Radio-hydraulic control technology combines the advantages of electro-hydraulic control technology and wireless communication technology. It can be widely used in fields such as engineering machinery, not only improving the automation level and operability of engineering machinery, but also improving the working environment for operators and reducing misoperation accidents caused by limited vision. It has been widely used in industries such as construction and mining in engineering machinery, accelerating the process of national industrialization.

I. Basic Principles of Radio-Hydraulic Control Technology

The basic working principle of radio-hydraulic control technology: First, the radio-hydraulic control system digitizes the control commands of the operator or machine (including signal filtering, A/D conversion, etc.), converting them into easily processed digital signals; second, the digital command signals are encoded; third, after digital modulation by the transmission system, the command signals are transmitted to the remote receiving system as radio waves via the transmitting antenna. Finally, the receiving system receives the radio waves carrying the control commands through the receiving antenna, demodulates and decodes them into control commands, and controls various types of valves.

Because radio-hydraulic control technology plays an important role in the field of engineering machinery, it has received increasing attention from various countries, which have invested a lot of Technology and funds in research and development. Although infrared remote control can also achieve remote control of electro-hydraulic control technology, infrared remote control has high requirements for the working background, high energy consumption, short transmission distance (generally not exceeding 10 meters), and must be in a straight line, with no obstacles in between, and is easily affected by industrial heat radiation, making radio-hydraulic control technology the main direction of current research.

II. Research Status and Trends of Radio-Hydraulic Control Technology

(I) Research Status of Radio-Hydraulic Control Technology

Initially, remote-controlled electro-hydraulic control systems all used wired remote control. As early as the early 1960s, people were able to use tow cable remote control devices to control manual and electro-hydraulic multi-way valves on hydraulic machinery. During operation, the linear proportional signals output by the bidirectional single-axis joystick on the tow cable remote control device were used to control the electro-hydraulic proportional multi-way valve. The signals of the line control box joystick could fully simulate the actions of the manual lever on the hydraulic multi-way valve. Although this method allows operators to control mechanical equipment outside the operating area, the attenuation of the control signal in the cable limits the remote control distance. At the same time, the presence of the cable affects the flexibility of operation, and meters of cable are often the main cause of production accidents.

With the maturity of radio technology, it became possible to introduce radio technology into electro-hydraulic control systems. Since radio-hydraulic control technology transmits control commands through radio waves, it completely eliminates the potential hazards caused by tow cable remote control devices. However, early radio-hydraulic control systems could only transmit simple commands, such as: open/close commands. Enter the 1970s, with the advent of large-scale integrated circuits and dedicated microprocessors, more reliable handheld wireless remote control systems were developed. Later, with the rapid development of digital processing technology and the increasing maturity of wireless digital communication technology, the advantages of digital communication technology, such as strong anti-interference ability and ease of processing digital signals, gradually improved the anti-interference performance of the remote control system and greatly improved safety performance; at the same time, the rapid development of analog integrated circuit design and the successful development of various high-precision analog-to-digital converters (A/D) and digital-to-analog converters (D/A), and their application in radio-hydraulic control systems, enabled radio-hydraulic control systems to not only transmit switching signals, but also transmit analog control quantities and have higher resolution of control commands, which means that radio-hydraulic control systems can not only control ordinary electromagnetic switching valves, but also proportional valves.

Because radio-hydraulic control technology has both the advantages of electro-hydraulic control technology and the advantages of wireless technology, it has a wide range of applications, especially in the field of engineering machinery. Typical applications of radio-hydraulic control systems include industrial cranes, truck cranes, truck-mounted cranes, concrete pump (boom) trucks, and shield tunneling machine segment erecting machines.

In the early 1980s, companies such as Kraft TeleRobtics and John Deere in the United States successively developed wireless remote control systems and applied them to excavators, successfully launching remote-controlled excavators. A typical example is John Deere's 690CR remote-controlled excavator.

In 1983, Komatsu Ltd. in Japan researched and developed wireless radio control for micro-motion control and compound actions of various working devices, and successfully modified the PC200-2 hydraulic excavator.

In 1987, HBC in Germany successfully developed an industrial wireless radio remote control device for use in the field of engineering machinery. This remote control device uses advanced digital communication technology, and the transmitted proportional control signal is safe, reliable, and practical, and has high resolution for the transmitted commands; using analog technology at the receiving end can make the acceleration and deceleration actions of the actuator fully proportional to the actions on the transmitter of the wireless radio remote control device, thereby achieving stepless control of the actuator. Using this, combined with electro-hydraulic proportional servo drive mechanisms, hydraulic proportional multi-way valves and electro-hydraulic proportional pressure reducing valves and ordinary electromagnetic control switching valves, wireless remote control of engineering machinery can be achieved. The proportional output signals (0-5V/10V, 4-20mA, PWM0-2A) used in the German HBC wireless remote control system can be matched with the signals of electro-hydraulic multi-way valves from multiple manufacturers, and can simulate manual operation to achieve coordination with the hydraulic control system.

Compared with the research and application of radio-hydraulic control technology abroad, China started relatively late and the technology is relatively backward. In 1997, Baoshan Iron & Steel Co., Ltd. in Shanghai introduced the HBC wireless remote control system and the Italian FABERCOM proportional hydraulic servo module to modify the ZY65 crawler loader produced by Yellow River Engineering Machinery Factory into a remote-controlled loader.

(II) Research Trends of Radio-Hydraulic Control Technology

With the rapid development of digital communication technology and very-large-scale integrated circuits, the application of digital communication technology and high-performance, high-integration integrated circuits in radio-hydraulic control technology has made the performance of radio-hydraulic controllers more perfect and reliability higher. They all drive the development of radio-hydraulic control technology, specifically manifested in the following aspects: (1) The rapid development of very-large-scale integrated circuits improves the reliability of the hardware circuit of the radio-hydraulic controller and provides the possibility of realizing more powerful functions;

(2) Digital communication technology improves the performance of the radio-hydraulic controller;

(3) Error correction coding technology improves the anti-interference ability of the radio-hydraulic controller.

III. Conclusion

Due to the multi-faceted advantages of radio-hydraulic proportional technology, it has been widely used in the field of engineering machinery. Applying this technology to engineering machinery will have important engineering application significance.