Study on Measurement Method and Control Model for the Seeding Downforce of Seeding Unit Based on Bilateral Depth Limiting

Consistent sowing depth and proper soil compaction can improve the emergence uniformity, which significantly impacts the subsequent seed growth and the final crop yield. A new downforce measurement method and four downforce control models were proposed to avoid instability in the sowing depth and inconsistent compression on both sides of the seed wall. The four downforce control models were to take the average downforce on both sides(DAVE), downforce on left sides(DLE), maximum downforce on both sides(DMAX), and minimum downforce on both sides(DMIN) as the current downforce feedback(DSU) for adjustment, respectively. The static bench test and field comparative test were carried out to verify the feasibility of the new downforce measurement method, and the optimal control model was selected from four models according to different soil conditions. The results of the bench test implied that there was a significant linear correlation between the signals of the force sensor and the downforce. The linear correlation coefficients on both sides were more than 99%. The results of the field comparative test indicated that there was no significant difference between groups in the sowing effect evaluation indexes of the four control models under the tilled field(TF). Compared with the other three control models, the DAVE control model had better performance in adjusting downforce, which enhanced the qualified index and consistency of sowing depth with an improvement of 0.55~1.67% and 0.07~0.37%, respectively. The results also demonstrated that there were significant differences in downforce on the DL and DR under the untilled field(UTF), due to the influence of ground undulation and soil differences. The DMIN control model outperformed the other three control models, with the qualified index and consistency of sowing depth increasing by 5 ~10%, 1.78~2.15%, respectively. Thus it can be seen that the new downforce measurement method and a proper downforce control model corresponding to different soil conditions could achieve better working quality.