Hydraulic valves are critical components in many hydraulic systems where the flow rate, pressure, or actuators need to be controlled. There are many types of electro-hydraulic control valves, like proportion valves, flapper-nozzle valves, or other valves with electronic controllers. With the development of materials, manufacturing, electronic technology, and computer technology, more power has been injected into electro-hydraulic control valves along with new demands. Hydraulic valves are being developed to adapt to the changing world and market, which has become more versatile and powerful. Since the principles of Industry 4.0 have been applied by many companies, electro-hydraulic control valves also need to achieve features from Industry 4.0
What are the requirements of Industry 4.0 for electro-hydraulic control valves?
The hydraulic valves should be available at remote terminals so they can be controlled and monitored. And the abilities of self-detection, fault diagnosis, function redefining, and integration should be added into valves for Industry 4.0. Digital technologies can make hydraulic valves accessible to the embedded system and they are linked to computers or mobile terminals. With the integration of digital controllers and other hardware like various transducers, the valve’s functions could be customized and extensible, besides online remote monitoring and the diagnosis can be implemented through CAN open or other communication technologies. The demand for Industry 4.0 to achieve valve self-diagnosis is not limited to the detection of simple faults such as electronic faults with sensors. Instead, intelligent and effective diagnosis of faults deep inside the valve can occur with limited state signals.
Control Technologies and Novel Valves
Actuators of Electro-Hydraulic Control Valves
Torque motors and electromagnetic solenoid actuators are very common converters, new electronic mechanical converters of valves are constantly coming out. There are many kinds of electronic mechanical converters that are used in electro-hydraulic control valves. Since there are a variety of electric actuators, electro-hydraulic control valves show better driving characteristics and various forms for different applicants with a lower cost and a greater efficiency. The flow rate, pressure, forces, or other system variables can be controlled with different closed-loop feedback signals. The development of electro-hydraulic control valves is the result of the interdisciplinary development of hydraulics, mechanical technology, electronics, materials, controls, and other disciplines, which can contribute to the development of Industry 4.0
Control Strategies on Traditional Valves
Electro-hydraulic control valves used to feature proportional-integral-derivative (PID) controllers; however, many model-based controllers are being developed due to digital technology, which makes an important contribution to Industry 4.0. Because of the PID controller’s effectiveness and practicability, it is widely used in electro-hydraulic control valves until now. In addition, there are also many improvement methods based on PID controllers and also a fuzzy-based PID controller is implemented into a piezoelectric actuator-based direct-drive valve also an optimal-tuning nonlinear PID controller for hydraulic systems is proposed. By adding optimal algorithms like some nonlinear elements, or just feedforward and compensation, the quality of the PID controller can be prompted.
With an improvement in the relative technical requirements for higher controller performance, studies regarding the electro-hydraulic valves’ controller based on a model or process are increasing, especially for digital controllers.
Valves with Separate Meter-in and Meter-out Orifices
Traditional hydraulic valves like proportional valves link the meter-in and meter-out orifices in one spool to regulate the flow. They are mechanically coupled and bring drawbacks for poor mobility and high energy-consumption, which don’t meet the requirements of high efficiency and energy savings for Industry 4.0.
For this problem the concept of separate control for meter-in and meter-out orifices was introduced. The meter-in and meter-out valve separately adopts the double valve spools structure to independently adjust its inlet and outlet throttling area, which increases the control freedom of the system and makes it possible to further improve the control and energy-savings performance of the valve and hence The valves with separate meter-in and meter-out orifices is a good control strategy in the hydraulic field. Compared with the traditional proportional valve control system, it has the potential to improve the energy-saving characteristics of the system and achieve electronic intelligent control. It has a wide variety of applications in the field of excavators, cranes, and other machinery.
On/Off Valves for Digital Hydraulics
Hydraulic components have characteristics of fluid flow discretization and control signal discretization called digital hydraulic components. Hydraulic systems with characteristics of digital hydraulic components are called digital hydraulic systems. Digital hydraulics has advantages in terms of its information capability, which is a significant direction for Industry 4.0.
On/off valves can turn a digital signal to a flow signal directly, which closely combines digital signals and hydraulics. There can be different on/off types valves such as needle valves, “mushroom” valves, pilot operated seat valves, spool valves, or other special types, which have different features for the response time and flow rate. Although the on/off valves have a fast response speed, its flow rate is always small. Parallel technology that is based on the on/off valve or switching valve is a solution to that problem, like the digital flow control unit (DFCU).
