Digital Valve Research Articles

A model-based sliding mode control with intelligent distribution for a proportional valve driven by digital valve arrays

Parallel-connected digital valve arrays are commonly utilized in the pilot stage of the proportional directional valve to enhance dynamic performance and reliability. However, when the digital valve array is driven by a digital signal, it is difficult to optimally assign the signal pulses to each valve. If the assignment is not well executed, it can significantly reduce the switching uniformity of the digital valves or lead to performance degradation of the system. In this paper, a model-based sliding mode control strategy based on the intelligent distribution of control law is proposed and successfully applied to a proportional valve driven by digital valve arrays. The intelligent distribution strategy encompasses a logic distribution algorithm and a circular sliding distribution algorithm that automatically assigns control laws to different valves based on the rolling of the PWM signal cycle. Experimental results confirm that the proposed strategy not only simultaneously reduces the total number of valve switches and enhances the switching uniformity among the valves, but also adapts to the variation in the number of valves. The proposed strategy is not limited to the application of digital valve arrays, it is also applicable in other fields of multi-actuators driven by digital signals, and can simultaneously improve the control accuracy, lifetime, and maintenance friendliness.

Research on high precision flow control technology of low speed wind tunnel air supply system

Aiming at the shortcomings of traditional analog control valves and digital valves, a high-pressure air supply system with accurate flow control is designed. Firstly, the ER5000 controller and pilot proportional valve drive several diaphragm reducing valves to achieve the preliminary adjustment of air pressure. Secondly, a needle valve based on the PCM digital valve and equal percentage flow characteristics is used to achieve accurate control of gas flow. Then, the Venturi flow meter with a honeycomb and damping network is used to accurately measure the airflow. Finally, a PID flow control algorithm based on nonlinear self-tuning is proposed. The results show that the flow regulation range of the system reaches 0.1∼8 kg/s, the absolute control accuracy is better than ±3 g/s, and the relative control accuracy is better than ±0.04%. Moreover, the system has the characteristics of short regulation time, small overshoot, and good dynamic performance, which can achieve strong support for wind tunnel air supply tests.

Modeling and simulation analysis of a novel proportional water flow valve with a digital pilot stage

The position straightness of the hydraulic supports is the key factor to the intelligent fully mechanized mining, and the adjacent cylinder is the actuator used to pull the hydraulic support. However, the control component of the adjacent cylinder is electromagnetic on/off valve that cannot control the movement of adjacent cylinder proportionally. Therefore, a novel proportional water flow valve with a digital pilot stage is proposed to control the trajectory of adjacent cylinder precisely. The novel valve consists of a dual active cartridge main valve and a digital pilot valve that includes a high speed on/off valve A (HSV-A) and a throttle valve piloted by the high speed on/off valve B (HV-B). A coupling dynamic mathematical model of the flow valve is formulated and the dynamic characteristics of the valve is analyzed theoretically. The fluctuation of the throttle valve and main spool motion is also analytically calculated. In addition, the influences of the control parameters and key structural parameters on the throttle valve and the main valve's motion are analyzed on the basis of AMESim simulation respectively. The simulation results have demonstrated that the displacement fluctuation of the valve can be reduced by increasing the control frequency. The throttle valve closed-loop displacement fluctuation is about 0.2 mm and 0.1 mm when the control frequency is 100 Hz and 200 Hz. What's more, decreasing the main valve orifice diameter can also effectively lower the main valve displacement fluctuation, while it will diminish the main valve response speed at the same time.

