Abstract:

[Objective] In the three-dimensional rack layout used in industrialized eel (Monopterus albus) aquaculture systems, the breeding space extends substantially in the vertical direction, while the horizontal channels offer limited room for turning and maneuvering. Under such spatial constraints, manual bait feeding imposes considerable labor intensity, and operations at elevated rack levels are especially difficult. Moreover, existing general-purpose agricultural and aquacultural equipment is poorly suited to these narrow, vertically extended breeding environments characterized by restricted horizontal clearances and multi-tier structures. To address the pressing need for automated and reliable bait delivery in such specialized aquaculture facilities and to reduce the heavy reliance on manual labor in factory-based eel farming, a dedicated three-dimensional bait-delivery robot for eel aquaculture was designed, developed, and systematically integrated. [Methods] The proposed robot integrated several key mechanical and electronic subsystems into a unified platform. The mobility subsystem comprised a dual-steering-wheel omnidirectional mobile chassis, which provided flexible translational and rotational movement capabilities essential for navigating narrow breeding channels with limited turning space. The vertical access subsystem featured a nested gantry lifting mechanism driven by timing-belt pulley groups arranged in series, providing substantial vertical travel range to access multiple tiers of the three-dimensional breeding racks. The manipulation subsystem consisted of a six-degree-of-freedom robotic arm capable of precise positioning and orientation adjustment for accurate bait placement at designated feeding points. These mechanical components were governed by a comprehensive electronic control system organized with a master-slave architecture. Specifically, an RK3588 industrial core board served as the master controller, responsible for high-level task scheduling, navigation planning, and coordination among the various subsystems, while a programmable logic controller (PLC) performed real-time, low-level scheduling and control of the fork mechanism and the lifting motors. For autonomous navigation and localization within the facility, two 2D Light Detection and Ranging (LiDARs) were deployed for simultaneous localization and mapping (SLAM), enabling the robot to construct accurate environmental maps and navigate reliably within the complex breeding facility layout. For robotic arm manipulation, the MoveIt 2 framework together with the Open Motion Planning Library (OMPL) was employed for collision-free path planning, ensuring safe and efficient arm movements within the constrained 3D workspace. Through this integrated electromechanical and software design, the robot addressed the bait-delivery challenges posed by three-dimensional eel aquaculture environments and performed fixed-point bait feeding operations at various elevated levels of the breeding racks. [Results and Discussions] Field tests were conducted at the Zhuanghang Comprehensive Experimental Station in Shanghai to rigorously evaluate the robot's navigation and manipulation performance under realistic operational conditions. The results showed that the navigation-to-point repeatability was better than 2.0 cm, with a maximum deviation radius of 2.14 cm, indicating highly reliable positioning performance that satisfied the precision requirements for mechanical arm-based bait delivery. In terms of manipulation reliability and task execution capability, across 192 actual bait-delivery attempts conducted during the field trials, the single-attempt success rate reached 98.44%, reflecting the robustness of the grasping and placement operations in the actual aquaculture environment. Furthermore, when evaluated against a comprehensive baseline of 200 planned operations encompassing the entire workflow from autonomous navigation to precision bait delivery at designated rack positions, the overall system success rate was 94.50%, demonstrating consistent and robust operational capability under extended field conditions and validating the practical feasibility of the integrated robotic system for industrialized aquaculture applications. [Conclusions] The robot meets the accuracy and efficiency requirements for automated bait-feeding in industrialized eel aquaculture and can reduce the labor cost and physical burden associated with manual bait-feeding operations. These results may support the transition of eel aquaculture from labor-intensive manual operation toward automated and unmanned intelligent farming and may help improve the economic viability of factory-based aquaculture practices.

Key words: omnidirectional mobility, lifting mechanism, manipulator, three-dimensional eel farming, bait-feeding robot