Proportional Directional Valve Research Articles

Development of a new high-precision friction test platform and experimental study of friction characteristics for pneumatic cylinders

In order to achieve high-precision pneumatic cylinder friction test, this paper proposes a new direct measurement method based on electric cylinder in which the axially acting forces from the compressed air in the two facing pneumatic cylinders cancel each other out and the detected value of the force transducer is just friction. For the sake of the implementation of the method, a new low-cost test method for identifying deadband of proportional directional valve was proposed, and a set of fuzzy PI constant pressure control system was designed to cope with a certain degree of leakage in the chamber. Based on the above, a friction test platform with two pneumatic cylinders facing each other was eventually built to study the influence of pressure, pressure difference, and piston speed on the friction of two commonly used different types of pneumatic cylinders. Through multiple sets of tests, it is found that when the lip seals are used in pairs between the piston and the inner wall of the cylinder, the friction between the piston and the cylinder is only related to the sum of the two chamber pressures, but not to the pressure difference between the two chambers. When the O-ring seal is used between the piston and the inner wall of the cylinder, the friction between the piston and the cylinder is related not only to the pressure of the two chambers, but also to the pressure difference between the two chambers. In addition, a series of comparative tests with the traditional single-cylinder friction test method directly demonstrate the effectiveness of the proposed new method.

Validation of a Simulink Model for Simulating the Two Typical Controlled Ventilation Modes of Intensive Care Units Mechanical Ventilators

Mechanical ventilators are vital components of critical care services for patients with severe acute respiratory failure. In particular, pressure- and volume-controlled mechanical ventilation systems are the typical modes used in intensive care units (ICUs) to ventilate patients who cannot breathe adequately on their own. In this paper, a Simulink model is proposed to simulate these two typical modes employed in intensive care lung ventilators. Firstly, these two modes of ventilation are described in detail in the present paper. Secondly, the suggested Simulink model is analysed: it consists of using well-established subroutines already present in Simulink through the Simscape Fluids (gas) library, to simulate all the pneumatic components employed in some commercial ICU ventilators, such as pressure reducing valves, pressure relief valves, check valves, tanks, ON\OFF and proportional directional valves, etc. Finally, the simulation results of both modes in terms of pressure, tidal volume, and inspired/expired flow are compared with the real-life quantitative trends taken from previously recorded real-life experiments in order to validate the Simulink model. The accuracy of the model is high, as the numerical predictions are in good agreement with the real-life data, the percentage error being less than 10% in most comparisons. In this way, the model can easily be used by manufacturers and start-ups in order to produce new mechanical ventilators in the shortest time possible. Moreover, it can also be used by doctors and trainees to evaluate how the mechanical ventilator responds to different patients.

Establishment and Experimental Verification of a Nonlinear Position Servo System Model for a Magnetically Coupled Rodless Cylinder

The nonlinear characteristics of the pneumatic servo system are the main factors limiting its control accuracy. A new mathematical model of the nonlinear system of the valve control cylinder is proposed in order to improve the control accuracy of the pneumatic servo system. Firstly, the mass flow equation of the gas flowing through each port is established by analyzing the physical structure of the proportional directional control valve. Then, the dynamic equation of the system is set up by applying the Stribeck friction model for the friction model of the valve control cylinder and building a pneumatic circuit experiment to identify the friction model parameters. Finally, the correctness of the mathematical model is verified by the inflation and deflation experiment of the fixed capacitive chamber and the servo controls experiment based on PID position. The Simulink simulation of the mathematical model better reflects the characteristics of the pneumatic position servo system.

Experimental and Numerical Analysis of Leakage Characteristics of Proportional Directional Valve

This article deals with the experimental and numerical analysis of the leakage characteristics of the proportional directional valve. These characteristics describe the flow through the directional valve in the region of the center position of the spool valve. The element under investigation is a three-position four-way directional valve with zero overlap and feedback from the valve spool position. The actual valve spool position is sensed by an inductive position sensor and processed by integrated electronics. By means of an offset on the integrated electronics, it is also possible to set the center position of the valve spool. By moving the valve spool, the size and direction of the working fluid flow in both directions can be controlled. Internal leakage occurs due to axial and radial clearances between the spool and the sleeve. The magnitude of the axial clearances that occur at the control edges is investigated. The blocked-line pressure sensitivity curve, leakage flow curve and center flow curve are determined by experimental measurements. Depending on the experimental measurement, the correction of the center position of the valve spool is then made using offset. The flow through the control edges at the center position of the valve spool was simulated using Ansys Fluent software. Subsequently, the geometry of the flow simulation model is adjusted. The adjustment is made to take into account manufacturing tolerances. Finally, the simulated dependencies including the effect of manufacturing tolerances are compared with the measured and analytically determined characteristics. Research background: Spool valve description, mathematical equations, flow analysis through valve, radial and axial clearance. Purpose of the article: Effect of axial clearance on leakage characteristic. Methods: Experimental measurements, numerical simulation. Findings & Value added: Determining the range of the center flow curve as a function of manufacturing tolerances

