## 3 Furrowing Depth Stability Control--Design of Profiling Adjustment Device
### Active Profiling Adjusting Device
#### 3.2.2 Pneumatic Driven Downforce Adjustment Device  
The pneumatic-driven downforce adjustment device mainly utilizes a pneumatic device instead of a mechanical spring, which is mounted on a parallel four-bar mechanism to achieve the adjustment of furrow depth by adjusting the seeding monobloc [57]. The MAXIMETRO series of pneumatic precision planners from MAXCHIO, Italy, provide uniform adjustment of furrowing depth using air springs [49; 58]. [PERSON] et al. designed a downforce adjustment mechanism based on a pneumatic drive device, using air pressure and temperature sensors to detect the working state of the pneumatic drive device through the airbag deformation to control the depth of the planter unit furrowing. The test results show that with the device in the high-speed operation of 10 km/h, the coefficient of variability of the depth of the sowing can still reach 6.97%, and the stability of the furrowing depth is high [59]. [PERSON] et al. designed an active adjustment system for sowing depth based on air springs and Flex sensors, which reduced the error by 40% compared with passive adjustment [60]. In order to reduce the influence of downforce on furrowing depth, [PERSON] et al. identified the critical parameters of the air spring that had a significant influence on the downforce according to gas-solid coupling simulation and optimized the key parameters to improve the stability of the furrowing depth of pneumatic active profiling adjusting device [61]. The pneumatic-driven downforce adjustment device has the advantages of better adaptability and lightweight. At the same time, the pneumatic shock absorber can withstand the impact of very high pressure and vibration and has a sound vibration-damping effect. However, the pneumatic pressure-driven downforce regulator requires an external pneumatic pressure source on the planter, which is costly [59]. The active profiling adjusting device can maintain a consistent sowing effect in operation without manual intervention relative to the passive profiling adjusting device. It can also improve seeding efficiency and reduce waste and manual labor costs while ensuring uniform crop growth. However, the active profiling adjustment device needs to be assisted by sensors, which is difficult and costly to develop. The passive profiling device has higher durability and lower operating costs than the active profiling device. It is more suitable for small plot operations. It is easy to operate and requires a lower educational level for farmers. However, the position of the mechanical spring needs to be adjusted to realize the adjustment of the downforce according to the experience before the operation, which is challenging to match with the actual conditions of the soil, although it can get better consistency of the sowing depth. Compared with the hydraulically driven downforce adjustment device, the pneumatic-driven downforce adjustment device requires an additional external pneumatic pump. This results in increased costs. The pneumatic-driven downforce adjustment device has a slower response time than the hydraulically driven downforce adjustment device. AgLeader has found that the response time of a downforce regulator can be reduced from 20 s to 1 s by utilizing the hydraulically driven downforce adjustment device developed by the company instead of the pneumatic-driven downforce adjustment device [62]. Therefore, the hydraulically driven downforce adjustment device is more suitable for plots with large surface undulations and is better suited for high-speed operations. The pneumatic-driven downforce adjustment device has better vibration-dampening properties than the hydraulically driven downforce adjustment device, which ensures better stability of the furrowing depth for less undulating ground. In summary, the current research on the profiling adjustment device is divided into two aspects. The first is to optimize the design of the traditional mechanical structure.