Based on the introduction of direct-acting electro-hydraulic servo valves, a mathematical model and Simulink simulation block diagram of the direct-acting electro-hydraulic servo valve servo control system were established, and simulations were performed, with the simulation results analyzed. 1 Introduction In recent years, the rapid development of engineering machinery and the expansion of the application fields of electro-hydraulic servo systems have placed higher technical demands on electro-hydraulic servo valves. Traditional nozzle-baffle type electro-hydraulic servo valves can no longer meet these requirements, thus necessitating a new type of electro-hydraulic servo valve. The direct-acting servo valve is a new type of electro-hydraulic servo valve. It eliminates the nozzle-baffle assembly, improving the valve's anti-contamination capability, and replaces the torque motor with a linear force motor. These advantages have led to its widespread attention since its introduction in the late 1990s. Research on electro-hydraulic servo control systems is directly related to improving the performance of servo valves, but research on direct-acting electro-hydraulic servo valve control systems is still relatively limited. Therefore, this paper establishes a mathematical model of the direct-acting electro-hydraulic servo valve control system and conducts simulation analysis using the Moog series direct-acting valve as an example. 2. Structure of a Direct-Acting Electro-hydraulic Servo Valve The Moog series direct-acting electro-hydraulic servo valve mainly consists of three parts: a linear force motor, a hydraulic valve, and an amplifier assembly, as shown in Figure 1. The linear force motor uses a permanent magnet hybrid differential motor, which improves valve performance and represents a significant advancement in electro-hydraulic servo valve technology in recent years. The amplifier assembly enables closed-loop real-time control of the valve core position and is fixed within the servo valve using a special connection technology. 3. Composition of the Direct-Acting Electro-hydraulic Servo Valve Control System Electro-hydraulic servo control systems have excellent control performance. Based on the controlled physical quantity, they can be divided into three types of servo systems: position, speed, and force. Among these three types of servo control, the most widely used is the electro-hydraulic position servo control system. The structure of the position control system for a direct-acting electro-hydraulic servo valve is shown in Figure 2. 4 Mathematical Model of Direct-Acting Electro-hydraulic Servo Valve Control System (1) Taking the control coil current of the direct-acting electro-hydraulic servo valve as the input signal and the valve core displacement as the output signal, the transfer function of the electro-hydraulic servo valve can be obtained from the design theory of servo valve: Where: Kv is the flow gain of the direct-acting electro-hydraulic servo valve; ωv is the corner frequency of the direct-acting electro-hydraulic servo valve; εv is the damping coefficient of the direct-acting electro-hydraulic servo valve. (2) Considering the displacement equation of the direct-acting electro-hydraulic servo valve, the transfer function of the hydraulic cylinder can be obtained as: Where: Kh is the speed stiffness of the hydraulic cylinder; ωh is the undamped natural oscillation frequency of the hydraulic cylinder; εh is the damping coefficient of the hydraulic cylinder. [IMG=Figure 1 Structural Diagram of Moog Series Direct-Acting Electro-hydraulic Servo Valve]/uploadpic/THESIS/2007/11/2007111614502558513B.jpg[/IMG] Figure 1 Structural Diagram of Moog Series Direct-Acting Electro-hydraulic Servo Valve [IMG=Figure 2 Composition Diagram of Direct-Acting Electro-hydraulic Servo Valve Position Control System]/uploadpic/THESIS/2007/11/2007111614542053669N.jpg[/IMG] Figure 2 Composition Diagram of Direct-Acting Electro-hydraulic Servo Valve Position Control System [IMG=Figure 3 Simulation Block Diagram of Direct-Acting Electro-hydraulic Servo Valve Control System]/uploadpic/THESIS/2007/11/20071116145448775768.jpg[/IMG] Figure 3 Simulation Block Diagram of Direct-Acting Electro-hydraulic Servo Valve Control System [IMG=Figure 4 [Unit step response of control system]/uploadpic/THESIS/2007/11/2007111614551747891R.jpg[/IMG] Figure 4 Unit step response of control system (3) The transfer function of the displacement sensor is: (3) Where: K[sub]f[/sub] is the gain of the displacement sensor; ω[sub]f[/sub] is the corner frequency of the displacement sensor. (4) In the electro-hydraulic servo valve, the servo amplifier generally adopts deep current negative feedback, and its transfer function is: (4) Where: K[sub]o[/sub] is the gain of the amplifier; ω[sub]o[/sub] is the corner frequency of the amplifier. From equations (1) to (4) and Figure 2, the open-loop transfer function of the direct-acting electro-hydraulic servo valve control system can be obtained as: (5) 5 Simulation model of direct-acting electro-hydraulic servo valve control system Using the Matlab/Simulink simulation tool, the simulation block diagram of the direct-acting electro-hydraulic servo valve control system can be established from equation (5) and Figure 2, as shown in Figure 3. The correspondence between the letters in Figure 3 and equation (5) is as follows: k1=Koωo, k2=Kvωv2, k3=Khωh2, k4=Kfωf, c1 =ωo, c2=ωv2, c3=ωf, m1=2ξvωv, m2=2ξhωh, m3=ωh2. 6. Simulation Results Taking the parameters of the Moog series direct-acting electro-hydraulic servo valve D633 as an example, the simulation of Figure 3 is performed. When a step signal is applied to the system, the response at its output is shown in Figure 4. It can be seen from Figure 4 that this curve is a typical step response curve of a third-order system. Therefore, the control system of the direct-acting electro-hydraulic servo valve is equivalent to a third-order system. In addition, it can be seen that under step signal excitation, the system's settling time, maximum overshoot, rise time, and other parameters describing the system's dynamic performance indicators are... 7 Conclusion (1) The mathematical model of the direct-acting electro-hydraulic servo valve control system was derived, which has important reference value for the engineering application and further research of the direct-acting electro-hydraulic servo valve. (2) A general simulation block diagram of the direct-acting electro-hydraulic servo valve control system was established. By using the block diagram and changing the parameters, the simulation results can be obtained directly. This method is convenient and practical. Proceedings of the Second Servo and Motion Control Forum Proceedings of the Third Servo and Motion Control Forum