Design and experiment of coconut picking robot with climbing

【Objective】Hainan Province, China’s largest tropical island province, has become a major national coconut-producing region thanks to its unique advantages in light and thermal resources. However, coconut picking operations still rely predominantly on traditional manual methods, facing numerous technical bottleneckssuch as high labor intensity and considerable risks associated with working at height, which result in high production costs and low picking efficiency. There is a clear gap between the current level of technological equipment for coconut picking and the requirements of industrial development. Therefore, research into coconut picking robots is beneficial for addressing these issues and reducing the reliance on manual picking. The primary technical challenges for coconut picking robots lie in the design of climbing devices and picking manipulators. In particular, the distinctive planting patterns and structural features of coconut trees in Hainan Province impose more stringent requirements on the adaptability and stability of climbing devices, as well as the precision and flexibility of the picking manipulator. Currently, significant technical deficiencies remain in the climbing performance of coconut picking robots under complex terrain conditions, and in the manipulator’s control accuracy in highaltitude working environments. To promote the mechanization of the coconut picking industry in Hainan Province, a climbing-type coconut picking robot has been designed in this study, with the aim of enhancing the mechanization level of coconut picking in Hainan Province.【Methods】The coconut picking robot mainly consisted of a climbing device, a picking manipulator, and an embedded remote control system. The climbing device adopted an annular main body structure to enhance overall stability, and to climb tree trunks of varying diameters through an adaptive mechanism. The picking manipulator was designed with a four- degree- of- freedom structure, allowing flexible adjustment of the chainsaw posture to accommodate coconut fruit stalks growing in different directions, thereby improving operational flexibility. By analyzing the forces on the climbing mechanism along the trunk, this study established a mechanical model for the robot’s uniform climbing and analyzed the mechanical conditions for stability maintenance. Guided by the theoretical framework of this model, the mechanism design was optimized, enabling stable climbing functionality of the robot. A remote image transmission control system for the picking robot was constructed using radio frequency communication methods, and a bidirectional communication link was established between the remote controller, climbing device, and picking manipulator, thereby enabling real-time monitoring and precise control of the robot’s motion status and operational processes.【Results】A cutting test platform for coconut cluster fruit stalks was constructed based on the coconut picking robot and a gripping test bench, and the cutting performance of the robot was tested. During the experiment, the variation in torque of the picking manipulator during the cutting process and the current fluctuation of the chainsaw at the end-effector were monitored. The results demonstrated that greater rotational speed during cutting resulted in higher peak torque, and the manipulator was able to rapidly return to a stable state after completing the sawing process. Throughout the sawing tests, the manipulator exhibited a smooth sawing process and effectively completed the cutting of coconut cluster fruit stalks. Additionally, full-cycle performance tests—encompassing climbing, harvesting, and descending—were conducted using 11 randomly selected coconut trees as test samples. The results showed that the coconut picking robot required an average operation time of 431.98 s to climb a 9.7 m coconut tree, complete the picking of a single cluster, and return to the ground, and the average climbing time was 107.31 s and an average single-cluster picking time was 259.6 s. Moreover, for coconut trees of similar height, the climbing time was mainly influenced by the trunk circumference and inclination.【Conclusion】The coconut picking robot designed in this study alleviates the labor intensity and risks associated with manual picking operations, reduces labor costs, enhances mechanization and intelligence, and promotes the development of the coconut industry. Field trials of the coconut picking robot have validated its performance in meeting picking requirements, thus providing technical support for the mechanization of coconut harvesting in Hainan Province.