Huanghuang Jin

Real-time and precise time synchronization are essential for multi-sensor fusion in simultaneous localization and mapping (SLAM) systems. Despite advances in multi-sensor time synchronization, achieving accurate, stable, and real-time synchronization is still difficult due to uncertainties like independent sensor internal clocks, transmission delays, and computational latencies. To address this issue, the authors propose a multi-sensor hard-time synchronization system (MS-HTSS) that provides deterministic time synchronization for SLAM multi-sensor fusion. A global navigation satellite system disciplined oscillator (GNSSDO) and quartz oscillator provide a unified time reference, and a ZYNQ-based hard synchronization adapter is used to synchronize high-frequency low-data-volume sensors (e.g., inertial measurement units (IMUs)) and low-frequency high-data-volume sensors (e.g., cameras). Compared to existing IMU data acquisition methods and multiple SLAM datasets, MS-HTSS’s IMU data has an average time interval of 4 ms, a time interval standard deviation of 0.001 ms, and a relative standard deviation (RSD) of 0.024%, demonstrating superior temporal precision, real-time performance, and robustness. The adapter performs hardware-level timestamping by triggering cameras with IMU signals and calculating precise image capture times, thereby mitigating transmission- and OS-induced timing errors. Experimental evaluations of FAST-LIO2 and VINS under the configurations adopted in this study demonstrate that temporally synchronized sensor data yield better trajectory accuracy and stability than unsynchronized ROS2 data. These results verify that the proposed MS-HTSS can improve the performance of open-source tightly coupled SLAM algorithms. The relevant design documents, source code, and test datasets are publicly available at https://github.com/EstherqqLiu/MS-HTSS.git.

This paper addresses the prescribed-time (PT) bounded consensus tracking problem for high-order nonlinear multi-agent systems subject to actuator faults, system uncertainties, and unmatched disturbances under directed communication topologies. A sufficient condition for PT bounded stability is established by introducing a smooth and bounded time-varying scaling function, which avoids singular time-varying scaling gains in the resulting control design. Based on this condition, an adaptive neural network-based control protocol is developed within a backstepping framework to approximate unknown nonlinear dynamics. To enhance implementability, a finite-time differentiator is incorporated to circumvent the explosion of complexity problem, while an adaptive fault compensation mechanism is constructed to address actuator effectiveness loss and bias faults. Rigorous Lyapunov analysis demonstrates that all closed-loop signals remain bounded and the consensus tracking errors converge to a small neighborhood of the origin within a user-specified time. Finally, simulation results are provided to illustrate the feasibility of the proposed approach and the bounded closed-loop behavior under the considered actuator-fault scenarios.

Despite extensive research on the effect of nitrogen flow rate on titanium nitride (TiN) coating properties, its influence on esthetic and engineering performance through microstructure control remains insufficiently explored. To simultaneously meet the requirements for surface strengthening and decorative esthetics in high-end stainless-steel crafts, TiN coatings were deposited on 304L stainless-steel substrates using multi-arc ion plating. The regulatory mechanisms and synergistic evolution laws of nitrogen flow rates (100, 200, and 300 sccm) on the microstructure, decorative properties (color and gloss), and engineering performance (adhesion strength, hardness, wear resistance, and corrosion resistance) of the coatings were investigated. At a nitrogen flow rate of 200 sccm, the coating exhibited a uniform and dense columnar crystal structure, as well as a saturated golden hue with high surface gloss. Additionally, the film–substrate adhesion, microhardness, tribological properties, and corrosion resistance reached optimal levels. In contrast, excessively low (100 sccm) or high (300 sccm) nitrogen flow rates resulted in coarse particles and blurred grain boundaries owing to uncontrolled droplet ejection or target poisoning, respectively, thereby deteriorating both appearance and engineering performance. These findings can inform the optimization of TiN coatings, enabling the design of surfaces that simultaneously meet esthetic and high-performance engineering requirements.

