Optimization design and experiment of the variable differential gear train planting mechanism

Abstract

In order to improve the adaptability of the planting mechanism for different plant spacings, a variable differential gear train planting mechanism based on precise pose and trajectory control was proposed by combining the open chain 2R rod group and the variable differential gear train. According to the pose requirements of receiving seedling point, transporting seedling point and planting point, three precise pose points of constrained planting trajectory were determined. Through the three-position motion generation structural synthesis method, combined with computer-aided optimization design software, a set of mechanism parameters that meet the planting requirements were optimized. Based on the optimized mechanism parameters, by only changing the coordinates of two trajectory shape control points, three planting trajectories with key point position information adapted to 300 mm, 400 mm and 500 mm plant spacing were obtained by interpolation, and three pairs of total transmission ratio of three groups of variable differential gear trains were calculated. When distributing the total transmission ratio of the mechanism, the fixed axis gear train and the differential gear train are combined. The fixed axis gear train included a pair of non-circular gear pairs and a pair of positive gear pairs, which were convenient for disassembly and assembly. The former drives the sun gear at variable speed, and the latter drives the planet carrier at uniform speed. Based on this structure, the transmission ratio of the positive gear pair is -1, and the transmission ratio of the differential gear train is 0.5. The sub-transmission ratio of the single-stage non-circular gear pair was calculated and the pitch curves of three pairs of noncircular gears were solved. Three pairs of non-circular gear pairs with different transmission ratios were replaced in turn and three sets of planting mechanisms were modeled in three dimensions. The virtual prototype motion simulation was completed by ADAMS software, and the physical prototype was built for vegetable pot seedling planting test. The theoretical solution was consistent with the attitude and trajectory of the actual test. When the test sample size was 100 plants, the actual average plant spacing was measured to be 303 mm, 402 mm, and 503 mm, with errors of 1.3%, 1.25%, and 1.88%. The width of the moving hole was 72 mm, 70 mm, and 71 mm, and the planting success rate were 94%, 96%, and 95%. The test results verified the correctness of the optimization design results of the mechanism, indicating that the variable differential gear train planting mechanism can adapt to a variety of plant spacing and has good planting effect.