Search

A control algorithm of fuzzy-PID controller with variable universe (VUFPID) was proposed to realize fast and accurate adjustment of tillage depth control on tractor-implement and adapt to the complex and changeable agricultural environments. The electro-hydraulic hitch system was modeled through transfer functions of the electrically operated hydraulic valve and the hydraulic cylinder. And the VUFPID controller was designed in accordance with the error of tillage depth and the error rate of tillage depth. Then, the designed controller was simulated by comparing with PID controller and fuzzy PID controller. Also, field experiments were conducted to assess stability of the proposed controller. According to the simulation results, the proposed controller can adjust the hitch system to the set depth more quickly and steadily than the other controllers, with the minimum tracking error of 1.13 mm for the simulation with sine signal, and the shortest response time of 0.261 s and lowest overshoot of 12.4% for the simulation with step signal. As for the field experiments, the results are in good agreement with the simulation results, and the proposed controller shows good stability with the maximum error of tillage depth of 7.8% at the set depth of 10–20 cm. The proposed controller has good adaptability and anti-interference in tillage depth control.

Collision avoidance ability is very important for autonomous agricultural vehicles, but the influence of different obstacles in agricultural environment is rarely taken into account. In this paper, a velocity control strategy for collision avoidance was proposed to adjust the velocity of autonomous agricultural vehicles according to the movement state and dangerous degree of the obstacles and the distance between the obstacles and the vehicles, thus to improve intelligence and safety of the vehicles. The control strategy involved two steps: collision prediction in dynamic environments with an improved obstacle space–time grid map, and velocity generator for collision avoidance with a cloud model. Simulations were conducted on the obstacle collision prediction and the designed cloud generator for velocity control respectively. Simulation results show that the proposed strategy can effectively predict collision with anti-disturbance ability for threat-free obstacles and rapid and accurate velocity output. And it realizes the real-time operation in dynamic environments with an average time of 0.2 s to predict collision. Additionally, field experiments including five trial schemes were performed to test the proposed velocity control strategy on an agricultural robot, where a haystack, a tractor and walking persons were regarded as static or dynamic obstacles. The results of the field experiments show that the proposed velocity control strategy has strong feasibility and effectiveness.

This paper proposed a structural design scheme of the hydraulic device of the electro-hydraulic controlled hitch system of a YM554A horticultural tractor with hydraulic device model, and the designed hydraulic device was simulated and tested to verify its performance. Results show that the motion of hydraulic actuator is stable with good response for tillage depth control, while the maximum lifting force of 10.62kN and the static settlement value of 13mm all meet the standard requirements. And the oil pressure changes rapidly with a large fluctuation with the plough position changed from transportation state to tillage state, but it quickly stabilizes, and as the tillage depth becomes larger, the oil pressure drops but remains basically stable with the maximum oil pressure change of 0.35MPa.

Before predicting the vibration characteristics of a tractor/implement system with front axle hydro-pneumatic suspension, it is essential to develop a dynamic model. The nonlinear stiffness and damping calculation equations for hydro-pneumatic suspension are derived and the complete three dimensional multibody dynamic model of the wheeled tractor/implement system is presented in this paper. The construction of the model considers the effect of implement and passive rub cabin suspension as well as front axle hydro-pneumatic suspension together. The vibration responses and the corresponding power spectral densities (PSD) of driver seat, cabin, chassis and implement under different forward speed and field road conditions gathered from the simulation using the models are in good agreement with experimental results, demonstrating the effectiveness of the proposed model. A comparative investigation on the dynamic effects of a passive cabin suspension, implement and front axle hydro-pneumatic suspension under four cases was made. The effects of front axle suspension and the implement on the rollover limit chart for the tractor system were also studied. Simulation results showed that the front axle hydro-pneumatic suspension will deteriorate the ride comfort of drivers but will improve pitch and roll stability. Passive cabin suspension plays a more important role in improving the ride comfort of drivers than the front axle hydro-pneumatic suspension does, while compromising the pitch stability to some extent. The implement will raise the riding comfort of drivers and the pitch stability of tractors, but dramatically worsen the roll stability. The presence of the front axle suspension and the implement improves the minimum slope angle and reduces the maximum slope angle. Furthermore, the effect of the initial nitrogen volume, the pressure of energy accumulators, and the orifice diameter of the small throttle valves on the vibration characteristics of the tractor system with the large throttle valve closed or fully opened is also investigated.

The dynamic model is significant for the analysis of the vibrational characteristics of the wheeled tractor system with implement and front axle hydropneumatic suspension. In this work, the nonlinear stiffness and damping equations are derived first. The dynamic coupling relationship among cabin, three-point hitch structure, and implement are figured out, and the dynamic model of the half agricultural wheeled tractor/implement system is presented considering the effects of three-point hitch structure, passive silent blocks of cabin, and front axle hydropneumatic suspension together. To validate the model, the power spectral densities (PSDs) of the driver seat, cabin, chassis, and implement acquired from numerical simulations are compared with those from experiments, respectively. Under different forward speeds, two groups of results match well. Based on the model, the influences of passive cabin suspension, implement, and front axle hydropneumatic suspension on the dynamical characteristics of the tractor system are investigated. Results indicate that the front axle hydropneumatic suspension will deteriorate the ride comfort of the driver but improve the handing stability. The passive cabin suspension reduces the operational stability while improving much more ride comfort than the front axle hydropneumatic suspension does. The driver’s comfortableness will be increased due to implement; meanwhile, handling stability will be compromised. Besides, the impacts of initial nitrogen volume, pressure of accumulators, and orifice diameter of throttle valves on the vibration characteristics of the tractor system are also inspected.

A multipurpose robot was designed to perform several tasks such as spraying and weeding in a greenhouse. Several operations were conducted by adding or removing sensing component(s), replacing actuator(s) and switching control software, with little or no change of the platform. A sliding mode control was applied to control motion of the robot in light of its kinematic model. Vision based algorithms were developed for navigation and operations of row planting crops, taking operations of spraying water and weeding by machine as examples. A vertical projection method was applied to calculate a guidance line for navigation. Preliminary tests were conducted to assess both guidance and operations of spraying and weeding in a greenhouse with green vegetable, respectively. Results showed that the robot traveled with a maximum lateral error of 47 mm, and sprayed with a productivity of 16-20 plants/min. Also, weeding action was taken in time. The designed robot has adaptability and versatility because the different operations can be achieved on the same platform.

A new method of vision-based guidance line detection is developed to find guidance line in row crop fields for agricultural machinery, which uses the mathematical morphology to process images and segment crops in images and to extract target crops. The guidance line is fit with the least-square method according to the centroids of individual target crops or/and the central points of several pixel rows of crops with a continuous region in image. The guidance line could be found easily in three kinds of row crop fields, such as individual crop plants with spacing in image, plants with continuous region in image, and plants with both features above. Then experiments were implemented by an agricultural robot in a vegetable field, and results showed that the algorithm enabled the robot to drive along crop row with a high accuracy ±29.5mm, and had an expected speed of image processing between 0.7s and 1.3s, which meets the needs of agricultural production. Therefore, the proposed algorithm has a good performance in accuracy and speed of image processing, and has robust performance for different crops.