Simulation and Test of Seedling Pot Grabbing by Spade End-effector
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摘要:
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。
Abstract:
In the mechanical replugging task in greenhouse, the residual matrix in plastic pan would not be beneficial for healthy seedling replugging which was caused by the endeffector removing bad seeding in previous transplanting procedure. A kind of spade endeffector was developed relatively to the needletype for the removing task. The aim was to reduce the residual matrix in the cell by increasing the contact area between the endeffector and matrix. The reasons of residual matrix in the endeffector grabbing procedure were deduced by the statics. The seedling pot would break and the matrix would collapse while the maximum cohesion in matrix was less than the total resistance which was synthesized by the gravity of seedling pot and the adhesion between the matrix and plug tray. Based on the discrete element analysis method, the seedling pot grabbing procedure by the spade endeffector was simulated by the enhanced discrete element method (EDEM). It was found that the performance of residual matrix was reduced while the cohesion of soil matrix was increased. Therefore, taking the matrix ratio and relative moisture content as the main factors and designing the experiment through the combined disc tests to measure the matrix adhesion and cohesion in the different main factors of matrix ratio and relative moisture. The aim was to find the conditions of matrix ratio and relative moisture while the cohesion was bigger than adhesion. The difference between cohesion and adhesion was the largest under the conditions of 60% of relative moisture content and 6∶3∶1 (peat∶vermiculite∶perlite) of matrix ratio. The average matrix removal rate by the spade endeffector reached 70.8%, which was superior to other conditions. Most of the matrix in the plastic hole can be removed under the conditions.