Abstract:
Chrysanthemums (
Chrysanthemum morifolium R.) can serve as one of the primary dual-purpose Chinese herbal medicines for both medicinal and edible applications. It is often the pressing demand for mechanical harvesting during production. The harvesting can directly determine both the quality and yield of chrysanthemum flowers. However, existing comb-brushing harvesters are limited to high missed-picking rates, low terrain adaptability, and flower damage. In this study, a comb-tooth drive device was designed for chrysanthemum harvesting. A systematic evaluation was also implemented on the chrysanthemum biomechanical properties using a universal testing machine. The results show that the chrysanthemums broke first at the stem under tensile or shear action. The tensile failure load of the stem was less than the shear load. Chrysanthemum picking machinery was required to minimize the damage and impurities for the high picking rate. A biomimetic structure was developed to compare the manual picking. The device consisted of a multi-row comb picking mechanism with the rotary-translational motion, a cylinder-driven gantry lifting, and a rubber crawler chassis with high soil viscosity in the chrysanthemum fields. Theoretical analysis and calculation showed that the structure and working parameters of the key components were obtained, such as the eccentric wheel transmission mechanism and picking comb teeth, as well as the required power for picking. The structural parameters of the picking comb teeth were verified after static simulation. The relationship between picking, working, and forward speed was determined in the picking trajectory. Real-time remote control of the forward and working rotation speed was realized using pulse-width modulation signals. The harvesting action was decomposed into three procedures: "plant separating and inserting, comb translational brushing, rotating flower throwing, and collecting". The better performance of this device was twofold. 1) Its comb teeth shared less impact, and then effectively reduced the collision damage to chrysanthemums, when inserted into the plants, compared with the existing comb-tooth circular rotation and shearing picking mechanisms; 2) Its picking trajectory also exhibited a larger longitudinal range, in order to effectively reduce the missed picking. A lifting system was equipped to improve the adaptability of the picking mechanism. The picking height was adjusted for the different chrysanthemum heights in order to effectively reduce the missed harvesting. There was a minimal forward thrust exerted by the picking component on the plant. The low-impact force was also generated by the comb teeth penetrating into the chrysanthemum plant. The Ansys-Adams module was used to simulate the interaction between chrysanthemums and machines. A systematic investigation was carried out to determine the damage mechanism of chrysanthemum harvesting. The critical acceleration was 4.49×10
6 mm/s
2 for the chrysanthemum picking and shedding. While the damage acceleration threshold was 1.125×10
7 mm/s
2. Simulation test showed that the optimal working speed was conducive to chrysanthemum picking. The optimal range of working speed was determined for the selection. Quadratic regression orthogonal models were established between field experimental and performance indicators. The optimal combination of the parameters was identified: comb tooth clearance of 8.0 mm, forward speed of 0.13 m/s, and picking speed of 21 r/min. The better performance was achieved in a picking rate of 73.55%, an impurity content of 4.51%, and a damage rate of 2.88%. This comb-tooth drive device can provide the theoretical and technical support for the mechanical chrysanthemum harvesting.