Proportional Directional Control Valve Research Articles

Discrete-Time Constrained Controller for Proportional Directional Control Valve-Based Electrohydraulic System With Parametric Uncertainty and Disturbances

Abstract This paper develops a discrete constrained controller for electrohydraulic system (EHS) controlled by proportional directional control (PDC) valve while taking parametric uncertainties into account. The proposed controller solves the discrete barrier Lyapunov function via convex optimization while taking into consideration the system constraints such as state and actuator constraints. The proposed control law successfully tracks the reference trajectory while satisfying the state and actuator constraints. It is proven that the tracking error always converges to an arbitrary small neighborhood which is validated using Lyapunov stability analysis. The effectiveness of the proposed discrete barrier Lyapunov function based constrained controller was verified in a simulation environment and also through experimentation. From the simulation and experimental results, it is clear that the proposed controller drives the load to accurately track the reference trajectory in the presence of uncertainty and unknown disturbances.

A new compressible flow model for pneumatic directional control valves

In this study, a new compressible flow model for small orifice openings in pneumatic proportional directional control valves has been proposed. It is crucial to precisely control pneumatic valves over all control ranges; yet, conventional flow models fail around the closed position of the valve. The main deficit of the existing studies in the literature is to assume constant values for the parameters of the flow model over changing operating conditions. It has been demonstrated that these rough assumptions are insufficient in precisely predicting the mass flow rate, particularly for small orifice openings. An enhanced experimental setup has been introduced to improve the effectiveness of the proposed model. The cracking pressure ratio and parameters of the model have been identified with experimental method. In the proposed model, new empirical coefficients have been established after a thorough investigation of the impact of supply pressure on the flow behavior of the valve. Validation studies of the model in both the filling and exhausting states of the valve have been carried out at various supply pressures and orifice openings, yielding rather promising modeling performances. In validation tests, the real pressure and the pressure produced by new model have been compared, and good agreement has been achieved with 0.0039% absolute error. According to the findings, the proposed improved flow model can be selected in precision pneumatic control applications.

Power control of a wind turbine using an electrohydraulically controlled active pitch control mechanism

The paper presents the numerical simulation of a horizontal axis wind turbine and the electrohydraulic system that maintains the constant frequency of the alternating current generator regardless of its load or the variation of the wind speed. As a starting point, the turbine parameters such as speed, torque and power were determined in relation to the angle of attack of the blades. In order to keep the frequency of the alternating current generator constant, the solution that adjusts the angle of attack of the blades was chosen using the active pitch control mechanism. This mechanism is controlled by a PID type controller, by controlling a proportional directional control valve that feeds the 3 orbital hydraulic motors, which are coupled in series so that the angle of the three blades is identical.

Pneumatic cylinder speed and force control using controlled pulsating flow

An application for accurate and low-cost force and velocity control of a pneumatic actuator, which can be used in any pneumatic circuit, is described in this paper. Control of a pneumatic cylinder is proposed via a pulsating flow technique. The technique uses on/off solenoid coils in the direction control valves in lieu of expensive servo controllers, such as proportional directional control valves. Pulsating air frequencies of 1.5, 3, and 4.5 Hz are applied by the designed circuit to investigate inlet constant pressures ranging from 1.72 to 5.17 × 105 Pa. The speed and force of a pneumatic cylinder rod are controlled using the generated pulsating flow and the results show success of idea of ​​controlling the speed and force of the pneumatic cylinder rod using the pulse flow technique. Empirical correlations suitable for later use in automatic control circuits are derived and are shown to exhibit an accuracy of up to ∼ 90–95.5% in predicting output force and velocity. It is also used to select the required frequency to obtain the speed and force required for the cylinder. To validate the pneumatic cylinder speed and force control using pulse flow technique, simulations are carried out using the Automation Studio program. The results show an improvement in control of the pneumatic cylinder mechanical performance and demonstrate that improvements are a function of the frequency of compressed air source pulses and pressure. An empirical correlation is also derived for predicting the cylinder rod speed and force at any source pressure and pulse frequency.

