Design and Experiment of an Autonomous Docking Device for an Unmanned Replenishment Vehicle for Large Sprayers

In order to address the problems of manual dependence, low replenishment efficiency, and insufficient operational continuity in unmanned field operations of large sprayers, an autonomous docking device for an unmanned replenishment vehicle was designed. The device is composed of three principal components: a robotic-arm docking system, a pesticide delivery system, and a docking control system. RTK positioning information is utilised to determine the relative position between the unmanned replenishment vehicle and the large sprayer. The robotic arm approaches the high-position filling port, and the end effector completes guidance, flexible compensation, and electromagnetic coupling. A geometric model of the robotic arm was established, and its workspace was analysed using the Monte Carlo method. Single-factor tests and response surface optimization tests were conducted to optimize the key parameters of the end effector, and robotic arm control accuracy tests and field collaborative docking tests were carried out to evaluate the performance of the device. The results showed that the workspace of the designed robotic arm covered the elevated filling-port area of the large sprayer and met the docking requirements within a vehicle spacing of 0.25–1.25 m. After parameter optimization, the predicted cumulative docking time of the end effector was 2.051 s. The field collaborative docking test showed that, within a vehicle spacing range of 25–125 cm, 56 of 60 docking trials were successful, giving an overall success rate of 93.33%. Within the medium-spacing range, stable docking was achieved with an average docking time of 44.10–47.89 s. The results indicate that the proposed autonomous docking device can support unmanned vehicle approach, robotic arm positioning, end-effector guidance, and stable pesticide replenishment of large sprayers.