# Design and Experiment of Grain Litter for Sorghum Harvester
## 3 Research on Structure and Parameters of Grain Lifter
### Parameter Determination of Helical Blade on the Surface of the Grain Lifter  
Considering that the stalk is close to the surface of the centralizer under the action of gravity and is gradually righted by the spiral leaves, the straightening point of the plant is the contact position between the stalk and the surface of the grain lifter. Assuming that the section radius of the grain lifter is \(r(x)\) at the distance from the tip \(x\), the absolute motion speed of the contact point between the stalk and the grain lifter in this section is \(v(x)\), and the angular velocity of the rotation of the grain lifter is \(\omega\), then:  
\[v(x)=\omega r(x)=\omega x\tan\beta \tag{10}\]  
Further, the contact point velocity is decomposed into sliding velocity \(v_{f}\) along the spiral blade and velocity \(v_{n}\) perpendicular to the spiral blade, then:  
\[v_{n}=v(x)\sin\alpha=\omega x\tan\beta\sin\alpha \tag{11}\]  
Here, only the backward push motion of sorghum plants is considered, so the speed is projected to the axis of the grain lifter, then:  
\[v_{z}=v_{n}\cos\alpha=\omega x\tan\beta\sin\alpha\cos\alpha=\frac{1}{2}\omega x \tan\beta\sin(2\alpha) \tag{12}\]  
Here,  
\(x\)--distance fm the tip of the grain lifter, cm;  
\(\omega\)--the angular velocity of the grain lifter during operation, rad/s;  
\(\beta\)--half of the cone angle of the grain lifter, \({}^{\circ}\);  
\(\alpha\)--helix angle of a spiral blade, \({}^{\circ}\). Since the grain lifter is installed at a tilt and the machine moves in a horizontal direction, the speed is further decomposed into a horizontal speed \(v_{h}\), then:  
\[v_{h}=v_{z}\cos\theta=\frac{1}{2}\omega x\tan\beta\sin(2\alpha)\cos\theta \tag{13}\]  
Considering that the walking process of the machine is a uniform motion, in order to ensure the stable righting of the sorghum stalk, the speed of the sorghum plant is required to be approximately equal to the speed \(v_{m}\) of the machine, namely:  
\[v_{h}=\frac{1}{2}\omega x\tan\beta\sin(2\alpha)\cos\theta=v_{m} \tag{14}\]  
So, the spiral angle of the grain lifter is:  
\[\alpha=\frac{1}{2}\sin^{-1}(\frac{2v_{m}}{\omega x\tan\beta\cos\theta}) \tag{15}\]  
Obviously, for the grain lifter, it is necessary to ensure that the stalk is in a stable state of motion during the lifting process, that is, the partial speed of the plant push speed in the horizontal direction is equal to the speed of the machine, the spiral angle of the helical blade varies with the distance x from the end of the grain lifter, and with the increase in the distance from the front of the grain lifter, the spiral angle gradually decreases. In order to reduce the risk of breaking the stem in the process of lifting the plant, the lifting speed should not be too high, so the size of the pitch s also changes along the axis, then:  
\[\tan\alpha=\frac{s}{2\pi x\tan\beta} \tag{16}\]  
So, the pitch of the grain lifter is:  
\[s=2\pi x\tan\beta\tan(\frac{1}{2}\sin^{-1}(\frac{2v_{m}}{\omega x\tan\beta\cos \theta})) \tag{17}\]  
It can be seen that in order to ensure that the conical spiral centralizer does not damage the plant during operation and the stalk is stably transported backward, the pitch of the grain lifter gradually changes from the front end to the end, so the initial speed of the plant is slow and then gradually accelerates to prevent the plant from squeezing and blocking in the process of lifting. Further, the size of the pitch is determined by the speed of the grain lifter and the distance from the tip of the grain lifter [25]. When the distance from the tip of the grain lifter is the maximum, that is:  
\[x_{\max}=l_{1} \tag{18}\]  
When the pitch reaches the maximum, taking into account the larger impact force generated when the grain lifter contacts with the plant during the operation process, it is easy to cause the loss of grain dropping. The speed of the harvester should not be too high, combined with the forward speed of the harvester and the speed of the grain chain, take 300-360 r/min, and substitute the relevant data, there are \(s\leq 35\) cm.