Characteristics Prediction Method of Electro-hydraulic Servo Valve Based on Rough Set and Adaptive Neuro-fuzzy Inference System

Synthesis characteristics of the electro-hydraulic servo valve are key factors to determine eligibility of the hydraulic production. Testing all synthesis characteristics of the electro-hydraulic servo valve after assembling leads to high repair rate and reject rate, so accurate prediction for the synthesis characteristics in the industrial production is particular important in decreasing the repair rate and the reject rate of the product. However, the research in forecasting synthesis characteristics of the electro-hydraulic servo valve is rare. In this work, a hybrid prediction method was proposed based on rough set（RS） and adaptive neuro-fuzzy inference system（ANFIS） in order to predict synthesis characteristics of electro-hydraulic servo valve. Since the geometric factors affecting the synthesis characteristics of the electro-hydraulic servo valve are from workers＇ experience, the inputs of the prediction method are uncertain. RS-based attributes reduction was used as the preprocessor, and then the exact geometric factors affecting the synthesis characteristics of the electro-hydraulic servo valve were obtained. On the basis of the exact geometric factors, ANFIS was used to build the final prediction model. A typical electro-hydraulic servo valve production was used to demonstrate the proposed prediction method. The prediction results showed that the proposed prediction method was more applicable than the artificial neural networks（ANN） in predicting the synthesis characteristics of electro-hydraulic servo valve, and the proposed prediction method was a powerful tool to predict synthesis characteristics of the electro-hydraulic servo valve. Moreover, with the use of the advantages of RS and ANFIS, the highly effective forecasting framework in this study can also be applied to other problems involving synthesis characteristics forecasting.

Simulation investigation on fluid characteristics of jet pipe water hydraulic servo valve based on CFD

Simulation investigation on fluid characteristics of the water hydraulic jet pipe servo valve （WHJPSV） is conducted through a commercial computational fluid dynamics （CFD） software package FLUENT. In particular, the factors to fluid characteristics of WHJPSV are addressed, which include diameter combination of jet pipe and receiver pipe, jet pipe nozzle clearance, angle between two jet receiver pipes and deflection angle of the jet pipe. It is concluded from the results that： （i） Structural parameters have great influences on fluid characteristics of WHJPSV, when d1 = d2 = 0.3 mm, α= 45 , b = 0.5 mm, and the simulation exhibits better fluid characteristics; （ii） The magnitude of the recovery pressure and flow velocity increase almost linearly with the deflection angle of jet pipe. The research work in this paper is important for determining and optimizing the structural parameters of the jet pipe and jet receiver. The relevant conclusions could be extended to the study of other water hydraulic servo control components.

Dynamic Modelling and Design of a Servomechanism for Hydraulic Directional-Control Valves

This paper analyses a control strategy applicable in heaVy-duty hydraulic Systems,namely, the introduction of a servovalve to achieve smoother operation of direCtional-control valves that serve also as flow-control valves over two fanges of operating conditions. A mathematical model of the dynamics of the System is etallished and design criteria are obtained from a linearised form of that model. The influence of variations in tile axial force on the spool of the main valve is investigated, and the use of the resultS in the design of systems of the proposed kind is discussed.

Mathematical Model of Steady State Operation in Jet Pipe Electro-Hydraulic Servo Valve

Jet pipe electro-hydraulic servo valve is the heart of feedback control systems,and it is one of the mechatronic components used for precision flow control application.It consists of several precision and ddicate components.The performance of the jet pipe servo valve depends on many parameters.During the developmental stage,it is very difficult to ascertain the function parameters.The steady-state analysis of jet pipe electro-hydraulic servo valve has been made to simulate its fluid characteristics （flowin,flow-out,leakage flow,recovery or load pressure,etc.） by mathematical modeling.Theoretical model was conducted on various affecting parameters on the pressure,the main flow rate of fluid,or leakage flow through the receiver holes.The major parameters studied are jet pipe nozzle diameters,receiver hole diameters,angle between the two centre-lines of receiver hole,nozzle offset,and nozzle stand-of distance.In this paper the research is important to determine and optimize the structural parameters of jet pipe servo valve.Thus,equations of the pressure and flow characteristics are set up and the optimal structural parameters of jet pipe are established.

