关键词: 大树土球, 原位捆绑, 模块化设计, 离散元, 响应面分析, 控制策略

Abstract:

Objective: Current manual binding soil balls of large tree roots is labour-intensive, requiring three-person coordination. To address the issues of manual reliance, low efficiency, and lack of available machinery in binding soil balls of large tree roots during transplantation, this paper designs an in-situ binding apparatus for large tree root soil balls along with its binding strategy. Method: By analysing manual binding trajectories, a modular positioning clamping mechanism was designed. This mechanism was adjusted radially with ten fastening bolts to accommodate large trees with trunk diameters ranging from 150 to 220 mm, ensuring coaxial alignment with the trunk. A composite motion combining gear-ring meshing transmission and synchronous belt drive were used to form a helical binding trajectory for precise angular control. An integrated tension control mechanism was used to stabilize strap tension and reduce errors. A discrete element model of the root-soil composite was established in EDEM. Shear and firmness tests validated a relative error below 5%. A three-factor quadratic orthogonal test was conducted for bundling and lifting container simulations, using soil retention rate and strap retention rate as evaluation metrics. Result: Orthogonal tests yielded optimised parameters: 18.5 diagonal wraps, 47° binding angle, and binding tension of 20 N. Under these conditions, soil retention rate reached 85.10% and fabric retention rate was 26.66%. The actual container lifting experiments verified that the maximum relative error was below 6% compared to simulation results, indicating the parameter reliability. A foam root ball test rig was designed for bench testing, determining the optimal speed combination with the circumferential stepper motor of 76.5 r·min^?1 and the vertical stepper motors of 45 r·min^?1. This configuration achieved a tension fluctuation rate ≤6% and a total binding time ≤210 s. Conclusion: Field trials were conducted on tree root balls with diameters ranging from 0.9 to 1.5 m using this speed combination. The overall bundling efficiency increases by a maximum of 39.69% and the soil retention rate increases a maximum of 8.41% compared to manual bundling. The device weighs 10.75 kg, and can be installed, wrapped, and disassembled by a single operator, significantly reducing labour intensity. When lifting and packing, a small amount of soil falls off and the root system is not damaged, validating the device's practicality, and providing a reliable solution for mechanizing large tree transplantation.

Key words: big tree soil balls, in-situ bundling, modular design, discrete element, response surface analysis, control strategy