###### Abstract  
Seed-fertilized drill machines with fluted rollers generally utilize a calibrated relationship between the fluted-roller rotation speed and mass flow rate to control the application rate. However, this relationship model gradually deteriorates with operating time and is easily affected by working conditions. To maintain the initial operating accuracy, a self-calibrating system for adjusting the control model parameters was designed. It utilizes the application-rate information and fluted-rollers rotation speed data during the operation process to dynamically establish the calibrated relationship. During the field tests performed 18 times, the self-calibrating system could dynamically re-calibrate the relationship model. After the model parameters were updated, the application rate control system maintained a high accuracy level, though the relative deviation of control parameters was relatively higher. The average relative deviations between actual and theoretical cumulative application rates were 0.97% and 1.22% for seeding and fertilizing, respectively, and the standard deviations were 0.69% and 0.62%. Correspondingly, the average relative deviations of control parameters were 7.29% and 7.86%, and the standard deviations were 1.16% and 3.06%. These results indicate that the proposed method with closed-looped control can maintain high-quality control performance and improve the productivity of the drill machine, which will benefit the agricultural production. application rate control; seed-fertilized drill machine; fluted rollers; parameters calibration +
Footnote †: journal: Medical  
depend on the relationship model between the mass flow rate of fertilizing or seeding and the rotation speed of the driving shaft to the control. Based on this relationship model, real-time control of the driving shaft rotation speed can be performed to control the application rate when the target application rate and vehicle speed are given [8]. This kind of open-looped control structure is simple and economic. The disadvantages are that it cannot eliminate the error caused by interference and the control accuracy easily decreases once the relationship model parameters change because of the change of working conditions. The closed-looped control structure can effectively suppress this interference and improve the response performance of the control system [9]. Closed-loop application-rate control structure has not been widely applied, due to the lack of efficient and real-time application-rate measurement sensors. Over the past 30 years, agricultural scientists and technicians around the world have conducted extensive research on seeding and fertilizing application-rate measurement sensors. The main techniques for application rate measurement include the photoelectric method [10; 11], impulse method [12; 13], capacitance method [14], and weighing method [15]. The principle of the photoelectric method is that the photoelectric sensor will be blocked in the process of material flow and a photoelectric signal will be generated. The quantity of material can be calculated by the sparse degree of the photoelectric signal to measure the mass flow rate. However, the characteristics of materials (such as density, moisture content, and transparency) will have an impact on the measurement accuracy, which needs to be calibrated frequently. At the same time, the probe gets easily covered with fertilizer powder, therefore, it needs to be cleaned regularly [16; 17]. The principle of the impulse method is that the material impacts the impulse sensor at a certain angle, and the measured impulse is converted into an electrical signal. The real-time application rate is then estimated indirectly by electrical signal intensity. The impulse method is mainly applied to the yield monitoring system of combine harvesters, and the yield map is obtained by combining the speed sensor and GPS (Global Positioning System) information. The impulse method is suitable for large-range mass flow rate detection [18; 19; 20].