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Pineapple is one of the four major tropical fruits with important profits. China has been the fifth-largest producer of pineapple in the world, particularly with a large number of planting areas. Manual harvesting cannot fully meet the large-scale production of pineapples at present. Mechanical harvesting can be expected to improve the efficiency of pineapple production with labor cost savings. It is of great significance to develop mechanized equipment for pineapple production. Among them, the lever-feeding pineapple harvester has been developed for the batch harvesting of pineapples. Compared with robotic picking, it is no necessary to adjust the working parameters during harvesting plants with different heights. Therefore, the harvest speed is much higher than that of the manual and robot. However, the low success rate has been confined to collecting and conveying the harvested pineapple fruit. Many pineapple fruits are prone to damage during transport. In this study, a double-row alternating toothed sieve was designed for pineapple collecting and conveying. The device served as the intermediate or transitional conveying mechanism between the fruit receiving plate and the baffle conveyor chain. The motion equation was then established for the tip of each of the tooth-shaped sieve plates in the double-row alternating tooth-shaped sieve. A systematic analysis was made on the motion trajectory of each tooth tip in the conveying mechanism. The structural parameters of the conveying mechanism were determined, such as the length and angle of the rods, and the spacing distance between the toothed sieve plates. After that, the mechanics model was established to express the contact between pineapple fruit and the tooth-shaped sieve plates. The pineapple fruit damage-free and bounce-free boundary conditions of the conveying speeds were obtained for the conveying mechanism using the mechanic model. Furthermore, the key influencing factors were determined as the experimental parameters, including the inclination angle of the receiving plate, the rotational speed of the picking device, and the rotational speed of the conveying mechanism. A three-factor three-level frame experiment was conducted using the BoxBehnken, with the success rate of pineapple fruit conveying and the number of retained fruits as the evaluation indicators. The combination of optimal parameters was then obtained using the regression model. The field test also showed that the average fruit conveying success rate was 94.87%, and the average number of retained fruits was 2 when the inclination angle of the receiving plate was 14°, the rotational speed of the picking device was 27 r/min. and the rotational speed of the conveying device was 70 r/min. Besides, there was no damaged fruit during conveying. The device can fully meet the needs of pineapple fruit conveying. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

All pineapples are harvested manually at present in China. But manual harvesting cannot fully meet the large-scale production against the ever-increasing greying workforce. Fortunately, automatic navigation can be expected to develop the pineapple harvester. In this study, a path planning algorithm was proposed as the navigation scheme to improve the mechanization and automation level of pineapple harvesting. An improved RRT* algorithm was also used for global path planning. Firstly, the self-heuristic idea was used to constrain the generation range of sampling points. Then, the bias probability pbias was introduced to generate the random sampling points. Specifically, the sampling points were randomly generated with the probability p in the space, when p>pbias. Otherwise, the target point was used as the sampling point, in order to decrease the blindness of sampling point generation. Thirdly, the gravitational field of the artificial potential field, and the concept of direction weight were introduced in the new node expansion. The weights wg and wk were assigned to the directions of the sampling and target point, respectively, where the direction was constrained in the expansion of the new node. Fourthly, the bidirectional expansion was used to speed up the iteration speed in the double-tree expansion. Finally, the greedy algorithm was applied to prune the redundant nodes of the path. The Cantmull-Rom interpolation function was also used to smooth the path corners. Three environments (including multiple obstacles, mazes, and narrow passages) were created to simulate the path planning process, in order to evaluate the performance among the improved navigation path planning, RRT* and bidirectional RRT* algorithm. Planning time, node number, and path length were selected as the indicators. Each algorithm experimented with 30 times in every single environment. The average, maximum, minimum, and standard deviation were calculated for the simulation data of the three indicators, respectively. The simulation results showed that the average planning time of the path planning algorithm in the three environments was 17.97%, and 46.12% higher than that of the RRT* and bidirectional RRT* algorithms, respectively, while the average programming speed was 4.7, and 2.2 times as rapid as that of the RRT*, and bidirectional RRT* algorithm, respectively. Furthermore, the average node number was 87.22% and 52.52% less than that of the RRT* and bidirectional RRT* algorithms, respectively. The average path length was 3.81% and 6.08% less than the RRT* and bidirectional RRT* algorithms, respectively. The field test showed that the planning time was only 14.12% and 20.34% of the RRT* and bidirectional RRT*, respectively. The iteration number was 80.89% and 69.70% less than that of the RRT* and bidirectional RRT*, respectively. In addition, the rotation angles larger than 60° on the path planned by RRT* and bidirectional RRT* algorithms were 1.56 and 2.06 times as much as that of the improved, respectively, and the rotation angles larger than 100° on the path were 1.55 and 2.18 times. The improved RRT* algorithm can fully meet the path navigation requirements of agricultural machinery in the field. The pineapple harvester can run along the planned path to the target point as moving with the speed of 0.2, 0.4, and 0.6 m/s, but the position and heading deviation increase with the moving speed. This finding can provide a sound reference for the navigation development in agricultural machines. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]