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篱壁式葡萄拨叶采收机器人作业方法与试验

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: A hedgerow is one type of conservation buffer in grape cultivation. Mechanical harvesting has been widely used for the hedgerow-type grapes. However, it is often required to locate the peduncles of the grapes under the vines and leaves occlusion during harvesting. In this study, a leaf-removing mechanism was proposed to push away the obscuring vines, followed by the harvesting of the grape bunches. A leaf-removing harvesting robot was also developed using collaborative robotic arms. The efficient and low-damage harvesting of the grapes was achieved in complex occlusion scenarios. Firstly, a quantitative discrimination model was constructed for the peduncle visibility. The relative length, relative direction, and continuity were integrated to determine a visibility coefficient in the 0-1 interval. The occlusion degree of the peduncles was assessed in real time, including high, medium, and low visibility. In the grape peduncles with medium to low visibility, the optimal intervention point was identified to remove the occlusions by vines and leaves. Secondly, a spatial quadrilateral was constructed according to the endpoints of the grape peduncle and the occluding branch. The limited-memory broyden-fletcher-goldfarb-shanno was employed for the fermat-torricelli point as the optimal intervention point. Furthermore, a nonlinear mapping model was constructed from the end cartesian space to the joint space, in order to simplify the inverse solution of the robotic arm. The joint angle of the robotic arm was obtained corresponding to the end pose. The independent harvesting was achieved by the grape harvesting arm for the grapes with the highly visible peduncles, and the leaf-removing harvesting for the grapes with the medium to low visibility peduncles. Finally, the quantitative discrimination of the peduncle visibility was performed on 100 groups of samples. The results showed that the better performance was achieved in a visibility discrimination accuracy of 91.0% and a Kappa coefficient of 0.9. Among them, the discrimination accuracy for the high visibility was 94.1%. Field test results indicated that the harvesting damage rate was below 10.0% for the grapes with the highly visible peduncles, the success rate was 70.0%, and the average single-arm harvesting time was 3.2 s per cluster. While the occlusion handling mechanism was adopted in the grapes with the medium to low visibility peduncles. In the grapes with the medium visibility peduncles, the harvesting damage rate was not more than 23.3%, the success rate was 53.3%, and the average leaf-removing harvesting time was 8.7 s. In the grapes with the low visibility peduncles, the harvesting damage rate was below 36.6%, the success rate was 40.0%, and the average leaf-removing harvesting time was 14.8 s per cluster. The occlusion handling mechanism effectively distinguished the peduncles with the different occlusion degrees, and then switched the operating modes, indicating a relatively high harvesting success rate. The efficient, low-damage harvesting of the grapes was fully met under complex occlusion conditions in the hedgerow-type vineyards. The finding can also provide a strong reference for the mechanical harvesting of the hedgerow-type grapes.

     

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