Search

Obstacle detection algorithm of a wide baseline stereovision system (WBSS) is proposed using deep learning for unmanned surface vehicle (USV). The WBSS is designed and constructed for a 7 m-class USV, which contains two fixed-focus cameras with a baseline length for 2 m. The obstacle detection algorithm contains three parts: firstly the sea-sky line is acquired by Hough transformation in an image, then the single shot multi-box detector (SSD) is adopted to detect the obstacles around the sea-sky line, and lastly F-KAZE algorithm is used for binocular image's feature matching in a nonlinear scale space. The performance of the obstacle detection for the WBSS is tested at Jiaozhou bay in Qingdao city, and the sea experiment results prove availability and accuracy of the proposed technology. [ABSTRACT FROM AUTHOR]

Sea–sky lines (SKLs) can provide valuable reference information for the obstacle avoidance systems of unmanned surface vehicles (USVs) because obstacles that can threaten the safety of USVs, such as ships and rocks, are generally located below SKLs. Existing methods detect SKLs only using gray, texture or line features in an optical image. However, the background features in images obtained by onboard cameras are complex and change continuously over time, which leads to poor robustness of these methods. Conversely, the method that we proposed in this paper detects SKLs according to the gray variation differences in the time domain between the sky, the SKL and the sea surface when the USVs actually move on the sea. In this way, we can decrease the gray complexity of the image data of different backgrounds, which reduces interference while enhancing the edge features of the SKLs to obtain superior robustness. The proposed method is tested on optical image sequences collected by the 'Jiu Hang 490' USV. The experimental results demonstrate that the average accuracy of SKL detection is higher than that of existing methods with approximately 10% improvement while maintaining computational efficiency. [ABSTRACT FROM AUTHOR]

To investigate the influence of K/Na ratio on the phase structure and electrical properties, 0.96 (KNa) NbO-0.04 (BiNa) ZrO lead-free piezoceramics with x = 0.35 ~ 0.60 were prepared by a conventional solid-state reaction method. The results indicate that a typical phase boundary of orthorhombic-tetragonal (O-T) exists at x = 0.39-0.55 by refining the K/Na ratio. The grain size of the ceramics becomes much larger as the K/Na increases, and the chemical compositions well keep in the ceramic matrix. The ceramics with x = 0.39 show enhanced electrical properties (e.g., d = 275 pC/N, k = 34.5 %, T = 330 °C, P = 27.5 μC/cm, and E = 10.5 kV/cm). It is considered that the observed enhanced piezoelectricity should be ascribed to the phase coexistence of O and T phases of the ceramics. [ABSTRACT FROM AUTHOR]

In this study, (BaCa)(TiSn)O- xCuO (BCTS- xCuO) lead-free piezoceramics were synthesized by the conventional solid-state method in order to decrease sintering temperatures. The effect of CuO content on the microstructure and electrical properties of (BaCa)(TiSn)O (BCTS) ceramics was systematically studied. The sintering temperature of BCTS- xCuO ceramics was decreased greatly by introducing CuO, and the grain size of these ceramics slightly increased with increasing x. When sintered at a low temperature of 1300 °C, the BCTS ceramic with x = 0.5 mol% CuO demonstrated an optimum electrical behavior: d ~ 367 pC/N, k ~ 48.7 %, T = 98 °C, and 2 P ~ 23.48 μC/cm. [ABSTRACT FROM AUTHOR]

0.95(NaK)NbO-0.05(BiK)ZrTiO (abbreviated as KNN-BKZT) ceramics were prepared by the conventional solid state method, and the effect of the Ti content on the surface morphology, crystalline structure, and electrical properties of KNN-BKZT ceramics were mainly investigated. With the increase of Ti content, the temperature of the orthorhombic-tetragonal (O-T) phases transitions shifted to lower temperatures, and the O-T phase boundary of KNN-BKZT ceramics was identified in the composition with 0 ≤ x ≤ 0.3 at room temperature. It was considered that the piezoelectric properties of the ceramics were enhanced significantly owing to the more possible polarization states resulting from the coexistence of two phases. The ceramic with x = 0.2 exhibited optimum properties: d = 260 pC/N, k = 0.38, and T = 323 °C. [ABSTRACT FROM AUTHOR]