## 3 Results and Discussion
### Double Threshing Drum Grading Chain Drive Dynamic Balance
Therefore, choose 80\({}^{\circ}\) as the phase of the tight side unbalance and 320\({}^{\circ}\) as the phase of the unbalanced amount. The amplitudes were L\({}_{\text{B1}}\) and L\({}_{\text{B2}}\), respectively. So vector \(\mathbf{OB_{1}}=(\text{L}_{\text{B1}}\cos\,280^{\circ},\,\text{L}_{\text{B1}}\, \sin\,280^{\circ})\), vector \(\mathbf{OB_{2}}=(\text{L}_{\text{B2}}\cos\,40^{\circ},\,\text{L}_{\text{B2}}\,\sin \,40^{\circ})\). That was:  
\[\left\{ \begin{array}{l}x_{B}=x_{B1}+x_{B2}\\ y_{B}=y_{B1}+y_{B2}\end{array} \right. \tag{13}\]  
The coordinates of \(\mathbf{OB_{1}}\), \(\mathbf{OB_{2}}\), \(\mathbf{OC}\), and \(\mathbf{OD}\) were substituted into Equations (12) and (13). \[\left\{ \begin{array}{l}L_{B1}=0.157\\ L_{B2}=0.01\end{array} \right. \tag{14}\]  
That was, the chain drive equivalent unbalance on the side of the active drum large sprocket was vector \(\mathbf{OB}\) (Coordinate value is 0.035, \(-\)0.149). The unbalanced amplitude was 0.153 mm/s and the unbalanced phase was 77\({}^{\circ}\). Generally speaking, the higher the rotation speed, the greater the chain vibrated. And also the force on the chain would change. The change of the sprocket wrap angle would also change the force phase of the sprocket, that was, the calculation of the equivalent unbalance of the chain drive was affected by the speed and wrap angle. Therefore, in order to obtain the accuracy of the equivalent unbalance of the chain drive, it was recommended to calculate the equivalent unbalance amount at the working speed and recalculate the equivalent unbalance amount when the transmission path changes. Double threshing drums were connected in parallel by the chain drive. The transmission characteristics based on the chain drive or the influence of the load on the unbalanced phase would affect the equilibrium state of the entire system. Therefore, the dynamic balance method of the double threshing drum step chain transmission can be determined on this basis. Based on the above modeling of the chain drive excitation response and analysis of a series of experimental data, the unbalance of the load had little effect on the unbalanced amplitude of the active drum through the transmission characteristics of the chain drive. After the load was driven, the transmission chain between the load and the driving drum generated a tensile force and a lateral vibration, which had an obvious influence on the unbalanced phase of the main driven drum. Therefore, when determining the double threshing drums dynamic balance method, the influence of load and chain drive on the unbalanced phase of the active drum would be considered. The influence of the transmission characteristics of the chain drive on the unbalanced amplitude of the active drum would not be considered. When determining the dynamic balance method of the double threshing drums of the grading chain drive, the main idea was multi-stage transmission and step-by-step balance. The double threshing drums combination of the multi-stage transmission was broken up. The balanced drum was regarded as a whole. The load was added step-by-step, and the balance was performed step-by-step, as shown in Figure 12.  
In order to balance the multi-threshing drums, some of the drive chains needed to be removed. The drum connected to the power input end was used as the active drum. The amount of unbalance was measured and dynamic balancing was performed. The remaining unbalance was used as the unbalance of the active drum itself in the multi-drums system \(\mathbf{OC}\). According to Equation (11), combined with the active drum chain drive equivalent unbalance \(\mathbf{OA}\), \(\mathbf{OB}\), the weight of the active drum, was calculated. The chain drive between the driven drum and the active drum was then install checked for whether the unbalance of the active drum met the requirements and then measured the unbalanced amount of the driven drum as its own unbalance _OC_. In the same way, the counterweight was calculated for the driven drum.