咬合式柑橘采摘末端执行器优化设计与试验

Optimization Design and Test of Occlusal End-effector for Picking Citrus

摘要:

针对柑橘自动化采摘末端执行器剪切果柄难度大的问题，设计了一种采用球形闭合进行咬合剪切果柄的柑橘采摘末端执行器。对柑橘果柄进行剪切力学特性研究，通过对果柄直径、剪切速度、果柄斜角、树叶阻挡数、刀片间隙5个因素进行剪切试验，基于最小二乘法多项式拟合建立响应面进行影响因素分析;对末端执行器进行几何建模，并以控制刀片间隙为主要约束条件，以增大拢果定位容差为优化目标建立参数优化模型，优化后拢果定位容差由9.2%~48.8%提升到26.0%~71.7%;对关键部件进行了有限元仿真，仿真得到球壳变形对刀片间隙的影响结果。最后设计柑橘采摘末端执行器样机，在柑橘果园进行实地采摘剪切性能测试，直径小于等于4 mm的果柄采摘断柄成功率达95%，满足柑橘采摘要求。

Abstract:

Aiming at the difficulty of citrus automatic picking, a terminal actuator using spherical closure for occlusion and shearing of citrus fruit stalks was designed. Firstly, the shearing mechanical properties of citrus fruit stalks were studied, and the effects of five factors on the peak shear force were analyzed, i.e., stalk diameter (2~4 mm), shear speed (20~200 mm/min), stalk angle (0~75°), number of leaves blocked (0~3 pieces), and blade gap (0.5~2 mm). The test results showed that the peak shear force required to shear citrus fruit stalks was increased with the increase of stalk diameter. With the increase of shear speed, the peak shear force was decreased, but not significantly. The stalk angle was one of the factors affecting the peak shear force. Between 0° and 30°, the stalk angle had little effect on the peak shear force, but when it was between 30° and 70°, the peak shear force was increased significantly with the increase of the stalk angle. The blockage of a few leaves had little effect on the peak shear force. Blade clearance was one of the main factors affecting the peak shear force. Large blade clearance had a great impact on shearing thin stalks, which may be difficult to shear off. Controlling the blade clearance within 1 mm was critical for the success rate of the end effector picking. The geometry modeling of the end-effector was carried out, and the parameter optimization model was established with the main constraint condition of controlling the blade gap and the optimization goal of increasing the fruit positioning tolerance. The fruit positioning tolerance was increased from the original 9.2%~48.8% to 26.0%~71.7%. The static analysis of the model was carried out and the selection of the electric push rod was completed. At the same time, the finite element simulation of the model was carried out, and the influence results of the spherical shell deformation on the blade gap were obtained, and the strength of the structure was checked. Finally, the prototype of the citrus picking end-effector was developed, and the field picking and shearing performance test was carried out in the citrus orchard. For the fruit stalk with a diameter less than or equal to 4 mm, the success rate of the fruit stalk breaking was 95%, meeting the requirements of picking citrus.