# Development and Field Testing of a Suspended Mulberry Branch Harvesting and Stubble Cutting Machine
## 3 Key Component Design
### Cutter Design
#### 3.1.3 Design of the Grain Separation Device  
During the process of agricultural machinery harvesting, the main function of the grain separation star wheel is to lift up the crops and guide them towards the cutting device. According to the Agricultural Machinery Design Handbook, the necessary condition for the normal operation of the grain separation star wheel is that the speed ratio (the ratio of the line speed of the separation wheel to the machine's forward speed) must be greater than 1. When the speed ratio is less than or equal to 1, the linear velocity of the grain separation star wheel is less than or equal to the forward speed of the machine. This means that the grain separation star wheel cannot effectively guide the crops backward, and the crops may tip forward or fail to be guided to the cutting device in a timely manner. Increasing the speed ratio can expand the working range of the star wheel and improve its effectiveness. However, under constant machine forward speed, excessively increasing the line speed  
Figure 5: Schematic diagram of the sawing device. (**a**) Front view. (**b**) Side view. of the star wheel may damage the mulberry branches. Based on practical experience, the recommended line speed of the separator blade should not exceed 3 m/s. The condition for the grain separation star wheel to achieve single-plant feeding is to ensure that only one mulberry tree is present between two adjacent star wheel teeth during forward harvesting. When a single feed finger of the star wheel completes one full rotation and accurately feeds a single mulberry tree, a continuous single plant feeding process is formed. As shown in Figure 6, the first mulberry tree is at point a. After being grabbed and longitudinally output by feed finger 1, the machine moves to position Sab, at which point the second mulberry tree moves from point b to point a. If feed finger 2 reaches point a in time or exactly at the right moment, it ensures that only one mulberry tree is fed per rotation of the finger. This process can be expressed by Equation (2) [31]:  
\[N_{b}\geq\frac{6v}{S_{ab}} \tag{2}\]  
where \(S_{ab}\) is the plant spacing of mulberry trees (m), with \(S_{ab}\) = 1 m taken, \(v\) is the tractor forward speed (m/s), with \(v\) = 2 m/s taken, and \(N_{b}\) is the rotational speed of the star wheel (r/min). It is calculated that: \(N_{b}\geq\) 60 r/min, that is, the linear velocity of the star wheel is \(v\geq\) 1.44 m/s. As shown in Figure 7, the grain separation device consists of a fixed frame and a movable frame. The fixed frame is welded to the cutting platform, while the movable frame is connected to the fixed frame by bolts, allowing for easy adjustment of the separation height and the longitudinal spacing between the separation star wheel and the saw blade in contact with the mulberry branches. The left-side separation star wheel is equipped with a hydraulic motor and bolted to the movable frame, with a torque sensor installed to monitor and output torque signals. The device uses a pair of external spherical vertical bearing housings (bolted to the movable frame) to provide stable support. A drive sprocket is located between the separation star disc and the spindle bearing housing, transmitting power to the other star disc via a chain. During operation, the separation star wheel rotates clockwise, conveying the mulberry branches to the right side in the direction of the machine's forward movement. The design of the upper guide rod is intended to prevent the branches from continuing to rotate with the star wheel if they have not been successfully  
Figure 6: Schematic diagram of continuous single plant feeding. separated, thus avoiding blockages. The hydraulic motor provides power and ensures that the separation star wheel operates smoothly at different speeds through chain transmission, effectively preventing mulberry branch blockages.