## 2 Materials and Methods
### Analysis of Sowing Depth Control Process
#### 2.3.2 Mechanical Analysis of Sowing Depth Adjustment Mechanism  
To facilitate the acquisition of the soil compressive force \(F_{Sy}\), the depth-limiting contact force \(F_{JC}\) between the gauge wheel arm and the depth-limiting block is monitored by a load pin.  
Figure 5 shows the structure of the sowing depth adjusting mechanism. Pulling the sowing depth adjusting handle can make the depth-limiting stopper move back and forth around the rotating axis D to adjust the target sowing depth. The load pin is installed in the contact position of the depth-limiting block and the gauge wheel arm, the periphery is wrapped in the depth-limiting block and fixed by the axle pin support, the gauge wheel arm and the gauge wheel are hinged in OA and the frame, respectively, and the working time of the gauge wheel arm swings around the point A and the contact limit with the depth-limiting block at the point B. The force analysis with point A where the gauge wheel arm is located as the research object shows that  
\[F_{Sy1}L_{x}+F_{JC}L_{x1}=0 \tag{7}\]  
\[F_{Sy1}=F_{Sy}\cos\theta_{c} \tag{8}\]  
where \(F_{JC}\) is the depth-limiting contact force, the contact force between the depth-limiting block and gauge wheel arm, and the direction is always perpendicular to OA, N; \(F_{Sy1}\) is the fractional force of \(F_{Sy}\) in the vertical OA direction, N; \(L_{x}\) is the effective length of the gauge wheel arm, mm; \(L_{x1}\) is the length of the force arm of \(F_{JC}\) on OA, mm; and \(\theta_{c}\) is the angle between the gauge wheel arm OA and the horizontal plane, \({}^{\circ}\).  
Figure 4: Schematic diagram of the upper and lower limits of the four-bar linkage: (1) integrated pressure-reducing cylinder (IPRC), (2) upper rod, (3) limit plate, (4) lower rod, (5) spring tie rod, (6) cylinder pressure plate, (7) top plate, (8) cylinder bracket.  
The value of the contact force \(F_{JC}\) can be measured by the sensor, and its value reflects the degree of compaction of the sidewall of the seed groove by the gauge wheel, and it can also be used as the basis for judging the sowing depth: as shown in Figure 1, the row unit is in state II, the floating of the gauge wheel causes the sowing depth to be too shallow, the value of the contact force \(F_{JC}\) is 0 and the compaction force \(F_{Sy}\) is only the weight of the gauge wheel. Unlike in state I, \(F_{Sy}\) is the effective compressive force, if \(F_{Sy}\) is maintained at 300 N, and at this time, according to Equations (7) and (8), the greatest value of the contact force \(F_{JC}\) is 300 N. To estimate the actual value of this contact force \(F_{JC}\), assuming that the impact force on the row unit due to surface heave is \(n\) times the mass of the row unit, the compressive force \(F_{Sy}\) at the gauge wheel is transformed into  
\[F_{Sy}=(n+1)m_{\max}g \tag{9}\]  
where \(m_{\max}\) is the full-load mass of the row unit, kg; and \(g\) is the gravitational acceleration, take 9.8 m\(\cdot\)s\({}^{-2}\).  
Joining Equations (7)-(9), the contact force \(F_{JC}\) is obtained as  
\[F_{JC}=\cos\theta_{c}\frac{(1+n)m_{\max}gL_{x}}{L_{x1}} \tag{10}\]  
The measured \(m_{\max}\) is about 120 kg, the angle \(\theta_{c}\) of the gauge wheel arm in the minimum sowing state is 30\({}^{\circ}\) and the force arm action ratio \(L_{x}\):\(L_{x1}\) of the contact force \(F_{JC}\) is 0.25. When \(n\) is taken as 2, the maximum contact force \(F_{JC}\) is 8700.5 N when substituted into Equation (10).