High precise control method for a new type of Piezoelectric electro-hydraulic servo valve

A new type of piezoelectric electro-hydraulic servo valve system was proposed. And then multilayer piezoelectric actuator based on new piezoelectric ceramic material was used as the electricity-machine converter of the proposed piezoelectric electro-hydraulic servo valve. The proposed piezoelectric electro-hydraulic servo valve has ascendant performance compared with conventional ones. But the system is of high nonlinearity and uncertainty, it cannot achieve favorable control performance by conventional control method. To develop an efficient way to control piezoelectric electro-hydraulic servo valve system, a high-precise fuzzy control method with hysteresis nonlinear model in feedforward loop was proposed. The control method is separated into two parts: a feedforward loop with Preisach hysteresis nonlinear model and a feedback loop with high-precise fuzzy control. Experimental results show that the hysteresis loop and the maximum output hysteresis by the PID control method are 4.22% and 2.11 μm, respectively; the hysteresis loop and the maximum output hysteresis by the proposed control method respectively are 0.74% and 0.37 μm, respectively; the maximum tracking error by the PID control method for sine wave reference signal is about 5.02%, the maximum tracking error by the proposed control method for sine wave reference signal is about 0.85%.

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.

Numerical Simulation and Experimental Study of Heat-fluid-solid Coupling of Double Flapper-nozzle Servo Valve

The double flapper-nozzle servo valve is widely used to launch and guide the equipment. Due to the large instantaneous flow rate of servo valve working under specific operating conditions, the temperature of servo valve would reach 120℃ and the valve core and valve sleeve deform in a short amount of time. So the control precision of servo valve significantly decreases and the clamping stagnation phenomenon of valve core appears. In order to solve the problem of degraded control accuracy and clamping stagnation of servo valve under large temperature difference circumstance, the numerical simulation of heat-fluid-solid coupling by using finite element method is done. The simulation result shows that zero position leakage of servo valve is basically impacted by oil temperature and change of fit clearance. The clamping stagnation is caused by warpage-deformation and fit clearance reduction of the valve core and valve sleeve. The distribution roles of the temperature and thermal-deformation of shell, valve core and valve sleeve and the pressure, velocity and temperature field of flow channel are also analyzed. Zero position leakage and electromagnet＇s current when valve core moves in full-stroke are tested using Electro-hydraulic Servo-valve Characteristic Test-bed of an aerospace sciences and technology corporation. The experimental results show that the change law of experimental current at different oil temperatures is roughly identical to simulation current. The current curve of the electromagnet is smooth when oil temperature is below 80℃, but the amplitude of current significantly increases and the hairy appears when oil temperature is above 80℃. The current becomes smooth again after the warped valve core and valve sleeve are reground. It indicates that clamping stagnation is caused by warpage-deformation and fit clearance reduction of valve core and valve sleeve. This paper simulates and tests the heat-fluid-solid coupling of double flapper-nozzle servo valve, and the obtained results provide the reference value for the design of double flapper-nozzle force feedback servo valve.

Analysis of the Internal Characteristics of a De ector Jet Servo Valve

In current research on deflector jet servo valves, the receiver pressure estimated using traditional two-dimensional simulation and theoretical calculation is always lower than the experimental data; therefore, credible information about the flow field in the prestage part of the valve can hardly be obtained. To investigate this issue and understand the internal characteristics of the deflector jet valve, a realistic numerical model is constructed and a three-dimensional simulation carried out that displays a complex flow pattern in the deflector jet structure. Then six phases of the flow pattern are presented, and the defects of the two-dimensional simulation are revealed. Based on the simulation results, it is found that the jet in the deflector has a longer core area and the fluid near the shunt wedge cannot resist the impact of the high-speed fluid. Therefore, two assumptions about the flow distribution are presented by which to construct a more complete theoretical model. The receiver pressure and prestage pressure gain are significantly enhanced in the calculations. Finally, special experiments on the prestage of the servo valve are performed, and the pressure performance of the numerical simulation and the theoretical calculation agree well with the experimental data. Finally, the internal mechanism described by the theoretical and numerical models is verified. From this research,more accurate numerical and theoretical models are proposed by which to figure out the internal characteristics of the deflector jet valve.

