Model Of Servo Valve Research Articles

Modeling and Fault Simulation of a New Double-Redundancy Electro-Hydraulic Servo Valve Based on AMESim

The feedback spring rod of the armature assembly was eliminated in the double-redundancy electro-hydraulic servo valve (DREHSV), which employed a redundant design in contrast to the typical double-nozzle flapper electro-hydraulic servo valve (DNFEHSV). The pilot stage was mainly composed of four torque motors, and the double-system spool was adopted in the power stage. Consequently, the difficulty of spool displacement control was increased. By artificially changing the structural parameters of the simulation model in accordance with the theoretical analysis through AMESim, this paper aimed to study the dynamics and static characteristics of the DREHSV. The advantage of redundant design was further demonstrated by disconnecting working coils and setting the different worn parts of the spool. On the test bench, the necessary experiments were performed. Through simulation, it was discovered that when the clogged degree of the nozzle is increased, the zero bias value increases, the pressure and flow gain remain unchanged, and the internal leakage decreases. The pressure gain changes very little, the flow gain close to the zero position grows, the zero leakage increases significantly, and the pilot stage leakage changes very little as a result of the wear of the spool throttling edge. The basic consistency between the simulation curves and the experimental findings serve to validate the accuracy of the AMESim model. The findings can serve as a theoretical guide for the design, debugging, and maintenance of the DREHSV. The simulation model is also capable of producing a large amount of sample data for DREHSV fault diagnosis using a neural network.

The investigation of a unbalanced barrel pitching system’s characteristics degradation and compensation under gradual erosion behavior

The unbalanced barrel pitching system is a typical electro-hydraulic coupling servo control system, the performance of which determines the response speed and hit probability of vehicle mounted weapon equipment. However, in the actual service process, its core component, the high precision jet pipe servo valve, will produce the gradual erosion of the pilot stage’s receivers and the power stage’s throttling edges, which will induce the performance degradation of the unbalanced barrel pitching system, and finally greatly reduce the performance of barrel weapons. Therefore, a pressure and position double loop state space model of unbalanced barrel pitching system including the core parameters of performance degradation is established. The erosion behavior mechanism model of jet pipe servo valve is constructed, and the performance degradation characteristics of the unbalanced barrel pitching control system under the condition of erosion are further analyzed. Finally, aiming at the double loop structure of internal pressure loop and external position loop, the RBF Network Adaptive Robust Sliding Mode-Proportional Integral Derivative two-stage controller of barrel system is designed, based on which the experimental platform of unbalanced barrel pitching control is built. The experimental results are in good agreement with the theoretical results, so the proposed control method can effectively suppress the degradation of internal structural parameters induced by erosion, that is, it can better compensate the performance degradation of barrel pitching system induced by gradual erosion behavior.

Temperature drift mechanism of deflector jet servo valve under temperature shock

To study the mechanism of the deflector jet servo valve under temperature shock, a complete temperature theoretical model is proposed in this article. The temperature change affects the performance change of the torque motor by affecting the drift of the air gaps’ thickness, the permanent magnets’ reluctance, and the magnetomotive polarization force. Moreover, the temperature variation will act on the flow coefficient of the pilot stage, the size of the deflector, and jet pan, which influences the performance of the pilot stage hydraulic amplifier. Furthermore, the armature components, including the stiffness of the spring tube, the stiffness of the feedback rod, and the armature’s arm of force, are also related to the temperature variation. Comprehensively, considering the interaction influence of these factors, by analyzing the electromagnetic characteristics of the torque motor, the fluid mechanics’ characteristics of the pilot stage hydraulic amplifier, and the temperature performance of the armature assembly, the temperature drift model of deflector jet servo valve is constructed, which is represented as a ninth-order nonlinear equation. Based on the equation, the influence of temperature on the control precision of the servo valve is analyzed. The calculation results show that in the range of 20°C–250°C, the impact of temperature on the control accuracy will exceed 30%, the flow coefficient is the most significant affecting on the control accuracy, followed by the structural deformation of the pilot stage is the second factor affecting the temperature drift, and other factors have little effect. Comparison with the experimental results, the temperature drift model of the deflector jet servo valve can predict the control accuracy caused by temperature and provide a theoretical foundation for the optimization of the deflector jet servo valve.