Generation mechanism of high-frequency oscillation in proportional valve with a high-speed on/off valves bridge as the pilot stage

A digital proportional valve has a main spool that operates with a high-speed on/off valves bridge as the pilot stage. However, this can cause the spool to undergo high-frequency oscillation during movement, leading to a slower valve response, lower control accuracy, and even control failure. Therefore, it is important to study the oscillation mechanism of the valve. To address this issue, we establish a detailed dynamic model of the digital proportional valve, and analyze the factors affecting the response performance of the proportional valve spool. A method of half-bridge control based on duty cycle is proposed to eliminate the oscillation. The influence regularity of each factor on the response performance of the valve is explored. It is proved that the control method of the high-speed on/off valves bridge and the Pulse-width modulation (PWM) signal-switching frequency of the high-speed on/off valves are the main reasons for the oscillation of the main spool. The proposed half-bridge control method based on duty cycle can eliminate the oscillation in a lower frequency range. In addition, the results show that the pilot oil pressure is an important contributor to the oscillation; the higher the pilot oil pressure, the easier the main spool oscillation occurs. However, the spool mass, oil temperature, and coil temperature of the high-speed on/off valve do not affect the stability of the digital proportional valve.

Comprehensive Numerical Analysis of a Four-Way Two-Position (4/2) High-Frequency Switching Digital Hydraulic Valve Driven by a Ring Stack Actuator

This paper presents a feasibility study using a commercially available ring stack actuator to develop a four way-two position (4/2) high frequency switching digital hydraulic valve. The excellent characteristics of multilayer piezoelectric actuators, such as a simple design, reduced moving parts, high reliability, and fast response, make them ideal for constructing this type of digital hydraulic valve. High frequency switching digital hydraulic valves (HFSVs), indeed, must be able to switch from fully open to fully closed positions in less than 5 ms, while maintaining minimal pressure losses and delivering large flows. The proposed valve architecture is assessed using well-established equations implemented in a Simulink model, allowing the hydraulic, mechanical, and electrical parts of the valve to be accurately simulated. The paper first provides a detailed description of the numerical model. Next, the hysteresis model of the ring stack actuator is validated against the data provided by the manufacturers on their website. Finally, the numerical results obtained with both open-loop and closed-loop control systems are presented. The simulations show that at a switching frequency of 200 Hz with maximum amplitude and duty cycle of the input pulse digital signal, the valve exhibits high average flow rates (~60 L/min), low average power consumption (~1500 W), and maintains a pressure drop of only 15 bar. Moreover, the simulations reveal that the control system is very effective since the valve switching time is within 1 ms.

A Novel Equivalent Continuous Metering Control With a Uniform Switching Strategy for Digital Valve System

Pulse number modulation (PNM) combined with pulse width modulation (PWM) control is an effective solution to improve the resolution of digital valve systems. However, the numerous discrete variables that use parallel <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</small> / <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">off</small> valves cause difficult control coordination and uneven switching. To address this issue, this article defines the equivalent spool displacement of the digital flow control unit by the number of PNM-controlled valves and the duty cycle of PWM-controlled valves to replace multiple discrete variables and develops the equivalent continuous metering control method. Furthermore, a uniform switching control strategy is proposed for the PWM-controlled valve using a uniformly distributed permutation for each <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</small> / <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">off</small> valve. The proposed control methods are verified by simulation on the built mathematical model of the equal-coded digital valve system. Experimental results for the displacement control of a hydraulic cylinder at 1 rad/s show that the average error of the equivalent continuous metering control is about 0.236 mm and the dispersion index reaches 20%, while the uniform switching control strategy achieves 80% with an average error of 0.215 mm. Simulated and experimental results demonstrate that the equivalent continuous metering control with a uniform switching strategy can almost evenly distribute switching numbers without compromising the accuracy of the displacement control.

Energy-Saving Testing System for a Coal Mine Emulsion Pump Using the Pressure Differential Flow Characteristics of Digital Relief Valves

