Digital Valve Research Articles

Dynamics Modelling and Control of a Novel Fuel Metering Valve Actuated by Two Binary-Coded Digital Valve Arrays

A fuel metering valve actuated by two binary-coded digital valve arrays (BDVAs) is proposed to improve the reliability of conventional fuel metering valves piloted by a servo valve. The design concept of this configuration is obtained from the structural characteristics of the dual nozzle-flapper and the flow regulation method of the digital hydraulic technology. The structure and working principle of the fuel metering valve are presented. Then, a mathematical model of the entire valve is developed for dynamic analysis. Subsequently, the mechanism of the transient flow uncertainty of the BDVA is revealed through simulation to determine the fluctuation in the velocity of the fuel metering valve. Furthermore, step response indicates that the delay time of the fuel metering valve is within 4.1 ms. Finally, to improve the position tracking accuracy of the fuel metering valve, a velocity feedforward proportional-integral controller with pulse code modulation is proposed. A series of comparative analyses indicate that compared with those of the velocity feedforward controller, the average and standard deviation of the position error for the proposed controller are reduced by 78 and 72.7%, respectively. The results prove the feasibility of the proposed valve and the effectiveness of the proposed control strategy.

Investigation of a Digital Hydraulic Valve Operated by Servo Motors

This paper describes a new type of digital hydraulic valve run by two servo motors. Digital hydraulics is a cutting-edge technology, which saves more exhausted energy than conventional hydraulic valves. It includes conventional valves, but its working principle is different. Similar or different size valves constitute a digital hydraulic valve assembly. When the assigned valves are opened, a certain amount of flow is obtained from the output of the valve assembly. To control a digital hydraulic valve, Pulse Number Modulation (PNM) Control technique is used for equal valve flow rates, while Pulse Code Modulation (PCM) is used for different valve flow rates. Valves are exerted by independently launched electric coils. Previous studies used controller board and external power booster circuits for coils. In this study, a new type of digital hydraulic valve is designed, manufactured, and tested with the PNM method. The studied valve body has two different valve groups. Every group includes 16 equal valves and 1 camshaft rotated by 1 servo motor. The servo motors are controlled by a PLC. The calculated performance index is found to be 5.1ms which is similar to the results of previous studies. The experimental results showed that the cam and servo motor controlled digital hydraulics is applicable to variable speed control hydraulic systems.

High dynamic digital control for a hydraulic cylinder drive

The control of hydraulic cylinders with digital hydraulic valves is often based on modulation principles like pulse-width modulation, pulse-code modulation, or pulse–frequency control. In many cases the dynamic drive performance using such control strategies is far below the natural dynamics of the system, since closed-loop controllers demand a certain phase margin for stability. However, some drive applications require a high dynamic response, which cannot be realized with common closed-loop concepts. In this article the design of a bang–bang feedforward control with regard to the dynamics of a hydraulic cylinder drive in accordance with the theory of optimal control is presented. The control achieves the maximum physical dynamic response and no remaining oscillations after the movement, which forms the basis of a high dynamic three-level position control for hydraulic drives. Furthermore, the influence of valve dynamics and pipe line dynamics with regard to the design of the digital valve control are considered by simulations.

Novel Hydraulic Turbine Governing System Based on Digital Cartridge Valve Technology

Digital cartridge governor, as a new direction of hydraulic turbine governor control, has been applied in engineering practice, but its relative theory and engineering application research are few. The engineering application of novel hydraulic turbine governing system based on digital cartridge valve technology is taken as the research object in this paper. Combining theory with engineering application, control strategies and rules of the digital cartridge turbine governor in key concerns of engineering applications such as closed-loop power regulation, isolated grid operation, the low-frequency de-excitation and the over-speed of load rejection of bulb turbine units are discussed, and engineering applications of digital cartridge turbine governor are summarized, which can be used for reference to solve some problems in the application of governor.

Hydraulic Switching Control Supplementing Speed Variable Hydraulic Drives

Primary control of linear motion by variable speed electric motors driving a hydraulic cylinder via a constant displacement pump is an established and successful concept with a frequent use in industry. One problem arises when low or zero motion speed has to be realized under high pump pressure conditions. Such load scenarios occur frequently in certain pressing processes, e.g., for sintering or veneering. Most pumps have a lower speed limit, below which critical tribological conditions occur which impair lifespan and efficiency. In addition, pump speed control and pump fluctuation suffer from the mixed lubrication conditions in such an operation range. For a circumvention of such low speed pump operation, a digital valve control concept is presented and studied in this paper. Valve control is used in load holding phases with low speed. Pressure is provided by an accumulator which is charged by the pump in short charging cycles at reasonable pump speeds. It is shown that the mean control error during load holding phase lies within the desired band and the fluctuations of the control force are lower than those of the pump control. In addition, the unfavorable pump operation conditions can be avoided via digital control.

