Reviewing Digital Hydraulic Technology.

 

Hydraulics Technology is Alive and Thriving Very Well.

Rumors of the death of Fluid Power were greatly exaggerated. In comparison, from only a few years ago, electronic control and more sophisticated components have advanced hydraulic power transmission well beyond their state of the art.

Since the emergence of digital hydraulic technology, it has achieved good results in intelligence, integration, energy saving, etc. After decades of development, and it has also attracted wide attention in the industry. However, for many years, the definition of digital hydraulic technology has differed between researchers, and there is no uniform definition. Such a situation affects the development of it to a certain extent.

Therefore, in this blog we will review the trends of digital hydraulic technology based on a large number of researches on it. At the same time we will try and forecast the development trend of it.

 

INTRODUCTION

Although the foundation and development of hydraulic technology can be traced back to the middle of the 17th century, the rapid development and application of it really began 100 years ago.

 

The development of electro-hydraulic servo-control technology began in the 20th century based on the continuous improvement of control theory and its engineering practice.

 

After that, with the support of microelectronics technology, the hydraulic control unit became able to integrate with microprocessor, electronic power amplifier and sensor. So, the dynamic control accuracy, intelligence, reliability and robustness of the hydraulic control unit were improved 

 

After referring to the concept of “digital” in electronic technology, digital hydraulic technology gradually develops and takes shape; it accelerates the pace of intelligent hydraulic technology, and because of its huge advantages compared with traditional proportional servo control technology, it has attracted extensive attention from researchers.

However, the definition of digital hydraulic technology has always been in dispute.The definition of digital hydraulic technology is not unified, which limits its development and application to some extent. With the intelligent and green development of global industry, only the technology meeting social needs can survive, and digital hydraulic technology is providing a feasible innovative development path for traditional hydraulic technology.

 

Classification of Digital Hydraulic Technology

Digital hydraulic technology can be divided into three main categories.:-

             

·Parallel Digital Hydraulic Technology

 

The parallel digital hydraulic technology requires all the components to be connected in parallel, and the composite states of all the components are controlled by modulated discrete digital signals.

 

·High-Speed Switching Digital Hydraulic Technology

 

In order to realize intelligent control of system output, high-speed switching digital hydraulic technology put forward high requirements for high-speed switching components which can switch quickly and continuously to output fluid flow with different discrete values.

 

·Stepping Digital Hydraulic Technology

The stepping digital hydraulic technology relies on precise stepping motor which controlled by modulated discrete digital signals.

 

Digital Hydraulic Components:-

As with the traditional hydraulic components, digital ones also contain three main categories:-

 

Digital control components  :-    Hydraulic valve 

Digital power components :-      Hydraulic pump, transformer and                                                                                  power control system 

Digital actuators  :-                     Hydraulic cylinder and motor.

And all kinds of components with different classifications of digital hydraulic technology also have different products.

 

Advantages of Digital Hydraulic Technology

 In 2013, the concept of “Industry 4.0” was officially launched at Hanover Industrial Expo, aiming to improve the intelligent level of the manufacturing industry. Industry believes that the concept of “Industry 4.0” is the fourth industrial revolution or revolutionary production method led by intelligent manufacturing.

 “Industry 4.0” mainly includes three aspects; namely, intelligent factories, intelligent production and intelligent logistics.

 As one of the important transmission technologies in industrial systems, the hydraulic system is required to be more energy efficient, more accurate and more reliable.

 However, as mentioned before, the low energy efficiency and high cost of conventional hydraulic technology are against such requirements. As the inheritor and innovator of traditional hydraulic technology, digital hydraulic technology is in line with “Industry 4.0.”

 Its unique technical features and advantages will provide technical support for the development of manufacturing industry in the developmental trend of “Industry 4.0.”    

So the advantages of the digital hydraulic system are:-

•  Fault-Tolerance Performance:-

The intelligent factory in “Industry 4.0” puts forward higher requirements for the fault-tolerant performance of hydraulic system, because it is an important factor to ensure production efficiency, and it is also one of the shortcomings of conventional hydraulic technology. 

But for the parallel digital hydraulic systems, fault-tolerance is an inherent feature. The components in parallel are independent of each other, and the system can maintain the original performance to a large extent when individual components fail.

• Precise Lossless Control:-

Intelligent logistics is one of the three themes of “Industry 4.0,” and it put forward higher requirements for the mobile outdoor robotic applications, wherein high power density, ruggedness and reliability are key features. 

So, the low efficiency of conventional proportional control can be a limitation. However, because the high-speed switching valves can turn on/off at high frequencies, the system does not cause excessive oil supply, so the accurate control with high energy efficiency has become the most prominent feature of high-speed switching digital hydraulic system.