Medical Grabbing Servo System with Friction Compensation Based on the Differential Evolution Algorithm

This paper introduces a pneumatic finger cylinder servo control system for medical grabbing. First, according to the physical structure of the proportional directional valve and the pneumatic cylinder, the state equation of the gas in the servo system was obtained. The Stribeck friction compensation model of a pneumatic finger cylinder controlled by a proportional valve was established and the experimental platform built. To allow the system output to better track the change in the input signal, the flow-gain compensation method was adopted. On this basis, a friction compensation control strategy based on a differential evolution algorithm was proposed and applied to the position control system of a pneumatic finger cylinder. Finally, the strategy was compared with the traditional proportional derivative (PD) strategy and that with friction compensation. The experimental results showed that the position accuracy of the finger cylinder position control system can be improved by using the friction compensation strategy based on the differential evolution algorithm to optimize the PD parameters.

Research on the performance of a novel electro-hydraulic proportional directional valve with position-feedback groove

Accurate posture control of hydraulic roof supports, which use pressurized water as their fluid power source, is an important part and research direction of intelligent fully mechanized mining face. At present, the large flow on/off directional valve used on the hydraulic roof support cannot meet the requirement of precise posture control of the roof support. To overcome the conundrum, a novel two-position three-way electro-hydraulic proportional directional flow valve for hydraulic roof support is proposed. The new valve contains two pilot stages and two main spools. The two pilot stages cooperate with each other to control the movement of the two main valve spools, which are the inlet valve spool and the outlet valve spool. The inlet valve spool adopts the Valvistor principle. The valve can realize manual pilot control and electro-hydraulic proportional flow control of the passage P-A, which has been verified by a simulation model. In this paper, the static and dynamic mathematical models of the new proportional valve are established, and the key parameters affecting the valve performances are analyzed and verified by the simulation model. An optimization control scheme is proposed to overcome the influence of supply pressure, P-A pressure difference, and nonlinear interference force on steady-state displacement and response speed of the valve. The results show that this optimization method can significantly improve the response speed of the spool and promote the linearity of spool displacement under a slope signal. In addition, the fluctuation of chamber pressure and spool displacement caused by the discontinuous flow of a fast switching valve is systematically analyzed. The analysis shows that increasing pulse-width modulation carrier frequency is an effective way to reduce fluctuation amplitude. The research provides a new design idea and control method for an electro-hydraulic proportional directional valve of hydraulic roof support.

An Adaptive Robust Controller for Hydraulic Robotic Manipulators with a Flow-Mapping Compensator

Proportional directional control valves have flexible control functions for the control of various hydraulic manipulators. It is foreseeable that the application of proportional directional control valves will be further expanded. However, due to its own structure, its important parameter, flow gain, is complex, and it has a complex functional relationship with valve opening and temperature. The variable flow gain reduces the performance of a strictly derived nonlinear controller. Therefore, it is necessary to consider the nonlinearity of flow gain in the controller design. In order to solve the above problems, this paper proposes an adaptive robust controller for a hydraulic manipulator with a flow-mapping compensator, which takes into account the nonlinear flow gain and improves the performance of the nonlinear controller. First, we established an adaptive robust controller of the hydraulic manipulator to obtain the load flow of the control input valve. Then, the function of flow gain, input voltage, and temperature are calibrated offline using cubic polynomial, and the flow-mapping compensator is obtained. Finally, we calculate the input voltage based on the flow-mapping compensator and load flow. The flow-mapping compensator further reduces the uncertainty of the model and improves the robustness of the system. By using the proposed controller, the control accuracy of the hydraulic manipulator is significantly improved.

