白芦笋选择性收获机末端执行器作业分析与试验

为实现白芦笋高效、低损伤采收,设计了一种适用于白芦笋选择性收获机的末端执行器,并推导出一种驱动力的计算方法。为驱动末端执行器完成入土、剪切、夹持、拔取等动作,需对其入土驱动力、剪切力以及夹持力等控制参数给出定量描述。首先,针对入土驱动力问题,利用DEM仿真建立末端执行器-土壤离散元模型,研究末端执行器与土壤作用过程,分析末端执行器入土驱动力;其次,从切割白芦笋和土壤两方面分析末端执行器的剪切力,利用万能试验机与DEM仿真建立白芦笋-末端执行器-土壤的互作用模型,借助万能试验机模拟末端执行器的刀片切割白芦笋过程,确定白芦笋剪切强度,结合从DEM仿真角度测得末端执行器刀片切割土壤所需的剪切力,确定末端执行器剪切力参数范围;再次,通过万能试验机模拟末端执行器夹持白芦笋过程,确定白芦笋抗压强度,结合从DEM仿真角度分析末端执行器在土壤中完成夹持动作所需的夹持力,确定末端执行器夹持力参数范围。最终,确定末端执行器入土驱动力FRT195 N、剪切力FJQ1.8 N、夹持力FJC13 N的参数范围。根据确定的末端执行器的参数范围,选取几组参数组合进行田间采收试验,试验结果表明:在入土驱动力200 N、剪切力2 N、夹持力11 N的参数组合下,白芦笋的采收率大于99%,损伤率小于3%,损伤率的数值在可接受范围内,符合白芦笋低损伤采收的要求,为白芦笋选择性收获机实现选择性、低损伤采收提供了一定的理论支持。

Analysis and Experiment on Selective Harvesting Mechanical End-effector of White Asparagus

In order to achieve high efficiency and low damage recovery of white asparagus, an end effector was designed for selective harvesting of white asparagus, and a calculation method of driving force was derived. In order to drive the end effector to complete the action of earth, shear, clamping and pulling, the control parameters such as driving force, shear force and clamping force must be described quantitatively. Firstly, aiming at the problem of driving force, DEM simulation was used to establish the end-effector-soil discrete element model, the process of end-effector and soil was studied, and the driving force of end-effector was analyzed. Secondly, the shearing force of the end-effector was analyzed from the cutting of white asparagus and soil. The interaction model of white asparagus-end-effector-soil was established by universal testing machine and DEM. The shearing strength of white asparagus was determined by means of universal testing machine. And the shearing force of cutting the soil was determined from the DEM simulation, and the range of shearing force parameters of end-effector was determined. Thirdly, the process of the end-effector holding the white asparagus was simulated by the universal testing machine. And the compressive strength of white asparagus was determined, and the clamping force required by the end-effector in the soil was analyzed from the DEM simulation, and the range of the clamping force parameters of the end-effector was determined. Finally, the parameters range of the driving force FRT>195N, the shear force FJQ>1.8N, and the clamping force FJC<13N were determined. According to the parameters of the end-effector, a few combinations of parameters were selected for field harvesting test. The results showed that the recovery rate of white asparagus was more than 99% and the damage rate was less than 3% under the conditions with driving force of 200N, shear force of 2N and the parameters of clamping force of 11N. The damage rate was within acceptable range, which was accorded with the requirements of low damage of white asparagus, and provided theoretical support for selective harvesting of white asparagus and low damage recovery.