Improved separated-parameter calibration method for binocular vision measurements with a large field of view.

Large field-of-view (FOV) calibration is indispensable to ensure the accuracy of vision measurement systems for large aviation components. We propose an improved separated-parameter calibration method for large-FOV binocular vision measurements with a high flexibility and accuracy. Firstly, the camera parameters are separately calibrated according to the sub-area features of image. Subsequently, based on the spatial-calibration accuracy, a stereoscopic calibration object is devised. The mean error of the proposed method is experimentally obtained as 0.13 mm for a FOV of 2.0 m × 1.5 m. Its feasibility and effectiveness for the measurement in the field is validated by workshop calibration.

A Knowledge-Driven Approach for 3D High Temporal-Spatial Measurement of an Arbitrary Contouring Error of CNC Machine Tools Using Monocular Vision.

Periodic health checks of contouring errors under unloaded conditions are critical for machine performance evaluation and value-added manufacturing. Aiming at breaking the dimension, range and speed measurement limitations of the existing devices, a cost-effective knowledge-driven approach for detecting error motions of arbitrary paths using a single camera is proposed. In combination with the PNP algorithm, the three-dimensional (3D) evaluation of large-scale contouring error in relatively high feed rate conditions can be deduced from a priori geometrical knowledge. The innovations of this paper focus on improving the accuracy, efficiency and ability of the vision measurement. Firstly, a camera calibration method considering distortion partition of the depth-of-field (DOF) is presented to give an accurate description of the distortion behavior in the entire photography domain. Then, to maximize the utilization of the decimal involved in the feature encoding, new high-efficient encoding markers are designed on a cooperative target to characterize motion information of the machine. Accordingly, in the image processing, markers are automatically identified and located by the proposed decoding method based on finding the optimal start bit. Finally, with the selected imaging parameters and the precalibrated position of each marker, the 3D measurement of large-scale contouring error under relatively high dynamic conditions can be realized by comparing the curve that is measured by PNP algorithm with the nominal one. Both detection and verification experiments are conducted for two types of paths (i.e., planar and spatial trajectory), and experimental results validate the measurement accuracy and advantages of the proposed method.

A Novel Vision-Based Pose Measurement Method Considering the Refraction of Light.

Nowadays, due to the advantages of non-contact and high-speed, vision-based pose measurements have been widely used for aircraft performance testing in a wind tunnel. However, usually glass ports are used to protect cameras against the high-speed airflow influence, which will lead to a big measurement error. In this paper, to further improve the vision-based pose measurement accuracy, an imaging model which considers the refraction light of the observation window was proposed. In this method, a nonlinear camera calibration model considering the refraction brought by the wind tunnel observation window, was established first. What's more, a new method for the linear calibration of the normal vector of the glass observation window was presented. Then, combining with the proposed matching method based on coplanarity constraint, the six pose parameters of the falling target could be calculated. Finally, the experimental setup was established to conduct the pose measurement study in the laboratory, and the results satisfied the application requirements. Besides, experiments for verifying the vision measurement accuracy were also performed, and the results indicated that the displacement and angle measurement accuracy approximately increased by 57% and 33.6%, respectively, which showed the high accuracy of the proposed method.

Improved camera calibration method based on perpendicularity compensation for binocular stereo vision measurement system.

High-precision calibration of binocular vision systems plays an important role in accurate dimensional measurements. In this paper, an improved camera calibration method is proposed. First, an accurate intrinsic parameters calibration method based on active vision with perpendicularity compensation is developed. Compared to the previous work, this method eliminates the effect of non-perpendicularity of the camera motion on calibration accuracy. The principal point, scale factors, and distortion factors are calculated independently in this method, thereby allowing the strong coupling of these parameters to be eliminated. Second, an accurate global optimization method with only 5 images is presented. The results of calibration experiments show that the accuracy of the calibration method can reach 99.91%.