Most energy-saving testing methods for plunger pumps use hydraulic motors. The loading test of coal mine emulsion pumps generally uses an overflow valve as the loading unit, which is characterized by high energy consumption. The coal mine emulsion pump uses emulsion as the transmission medium, and the viscosity and lubricity of the emulsion are much lower than those of hydraulic oil, which creates great difficulties in the development of high water-based hydraulic products. The nominal flow rate of the emulsion motor is much smaller than that of the emulsion pump, and there is no mature and reliable water-based flow control valve. Based on the above reasons, traditional energy-saving testing methods cannot be utilized for the testing process of emulsion pumps. The loading test of emulsion pumps generally uses an overflow valve as the loading unit, and during the testing process, all electrical energy is converted into internal energy, resulting in very high energy consumption. This article proposes an energy-saving testing system for emulsion pumps based on multiple emulsion motors in parallel. In order to solve the flow regulation problem of each parallel branch, a flow-intelligent control algorithm is proposed that utilizes the pressure difference flow characteristics of digital relief valves combined with artificial neural network predictive control. Firstly, the feasibility of the proposed system and method is theoretically verified through the analysis of the mathematical model of the digital relief valve. Secondly, further verification is carried out by establishing simulation and testing platforms. The simulation results show that the energy recovery efficiency of the system exceeds 53%. The experimental results show that the proposed testing system has a pressure control error of less than 1%, a flow control error of about 5%, and a maximum overshoot of about 9 L/min relative to the steady-state flow rate. The control accuracy and system stability are high.

Research on high water-based digital valve with dual-spool and control strategy

The straightness control of the working face is the key technology to realize intelligent production of coal mines. However, the discontinuity of on–off hydraulic components of the existing underground working face cannot meet the needs of intelligent straightness control. A new type of dual-spool high water-based digital valve with a motor ball screw as the driving element is proposed as a solution to this problem. In this paper, the force of the valve is firstly analyzed, and it is found that the force of the movement of the valve core can be equivalent to the disturbance of the motor. The control of the valve core is essentially displacement control. In addition, a mathematical model of the valve is established, and sliding mode control with a high-gain observer is proposed to overcome time-varying characteristics of the load. Theoretical analysis indicates that the proposed controller ensures asymptotic stability with existing uncertain disturbances. Moreover, a system based on MATLAB/Simulink simulation model is developed to further verify the performance of the proposed algorithm. Compared with traditional sliding mode control and proportional integral derivative, the proposed algorithm can still improve the tracking accuracy and robustness along with 0.05 mm error under strong time-varying interference. The valve reaches the required flow in around 0.2 s, which is sufficient for the majority of work surface application situations. The research proposes a novel design concept and control approach for straightening coal mine scraper conveyors.

3D fabricated PDMS digital pressure controllers for miniature pneumatic systems

1Automatic and programmable pressure controllers are critical to miniature pneumatic systems employing pressurized air to transport and manipulate fluidic samples. 2We have successfully demonstrated (1) a digital pressure control scheme containing active converters and passive regulators that can be readily miniaturized and automated, (2) a 3D PDMS fabrication and integration scheme that can realize on-chip and self-contained pressure controllers for miniature pneumatic systems, and (3) pressure controllers that can switch downstream air pressure between specific levels on demand. 3In the proposed pressure controller, a regulator is utilized to yield a steady air output, whose pressure is determined by a serial digital-to-analog converter and switched between specific levels on demand. 4More specifically, a converter guided diaphragm bypasses a certain portion of the input air to reduce and stabilize the output pressure. 5In the prototype demonstration, PDMS structures were duplicated using 3D-printed molds, bonded and integrated on chip or into self-contained pressure controllers of 25 cm3 in volume. 6Four-digit converters were employed to realize pressure output at 16 evenly spaced levels. 7The errors of the measured output pressure were less than 2.4% of the target pressure while the fluctuations were below 1.2%. 8It was also demonstrated that the switching time between pressure levels was less than 0.3 seconds when digital valves operating at 10 Hz were utilized. 9As such, the demonstrated miniature pressure controllers could replace their bulky/costly counterparts, and automatic and programmable control of pneumatically driven systems could potentially be realized.

