Abstract : Addressing the shortcomings of conventional pneumatic servo systems, this paper introduces a liquid medium into the pneumatic servo system based on traditional pneumatic-hydraulic linkage technology and performs closed-loop control, thus constructing a novel pneumatic-hydraulic composite medium transmission system—the pneumatic-hydraulic joint control servo system. It utilizes the adjustment of the variable damping force of the liquid to change the dynamic characteristics of the system and achieves some special functionalities. Experiments have demonstrated that the pneumatic-hydraulic joint control servo system achieves high stiffness, high precision, and high frequency response that are difficult for conventional pneumatic servo systems to reach, which has significant theoretical and practical implications for broadening the application fields of pneumatic technology. Keywords : Pneumatic-hydraulic linkage, pneumatic servo system 0 Introduction Whether in modern or traditional machines, the transmission system is a crucial link in energy transmission and regulation. Common transmission methods include mechanical, fluid, electric, and magnetic methods, each with its own characteristics. Based on these characteristics, composite transmission methods such as mechanical-hydraulic, electro-hydraulic, electrical, and electromechanical have been invented. However, among these composite transmission methods, the combination of pneumatic and hydraulic transmission has received relatively little research, and many potential advantages of combining these two transmissions remain to be revealed. The discussion in this paper focuses on the characteristics of this gas-liquid composite medium transmission. [b]1 Combination of pneumatic and hydraulic transmission Pneumatic transmission has the following advantages:[/b] (1) Air is readily available and pollution-free. (2) Air is easy to store due to its compressibility and transmits quickly due to its low viscosity. (3) It is very suitable for harsh environments such as flammable and explosive, strong radiation, and dusty environments. These characteristics sometimes necessitate the use of pneumatic transmission, and it is precisely these advantages that enable pneumatic transmission to be combined with other transmission methods, including hydraulic transmission. This paper refers to this traditional pneumatic and hydraulic combined transmission system as a pneumatic-hydraulic linkage system. Perhaps the earliest and most successful example of pneumatic-hydraulic linkage is the widespread application of accumulators. Other commonly used components, such as pneumatic-hydraulic directional valves and pneumatic servo valves, have pilot valves or pre-stages controlled by pneumatic pressure, while the power stage remains a hydraulic spool valve. Other common actuators include pneumatic-hydraulic booster cylinders and pneumatic-hydraulic damping cylinders. There are also auxiliary components such as pneumatic-hydraulic converters, and some special components, such as power heads for pneumatic-hydraulic milling heads and pneumatic-hydraulic boring heads in combination machine tools. [b][align=center]For more details, please click: Pneumatic-hydraulic Linkage and Pneumatic-hydraulic Control[/align][/b]