## 5 Furrowing Depth Stability Control--Automatic Control System
### Multi-System Fusion Regulation  
Setting only a separate downforce control or sowing depth control still affects the stability of sowing depth and cannot meet the requirements of precision sowing [88]. For this reason, experts and scholars in relevant fields proposed multi-system fusion regulation to realize real-time monitoring and on-site evaluation of sowing depth. [PERSON] et al. developed a depth control system for a cereal seeder that complies with the ISO 11783 communication standard. Using eight sensors to measure the angle and distance of the planter and estimating the working depth based on the acquired signals, the control system operates at a frequency of 10 Hz, which allows the planter to realize that with its error of no more than 10 mm at driving speeds of up to 10 km/h and improves the stability of the furrowing depth of the cereal-based planter [89]. [PERSON] et al. designed a downforce seeding depth monitoring and evaluation system based on CAN bus communication, which utilizes angle and axle pin sensors to detect the seeding depth and downforce and improves the response speed of the pneumatic-drive unit system. The test results showed that the minimum sowing depth pass rates corresponding to left zone control, proper zone control, mechanical adjustment, and self-weight adjustment were 91.92%, 92.53%, 70.44%, and 58.72%, respectively. The sowing depth monitoring and evaluation system substantially improved the sowing depth stability of the planter compared with mechanical and self-weight adjustment [90]. In order to improve the stability of the furrow profiling system for sloping cropland with large surface undulations, [PERSON] et al. designed an agricultural terrain profiling system that can adapt to the tilting of the terrain undulations. The experimental results showed that the elevation mimicry error was 1.61 mm, and the slope error was 0.56\({}^{\circ}\) at the operating speed of 2 km/h, which provided an experimental platform for the seeding depth control system [91]. The use of separate downforce control or seeding depth control is less costly and easier to develop than multi-system fusion regulation. Due to the time required for sensor transmission and system processing, the speed of seeder advancement varies each time, so it is difficult for the system to accurately control the operation of the profiling components, which will lead to advancement or lagging of the seeder profiling. This error can be reduced by using simple feedback regulation of the system. However, due to the complexity of field operating conditions, feedback control of downforce or seeding depth alone does not meet the requirements of precision seeding. Multi-system fusion adjustment is usually real-time monitoring and field evaluation of seeding depth. Compared with separate feedback control of downforce or sowing depth, it can adjust the operating status of the profiling components according to the planter in real time and improve the operating accuracy. From the above analysis, pure downforce control or sowing depth control is not enough to maintain the stability of sowing depth. In order to improve the stability of sowing depth, scholars at home and abroad have gradually integrated downforce control and sowing depth control to realize real-time monitoring and on-site evaluation of sowing depth to achieve the requirements of precision sowing. Presently, domestic and foreign research on the depth of furrow profiling control systems mainly focuses on flat land, and there are more mature products in the application market. However, more studies should be conducted on sloping cultivated land with large surface undulations. Due to the large ups and downs of sloping cultivated land, the traditionally designed furrowing depth control system can only cope with the ups and downs of sloping land. It is challenging to cope with sloping land's left and right ups and downs. It is easy to cause inconsistency in sowing depth. China's hilly and mountainous arable land accounts for one-third of the national area.