Digital Hydraulic Valve Research Articles

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.

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.

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.

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.

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.

Design and Experimental Research of a Miniature Digital Hydraulic Valve.

A digital hydraulic valve is an important component of the digital hydraulic system, and its performance is directly related to the system function. In order to make the valve system more competitive in dimension, digital valve miniaturization is an important research point. A new micro digital valve is designed, which is analyzed from the mechanical structure and magnetic circuit mechanism, and the design difficulties are also expounded. The four subsystems and switching characteristics of the valve are theoretically analyzed and simulated. In order to test the performance of the valve, a test system is designed, and performance of the new micro valve is tested. The test results show that the switch characteristic analysis of the valve is correct. The comparison between the test curve and the simulation curve is carried out, which demonstrates that the accuracy of the simulation model is reasonable. The theoretical analysis of the new micro digital valve is consistent with experiments.

High-linear digital hydraulic valve control by an equal coded valve system and novel switching schemes

This study proposes a novel digital hydraulic valve system using multiple equal size on/off valves and a circulating switching control, with an aim to increase the resolution and the linearity of t...

Selective Laser Melted Digital Hydraulic Valve System

Abstract The purpose of this article is to investigate the possibility of manufacturing a digital hydraulic valve system using additive manufacturing and to identify the challenges and benefits of doing so. In this study, an existing hydraulic valve manifold, operating at pressures up to 25 MPa, was redesigned for selective laser melting (SLM) and further optimized with computational fluid dynamics. Certain dimensioning challenges were encountered because laser melting is not yet accurate enough for some features, but these challenges were circumvented. The manifold was successfully manufactured from tool steel and tested for maximum operating pressure and flow capacity. Due to the improved flow channels, the selective laser melted manifold provided up to 49% reduction in the energy losses caused by flow resistance. This article demonstrates that SLM can be used to improve the performance of hydraulic valves and that the cost of SLM manifolds is feasible for high-end valve assemblies.

Dynamic modeling of a 2-dof parallel electrohydraulic-actuated homokinetic platform

Thrust vector control (TVC) is used to control the attitude of spacecraft. The most widespread method to connect the nozzle assembly and rocket consist of a gimbal joint in the case of liquid-propellant or a flexible bearing in the case of solid-propellant. Traditionally, two electrohydraulic linear actuators that are controlled by servovalves tilt the rocket nozzle. However, in this work, TVC is treated as a robotic system and the connection between the platform and the fixed base is achieved using a constant velocity joint. Instead of a servovalve, a novel proportional digital hydraulic valve is proposed. The position feedback is provided through a real-time attitude estimation based on the orientation matrix by using an inertial measurement unit (IMU). Platform kinematics modeling is performed. Dynamics modeling is developed using Newton-Euler formulation. Hydraulics modeling is presented with the description of the electrohydraulic system. Due to the linear behavior of the control valve, a simple pure proportional controller is considered. An experimental validation showed that the proposed system achieves good position tracking without instabilities.

Model-based force and position tracking control of an asymmetric cylinder with a digital hydraulic valve

AbstractThis paper presents a model-based control solution for large inertia systems controlled by a fast digital hydraulic valve. The solution is based on model-based force control and it is shown that the cylinder chamber pressures have first order dynamics with the proper parameter selection. The robust stability is analyzed under unknown load mass, bulk modulus, and delay, and it is shown that a simple cascaded P + PID controller results in good control performance and robustness. The simulated results show smooth and stable response with good tracking performance despite large variations in the load mass and bulk modulus.

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.

Equal Coded Digital Hydraulic Valve System – Improving Tracking Control with Pulse Frequency Modulation

Previous research on digital fluid power indicates down-scaling to be beneficial to the characteristics of digital valves. This theoretical aspect yields to use equal size on/off valves in digital hydraulic valve systems. A simple miniaturized on/off valve, having orifice diameter of 0.7mm, have been developed to study the feasibility of this approach. A manifold manufacturing technology also has been developed to facilitate a compact framework for the valve system containing dozens of the miniature valves. The first equal coded valve system prototype contains 16 miniature valve prototypes. A natural modulation method for an equal coded valve system is Pulse Number Modulation (PNM), where the output depends on the number of activated valves. With this modulation method, resolution of the output is equivalent to the number of the valves in the control edge. Limited resolution hampers the tracking control performance especially at low velocity where small steps in flow rate are required. The main purpose of this paper is to study the feasibility of Pulse Frequency Modulation (PFM) to improve the controllability of the equal coded valve system at the velocities below the minimum velocity of PNM control. Poor controllability at low velocities is one of the main challenges of the digital hydraulic valve systems. Characteristics of the PFM method are analysed and an experimental study is carried out to measure the improvement of the PFM method on the tracking control performance. The study indicates that the PFM method is an effective way to improve tracking control performance at low velocity.

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.

Based on Fluid Digital Transmission and Control Theory on Application of Digital Hydraulic Valve

A digital hydraulic valve is a new control theory and method, it is through the electronic control unit installed in a conventional valve, and integrated processing, the formation of a wide variety of digital valve，By the digital-to-analog conversion element is directly connected with the computer. Using the computer output pulse number and frequency to control electro hydraulic system pressure and measurement. The system proposed can make the hydraulic system has the advantages of high efficiency, high speed, high reliability. And used Matlab/Simulink software to control system performance simulation analysis, experiment and simulation results show that, this system has great application prospect and practical value.

Genetic Optimization of a Fast Solenoid Actuator for a Digital Hydraulic Valve

A fast response electromagnet to actuate a digital hydraulic valve was designed. A computational model of the electromagnet was optimized for fast response and low energy consumption using a finite element method and genetic optimization. The actuator was constructed and attached to a commercial valve body, and measurements were made validate the computational model. The new actuator greatly increased the applicability of the valve in digital hydraulics applications.