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When traversing soft and rugged terrain, a planetary rover is susceptible to slipping and sinking, which impedes its movement. The real-time detection of wheel sinkage in the planetary wheel-on-limb system is crucial for enhancing motion safety and passability on such terrain. Initially, this study establishes a measurement of wheel sinkage under complex terrain conditions. Subsequently, a monocular vision-based wheel sinkage detection method is presented by combining the wheel–terrain boundary with the wheel center position (WTB-WCP). The method enables the efficient and accurate detection of wheel sinkage through two-stage parallel computation of the wheel–terrain boundary fitting and wheel center localization. Finally, this study establishes an experimental platform based on a monocular camera and the planetary rover wheel-on-limb system to experimentally validate and comparatively analyze the proposed method. The experimental results demonstrate that the method effectively provides information on the wheel sinkage of the planetary rover wheel-on-limb system, and the relative errors of the method do not exceed 4%. The method has high accuracy and reliability and is greatly significant for the safety and passability of planetary rovers in soft and rugged terrain. [ABSTRACT FROM AUTHOR]

The existing formulas for the synthetic aperture radar (SAR) Doppler centroid estimation standard deviation (STD) suffer from various limitations, especially for a dynamic sea surface. In this study, we derive an improved version of these formulas through three steps. First, by considering the ocean wavenumber spectrum information, a new strategy for determining the number of independent samples of the sea wave velocity field is adopted in the new formula. This is contrary to the method used in the existing formulas, where the number of SAR geometric resolution cells is taken as the number of samples assuming that adjacent SAR resolution cells are statistically uncorrelated. Second, the pulse repetition frequency and Doppler bandwidth are decoupled in the new formula, unlike in the existing formulas where they are unchangeably related to each other. Third, the effects of thermal noise and Doppler aliasing are jointly quantified in a mathematically exact manner instead of being treated separately, as in the existing formulas. Comprehensive SAR raw data simulations for the ocean surface show that the new formula has a better performance in predicting the Doppler centroid estimation STD than the existing formulas. [ABSTRACT FROM AUTHOR]

Metal-matrix-impregnated diamond composites are used for fabricating many kinds of diamond tools. In the efforts to satisfy the increasing engineering requirements, researchers have brought more attention to find novel methods of enhancing the performance of impregnated diamond composites. In this study, deep cryogenic treatment was applied to Fe–Co–Cu-based diamond composites to improve their performance. Relative density, hardness, bending strength, and grinding ratio of matrix and diamond composite samples were measured by a series of tests. Meanwhile, the fracture morphologies of all samples after the bending strength test were observed and analyzed by scanning electron microscope. The results showed that the hardness and bending strength of matrix increased slightly after deep cryogenic treatment. The grinding ratio of impregnated diamond composites exhibited a great increase by 32.9% as a result of deep cryogenic treatment. The strengthening mechanism was analyzed in detail. The Fe–Co–Cu-based impregnated composites subjected to deep cryogenic treatment for 1 h exhibited the best overall performance. [ABSTRACT FROM AUTHOR]

Metal matrix-impregnated diamond composites are widely used for fabricating diamond tools. In order to meet the actual engineering challenges, researchers have made many efforts to seek effective methods to enhance the performance of conventional metal matrices. In this work, tungsten carbide (WC) nanoparticles were introduced into WC-Bronze-Ni-Mn matrix with and without diamond grits for improving the performance of conventional impregnated diamond composites. The influence of WC nanoparticles on the microstructure, densification, hardness, bending strength and wear resistance of matrix and diamond composites were investigated. The results showed that the bending strength of matrix increased up to approximately 20% upon nano-WC addition, while densification and hardness fluctuate slightly. The grinding ratio of diamond composites increased significantly by about 100% due to nano-WC addition. The strengthening mechanism was proposed according to experimental results. The diamond composites with 2.8 wt% nano-WC addition exhibited the best overall properties, thus having potential to apply to further diamond tools. [ABSTRACT FROM AUTHOR]

The collision between the boom of the autocrane and the obstacle may cause serious equipment damages or casualties. With the development of 6G technology, data between multiple autocranes could be shared in real time, which makes it possible to finely control the autocranes. In order to avoid collision accidents, a collision avoidance strategy is proposed in this paper. This strategy focuses on the evaluation of the collision urgency and different evaluation methods are designed to match the three basic exercise modes of the boom. Based on the collision urgency, the control strategy is then put forward to ensure the boom's safety in every collision risk level. Additionally, two special cases are also considered to guarantee that all parts of the boom, except for the end, will not hit the obstacle. Lastly, a semi-physical testing platform is established to test the performance of the proposed collision avoidance strategy. [ABSTRACT FROM AUTHOR]

