篱壁式葡萄拨叶采收机器人作业方法研究与试验

    Method and experiment for a hedgerow-type grape leaf-removing and harvesting robot

    • 摘要: 针对篱壁式葡萄机械采收时藤叶遮挡导致葡萄果梗定位难、采收成功率低等问题,该研究提出了一种拨叶采收作业的遮挡处理方法。为实现遮挡环境下的采收作业,构建了果梗可见性量化判别模型,确定葡萄果梗的可见性系数,基于费马-托里拆利点提出干预点规划算法,确定最优遮挡干预点。为简化机械臂逆解求解过程,构建了从末端笛卡尔空间到关节空间的非线性映射模型,快速求解末端位姿相应机械臂的关节角度。田间试验结果表明,果梗可见性系数Svis>0.7时,高可见性果梗葡萄的采收损伤率低于10.0%,采收成功率为70.0%,平均采收时间3.2 s/串;0.4<Svis≤0.7时,中可见性果梗葡萄的采收损伤率低于23.3%,成功率为53.3%,平均拨叶采收时间8.7 s/串,Svis≤0.4时,低可见性果梗葡萄的采收损伤率低于36.6%,成功率为40.0%,平均拨叶采收时间14.8 s/串。所提出的遮挡处理方法能有效区分不同遮挡果梗的葡萄并自动切换作业模式,具备较高的采收成功率,满足篱壁式葡萄园复杂遮挡的葡萄高效、低损伤自动化采收需求,可为篱壁式葡萄机械化、自动化采收机械设计与研制提供参考。

       

      Abstract: In the mechanical harvesting of fence-type grapes, the occlusion by vines and leaves makes it difficult to locate the peduncles of grapes, which affects the harvesting success rate. In order to solve this problem, this study proposed a novel leaf occlusion handling method for grape harvesting, where the act of removing obscuring vines and leaves was followed by the harvesting of the grape bunches. Based on collaborative mechanical arms, a fence-type grape leaf-removing and harvesting robot was developed to achieve efficient and low-damage automated harvesting of grapes in complex occlusion scenarios. The fence-type grape leaf-removing and harvesting robot included visual perception module, mechanical arm and end effector module, mobile chassis module, and data processing and storage module. Firstly, taking relative length, consistency of orientation and continuity as the key indicators, a quantitative discriminant model of peduncle visibility was constructed by calculating the visibility coefficient of grape peduncles. This model determined a visibility coefficient in the 0~1 interval, enabling objective assessment of the visibility degree of peduncles, including high peduncle visibility, medium peduncle visibility, and low peduncle visibility. For grape peduncles with medium and low visibility, this paper identified the optimal intervention point for removing occlusions by vines and leaves. A spatial quadrilateral was constructed using the endpoints of the grape peduncle and the occluding branches. The Limited-memory Broyden-Fletcher-Goldfarb-Shanno method was employed to solve for the Fermat-Torricelli point as the optimal intervention point. Then, the optimal intervention point was used to remove occlusions by vines and leaves by the mechanical arm. After the occlusion by vines and leaves was removed, the harvesting arm completed the harvesting operation. The timing deviation of the two arms not exceeded 0.3s. In order to simplify the inverse solution process of the mechanical arm, a nonlinear mapping model from the end Cartesian space to the joint space was constructed. This model could quickly solve the joint angle of the robotic arm corresponding to the end pose. The predicted average root mean square error of the first five joint angles was 7.848° in the harvesting arm and 7.128° in the intervention arm, and the coefficient of determination was not less than 0.98. The inference time does not exceed 0.002 06 s, which meets the needs of real-time control. This study achieved independent harvesting by the grape harvesting arm for grapes with highly peduncle visibility, as well as leaf-removing harvesting operations for grapes with medium and low peduncle visibility. Quantitative discrimination of peduncle visibility was performed on 100 groups of samples. The results showed a visibility discrimination accuracy of 91.0% and a Kappa coefficient of 0.9. Among these, the discrimination accuracy for high peduncle visibility was 94.1%. Field test results indicated that for grapes with highly peduncle visibility, the harvesting damage rate was below 10.0%, the harvesting success rate was 70.0%, and the average single-arm harvesting time was 3.2s per cluster. For grapes with medium and low peduncle visibility, the leaf occlusion handling method was adopted. Among these, for grapes with medium peduncle visibility, the harvesting damage rate was below 23.3%, the harvesting success rate was 53.3%, and the average leaf-removing harvesting time was 8.7s. For grapes with low peduncle visibility, the harvesting damage rate was below 36.6%, the harvesting success rate was 40.0%, and the average leaf-removing harvesting time was 14.8s per cluster. The proposed leaf occlusion handling method could effectively distinguish peduncles with different occlusion degrees and automatically switch operating modes, featuring a relatively high harvesting success rate. It meets the requirements for efficient, low-damage automated harvesting of grapes under complex occlusion conditions in fence-type vineyards, and provides a reference for the design and development of mechanized and automated harvesting machinery for fence-type grapes.

       

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