ПОВЫШЕНИЕ ЭФФЕКТИВНОСТИ СИСТЕМ УПРАВЛЕНИЯ ЭЛЕКТРИЧЕСКИМИ РЕЖИМАМИ ЭЛЕКТРОДУГОВЫХ ПЕЧЕЙ ЗА СЧЕТ ПРИМЕНЕНИЯ АДАПТИВНОГО РЕГУЛЯТОРА ИМПЕДАНСА

The article discusses an improved automatic electrodes movement control system for electric arc furnaces (arc steel-making furnaces and ladle-furnace installations), which improves the dynamic parameters of the quality of secondary electrical circuit impedance (s) control due to the use of a new structure of a nonlinear adaptive impedance controller. The use of an improved control system stabilizes the metal charge melting process in arc steel-making furnaces as well as the liquid steel heating process in ladle-furnace installations with intensive bottom blowing. This allows for the technical effect of reduced operating time under current and reduced specific power consumption in electric arc furnaces. The non-linear adaptive impedance controller provides full linearization of control loops, including a proportional directional control valve (servo valve) with a non-linear control characteristic and a secondary electrical circuit with a non-linear dependence of impedance on the arc length. The research used a complex mathematical model of the electric circuit of an electric arc furnace, hydraulic drives for moving electrodes and an automatic control system for moving electrodes, implemented in the MATLAB Simulink mathematical package. The effectiveness of the improved control system in the conditions of the existing metallurgical production was evaluated against the example of the “RADUGA NPA PK” control system, developed at the Federal State Budgetary Educational Institution of Higher Education “MSTU im. Nosov” and a ladle-furnace operating at the installation in the electric steel-smelting shop of PJSC “Magnitogorsk Metallurgical Plant”. The developed improved control system can be used in other modern electric arc furnaces of various capacities operating at metallurgical enterprises in Russia and abroad.

Methodology for expressing the flow coefficients of coupled throttling grooves in a proportional—directional valve

Calculating the flow coefficient of a spool-valve is complicated due to the coupling-throttling effect in the throttling grooves of a proportional-directional valve. In this paper, a methodology for expressing the flow coefficient of coupled throttling grooves is proposed to resolve that difficulty. With this purpose, an approach of a 3D numerical simulation and an experimental bench were introduced based on the prototype of a commercial proportional valve. The results show consistency between the numerical simulation and the bench test. Based on that, the concept of ‘saturation limit’ is introduced to describe the value gap between the current and saturated flows, so that the flow-coefficient saturation limit of the prototype in the process can be deducted. Accordingly, an approximate flow coefficient suitable for coupled throttling grooves within finite variable space, which is based on three typical throttling structures (i.e. O-shape, U-shape, and C-shape) of the coupled throttling grooves, is obtained based on an orthogonal test. The model results are consistent with the numerical and experimental results, with maximum errors of less than 5.29% and 5.34%, respectively. This suggests that the proposed method is effective in approximating the flow coefficient.

Dynamic characteristics study on the two-stage safety valve used on hydraulic support under impact loading

1. Amirante R., Distaso E., Tamburrano P., 2016, Sliding spool design for reducing the actuation forces in direct operated proportional directional valves: Experimental validation, Energy Conversion and Management, 19, 399-410. CrossRef Google Scholar

Energy saving and Fuzzy-PID position control of electro-hydraulic system by leakage compensation through proportional flow control valve

In this article, the focus is on the energy efficiency along with the position control of the linear actuator used in heavy earth moving equipment. It is quite evident that linear actuators are one of the critical machinery components used in the construction and mining activities like in booms of excavation equipment. The proposed work employed two different hydraulic circuits and a contrast has been carried out in terms of the energy efficiency. In one hydraulic circuit, the conventional proportional directional control valve (PDCV) is used for the position control. In another one, an innovative solution of using proportional flow control valve (PFCV) by creating artificial leakage between the two ends of the actuator is evaluated according to its energy efficiency. The extra flow coming from the pump during position control is by-passed by PFCV rather than the pressure relief valve in PDCV. This reduces the energy loss in the form of heat and increases the efficiency of the hydraulic circuit. The simulation of the hydraulic circuit is performed using MATLAB/Simulink and results are compared with the experiments and it is found that hydraulic circuit using PFCV is 8.5% more energy efficient than the conventional circuit using PDCV. The position control of the actuator is done using PID controller tuned by the fuzzy controller.

