Nowadays, color-coded patterns are widely used to make real-time 3D shape measurement possible based on fringe projection profilometry (FPP). However, color crosstalk between the color camera remains a primary limitation of this method. In order to reduce the influence of color crosstalk on the phase retrieval accuracy, an accurate color crosstalk coefficient calibration method is proposed for color decoupling in this work. Firstly, based on the orthogonal fringe projection mode, the influence of color crosstalk coefficients on wrapped phase error is theoretically derived. Meanwhile, the truth phase values are generated based on smooth surface polynomial fitting to eliminate phase artifacts. Finally, by projecting the designed color orthogonal fringe patterns onto a standard plate, separate images from R, G and B channel could be obtained to extract the phase error, which can be further used for color channel crosstalk coefficients calibration. Multiple experiments with a standard white plate and sphere have verified that the method effectively improves phase quality, making it suitable for fast and accurate 3D shape measurement.
High-accuracy spatial distance measurement is essential to scientific research and equipment manufacturing, and industrial production control. To meet the demand of high-performance measurement, a distance measurement approach based on microwave photonic technology is proposed, in which two electro-optic modulators are connected in series. The first one is employed for performing transmission signal and the second is used for modulating echo signal, forming a vector superposition of microwave signal. By microwave frequency sweeping, the measured distance can be resolved from the microwave amplitude spectrum. To verify the performance of the proposed approach, a proof-of-concept experiment is carried out. The measurement results show that an accuracy of ±0.5 mm is obtained.
For the trans-scale three-dimensional (3D) measurement in regular-size space and industrial applications, there are many deficiencies and application limitations for traditional measurement methods. Reference to the three axes architecture of traditional instruments, a novel non-orthogonal shafting laser sensor is proposed. The novel sensor is mainly composed of two non-orthogonal shafting laser sensing modules, and each module is made up of two one-dimensional rotary tables and one collimated laser. In the novel laser sensing module, the three axes represent a non-orthogonal shafting architecture, with no orthogonal and intersecting requirements. The manufacturing and application costs are greatly reduced. A high-accuracy calibration method based on coordinate measuring machine and image processing is introduced. An improved perspective projection transform model and attitude kinetic model described by quaternion are adopted to calculate the 3D coordinates of spatial points. The simulation and experimental results showed that a maximum error less than 0.1 mm was detected from 100 mm to 500 mm. It is proved that trans-scale 3D measurement is feasible with the proposed non-orthogonal shafting laser sensor.
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