Design and experiments of the clipping-stem type non-circular gear transplanting mechanism for corn pot seedlings

Corn is one of the most important grain crops with a wide range of planting areas in recent years. The planting mode of corn is divided mainly into the field direct seeding and the pot seedling transplanting. Among them, the corn pot seedling transplanting is one of the dryland transplanting ways to obtain a high yield. However, manual transplanting cannot fully meet the large-scale requirement of the planting quality, due to the high cost, high labor intensity, and low efficiency. Fortunately, mechanized transplanting can be expected to reduce the labor intensity for the high yield. Therefore, there is an urgent need for mechanized equipment for corn pot seedling transplanting in the corn industry. In this study, a clipping-stem, non-circular gear and five-bar transplanting mechanism was designed for the corn pot seedling, in order to realize the integrated transplanting trajectory of corn pot seedling picking and planting. Taking the corn pot seedling as the research object, a systematic analysis was performed on the physical and mechanical properties of pot seedlings, including the moisture content, physical morphological characteristics, the force of picking seedlings, and the force of breaking the stem. The kinematics and mathematical models were established to clarify the working principle of high accuracy, four poses, non-circular gear and five-bar mechanism. The optimization target of the transplanting mechanism was determined to combine the physical and mechanical properties of corn pot seedlings with the agronomic requirements of transplanting. The auxiliary software of optimization design was also compiled using Matlab platform. A series of mechanism parameters were optimized to fully meet the target values, including the bar length of the mechanism, the non-circular gear transmission ratio, the gear pitch curve, and the theoretical analysis trajectory. The simulation experiment of the virtual prototype was then carried out in Adams software using a three-dimensional model of the mechanism. The simulation of static trajectory was basically consistent with the theoretical analysis. The idle experiment was also performed on the transplanting and bench test. The transplanting experiment was carried out on a self-designed experiment bench, where the transplanting frequencies were 40, 50, and 60 plants/min, respectively. A tray of corn pot seedlings was used in each group of experiments. The results showed that there was a relatively consistent performance in the actual trajectory of the transplanting mechanism, the simulation, and the theoretical. Furthermore, the success rate of picking seedlings decreased, whereas, the lodging rate and the injury rate of seeding increased, and the final qualified rate of planting decreased with the increase of transplanting frequency. Specifically, the success rate of picking seedlings was above 95%, while the lodging rate of seedlings was within 4%, and the injury rate of seedlings was within 2% under the transplanting frequency of 40-60 plants/min. In the bench experiment, the success rate of picking seeding was 95.04%, the lodging rate of seeding was 3.31%, the injury rate of seeding was 1.65%, and the qualified rate of planting was 90.08% when the transplanting plant spacing was 300 mm and the frequency was 60 plants/min. The optimization fully met the harsh requirements of dryland planting machinery. A better transplanting performance was achieved with the optimal seed spacing of transplanting and the high uprightness for the corn pot seedling. The feasibility of the actual transplanting mechanism was also verified to ensure the correctness of the comprehensive theoretical design. The finding can provide an important reference to optimize the integrated transplanting machine for corn pot seedling picking and planting.