## 3 Control Strategy
### Control Law  
The overall control process of the AISCS of Figure 2 is illustrated in Figure 3. When the joystick returns to the middle position, the controller detects that the pressure differential of the joystick is under the preset small positive value and sends the pilot control oil to the multi-way valve to make it work at the middle position. The proposed AISCS is to control EM speed to be switched between the different values, including the switch from the normal working speed to the first idle speed, the second idle speed, and that from the two idle speeds to its normal working speed. When reducing EM speed, the main consideration is the energy saving of the system. While the set value of the idle speed is the primary factor that influences the energy consumption. When the idle mode is cancelled, the control performance is the main consideration. Therefore, the time for building up the pressure of the pump should be smooth and short. Taking the self-suction capacity of the pump into account, the first level idle speed is set to 800 rpm and the second level idle speed is set to 500 rpm, because the HA can help the pump to build up the pressure quickly. During the different process, the control strategy changes accordingly. The control strategy is based on the following principles. Figure 3: Overall control diagram of the AISCS. When the time of the joystick backs to the middle position is longer than time \(T_{1}\), the controller makes the EM speed reduce to the first level idle speed \(n_{1}\) to reduce the energy loss. Meanwhile, the maximum load pressure \(p_{\rm Lmax}\) is adopted to decide to charge the HA by the pump or not. When the pressure differential between the maximum load pressure and the HA is larger than the preset value \(\Delta p_{\rm ac}\), then the solenoid directional valves 1 and 2 are powered on. Then the pump charges the HA via solenoid directional valve 1. After the pressure of the HA increases to the upper limited value, the solenoid directional valves 1 and 2 are powered off. The pump is connected to the tank through solenoid directional valve 2 and is unloaded. Mode 2: Second level idle mode  
With an HA in AISCS, the HA had store a certain amount of energy in the first level idle mode. When the time of the joystick backs to middle position is longer than time \(T_{1}+T_{2}\) and the pressure of HA is under the threshold values, then the controller makes the EM work at the second level idle speed \(n_{2}\), which is lower than the first level idle speed \(n_{1}\) to further reduce the energy consumption. Mode 3: Idle mode is cancelled  
When the joystick leaves its middle position, the AISCS is cancelled. In a HE, the joysticks are the most common interfaces between the drivers and the hydraulic manipulators. The target velocity of the actuator is characterized by the status of the joystick. The joystick signal gives a pressure differential. The target velocity of the actuator is the control object, which is compared with the joystick command through a conversion gain, as shown in Equation (2). When considering the dynamic response of EM, it cannot quickly reach to the normal speed which is usually about 1800 rpm. That is to say, the pump cannot build up the pressure quickly to drive the actuator. Hence, the actuator should be driven by the pump and the HA. In this case, both the solenoid directional valves 1 and 2 are powered on. The stored oil in the HA is released through solenoid directional valve 1 to the inlet of the multi-way valve to help the pump build up the pressure quickly to drive the actuator. The pressure of HA decreases with the discharging process and the load pressure changing, according to the pressure of HA. When the pump pressure is larger than the HA pressure, the solenoid directional valve 1 is powered off, and the actuator is driven by the pump only. The proportion of the flow rate supplied by the HA and the pump is scheduled to achieve a smooth and quick movement of the actuator.