Characteristic Analysis of Digital Emulsion Relief Valve Based on the Hydraulic Loading System

In the hydraulic loading system, the performance of digital relief valve plays an important role in the dynamic response of load. However, the research on large-flow emulsion relief valve is still far from perfect. In this paper, digital relief valve is taken as the research object. Based on pilot-operated relief valve, a digital control scheme using a linear stepping motor is adopted to regulate the working pressure of relief valve. The structure of relief valve is analyzed and optimized from the aspects of dynamic and internal flow field characteristics to obtain a good working performance. To obtain its accurate working characteristic, the structural model and digital control system of relief valve are established by AMESim and Simulink, respectively, for electrohydraulic cosimulation. The results show that digital relief valve has a better characteristic of real-time dynamic pressure regulation. Therefore, the digital control system could improve the dynamic performance of relief valve, and the design of digital relief valve structure is reasonable and feasible. The simulation method employed in this paper provides a better theoretical basis and reference for the comprehensive research of digital large-flow emulsion relief valves based on the hydraulic loading system.

Characterization of energy consumption of new piezo actuator system used for hydraulic on/off valves

This paper presents a newly developed four-way digital piezo valve system composed of four high-response on/off piezo valves. The main part of the new on/off piezo valves introduces the piezo actuator system, which can be used instead of conventional solenoids. One of the important aspects related to the energy consumption of hydraulic linear drives is the use of energy-efficient hydraulic valves that require low switching energy and low holding power consumption. The first part of the paper presents the theoretical background of piezo technology, which is very important for understanding the properties of piezoelectric actuators. It is followed by a detailed description of the new piezoelectric actuator system used in on/off valves and four-way digital piezo valve system. The main part presents a thorough experimental analysis of the electrical energy consumption of the new piezoelectric actuator system, which can be used both as an actuator of hydraulic high-response on/off valves as well as an energy-efficient micropositioner. To validate the electrical switching energy and the holding power consumption of the new piezoelectric actuator system, several existing on/off valves were used as reference. The experimental analysis shows a huge reduction of electrical energy consumption when using the new piezo actuator system for hydraulic on/off valve actuation. Especially the holding power consumption in the stationary active state is about 6 times lower compared to other hydraulic on/off valves.

Research on a new type of buffering valve for vehicle shifting

The traditional buffering valve for vehicle shifting mainly relies on the throttle hole and spring to control the pressure in the clutch. However, its accommodative facility and adaption are inferior. Therefore, two–dimensional (2D) digital technology is proposed to be applied to the vehicle shift buffering area, and the 2D digital buffering valve is designed. This study introduces the structure and working principle of the 2D digital buffering valve and establishes the mathematical model of the 2D digital buffering valve. The classical proportional–integral–differential control algorithm is adopted and Matlab/Simulink is used to simulate its control model. Finally, an experimental study is carried out. The study results show that when the frequency is 50 Hz, the amplitude of the valve output pressure decays to −3 dB, and when the frequency is 60 Hz, the phase of the valve output pressure lags by 90°. The output of the 2D digital buffering valve meets the requirement of the change of the oil pressure in the clutch during the vehicle shifting process. The control precision of its buffering pressure characteristic reaches 15%. The simulation and test results of the buffering valve are consistent, which verifies the correctness of the simulation model.

A Review of Switched Inertance Hydraulic Converter Technology1

Abstract Digital hydraulics is a new technology providing an alternative to conventional proportional or servovalve-controlled systems in the area of fluid power. Digital hydraulic applications, such as digital pumps, digital valves and actuators, switched inertance hydraulic converters (SIHCs), and digital hydraulic power management systems, promise high-energy efficiency and less contamination sensitivity. Research on digital hydraulics is driven by the need for highly energy efficient hydraulic machines but is relatively immature compared to other energy-saving technologies. This review introduces the development of SIHCs particularly focusing on the work being undertaken in the last 15 years and evaluates the device configurations, performance, and control strategies that are found in the current SIHC research. Various designs for high-speed switching valves are presented, and their advantages and limitations are compared and discussed. The current limitations of SIHCs are discussed and suggestions for the future development of SIHCs are made.