Output Waveform Analysis of an Electro-hydraulic Vibrator Controlled by the Multiple Valves

The existing research of the electro-hydraulic vibrator mainly focuses on system stability, working frequency width and output waveform distortion. However, this high frequency performance of the electro-hydraulic vibrator is difficult to be improved greatly due to fast insufficiently frequency response of the servo valve itself and limited compensation capability of the control structure in the vibrator system. In this paper, to realize high frequency vibration, an improved two-dimensional valve （here within defined as a 2D valve） as a main control component is adopted to the parallel connection with a servo valve to control the electro-hydraulic vibrator, Because the output waveforms of this electro-hydraulic vibrator are incapable to be verified through timely feedback as in the conventional electro-hydraulic servo system, the analysis to the output waveform becomes crucial to the design and control of the electro-hydraulic vibrator. The mathematical models of hydraulic actuation mechanism and the orifice area of the parallel valves connection are established first. And then the vibration process is divided into two sections in terms of the direction of the flow, the analytical expression of the excited waveform is solved. Based on relationships exist between working states and the control parameters the analytical results, the vibration boundary positions and the are derived. Finally an experimental system was built to validate the theoretical analysis. It is verified that this electro-hydraulic vibration system could achieve high working frequency, up to 2 000 Hz. The excited waveform is similar to the sinnsoidal waveform. And the ascent and decent slopes of the waveforms are somewhat asymmetrical. This asymmetry is not only caused by the change of the direction of the elastic force but also dependent on the bias position of the vibration. Consequentky the distortion of effective working waveform is less tha~ 10%. This electro-hydraulic vibrator controlled by the multiple valves could not only greatly enhance the working frequency but also precisely control the vibration characteristic variables such as waveform shape.

Research and Development of Electro‑hydraulic Control Valves Oriented to Industry 4.0:A Review

Electro-hydraulic control valves are key hydraulic components for industrial applications and aerospace,which controls electro-hydraulic motion.With the development of automation,digital technology,and communication technology,electro-hydraulic control valves are becoming more digital,integrated,and intelligent in order to meet the requirements of Industry 4.0.This paper reviews the state of the art development for electro-hydraulic control valves and their related technologies.This review paper considers three aspects of state acquisition through sensors or indirect acquisition technologies,control strategies along with digital controllers and novel valves,and online maintenance through data interaction and fault diagnosis.The main features and development trends of electro-hydraulic control valves oriented to Industry 4.0 are discussed.

Influence of Magnetic Reluctances of Magnetic Elements on Servo Valve Torque Motors

The current research of electro-hydraulic servo valves mainly focuses on the vibration, pressure oscillating and source of noise. Unfortunately, literatures relating to the study of the influence of the magnetic reluctances of the magnetic elements are rarely available. This paper aims to analyze the influence of the magnetic reluctances of the magnetic elements on torque motor. Considering these magnetic reluctances ignored in previous literatures, a new mathematical model of servo valve torque motor is developed and proposed based on the fundamental laws of electromagnetism. By using this new mathematical model and the previous models, electromagnetic torque constant and magnetic spring stiffness are evaluated for a given set of torque motor parameters. A computer simulation by using AMESim software is also performed for the same set of torque motor parameters to verify the proposed model. The theoretical results of electromagnetic torque constant and magnetic spring stiffness evaluated by the proposed model render closer agreement with the simulation results than those evaluated by the previous models. In addition, an experimental measurement of the magnetic flux densities in the air-gaps is carried out by using SFL218 servo valve torque motor. Compared with the theoretical results of the magnetic flux densities in the air-gaps evaluated by the previous models, the theoretical results evaluated by the proposed model also show better agreement with the experimental data. The proposed model shows the influence of the magnetic reluctances of the magnetic elements on the servo valve torque motor, and offers modified and analytical expressions to electromagnetic torque constant and magnetic spring stiffness. These modified and analytical expressions could provide guidance more accurately for a linear control design approach and sensitivity analysis on electro-hydraulic servo valves than the previous expressions.