Cellulose nanocrystal thermal smart molecular brushes with upper critical aggregation temperature.

Grafting thermo-responsive polymers onto cellulose nanocrystals (CNCs) and achieving critical temperature regulation has drawn significant research interest. The thermal transition behavior of CNCs can be controlled by adjusting the polymer molecular brushes on the CNCs surface. We synthesized poly((2-dimethylamino) ethyl methacrylate) (PDMAEMA) grafted CNCs via surface-initiated reversible addition-fragmentation chain transfer, followed by modifying PDMAEMA brushes into poly-3-dimethyl(methacryloyloxyethyl) ammonium propane sulfonate (PDMAPS) brushes via quaternization. The critical temperature was regulated by modifying and grafting of poly (ethylene glycol) methacrylate. Found the thermal stimulus-responsive type and transition point of CNCs can be controlled by adjusting the surface molecular brushes. Ultraviolet-visible spectroscopy and dynamic light scattering analyses indicated that CNC-PDMAEMA aggregated above 70 °C, whereas CNC-PDMAPS aggregated below 31 °C. The thermo-responsive materials based on CNCs exhibited a conversion from a lower critical aggregation temperature to an upper critical aggregation temperature (UCAT) type. CNC-PDMAPS-mPEG was obtained by modifying and grafting for UCAT to be regulated to approximately 37 °C, which is close to the human body temperature. CNC-PDMAPS and CNC-PDMAPS-mPEG exhibited only microscopic alterations and could encapsulate and release substances. Therefore, they demonstrate considerable potential for biomedical applications.

Self-Assembly of a 3D Hollow BiOBr@Bi-MOF Heterostructure with Enhanced Photocatalytic Degradation of Dyes.

Considering the flexibility, adjustable pore structure, and abundant active sites of metal-organic frameworks (MOFs), rational design and fine control of the MOF-based hetero-nanocrystals is a highly important and challenging subject. In this work, self-assembly of a 3D hollow BiOBr@Bi-MOF microsphere was fabricated through precisely controlled dissociation kinetics of the self-sacrificial template (BiOBr) for the first time, where the residual quantity of BiOBr and the formation of Bi-MOF were carefully regulated by changing the reaction time and the capability of coordination. Meanwhile, the hollow microstructure was formed in BiOBr@Bi-MOF through the Oswald ripening mechanism to separate photogenerated electron-hole pairs and increase the adsorption capacity of Bi-MOF for dyes, which significantly enhanced the photocatalytic degradation efficiency of RhB from 56.4% for BiOBr to 99.4% for the optimal BiOBr@Bi-MOF microsphere. This research broadens the selectivity of semiconductor/MOF hetero-nanocrystals with reasonable design and flexible synthesis.

Investigation of Damage Reduction When Dry-Drilling Aramid Fiber-Reinforced Plastics Based on a Three-Point Step Drill.

Aramid fiber-reinforced plastic (AFRP) is widely used in bullet-proof and armor structures, and is difficult to drill because of the high-toughness aramid fibers with ductile fracturing-differently from carbon fiber. Therefore, drilling quality cannot be ensured by the drilling used for carbon fiber-reinforced plastic, and frequently, delamination and burrs occur in the drilling process. This article first established a two-dimensional cutting model for analyzing the fiber deformation and material interface cracking. According to the model, reducing the thrust force and the radial force of the edge on the fibers is an effective way to reduce the fiber deformation, and a three-point step drill is proposed further. Comparative experiments were carried out among twist drilling, candle core drilling and three-point step drilling under three drilling parameters. The results show that the three-point step drill changed the traditional cutting behavior on the drill-exit material into a compound process. Finally, the AFRP was cut effectively with the novel drill with a small thrust force, and the delamination and "burrs area" were reduced through different drilling parameters. In summary, the three-point step drill can drill the AFRP without delamination and burrs with 0.02 mm/rev, which provides a new solution of cost-effective production for AFRP manufacturers.