## 4 Experiment Research
### Control Performance  
The control performance is used to evaluate the responsiveness of the pressure of the actuator's cylinder to follow the signal that is produced by the joystick. If the pressure of the actuator cylinder can reach its target value quickly and smoothly, it is considered as a good control performance. Figure 5 shows the EM speed of the AISCS and joystick pressure according to the state of the joystick. It can be seen that the EM speed changes according to the state of the joystick. The joystick backs to the middle position and the actuator stops to work at time 7 s. When the controller detects the joystick staying at middle position for 8 s, which means that the actuator stops working for 8 s, and then the controller makes the EM work at the first level idle speed (800 rpm) from time 15 s. After 20 s and if the joystick is still at the middle position, then the controller makes the EM work at the second level idle speed (500 rpm) from time 35 s to further reduce the energy consumption. When the controller detects the joystick leaves the middle position, it makes the EM accelerate to its normal working speed (1800 rpm). Hence, the EM can switch the speed among the normal speed \begin{table}
\begin{tabular}{l l l} \hline \hline
**Key Components** & **Parameter** & **Value** \\ \hline \multirow{3}{*}{Actuator} & Rod diameter/mm & 35 \\  & Cylinder diameter/mm & 63 \\  & Maximum stroke/mm & 100 \\ \hline \multirow{3}{*}{Electric motor} & Power/kW & 8 \\  & Rated speed/(rpm) & 1800 \\ \hline Pump & Displacement/(mL\(\cdot\)r\({}^{-1}\)) & 16 \\ \hline \multirow{3}{*}{Hydraulic accumulator} & Volume/L & 1.6 \\  & Pre-charge pressure/MPa & 2 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Key parameters used in the test rig. Figure 4: Layout of the test rig. (1800 rpm), first level idle speed (800 rpm), and the second level idle speed (500 rpm), judging by the control strategy. Figure 6 describes the pressures of the HA, pump, joystick, and load during the proposed ASICS process. When the joystick backs to the middle position at time 7 s, the actuator stops, therefore, the velocity and the pressure of the actuator are close to zero and the pump is unloading. When the system works at the first level idle mode at time 15 s, the actuator still does not work, while the pump supplies the oil to the HA and both the pressures of the HA and pump rise until the pressure of the HA reaches the upper limited value. Then, the pump is unloading through the solenoid directional valve 2. When the joystick leaves the middle position at time 40 s, both the HA and the pump supply the oil to the actuator to make it work quickly. As the EM speed cannot reach its target speed as quickly as possible, the outlet pressure of the pump is less than the load pressure, while the pressure of the HA is above the load pressure. Accordingly, only the HA can drive the actuator in this working mode at the time from 40 s to 44.6 s. The pressure differential between the HA and the load pressure almost keeps constant to ensure that the HA have the capability to release the oil to the actuator. This indicates that the HA can be an auxiliary energy to build up the pressure of the actuator quickly. When the outlet pressure of the pumps reaches the pressure of the HA, the HA stops to work and only the pumps drive the actuator. Even though it takes 2-5 s for the EM's acceleration process, the system can still build up the pressure quickly. Hence, the pressure differential control strategy can guarantee the control performance for the actuator. Both Figures 5 and 6 indicate that the proposed ASICS can realize the preset goals and the control strategy works well. Figure 7 shows the pressures of the non-rod chamber of the actuator cylinder under different pressure differential in the proposed ASICS process. The pressure differential \(\Delta p\) may influence the dynamic response of the actuator movement. The larger the pressure differential, the more quickly the actuator pressure is built up.