Research on the jet characteristics of the deflector–jet mechanism of the servo valve

In view of the complicated structure of the deflector-jet mechanism,a mathematical model based on the turbulent jet flow theory in the deflector-jet amplifier is proposed.Considering the energy transformation and momentum variation,an equation of the flow velocity distribution at the key fluid region is established to describe the morphological changes of the fluid when it passes through the deflector and jets into the receiver.Moreover,the process is segmented into four stages.According to the research results,the oil enters the deflector and impinges with the side wall.Then one part of the oil＇s flow velocity decreases and a high pressure zone is formed by the oil accumulation,the other part of the oil reverses out of the deflector along the side wall.Prior to entering the receiver,the flow is a kind of plane impinging jet.Virtually,the working pressure of the receiver is generated by the impact force,while the high speed fluid flows out of the receiver and forms a violent vortex,which generates negative pressure and causes the oil to be gasified.Compared with the numerical simulation results,the turbulent jet model that can effectively describe the characteristics of the deflector-jet mechanism is accurate.In addition,the calculation results of the prestage pressure characteristic have been verified by experiments.

2D SIMPLIFIED SERVO VALVE

A novel pilot stage valve called simplified 2D valve, which utilizes bothrotary and linear motions of a single spool, is presented. The rotary motion of the spoolincorporating hydraulic resistance bridge, formed by a damper groove and a crescent overlap opening,is utilized as pilot to actuate linear motion of the spool. A criterion for stability is derivedfrom the linear analysis of the valve. Special experiments are designed to acquire the mechanicalstiffness, the pilot leakage and the step response. It is shown that the sectional size of thespiral groove affects the dynamic response and the stiffness contradictorily and is also verysensitive to the pilot leakage. Therefore, it is necessary to establish a balance between the staticand dynamic characteristics in deciding the structural parameters. Nevertheless, it is possible tosustain the dynamic response at a fairly high level, while keeping the leakage of the pilot stage atan acceptable level.

EXPERIMENTAL INVESTIGATIONS OF CAVITATION EFFECTS ON FLOW CHARACTERISTICS OF SMALL ORIFICES AND VALVES IN WATER HYDRAULICS

The flow characteristics and cavitation effects of water passing throughsmall sharp-edged cylindrical orifices and valves of different shapes in water hydraulics areinvestigated. The test results using orifices with different aspect ratios and different diametersshow that the flow coefficients in the case of non-cavitating flow are larger than that of flow inthe case of cavitation occurrence. The flow coefficients of flow with cavitation initially decreaseas Reynolds number increases and ultimately tend to be of constant values close to contractioncoefficient. Large aspect ratio has an effect of suppressing cavitation. The experimental resultsabout disc valves illustrate that the valves with sharp edge at large opening are less affected bycavitation than that at small opening. Throttle with triangle notch has better anti-cavitationability than that with square notch. The flowrate of the throttle with square notch is significantlyaffected by the flow direction or the flow passage shape.

High Speed On/Off Valve Control Hydraulic Propeller

The work-class remotely-operated-underwater-vehicles（ROVs） are mainly driven by hydraulic propulsion system,and the effeciency of hydraulic propulsion system is an important performance index of ROVs.However,the efficiency of traditional hydraulic propulsion system controlled by throttle valves is too low.Therefore,in this paper,for small and medium ROVs,a novel propulsion system with higher efficiency based on high speed on/off valve control hydraulic propeller is proposed.To solve the conflict between large flow rate and high frequency response performance,a two-stage high speed on/off valve-motor unit with large flow rate and high response speed simultaneously is developed.Through theoretical analysis,an effective fluctuation control method and a novel pulse-width-pulse-frequency-modulation（PWPFM） are introduced to solve the conflict among inherently fluctuation,valve dynamic performance and system efficiency.A simulation model is established to evaluate the system performance.To prove the advantage of system in energy saving,and test the dynamic control performance of high speed on/off valve control propeller,a test setup is developed and a series of comparative experiments is completed.The smimulation and experiment results show that the two-stage high speed on/off valve has an excellent dynamic response performance,and can be used to realize high accuracy speed control.The experiment results prove that the new propulsion system has much more advantages than the traditional throttle speed regulation system in energy saving.The lowest efficiency is more than 40%.The application results on a ROV indicate that the high speed on/off valve control propeller system has good dynamic and steady-state control performances.Its transient time is only about 1 s-1.5 s,and steady-state error is less than 5%.Meanwhile,the speed fluctuation is small,and the smooth propeller speed control effect is obtained.On the premise of good propeller speed control performance,the proposed high speed on/off valve control propeller can improve the effeciency of ROV propulsion system significantly,and provides another attractive ROV propulsion system choice for engineers.

