Electro-hydraulic Force Control Research Articles

An Electrohydraulic Force Control System for Large-Scale Force Calibration

An Electrohydraulic Force Control System for Large-Scale Force Calibration

Robust Nonlinear Control Scheme for Electro-Hydraulic Force Tracking Control with Time-Varying Output Constraint

This paper presents a robust nonlinear control scheme with time-varying output constraint for the electro-hydraulic force control system (EHFCS). Two typical double-rod symmetrical hydraulic cylinders are employed to simulate force environments in the EHFCS. Therefore, in order to improve the performance of the EHFCS, firstly, the model of the EHFCS is established with taking external disturbances, parameter uncertainties as well as structural vibrations into consideration. Secondly, in order to estimate external disturbances, parameter uncertainties and structural vibrations in the EHFCS and compensate them in the following robust controller design, two disturbance observers (DOs) are designed according to the nonlinear system model. Thirdly, with two estimation values from two DOs, a time-varying constraint-based robust controller (TVCRC) is presented in detail. Moreover, the stability of the proposed controller is analyzed by defining a proper Lyapunov functions. Finally, in order to validate the performance of the proposed controller, a series of simulation studies are conducted using the MATLAB/Simulink software. These simulation results give a fine proof of the efficiency of the proposed controller. What’s more, an experimental setup of the EHFCS is established to further validate the performance. Comparative experimental results show that the proposed controller exhibits better performance than the TVCRC without two DOs and a conventional proportional integral (PI) controller.

Design and experimental evaluation of feedforward controller integrating filtered-x LMS algorithm with applications to electro-hydraulic force control systems

The control purpose of an electro-hydraulic force control (EHFC) system is to real time replicate the force exerted on a structure in laboratory so as to simulate loads that cannot otherwise be generated naturally. In contrast to electro-hydraulic position control system, the tracking performance of EHFC system is always limited. To enhance the force replication accuracy of EHFC systems, a feedforward inverse controller integrating filtered-x LMS adaptive algorithm is presented in this paper. The proposed controller comprises a feedforward inverse controller and an adaptive controller. The feedforward inverse controller working as an inner loop is firstly established by directly cascading the designed parametric inverse transfer function to the EHFC system with proportional integral controller and the inverse transfer function is obtained with the implementation of system identification and zero magnitude error tracking technology. Then, the adaptive controller employing the filtered-x LMS algorithm acting as an outer loop is further combined with the feedforward controller to deal with the error occurred in the inverse model design procedure. Therefore, the proposed controller is an easy-to-implement strategy and can effectively enhance the force replication performance for both phase delay errors and amplitude mismatch errors. Finally, a series of experiments are carried out on a real EHFC test rig by means of xPC target technology, and the experimental results indicate that the proposed controller has a relatively better tracking accuracy compared with the proportional integral controller and the feedforward controller. It is also worth noting that the proposed controller can also be extended to other servo control systems where high accuracy tracking performance is required.

Research on Electro-Hydraulic Force Servo Control System Based on Adaptive Neural Network Control Strategy

It is unchangeable fact that there is great stiffness spring flexible load in electro-hydraulic force servo control system, and there is low oscillation frequency second order differential link in the numerator of the transfer function. On the other hand, the frequency response ability of the system is influenced badly from the link and the system may oscillate easily even is instability. Aiming at this special performance of the electro-hydraulic force servo control system and its small open loop gain characteristic, the adaptive neural network control strategy is adopted to the controller of the electro-hydraulic force servo control system this special performance system in order to improve the dynamic performance of the system. The model of the system with the adaptive neural network control strategy is built and the simulation and experiment study is done. Comparing the control result of the controller with the adaptive neural network control strategy to the control result of the controller with the traditional PID, and from the results of simulation and experiment, we can know that the mathematic model of the electro-hydraulic force control system controlled by the adaptive neural network control strategy is correct, and we can find that the controller with the new designed control strategy can not only increase the frequency response ability of system, but also improve the precision of system, and the controller can quicken the response ability of the system obviously.