CFD-Based Physical Failure Modeling of Direct-Drive Electro-Hydraulic Servo Valve Spool and Sleeve.

Direct-drive electro-hydraulic servo valves are used extensively in aerospace, military and control applications, but little research has been conducted on their service life and physical failure wear. Based on computational fluid dynamics, the main failure forms of direct-drive electro-hydraulic servo valves are explored using their continuous phase flow and discrete phase motion characteristics, and then combined with the theory of erosion for calculation. A mathematical model of the direct-drive electro-hydraulic servo valve is established by using Solidworks software, and then imported into Fluent simulation software to establish its physical failure model and carry out simulation. Finally, the physical failure form of the direct drive electro-hydraulic servo valve is verified by the simulation results, and the performance degradation law is summarized. The results show that temperature, differential pressure, solid particle diameter and concentration, and opening degree all have an impact on the erosion and wear of direct-drive electro-hydraulic servo valves, in which differential pressure and solid particle diameter have a relatively large impact, and the servo valve must avoid working in the range of high differential pressure and solid particle diameter of 20–40 um as far as possible. This also provides further theoretical support and experimental guidance for the industrial application and life prediction of electro-hydraulic servo valves.

Comprehensive mechanics‐based virtual model of NHERI@UCSD shake table—Uniaxial configuration and bare table condition

AbstractA mechanics‐based virtual model of the NHERI@UCSD large high‐performance outdoor shake table (LHPOST) in its uniaxial configuration and under bare table condition is presented. The virtual model includes: (i) a reprogrammed version (i.e., virtual replica) of the actual controller, (ii) a servovalve model including servovalve spool dynamics and two independent servovalve flow nonlinearities for each of the four servovalves of the system, (iii) an actuator model for each of the two single‐ended actuators, (iv) two accumulators modeling the average supply pressure drop at the entrance of the servovalves, and (v) a one‐degree‐of‐freedom mechanical subsystem model. Based on forced vibration test results for the foundation block, it was found that the soil‐foundation compliance effects do not need to be included in the virtual model of the LHPOST. The virtual model presented is able to predict accurately the actual shake table platen response under narrow and broadband inputs with the controller gains set to the same values as on the actual shake table. Moreover, the fourth stage spool displacements and actuator driving force from actual tests are reproduced accurately by the virtual model. The mechanics‐based virtual model presented in this article can be coupled with FE models of specimens to be tested on the LHPOST and can be used to improve the signal reproduction fidelity of the LHPOST and to develop more advanced model‐based shake table controllers.

A review of simplified servovalve models for digital twins of electrohydraulic actuators

The development and detail design of complex electrohydraulic actuators for aircraft flight controls require the use of accurate, high fidelity fluid-dynamic simulations in order to predict the behaviour of the system within its whole operating envelope. However, those simulations are usually computationally expensive, and simplified models are useful for the preliminary design phases and real-time health monitoring. Within this context, this work presents a review of low fidelity models for the fluid-dynamic behaviour of an electrohydraulic servovalve. Those are intended to run in real time as digital twins of the physical system, in order to enable the execution of diagnostic and prognostic algorithms. The accuracy of the simulations is assessed by comparing their results against a detailed, physics-based high fidelity model, which computes the response of the equipment accounting for the pressure-flow characteristics across all the internal passageways of the valve.