Simple Push-Type Wave Generating Method Using Digital Rotary Valve Control

The important parameters to describe waves are their amplitude and length. In order to make it easier to improve wave amplitude and facilitate wave experiment, a simple push-type wave generating method using digital rotary valve control was proposed and different wave amplitudes were generated by the new method. After the mathematical model of the new method had been established, numerical analysis based on the linear wave theory was carried out by means of Matlab/Simulink software tools, and experiments were conducted on the push-type wave maker to ascertain the validity of the established model and the numerical simulation results. It shows that both experimental and theoretical results agree relatively well, and the plate motion frequency and amplitude of the push-type wave maker can be continuously adjusted and the various required regular waves can be obtained. Although the wave amplitude and length descends with the increasing of working frequency, the wave amplitude can be improved conveniently by setting the axial opening width of the valve and the oil supply pressure of system. The wave length remains unchanged with the axial opening width and the oil supply pressure change. The research indicates that different regular waves can be easily generated by the new method and the wave amplitude can be further improved in a certain plate motion frequency range.

Steady-state modelling and performance of a rotary direct drive digital valve

A rotary direct drive digital valve driven by a stepper motor was proposed. By analysing its working principle, the steady-state mathematical model reflecting the relationship between the pressure, the flow and the angular displacement was deduced. Based on this mathematical model, the models of the null valve coefficients, the zero leakage flow and the steady-state flow torque were given. The simulation shows that the relationship between the pressure and the flow of the rotary valve is nonlinear; however, under a constant load pressure, the flow characteristics and the steady-state flow torque characteristics of the rotary valve with rectangular throttle orifices are linear. The experimental results show that the flow is directly proportional to the steps of the stepper motor, and the proposed mathematical models are valid.

Investigation on positioning control strategy and switching optimization of an equal coded digital valve system

This article concerns high accuracy positioning control with switching optimization for an equal coded digital valve system. Typically, pulse number modulation control cannot realize micro-positioning due to the characteristics of step-wise flow variation, therefore, a new position controller consisting of a model-based pulse number modulation and a differential pulse width modulation strategy is proposed to control the position of a hydraulic cylinder at high and low velocity cases, respectively. In addition, in order to solve several problems caused by the pulse number modulation and differential pulse width modulation, such as increased number of switchings and large difference among number of switchings of valves, a switching optimization consisting of a switching cost function, a circular buffer and a circular switching method is proposed. An adaptive weight of the switching cost function is proposed for the first time to reduce the total number of switchings under different pressure differences and its design criterion is presented. A circular buffer and a new circular switching method are used to improve the degree of equal distribution of switchings when the pulse number modulation and differential pulse width modulation are used, respectively. Comparative experimental results indicated that the average and the minimum positioning error for the proposed controller are only 10 and 1 μm, respectively. The number of switchings and the degree of equal distribution of switchings are significantly optimized. Moreover, the pressure fluctuations caused by the proposed controller remain acceptable.

Measurements of a Novel Digital Hydraulic Valve Comprising a Cushioning Feature

Abstract This article presents simulation data and measurements of a novel valve concept that features a soft landing concept. The purpose is to validate the design framework that has been applied to design the valve. The experimental results are obtained with a test rig manufactured specifically for this type of valve design. The validation includes studying the valves switching dynamics, cushion pressure dynamics, and movement-induced flow (MIF). The tests show that the tendencies are captured accurately although the exact magnitudes of forces do not match fully and a noticeable difference between simulated and measured plunger position is revealed. This amounts in a significant difference in the cushion pressure. Therefore, the pressure model is validated by using the measured lift and velocity derived hereof and this shows sufficient correspondence between the two pressures.

Optimal Fluctuation Regulation Method in Low-Speed Digital Piston Pump

AbstractIn digital displacement pump (DDP), the states of valves are nonlinear correlation with the instantaneous flow rate and flow fluctuation. For low-speed working condition, the digital valve has potential to switch several times to improve flow fluctuation. So, the relationship between the valve states and the flow rate is decoded, and a novel optimal fluctuation regulation (OFR) method including OFR-strict (OFR-S) and OFR-relaxation (OFR-R) is designed in this paper. The periodicity and the symmetry of OFR methods are proved and an optimal solution in the predefined minimum characteristic interval (MCI) is realized. Compared to the traditional sequential, partial, and pulse width modulation (PWM) methods, OFR-S has the minimum flow fluctuation, while OFR-R is preferred in low-speed ratio to reduce the digital valve switching frequency. At last, the effects of valve delay and oil compressibility are analyzed. As a theoretical precise optimal solution, OFR method demonstrates its ability in handling nonlinear problems in MCI. And it definitely will be a good base for the nonlinear controller design in the future.