In our investigation of the influence rules and mechanisms of the building orientation on the surface properties of 316L stainless steel created via selective laser melting, we used X-ray diffractometry, scanning electron microscopy, and electron backscatter diffraction to investigate the phases, microstructures, and textures of specimens. In addition, we employed a digital microhardness tester, friction, and wear-testing apparatus, along with an electrochemical workstation, to examine variations in the surface properties. The results indicated that the surface phase compositions of the specimens with different building orientations were similar; however, they displayed anisotropic behavior in grain size, orientation, and texture. Notably, the surface densification of the specimens at 0°, 30°, 45°, and 60° initially decreased before subsequently increasing. In contrast, the surface roughness showed a pattern of first increasing and then declining. Moreover, the microhardness, wear resistance, and corrosion resistance decreased with an increasing inclination angle.

For the dynamic magnetic detection platform represented by airborne magnetic anomaly detection, the magnetic field measured by the vector magnetometer is easily affected by the rapid attitude change. Therefore, traditional anti-submarine aircraft are equipped with scalar magnetometers that are less affected by changes in the carrier attitude. However, the scalar magnetometer can only measure the total magnetic field signal, and its measurement information is single. It contains a time-varying environmental magnetic field signal, including the geomagnetic field, which is difficult to effectively reject. This brings great difficulties to the single real-time location of a magnetic anomaly target. This paper proposes a target correlation detection method based on the normalized magnetic moment that can effectively solve the above problems, considering the rotational invariance of magnetic anomaly measurements for dynamic magnetic exploration platforms and the efficient detection methods required for the single real-time positioning of targets. Correlation detection based on the normalized magnetic moment characteristic function and characteristic time search based on the correlation detection are included. Simulation and experimental results verify the single-point real-time positioning ability of the improved detection method within an effective operating distance. This method has strong usability for actual magnetic anomaly detection of underwater targets.

Since submarines are mostly made of ferromagnetic materials, anti-submarine warfare aircraft detect submarines using all kinds of magnetometers. In order to make the submarine magnetically silent, it is usually equipped with degaussing coils to neutralize the magnetic anomaly. However, with the increased size of the submarine, more coils are needed by conventional degaussing methods, and the degaussing system becomes complex to design and implement. To simplify the design of submarine degaussing coils and improve their degaussing accuracies, this paper presents a novel and efficient method of the degaussing coil design, which is based on the simplest equivalent model of multiple magnetic dipoles. First, the influence of the magnetic moment and spatial distribution of multi-magnetic dipoles on the equivalent effects with different spatial scales were studied. Then the simplest model of multiple magnetic dipoles was proved to capably model complex ferromagnets. We simulated the degaussing coils of a submarine by COMSOL Multiphysics software to verify the validity of the simplest modeling method and the design of the coils. The simulation results show that the magnetic anomaly induced by the submarine was reduced by at least 99% at different ranges.

In certain scenarios, such as detection of unexploded ordnance (UXO), submarines, and intruders, magnetic anomaly detection (MAD) is an effective method due to the magnetic field advantages of small operating power, strong penetrability, and strong anti-interference ability. However, variability in the background geomagnetic field and low signal-to-noise ratio (SNR) in MAD cannot be avoided. In this article, we propose a MAD method employing an improved orthogonal basis function (OBF) for the magnetic tensor contraction decomposition. The orthogonal basis decomposition approach makes the best use of modeling the MAD output signal, whereas the magnetic tensor contraction aid in avoiding the background field problem. Furthermore, by increasing the baseline length of the magnetic gradiometer, the SNR can also be improved in some manner. A dual magnetic gradiometer framework is introduced to fulfill the demand of the magnetic anomaly localization. From our simulation results, the proposed method improves the SNR of the MAD raw signal and is capable of detecting and locating the magnetic anomaly. Moreover, field test has been carried out to evaluate the performance of the proposed method.

There is always a relative motion between the magnetometer and the magnetic target. Especially when both are moving, in certain scenarios, the magnetometer is demanded to have the capability of point-by-point and real-time positioning. In this letter, we deduce normalized gradient formulas based on the total field gradient (TFG) and the tensor module gradient (TMG) of the target, respectively. In addition, we analyze the capability of these two formulas to determine the direction of the target. Afterward, the none-asphericity-error method based on the union of aforementioned formulas (TFG-TMG) is proposed. Simulation results show that the union method has no asphericity error on magnetic target localization as well as evaluating the magnetic moment of the target. Even in some noisy environment, the direction error is smaller than 1° and the mean error of the magnetic moment is smaller than 5% of the magnetic moment of the target.