Design and experiment of the dual-parameter joint control system for forest and fruit orchards

Fertilizer distribution devices are often required for the real-time adjustment of the fertilization amount in orchards. In this research, a chain-type ditching and fertilizing machine was designed for fertilizer distribution in forest and fruit orchards. A dual-parameter joint control system of the machine was also proposed for advanced fertilization. BeiDou navigation satellite system (BDS) was integrated to realize the automatic driving of the tractor. The efficiency and precision of the fertilization were greatly improved using a control system. The longitude and latitude coordinates of the orchard area were accurately acquired to determine the fertilization amount through satellite messages. The optimal fertilization was obtained to fully meet the specific requirements of soil and crop conditions. At the same time, the forward speed of the tractor was considered to capture the dual-parameter adjustment. A pre-established table of the system was then obtained to determine the fertilizer outlet height and the fertilizer discharge speed. As such, the fertilization was precisely adjusted under different situations in the orchard. In terms of the fertilizer outlet height, the stepper motors were used to combine with the displacement sensors. Accurate power was provided for the height adjustment. The displacement sensor was used to precisely measure the actual height of the fertilizer outlet. The measured and target values were compared to timely adjust the fertilizer outlet height at the optimal position. A position-type proportional integral derivative (PID) control was adopted to adjust the opening degree of the proportional speed control valve in real time, according to the deviation between the actual and target speed. Thereby the real-time regulation of the hydraulic motor speed was obtained to optimize the performance of the PID controller. Furthermore, the joint simulation was carried out using AMESim and Matlab/Simulink. The PID parameters were accurately tuned after the simulation. A series of static calibration experiments were conducted to obtain the relationship between the motor speed and the duty cycle. After that, the speed adjustment experiments were carried out to verify the simulation. The optimal control system was achieved using PID parameters after repeated tests and adjustments. The re-tuned parameters were K_p = 0.029, K_i = 0.05, and K_d= 0.000 7. The speed-tracking performance of the system was also validated at low, medium, and high speeds under dynamic load conditions. The results showed that all three speeds were achieved in the rapid responses. For example, the overshoots were 16, 2.28, and 2.3 r/min, respectively, at the low, medium, and high speeds. And the time to reach the steady state was 5.5, 2, and 1.5 s, respectively. Moreover, the steady-state errors at all three speeds were relatively small, indicating the excellent stability and control accuracy of the system. Finally, the fertilization tests were carried out to evaluate the overall performance of the system. Both the fertilizer outlet height and the fertilizer discharge speed were adjusted in real time, according to the real requirements. The average amounts of fertilization were 2.824 and 3.810 kg/m, respectively, in the fertilization areas with the target fertilization amounts of 2.75 and 3.61 kg/m, respectively. The relative errors between the average and target fertilization amounts were 4.590% and 5.546%, respectively, while the coefficients of variation were 7.487% and 4.720%, respectively. The high fertilization accuracy was achieved through the real-time adjustment of the fertilization amount in orchards. In conclusion, the research findings can provide a valuable reference for the variable application of organic fertilizer in orchards. This control system can also share great potential in the agricultural field, in order to improve the efficiency and quality of fertilization.