The Influence of Transmission Line Dynamics on the Performance of Digital Flow Control Units (original) (raw)
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A unique method of improving energy efficiency in fluid power systems is called digital flow control. In this paper, binary coding control is utilized. Although this scheme is characterized by a small package size and low energy consumption, it is influenced by higher pressure peaks and larger transient uncertainty than are other coding schemes, e.g., Fibonacci coding and pulse number modulation, consequently resulting in poor tracking accuracy. This issue can be solved by introducing a delay in the signal opening/ closing of the previous or subsequent valve, thus providing sufficient time for state alteration and valve processes. In a metering-in velocity control circuit, a feedforward neural network controller was used to create artificial delays according to the pressure difference over the digital flow control unit (DFCU) valves. The delayed signal samples fed to the controller were acquired through the genetic algorithm method, and the analysis was performed with MATLAB software.
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ASME/BATH 2015 Symposium on Fluid Power and Motion Control, 2015
In digital hydraulic systems, switching valves have opening and closing times in the range of a few milliseconds. Due to this fast switching, high bandwidth pressure pulsation is excited, which is the stimulus for airborne noise up to some kilohertz. Since the human ear is very sensitive to audible noise in this frequency range, an analysis of the influence of the valve’s opening curve on the pressure surge in the pipe system is intended. The study is based on simulations employing dynamic pipe models for linear wave propagation and laminar fluid flow. In particular, a simple pipe system with a valve at one end and a pressure boundary at the other end of the pipe is investigated. It is shown, how the valve opening characteristics of spool and seat type switching valves influences the pipe responses. Also the role of parasitic inductances due to the valve block bores is discussed and it is shown how the switching characteristics influences the dynamical effects on the pressure pulsat...
Is the future of fluid power digital?
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Discussion: Is the future of fluid power digital?
Proceedings of the Institution of Mechanical Engineers, Part I: Journal of Systems and Control Engineering, 2012
Imagine the scenario in which an electric motor company came to the (correct) conclusion that the power density of hydraulic pumps and motors is much higher than that of electric generators and motors. Then imagine that the board of this company gave the (wrong) instruction to the R&D department to utilize the concept of hydrostatic machines to develop electric generators and pumps with the same power density as their hydraulic equivalents. The reasoning of the board parallels the reasoning of the Forward Look article 1 in which Rudolf Scheidl, Matti Linjama and Stefan Schmidt argue that the future of fluid power will become partly digital: ''The overwhelming success of digital concepts in information, communication and power electronics, as well as the analogy between electrical and fluid power systems, suggest that digital concepts should be beneficial in fluid power''. Or, to recast this statement: ''The overwhelming success of feathers for making birds fly, as well as the analogy between birds and fish, suggests that feathers should also be beneficial for fish''. In addition the authors emphasize that ''the positive connotations of the word 'Digital' are good selling points''. Do not be mistaken! I am a strong supporter of research in digital hydraulic systems, although I am not at all convinced that the future of fluid power will be digital. To quote Einstein: ''If at first, the idea is not absurd, then there is no hope for it.'' A lot of research in digital fluid power I consider to fall in the category 'absurd', in the sense of 'out of tune' or 'dissonant' with the ruling technology, and I am very curious to see what will be useful in the end. The idea to copy successful electrical concepts in the design of hydraulic systems and components is as old as the hydraulic industry itself. Examples are 'fluidics' or 'fluidic logics' in which a fluid flow is directed in order to perform analog or digital operations, similar to electronic devices. 2 The authors of the Forward Look article refer to another example, AC hydraulics, in which the principle of a three-phase a.c. network is converted to a three-phase alternating flow network. 3,4 Other examples are 'switched reactance hydraulics' 5 and 'PWM electrohydraulic control systems'. 6 Aside from some niche applications, none of these promising developments has been applied successfully in the market. In 2011, Linjama presented an overview of the stateof-the-art of digital fluid power. 7 In that article he
Directly Digital Flow Controller
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An improved directly digital flow controller is evaluated for its ability to modulate gas flow rates. As in the older device, the "GasDAC" (named for its similarity to a weighted-resistor digital-to-analog converter) is capable of controlling gas flow in a linear and reproducible manner with the advantage of having an adjustable range of flow rates. The new design incorporates venting to prevent "puffing" when the individual flow channels are opened. The temporal characteristics of the GasDAC are also examined; modulation frequencies of 10 Hz with various types of waveforms are possible with the new device.
Automatic Control Valve–Induced Transients in Operative Pipe System
Journal of Hydraulic Engineering, 1999
In most cases, the final configuration of complex pipe networks is attained simply by connecting subsystems initially designed to work separately. Thus, automatic control valves (ACV) are often installed in the confluence nodes where the subsystems meet. The present paper deals with the response and hydraulic behavior of ACVs, topics on which data are scarce. More precisely, attention is focused on transients, which occur in a water-distribution pipe system in operation due to the action of an ACV, both from an experimental and numerical point of view. The aim of the water-hammer field tests is to enlarge the amount of the experimental data concerning unsteady-state flow processes in operating pipe systems. The numerical model extends to field conditions and ACVs laboratory work on the hydraulic characterization of valves and the unsteady-state friction simulation.
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The switched inertance hydraulic converter (SIHC) is a new technology providing an alternative to conventional proportional or servo-valve-controlled systems in the area of fluid power. SIHCs can adjust or control flow and pressure by means of using digital control signals that do not rely on throttling the flow and dissipation of power, and provide hydraulic systems with high-energy efficiency, flexible control, and insensitivity to contamination. In this article, the analytical models of an SIHC in a three-port flow-booster configuration were used and validated at high operating pressure, with the low-and high-pressure supplies of 30 and 90 bar and a high delivery flow rate of 21 L/min. The system dynamics, flow responses, and power consumption were investigated and theoretically and experimentally validated. Results were compared to previous results achieved using low operating pressures, where low-and high-pressure supplies were 20 and 30 bar, and the delivery flow rate was 7 L/min. We concluded that the analytical models could effectively predict SIHC performance, and higher operating pressures and flow rates could result in system uncertainties that need to be understood well. As high operating pressure or flow rate is a common requirement in hydraulic systems, this constitutes an important contribution to the development of newly switched inertance hydraulic converters and the improvement of fluid-power energy efficiency.