Measurements of ocean surface currents in coastal waters are crucial for improving our understanding of tidal atlases, as well as for ecosystem and water pollution monitoring. This paper proposes an improved method for estimating the baseline-to-platform speed ratio (BPSR) for improving the current line-of-sight (LOS) velocity measurement accuracy in coastal waters with along-track interferometric synthetic aperture radar (ATI-SAR) based on eigenvalue spectrum entropy (EVSE) analysis. The estimation of BPSR utilizes the spaceborne along-track interferometry and considers the effects of a satellite orbit and an inaccurate baseline responsible for azimuth ambiguity in coastal waters. Unlike the existing methods, which often assume idealized rather than actual operating environments, the proposed approach considers the accuracy of BPSR, which is its key advantage applicable to many, even poorly designed, ATI-SAR systems. This is achieved through an alternate algorithm for the suppression of azimuth ambiguity and BPSR estimation based on an improved analysis of the eigenvalue spectrum entropy, which is an important parameter representing the mixability of unambiguous and ambiguous signals. The improvements include the consideration of a measurement of the heterogeneity of the scene, the corrections of coherence-inferred phase fluctuation (CPF), and the interferogram-derived phase variability (IPV); the last two variables are closely related to the determination of the EVSE threshold. Besides, the BPSR estimation also represents an improvement that has not been achieved in previous work of EVSE analysis. When the improved method is used on the simulated ocean-surface current LOS velocity data obtained from a coastal area, the root-mean-square error is less than 0.05 m/s. The other strengths of the proposed algorithm are adaptability, robustness, and a limited user input requirement. Most importantly, the method can be adopted for practical applications. [ABSTRACT FROM AUTHOR]

A metal-based matrix is usually used for the fabrication of diamond bits in order to achieve favorable properties and easy processing. In the effort to reduce the cost and to attain the desired bit properties, researchers have brought more attention to diamond composites. In this paper, Fe-based impregnated diamond composites for drill bits were fabricated by using a pressureless infiltration sintering method at 970 °C for 5 min. In addition, boron was introduced into Fe-based diamond composites. The influence of boron on the density, hardness, bending strength, grinding ratio, and microstructure was investigated. An Fe-based diamond composite with 1 wt % B has an optimal overall performance, the grinding ratio especially improving by 80%. After comparing with tungsten carbide (WC)-based diamond composites with and without 1 wt % B, results showed that the Fe-based diamond composite with 1 wt % B exhibits higher bending strength and wear resistance, being satisfactory to bit needs.

Metal matrix-impregnated diamond composites are widely used in diamond tool manufacturing. In order to satisfy the increasing engineering requirements, researchers have paid more and more attention to enhancing conventional metal matrices by applying novel methods. In this work, ZrO₂ nanoparticles were introduced into the WC-bronze matrix with and without diamond grits via hot pressing to improve the performance of conventional diamond composites. The effects of ZrO₂ nanoparticles on the microstructure, density, hardness, bending strength, and wear resistance of diamond composites were investigated. The results indicated that the hardness and relative density increased, while the bending strength decreased when the content of ZrO₂ nanoparticles increased. The grinding ratio of diamond composites increased significantly by 60% as a result of nano-ZrO₂ addition. The enhancement mechanism was discussed. Diamond composites showed the best overall properties with the addition of 1 wt % ZrO₂ nanoparticles, thus paving the way for further applications.

This research was carried out to investigate the influence of Sr-Sb on the microstructures and mechanical properties of Al-18 wt % Mg₂Si-4.5Cu alloys. After the addition of 0.2 wt % Sr-Sb, the morphologies of primary Mg₂Si transformed from equiaxed dendrite to cube in as-cast alloys and the average size of primary Mg₂Si decreased from ~50 to ~20 μm. The shape of eutectic Mg₂Si changed from Chinese script to short rod. After extrusion and T6 heat treatment, the ultimate tensile strength of modified alloy at room temperature (RT) and 100 °C increased respectively from 229 to 288 MPa, and from 231 to 272 MPa. The elongation-to-failure only slightly improved from 2.9% to 3.8% and from 3.3% to 3.7% at RT and 100 °C, respectively. The tensile fracture surface revealed a transition from brittle fracture to ductile fracture after modifying by 0.2 wt % Sr-Sb.