Analysis of seedling-picking trajectory error in gear train seedling pick-up mechanisms considering center-distance errors

• Analyzes the influence of center distance error on the error of seedling picking trajectory. • Analyzes the influence of center distance error on the error of the velocity and acceleration changes of the needle tip of the seedling. • Establishes the error and movement variance models of the coordinates and kinematic parameters (velocity, acceleration) of the needle tip of the center distance error in the firstly and secondary transmission. • Analyzes the influence of center distance angle error on the error of seedling trajectory. To improve the success rate of seedling-picking, this study investigates the influence of center-distance errors (CDE) on the seedling-picking trajectory of a planetary gear–based seedling pick-up mechanism (SPUM). The mathematical model of kinematic parameters of needle-tip was developed to characterize the resulting variations in coordinates and associated, incorporating multiple types of CDE—including first-stage transmission (FST), second-stage transmission (SST), and angular misalignment between the two stages. The effects of first-stage CDE (△ h = 0.05–0.30 mm), second-stage CDE (Δ L 2 = 0.05–0.30 mm), and angular misalignment (Δ δ 1 = −1–1°) between the two stages on the displacement, velocity, and acceleration of the needle-tip were quantitatively analyzed. In addition, the relationships among CDE, tooth backlash, and trajectory deviation were examined. The results show that a first-stage CDE of 0.3 mm leads to a maximum needle-tip coordinate deviation of approximately 4 mm, and larger CDE cause markedly greater fluctuations in the seedling-picking trajectory. These findings demonstrate that precise calibration and control of center-distance are essential during both the design and manufacturing of SPUM.