Coincidence of pressure pulsations with excitation of mechanical vibrations of hydraulic system components: An experimental study

This paper discusses certain excitations that affect the components of hydraulic systems: pipes and valves. The negative effects of low-frequency noise and vibration on humans were also pointed out. Particular attention is given to the effect of pulsatile flow on the structure of hydraulic components. Pressure pulsations in a hydraulic system have been shown to generate and transmit mechanical vibrations across a wide spectrum of frequencies, and the negative consequences of this phenomenon have been pointed out. Based on the latest generation of proportional directional control valve, a special stand was built to generate pressure pulsations over a wide frequency range (up to 350 Hz). Amplitude-frequency spectra of mechanical vibrations and pressure pulsations were used instead of time courses in the considerations. The paper concludes that effort must be made to reduce the amplitudes of pressure pulsations in hydraulic systems, particularly in the low-frequency spectrum.

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.

Kinematic Modelling and Motion Mapping of Robotic Arms

Robotic systems are known for their precision and accuracy. To achieve a desired set of operating parameters the system must have a good control system. Robotic arms can vary in size shape and purpose of use. With increasing DOF (Degree of Freedom) the complexity of the system increases and hence a DAQ system is required to check various parameters of the process. This paper discusses the implementation of kinematic and inverse kinematic modelling of a 6 Degree of Freedom (DOF) hydraulic arm in MATLAB environment. The forward kinematic model is based on Denavit-Hartenberg parameters. To obtain a given set of position and orientation of end effector, inverse kinematics gives the required set of joint angles. Potentiometers mounted on arm joint are used as the prime feedback elements for extracting the joint angles. All six joints of the arm are revolute joints. The values of potentiometer obtained are compared to the desired input values. Proportional direction control valve is the main controlling element of the hydraulic circuit. The forward and inverse kinematics is validated and implemented in MATLAB robotics toolbox (developed by Peter Croke). A GUI is also used to ease the process of retrieving and feeding the information in the system. The results of forward and inverse kinematics from MATLAB are verified by the physical model discussed in this paper.

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.

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.

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.

Nonlinear Model Establishment and Experimental Verification of a Pneumatic Rotary Actuator Position Servo System

In order to accurately reflect the characteristics and motion states of a pneumatic rotary actuator position servo system, an accurate non-linear model of the valve-controlled actuator system is proposed, and its parameter identification and experimental verification are carried out. Firstly, in the modeling of this system, the mass flow rate of the gas flowing through each port of the proportional directional control valve is derived by taking into account the clearance between the valve spool and the sleeve, the heat transfer formula is used to the derivation of the energy equation, and the Stribeck model is applied to the friction model of the pneumatic rotary actuator. Then, the flow coefficient, the heat transfer coefficient and the friction parameters are identified by the model and pneumatic test circuits. After the verification experiment of the mass flow rate equations, the charging and discharging experiment reveals that the model can clearly show the effect of clearances on gas pressure changes and describe the effect of heat transfer on gas temperature changes. Finally, the results of model verification indicate that the simulation curves of rotation angle and two-chamber pressures are consistent with their experimental values, and the non-linear model shows high accuracy.

Study of Losses and Energy Efficiency of Hydrostatic Drives with Hydraulic Cylinder