Analysis of the interaction effects between double shaking tables and test structure

Electrohydraulic shaking tables provide a direct means to evaluate structural performance under actual vibration conditions. The control–structure interaction is one of the most important reasons for the degradation of the control performance of the shaking table. This article establishes a series of novel analytical models to investigate the control–structure interaction effects between double shaking tables and test structure. These models are the model of shaking table, the model of control error signal, the flow requirement model of servo valve, the force requirement model of actuator, and the resonance response model of structure. Based on the analytical models of the flow requirement model of servo valve, force requirement model of actuator, and resonance response model of structure, a comprehensive simulation study is conducted under different structural conditions. The study reveals the influence trend and the influence degree of the control–structure interaction on the models. Furthermore, the applications in experiments, the suggestions for the designing of the shaking table, and the deeper explorations of the control–structure interaction are obtained.

Quality Prediction and Discussion of an Abrasive Flow Precision Polishing Baffle Servo Valve Nozzle Based on Orthogonal Experiments

Through range and variance analyses of an orthogonal experiment, the key factors of abrasive flow precision polishing (AFPP) are confirmed. The influence of grinding speed, abrasive concentration and abrasive particle size parameters on AFPP is secondary to action factors. The optimum AFPP process parameters are obtained. Under these parameters, the Ra value of the surface roughness of the nozzle orifices is acceptable. From 0.679 µm before abrasive flow polishing (AFP) to 0.143 µm, the quality of small holes improved obviously. The quality prediction model of the AFPP baffle servo valve is established through experimental research and data calculation, which can effectively predict the surface quality of the AFP baffle servo valve nozzle. The results of the AFP experiment show that the prediction model is effective and feasible and can obtain the best surface quality. The research results can provide theoretical guidance and technical support for the development of quality control technology of AFPP nozzles.

Proposal of a new simplified fluid dynamic model for aerospace servovalves

Highly detailed computer models are required for design and development of modern flight control systems, capable of emulating with high accuracy the behaviour of on-board equipment. At the same time, different simplified models are needed, specifically intended for operations such as the optimization of preliminary design and the development of diagnostic or prognostic strategies. These simplified models are required to combine sufficient levels of accuracy and reliability with reduced computational costs, to minimize the computational burden associated with prognostic and optimization algorithms. In this work, we focus on electro-hydraulic actuators, since they are critical subsystems in terms of safety and availability of the aircraft. Advanced monitoring and prognostic algorithms require new numerical models, combining an acceptable computational effort with a satisfying ability to simulate their performance and dynamics. To this purpose, this paper proposes a new simplified numerical model of the servovalve fluid-dynamic behaviour. This numerical algorithm, based on a very compact semi-empirical formulation, is intended to take into account in a simplified but sufficiently accurate way several typical effects related to the SV spool geometry and the operating conditions. To evaluate the approximations introduced by this model into a system-level simulation, it has been integrated into a dedicated numerical model simulating a simple electrohydraulic on-board actuator, and compared with a higher fidelity servovalve model.

Theoretical model and characteristics analysis of deflector-jet servo valve’s pilot stage

To analyze the deflector-jet servo valve’s internal flow characteristics, a theoretical model of the complicated flow distribution in the deflector plate is established based on the offset jet attachment theory. When the deflector plate offsets, jet attachment parameters are attained to figure out the jet’s bending and colliding process. On this basis, an analytical method of acquiring the pilot valve’s pressure gain is derived. According to an actual pilot stage’s structure, pressure gain calculations are carried out. Meanwhile, the pilot valve’s mesh model is established for numerical simulation in order to examine the accuracy of the theoretical model. Calculation and numerical simulation show that the final oil jet is not sensitive to the deflector plate’s movement, which directly reveals the pressure stabilizing effect of the V-shaped structure on the deflector plate. Moreover, the experiment on the pressure gain is accomplished and experiment results verify the accuracy of the analytical calculation.