• High Accuracy Sensorless Control

Precise position control is an important actuation function in intelligent manufacturing. The conventional approach uses a cylinder with a precise position sensor and a closed loop control via a proportional or servo valve.

 Although its control accuracy is very high, the costs and low reliability caused by sensor, cabling, connectors and controller input modules are the main factors limiting the conventional proportional or servo valve system’s application. 

So, the avoidance of such sensors is an effective measure to improve system reliability and make it survive and develop in “Industry 4.0.” And digital hydraulic technology is providing possible approaches of high accuracy sensorless control.

 

Overview of Advantages and Challenges of Digital Hydraulic Technology:-

By integrating the technical features of parallel digital hydraulic system and high-speed switching digital hydraulic system, it can be seen that digital hydraulic technology has unique advantages over traditional hydraulic technology.

• Digital hydraulic technology directly adopts the digital signal to control without D/A conversion, which simplifies the control mode; makes the signal data storage, processing and transmission more convenient; and has stronger disturbance rejection ability, which is helpful for improving the robustness of the system.
• The digital hydraulic system has a better integration and programmability which can improve the application and maintenance performance of the system. It also facilitates networking of the system.
• The performance of the system depends on the control of the combination state of components rather than the performance of individual components. Therefore, simple and reliable components can be widely used to improve the robustness and fault-tolerance performance of the system.
• The digital hydraulic system avoids the use of proportional and servo components, and it improves the anti-pollution performance.
• It is easier to realize independent metering control. And because of the switching control mode, the system can reduce the throttle loss and improve efficiency.
• Digital hydraulic technology has obvious advantages, but there are also challenges to limit its application.
• The high frequency switching of the components can cause noise and pressure impact.
• The durability of high-speed switching hydraulic technology severely limits its application at present.
• The parallel digital hydraulic technology needs to use a large number of components, and such a situation would cause a dramatic increase in size and cost.
• A complex, unconventional control strategy would also bring difficulties to the application of digital hydraulic technology.

 

 Developing Trend of the Digital Hydraulic Technology:-

After decades of research, digital hydraulic components have formed a series of products with complete functions and various categories. Some products have been used in aerospace, construction machinery, shipbuilding industry and other industries; its technology has become increasingly mature.

 However, under the development trend of high speed, high pressure and high power to weight ratio of hydraulic system, the problems such as lower flow rate, lower allowable pressure and serious dispersion of system have also become more prominent. 

To solve such problems, researchers have also invested a lot of energy into optimizing the existing digital hydraulic products. Some of the research results have not only been applied in engineering, but also evolved into some developmental direction of digital hydraulic technology.

•  Development of a New Valve Prototype

High-speed switching digital hydraulic technology puts forward the technical index of switching frequency 500 Hz (that means the opening time is 2 ms) for high-speed switching valve. 

However, the flow rate of the current valve which can reach such a technical index is generally small. So, the valves cannot satisfy the need of continuous switching control under large flow. 

Therefore, many research institutions and universities have invested a lot of resources in the R&D of new valves, and they had put forward different valve prototypes, but few valve products can be put into industrial applications.

 It can be concluded that the R&D of new high-speed switching valves with high working pressure and large flow rate will become an inevitable trend of digital hydraulic technology.

 

• Integration of Digital Hydraulic Technology

Parallel digital hydraulic technology and high-speed switching digital hydraulic technology, are two main branches of current digital hydraulic technology; they have their own unique technological advantages and face different challenges.

 Therefore, it is also a research direction of digital hydraulic technology to combine the two main branches of current digital hydraulic technology and take their respective advantages. 

 

• Improvement of Energy Efficiency

One of the important characteristics of digital hydraulic technology which is different from traditional hydraulic technology, is that it can realize intelligent hydraulic energy supply based on the system requirements.

 So, digital hydraulic components, such as the digital hydraulic pump-motor, digital hydraulic transformer, etc., all have high energy efficiency in theory, but that still needs a lot of experimental verification and optimization. 

Therefore, improving energy efficiency is also an important development trend of digital hydraulic technology.

 

Conclusion:-

The definition of Industry 4.0 promotes the progress of the whole society and industrial system. Only the technology that meets the needs of society can survive and develop.

 And digital hydraulic technology provides a feasible way for the traditional hydraulic industry to develop in the direction of intelligence and greenness. At the same time, as the innovation of and successor to traditional hydraulic technology, digital hydraulic technology will certainly make fluid power technology developing in line with “Industry 4.0.” 

With continuous in-depth research, digital hydraulic technology will continue to innovate. More mature digital hydraulic components will also have more extensive engineering application prospects.

With the continuous promotion of “Industry 4.0” in the world, traditional hydraulic technology has been marginalized because of its low energy efficiency and lack of intelligence.

 The digital hydraulic technology will be able to make up for the defects of the traditional hydraulic technology, and play a greater role in intelligent factories and intelligent manufacturing.