Motion Control Design and Parameter Optimization of an Alternating Seedling Picking and Dropping System for a Two-Row Automatic Transplanter

To address the numerous operational steps and structural complexity associated with existing two-row automatic transplanters that use stepwise tray conveying, whole-row seedling picking with multiple claws, and rotary seedling distribution, an alternating seedling picking and dropping system was developed. The system combines trays that remain stationary during picking, left and right claw groups that alternately pick and drop seedlings, and a fixed seedling distribution device that alternately feeds seedlings to the planting units. The seedling trays are mounted on a two-station rotary platform and remain stationary during picking. Linear motion modules drive two groups of picking claws, each consisting of two claws, in the longitudinal and transverse directions to pick and drop seedlings. Two groups of fixed seedling distribution tubes receive the seedlings and sequentially feed them to the duckbill planting units. To achieve precise and efficient seedling picking, a picking path was planned based on the tray cell arrangement, and an S-curve acceleration and deceleration strategy was applied to determine motion timing parameters for different seedling positions. Based on the receiving window of the planting mechanism, spatial and temporal matching relationships were established among the seedling picking, dropping, and planting processes. The continuous operating sequence for an entire tray was calculated to determine the operating parameters and time margins at each picking position. Experiments and parameter optimization were conducted to investigate the effects of the distribution tube opening instant, planting frequency, and seedling receiving height on seedling receiving deviation. The selected operating parameters were a distribution tube opening instant of 0.56 s, a planting frequency of 51 seedlings per row per minute, and a seedling receiving height of approximately 49 mm. Separate machine tests yielded a picking and dropping success rate of 96.48% and a receiving success rate of 100% under the selected operating conditions. These results support the feasibility of the proposed system under the conditions evaluated.