Hydraulic is a term in the machinery industry and electromechanical industry. Hydraulics can use power transmission to become hydraulic transmission. Hydraulic pressure can also be used as a control method and is called hydraulic control.
Hydraulic transmission uses liquid as the working medium and uses the pressure energy of the liquid to transmit power.
Hydraulic control is a control that uses pressured liquid as a control signal transmission method. The control system composed of hydraulic technology is called hydraulic control system.
A complete hydraulic system consists of five parts, namely energy device, execution device, control and adjustment device, auxiliary device, and liquid medium. Hydraulic is widely used in industrial and civil industries due to its large transmission power and easy transmission and configuration. The function of the actuators (hydraulic cylinders and hydraulic motors) of the hydraulic system is to convert the pressure energy of the liquid into mechanical energy to obtain the required linear reciprocating or rotary motion. The function of the energy device (hydraulic pump) of the hydraulic system is to convert the mechanical energy of the prime mover into the pressure energy of the liquid.
Pneumatic transmission technology is an energy transmission technology that uses compressed air as the medium and air source as the power. It has high working reliability, long service life and no pollution to the environment, so it is often used in the driving system of manipulators. Air pressure technology. The manipulator is generally composed of an execution system, a drive system, a control system and an artificial intelligence system. It mainly completes actions such as movement, rotation, and grabbing. Compared with other types of manipulators, pneumatic manipulators have the characteristics of simple structure, low cost, easy control and convenient maintenance.
The development history of hydraulic transmission
Hydraulic transmission and pneumatic transmission are called fluid transmission, which is an emerging technology developed based on the hydrostatic pressure transmission principle proposed by Pascal in the 17th century. In 1795, the British Joseph Braman (1749-1814) used water as a working medium in London and applied it to industry in the form of a hydraulic press, creating the world's first hydraulic press. In 1905, the working medium was changed from water to oil, which further improved it.
After the First World War (1914-1918), hydraulic transmission was widely used, especially after 1920, it developed more rapidly. Hydraulic components only began to enter the formal industrial production stage in about 20 years at the end of the 19th century and the beginning of the 20th century. In 1925, F.Vikers invented the pressure-balanced vane pump, which laid the foundation for the gradual establishment of the modern hydraulic component industry or hydraulic transmission. In the early 20th century, G. Constantimsco conducted theoretical and practical research on energy wave transmission; in 1910, he made contributions to hydraulic transmission (hydraulic couplings, hydraulic torque converters, etc.). These two areas have been developed.
During World War II (1941-1945), 30% of American machine tools used hydraulic transmission. It should be pointed out that the development of hydraulic transmission in Japan is nearly 20 years later than that in European and American countries. Around 1955, Japan rapidly developed hydraulic transmission, and the "Hydraulic Industry Association" was established in 1956. In the past 20 to 30 years, Japan's hydraulic transmission has developed rapidly and ranks first in the world.
Hydraulic transmission has many outstanding advantages, so it is widely used, such as general industrial machinery. Plastic processing machinery, pressure machinery, machine tools, etc. used in industry; engineering machinery, construction machinery, agricultural machinery, automobiles, etc. in mobile machinery; metallurgical machinery, lifting devices, roller adjustment devices, etc. used in the steel industry; flood control used in civil engineering and water conservancy projects Gates and dam devices, riverbed lifting devices, bridge control mechanisms, etc.; power plant turbine speed control devices, nuclear power plants, etc.; deck hoisting machinery (winches), bow doors, bulkhead valves, stern thrusters, etc. for ships; Giant antenna control devices, measurement buoys, lifting and rotating stages for special technologies; artillery control devices, ship anti-rolling devices, aircraft simulations, aircraft landing gear retracting and retracting devices and rudder control devices for military industry.
Advantages and Disadvantages of Hydraulic Transmission
Compared with mechanical transmission and electrical transmission, hydraulic transmission has the following advantages:
1. Various components of hydraulic transmission can Conveniently and flexibly arranged as needed.
2. Light weight, small size, small movement inertia and fast response speed.
3. It is easy to operate and control, and can achieve a wide range of stepless speed regulation (speed regulation range up to 2000:1).
4. Overload protection can be automatically realized.
5. Mineral oil is generally used as the working medium, and the relative moving surfaces can be self-lubricated and have a long service life;
6. It is easy to achieve linear motion/
7. It is easy to realize the automation of the machine. When electro-hydraulic joint control is adopted, not only a higher degree of automatic control process can be achieved, but also remote control can be achieved.