Disturbance Rejection Control With Voltage Constraint for Electro-Hydraulic System Involving Unknown Dead-Zones and Drastic Supply Pressure Variation

In the article, we use the proportional directional valve (PDV) with unknown dead-zones to regulate the electro-hydraulic system (EHS) which has parametric uncertainties including the drastic supply pressure variation; moreover, the external disturbance occurs when the EHS works; in addition, the control voltage applied to the PDV is expected to satisfy the prescribed bound. All of these factors make controller design a challenging problem. The unknown dead-zones, the external disturbance, the drastic supply pressure variation and other parametric uncertainties are viewed as a total disturbance which can be estimated by the linear extended state observer (LESO). Furthermore, a novel robust disturbance rejection position controller with voltage constraints is proposed to compensate for the dead-zones and improve the tracking performance of the EHS regulated by the PDV when the drastic supply pressure variation and the external disturbance occur. The stability analysis is given to ensure that the tracking error of the closed-loop EHS regulated by the proposed controller can converge to the arbitrarily small neighborhood of the origin. Experiments are carried out to verify the effectiveness of the proposed control method. Comparative experimental results demonstrate that the proposed controller can make the load follow the reference trajectory accurately in the presence of the unknown dead-zones and the external disturbance when the supply pressure varies drastically.

Simulink Modelling For Simulating Intensive Care Mechanical Ventilators

This paper proposes a modelling approach for simulating mechanical ventilators for intensive care units (ICUs). The shortage of ventilators during the coronavirus disease 2019 (COVID-19) pandemic has focused attention on their design and performance. The proposed modelling approach consists in using the Mathworks®Simulink software tool and the SimScape Fluids (gas) library, so as to use well-established subroutines to simulate all the pneumatic components of typical ventilators for ICUs, such as the pressure reducing valves, pressure relief valves, check valves, tanks, ON\OFF and proportional directional valves, etc. The patient is simulated by setting the values of lung compliance and pressure losses occurring in the trachea. The proposed modelling approach is used in this paper to simulate a pneumatic scheme employed in some commercial ventilators. The model allows a very accurate prediction of fundamental parameters, such as the inspiratory flow rate, the inspiratory pressure, the end-expiratory pressure. Since the software interface is user-friendly, it can easily be used by manufacturers to correctly choose the geometrical and operating parameters of the components during the design stage or to assess different scenarios.

The use of innovative solutions improving selected energy or environmental indices of hydrostatic drives

This paper consists of three parts. The first part presents an exemplary application of a state-of-the-art proportional directional valve in hydrostatic gear starting. It is shown that through a proper directional valve control algorithm one can shape the pressure during the starting of the gear, reducing in this way the accompanying system noise. The second part describes the digital fluid power (DFP) technology. Its main advantage is the system’s simple design. One type of valve in 2 or 3 different sizes is sufficient to perform all the functions. In comparison with the often-used proportional valve, such a valve (called a binary valve), is characterized by simple circuitry, the absence of a position sensor, greater tolerance and lower sensitivity to impurities. An exemplary implementation of the DFP system as an additional drive in an off-road vehicle is presented. The third part describes the kinetostatic method for determining hydraulic system control parameters in order to increase the energy or environmental performance of the machine through the stabilization of the primary energy source and the selection of proper recuperation system components.

Experimental and numerical analysis on the surge instability characteristics of the vortex flow produced large vapor cavity in u-shape notch spool valve

The u-shape notch, one of those representative types of throttling notch, is widely applied in the spools of hydraulic proportional directional valves. Because of its vacuum-suction nozzle-structural effect, the u-shape notch usually possesses relatively large flow capacity, while produces drastic cavitation as well. In this paper, the notch flow characteristics to form the large vapor cavity and its surge instability characteristics are discussed by experimental and numerical analysis. It is found that, instead of the vena contracta flow, but the notch vortex flow creates the more suitable low pressure condition for cavitation inception, with the helical-stream-trend to form the cavity spiral shape with clear vapor-liquid interface. Compared with the RANS turbulent model, the LES turbulent model associated with the multi-phase cavitation model reproduce the cavity volume and the spiral shape better, while the ISO surface of vapor volume fraction number equal to 0.6 is used to approximately represent the two-phase interface. In appropriate notch configurations, the vapor cavity shows surge instability, which couples the fluctuation of flow parameters with the mass transfer process. The notch flow resistance seems to play an important role on the surge behavior, since with the decrease of the notch depth, the harmonic oscillation turns into damped oscillation, while with the increase of the notch opening, the oscillation intensifies, and even gets disturbed from the downstream vapor shedding. The biggish notch flow resistance may suppress the surge instability, but reduce the flow capacity as well. It may be not easy to figure out an optimal notch structure only. However, using more number of larger flow resistance notches to replace few number of smaller flow resistance notches may be a positive suggestion.

