Landing on unmanned surface vehicles (USV) autonomously is a critical task for unmanned aerial vehicles (UAV) due to complex environments. To solve this problem, an autonomous landing method is proposed based on a multi-level marker and linear active disturbance rejection control (LADRC) in this study. A specially designed landing board is placed on the USV, and ArUco codes with different scales are employed. Then, the landing marker is captured and processed by a camera mounted below the UAV body. Using the efficient perspective-n-point method, the position and attitude of the UAV are estimated and further fused by the Kalman filter, which improves the estimation accuracy and stability. On this basis, LADRC is used for UAV landing control, in which an extended state observer with adjustable bandwidth is employed to evaluate disturbance and proportional-derivative control is adopted to eliminate control error. The results of simulations and experiments demonstrate the feasibility and effectiveness of the proposed method, which provides an effective solution for the autonomous recovery of unmanned systems.

A gripper is the critical component of the robot end effector for the automatic harvesting of fruit, which determines whether the fruit can be harvested intact or undamaged. In this paper, a robotic gripper mechanism based on three-finger and variable-angle design is designed and analyzed for spherical or cylindrical fruit picking. Among the three fingers of the mechanical gripper, two fingers are rotatable through a pair of synchronous gears to ensure enough contact area for the grasping surfaces, which adapt to fruits of different sizes, such as cherry, loquat, zucchini, and so on. Furthermore, the mathematical relationship between gripper driving force and finger gripping force is obtained by the kinematic analysis of the gripper to realize stable grasping, and a grasping index is employed for the structural parameter optimization of our gripper. The grasping motion is analyzed, and the kinematic simulations are carried out, when the driving speeds of the gripper are 5 mm/s, 10 mm/s, and 15 mm/s, respectively. The system transfer function related to driving speed is obtained by curve fitting. Then, the grasping experiments are conducted with various spherical and cylindrical fruit, of which the weights are between 8 and 300 g and the diameters are from 9 to 122 mm. The experimental results demonstrate that our gripper has good kinematic performance and fruit adaptability. At the same time, the grasping is stable and reliable while no obvious damage appears on the fruit surface.

The energy of rotating machinery exists widely in the environment. It is of great significance to collect and utilize the energy of rotating machinery for sustainable development. In this paper, a novel piezoelectric and electromagnetic energy harvester, which is capable of generating electrical energy under rotary excitation, is proposed based on array magnetic coupling. The working principle of this kind of energy harvester is analyzed. And the energy output modeling of the harvester is developed and output results are simulated. Based on the experimental test platform built in the laboratory, the output characteristics of the piezoelectric and electromagnetic energy harvester are tested. Results show that the maximum output power of the proposed energy harvester reaches 182 mW when the excitation speed is 120 rpm. Furthermore, both the piezoelectric module and the electromagnetic module can reach the maximum output power at the excitation speed of 120 rpm.

In this paper, the mean shift (MS) tracker embedded with grey prediction is proposed for visual object tracking. As the basic model of grey prediction, grey model [GM(1,1)] is employed to predict object location with few historical information. The predicted location is taken as the initial point of MS iteration instead of the previous tracking result in the original MS tracker. The prediction equation of GM(1,1) is simplified to reduce computation, and the occlusion degree is determined by the Bhattacharyya coefficient and a set threshold. If the degree exceeds a certain limit, the MS iteration may not converge to the true result and the object location is replaced with the predicted location to prevent failure tracking. The experimental results show that the proposed approach can effectively deal with the problems of fast-moving and serious occlusion and has a better performance than the original MS tracker and the MS tracker with particle filter.

Wind energy has characteristics of abundant reserves and wide distribution. It is a feasible solution by collecting wind energy to supply sustainable power for sensors. The proposed wind energy harvester mainly consists of a wind-induced rotating unit and some electromagnetic units (EMUs). The inner permanent magnets (PMs) rotate under the drive of the wind-induced rotating unit, while the outer PMs in the EMUs move under the action of magnetic repulsion. The EMUs are evenly distributed along the circumference, and the coil fixed-magnet moving structure is adopted to reduce the difficulty of lead layout. The PMs are installed inside the coil at an inclined angle, and can achieve self-reset under the action of gravity when magnetic repulsion force is less than gravitational component along the slope. In order to explore the mechanism of the magnet reciprocating cutting magnetic flux lines in EMUs, the magnetic force changes during magnetic repulsion and self-reset movement are analyzed. The finite element method is used to analyze the influence of magnet layout on magnetic induction intensity to determine the optimal number configuration of EMUs. The experimental results show that the circumferential layout of 5 EMUs is more reasonable and the energy collected is larger, and the optimal number ratio is two inner PMs and three outer PMs, respectively. When wind speed is set to 5.5 m s⁻¹, the harvester can output a power of 6.16 mW with a load of 10 Ω and the efficiency is 13%, which significantly reduces 25%–40% reset energy loss commonly associated with traditional spring-based mechanisms.