Foreword
Hydraulic servo systems are widely used due to their advantages such as light weight, small size, and high torque. However, due to factors such as oil leakage and oil contamination, hydraulic servo systems generally exhibit time-varying and nonlinear parameters, especially nonlinear flow in valve-controlled power mechanisms. With the development of computer technology, hydraulic transmission technology has evolved into a complete automation technology encompassing transmission, inspection, and control. Because electro-hydraulic servo systems have significant uncertainties and interference, high requirements are placed on them.
Due to the significant economic benefits and potential value of electro-hydraulic servo systems, they have attracted considerable attention from scholars in the fields of hydraulics and control, and have become a cutting-edge topic in this field. Since electro-hydraulic servo systems are typical passive force control systems, redundant forces arise during dynamic loading caused by the active movement of the servo system. These redundant forces, mixed into the loading system, not only severely affect loading accuracy but also adversely impact other control performance aspects; many important performance indicators of electro-hydraulic servo systems are related to these redundant forces. To overcome the problem of redundant forces, scholars both domestically and internationally have proposed and applied various methods. Among them, redundant force suppression based on the principle of structural invariance is the most widely used active disturbance reduction method. One organization has applied it to the aerodynamic load simulation platform of the 3-4FM missile, and it has been successfully used for loading helicopter rotors, as well as for loading ship servos and aircraft landing gear, all with satisfactory results.
Electro-hydraulic position servo systems are primarily used to solve position tracking control problems. Their fundamental task is to achieve timely and accurate tracking of the controlled variable to the given variable through an actuator, while maintaining sufficient control precision. The dynamic characteristics of an electro-hydraulic servo system are a crucial indicator for evaluating its design and debugging level. It consists of an electrical signal processing unit and several hydraulic components. The dynamic performance of these components interacts and restricts each other, and the system itself contains nonlinearities, resulting in complex dynamic performance. Therefore, the design and simulation of electro-hydraulic servo control systems are receiving increasing attention.
1. Mathematical Model of Electro-hydraulic System
For the sake of simplicity in the derivation, appropriate assumptions need to be made in the mathematical modeling. In addition, the loading hydraulic cylinder and the equivalent load can be considered as a rigid connection, and the force sensor has high stiffness, so its elastic deformation is ignored. Since precise displacement loading of the servo motor is required in practice, its internal motion and interaction forces are not within the scope of this study. The servo motor system uses its displacement as the input to the loading system, and based on this, the electro-hydraulic servo loading system is studied.
3. MATLAB simulation
The performance of a conventional PID controller depends on the tuning of parameters Kp, Ki, and Kd. Good parameter tuning results in good control, and vice versa. There are generally two methods for parameter tuning: theoretical design and experimental determination. Through extensive experimentation, the PID parameters chosen were: Kp=1.1, Ki=0.2, and Kd=0.01. The Simulink fuzzy PID servo system simulation model is shown in Figure 3, and the simulation results in Simulink are shown in Figure 4.
Figure 3 Simulink fuzzy PID servo system simulation model
Figure 4 Simulation diagram of PID control
Simulation results show that, with the same set parameters, adding a PID controller to adjust the PID parameters in real time can better control the controlled object. Once the PID parameters are fixed, their applicability under time-varying conditions is greatly limited. By adjusting the parameters online, the control performance can be kept in the optimal state, resulting in better control accuracy and robustness.
4. Conclusion
This paper addresses the problem of significant redundant force and the difficulty in fully compensating for structural invariance during passive loading of electro-hydraulic systems. The entire control system was modeled and simulated. The modeling process and simulation results demonstrate that establishing a correct mathematical model and conducting analysis and simulation of the system's dynamic characteristics can effectively predict the system's output, providing an understanding of the system's operating state and improving the efficiency of system design and analysis. Reliability verification using MATLAB/Simulink simulation shows that the system possesses advantages such as high control accuracy, good stability, and ease of use.
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