Abstract Energy efficiency of hydrostatic transmissions, and especially efficiencies of drives with motor speed controlled by throttle, as well as efficiency of hydraulic servomechanisms can in fact be higher than the efficiency values most frequently given by the respective literature in this field. With the progress achieved in recent years in the development of hydraulic systems it is becoming necessary to develop methods for precise energy efficiency calculation of such systems. It is difficult to imagine that more and more, better and better machines and control elements could be used without the possibility of a mathematical tool at our disposal to enable an accurate analysis and assessment of behavior of the system in which such machines and control elements have been applied. The paper discusses energy savings using mathematical model of losses in elements, the energy efficiency of the system. There are possibilities to reduce energy losses in proportional control systems (in the pump, in the throttle control unit, especially in the cylinder), and thus to improve the energy efficiency of the throttling manifold. The considerations allow for comparison of the loss power resulting from the applied hydraulic control structure of the hydraulic cylinder and the power consumed by the pump from the electric motor that drives it, the power necessary to provide pump-driven hydraulic cylinder. The article shows the impact on the output (useful) power consumed in the considered systems, and the impact on the power consumed of the loss power in the individual elements. The paper presents also formulas of loss power, formulas of energy efficiency connected with investigated hydrostatic drives, two schematic diagrams of hydraulic systems, their principle of operation and problems of studying losses in elements and energy efficiency characteristics of systems consisting of a feed assembly, control set and cylinder. It also includes a subject matter connected with an energy loss power of hydrostatic systems with hydraulic cylinder controlled by proportional directional control valve. Diagrams of loss power of two hydraulic systems worked at the same parameters of speed and load of a cylinder, which were different due to structure and ability of energy saving, were presented and compared.

Nonlinear PID actuator speed control in inverter based electro-hydraulic systems subjected to external leakage

ABSTRACT Actuators of constant speed operation in hydraulic power systems are highly required in many applications such as steel sheet rolling and pressing operations. To achieve this, a variable pump and/or control valve may be used to control the actuator speed in different operating conditions. A mathematical model of the selected hydraulic system and its components has been carried out using SIMULINK to study its static and dynamic characteristics. A direct comparison between the mathematical model results and experimental results of the same hydraulic system published by the author has been introduced. For the experimental and the mathematical models, a linear and nonlinear PID control algorithm has been applied for pump speed control and proportional directional control valve in the presence of system disturbance, herein is an external leakage, to maintain the actuator velocity constant either by controlling the pump speed or the proportional directional control valve with achieving the minimum error. The nonlinear control PID showed a better system response than the PID controller and reduced the error hence improved the system response. It has been shown that the proportional valve control is better than the pump speed control for different external leakage, 5–10%, with an error of the order 3% from the setting velocity.

Energy Saving Systems of Hydrostatic Drives for Ship Deck Machines

Abstract A control system with a proportional directional throttling control valve or a directional control servo valve, controlling a cylinder (linear hydraulic motor) is used in the ship steering gear drive, in the controllable pitch propeller control, in the variable capacity pump control system for hydraulic deck equipment motors or fixed pitch propellers in small ships (for example ferries). Energy savings in a constant capacity pump operation can be achieved by means of overflow valve controlled by the oil outlet pressure between the directional throttling control valve and the cylinder. Although structural volumetric losses cannot be eliminated in such a system, but it is possible to reduce considerably structural pressure losses, mechanical losses and volumetric losses in the pump, and mechanical losses in the cylinder too. The paper discusses these energy savings using an earlier developed by Paszota mathematical model of losses in elements, the energy efficiency of the system and the operating range of the cylinder. The paper also presents a comparison of the energy behavior of two widespread structures of hydrostatic systems: a standard individual systems with a throttling steering fed by a constant capacity pump. Both system solutions are described and equations of the total efficiency η of the system are presented. Diagrams of energy efficiency of two hydraulic systems working at the same parameters of a speed and a load of hydraulic linear motor, which were different due to structure and ability of energy saving, were presented and compared.

The Characteristic Improvement of Electromagnetic Proportional Directional Control Valve

The electromagnetic proportional directional control valve is widely used in hydraulic control system and its typical faults are not enough electromagnetic force and too high temperature rise to burn out the coil. The magnetic field and coil temperature field distribution of the control valve are modeled and analyzed by using the finite element method. The influence laws of the geometry and parameters on electromagnetic force are analyzed. Furthermore, the influence of coil control current and heat transfer coefficient on the temperature rise of coil is analyzed, which provides a theoretical basis for the reliability optimization design of electromagnetic proportional directional control valve.

