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Many plug seedling grippers have a complex structure and bulky volume in design. They have poor performance in holding substrate and keeping a high integrity rate. In this paper, a new multi-needle seedling gripper is proposed. Based on the elasto-plastic contact model (ECM) in the EDEM, numerous particles with different material properties are modeled to simulate real seedling substrate and to study the interaction between steel needle and growing substrate. Taking the medium integrity rate as an evaluation index, explore the influence of different needle diameters, insertion depths, and insertion and grabbing speeds on the substrate integrity through the response surface method. The optimized technical parameters of the gripper was obtained through Design-Expert. The results show that the insertion depth of needles has a significant effect on the integrity of the raising medium, and the optimal depth is 40 mm. Insertion and grasping speed and depth have an interaction effect, while other factors have no significant influence on substrate integrity. Optimization results imply that when the diameter of the needle was 3 mm, the insertion depth was 40 mm, and the insertion and grabbing speed was 1 m/s, the growing medium integrity rate was the highest, reaching 89.10%. Under these parameters, prototype tests were conducted, and the highest medium integrity rate was 87.34%, which increased by an average of 7.25% compared with existing studies. The research has reference value for improving the operation quality of the plug seedling transplanter and the design of the seedling gripper. It also shows that solving problems of needle-discrete substrate interaction based on the discrete element method is feasible.

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