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
Singular configurations must be avoided in path planning and control of a parallel manipulator. However, most studies rarely focus on an overall singularity loci distribution of lower-mobility parallel mechanisms. Geo...Singular configurations must be avoided in path planning and control of a parallel manipulator. However, most studies rarely focus on an overall singularity loci distribution of lower-mobility parallel mechanisms. Geometric algebra is employed in analysis of singularity of a 3-RPS parallel manipulator. Twist and wrench in screw theory are represented in geometric algebra. Linear dependency of twists and wrenches are described by outer product in geometric algebra. Reciprocity between twists and constraint wrenches are reflected by duality. To compute the positions of the three spherical joints of the 3-RPS parallel manipulator, Tilt-and-Torsion angles are used to describe the orientation of the moving platform. The outer product of twists and constraint wrenches is used as an index for closeness to singularity（ICS） of the 3-RPS parallel manipulator. An overall and thorough perspective of the singularity loci distribution of the 3-RPS parallel manipulator is disclosed, which is helpful to design, trajectory planning and control of this kind of parallel manipulator.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Supported by National Natural Science Foundation of China(Grant No.51135008)Zhejiang Provincial Natural Science Foundation of China(Grant No.LZ14E050005)
文摘Singular configurations must be avoided in path planning and control of a parallel manipulator. However, most studies rarely focus on an overall singularity loci distribution of lower-mobility parallel mechanisms. Geometric algebra is employed in analysis of singularity of a 3-RPS parallel manipulator. Twist and wrench in screw theory are represented in geometric algebra. Linear dependency of twists and wrenches are described by outer product in geometric algebra. Reciprocity between twists and constraint wrenches are reflected by duality. To compute the positions of the three spherical joints of the 3-RPS parallel manipulator, Tilt-and-Torsion angles are used to describe the orientation of the moving platform. The outer product of twists and constraint wrenches is used as an index for closeness to singularity（ICS） of the 3-RPS parallel manipulator. An overall and thorough perspective of the singularity loci distribution of the 3-RPS parallel manipulator is disclosed, which is helpful to design, trajectory planning and control of this kind of parallel manipulator.