Adaptive Dynamic Surface Control of Pneumatic Servo Systems With Valve Dead-Zone Compensation

An adaptive dynamic surface controller (ADSC), which comprises an online parameter estimator and a robust control law, is developed for the pneumatic servo systems driven by the proportional directional control valves. Departing from the use of time-consuming offline fitting of the orifice area to accommodate the effect of valve dead zone, this paper employs the least-square-type indirect parameter estimation algorithm with online condition monitoring to estimate the dead-zone parameters and some other important model parameters. These accurate estimates of model parameters are utilized in the development of a precise position tracking controller for the single-rod pneumatic actuator. By using the dynamic surface control technique to synthesize the robust control law, the problem of “explosion of complexity” in traditional backstepping design method is avoided. The stability of the closed-loop system is proved by the means of the Lyapunov theory. The obtained extensive comparative experimental results verify the effectiveness of the proposed valve dead-zone compensation strategy and the high-performance nature of the ADSC in practical implementation.

Modelling and experimental studies on a proportional valve using an innovative dynamic flow-rate measurement in fluid power systems

A numerical model of a servoactuator and of a four-port proportional direction control valve has been developed. Mechanical and hydraulic elements have been simulated in the LMS Amesim® environment. The complete model has been validated on the basis of the experimental time histories of the actuator velocity and of the flow-rate controlled by the proportional valve. The validation data have been acquired on a fluid power system used to test electro-hydraulic servovalves according to ISO 10770-1 standard. The measurement of the instantaneous flow-rate through the valve has been performed with an innovative high-dynamics flowmeter, recently developed for high-pressure liquid flows. Furthermore, the model predicted static characteristic of the proportional valve has been compared with a corresponding experimentally derived curve and an analysis of the cause-and-effect relationships has been carried out for the valve static performance. Measured data on valve leakages have also been presented in order to complete the steady-state characterization of the tested valve. The developed model of the hydraulic system has been then applied to realize the Bode diagram of the proportional valve, which is expressed in terms of instantaneous flow-rate as a function of the sinusoidal driving command, as well as the Bode diagram of the subsystem made up of the proportional valve and of the linear actuator. The latter Bode graph is plotted in terms of piston velocity as a function of the sinusoidal driving command provided to the valve. The comparison between the two Bode diagrams has confirmed the accuracy of the ISO procedure, which is based on the assumption of negligible delay introduced by the dynamic response of the servo-actuator and by the oil compressibility. A reliable and cost-saving methodology, which uses the innovative flowmeter instead of the low inertia servo-actuator, is proposed as an alternative to the ISO standard for testing the dynamic response of proportional valves.

Analysis and compensation for the cascade dead-zones in the proportional control valve

The four-way proportional directional control valve has been widely used as the main stage spring constant for the two-stage proportional control valve (PDV). Since a tradeoff should be made between manufacturing costs and static performance, two symmetry dead-zones are introduced in the main stage spring constant: the center dead-zone caused by the center floating position and the intermediate dead-zone caused by the intermediate position. Though the intermediate dead-zone is much smaller than the center dead-zone, it has significant effect on the dynamic position tracking performance. In this paper, the cascade dead-zones problem in a typical two-stage PDV is analyzed and a cascade dead-zones model is proposed for the main stage spring constant. Then, a cascade dead-zones inverse method is improved with gain estimation and dead-zone detection to compensate the dead-zone nonlinearity. Finally, a digital controller is designed for verification. The comparative experimental results indicate that it is effective to reduce the large position tracking error when the proposed method is applied.

Dynamic analysis and estimator design of a hydraulic drive system

This paper deals with the dynamic analysis and state of the art estimator design through system inversion of a pedagogical hydraulic system, comprising variable displacement axial piston pump, high speed low torque hydraulic motor, proportional direction control valve, loading pump (bent axis) and a pressure relief valve at loading circuit. The hydraulic system has been modeled for simulation study and both the transient and the steady state responses have been validated experimentally. The necessary and sufficient conditions for the system to be observable have been obtained with respect to the minimum number of sensors placement. Thereafter, an estimator adaptive to varying load condition has been designed to have a good estimate of all the states using minimum sensors. All the estimated states have been compared with the responses from the test bed.