Plant pathogen detection on a lab-on-a-disc using solid-phase extraction and isothermal nucleic acid amplification enabled by digital pulse-actuated dissolvable film valves

By virtue of its ruggedness, portability, rapid processing times, and ease-of-use, academic and commercial interest in centrifugal microfluidic systems has soared over the last decade. A key advantage of the LoaD platform is the ability to automate laboratory unit operations (LUOs) (mixing, metering, washing etc.) to support direct translation of ‘on-bench’ assays to ‘on-chip’. Additionally, the LoaD requires just a low-cost spindle motor rather than specialized and expensive microfluidic pumps. Furthermore, when flow control (valves) is implemented through purely rotational changes in this same spindle motor (rather than using additional support instrumentation), the LoaD offers the potential to be a truly portable, low-cost and accessible platform. Current rotationally controlled valves are typically opened by sequentially increasing the disc spin-rate to a specific opening frequency. However, due lack of manufacturing fidelity these specific opening frequencies are better described as spin frequency ‘bands’. With low-cost motors typically having a maximum spin-rate of 6000 rpm (100 Hz), using this ‘analogue’ approach places a limitation on the number of valves, which can be serially actuated thus limiting the number of LUOs that can be automated. In this work, a novel flow control scheme is presented where the sequence of valve actuation is determined by architecture of the disc while its timing is governed by freely programmable ‘digital’ pulses in its spin profile. This paradigm shift to ‘digital’ flow control enables automation of multi-step assays with high reliability, with full temporal control, and with the number of LUOs theoretically only limited by available space on the disc. We first describe the operational principle of these valves followed by a demonstration of the capability of these valves to automate complex assays by screening tomato leaf samples against plant pathogens. Reagents and lysed sample are loaded on-disc and then, in a fully autonomous fashion using only spindle-motor control, the complete assay is automated. Amplification and fluorescent acquisition take place on a custom spin-stand enabling the generation of real-time LAMP amplification curves using custom software. To prevent environmental contamination, the entire discs are sealed from atmosphere following loading with internal venting channels permitting easy movement of liquids about the disc. The disc was successfully used to detect the presence of thermally inactivated Clavibacter michiganensis. Michiganensis (CMM) bacterial pathogen on tomato leaf samples.

Sliding Mode Control of Digital Directional Valve Drive System Based on New Approach Rate

As an important development direction of hydraulic control components, static and dynamic properties of the spool drive mechanism determine the dynamic and static performance of the digital valve. For the study, permanent magnet synchronous motor and screw nut unit are used as the core drive mechanism for digital directional valve. To solve the practical problems that permanent magnet synchronous motor can not meet the performance requirements of digital directional valve in terms of spool position control accuracy and response speed, a sliding mode variable structure control algorithm with improved approach rate is registered, then the controller is devised and applied to position high-performance control of spool drive mechanism of digital directional valve. The simulation platform of digital directional valve drive system is built by MATLAB/Simulink software and compared with the control effect of traditional PI control algorithm. The emulation results show that can improved approach rate sliding-mode controller can be good for raise the speed of response and reinforce the trueness of the dynamic tracking accuracy of the system, has good dynamic response characteristics, and satisfies the performance requirements of digital directional valve.

Testing Method for Intelligent Loading of Mining Emulsion Pump Based on Digital Relief Valve and BP Neural Network Control Algorithm

The mining emulsion pump is mainly used on a fully mechanized coal mining face, but it is rarely used on other occasions, so research on its loading test method is relatively limited. This paper proposes the application of a digital relief valve to the emulsion pump loading test. In addition, the small number of plungers in the emulsion pump will lead to large flow pulsation and pressure pulsation, and the nominal flow of different types of emulsion pumps varies greatly. These factors lead to the deficiency of a traditional PID control algorithm in control accuracy and efficiency. In order to improve control accuracy and efficiency, firstly, the influence of the flow rate of the tested pump and extension of the linear stepping motor shaft on the working pressure is studied. A backpropagation (BP) artificial neural network (ANN) model is used to fit a functional relationship between the three parameters. The flow rate of the tested pump and target pressure were provided as inputs to predict the extension of the linear stepping motor shaft, thereby realizing the remote intelligent control of the system pressure. Next, a BP ANN model is constructed, and its reliability is verified; the BP neural network algorithm and proportional-integral-derivative (PID) algorithm are compared through simulation. The simulation results show that the BP neural network algorithm has high control accuracy and small overshoot. Finally, two pumps with different flows are tested in a self-developed digital relief valve and test platform. The test results show that the proposed loading test method is intelligent and efficient, and it has high accuracy.

