基于Micro-CT的黄瓜苗坨夹取破损检测及取苗参数优化

Plug damage detection and parameter optimization of picking up cucumber seedlings from tray cells based on Micro-CT

为了减小自动移栽时取苗爪夹取苗坨的破损,利用X射线Micro-CT对处于夹取状态的黄瓜苗坨进行检测,用阈值分割方法将根系和孔隙从断层图片中分割提取并三维重构。在垂直和水平方向将苗坨划分成6等份,对根系和孔隙的体积和分布密度进行统计,得出夹取过程中根系未发生显著位移,根系的作用是将基质缠绕包裹住,防止苗坨散坨;孔隙的体积和分布密度变化非常显著,新生孔隙的聚集和裂缝的形成是导致苗坨破损的主要原因。苗坨中夹针收缩移动的区域、夹针的顶端部位和苗坨的顶部是破损的主要部位,用这3个区域孔隙体积的增加量作为评价苗坨破损量的指标,对圆形和扁形2种夹针,在夹针直径为2、2.5和3 mm,夹取初始角为7°、9°和11°时进行扫描试验,得出在夹针收缩量为5 mm时,减小夹针直径和增大夹持初始角可以减小苗坨破损量,相同夹取条件下圆针夹取苗坨的破损量小于扁针;在夹取力等于苗坨屈服点的抗压力7.31 N时,圆针和扁针的收缩量分别为4.75和4.26 mm,此时孔隙体积的增加量分别为843.7和786.1 mm^3,扁针夹取苗坨的破损量小于圆针。以苗坨质量损失25%作为考核指标,在自动取苗机构上进行试验,结果表明,在夹针直径为2 mm,夹取力和夹取初始角分别为7.31 N和11°时,苗坨的破损率为6.3%,小于其他参数的试验结果,与Micro-CT扫描分析的结论一致。

The root cause for transplanting failure is the damage of plug which clamped by clamper when transplanterautomatically transplants vegetable plug seedlings. To reduce the damage of plug, in this study, we prepared 128-hole platecultivation of cucumber seedlings using the peat, perlite and vermiculite mixed in a volume ratio of 3：1：1. We used X-rayMicro-CT to test non-destructively three states of cucumber seedlings plug： pin： not inserted into the plug, pin into the plug,and pin contraction to maximum displacement. In the tomogram, root threshold was obtained as 93-102, and pore thresholdwas obtained as 0-16. Roots and pores were segmentation extracted and 3D reconstructed from tomogram by using thresholdsegmentation method. The plug was divided into six equal parts vertically and horizontally. Root distribution density wasdefined as the ratio of every part in the area where the root volume and volume of plug. The pore density was defined as theratio of every part of the pore volume and volume of plug. The volume and distribution density of root and pore werecalculated by SPSS18 software. It was concluded that there was no significant （P〉0.05） displacement for root during theclipping, and its role was wrapping around the substrate to prevent the plug scattered. The change for pore volume anddistribution density was very significant （P〈0.05）, new pores and cracks mainly appeared around the pin and between the pins.Pores accumulation and cracks formation were the main cause for plug damage. We then treated the increments of porevolume around the pin as the evaluation of broken seedlings indicators. For the two kinds of pins： Circular and flat, scanningtests and analyzes were carried out. When pin diameters were 2, 2.5 and 3 mm, and the initial angles of clamp were 7°, 9° and11°, the results showed that increments of pore volume increased as the pin diameter increased, and decreased as the initialangles of clamp increased. When shrinkage of pin was 5 mm; increment of pore volume of circular pin was less than flat pin inthe same condition. When clamp force equaled to the anti-stress of yield point for seeding plug as 7.31 N, shrinkage of circularand flat pins were 4.75 and 4.26, respectively; increments of pore volume were 843.7and 786.1 mm3, the damage of plugwhich clamped by flat pin was less than circular pin. We set the shape, diameter, initial angle and shrinkage amount of pin astest factor, and set damage rate of seeding plug as assessment indicators. Then the test was carried out by two fingers and fourpins structure seedling clawing. Plug was damaged severely when root lump weight lost more than 25%. Test result showedthat damage rate of seeding lump was 6.3% which was less than test results of other parameters when the diameter of flat pinwas 2 mm; clamping force and clamping initial angle were 7.31 N and 11°, respectively. The results of the test were inagreement with the results of Micro-CT scanning. Overall, this research provides a new approach to the design for automotivetransplanter, the resulting optimization parameters could be used as theoretical basis for the selection of seedling clamperdesign and take seedling parameters.