Abstract:The adequate seeding downforce and consistent sowing depth are beneficial to improve the seedling quality in the precision planting operation. To avoid the problems of undesired soil compaction and uneven germination caused by the change of soil conditions, and realize the intelligent monitoring and evaluation of the sowing quality, the design of a downforce and sowing depth monitoring and evaluation system was presented for the multi rowcrop planter. The system was mainly composed of downforce measurement device, sowing depth measurement device, electronic control unit (ECU) for data acquisition and actuator control, GNSS receiver, intelligent terminal and pneumatic driving device. The downforce and sowing depth measurement devices were applied to measure the downforce acting on the gauge wheels and the sowing depth based on the axle pin sensor and the angle sensor of limit shank respectively. The pneumatic driving device was used to provide the necessary downforce, which mainly included airspring, gas generator, electricgas proportional valve and gas tank. In order to quickly replenish the air loss caused by the rapid regulation of downforce and improve the response speed of the system, a section control method for the pneumatic driving device was adopted, and the gas generator with a double cylinder air pump was driven by a hydraulic motor. In addition, a human machine interface (HMI) of the intelligent terminal and the control program of ECU were developed based on controlled development system (CoDeSys) programming environment to realize the realtime monitoring and evaluation of seeding quality through CAN bus communication. To improve the accuracy of measurement, the static modeling tests of sowing depth and downforce were conducted on an indoor test platform and a downforce measurement model integrating sowing depth variable was established. The response characteristic test of the control system showed that the step response overshoot was less than 5.97%, and the adjustment time was positively related to the control rowunit number and the set air pressure in the range of 0.1~0.6MPa, which was not more than 2.35s for the six rowunits planter. Furthermore, in order to test the performance of the system, field performance experiments were carried out with four control modes (left section control with 600 N target downforce, right section control with 300N target downforce, mechanical adjustment with helical spring and dead weight adjustment of rowunit) and three setting sowing depths (25mm, 50mm and 75mm). The experiment of soil compaction and sowing downforce control showed that the section control method could achieve more stable soil compactness, and the right section control method could achieve the optimal downforce stability in the shallow rotary tillage filed with no less than 95.78% qualified rate. The experiment of sowing depth control effect showed that the quality of sowing depth was decreased significantly with the increase of setting sowing depth. In the depth range of 25~75mm, the minimum qualified rates of left section control, right section control, mechanical adjustment and dead weight adjustment were 91.92%, 92.53%, 70.44% and 58.72%, the corresponding maximum standard deviations (SD) were 2.22mm, 3.11mm, 3.69mm and 7.70mm, and the corresponding maximum coefficients of variation (CV) were 3.52%, 4.40%, 4.96% and 14.01%, respectively. The above results showed that the system with section control method could improve the consistency of sowing depth and accuracy of downforce, and had better performance of sowing depth and downforce control than the system with mechanical adjustment and dead weight adjustment methods.
