仿手指拨动切割式柑橘采摘末端执行器设计与试验

    Design and experiment of the end effector for citrus picking imitating finger plucking and cutting

    • 摘要: 针对柑橘枝叶遮挡严重、果柄难以准确定位且倾角差异大而导致传统末端执行器采摘成功率低、留柄长度过长、效率不高等问题,该研究以脐橙为研究对象,提出了一种仿手指拨动柑橘果实并被动切割果柄的末端执行器。首先对脐橙尺寸及果柄的直径、倾角及剪切力等物理力学特性参数进行测定,基于此设计了三指构型末端执行器整机结构。该结构采用两并排组合的V型切割装置,并由曲柄-滑块-摇杆机构驱动其往复运动。进而对V型切割装置进行理论计算,确定了切割刀片的安装倾角、开口夹角及对应的剪切力峰值等参数,并对不同夹角条件下的切割力峰值进行仿真验证,结果表明,当夹角为10°、倾角为6°时切割力峰值最小。然后对曲柄-滑块-摇杆机构进行结构参数设计并建立运动学模型,仿真分析表明,该机构在多指构型拨动果实并完成切断果柄的过程中具有急回特性。最后搭建末端执行器样机并开展果园采摘试验,采摘成功率达95.38%,脐橙损伤率为0,采摘效率为6.50 s/个,同时对电机转速及采后留柄长度开展两因素三水平正交试验,结果表明,当电机转速为30 r/min时,柑橘采后留柄长度最短,仅为19.8 mm。该末端执行器能够实现复杂果园枝叶遮挡工况下的果实高效无损采摘,提高采摘成功率及效率,研究成果可为采摘机器人末端执行器的研发提供技术参考。

       

      Abstract: China is a major citrus producer in the world. In the southern regions of our country, citrus is the fruit with the largest planting area and the most important economic status. However, citrus picking faces challenges like branch shading, difficulty locating fruit stalks, and varying stalk angles, causing low success rates and efficiency with traditional end effectors. This study takes navel oranges as the research object. This paper proposes a new type of end effector for fruit picking that mimics the manipulation of citrus fruits by fingers and passively cuts the fruit stalks. First, the physical parameters of the navel orange, such as its size, the diameter of the fruit stalk and the inclination angle, are determined. Then, the mechanical parameters such as the shear force and Young's modulus of the navel orange fruit stem are measured using the electronic universal testing machine. Based on the measurement data, the overall structure of the three-finger configuration end effector composed of two V-shaped cutting blades combined side by side is designed. The transmission mechanism of the crank-slider-rocker connecting rod mechanism is adopted to drive the reciprocating motion of the fingers, thereby prodding the citrus fruits and cutting the fruit stalks to achieve the picking function. For the design of the V-shaped cutting device, parameters such as the installation inclination angle of the V-shaped cutting blade, the opening angle of the blade, and the peak force range are determined through theoretical calculation. The peak cutting force under different included angle conditions is simulated and verified by using Ansys software. The simulation results show that the peak cutting force of the V-shaped cutting blade is the smallest when the included angle is 10° and the inclination angle is 6°. For the crank-slider-rocker transmission mechanism, its structural parameters are designed through theoretical calculation. Kinematic simulation analysis is carried out through Adams software, and it is determined that the transmission mechanism has a sharp rotation characteristic during the process of cutting fruit stalks. Finally, outdoor orchard picking tests are conducted on the trial-produced new type of end effector. The success rate of picking is 95.38%, the damage rate of navel oranges is 0, and the picking efficiency is 6.50 seconds pel orange. Meanwhile, a two-factor three-level orthogonal experiment is conducted on the citrus picking operation parameters and the post-harvest fruit stalk length. The variance analysis of the test data are performed using the Design-Expert software. The result shows that when the motor speed is 30 r/min、minhe post-harvest fruit stalk length of citrus is the shortest, only 19.8mm. This end effector can achieve rapid and non-destructive fruit picking under complex conditions where branches and leaves in the orchard are blocked, improving the success rate and efficiency of fruit picking. The research results can provide technical references for the development of the end effector of the picking robot.

       

    /

    返回文章
    返回