Design and optimization of transplanting mechanism with planetary gear train composed of helical gears and noncircular bevel gears

Abstract: In order to obtain high-quality wide-narrow distance planting trajectory that can solve the problems such as large horizontal offset of picking seeding trajectory in inclined and shaping wider plant hole, a wide-narrow distance transplanting mechanism with spatial planetary gear train composed of non-circular bevel gears and crossed cylindrical gears was put forward based on spatial planetary gear train composed of elliptical bevel gears and crossed cylindrical gears. Non-circular bevel gears were better than traditional gears, such as circular gears and elliptical gears. In addition, the pitch curve of the non-circular bevel gear was general so that this mechanism could achieve more potential spatial planting trajectories. Transplanting mechanism with this kind of bevel gears was one kind of spatial non-uniform velocity transmission mechanism which could obtain the spatial planting trajectory that met diverse agronomic requirements. The theory of wide-narrow distance transplanting mechanism was introduced and the optimization goal of planting trajectory was designed. A smooth, continuous and closed spherical curve was designed by fitting the free form spline, which was used to represent the big end pitch curve of non-circular bevel gear. The equations of spherical big end pitch curve were given. Based on the D-H matrix transformation, the kinematics optimization model of mechanism was built up. The key points' displacements of transplanting mechanism were calculated. Several main parameters affecting the wide-narrow distance planting trajectory were analyzed. The shape of non-circular bevel gear's big end pitch curve played a major role in the shape of wide-narrow distance planting trajectory; the initial angle of planetary carrier was a key parameter affecting the posture of wide-narrow distance planting trajectory; the staggered angle of non-circular bevel gear pair and bevel gear pair's cone distance had decided the offset of picking and taking seeding trajectory. A optimization program about wide-narrow distance transplanting mechanism was written to study the kinematics, and a set of optimal parameters meeting the working requirements of wide-narrow distance rice transplanter was obtained by the method of human-computer conversation afterward. The lateral optimal trajectory and ratio formed by spatial planetary gear train composed of non-circular bevel gears and spatial planetary gear train composed of elliptical bevel gears were compared. The advantage was the smaller horizontal offset and lower speed of picking seeding trajectory; the time of pushing seedling period and returning period were much less; the probability that took back the rice seedling was decreased; and the overall height of wide-narrow distance planting trajectory was raised. A three-dimensional model of wide-narrow distance transplanting mechanism was obtained. Virtual prototype test was performed by the software named Adams and a model machining of the transplanting mechanism as well as its testing was made, and the shape of tow trajectory was almost same. The result showed that the transplanting mechanism with spatial planetary gear train composed of non-circular bevel gears and crossed cylindrical gears could fulfill the requirement of wild-narrow distance rice transplanter and had better performance than transplanting mechanism with spatial planetary gear train composed of elliptical bevel gears and crossed cylindrical gears.