilometry is generally used to measure the 3D shape of an object. In oblique-angle projection, the grating fringe cycle is broadened on the reference surface. A well-fitted, convenient, and quick cycle correction method is proposed in this study. Based on the proposed method, an accurate four-step phase shift method is developed. Comparative experiments show that the fringe projection profilometry based on the novel phase shift method can eliminate cycle error and significantly improve measurement accuracy. The relative error of the measurement is less than 1.5%. This method can be widely employed for measuring large objects.

In panoramic three-dimensional (3D) shape measurement based on a turntable, the point cloud registration accuracy is greatly affected by the calibration of the rotating axis. To improve the calibration accuracy of the rotating axis, a calibration method based on an auxiliary camera is proposed. The calibration procedure uses a checkerboard and an auxiliary camera. Firstly, the checkerboard is rotated on the turntable to determine the rotation axis, and is used to calibrate the relative orientation of the auxiliary camera and the measurement camera, so that the two cameras have the same world coordinate system. Then, the origin point of the coordinate of the rotation axis is obtained by the auxiliary camera, and the Z-axis direction is taken as the direction of the rotation axis. Finally, the 3D shape of the multi-view is measured by the fringe projection system, and the rotation registration is completed according to the rotation axis vector. The proposed method does not need to reconstruct the 3D coordinates of multiple points when the rotating axis is calibrated. The experimental results show that the proposed method effectively improves the calibration accuracy of the rotation axis vector, and reduces the complexity of the calibration process.

A common-path laser interferometer is introduced. Its most important feature is that two optical arms are entirely in a common path. Laser Doppler and laser polarization interference technologies are used in the proposed optical system. An experiment setup is established. The primary experimental result shows that this common path method is very feasible. The resolution is 0.72 nm within a 0.01 mm range, and the highest velocity is 0.56 mm/s. There is much room to improve its performance.

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