一种管道水培叶菜变方位包络定心抓取方式

Centering grabbing with variable orientation envelope for hydroponic leafy vegetables cultivated in pipeline

将不同位姿的水培叶菜包络定心夹持到种植孔中心取出,是实现茎秆精准根切,避免根部残留在管道内的关键。针对定方位抓取方式在一些方位上对叶菜向心包络扶起作用小,抓取成功率低的问题,该研究提出一种在夹持过程中使夹手相对种植孔中心转动的变方位抓取方式。以水培绿宝芥蓝为抓取对象,建立夹手张开伸入、绕种植孔中心转动及闭合夹紧时的尺寸参数关系模型;构建包络定心夹持多刚体动力学仿真模型,对初始倾角为50°、65°和80°,相对种植孔边缘周向均布的8个方位P_(1)~P_(8)上的芥蓝进行包络夹持过程仿真分析;搭建抓取试验平台,对初始倾角为45°~60°、>60°~75°和>75°~90°,方位为P_(1)~P_(8)的芥蓝进行抓取试验。分析确定两手指初始张开角为15°,闭合夹角为30°,夹手变方位转动角为45°,夹手转动速度为两手指转动速度的2倍。仿真获得的变方位夹持倾角为82.18°~88.96°,定方位夹持倾角80.32°~88.57°;抓取试验获得的变方位抓持倾角为82.83°~89.65°,定方位抓持倾角70.70°~89.27°,仿真与试验结果具有较好一致性,且变方位夹持倾角定方位夹持倾角更接近90°,表明变方位夹持不同位姿芥蓝的向心包络扶起作用效果更好。3种初始倾角的变方位抓取试验获得的成功率均值分别为91.67%、95.83%和100.00%,定方位抓取成功率均值分别为87.50%、91.67%和100.00%,表明初始倾角越大抓取机构可获得的抓取成功率越高,变方位抓取初始倾角小的芥蓝可获得更高的成功率;不计P2方位双层手指伸入碰倒芥蓝样本,变方位抓取获得的最小抓取成功率均值为91.70%,相比定方位在P_(1)~P_(8)方位上均具有更好的包络定心抓取效果。研究可为管道水培叶菜采收装备的研制提供依据。

Hydroponic leafy vegetables can be enveloped and then clamped into the center of the planting hole in the cultivated pipeline,in order to avoid the root residues for the accurate root cutting of stems.However,the centering envelope grabbing mechanism with the fixed orientation can vary greatly with the different initial inclination angle and the position of hydroponic leafy vegetables.In this study,a variable orientation grabbing mechanism was proposed to adjust the orientation relative to the center of the planting hole during grabbing.Taking Lvbao hydroponic Chinese kale as the research material,the related properties were measured to determine the structural parameters.The initial opening angle of 15°,the closing angle of 30°,the rotating angle of 45°,and two times rotating speed of the two fingers were determined for the gripper during envelope grasping.A comparison test was performed on the grasping performance and success rate of the fixed and variable orientation grabbing mechanism with different initial inclination angles and positions using multi-body dynamics simulation with ADMAS software and laboratory grabbing test.The simulation results showed that the clamping inclination angle increased significantly with the increase of the initial inclination angle.At the initial inclination angles of 50°,65°,and 80°,the mean clamping inclination angles of 84.25°,85.86°and 87.76°for the variable orientation centering and clamping state,were better than those of 82.17°,83.73°and 86.41°for the fixed orientation approach.At the position of P1-P8,the mean clamping inclination angles of 84.89°,85.93°,84.81°,86.86°,85.16°,86.47°,86.70°,and 86.78°for the variable orientation centering and clamping state,were better than those of 82.67°,85.09°,84.64°,85.09°,84.13°,83.17°,83.94°,and 83.53°for the fixed orientation.The grabbing test also show that the grasping inclination angle increased,as the initial inclination angle increased.In the inclination angles of 45°-60°,>60°-75°,and>75°-90°,the mean grasping inclination angles of the variable orientation grabbing at different positions were 85.78°,87.91°,and 87.57°,respectively,which were better than those of 83.08°,85.00°and 86.76°for the fixed orientation.At the position of P1-P8,the mean grasping inclination angles of 87.18°,87.10°,84.83°,88.13°,87.63°,86.90°,87.92°,and 88.21°for the variable orientation grabbing,were better than those of 80.89°,86.98°,88.07°,85.88°,81.56°,83.99°,85.51°,and 86.68°for the fixed orientation.In the hydroponic Chinese kale with different initial inclination angles,the mean values of grabbing success rate were 91.67%,95.83%and 100.00%for the variable orientation,which were better than those of 87.50%,91.67%and 100.00%for the fixed orientation.Except for the P_(2) position,the mean values of grabbing success rate of variable orientation grabbing at different position were higher than those of the fixed orientation.It infers that the simulation was consistent with the test.The variable orientation grabbing was more applicable for the better performance of the centering envelope grabbing mechanism.High-speed photographic images presented that the main reason for the grabbing failure at P_(2) was that the double-layer finger was directly contacted and pushed with the extended leaves of the hydroponic Chinese kale during entering and positioning.Therefore,it can be expected to avoid the collision of the fingers and the extended leaves in future.The finding can provide a strong reference for the harvesting equipment of hydroponic leaf vegetables.