## 5 System Servo Performance Evaluation and Verification  
### Analysis of Simulation Results  
The effects of these six factors on the equivalent stabilization accuracy and speed stability are obtained by simulation, which correspond to two six-dimensional seven-order square matrices, and the data volume of each square matrix is 76 = 117,649. The statistics of servo performance indicators are shown in Figure 5. The equivalent stabilization accuracy is distributed between 0.37 mrad and 1.1 mrad, and there are seven obvious peaks, which are exactly the same as the equal number of disturbance factors, as shown in Figure 5a. The speed stability is distributed between 0.005 rad/s and 0.24 rad/s, and 57% of the data is distributed within 0.03 rad/s, as shown in Figure 5b.  
In order to obtain the mapping relationship between transmission performance, load performance and system servo performance, the equivalent stabilization accuracy and speed stability are normalized and weighted as the comprehensive evaluation indicator  
\begin{table}
\begin{tabular}{l c c c c c c} \hline \hline
**Factors** & **Level 1** & **Level 2** & **Level 3** & **Level 4** & **Level 5** & **Level 6** & **Level 7** \\ \hline Friction torque & 0.5 & 0.67 & 0.83 & 1 & 1.33 & 1.67 & 2 \\ Transmission error & 0.5 & 0.67 & 0.83 & 1 & 1.33 & 1.67 & 2 \\ Backlash & 0.5 & 0.67 & 0.83 & 1 & 1.33 & 1.67 & 2 \\ Road disturbance & 0 & 0.33 & 0.67 & 1 & 1.33 & 1.67 & 2 \\ Equivalent inertia & 1 & 1.1 & 1.2 & 1.3 & 1.4 & 1.5 & 1.6 \\ Mass unbalanced & 0.5 & 0.67 & 0.83 & 1 & 1.33 & 1.67 & 2 \\ \hline \hline \end{tabular}
\end{table}
Table 2: The simulation parameters of the six factors.  
Figure 5: The statistics of (**a**) equivalent stabilization accuracy, (**b**) speed stability, (**c**) comprehensive servo performance.  
of system servo performance. The statistics of the comprehensive servo performance are shown in Figure 5c.  
By using a single factor as the independent variable and the servo performance indicator as the dependent variable, the influence of the single factor is obtained, as shown in Figure 6. In the figure, friction torque is represented by \(T_{f}\), transmission error is represented by \(\theta_{e}\), backlash is represented by \(\theta_{h}\), road disturbance torque is represented by \(T_{L}\), equivalent inertia is represented by \(J_{L}\), and mass unbalanced torque is represented by \(T_{b}\).  
It can be seen from the figure that friction torque has the greatest impact on equivalent stabilization accuracy, and road disturbance torque has the greatest impact on speed stability. In the comprehensive servo performance indicator, the increase of friction torque and road disturbance torque rapidly causes the deterioration of the comprehensive servo performance. The introduction of road disturbance torque will reduce the servo performance of the system, and when the road disturbance torque increases by 25%, the servo performance of the system decreases by about 12%. In the six performance indicators, only by reducing the friction torque can the servo performance of the system be improved. When the friction torque is reduced by 25%, the servo performance of the system is increased by about 17%. In the other four performance indicators, the change of transmission error and backlash has little impact on the system servo performance, and its level becomes larger, which makes the system servo performance worse.  
In this section, the mapping relationship between internal and external disturbances and servo performance is obtained through simulation analysis, and the conclusion that friction torque and road disturbance torque are the most important factors affecting the servo performance of the system is obtained. The mapping relationship quantifies the common sense conclusion, clarifies the measures to improve the servo performance of the system, and provides a reference for the design of the ISP.