Electrohydraulic force control design of a hardware-in-the-loop load emulator using a nonlinear QFT technique

This paper presents the design of a robust force control system for an electrohydraulic load emulator utilized as part of a hardware-in-the-loop flight simulation experiment. In this application, the force controlled hydraulic actuator is used to artificially recreate in-service loads upon a second hydraulic flight actuator operated in closed-loop position control. Electrohydraulic force control is more difficult than electrohydraulic position tracking because the load dynamics influence the force transfer function in a way that makes it challenging to develop an accurate force tracking system using simple feedback control. Nonlinear quantitative feedback theory (QFT) is applied in this paper to address this issue. First, an effective and robust feedback controller is designed by nonlinear QFT to desensitize the force control loop to nonlinear servovalve flow/pressure effects and typical system uncertainties. A secondary compensator is also designed within the QFT framework to extend the force tracking bandwidth with respect to the load motion. Experiments demonstrate acceptable force tracking performance within the scope of a representative flight-simulation experiment.

Research on Flow Press Servo-Valve Controlling Electro-Hydraulic Force Control System and Nonlinear Performance Analysis

The configuration and the work principle of the flow press hydraulic servo-valve was introduced in this paper, based on this and electromagnetic basic theory, the mechanics analysis of every main parts of the flow press hydraulic servo-valve and the liquid basic theory especially the flow continuity equation, the mathematic model of the flow press sever-valve was built, during the process of building the model, the author took into account the load moment brought by the pair of spray nozzles flow force and the load moment brought by the force couples back pole and the fundamental equation of the force moment motor. On the other hand, the author analyzed the influence of the nonlinear factor to system performance, and the nonlinear factor was valve port overlap length disaccord caused by machining error. The mathematic model of the electro-hydraulic force control system controlled by the flow press servo-valve with valve port error was built. The results of simulation and experiment showed that valve port error badly influenced the system performance, and that valve port error was the main reason of the pressure higher than the supply pressure, which is one of the two cylinder cavities. The simulation curve and the experiment curve were accord compared by system simulation and experiment results, so we can know that the mathematic model of the flow press sever-valve and of the electro-hydraulic force control system controlled by the flow press servo-valve is correct.

Study of Electro-Hydraulic Force Control System Controlled by Flow Press Servo-Valve and Nonlinear Performance Analysis

The mathematic model of the flow press sever-valve was built in this paper, during the process of building the model, the author took into account the load moment brought by the pair of spray nozzles flow force and the load moment brought by the force couples back pole and the fundamental equation of the force moment motor. On the other hand, the author analyzed the influence of the nonlinear factor to system performance, and the nonlinear factor was valve port overlap length disaccord caused by machining error. The mathematic model of the electro-hydraulic force control system controlled by the flow press servo-valve with valve port error was built. The results of simulation and experiment showed that valve port error badly influenced the system performance, and that valve port error was the main reason of the pressure higher than the supply pressure, which is one of the two cylinder cavities. The simulation curve and the experiment curve were accord compared by system simulation and experiment results, so we can know that the mathematic model of the flow press sever-valve and of the electro-hydraulic force control system controlled by the flow press servo-valve is correct.

Identification and Modeling of Electrohydraulic Force Control of the Material Test System (MTS)

In the heavy-duty material test device, an electrohydraulic force servo system is usually utilized to load the tested samples. The signal from the pressure sensor is compared with the instruction and the difference between them is then fed to a digital servo valve to form a closed loop control to the target force. The performance of the electrohydraulic force servo system is not only closely related to how accurate to feed the flow rate to the hydraulic cylinder, but also the stiffness of the system which is dominated by the compressibility of oil. Thus the clarification of the characteristic parameters becomes the key of the solution to optimal force control. To identify the electrohydraulic force servo system various step signals are input to excite the dynamic response of the system. From the relationship between the step magnitude and the force response, the system model and the key control parameters are determined. The electrohydraulic force servo system is identified as a first order system with time constant varied with the pressure. Based on the identification of the system optimal control parameters are finally obtained and force rate error is reduced to 0.2% from original 3%.

タイムディレイコントロール法による電気・油圧サーボ系の力制御

The time delay control (TDC) method has been applied to a force control system of an electrohydraulic servo mechanism with spring and inertial loads. The modeling error and the disturbance of the system can be estimated and compensated through the use of the TDC method. Two types of a simple linear model of the controlled object are used to discuss the effects of modeling. As the state variable, design model-1 uses cylinder force and design model-2 uses cylinder force together with piston velocity. Simulation and experimental results show that the TDC system with design model-2 is more effective for the case of rapid change of piston speed.The results of this research show that robust control of an electrohydraulic force control servo mechanism can be realized with simple control a system by TDC.