• The male average thinning rate increases to 83.6%, and the route was effectively shortened. • Used the strategy of using each main branch as a sub-regional. • The concept of sub-region male flower density grading is proposed. • Integrating three route planning algorithms for mechanical flower thinning. Walnut male catkins commonly appear in clusters and are irregularly distributed across the tree, which makes it difficult to generate a continuous path during mechanical thinning. To reduce energy consumption and simplify route planning, a method termed continuous route planning of extensive and efficient mechanical thinning for walnut male flower based on density grading (CRPE′-DG) is proposed via a sub-regional route-planning strategy along the main branches. This method incorporates and improves the Density-Based Spatial Clustering of Applications with Noise (DBSCAN), B-Spline fitting, and Makima interpolation algorithm to generate end-effector motion routes for the robotic arm. The performance of CRPE′-DG is evaluated in terms of dispersion degree, thinning rate, and route length. The Interquartile Range ( IQR ) of the dispersion of male flowers at high-density levels is consistently lower than that at low-density levels. On average, the dispersion degree is reduced by 57.5% and 31.9% compared with the 5th-order and 7th-order polynomial fitting algorithms, respectively. The average thinning rate using the CRPE′-DG method has been increased to 83.6%, which is 11.3% and 6.3% higher than the 5th-order and 7th-order algorithms. Meanwhile, the average route length is shortened by 15.3%, 18.0%, and 14.1% compared with the 5th-order, 7th-order, and traditional B-spline algorithms, respectively, with a maximum reduction of 28.0% in sample 1. These results demonstrate that CRPE′-DG can effectively improve thinning efficiency, generate more continuous routes, and reduce energy consumption, thereby supporting sustainable agricultural development.
Liu et al. (Sun,) studied this question.