Digital Valve System Research Articles

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.

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.

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.

High-flow rate miniature digital valve system

AbstractDigital hydraulic valve systems can offer several benefits compared to spool-type proportional valves, such as faster response, more flow capacity, better fault tolerance and individual metering. However, the digital valve systems currently available are large, heavy and slow and therefore there is a need to miniaturise them and simultaneously make them faster. This article describes the design and performance of a digital valve system which can be used to replace a proportional valve with ISO 03 (NFPA D03, CETOP 3, NG6) standard interface. The valve system consists of 32 pilot operated miniature on/off valves which form four independently controlled metering edges. The valve system has small dimensions (176 × 49 × 72 mm) even though it contains integrated control electronics, its response time is approximately 2 ms and flow capacity per metering edge is 30 l/min at Δp = 0.5 MPa. These properties are good, however, improvements are required to reduce the leakage caused by the pilot valves, which c...

Mechatronic Design of Digital Hydraulic Micro Valve Package

Digital hydraulic valve system is a new kind of hydraulic control valve assembly, which has potential to save energy and improve performance of valve controlled actuators. The typical digital valve system has 4-6 parallel connected on/off valves per control edge totaling 16-24 valves in the four-way valve configuration. The flow capacities of the parallel connected valves are set according to the powers of two such that it is possible to achieve 2N different flow rates with N valves. An alternative approach is to use equally sized valves, which means that N parallel connected valves give only N+1 different flow rates. This approach has several benefits, but the number of valves becomes very large. This paper shows that it is possible to implement valve assembly having 128 miniaturized valves, such that it can be installed instead of traditional CETOP3 servo or proportional valve. Careful electromagnetic optimization and mechatronic design are used together with novel manufacturing methods and new type of power electronics. The prototype is build and experimentally studied and results show that the performance of this kind of digital valve system is superior to traditional four-way control valves in terms of response time and fault tolerance.

Pilot operated miniature valve with fast response and high flow capacity

This paper introduces a pilot operated miniature digital hydraulic valve with a high flow capacity, in comparison to the size of the valve, and a fast response. The valve is designed to be used as a part of a digital valve system, which consists of a large number of similar valves. This paper presents the structure of the valve as well as the response time, flow capacity and leakage measurements of the prototype. The presented valve has a volume of approximately 4 cm3 and a flow capacity of 9 l/min with a 3.5 MPa pressure difference. Its response time is approximately 1 ms and the maximum operating pressure exceeds 30 MPa.

Energy Efficiency of Three-Chamber Cylinder with Digital Valve System

Commonly used hydraulic cylinders have piston and piston rod. Piston divides the inside of the cylinder in two chambers and pressure affecting the piston generates the linear motion. Use of distributed valve system enables several control modes in a system of this type because different control edges can be controlled independently. These control modes can be used for decreasing energy consumption and improving controllability. Traditional hydraulic cylinder has only a limited number of control modes, but by utilizing a multi-chamber cylinder the number of control modes can be increased. In this paper, a three-chamber cylinder is studied using measurements and simulations. The control of the cylinder is presented and measurements are done in a 1-DOF boom mock-up to show the operation of the system in practice. A simulation model is built to investigate further the energy saving capability of the system. The studies show that losses can be significantly reduced by replacing traditional cylinder drives with multi-chamber cylinders.

Jammed on/off Valve Fault Compensation with Distributed Digital Valve System

AbstractThe digital valve system is an on/off valve based directional flow control valve capable of accurate control of hydraulic actuators. The presented system has good features concerning fault tolerance since it can detect, diagnose and compensate faults on-line. This paper concentrates on fault compensation when a valve has jammed in the open—position and the system has internal leakage. The system can adapt to the fault and continue operation with only a small degradation in performance. This feature is unique in the area of hydraulics since the system has no extra components added. The cost for this compensation is increased calculation in the controller and increased energy consumption if a fault occurs. If these downsides can be accepted the system can be considered fault-tolerant and it could be used even in critical applications where failing is not an option. Fault tolerance can also be introduced as standard in every modern hydraulic application where good performance and fault tolerance are ...

Microcomputer Control of a Small-Scale Ethanol Distillation System

Amicrocomputer-controlled digital valve system was developed to control the temperature, and hence the quality, of ethanol-water vapors leaving the product column of a small-scale distillation system. The temperature was controlled by regulating the water flow through an internal reflux coil. The temperature of the product vapor was controlled within ±0.3°C. The temperature sensing devices permitted an overall temperature control accuracy of ±0.5°C. A temperature monitoring routine was developed to read and display system temperatures, and a storage routine kept a record of temperatures and reflux condenser water flowrates