Working parameters optimization and experimental verification of inclined-inserting transplanting manipulator for plug seedling

Abstract: The transplanting manipulator is the equipment that directly contacts with seedlings, and its development and optimization is important for mechanical transplanting of plug seedlings. This paper has designed an inclined-inserting transplanting manipulator for automatic transplanting of plug seedlings in greenhouse. The manipulator adopts the extracting method that extracts the seedling directly after the steel needles have been inserted in the growth medium with an angle. As a result, the extracted plug seedlings will have sufficient integrity for further growth. Moreover, this manipulator extracts seedlings with four steel needles to ensure the uniformity of insertion point, and the total inserting motion of four steel needles just uses single driver. Furthermore, this paper is aimed at optimizing the operation parameters of transplanting manipulator and focused on the success rate. Based on the force analysis of plug seedlings in the extracting process, the stress relation equation is obtained to determine the key factor that mainly influences the success rate. The result shows that the extracting resistance and the limit break force are the major factors determining the extracting force. The extracting resistance can be obtained by the test, and the limit break force is the key factor for the success rate. In addition, the inserting distance, inserting depth and inserting angle of steel needle are determined as key parameters for the limit break force by the analysis of structure and operation principle of transplanting manipulator. The optimization test is conducted to obtain the maximum value of the limit break force and the optimal parameters of transplanting manipulator. The seedlings of anthurium which are planted in the 128 plug trays are selected as the test materials. Moreover, the response surface method is used to design the optimization test with considering the comprehensive effect of multi-factor to limit break force. In the optimization test, the limit break force is determined as the test index. Meanwhile, the 3 variables, i.e. inserting distance, inserting depth and inserting angle of steel needle, are selected as the test factors. And an adjustable prototype of transplanting manipulator is used to the extracting test, and the FGS-500TV-S digital force gauge is used to measure the limit break force. As a result, the model of the regression equation is obtained by the test. The adequacy of the model of the regression equation is evaluated by the analysis of variance. The result indicates that, the F-values of model and various factors are very significant（P＜0.01）, the F-value of lack of fit is not significant, and the model is reasonable for predicting the actual situation. After that, the three-dimensional (3D) response surface is drawn and analyzed. And it is found that the response surface for 3 variables is the type of quadratic convex surface. The result also proves that the test model is able to obtain the optimized value. Finally, using optimization function of Design-expert software, the optimal parameters for maximizing the limit break force are determined. The optimal combination of operation parameters is as follows: the inserting distance is 11.5 mm, the inserting depth is 43 mm, and the inserting angle is 14°, which achieve the maximum value of the limit break force of 3.89 N. The performance of optimized transplanting manipulator is examined by the test. The result proves that it can finish the task of seedling transplanting with excellent performance, and archive the 98% success rate. The optimal operating parameters are reliable, stable and can be applied in practical operation.