Mechanical analysis of seedling detaching from movable tray and influence factors of adhesion

Abstract: In order to solve the problem that adhesion force between the seedling pot and the seedling tray caused the damage in seedling pot in the process of seedling transplantation, and further affected the success rate of picking seedling and the growth of seedling after transplantation, the force analysis of the seedling pot and the side plate in the opening process of movable tray was carried out. It was found that there was a positive correlation between adhesion force and opening peak force of the movable tray, a negative correlation between the dip angle of side plate of movable tray and the adhesion force of the seedling pot, a positive correlation between the moisture content of soil matrix and adhesion force of the seedling pot, and a positive correlation between the speed of opening parts of movable tray and the adhesion force of the seedling pot. In order to further study the influence of various factors on the adhesion force of the seedling pot, the response surface method was used to design the optimization test. During the test, the rape seedlings which were planted in the movable tray were selected as the test materials. The opening peak force of the movable tray which expressed the adhesion force was selected as evaluation index. The 3 variables: the dip angle of side plate of movable tray, the speed of opening parts of movable tray, and the moisture content of soil matrix were selected as the test factors. The experimental data were analyzed in Design-Expert software and the model of the regression equation was obtained. The adequacy of regression equation model was evaluated by analysis of variance. The results indicated that the F-value of model was significant (P<0.05), and the F-value of lack of fit was not significant (P>0.05), and the model was reasonably good for predicting the actual situation. Moreover, the 3D response surface was plotted and analyzed and the results showed that the optimized values could be obtained from the test model. Finally, the optimal combination of parameters could be obtained by using optimization function in Design-Expert software. The optimal combination of parameters was as follows: the dip angle of the side plate of movable tray was 9.24°, the moisture content of the seedling pot was 55%, and the speed of opening parts of movable tray was 7.98 mm/s, which achieved a minimum value of opening peak force of 6.97 N. In other words, operators could get a minimal adhesion force between the seedling pot and the movable tray. The verification tests were carried out and the results showed that the opening peak force was 7.12 N and the error was 2.1%. The soil matrix loss rate of seedling pot was 3.14%, compared with the minimum matrix loss rate of 4.39% in the seedling removal test. The matrix loss rate decreased significantly. So, the adhesion force between the seedling pot and the movable tray was minimal when the optimized parameter combination was used in the test. By adjusting the combination of parameters of each factor, the adhesion force between the seedling pot and the side plate could be reduced in the opening process of movable tray, so as to reduce the loss rate of the soil matrix. Therefore, this study has laid an important theoretical foundation and reference basis for further exploring the mechanism of soil matrix damage in the mechanized transplanting process of rape seedling.