Design and experiment of the double row alternating toothed sieve pineapple conveying mechanism

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 Box-Behnken, 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.