Introduction to the characteristics and principles of electro-hydraulic actuators
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The input signal of the electro-hydraulic actuator is an electrical signal, and the power source for the output actuator is hydraulic oil. Therefore, it is particularly suitable for applications with high thrust, large stroke, and high-precision control. In large power plants, electro-hydraulic actuators are often used in control systems such as main steam valves to achieve high thrust.
Compared with electric actuators, electro-hydraulic actuators have greater thrust or thrust torque due to the use of hydraulic mechanisms. But hydraulic systems require more complex control of oil pressure pipelines and oil circuit systems, such as controlling hydraulic oil temperature, pressure, etc., as well as supplementing oil and oil circulation. Compared with pneumatic piston actuators, electro-hydraulic actuators use hydraulic cylinders instead of cylinders. Due to the incompressibility of hydraulic oil, the response speed can reach 1000mm/s, which is faster than pneumatic piston actuators. The positioning of the stroke is precise, and the control accuracy is high (up to 0.5 levels). Its stroke can be very long (up to lm), the output thrust torque is large (up to 60000Nm), and the output thrust is large (up to 25000N).
The electro-hydraulic actuator converts the input standard current signal into the mechanical energy of the electric motor, using hydraulic oil as the working medium. The mechanical energy of the electric motor is converted into the pressure energy of the hydraulic oil through power components (such as hydraulic pumps), and through pipelines and control components, the hydraulic energy is converted into mechanical energy by the actuator, driving the valve stem to complete linear or angular motion. Therefore, it has the advantages of fast response of electric actuators and high thrust of piston actuators. But due to the use of hydraulic oil, there are problems such as leakage in the oil system
The basic hydraulic transmission system consists of directional control circuit, pressure control circuit, and flow control circuit. Directional control circuits can use directional valves, one-way valves, etc; The pressure control circuit can use pressure relays, pressure reducing valves, etc; The flow control circuit can use throttle valves, speed regulating valves, etc. In addition, some auxiliary control circuits are required, such as balance control circuit, pressure relief control circuit, boost and speed increase control circuit, etc. To ensure the normal operation of the electro-hydraulic actuator, two sets of hydraulic transmission oil systems are usually used, with one system in operation and the other as a backup.
Similar to electric actuators, electro-hydraulic actuators also use position feedback devices to form a feedback control system. It improves the control accuracy of the entire system and enhances its dynamic characteristics. However, due to its high cost and complex piping system, it is only adopted in applications that require high thrust and thrust torque. Its characteristics are as follows.
Under the same output power conditions, hydraulic transmission devices have small volume, light weight, compact structure, low inertia, and fast response.
2. It can achieve stepless speed regulation over a wide range, and can output large thrust and torque.
3. The transmission is seamless, the movement is smooth, and frequent reversing operations can be achieved. Easy to operate, easy to achieve automation, easy to implement complex automatic control of jD turn sequence, easy to implement overload protection.
4. The viscosity of hydraulic oil is greatly affected by environmental temperature and is not suitable for long-distance transmission control.
5. High requirements for control devices, requiring feedback device assembly to form closed-loop control. According to the different mechanical quantities such as displacement, velocity, and force as controlled variables, the feedback detection device also has displacement detection