With the application of digital, intelligent, and new materials for 3D printing technology, the hydraulic valve package for digital hydraulic systems can be completed with advanced 3D printing technology by optimizing the flow paths. This will significantly shorten the manufacturing cycle of the valve package, improve the machining accuracy, and help achieve intelligent manufacturing for the digital hydraulic valve package. Digital hydraulics is a qualitative leap for traditional hydraulic systems, which shows a huge potential and market in Industry 4.0.
Communication and Human–Machine Interaction
Modern factories need to build a network of sensing, measurement, and control, which covers the whole production process. Therefore, as an important control component of modern factories, the electro-hydraulic valve also needs to have a measurement function for the pressure, flow, and other signals. Meanwhile, the control function is necessary for quick debugging and integration according to the working conditions, as well as a quick information exchange function for communication through a bus or Ethernet
Fieldbus-Based Communication Modes
Fieldbus technology makes the hydraulic valve an independent control element that can achieve decentralized control and centralized management in the industrial field. At the same time, the hydraulic valve and the hydraulic cylinder can form a decentralized independent axis controller by a Fieldbus. The Fieldbus connects the communication unit, which is composed of the electro-hydraulic valve and its pressure, flow, and position sensors, with other hydraulic units, electronic units, and central industrial control units to form a data interaction network. This can achieve control of the entire hydraulic system and the collection of basic information.
With the process of digitalization in the hydraulic industry, there is a growing demand for a remote monitoring capability of electro-hydraulic valves. Many enterprises have released a series of hydraulic valves with a communication interface. Most of those valves equip Fieldbus interfaces since they have a huge application market and mature hardware technology. ATOS DLHZO-TEZ series valves and MOOG D636 provide CAN, Profibus DP, EtherCAT interface for users to choose from. HYDAC P4WERE06 integrates the LIN interface. Parker D1FC integrates EtherCAT. Some other control blocks, like HAWE PSL series, Danfoss PVG series, Eaton CMA200, integrate the CAN bus interface.
Bluetooth-Based Communication Modes
In some industrial scenes, where the electro-hydraulic valves do not have enough place for communication cables, it is necessary to make the communication networks wireless. On the other hand, wireless communication networks can make it convenient for engineers to debug these valves and to monitor the equipment states. In regard to the demand for wireless communication networks, some enterprises have released products that are integrated with Bluetooth. SUN 7904A24, a proportional cartridge valve, integrates Bluetooth. HAWE RV2S-BT integrates Bluetooth, which makes valves convenient and intelligent to control, monitor and manage.
IO-Link-Based Communication Modes
There are lots of Fieldbus standards in different industries, which makes it a huge challenge for users to connect with sensors, actuators, and valves with different communication interfaces in a project. A communication interface called IO-Link can solve this problem. IO-Link is an open standard so that products that are integrated with IO-Link can almost connect with any equipment with a different Fieldbus. This advantage makes it easier for these products to combine with other pieces of equipment that has an independent control system. However, it can only achieve point-to-point communication, and it cannot combine multiple devices into one communication network without the IO-Link Master or the IO-Link Hub. Rexroth 4WRPEH is a product that is integrated with IO-Link.
Human–Machine Interaction Software
As a hardware basis, those interfaces can build a huge communication network. However, what makes it incredible is the software behind the network. We can control, monitor, and manage those valves remotely and in real-time using PC software, such as ATOS Z-SW, Parker ProPxD, MOOG Valve, and Pump Configuration Software. At the same time, some valve faults, such as communication errors, hardware errors, and overloading the overloading the power supply voltage, can be diagnosed remotely by that software. Some other applications are designed for those mobile devices, such as SUN AmpSet Blue and HAWE eControl.
Electro-hydraulic control valves experienced a long-time development from a pure mechanical structure to mechatronics hydraulics integration. In addition, electro-hydraulic control valves are currently being integrated with digital technology and a variety of communication technologies. Since Industry 4.0 is an ongoing revolution, electro-hydraulic control valves should show its vitality with new technology. The valves oriented to Industry 4.0 can be intelligent with the abilities to acquire state information, monitor and perform diagnoses online, and provide more efficient control.
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