Hydraulic, pneumatic, electric transmission selection experience
1. The power to weight ratio is required to use hydraulic transmission
Since the working pressure of the hydraulic system can be higher (such as 32MPa or higher), the ratio of the corresponding transmission power to the weight of the actuator (hydraulic cylinder, hydraulic motor) is larger. The ratio of the power that can be transmitted by electrical transmission or pneumatic transmission to the weight of its actuator (motor, cylinder) is small, (for example, the weight of the hydraulic motor is only 10% to 12% of the same power motor). Therefore, hydraulic transmission should be selected in situations where the power to weight ratio is larger.
2. Electric drive should be used as far as possible for light load and high precision position control
In the case of small load and high control accuracy, it is best to use electrical transmission, because the control accuracy of electrical transmission is high, and the power supply is relatively easy to obtain (as long as the wire can be used). The corresponding hydraulic transmission and pneumatic transmission require hydraulic or air source, the establishment of hydraulic source and air source is much more complicated than the power supply, and the electrical transmission can also obtain higher control accuracy. Therefore, when the load is not large and the accuracy is high, the electric drive should be selected first.
3. Pneumatic transmission should not be used when the load is large and the response is fast
Because the pressure of the pneumatic transmission can not be too high (generally used air pressure is not greater than 1MPa), the driving load can not be too large. In addition, because the gas is compressible and the gas capacity is large, its response is slow, so when the dynamic response is fast, the pneumatic transmission can not meet the requirements.
4. Require stepless speed change and large speed range to use hydraulic transmission
The hydraulic system can achieve the purpose of variable speed as long as the flow rate is adjusted. Generally, the speed control valve can be used to achieve stepless speed change, and the adjustment range is relatively large, such as the speed control range of the hydraulic system can reach more than 200, and the motor speed control range is only about 20.
5. It is not suitable to use pneumatic transmission when low speed and high stability are required
Pneumatic transmission because the pressure is not high, so the load can not be too large. Relatively speaking, the proportion of friction in the total load is larger than the proportion of hydraulic or electrical transmission. And the change of friction at low speed is also large (especially when dynamic friction and static friction are exchanged (or repeatedly)), so at low speed, pneumatic equipment is prone to crawling, and because of the compressibility of gas, it aggravates the production of crawling. Therefore, it is not appropriate to use pneumatic transmission in the case of low speed and high stability, and it is appropriate to use hydraulic transmission.
6. Pneumatic or hydraulic transmission should be used for linear reciprocating movement
Since the motor output is rotary motion, if the load is required to make linear reciprocating motion, it is necessary to add a mechanical mechanism (such as pinion and rack mechanism), the rotational motion of the motor output is transformed into linear motion, and the hydraulic cylinder or cylinder is generally made linear reciprocating motion, so it can directly drive the load to make linear reciprocating motion, so the structure is simple.
7. Pneumatic transmission is not suitable for systems requiring large stiffness
Because the compressibility of the gas is large, the stiffness of the pneumatic system is smaller than that of the hydraulic system, so the system requiring large stiffness is not suitable for pneumatic transmission, but for hydraulic transmission.
8. Pneumatic and hydraulic transmission should not be used on occasions requiring high efficiency
Because the flow regulation of the hydraulic system and the pressure system is mostly throttled, the resistance loss is large, so the efficiency is low, and the efficiency of the whole system is generally not more than 50%. Even if the volume speed regulation is used, its total efficiency will not exceed 85%, and the total efficiency of the electrical transmission plus gear transmission system can often reach more than 90%, so it is appropriate to use electrical transmission in the case of high efficiency, and it is not appropriate to choose hydraulic or pneumatic transmission.
9. Electric and hydraulic transmission should not be used for ultra-high speed rotation or reciprocating motion, and pneumatic transmission should be selected
To make the motor rotate at high speed, it is necessary to increase the speed gear device, and the volume of friction is also large when the growth rate is larger. Hydraulic transmission is also not easy to get too high a speed. Only pneumatic transmission can have a high flow rate because of the small gas viscosity and low resistance. Therefore, the movement speed can be very high, such as the speed of the pneumatic internal grinding head can reach 100000r/min, and the number of impacts of the pneumatic rock drill can reach 3,500 reciprocating times per minute.
10. Low speed and large torque occasions should not use pneumatic and electrical transmission, should choose hydraulic transmission
In the case of low speed and large torque, the pneumatic transmission is not easy to obtain a large torque, and the electrical transmission is not easy to obtain a stable low speed (the reducer must be added). Only in the hydraulic transmission system using low speed high torque hydraulic motor, can achieve the low speed high torque requirements, the minimum stable speed can reach 1 r/min, the maximum torque can be greater than 40000N·m.
11. Air pressure and hydraulic transmission are used for overload protection
Hydraulic and pneumatic transmission systems can be easily protected against overload with safety valves. And after the end of the overload can automatically continue to operate, do not need to restart. The electrical or mechanical transmission overload protection device is more complex, and often must be restarted after the end of the overload.
12. Pneumatic and hydraulic transmission should not be used on occasions with strict transmission ratio requirements
Because the internal and external leakage of the hydraulic system changes with the working pressure and temperature, its transmission ratio is difficult to keep constant. As for pneumatic transmission, it is more difficult to maintain a constant transmission ratio due to the large compressibility of air. Therefore, hydraulic and pneumatic transmission can not maintain a strict transmission ratio as mechanical transmission.
13. Hydraulic transmission is not suitable for long-distance power transmission
Because the power transmission of hydraulic transmission is achieved by pipelines. Therefore, the length of the pipeline will be long when it is transmitted over long distances. The installation layout is inconvenient and the cost increases. In addition, the power loss of the pipeline is also large. Therefore, it is best to use electrical transmission when transferring power over long distances.
14. Hydraulic transmission should not be used in harsh environments
Winter temperatures below -25 °C, even if the use of anticoagulant hydraulic oil, field operation of hydraulic equipment can not work reliably. If you work under this condition, it will bring varying degrees of damage to the parts in the pump and the hydraulic cylinder seals. Flammable and explosive, dust and water and other harsh environments are generally not suitable for hydraulic transmission.
The viscosity of hydraulic oil is related to temperature, and the higher the temperature, the smaller the viscosity. Therefore, when the temperature changes greatly, the viscosity changes greatly, the corresponding system leakage changes greatly, and the flow resistance of the pipeline changes greatly (because the flow resistance is proportional to the viscosity). Therefore, when the temperature change of the originally adjusted parameter is large, the parameter change is also large, resulting in temperature drift. The control precision of the system is reduced accordingly.