Damping adjustment utilizing digital electrorheological valves with parallely segmented electrodes

A digital ER-valve with a segmentation of its electrode in the parallel direction to the flow leads to a change in the gradient of the volume flow rate-pressure difference characteristic in both valve’s ends. When such a valve is used in a damper, it presents an opportunity to have a damper with an adjustable damping constant. Despite its promising features, there is no experimental investigation yet found for this kind of digital ER-valve. In this work, a new model to describe the valve behavior is proposed and a comparison with the experimental results is presented. The experimental results show that the damping constant is able to be varied by changing the excitation pattern of the valve. Additionally, the comparison with the model shows that the measurement results and the model are in agreement. It proves that the new model is able to describe the behavior of such digital valve better compared to the existing model.

Development of a Dual Supply H-Bridge Amplifier for High Speed Actuation of Digital Hydraulic Switching Valves

For many digital hydraulic systems, fast and precise valve actuation is a key to improve efficiency and performance. Such an actuation may be achieved by optimizing the valve design from a mechanical and hydraulically point of view. But additionally, power electronics for valve actuation has to be given also high attention since it can have significant influence on valve dynamics, particularly in case of high-speed actuation with switching times in the range of 1 ms or less. Such actuation poses requirements that are not met by standard power electronics. These requirements are analysed in this paper and a proper schematic for the power electronics is derived. Measurements with a corresponding prototype prove that a fast, precise and very repeatable valve actuation can be achieved if the power electronics is conceived according to the characteristics of high speed valves.

Focus on materials, semiconductors, vacuum, and cryogenics

Focus on materials, semiconductors, vacuum, and cryogenics

Digital valve system for ITER remote handling – Design and prototype testing

ITER-RH system is used to exchange the divertor’s 54 cassette assemblies in the vessel. Water hydraulics and servo valves are currently used in the task but concerns exist with robustness and availability of suitable components. An alternative option is to use digital technology where on/off valves and intelligent control is used to produce proportional output. So far, no proper high-pressure on/off valves existed in the market and therefore a new concept was developed and tested with promising results. A mock-up of the remote handling system was used as test bench. The system was simulated in order to dimension the valve system and to tune the valve controller. A complete valve package with 16 prototype on/off valves and a manifold was manufactured and long-term tests of 60 working days was conducted. A new level of performance was demonstrated throughout the tests as tracking accuracies were approximately ten times better than with servo valve. Although some design faults where detected and system had faulty components, tracking accuracy was very good. Tracking and positioning capability of digital valve system exceeds all requirements and seems applicable for ITER RH application.

Numerical Model of Digital Valve-Controlled Active Air Bearing

An active air thrust bearing controlled by an Arduino board and digital valves is described. A numerical model for the complete system is developed to design the control and perform a sensitivity analysis based on geometric parameters such as the conductance of the valves. Model validation is based on experimental open-loop and closed-loop tests. The purpose of the model is to determine the range of force and air gap height in which the pad can be controlled.

A Microfluidic Cell Stretch Device to Investigate the Effects of Stretching Stress on Artery Smooth Muscle Cell Proliferation in Pulmonary Arterial Hypertension

A microfluidic cell stretch device was developed to investigate the effects of stretching stress on pulmonary artery smooth muscle cell (PASMC) proliferation in pulmonary arterial hypertension (PAH). The microfluidic device harbors upper cell culture and lower control channels, separated by a stretchable poly(dimethylsiloxane) membrane that acts as a cell culture substrate. The lower channel inlet was connected to a vacuum pump via a digital switch-controlled solenoid valve. For cyclic stretch at heartbeat frequency (80 bpm), the open or close time for each valve was set to 0.38 s. Proliferation of normal PASMCs and those obtained from patients was enhanced by the circumferential stretching stimulation. This is the first report showing patient cells increased in number by stretching stress. These results are consistent with the abnormal proliferation observed in PAH. Circumferential stretch stress was applied to the cells without increasing the pressure inside the microchannel. Our data may suggest that the stretch stress itself promotes cell proliferation in PAH.