机器人采摘葡萄果穗振动仿真与试验

针对机器人摘取及移送过程中导致的果穗振动与果粒脱落问题,提出了一种面向穗轴激励输入的果穗振动仿真模型。以葡萄为研究对象,在果穗"梗-果"结构特性基础上,提出了"挠性杆-铰链-刚性杆-质量球"复合果穗模型,并由试验确定了模型中各级梗间铰链弹性系数与阻尼系数、果粒尺寸与质量的正态分布规律,获得了主穗轴的抗弯特性。进而利用激光3D扫描重构得到梗系统,根据试验结果分别进行刚性、挠性杆件定义和果粒与梗间铰链的添加,构建得到果穗振动仿真模型。通过仿真精度验证试验发现,在激励作用的加速、匀速和减速阶段,经正态分布统计仿真与实测中果穗的各果粒摆角均值与标准差相差均在2%和6.6%以内,表明不同阶段其精度均良好。最终利用该模型分析了不同激励方式及不同采摘阶段对果穗振动的影响。果穗振动仿真模型的建立,为实现各类果穗的机器人"减振低脱"采摘提供了有力的分析工具。

Simulation and Test of Grape Fruit Cluster Vibration for Robotic Harvesting

To reduce the serious vibration and fruit dropping that may occur in high speed robotic harvesting of fruit clusters, a simulation model of fruit cluster vibration is necessary to vibration law discovery, influencing factor analysis and optimal control study. To achieve all of the above objectives, the simulation model must take into account of the individual difference of component properties and embody the complex multilevel stem structure, multiple fruits distribution and multiplex excitation transmission. Therefore, a flexible rod hinge rigid rod mass composite model was first put forward based on the structure of stem fruit system of grape cluster, and viscoelastic property of hinges and bending property of main spike stalk were determined by large sample tests. Then, simulation model of grape fruit cluster was constructed by reconstitution of the solid stem system with 3D laser scan, replacement of main spike stalk with flexible rod, random addition of fruits and definition of different components according to their normal distribution from the above test results. The accuracy of the simulation model was verified by experiments, and error of the mean value and standard deviation of fruit relative swinging angle under different excitation methods are within 2% and 6.6%, respectively. Finally, the effects of various excitation methods and harvesting stages on cluster vibration were analyzed with this model. To conclude, the successful establishment of this simulation model of grape fruit cluster provides an excellent analytical tool for robotic low vibration and anti fall harvesting of various fruit clusters.