Structured light technology is typical for capturing 3D point cloud data. This paper proposes a 3D reconstruction system to obtain point cloud data of complex objects based on nine-order Gray code and an eight-step structured light projection combined with a phase shift and phase unwrapping method. In this system, two projectors serve as bilateral projectors for structured light, along with a camera and rotating platforms. These components were used to obtain point cloud data from multiple perspectives, which helps avoid the shadow areas caused by a single projection angle and provides complementary point cloud data. The point clusters scanned under each perspective were transformed into the same coordinate system. Furthermore, a distance-based point cloud noise removal algorithm was proposed to optimize platform noise and facilitate point cloud data fusion. The experimental results proved that the system effectively captures 3D point cloud data for complex objects. The dimensional quantitative analysis of an aero engine blade was also performed.

Reliable and accurate calibration for a four-quadrant detector (QD) is a prerequisite for high-accuracy laser auto-collimation measurements. However, the calibration accuracy is limited largely by the non-linearity of QD, especially for large-range detection. To address this issue, an improved calibration method of QD based on Bayesian theory in laser auto-collimation measurement is proposed in this paper. First, the non-linearity problem of QD is analyzed, and for accurate calibration of QD, a high-precision identification model based on Bayesian theory is presented. An analytical expression between the output signal of QD and the position of the laser spot is established, and then a calibration system with laser drift compensation to avoid influences from the laser source as a datum is constructed. A series of experiments is conducted to verify the performance of the improved calibration method. The results reveal that the improved method can effectively enhance the calibration accuracy of QD and reduce the residuals in root mean square error by 86% compared to the 15-order polynomial fitting over a detection range of ± 1 m m . The comparison experiments also demonstrate that the proposed calibration method has advantages over the conventional method in terms of accuracy and robustness.

We propose a single-shot wavelength-selective quantitative phase microscopy by annular white-light illumination, polarization-phase-division, and parallel phase-shifting. Compared to conventional multi-wavelength incoherence digital holography, the proposed microscopy presents the following merits: no switching of illumination or mechanical scanning, high spatiotemporal phase sensitivity, and single-shot reconstruction at each wavelength. Experiments validate these characteristics by quantitative phase imaging of gratings, cells, and tissues.

This paper proposes a distortion correction algorithm based on absolute phase maps for a dual-projector, single-camera structured light 3D shape measurement system. Distortion correction is performed separately for the projector-camera pairs on the left and right. By projecting a ninth-order complementary Gray code combined with the eight-step phase-shifting method onto a white board, absolute phase maps are obtained, solving the impact of radial and tangential lens distortion. A sub-pixel level distortion error lookup table is introduced to address the influence of residual error after distortion correction on measurement accuracy, improving the overall precision by at least 95.7%. Experiments demonstrate that the dual-projector, single-camera structured light 3D shape measurement system expands the system’s measurement range while reducing shadowing issues caused by single-projector illumination. The proposed distortion correction and error compensation algorithms effectively enhance the overall measurement accuracy of the system and significantly improve issues like warping caused by distortion.

The simultaneous measurement of all six degrees of freedom of motion error for a linear stage is significantly faster than methods that measure each degree of freedom separately. However, in current simultaneous measurement methods, error crosstalk issues significantly affect measurement accuracy. In this paper, a direct and simple crosstalk decoupling simultaneous measurement method to determine the six degrees of freedom of motion error of a linear stage is proposed. Based on the combination of single-frequency laser interferometry and laser self-collimation, a novel, to the best of our knowledge, optical configuration with a complete error decoupling relationship is designed, and a mathematical model is derived for error decoupling to address the crosstalk issue. A prototype system based on the new method is developed, and experiments are conducted to verify its effectiveness. Analysis shows that, compared with a commercial laser interferometer for linear stage measurement, the deviations of the positioning, horizontal straightness, vertical straightness, roll, pitch, and yaw errors are ± 0 . 50 µ m , ± 0 . 58 µ m , ± 0 . 50 µ m , ± 1 . 02 i n . , ± 0 . 72 i n . , and ± 0 . 87 i n . respectively, over a 200 mm measurement range.