Working principle and design of the multi-flexible fingered roller pineapple harvesting mechanism

Abstract: Pineapple has been the third-largest yield of tropical fruit after banana and mango in recent years. Current mechanical harvesting of pineapple cannot fully meet the large-scale production during this time, particularly in the early stage. In this study, a multi-flexible fingered roller mechanism was proposed for pineapple harvesting to simulate the fruit detachment process after the manual breaking. The breaking moments of the pineapple abscission layer were measured in the solution by the universal electronic testing machine. A mechanized pineapple harvesting was conducted to evaluate the bending moment for the break of the abscission layer at the calyx of the pineapple under the action of two rows of flexible fingers. Then, the large deformation of a flexible finger was characterized using the pseudo-rigid body theory, when the flexible finger interacted with the pineapple. The load was applied on the end of the flexible finger to record the force-displacement data, and further compare the experimental and simulation data. Furthermore, the harvesting mechanical model and the evaluation function under the critical damage condition of pineapple were established, according to the harvesting mechanism model, as well as the physical and mechanical features of the pineapple. The feasible parameters of the harvesting mechanism were calculated for enabling harvesting. An experimental device was also developed for the trial. The harvesting experimental device was mounted on the high ground clearance tractor for testing. The performance indicators of the harvester were analyzed, according to the three evaluation criteria of harvesting rate, damage rate, and operation efficiency. Experimental results showed that the most pineapple fruits were harvested successfully, where the two rollers of the harvesting machinery inclining at the angle of the 35°, the length of the left flexible fingers was 120 mm, the clearance between each of the left flexible fingers was 30 mm, the length of the right flexible fingers was 150 mm, and the clearance between each of the right flexible fingers was 10 mm. The harvesting and damage rates were 85% and 5%, respectively, where the average harvest time of a single fruit was about 1s, indicating the harvesting machinery was fully meet the requirement of pineapple harvesting. In the unsuccessful harvesting, the failure resulted from the mismatched flexible finger length, fruit size, harvesting posture, and position. Specifically, the relatively small fruit diameter probably led to the insufficient contact between the flexible finger and the pineapple, further requiring the too small bending moment for the break of the abscission layer at the calyx of the pineapple. If the harvesting position was too high, the contact position between the two flexible fingers and the pineapple was almost at the same horizontal height, where the bending moment cannot be formed. The harvest damage was mainly attributed to the excessive size of some pineapple fruits and an excessive extrusion force formed when fingers interacted with pineapple fruit. This finding can provide a strong reference for the pineapple harvesting machinery.