Design and field testing of the air-suction machine for picking up Chinese jujube fruits

Abstract:【Objective】Nowadays the jujube harvesting in Xinjiang area is still based on manual or semimechanizedoperations，and the production process is very difficult. Abundant demand of labor andlong-time operating have resulted in a higher production cost and lower efficiency, which greatly limitsthe development of jujube industry, so the research on mechanized harvesting for jujube fruits can behelpful to solve the problems with an objective to reducing the labor’s number and intensity, as well asshortening the harvesting period. Because the mechanized transport and impurity removal have notbeen solved, they are apparently considered as the main shortcomings of harvesting jujube. Especially,the current jujube growing in Xinjiang area is based on HD planting with the small scale and differentvarieties, which are directly limiting the development of large- scale harvesting machines. Comparedwith the other processes of jujube industry, the mechanization level of jujube harvest is very low. In orderto promote the whole mechanization level of jujube industry and increase the output efficiency, it isvery urgent for us to develop the appropriate harvesting machine for jujube. In the present study, a newtype of air- suction machine with smallsize and great adaptability for picking up jujube was designed. 【Methods】This machine was designed with negative pressure to pick up the‘Gray’jujubes, so the parameterof suspension velocity was the key to separate the jujube fruits from impurities, and a new deviceincluding wind velocity sensor, observation tube and frequency converter was developed to test thesuspension velocity and acquire the parameters, and thus the ranges of suspension velocity on‘Gray’jujube were 17.2-21.4 m· s-1 and 15.1-18.4 m· s-1, respectively, and this machine was designed to pick upand transport the jujube fruits dropped on the floor by negative pressure. The structure was mainly composedof pipette, delivery hose, separating box, shredding device, discharging device, tilting screen,walking system and transmission mechanism; and the fan and forward powers were provided by a smalldiesel engine. When the machine was working, the fruits and impurities dropped on the floor were collectedfrom the ground by pipette and delivery hose, and then transported into the separation box by theair flow, and thus the fruits and impurities were separated by the fence, and the debris were removed inthe separation box. The results showed that the impurities included branches, leaves and light debris. Sothe fence spacing was designed as 15 mm for fruits to pass through. According to testing, the three-axissize, volume and density; and the shredded cleaning device could smash impurities and prevent theblockage. Y112M-2.C2 centrifugal fan was selected as the important device to apply in the machinebased on the airflow conveying theory, the route and pressure losses were taken into consideration inthe equations, and the unloading capacity was also calculated by the airflow transport; when the fruitsfell into the box and were discharged through the discharging device, the efficiency of discharging devicewas calculated as 25 r ·min-1. Then the fruit was directly discharged on the tilting screen and slid intothe collecting frame by the unloading device, the clods, stones and jujubes were separated by the tiltingscreen, and the impurities were cleared to crush by the debris and discharged from the fan outlet.【Results】The field testing verified that the performance of this machine was perfect, and the pickingup efficiency, impurity removal rate, fruit damage rate and missing rate were considered as the key indexesto estimate the performance, and the results showed that the picking efficiency of this machinecould reach 220 kg·h-1 and 285 kg·h-1, respectively, and the impurity rates were 3.75% and 4.28%. Thedamage rates after picking-up were 3.15% and 4.05%, and the picking rates were 92.20% and 90.65%,respectively. So this machine could basically meet the design requirements with 16 hours continuous operationsin Xinjiang HD jujube orchards, and the size of machine is suitable for using in the dwarf HDplantings in Xinjiang area.【Conclusion】The air-suction machine for picking up jujube fruits could reducethe labor intensity, shorten the harvesting operation period, reduce the labor cost, improve themechanization leveland promote the development of jujube industry, and this machine has a great marketappeal in the jujube industry. The analysis and calculations have determined the mechanical and operatingparameters of key components. The field testing of the jujube suction harvesting prototype machineverifies that the performance could meet the harvesting requirement, and it is beneficial to the furtherdesign and optimization of pneumatic jujube harvesting machinery.