Joint Control of the Upper Limb Exoskeleton Based on Fuzzy-PD

In order to achieve a good servo control effect of the upper limb exoskeleton, Fuzzy-PD controller is applied to the control system. Through the analysis of the hydraulic system, the mathematical model of electro-hydraulic servo valve and hydraulic cylinder are been established. Then the principle of fuzzy PD controller is been introduced. The linguistic variables, the membership functions and the fuzzy control rules are also been determined. Finally the MATLAB is used to simulate the upper limb exoskeleton. The result of the simulation shows that Fuzzy-PD controller has a better effect compared to the PID controller.

Application of Modelica/MWorks on modeling, simulation and optimization for electro-hydraulic servo valve system

Electro-hydraulic servo valve is a typical complicated multi-domain system constituted by mechanical, electric, hydraulic and magnetic components, which is widely used in electro-hydraulic servo systems such as construction machinery, heavy equipment, weapon and so forth. The traditional method of modeling and simulation of servo valve is based on block diagram or signal flow, which cannot describe the servo valve system from components level nor be used in modeling and simulation of overall servo systems. In the procedure of traditional method, computational causality must be involved in modeling of servo valve, which is inconvenient to execute modification on components or parameters. Modelica is an object-oriented modeling language which is suited for large, complex, heterogeneous and multi-domain systems. The key features of Modelica are multi-domain, object-oriented and non-causal, which are suitable for modeling of servo valve and make the model readable, reusable, and easy to modify. The simulation results show similar curves with traditional method. This new servo valve modeling and simulation method can provide the engineers a more efficient way to design and optimize a servo valve and an overall servo system.

Pneumatic servo valve models based on artificial neural networks

This paper presents a study where static models for the flow stage of three-port pneumatic servo valves are obtained using artificial neural networks. A new approach to build the models is introduced in detail. This approach considers two distinct models: for simulation purposes, the air mass flow is determined for a given working pressure and command input; for control purposes, the command input is determined given the working pressure and the desired air mass flow. This approach enables the use of air mass flow as the synthesized control action, thus rendering the overall pneumatic system affine. Therefore, control techniques requiring this condition on the system model can be directly used. The use of this approach in two different industrial pneumatic servo valves is presented in detail. A comparison between the different characteristics of each servo valve is also provided.

Dynamic performance of a nonlinear non-dimensional two stage electrohydraulic servovalve model

Electrohydraulic servosystems are commonly used in various engineering applications due to their high power-to-weight ratio, good performance, and ease of control. An electrohydraulic servovalve is an essential item of fluid power servomechanism where fast response, high power output and working fidelity are necessary. A full description of the dynamic performance of a two stage electrohydraulic servovalve is presented. Nonlinear Non-dimensional mathematical model has been developed for that purpose. The system main equations could be derived in minimal symbolic forms; which facilitates a subsequent numerical simulation in order to investigate the static and dynamic behaviors. In addition to a step response, ramp and sinusoidal inputs responses are investigated. The model has been coded in the software package Matlab/Simulink (Liuping, Modern control systems analysis and design using Matlab and Simulink, Springr-Verlag, London, 2009). The use of the non-dimensional form enables designer to expect the valve behavior of the same shape but with different sizes.

Modelling and dynamics of a servo-valve controlled hydraulic motor by bondgraph

A comprehensive model of a closed-loop servo-valve controlled hydro-motor drive system has been made using Bondgraph simulation technique (Thoma, 1990) [17]. The validation of the servo-valve model is obtained first by the established results of Gordic et al., 2004 [10]. The dynamic performance of the complete system has been studied with respect to the variation of the parameters of the PI controller that drives the servo-valve.

