Design and parameter optimization of corn head with wheel type rigid-flexible coupling snapping device to reduce loss

Grain loss rate is one of the most important performance index of corn head in mechanized harvesting. Seed harvesting is the main development direction of mechanized corn harvesting. The characters of seed harvesting corn variaty increased the urgency to reduce grain loss on corn head. The paper was proposed to solve the problem of grain loss on corn head. Theoretical analysis was conducted to the snapping process. Corn ear was subjected to pull force by the snapping rolls and the pull force transferred by corn stalk. Corn kernels were divided into 2 types due to their force condition. A kernel at the bottom end of corn ear was subjected to reaction forces by stripper plates, corn cob and the adjacent kernels and shear force by the pedicel. Kernels out of contact with the stripper plates were subjected to reaction forces by the adjacent kernels, pull force and shear force by corn cob. As the impact force was related to the impact time according to the theorem of impulse, the paper analyzed collision model between corn ear and stripper plates in the snapping process. A mathematical model was obtained about the impact time and intrinsic parameters of the system. The impact time was dependent on system mass, stiffness coefficient and damping coefficient, which laid on the mechanical structure and materials of collision objects. So, the impact force would decrease as the impact time could be prolonged by reducing the stiffness coefficient and raising the damping coefficient. The quantity of shed kernels could be reduced consequently. The paper proposed a corn head with wheel type rigid-flexible coupling snapping device to reduce loss. The corn head consisted of the frame, gear-box, snapping rolls, gathering chain, wheel type rigid-flexible coupling snapping device, and chain wheels. The wheel type rigid-flexible coupling snapping device consisted of snapping wheel axle, spring seat axle, supporting axle, buffer spring, and snapping wheel frame. Force analysis was conducted on the snapping wheel. According to the force conditions and dimension boundary condition, the structure diameters of snapping wheel, snapping wheel frame, and buffer spring were confirmed. In order to obtain the optimal parameters with the minimum loss rate of wheel type rigid-flexible coupling snapping device, the optimization experiments were conducted of the factors at 3 different levels. In the optimization experiments, the snapping wheel radius was designed at 10, 15 and 20 mm respectively, the flexible body thickness was at 2, 4 and 6 mm respectively, the snapping rolls rotating speed at 700, 800 and 900 r/min respectively. The Response Surface Analysis method was used to design the experiments. The software Design-Expert 8.0.6.1 was used to analyze the data. Regression equation was induced according to the experiment and analysis above. The optimal combination of wheel type coupling snapping device was as follows: The snapping rolls rotating speed was 700 r/min, the snapping wheel radius was 15 mm, the flexible body thickness was 4 mm. Verification contrast test was conducted between corn head with wheel type rigid-flexible coupling snapping device and the one with snapping rolls and stripper plates on corns at different moisture contents. As the kernels moisture contents were 21.8%, 16.7% and 13.4%, the grain loss rate decreased 53.4%, 48.6% and 47.0% respectively. This study provides not only theoretical basis but also design reference for the improvement of corn harvester design.