Analysing the penetration and droplet deposition characteristics in the canopy of fruit trees is critical for optimising the operational parameters of air-assisted spraying equipment, achieving precise application of chemicals, and improving the effectiveness of fruit tree pest and disease control. We used a mobile LIDAR system to detect the tree canopy characteristics and optical porosity and conduct wind tunnel experiments to investigate the interaction between the tree canopy, the airflow field, and the droplet penetration ratio in the canopy of fruit trees. The results show that the relative wind velocity decreases rapidly during canopy penetration, and that the minimum value occurs at the back of the canopy. The smaller the optical porosity, the greater the reduction in wind velocity is. The quadratic exponential regression model had the highest coefficient of determination (R²) (0.9672) and the lowest root mean square error (RMSE) (5.56%). This paper provides information on optimising the spraying parameters, improving the pesticide utilisation rate, and selecting the optimum spraying conditions and application parameters.

Multi-rotor plant protection Unmanned Aerial Vehicles (UAVs) have suitable terrain adaptability and efficient ultra-low altitude spraying capacity, which is a significant development direction in efficient plant protection equipment. The interaction mechanisms of the wind field, droplet, and crop are unclear, and have become the bottleneck factor restricting the improvement of the deposition quality. This paper suggests a method to study the influence of the pesticide load on the detailed distribution law of downwash for a six-rotor UAV. Based on a hexahedral structured mesh, a 3D numerical calculation model was established. Analysis showed that the relative errors between the simulated and measured velocities in the z-axis were less than 11% when the downwash air flow was stable. Numerical simulations were carried out for downwash in hover under 0, 1, 2, 3, 4, and 5 kg loads. The effect of load on the airflow was evident, and the greater the load was, the higher the wind speed of downwash would be. Then, the influence of wing interference on the distribution of airflow would be more pronounced. Furthermore, under the rotation of the rotor and the extrusion of external atmospheric pressure, the “trumpet” phenomenon appeared in the downwash airflow area. As an extension, the phenomenon of the “shrinkage–expansion” was shown in the longitudinal section under heavy load, while the phenomenon of “shrinkage–expansion–shrinkage” was present under light load. After that, based on the detailed analysis of the downwash wind field, the spray height of this multi-rotor UAV was suggested to be 2.5 m or higher, and the nozzle was recommended to be mounted directly under the rotor and to have the same rotation direction as the rotor. The research in this paper lays a solid foundation for the proposal of the three-zone overlapping matching theory of wind field, droplet settlement, and canopy shaking.

In this article, the motion control problem of hydraulic lifting systems subject to parametric uncertainties, unmodeled disturbances, and a valve dead-zone is studied. To surmount the problem, an active disturbance rejection adaptive controller was developed for hydraulic lifting systems. Firstly, the dynamics, including both mechanical dynamics and hydraulic actuator dynamics with a valve dead-zone of the hydraulic lifting system, were modeled. Then, by adopting the system model and a backstepping technique, a composite parameter adaptation law and extended state disturbance observer were successfully combined, which were employed to dispose of the parametric uncertainties and unmodeled disturbances, respectively. This much decreased the learning burden of the extended state disturbance observer, and the high-gain feedback issue could be shunned. An ultimately bounded tracking performance can be assured with the developed control method based on the Lyapunov theory. A simulation example of a hydraulic lifting system was carried out to demonstrate the validity of the proposed controller.

Multi-rotor plant protection Unmanned Aerial Vehicles（UAV）has good terrain adapt ability and efficient ultra-low altitude spraying capacity，which is one of the important development directions of efficient plant protection equipment.However，the interaction mechanisms of wind field，droplet and crop under flight operation are unclear，which has become the bottleneck restricting the improvement of the deposition distribution quality.This study aims to analyze the problems such as insufficient correlation studies and unclear deposition mechanism of various elements in the spray application of plant protection UAV.This study focuses on the whole process of generation，settlement，deposition and drift of pesticide droplet.And based on the previous research，this paper discussed the research status of spray pesticide liquid with nozzle，the interaction between the wind field and the droplet，as well as the coupling of the wind field，the droplet and the canopy.The effect of nozzle atomization on spray effect，the distribution law of wind field under hover and flight conditions of plant protection UAV，the distribution law of droplets deposition and drift in canopy under flight spary conditions were analyzed separately.Based on the above discussion，the application background，research progress and empirical models of aviation application technology at home and abroad were reviewed.Some problems that need to be solved in the spary application process of multi-rotor plant protection UAV were identified.The matching and relationships between nozzle selection（hydraulic nozzle，centrifugal nozzle，etc.）and working parameters（pressure，speed，Angle，flow，etc.），UAV flight parameters（flight speed，rotor rotation speed，etc.），pesticide characteristics（density，viscosity，surface tension，etc.）and initial parameters of liquid droplets（particle size distribution，initial velocity）are not clear，a suggestion was proposed to establish a nozzle selection decision-making expert system for multi-rotor plant protection UAV spray scene.In terms of the coupling effect of flight combination wind field（rotor downwash flow，upwind flow，natural cross wind），pesticide liquid droplets（physical property parameters after atomization），crop canopy（Stems，branches，leaves of a typical growth cycle of a crop），field environment（temperature，humidity）and operation parameters（flight speed and altitude），a proposal was put forward to establish a three-phase coupling model of combined wind field- pesticide liquid droplet-crop canopy based on scientific assumptions of deposition effects.Finally，the future development of application technology of Multi-rotor plant protection UAV was prospected.

Objective The orchard sprayer has been widely used in spray application and other related fields for orchards.However，there is a bottleneck problem that the weak wind force of the air supply system makes it difficult for the droplets at the nozzle outlet to be transported to the target canopy. Method In order to solve the problem，the design of Laval nozzle applied to air delivery nozzle was proposed.Based on the principle of airflow velocity growth in Laval nozzle，requirements for the integration of agricultural machinery and agronomy，the design principles of air assisted nozzle was derived，the parameters of throat at the end of the nozzle was also determined.The wind performance test platform of the air assisted nozzle was built，and the computational fluid dynamics（CFD）dynamic numerical simulation model of the flow field for the nozzle was also established.The results of wind field test showed that the relative error of wind speed value reached 8.5% at the strongly affected area of turbulence.Considering the influence of test error and turbulence fluctuation，it is reliable to use CFD method to assist the design of air delivery system for orchard sprayer.Based on Reynolds N-S equation and RNG k- ɛ turbulence model，transfer method of flow field parameters between interface areas，pressure based coupling scheme，the overall CFD flow field dynamics calculation model of orchard sprayer air conveying system was established. Result The results show that the design of the Laval nozzle at the end of the nozzle has a strong improvement effect on the internal wind speed of the pipeline，the maximum increase in wind speed of the air delivery system reaches 152.42%，with an average increase of 133.56%；the overall standard deviation of the output wind speed of 10 nozzles in the air delivery system is 0.66. Conclusion The air delivery system based on Laval nozzle is well-designed，the system overcomes the problem of choked phenomenon for air assisted nozzle and significantly improves the wind performance of the air delivery system.