针对针式末端执行器夹持移栽后穴孔内基质残留较多的问题,设计了一种指铲式末端执行器,通过增大指铲与苗钵基质的接触面积,减少穴孔内基质的残留。通过静力学分析找出末端执行器提取苗钵后基质残留的原因:基质间的最大内聚力小于由基质...针对针式末端执行器夹持移栽后穴孔内基质残留较多的问题,设计了一种指铲式末端执行器,通过增大指铲与苗钵基质的接触面积,减少穴孔内基质的残留。通过静力学分析找出末端执行器提取苗钵后基质残留的原因:基质间的最大内聚力小于由基质与穴盘间的粘附力和苗钵重力合成的总阻力时,苗钵出现破裂,基质塌陷。基于离散单元法,通过EDEM(Enhanced discrete element method)仿真分析了指铲式末端执行器对土壤基质的抓取过程,发现随着土壤基质内聚力的提高基质残留的现象得到改善;将基质配比和含水率条件作为主要影响因素,通过组合测盘试验测量在不同基质配比和含水率试验条件下的粘附力和内聚力变化,寻找内聚力大于粘附力的基质配比和含水率条件。试验表明,当相对含水率为60%、基质配比为6∶3∶1(泥炭∶蛭石∶珍珠岩)时,内聚压强和粘附压强的差值最大,在该条件下,指铲式末端执行器对劣质苗钵穴孔基质的平均剔净率达到70.8%,优于其他作业条件,可剔除穴孔内大部分基质。展开更多
Mechanical vibration is an effective fruit harvesting method.To evaluate the dynamic characteristics of dwarf Chinese hickory(Carya cathayensis Sarg.)trees and the influence of the tree structure on transmission and a...Mechanical vibration is an effective fruit harvesting method.To evaluate the dynamic characteristics of dwarf Chinese hickory(Carya cathayensis Sarg.)trees and the influence of the tree structure on transmission and attenuation of dynamic response,a new method was proposed based on acceleration admittance measurement on dwarf Chinese hickory trees in orchard environment under impact excitation.The primary resonance frequencies of the tree can be determined based on the acceleration admittance measurement.The effect of the tree structure on the vibratory transmission was quantified using the attenuation ratio of the acceleration admittance.A 5-year-old dwarf Chinese hickory tree sample was tested.The responses at three resonance frequencies(5,9 and 12 Hz)were analyzed because they were identified as the most effective bands of excitation for the main part of the tree specimen.The results reveal that the variation of the dynamic response along the testing tree is greatly related to the Chinese hickory tree structure.The attenuation ratio of the acceleration admittance at the branch crotches indicates the leader top crotch may amplify the acceleration admittance no matter what the crotch angle and the branch diameter is.Unlike the crotches,the branch chain nodes generally have negative influence on the acceleration admittance along the branch chains which heavily depend on the branch chain configuration.The branch chains with a chain angle no less than 150°and a wood diameter ratio close to 1.0 could produce little influence on the vibration transmission.For those branches with chain angle less than 150°,the vibration was generally attenuated at their chain nodes at three resonance frequencies.To impose impact excitations on the tree,high mechanical harvesting efficiency could be achieved on those branch chains which are almost straight and uniform.展开更多
文摘针对针式末端执行器夹持移栽后穴孔内基质残留较多的问题,设计了一种指铲式末端执行器,通过增大指铲与苗钵基质的接触面积,减少穴孔内基质的残留。通过静力学分析找出末端执行器提取苗钵后基质残留的原因:基质间的最大内聚力小于由基质与穴盘间的粘附力和苗钵重力合成的总阻力时,苗钵出现破裂,基质塌陷。基于离散单元法,通过EDEM(Enhanced discrete element method)仿真分析了指铲式末端执行器对土壤基质的抓取过程,发现随着土壤基质内聚力的提高基质残留的现象得到改善;将基质配比和含水率条件作为主要影响因素,通过组合测盘试验测量在不同基质配比和含水率试验条件下的粘附力和内聚力变化,寻找内聚力大于粘附力的基质配比和含水率条件。试验表明,当相对含水率为60%、基质配比为6∶3∶1(泥炭∶蛭石∶珍珠岩)时,内聚压强和粘附压强的差值最大,在该条件下,指铲式末端执行器对劣质苗钵穴孔基质的平均剔净率达到70.8%,优于其他作业条件,可剔除穴孔内大部分基质。
基金financially supported by the National Natural Science Foundation of China(Grant No.51475433,51175476)the Research Fund for the Doctoral Program of Higher Education of China(RFDP)(Grant No.20113318110001)+1 种基金the Program for Scientific Research Innovation Team of Zhejiang Sci-Tech University(Grant No.13020049-Y)the 521 Talent Plan of Zhejiang Sci-Tech University.
文摘Mechanical vibration is an effective fruit harvesting method.To evaluate the dynamic characteristics of dwarf Chinese hickory(Carya cathayensis Sarg.)trees and the influence of the tree structure on transmission and attenuation of dynamic response,a new method was proposed based on acceleration admittance measurement on dwarf Chinese hickory trees in orchard environment under impact excitation.The primary resonance frequencies of the tree can be determined based on the acceleration admittance measurement.The effect of the tree structure on the vibratory transmission was quantified using the attenuation ratio of the acceleration admittance.A 5-year-old dwarf Chinese hickory tree sample was tested.The responses at three resonance frequencies(5,9 and 12 Hz)were analyzed because they were identified as the most effective bands of excitation for the main part of the tree specimen.The results reveal that the variation of the dynamic response along the testing tree is greatly related to the Chinese hickory tree structure.The attenuation ratio of the acceleration admittance at the branch crotches indicates the leader top crotch may amplify the acceleration admittance no matter what the crotch angle and the branch diameter is.Unlike the crotches,the branch chain nodes generally have negative influence on the acceleration admittance along the branch chains which heavily depend on the branch chain configuration.The branch chains with a chain angle no less than 150°and a wood diameter ratio close to 1.0 could produce little influence on the vibration transmission.For those branches with chain angle less than 150°,the vibration was generally attenuated at their chain nodes at three resonance frequencies.To impose impact excitations on the tree,high mechanical harvesting efficiency could be achieved on those branch chains which are almost straight and uniform.
