折断分离式菠萝采摘末端执行器设计与试验

Design and Experiment of Breakaway Separation Type Pineapple Harvesting End-effector

摘要:

根据菠萝果实和茎秆结合处存在截面突变的生物学特征，设计了一种仿人工掰折采摘方式的折断分离式末端执行器，关键部件包括直线导向套和曲线导向套2部分。基于菠萝果-茎断裂原理进行力学特性试验，结果表明，最大折断转矩、最大折断角度和临界损伤力分别为3.64 N·m、67.4°和178.72 N。建立菠萝夹持机构运动学模型，以传力比大于等于1.25和尺寸紧凑为约束目标，得到直线导向套中直线导轨长度为60 mm和各连杆尺寸;基于静力学分析得到曲线导向套中曲线导轨螺旋角为45°，驱动力为90 N。建立仿真模型，分析菠萝采摘过程植株力学特征，求解夹爪与果实的接触力峰值。试制样机并进行采摘试验，试验结果表明，抓取成功率100%，采摘成功率86.7%，验证了末端执行器的可靠性，研究结果可为菠萝机械化采摘提供参考。

Abstract:

Based on the geometric features of the pineapple's outer shape, the easy breakage at the calyx joint and the brittleness of the stem biological characteristics, a breakaway separation type end-effector that mimics the manual breaking method of harvesting was designed. The key components of this harvesting device included a linear guide sleeve and a curved guide sleeve. Mechanical property tests based on the principle of pineapple fruit-stem fracture showed that the maximum breaking torque, maximum breaking angle, and critical damage force were 3.64 N·m, 67.4°and 178.72 N, respectively. A kinematic model of the pineapple clamping mechanism was established, with the goal of achieving a force transmission ratio at least 1.25 and a compact size. Optimizing with Matlab, the length of the linear guide rail in the linear guide sleeve was determined to be 60 mm and the dimensions of each link were obtained. Based on static force analysis, it was found that the driving force magnitude was related to the helix angle of the curved guide rail in the curved guide sleeve. A smaller helix angle resulted in increased overall size and weight, while a larger helix angle caused the thickness of the curved guide sleeve to be less than the diameter of the guide column, making it impossible to break the pineapple. Therefore, the middle value of 45° was chosen as the helix angle, and the driving force was obtained as 90 N. A simulation model was established to analyze the mechanical properties of the pineapple plant during the harvesting process, comparing the peak contact force between the gripper and the fruit with the critical damage force. A prototype was trial-produced and harvesting tests were conducted. The test results showed that the grasping success rate was 100% and the harvesting success rate was 86.7%, which verified the reliability of the end-effector. The research results can provide a reference for the mechanized harvesting of pineapples.