拨杆喂入式菠萝采收机构设计与试验

为解决菠萝采收效率低、成本高等问题，该研究根据菠萝果实的几何特征和花萼结合处易折断、茎秆较脆等生物学特性设计了一种拨杆喂入式菠萝采收机构，分析了影响收获效率的主要因素，包括：拨禾轮半径、拨禾轮转速、履带行走机的前进速度等，并确定了关键部件的结构和运动参数。在对菠萝果实与茎秆分离的运动学和动力学分析的基础上，确定了菠萝果实在花萼与茎秆连接处或在靠近花萼的茎秆处断裂的力学依据，其中成熟度较高时，菠萝花萼处的脱落区结合强度较小，受切应力作用而断裂；成熟度较低时，茎秆较细处因弯曲过大而断裂。建立采收过程的多体运动学仿真模型，分析了收获过程中菠萝植株的力学和动力学特征，求解不同运动情况下拨杆接触果实时的接触力峰值。两因素五水平正交台架试验表明，菠萝收获效果最佳的参数组合为前进速度0.4 m/s、拨禾轮转速22.8 r/min。最优参数组合的田间试验结果表明：拨杆喂入式菠萝收获机进行收获作业时工作顺畅，采收后的植株生长状态良好；菠萝果实收获成功率为84%，损伤率为9.53%，综合评价指标为85.94%。研究结果可为菠萝采收机械的研究提供参考。

Feeding-type harvesting mechanism with the rotational lever for pineapple fruit

The pineapple industry has been one of the major economic sources in tropical and subtropical regions of China. However, the pineapples are still harvested manually at present. A serious harm can be from the hard stalk and many prickly thorns at the fruit surface and both edges of every leaf. Mechanical equipment can be expected to promote harvesting speed and labor cost savings. Previous studies focused mainly on vision identification, robotic end-effector, and collection devices for a long period of time in this field. But most can stay in the theoretical research stage so far. Only a few commercial applications of supply conveyors or transport trolleys have been used to collect manually harvested pineapples. In this study, a feeding-type mechanism with a rotational lever was proposed for pineapple harvesting, according to the geometric characteristics of pineapple fruit and the biological properties of easy breakage at the junction of the calyx and brittle stalks. This pineapple harvesting mechanism has also removed the adjustment of relative posture corresponding to the individual fruits during harvesting. The harvester was firstly advanced at a certain speed, and then the rotational lever that fixed on a wheel exerted a contact force on the fruit surface when contacting with the pineapple fruit. This force applied to the fruit acted on the combination of the stalk and the calyx, leading to a shear stress generated by the deformation of the stalk or a tensile stress at the fruit-stalk combination zone or at a point below the combination. The fracture finally occurred in the stalk, as the shear stress was greater than the maximum shear stress of the stalk. A systematic investigation was implemented to determine the influencing factors of harvesting efficiency. The main factors included the radius and the rotating speed of the rotational lever fixing wheel, as well as the forward speed of the high-bed traveler. The optimal parameters were then determined as follows: the radius of the rotational lever fixing wheel was 210 mm, the rotating speed was 9-48 r/min, and the forward speed was 0.1-0.4 m/s. Meanwhile, the kinematic and kinetic analysis was performed on the detachment process of pineapple fruit from the stalk. The detachment mechanism of pineapple fruit was obtained at the calyx-stalk junction or at the stalk near the calyx. A mechanical and kinematic model was established using ADAMS software. The peak contact forces were then optimized under various motion states in the combinations of simulation parameters. A two-factor and five-level orthogonal bench test indicated that the optimal combination of parameters was the forward speed of 0.4 m/s and the rotating speed of the fixing wheel of 22.8 r/min. A harvesting success rate of 84%, a damaged rate of 9.53%, and an overall yielding ratio of 85.94% were achieved in the preliminary field trials using the optimal combination of parameters obtained in bench tests. Besides, the field test showed that this pineapple harvester worked smoothly and the postharvest plants grew well without plant emergence and reproduction. The finding can provide a strong technical reference for the mechanized batch harvesting of pineapple fruits.