## 3 Furrowing Depth Stability Control--Design of Profiling Adjustment Device
### Passive Profiling Adjusting Device
#### 3.1.1 Parallel Four-Bar Mechanism and Depth-Limiting Wheel  
In order to improve the profiling effect of the parallel four-bar mechanism, [PERSON] and [PERSON] et al. designed a bidirectional parallel four-bar profiling mechanism. It can realize left-right and up-down profiling of planter units, which improves the profiling effect of no-tillage seeders for uneven surfaces such as sloping cultivated land [36; 37]. [PERSON] et al. designed a forward speed compensation mechanism on a corn planter, the key component of which is a parallel four-bar mechanism that uses the guide rod for horizontal speed compensation. Based on theoretical analysis, the fundamental parameters affecting the stability of seeding depth are sub-crank length, main crank angular velocity, and center distance, and the experimental results show that the qualification rate of seeding depth of the device can reach 94.89% after optimization of critical parameters [38]. The profiling wheel rolls along the ground under the action of the parallel four-bar mechanism and the downforce adjusting device. Even in the undulating ground, it can still play the role of depth-limiting profiling. According to the different arrangement positions of the depth-limiting wheel, the profiling adjustment device can be divided into three types: front profiling, rear profiling, and synchronized profiling, as shown in Figure 2[25]. The front profiling wheel is installed at the front end of the planter, and a soil covering and compacting device is usually installed at the rear. [PERSON] designed a narrow-row dense-planting soybean planter with front profiling and carried out force analysis and parameter optimization of the profiling mechanism to improve the stability of the profiling adjusting device for the depth of furrow opening on upward and downward slopes [39]. The MECAV4 series of precision planters from MONSEM in the United States installs a clad cleaner in front of the planter unit, which compacts the soil and controls the depth while clearing the clods and stones. The front position profiling reduces the width of the planter unit, and the planter unit has good passability [30]. However, the front position profiling mechanism is prone to the problem of profiling advancement, which affects the depth of furrow opening [40]. The rear position profiling wheel is mounted on the rear end of the planter, while the depth-limiting wheel can act as a compacting device. Nonghaha \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Model Number** & **Enterprise Name** & **Machine Pictures** & **Sowing Crops** & **Main Features** \\ \hline
2 BMJZ Series No-Till & & & & Mechanical \\ Planter [34] & Doublelan & & & spring-loaded \\  & & & & downforce adjustment, \\  & & & & row spacing 45–65 mm \\  & & & & adjustable \\ \hline
2 BYFS Series No-Till & & & & Mechanical \\  & & & spring-loaded rear \\  & & & & profiling adjustment, \\  & & & & independent floating \\  & & & & compacting wheel \\ \hline \hline \end{tabular}
\end{table} 
Table 2: _Cont._  
Figure 2: Type of depth-limiting wheel arrangement. 2 BYFSF-4 corn no-tillage fertilizer precision sowing machine is a model with more rear imitation application, which adopts a one-piece drive shaft, with ample transmission power and consistent rotational speed of rows of planter unit, which still does not affect the normal sowing in the case of skidding of a particular row of ground wheels [35]. The rear position imitation reduces the width and weight of the seeding unit, and the planter unit has good passability. However, the rear imitation mechanism is prone to imitation lag, which affects the depth of the furrow opening. The most widely used profiling wheel arrangement is synchronized profiling. Synchronized profiling wheels are arranged on both sides of the furrow opener, which has a good synchronization effect and avoids profiling advancement or lagging. The John Deere 1775 NT is one of the iconic synchronized profiling planners, capable of high-speed precision seeding in no-till situations [41]. [PERSON] et al.