Of course, hydraulic transmission also has some disadvantages:
1. Due to the large resistance and leakage of fluid flow, the efficiency is low. If not handled properly, leaks will not only contaminate the site, but may also cause fires and explosions.
2. Since the working performance is easily affected by temperature changes, it is not suitable to work under very high or very low temperature conditions.
3. Hydraulic components require higher manufacturing precision, so they are more expensive.
4. Due to the leakage and compressibility of the liquid medium, a strict transmission ratio cannot be obtained.
5. When the hydraulic transmission fails, it is difficult to find out the cause; use and maintenance require a high technical level.
The composition and function of the hydraulic system
A complete hydraulic system consists of five parts, namely power components, actuating components, control components, spare parts and hydraulic oil.
The function of the power component is to convert the mechanical energy of the prime mover into the pressure energy of the liquid. It refers to the oil pump in the hydraulic system, which provides power to the entire hydraulic system. The structural forms of hydraulic pumps generally include gear pumps, vane pumps and plunger pumps. Their performance comparison is shown in 1-1
The function of actuators (such as hydraulic cylinders and hydraulic motors) is to move the liquid Pressure energy is converted into mechanical energy, which drives the load to perform linear reciprocating or rotary motion.
Control components (i.e. various hydraulic valves) control and regulate the pressure, flow and direction of liquid in the hydraulic system. According to different control functions, hydraulic valves can be divided into force control valves, flow control valves and directional control valves. Pressure control valves are further divided into flow valves (safety valves), pressure reducing valves, sequence valves, pressure relays, etc.; flow control valves include throttle valves, adjustment valves, diverter and collector valves, etc.; directional control valves include one-way valves, Hydraulic control check valve, shuttle valve, reversing valve, etc. According to different control methods, hydraulic valves can be divided into on-off control valves, fixed value control valves and proportional control valves.
Auxiliary components include oil tanks, oil filters, oil pipes and pipe joints, sealing rings, pressure gauges, oil level and oil temperature gauges, etc.
Hydraulic oil is the working medium that transmits energy in the hydraulic system. There are several categories such as various mineral oils, emulsions and synthetic hydraulic oils.
Edit this section of the three major chronic diseases of the hydraulic system
1. Heat generation. Due to the different flow rates of various parts of the power transmission medium (hydraulic oil) during the flow process, there is a certain amount of heat inside the liquid. There is internal friction, and there is also friction between the liquid and the inner wall of the pipeline. These are the reasons for the increase in the temperature of the hydraulic oil. The increase in temperature will cause internal and external leakage to increase and reduce its mechanical efficiency. At the same time, due to the higher temperature, the hydraulic oil will expand, resulting in increased compressibility, making the control action unable to be transmitted well. Solution: Heating is an inherent characteristic of the hydraulic system and cannot be eradicated but can only be mitigated as much as possible. Use good quality hydraulic oil, avoid elbows in the layout of hydraulic pipelines, and use high-quality pipelines, pipe joints, hydraulic valves, etc.
2. Vibration Vibration in the hydraulic system is also one of its chronic diseases. The impact caused by the high-speed flow of hydraulic oil in the pipeline and the impact caused by the opening and closing of the control valve are all causes of system vibration. Strong vibration will cause errors in system control actions, and may also cause errors in some of the more precise instruments in the system, leading to system failure. Solution: The hydraulic pipeline should be fixed as much as possible to avoid sharp bends. Avoid frequent changes in the direction of liquid flow, and take vibration reduction measures when unavoidable. The entire hydraulic system should have good vibration reduction measures, and at the same time, the impact of external vibration sources on the system should be avoided.
3. Leakage Leakage in the hydraulic system is divided into internal leakage and external leakage. Internal leakage refers to the leakage process occurring inside the system, such as leakage on both sides of the hydraulic cylinder piston, leakage between the control valve spool and the valve body, etc.
Although internal leakage will not cause loss of hydraulic oil, due to the occurrence of leakage, the established control actions may be affected until it causes system failure. External leakage refers to leakage that occurs between the system and the external environment. Direct leakage of hydraulic oil into the environment will not only affect the working environment of the system, but also cause insufficient system pressure and cause failure. Hydraulic oil leaking into the environment also poses a fire hazard. Solution: Use better quality seals to improve the processing accuracy of the equipment.
Another: Regarding the three major diseases of the hydraulic system, someone has summarized: "Fever, diarrhea and diarrhea" (the summarizer is from the Northeast)
Hydraulic system
p>Used in lifts, excavators, pumping stations, dynamic compactors, cranes, and other large industries, construction, factories, enterprises, as well as lifts, lifting platforms, boarding bridges and other industries.