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.