Flow control characteristics of the digital and mechanical redundancy control electric modulation valve

Flow control characteristics of the digital and mechanical redundancy control electric modulation valve

Mathematical model and PID control of a hydraulic motor using on/off solenoid valve

Hydraulic motors have a high power capacity that makes them commonly used in different applications. These applications require precise control of hydraulic motors’ position, velocity, and force. Digital hydraulic valves are commonly used in hydraulic power systems. The high-speed on/off valves (HSVs) are digital valves usually used in flow or pressure control where high dynamic performance is required to improve the control accuracy. This paper aims to present an accurate method of controlling a hydraulic motor using HSV and PID control. A mathematical model of the whole system is presented. This model allows predicting the system response and refining the control gains to reach the desired response. The model parameters are obtained by experimental measurement, or typical values are used. The model is implemented using MATLAB and SIMULINK. Then it is validated experimentally using some tests. The designed control method is implemented on the motor using NI myRIO as a controller, which is coded by LabVIEW software

Research on Buffer Characteristics of a New 2D Digital Buffer Valve for Vehicle Shift

The clutch is currently developing towards high power, high stability, and intelligent operation. The traditional hydraulic buffering valve mostly uses a passive hydraulic buffer valve or a high speed on-off valve and a proportion valve. It has a single buffering characteristic and poor adaptability. It is difficult to meet the requirements. Therefore, a new theory and a new method are proposed. In the field of clutch oil pressure control, the 2D digital buffer valve is designed using 2D digital technology. The structure of the 2D digital buffering valve is described. Based on the working principle of the valve, a mathematical model is set up. MATLAB/Simulink is used to solve the model. The results are analyzed in this paper. Finally, a valve test platform is built and an experimental study carried out. The research indicates that the 2D digital buffering valve has a good static characteristic. The linearity is 9.25%, and the hysteresis is 0.106. The response time of the 2D digital buffer valve is about 55 ms, and the valve overshoot is only 18.62%. During shifting, the maximum deviation is 0.165 MPa, and the steady-state error is 0.056 MPa. Different buffer control signals as the input and the output of the valve can follow the input change. The experimental and simulation results are consistent. The rationality of the mathematical model has been verified.

Study on the Digital Hydraulic Driving System of the Belt Conveyor

The electrohydraulic equipment of the coal gangue belt conveyor has been widely studied in recent years, but studies have been limited to the traditional hydraulic system with proportional valve and servo valve as control elements. Because of their own structural characteristics, proportional valves and servo valves have inherent defects such as low reliability, high cost and a long debugging cycle. It is necessary to carry out technological innovation and upgrading. This paper presents a hydraulic system scheme which uses digital valves instead of proportional valves and servo valves to control the belt conveyor propulsion system. Firstly, the system scheme is described in detail. Secondly, the simulation model of the control element digital valve is established, and its dynamic characteristics are analyzed in detail. Finally, the displacement tracking control of the new system is carried out to verify the feasibility of the proposed control scheme. The results show that the new digital hydraulic control system can effectively achieve the displacement control function of the belt conveyor propulsion system.