Fault Diagnosis in a Hydraulic Position Servo System Using RBF Neural Network

Considering the nonlinea r, time-varying and ripple coupling properties in the hydraulic servo system, a two-stage Radial Basis Function （RBF） neural network model is proposed to realize the failure detection and fault localization. The first-stage RBF neural network is adopted as a failure observer to realize the failure detection. The trained RBF observer, working concurrently with the actual system, accepts the input voltage signal to the servo valve and the measurements of the ram displacements, rebuilds the system states, and estimates accurately the output of the system. By comparing the estimated outputs with the actual measurements, the residual signal is generated and then analyzed to report the occurrence of faults. The second-stage RBF neural network can locate the fault occurring through the residual and net parameters of the first-stage RBF observer. Considering the slow convergence speed of the K-means clustering algorithm, an improved K-means clustering algorithm and a self-adaptive adjustment algorithm of learning rate arc presented, which obtain the optimum learning rate by adjusting self-adaptive factor to guarantee the stability of the process and to quicken the convergence. The experimental results demonstrate that the two-stage RBF neural network model is effective in detecting and localizing the failure of the hydraulic position servo system.

GIANT MAGNETOSTRICTIVE ACTUATOR IN SERVO VALVE AND MICRO PIPE ROBOT

Performance of giant magnetostrictive material (GMM) is introduced. Principleof work, basic structure and key techniques of giant magnetostrictive actuator (GMA) are analyzed.Its dynamic models of magneto-mechanical coupling are established. The structure and principle ofthe pneumatic servo valve and the micro pipe robot with new homemade GMM are presented. Theexperiment is carried out under typical working conditions. The experiment results show that the GMMpneumatic servo valve has wide pressure control characteristics, good linearity, and fast responsespeed. The movement principles of the GMM robot system are reliably feasible and its maximal movingspeed is about 8 mm/s. It is preferable to the driving frequency of the robot within 100 approx 300Hz.

Fuzzy iterative learning control of electro-hydraulic servo system for SRM direct-drive volume control hydraulic press

A new kind of volume control hydraulic press that combines the advantages of both hydraulic and SRM(switched reluctance motor) driving technology is developed.Considering that the serious dead zone and time-variant nonlinearity exist in the volume control electro-hydraulic servo system,the ILC(iterative learning control) method is applied to tracking the displacement curve of the hydraulic press slider.In order to improve the convergence speed and precision of ILC,a fuzzy ILC algorithm that utilizes the fuzzy strategy to adaptively adjust the iterative learning gains is put forward.The simulation and experimental researches are carried out to investigate the convergence speed and precision of the fuzzy ILC for hydraulic press slider position tracking.The results show that the fuzzy ILC can raise the iterative learning speed enormously,and realize the tracking control of slider displacement curve with rapid response speed and high control precision.In experiment,the maximum tracking error 0.02 V is achieved through 12 iterations only.

Nonlinear control for a class of hydraulic servo system

The dynamics of hydraulic systems are highly nonlinear and the system may be subjected to non-smooth and discontinuous nonlinearities due to directional change of valve opening, friction, etc. Aside from the nonlinear nature of hydraulic dynamics, hydraulic servo systems also have large extent of model uncertainties. To address these challenging issues, a robust state-feedback controller is designed by employing backstepping design technique such that the system output tracks a given signal arbitrarily well, and all signals in the closed-loop system remain bounded. Moreover, a relevant disturbance attenuation inequality is satisfied by the closed-loop signals. Compared with previously proposed robust controllers, this paper's robust controller based on backstepping recursive design method is easier to design, and is more suitable for implementation.

Numerical investigation of cavitating flow behind the cone of a poppet valve in water hydraulic system

Computational Fluid Dynamics (CFD) simulations of cavitating flow through water hydraulic poppet valves were performed using advanced RNG k-epsilon turbulence model. The flow was turbulent, incompressible and unsteady, for Reynolds numbers greater than 43 000. The working fluid was water, and the structure of the valve was simplified as a two dimensional axisymmetric geometrical model. Flow field visualization was numerically achieved. The effects of inlet velocity, outlet pressure, opening size as well as poppet angle on cavitation intensity in the poppet valve were numerically investigated. Experimental flow visualization was conducted to capture cavitation images near the orifice in the poppet valve with 30° poppet angle using high speed video camera. The binary cavitating flow field distribution obtained from digital processing of the original cavitation image showed a good agreement with the numerical result.