Abstract:Aiming at the problem that on-film transplanting of sweet potato transplanters failed to meet the agronomic requirements of "small film opening and more buried nodes",based on the agronomic requirements of hull-shaped transplanting for sweet potato seedlings, an idea of pressing and cutting was proposed, and a reciprocating direct-insertion on-film transplanting device for sweet potato seedlings was designed. The overall structure and working principle of the device were elaborated, the structural parameters were determined, and a mathematical model of transplanting motion was established. Taking the transplanting trajectory of the device as research object, with driving speed ratio, installation angle of seedling inserting rod and length of seedling inserting rod as factors, and theoretical film opening area and theoretical length of sweet potato seedlings in ridge as indicators, trajectory simulation tests were carried out. The single-factor experiment determined the influence laws and optimal parameter ranges of each factor, with the driving speed ratio being 1.92~2.40(°)/mm, the seedling insertion mounting angle of 80°~100°, and the seedling insertion length of 180~220 mm. A three-factor three-level bench orthogonal test was conducted under the conditions of transplanting depth of 80 mm and within the optimal parameter ranges, and the optimal parameter combination was obtained: driving speed ratio was 2.24(°)/mm, installation angle of seedling inserting rod was 90°, and length of seedling inserting rod was 204 mm, corresponding to a film opening area of 1580 mm2 and a length of sweet potato seedlings in ridge of 234 mm. Field verification results showed that under the conditions of transplanting depth of 80 mm and the optimal parameter combination, the actual film opening area was 1680 mm2 and the length of sweet potato seedlings in ridge was 221 mm, with relative errors of 6.1% and 5.8% compared with the bench test, respectively. Both errors were within an acceptable range, and the design objectives were achieved.