Adaptive Robust Position Control of Electro-Hydraulic Servo Systems with Large Uncertainties and Disturbances

In this paper, a novel adaptive robust control (ARC) scheme is proposed for electro-hydraulic servo systems (EHSSs) with uncertainties and disturbances. All dynamic functions in system dynamics are effectively approximated by multi-layer radial basis function neural network (RBF NN)-based approximators with online adaptive mechanisms. Moreover, neural network-based disturbance observers (NN-DOBs) are established to actively estimate and efficiently compensate for the effects of not only the matched/mismatched but also the imperfections of RBF NN-based approximators on the control system. Based on that, the nonlinear robust control law which integrates RBF NNs and NN-DOBs is synthesized via the sliding mode control (SMC) approach to guarantee the high-accuracy position tracking performance of the overall control system. Furthermore, the problem of the combination between DOBs and RBF NNs is first introduced in this paper to treat both disturbances and uncertainties in the EHSS. The stability of the recommended control mechanism is proven by using Lyapunov theory. Finally, numerical simulations with several distinct frequency levels of reference trajectory are conducted to convincingly demonstrate the effectiveness of the proposed approach.

Characteristics of Hydraulic and Electric Servo Motors

Until the 1970s, hydraulic actuators were widely used in many mechanical systems; however, recently, electric motors have become mainstream by virtue of their improved performance, and hydraulic motors have largely been replaced by electric motors in many applications. Although this trend is expected to continue into the future, it is important to comprehensively evaluate which motor is most suitable when designing mechanical systems. This paper presents the results of a survey of the performance of electric and hydraulic servo motors and aims to provide quantitative data that can be used as a reference for selecting appropriate motors. We surveyed AC, AC direct, brushless DC, and brushed DC electric motors and swash plate-type axial piston, bent axis-type axial piston, crank-type radial piston, and multistroke-type radial piston hydraulic motors. Performance data were collected from catalogs and nonpublic data. We compared and evaluated the characteristics of these diverse servo motors using indexes such as torque, rotating speed, output power, power density, and power rate.

A novel electro-hydraulic servo steering system for Ackermann steering of heavy multi-axle vehicle

Ackermann steering is important for the steering performance of heavy multi-axle vehicle. When Ackermann steering condition is not satisfied, it will lead to abnormal tire wear. Traditional trapezoidal mechanism of heavy multi-axle vehicle is a single degree of freedom (DOF) mechanism, which is difficult to completely realize Ackermann steering. In this paper, a new two DOF electro-hydraulic servo steering system (TDEHSSS) by using a variable length tie rod is proposed for solving the issue. First, a complex nonlinear dynamic model of TDEHSSS is established. This model includes the two DOF mechanical model based on a Lagrange equation, the valve-controlled double steering power cylinders model and the valve-controlled tie rod cylinder model. Then, a simulation model is built through MATLAB/Simulink and the simulation results show that TDEHSSS can realize the proposed requirement. At last, a test bench is founded to verify model. It is indicated that the simulation and experimental curves are consistent, showing that mathematical model is in accordance with the experimental system. This research is valuable for analyzing TDEHSSS, designing advanced controllers, and finally realizing Ackermann steering for heavy multi-axle vehicles.

Position Output Adaptive Backstepping Control of Electro-Hydraulic Servo Closed-Pump Control System

A nonlinear adaptive backstepping control method was proposed to address the system parameter uncertainty problem in the position control process of an electro-hydraulic servo closed-pump control system. This control strategy fully considers the parameter uncertainty of the nonlinear system and establishes the adaptive rate of the uncertain parameter to adjust the parameter disturbance online in real time, thereby improving the accuracy and robustness of the control system. A pump control system experiment platform was used to verify the feasibility of the controller. The experimental results showed that the proposed control strategy provided a good control effect. The pump control system can be controlled with high precision, with a steady-state control accuracy of ±0.02 mm, which serves as a good foundation for the engineering application and promotion of the pump control system.

Decoupling Control of a Multiaxis Hydraulic Servo Shaking Table Based on Dynamic Model

Hydraulic servo shaking table is an essential testing facility to simulate the actual vibration situation in real time. As a parallel mechanism, multiaxis hydraulic servo shaking table shows strong coupling characteristic among different degrees of freedom. When the multiaxis hydraulic shaking table moves to one direction, some unnecessary related motions will appear in other directions, which seriously affect the control performance. An effective approach to decouple motions in command direction and in unnecessary related directions is an urgent need for a higher precision control performance. In this work, the coupling phenomena and reasons of the multiaxis hydraulic servo table are analyzed based on dynamic model of a multiaxis hydraulic servo shaking table. In this regard, multiaxis hydraulic servo shaking table with strong coupling within the physical space is transformed into a set of single-input single-output systems that are independent of each other in the modal space. A decoupling control strategy is proposed in modal space to restrain the coupling motions. Simulation and experimental results show that the proposed control strategy can effectively improve the control performance and the decoupling effect.

Sliding Mode Control of Electro-Hydraulic Servo System Based on Optimization of Quantum Particle Swarm Algorithm

This paper investigates a sliding mode controller based on quantum particle swarm optimization algorithm (QPSO) to solve the nonlinearity of electro-hydraulic servo systems, external disturbance problems, and jitter of sliding mode controller. The electro-hydraulic servo system state space equations are established, constructing the sliding surface according to the tracking error and obtaining the output of the sliding mode controller. The ITAE metric is used as an adaptation function of the QPSO algorithm to evaluate the parameters in the sliding mode controller, which has good engineering utility and parameter selectivity. The QPSO algorithm is used to increase the randomicity of the search and to expand the search space, which can effectively prevent falling into a local optimum solution. Finally, a comparative simulation is presented to illustrate global search performance of QPSO algorithm and the effectiveness and applicability of the proposed control method.