Design and experiment of the target-oriented spraying system for field vegetable considering spray height

A target-oriented spraying system was designed for the field vegetables using height data, in order to explore the effect of spray height on accuracy. A systematic analysis was made to determine the structure and working principle of the target-oriented spraying system. High-speed photography was also utilized to identify the lagging characteristics of all the links in the target-oriented spraying operation. The delay time of each part was selected to establish the target-oriented spraying lag model. As such, a target-controlled injection was proposed to integrate the target location, target shape, spray speed, and spray height. A steady-pressure and target-oriented spraying control system was then designed to combine the target recognition, target-oriented spraying control, and voltage stabilizing control using the C37 controller. Among them, an industrial camera was utilized to capture the position information of the target for the spraying control system. During the operation, the initial spray pressure of the system was first set to determine the difference between the spray pressure and that from the pressure sensor. Then, the duty cycle of the Pulse-Width Modulation (PWM) signal was adjusted in real time to change the valve opening of the electric ball valve. Finally, the real-time adjustment of the spray pressure was realized to stabilize the spray system. Once the difference between the set pressure and that from the sensor was within 10% of the set pressure value, no operation was made to avoid the impact of frequent adjustment of valve opening on the service life of the electric ball valve. The C++ programming language was used to develop the field operation software in the Windows system. The target spray system was mainly divided into the image display, the serial port control, the parameter display, and the equipment control modules. The software operation interface was used to dynamically display the original image or processing data as required. The image display area was divided into four parts, each of which corresponded to the different nozzles 1-4. The target position of nozzles was then monitored using video tracking. Once the target contacted the set positioning line, the upper computer was used to send a trigger signal through the USBCAN converter, including the fixed distance between the target and the bottom of the field of view, while the vertical projection length of the target in the traveling direction to the C37 controller. At the same time, the controller adjusted the delay time to encode the speed by the encoder and the spray height obtained by the ultrasonic sensor. The lag distance was then compensated to complete the precise control of the opening and closing of electromagnetic valves for the target-oriented spraying. Finally, the performance test of the target-oriented spraying system was carried out to verify the simulation. When the walking speed was 0.52 m/s, the Mean Absolute Error (MAE) and Root Mean Square Error (RMSE) of the target with the height information were less than 3.63 and 4.26 cm, respectively, which were reduced by 4.30 and 4.57 cm, respectively. The effective spraying rate was less than 92.6%, indicating the feasibility of the fusion height information for the target-oriented spraying control. The field experiment showed the effective spraying rate decreased with the increase in speed. Specifically, the effective spraying rate on the target-oriented system reached 93.5%, while the average effective coverage was 80.2% when the speed was less than 0.49 m/s, compared with the continuous spraying method, the drug saving rate of target-oriented spraying can reach 33.8%. Consequently, the system can fully meet the target operation requirements of wide row spacing crops in the field.