Optimized design and experiment of the precise obstacle avoidance control system for a grape interplant weeding machine

Weeds have generally seized the growth resources of grapes, resulting in the aggravation of plant diseases and insect pests for the reduced grape quality, particularly the yield reduced by 10% to 20%. Therefore, weed removal is one of the most important steps in the vineyard. The current obstacle avoidance system in an automatic obstacle avoidance weeder can be operated bilaterally in the hedge-frame grape cultivation. Most obstacle avoidance action was controlled by the switches, where the obstacle avoidance stroke was fixed. However, a relatively low effect of weeding often occurred, due mainly to the obstacle avoidance action stroke cannot be accurately controlled, according to the position of obstacles. In this study, a highly precise control system of obstacle avoidance was optimized to design in an interplant weeding machine, according to the principle of copying control. The specific system consisted of the signal acquisition of obstacle avoidance, program control, hydraulic actuator, and the obstacle avoidance monitoring feedback part. A closed-loop control system was also composed of signal acquisition, hydraulic actuator, and monitoring feedback part, according to the requirements of precise obstacle avoidance. The signal acquisition of obstacle avoidance was run to collect the angle change of signals ?β in real time when the weeding cutter moved to the position close to the obstacle. A voltage signal was then converted to transmit for the control system. The theoretical action stroke of the hydraulic actuator was calculated by the control system, where the signal was converted and output to the hydraulic actuator in the θ Angular variation ?β size. At the same time, the displacement sensor of obstacle avoidance monitoring feedback transmitted the actual action stroke to the control system for the precise adjustment of the action stroke of the hydraulic cylinder. The structure of the hydraulic circuit was optimized to realize the precise control of obstacle avoidance under the combination of hydraulic and electronic control. Static calibration was carried out for the precise control program of obstacle avoidance. Specifically, the effective stroke range was 5-145 mm for the calibration hydraulic cylinder and the feedback displacement sensor, and the effective stroke of the signal acquisition displacement sensor was 0-70 mm. PID parameters were set in the control program at the speed of 440 mm/s, where the optimal PID parameters were finally determined as P=0.034 3; I=127.78; D=0. The target center distance curve of the hydraulic cylinder was well fitted to the actual center distance curve, indicating an accurate, quick and stable implementation of the obstacle avoidance process. Recurdyn was used to simulate the precise obstacle avoidance operation in a weeding machine under the condition of straight obstacles. The coverage rate of the weeding operation was calculated to analyze the movement track of the weeding cutter disc. An optimal speed of the weeding cutter disc was selected as 200 r/min. Taking the operation speed of the machine as the experimental factor, the weeding coverage rate, and the damage rate of the fruit tree as evaluation indexes, field tests were carried out in the Scientific Research Test Base of China Agricultural University Zhuozhou, Hebei Province in June 2021. The results were as follows: The average coverage rate of weeding was 94.82%, 94.36%, 93.97%, and 92.60% at the machine speed of 260, 320, 380, and 440 mm/s, and the fruit tree damage rate was 1.67%, 1.78%, 1.92%, and 2.08%, respectively. The best comprehensive effect of weeding coverage rate and the highest operational efficiency was achieved at the operation speed of 380 mm/s. The average weeding operation coverage rate was 93.97% in the test, and the machine weeding operation coverage rate under the original obstacle avoidance control system was about 90.02%. The coverage rate of weeding operation increased by 4.39% at the same machine operation speed. Consequently, there was an excellent performance obstacle avoidance weeding in the highly precise control system of obstacle avoidance. This finding can provide a sound reference for further optimization of the interplant weeding machines in the modern orchards.