Multi-objective Optimization of Sheet Structure in Threshing Process

In order to explore the relationship between the process parameters of the threshing process and the structural characteristics of the post threshing sheet, and to find the optimal process parameters, a multi-objective optimization model was established based on the temperature and humidity of the secondary moistening material, threshing frequency, and pneumatic machine frequency, as well as the structural characteristics of the post threshing sheet. The raw material was initial flue-cured tobacco Yun 87 from the Yunnan production area in 2022. Then, a multi-objective optimization model was built based on the linear equation system, and 9 sets of optimal process parameter combinations were obtained by solving the model. Validation experiments were designed and conducted. The results show that the proportion of sheet structure characteristics has a strong linear correlation with various key process parameters(the value of R were 0.776, 0.809, 0.779, 0.722, 0.664, respectively). The optimal parameters were moisture content during conditioning at 18.1%, conditioning temperature at 45.6 ℃, the frequency of first-stage threshing unit is 42.3 Hz, the frequency of second-stage threshing unit is 40.7 Hz, the frequency of third-stage threshing unit is 44.4 Hz, the frequency of first-stage pneumatic unit is 40.8 Hz, the frequency of second-stage pneumatic unit is 37.5 Hz, the frequency of ninth-stage pneumatic unit is 46.1 Hz. Under the optimized condition, the rate of large and medium-sized leaves has significantly increased, while the stem content in the strips has decreased. It indicated that adjusting the conditioning temperature, moisture content, the frequency of threshing unit, and the frequency of pneumatic unit appropriately is beneficial for improving the proportion of structural characteristics.