PID Parameters Optimization Using Genetic Algorithm Technique for Electrohydraulic Servo Control System

Electrohydraulic servosystem have been used in industry in a wide number of applications. Its dynamics are highly nonlinear and also have large extent of model uncertainties and external disturbances. In order to increase the reliability, controllability and utilizing the superior speed of response achievable from electrohydraulic systems, further research is required to develop a control software has the ability of overcoming the problems of system nonlinearities. In This paper, a Proportional Integral Derivative (PID) controller is designed and attached to electrohydraulic servo actuator system to control its angular position. The PID parameters are optimized by the Genetic Algorithm (GA). The controller is verified on the state space model of servovalve attached to a rotary actuator by SIMULINK program. The appropriate specifications of the GA for the rotary position control of an actuator system are presented. It is found that the optimal values of the feedback gains can be obtained within 10 generations, which corresponds to about 200 experiments. A new fitness function was implemented to optimize the feedback gains and its efficiency was verified for control such nonlinear servosystem.

Simulation of Automatic Position Control in an 8-High Cold Rolling Mill Hydraulic System

This paper presents the modelling and simulation of automatic position control (APC) in an 8-high cold rolling mill hydraulic system built by CERI (Capital Engineering and Research Incorporation). Key feature of the rolling mill APC system is introduced. From modelling, the servo valve and cylinder models are built, and from simulation the dynamic response of the system can be predicted for selecting system components and optimizing system performance. As system dynamic response is not only depending on the servo valve but also on all components in the system, root locus method is applied to analyze APC system dynamic response. Simulation results with different parameters are compared. Additionally, compared with a 6-high cold rolling mill APC system, the APC system dynamic responses of CERI 8-high rolling mill can reach better results than those obtained in the 6-high rolling mill system.

Research on Electro-Hydraulic Load Simulator Based on Building Model of Flow Press Servo Valve

The model of flow press servo valve is built in this paper, during building the model, the author emphatically analyses the flow equation and force (torque) balance equation of every part of the valve, at the same time, all levels sub-models are organic combined according to power flow direction, signal flow direction of elements and causality, then we get the bond graph model of the flow press servo from this way. Adapting flow press servo valve and flow servo valve to concurrently control load system has its great advantage in restraining the superfluous force of the electro-hydraulic load simulator system, the performance such as load precision of system is enhanced greatly according to this method. Based on the system bond graph model, and by comparing the simulation curves and experiment curves, we can know that the simulation curves basically tally with the experiment curves, the bond graph models are validated right, which are flow press servo valve bond graph model and double valves concurrently control the electro-hydraulic load simulator system bond graph model. Simultaneity, the bond graph models in this paper take on generality, they are can be used on other aspects, such as other valve controlling cylinder system simulation, design and control strategy theory research.

Experimental and theoretical study of the electrical failures in a fault-tolerant direct-drive servovalve for primary flight actuators

The current paper deals with the study of the electrical failures in fault-tolerant flight actuators, with particular reference to the short circuits of the servovalve coils. A high-fidelity model of the servovalve of a modern fly-by-wire actuator is developed and validated through experiments, focusing attention on the characterization of the component dynamics in case of partial and total short circuits of the direct-drive motor coils. The servovalve model is then used to simulate a typical on-ground built-in-test procedure to determine the limit condition for the detection of a partial short circuit. Finally, once different possible combinations of short circuits are injected, the degradation of performances of the whole actuator is characterized through experiments, and the servovalve model is used to justify the test results, highlighting and discussing the effects of the failures on the system dynamics.

Model-based control of a 6-dof electrohydraulic Stewart–Gough platform

Abstract In this paper, a novel model-based controller for a six Degree-of-Freedom (dof) electrohydraulic Stewart–Gough platform is developed. Dynamic models of low complexity are employed that describe the salient dynamics of the main electrohydraulic components. Rigid body equations of motion and hydraulics dynamics, including friction and servovalve models are used. The developed feedback controller uses the system dynamic and hydraulic model to yield servovalve currents, so that the error dynamics converge asymptotically to zero, independent of load variations. In this approach, force, pressure or acceleration feedback is not required. Simulations with typical desired trajectory inputs are presented and a good performance of the controller is obtained. The proposed methodology can be extended to electrohydraulic serial or closed-chain manipulators and simulators.