Design and test of the differential speed counter-rotating drum type device for peanut picking

Peanut (Arachis hypogaea L.) is an annual herbaceous plant of the Leguminosae family in Rosales, which is the fourth largest cash crop in the world. Peanut production can also promote edible oil supply and food consumption. Mechanical peanut sowing and harvesting are often required for actual production, especially for pod picking in harvesters. However, the widely used peg-tooth drum-type peanut picking devices severely restrict the harvesting quality and efficiency. Peanut picking devices are also limited to the incomplete pod picking and high pod breaking rate in the current full feeding harvester. In this study, a drum-type peanut picking device was designed with differential speed counterrotation. A dynamic model was also established for the interaction mechanics between peanut pods and the inner/outer picking drums, including the axial transport model of materials on the spiral blade of the inner drum, the force model of pods under the action of the outer drum, and the collision damage model of peanut pods using Hertz contact theory. The structural parameters of picking mechanisms were optimized after theoretical derivation. A contact model was constructed using the discrete element method (DEM) in EDEM software. A calibrated bonded discrete element model of peanut vine and pods was established, according to the physical and biomechanical properties of the Yuhua 18 peanut variety in coastal saline-alkali land. A three-factor three-level quadratic regression orthogonal rotation combination test was conducted with the feeding rate, inner drum speed, and outer drum speed as the influencing factors, while the peanut pod picking net rate and breaking rate were selected as the response indices of harvesting performance. The ranges of the test factors were deduced after theoretical calculation. Design-Expert software was used to balance the response indices and the influencing factors. Parameter optimization was performed using the response surface method. The simulation results show that the optimal combination of working parameters was as follows: feeding rate of 3.3 kg/s, inner drum speed of 438 r/min, and outer drum speed of 45 r/min, under which the picking net rate reached 99.11% and the pod breaking rate was controlled at 1.1%. The field tests were conducted in accordance with the national standard (GB/T 8097-2008), with the original peg-tooth drum-type picking device as the control group. The test results show that the picking net rate of the device reached 99.02% and the breaking rate was less than 1.1%, which were significantly better than those of the original device with a picking net rate of 98.18% and a breaking rate of 2.04%. The field results were consistent with the simulation, which fully verified the simulation model and the high stability of the device. The picking net rate and breaking rate of the device fully met the mechanical harvesting standard of peanuts. This finding can provide a theoretical reference for the structural and parameter optimization of the drum-type peanut picking device with differential speed counterrotation during mechanical harvesting.