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2021-01-15
Pneumatic system overview
Gas exists in space in a certain state. The state of gas is usually represented by three parameters: pressure, temperature and volume. The change process of gas from one state to another is called the gas state change process. The relationship between the parameters when the gas state changes or is in equilibrium after the change is described by the gas state equation. Natural air can be regarded as ideal gas (gas without viscosity).
Pneumatic transmission and control use dry air (moisture-removed air without water vapor) as the working medium.
Air source power device refers to a device that provides the pressure and flow of compressed air required for the implementation of the device or work purpose. It is the core component of the pneumatic transmission and control system, usually an air compressor. Generally, the air conveying machinery with an exhaust pressure higher than 0.2Mpa is called an air compressor (referred to as an air compressor). According to the working principle, air compressors can be divided into two types: speed type and solvent type. Compressed air is compressed by the atmosphere, which is mixed with impurities such as dust and water vapor, which are mixed in the compressed air after being compressed. The compressed air output by the air compressor must be purified and dried, that is, dust, moisture, oil and other impurities mixed in the compressed air can be used as the power source of the pneumatic system.
The inlet and outlet pressure is relatively large, and negative pressure (vacuum) is formed at the suction port, and the air flow conveying machine whose exhaust port is directly connected to the atmosphere is called a vacuum pump, which is used as the power source in the vacuum adsorption system.
According to the form of lubrication, pneumatic actuators are divided into oil-supply pneumatic actuators, oil-free pneumatic actuators, and oil-free lubrication pneumatic actuators. According to the nature of movement, it is divided into cylinder, pneumatic motor, and swing motor. The pneumatic actuating element energy drive mechanism realizes linear reciprocating motion, swing, rotary motion or impact action. It is a transmission device that converts the pressure energy of compressed air into mechanical energy.
Pneumatic control components are various pneumatic devices used for signal sensing and conversion, logic control, parameter adjustment, etc., to ensure that the pneumatic actuators act correctly and reliably in accordance with the procedures specified by the pneumatic control system. Pneumatic control can generally be divided into two types: intermittent control and continuous control.
In the intermittent control (also known as on-off control) system, it is usually necessary to adjust the pressure and flow rate and control the air flow direction and on-off procedures. Pressure control valves, flow control valves, on-off directional control valves and pneumatic Logic components, etc. In the continuous control system, in addition to the control valves for pressure and flow adjustment, servo/proportional control valves are also used to continuously control the system. Pneumatic sensing elements and conversion elements are about to detect the controlled parameters and turn them into pneumatic sensing elements (such as various sensors and stroke valves, etc.), as well as elements that convert air signals, electricity, and hydraulic signals.
Pneumatic auxiliary components are some devices needed to purify, lubricate, muffle the compressed air and connect between components. Such as filters, lubricators, drains, mufflers, converters and pipe fittings.
The pneumatic system is a transmission system that uses air as the working medium. In a general pneumatic control system, in order to achieve the purpose of automatic control of the scientific research and production process, it usually consists of a pneumatic generator, a gas source processing device, a pneumatic control element, and a pneumatic control system. The actuator and pneumatic accessories are composed of several parts and components. It includes two parts: pneumatic transmission system and pneumatic control system.
According to the air supply mode, the pneumatic transmission system is divided into compressor direct supply type, air storage tank air supply type, and pipe network air supply type; according to the movement characteristics of the actuator, it is divided into: direct reciprocating movement, rotary movement, swing type; according to work The medium circulation mode is divided into open circulation and closed circulation.
The air pressure control system includes air valve control system (including electronic control and air control), logic element control system, and jet element control system. A typical pneumatic system consists of electric motors, air compressors, pressure control valves, directional control valves, flow control valves, stroke valves, logic elements, cylinders, mufflers, oil misters, oil-water separators, stop valves, pneumatic sensors, pressure gauges, It is composed of gas storage tank and safety valve.
Advantages and disadvantages of pneumatic systems
advantage:
Simple structure, convenient maintenance, low cost, quick return on investment. Good adaptability to working environment; able to work reliably in environments with wide temperature range, high humidity, dust, vibration, etc.; slight leakage will not pollute the environment, no fire and explosion Dangerous, safe to use; long working life, solenoid valve life can reach 30-50 million times, cylinder life can reach 2000-6000km; actuator output speed is high, linear motion can reach 15m/s; overload protection capability, actuator It will stop automatically when overloaded, and there is no danger of damage, and it will remain motionless under load when the power is insufficient. Disadvantages:
Due to the compressibility of air, the stability of the movement speed of the working parts is poor; the working pressure is low, and the output thrust of the pneumatic actuator is smaller than that of the hydraulic transmission; the speed of long-distance signal transmission is slow, and the air pressure signal transmission is not suitable for high-speed transmission complex circuits; Because the working pressure is low and the structure size should not be too large, the output force is small, usually not more than 10-40kN.
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