Simulation Research on Thermal Characteristics and Experimental Study on Electronic Control Board of the Miniature High-Speed Digital Valve

The miniature high-speed digital valve is essentially a kind of miniature system that contains many nonlinear factors and involves multifield coupling among electromagnetic, mechanical, and liquid ones. In this study, the dimension of an electromagnetic structure is normalized into a unified variable, and the numerical analysis method is used to optimize the values of each parameter size on the premise of satisfying the requirements. The electronic control board is the control signal input equipment of the valve. The input changes of voltage and current directly affect the thermal characteristics of the valve. The electronic control board is the power source of the digital valves, and their high speed partially depends on the characteristics of the electronic control board. In this study, a control board for miniature digital valves was developed, which realizes the rapid rise and fall of current and meets the design requirements. A new electronic control board is manufactured, and a control platform for the electronic control board is built. Experiments demonstrate that there is no delay in the current rise and fall, showing that the valve achieves its dynamic response target. Using the finite element analysis software Workbench to simulate it numerically, the temperature field distribution in the original structure is not uniform, which affects the magnetic properties of the electromagnetic field. To address this disadvantage, this study proposes to insulate the heat source with thermal insulation material, which will not affect the temperature distribution of the entire electromagnetic components. The simulations show that the proposed method is effective and reliable.

Study on Dynamic and Static Performance of a Micro Digital Hydraulic Valve.

Previous researchers mostly carried out simulation research and scattered experimental research on the static and dynamic characteristics of the digital valve, but did not form a systematic and in-depth study on the characteristics of the valve. Based on expounding the basic principles and functions of the valve and the test system, this paper carries out the test research under various variables for three kinds of static characteristics, including pressure differential-flow characteristics, signal-pressure characteristics, and signal-flow characteristics. The optimal control frequency of the valve is obtained from the comprehensive consideration of linear interval, linearity, and hysteresis. Three methods are systematically used to deeply study the dynamic characteristics, and the influencing factors of test results under various test conditions are analyzed. Through the research of this paper, it can provide relevant performance parameters for taking the digital valve as the system control element in the next step, and lay the foundation for the accurate control of the system.

Switching characteristics of a high-speed rotary valve for switched inertance hydraulic converters

The switched inertance hydraulic converter is a sub-domain of digital hydraulics which relies on digital switching to adjust pressure or flow instead of the dissipation of power by throttling, providing an energy-efficient alternative to conventional proportional or servo valve-controlled systems. The high-speed switching valve is a key component to realise the digital switching and its switching characteristics has significant effects on the performance of switched inertance hydraulic converters. In this article, the switching characteristics of a high-speed rotary valve are investigated. The switching orifice area of the valve is calculated based on the movement of the valve components with a consideration of the design of the valve body and leakage. This is validated using the computational fluid dynamics model and in experiments. The valve is theoretically modelled considering the switching orifice, leakage, transition throttling and compressibility effect, and the results are validated by computational fluid dynamics and experimental tests. The valve is able to deliver a flow rate of 40 L/min at a pressure drop of 10 bar and switch at the maximum frequency of 317 Hz, with a switching transition time of about 1 ms, which shows promising performance for the use in digital hydraulics. The theoretical and computational fluid dynamics models can assist the design and optimisation of digital high-speed rotary valves, which can be very useful for understanding, analysing and optimising the characteristics and performance of switched inertance hydraulic converters in digital hydraulics.

Lubrication characteristics analysis of slipper pair of digital valve distribution axial piston pump

The digital valve distribution axial piston pump is a swashplate rotary piston pump, the force on slippers is different from that of traditional axial piston pump. At the same time, the control strategy of the distribution valve will affect the pressure in the piston cavity, and then affect the oil film lubrication. According to these characteristics, the modeling method of oil film thickness field was proposed, and the force model of slipper pair and the numerical solution model of oil film lubrication of digital valve distribution axial piston pump were further established. The influence of swashplate rotation speed, swashplate inclination angle, and distribution valve control strategy on the characteristics of oil film lubrication were solved. The results show that the established thickness field model of oil film conforms to the stress characteristics of the slipper of the valve distribution pump. Increasing the swashplate rotation speed and the swashplate inclination angle is beneficial to optimize the oil film lubrication performance. The discharge valve should be opened in advance or closed in delay, which is beneficial to prevent eccentric wear and adhesion wear of slippers. The research results can provide theoretical basis for the optimal design of valve distribution axial piston pump.