High Precision Adaptive Robust Neural Network Control of a Servo Pneumatic System

In this paper, an adaptive robust neural network controller (ARNNC) is synthesized for a single-rod pneumatic actuator to achieve high tracking accuracy without knowing the bounds of the parameters and disturbances. The ARNNC control framework integrates adaptive control, robust control, and neural network control intelligently. Adaptive control improves the precision of dynamic compensation with parametric estimation, and robust control attenuates the effect of unmodeled dynamics and unknown disturbances. In reality, the unmodeled dynamics of the complicated pneumatic systems and unpredictable disturbances in working conditions affect the tracking precision. However, these cannot be expressed as an exact formula. Therefore, the real-time learning radial basis function (RBF) neural network component is considered for better compensation of unmodeled dynamics, random disturbances, and estimation errors of the adaptive control. Although the bounds of the parameters and disturbances for the pneumatic systems are unknown, the prescribed transient performance and final tracking accuracy of the proposed method can be still achieved with fictitious bounds. Asymptotic tracking performance can be acquired under the provided circumstance. The comparative experiments with a pneumatic cylinder driven by proportional direction valve illustrate the effectiveness of the proposed ARNNC as shown by a high tracking accuracy is achieved.

An Intelligent Adaptive Robust Controller Based on Neural Network for a Pneumatic System

Pneumatic actuator systems are widely applied in industrial automation. This paper proposes an intelligent adaptive robust controller(ARC) based on neural network(NN) to improve the applicability in a pneumatic servo system that consists of a pneumatic cylinder which is controlled by a proportional directional control valve. In this design, adaptive robust controller is provided with suitable control parameters automatically by a real-time neural network depending on feedback errors. So the ARC the tuning process that is time consuming and restricts the application of pneumatic systems is avoided. The experimental results show all the control parameters of ARC are converged and good control performance is achieved.

Flow control of a proportional directional valve without the flow meter

Flow control is one of the most important valve functions which can be realized using the signal obtained by flow meters. However, flow meters are not suitable for being installed on fast response systems or in compact space due to slow response and large volume. This paper proposes a computational flow feedback control method using a flow inferential measurement method and a proportional integral controller. The flow inferential measurement method uses an AdaBoost neural network to learn flow change regulation affected by spool displacement, pressure differential, and temperature with high accuracy and low overfitting. The flow calculation model is analyzed by global sensitivity analysis to find the effect proportion of each factor, and piecewise wavelet filter is used to reduce the noise effect of the key signal in the calculation. The AdaBoost neural network is found to be capable of recognizing the characteristic shapes of the flow function with an accuracy of ±2%. The controller receives the accurately calculated flow and adjusts the spool displacement to control the flow. The performance of the flow control method is evaluated in the experiments. The control error is controlled within ±3% and the effectiveness of the method is validated.

Deadzone compensation control based on detection of micro flow rate in pilot stage of proportional directional valve

The pilot operated proportional directional valves (POPDVs) with a flow rate ranging from 100 to 1000 L/min are widely used in electro-hydraulic systems (EHSs). The deadzone of the pilot stage valve and its control compensation could significantly affect the position control performance for the main stage valve that could directly affect dynamics of EHSs In this paper, it is concluded that micro flow rates exist at the intermediate position of the valve based on the analysis of the continuity equation of the flow in the control chamber of the pilot stage. The micro flow rate is helpful to eliminate the discontinuity and unsmooth domain in the previous inverse deadzone compensation function. An improved deadzone detection method is proposed to calibrate the pilot valve flow characteristics which include the micro flow rate. This new method avoids the threshold selection of the main valve spool displacement which affects the detected deadzone values. Its detection processes are realized based on the pilot flow rate characterized by the speed of the main valve spool and the pilot valve displacement characterized by the solenoid current. The deadzone compensation control strategy based on the improved deadzone detection method is also designed. The experimental results using the steady-state position tracking and sinusoidal position tracking methods are verified. It is concluded that the tracking accuracy of the main valve spool position is effectively improved with this control strategy.

Investigation on the dynamic characteristics and control accuracy of a novel proportional directional valve with independently controlled pilot stage

The pilot operated directional valves are widely used in hydraulic systems. For the purpose to improve the dynamic characteristics and control accuracy of the traditional valve, this paper proposes a novel pilot valve that employs two independent valve spools instead of the traditional port coupled valve spool. Due to the new structure, the influence of deadzone and damping on the performance of the valve is lightened; the dynamic characteristics and control accuracy of the valve are improved. Both of the open-loop simulation and experimental closed-loop position control of the entire valve demonstrate that the novel valve has impressive performance improvement of the entire valve. The results of experiments show that the -3dB-frequency of novel valve improves 61.5% in the case of single side control mode (SS) and 57.1% in the case of both side control mode (BS); the tracking error decreases from 6.21% to 2.6% in the case of SS and from 7.48% to 3.96% in case of BS.