1. Power to weight ratio is required to adopt hydraulic transmission
As the working pressure of the hydraulic system can be higher (for example, 32MPa or higher), so the corresponding transmission of power and actuators (hydraulic cylinders, hydraulic motors) is greater than the ratio of weight. Electrical transmission or pneumatic transmission can transmit power, and its actuators (motors, cylinders) are smaller than the weight ratio, (for example, the weight of the hydraulic motor is only 10% to 12% of the same power motor). Therefore, in the power to weight ratio requirements of the occasion should be selected hydraulic transmission.
2. Require stepless speed change, large speed range is appropriate to use hydraulic transmission
If the hydraulic system can adjust the flow, it can achieve the purpose of stepless speed regulation. Generally, the speed regulating valve can achieve stepless speed change, and the adjustment range is relatively large. For example, the speed regulation range of the hydraulic system can reach more than 200, while the speed regulation range of the motor is only about 20.
3. Linear reciprocating motion should be pneumatic or hydraulic drive
As the motor output is rotary motion, such as the load for linear reciprocating motion, it is necessary to add mechanical institutions (such as rack and pinion institutions), the motor output of rotary motion into a linear motion, and hydraulic cylinders or cylinders are generally used for linear reciprocating motion, so the load can be driven directly for linear reciprocating motion, so the structure is simple.
4. Low-speed large torque occasions should not use pneumatic and electrical transmission; it is appropriate to use hydraulic transmission
For low-speed large torque occasions, pneumatic transmission is not easy to obtain a large torque, and electrical transmission is not easy to obtain a stable low speed (must add another reducer). Only in the hydraulic transmission system using low-speed large torque hydraulic motor, to achieve the requirements of low-speed large torque, the minimum stable speed of up to 1 r/min, the maximum torque can be greater than 40,000N-m.
5. Pneumatic drives are not suitable when low speed and high stability are required.
Pneumatic drive because the pressure is not high, so the load cannot be too large. Relatively speaking, the proportion of friction in the total load is larger than the proportion of hydraulic or electrical drives. And low-speed friction changes are also larger (especially dynamic friction and static friction each other (or repeatedly) when converted), so at low speeds, pneumatic equipment is prone to crawling phenomenon, but also because of the gas has compression, more exacerbated by the generation of crawling. Therefore, the requirements of low-speed stability of the occasion should not be used pneumatic transmission, it is appropriate to use hydraulic transmission.
6. Ultra-high-speed rotation or reciprocating motion of the occasion should not be used in electrical and hydraulic transmission; pneumatic transmission should be used.
To make the motor rotate at high speed, speed up the gear device must be added to speed up the gear device, speed up the ratio of large volume of friction is also large. Hydraulic drive is not easy to obtain too high a running speed. Only the pneumatic drive due to gas viscosity
Only pneumatic transmission due to gas viscosity small resistance, can have a very high flow rate. Therefore, the movement speed can be very high, such as pneumatic internal grinding head speed up to 100000r/min, pneumatic rock drill impact up to 3500 times per minute reciprocating.
7. Pneumatic and hydraulic drives are used where overload protection is required.
Hydraulic and pneumatic drive systems can be simply overload protected with safety valves. And after the end of the overload can automatically continue to run, do not need to restart. The electrical or mechanical transmission overload protection device is more complex and often must restart after the end of the overload.
8. Load large response requirements should not be used when the pneumatic drive
As the pressure of the pneumatic drive cannot be too high (generally used gas pressure is not greater than 1MPa), so the driving load force cannot be too large. In addition, due to gas compression, gas capacity is larger, so its response is slower, so the dynamic response requirements fast, pneumatic drive cannot meet the requirements.
9. Require a large stiffness of the system should not be used pneumatic transmission
Because of the compression of the gas, the rigidity of the pneumatic system is smaller than the hydraulic system, so the rigidity of the system should not be used pneumatic transmission, and it is appropriate to use hydraulic transmission.
10. Require high efficiency occasions should not be used pneumatic and hydraulic transmission
Due to the hydraulic system and pneumatic system flow regulation mostly with throttle type, resistance loss is large, so the efficiency is low, the general efficiency of the whole system is not more than 50%. Even with volumetric speed control, its total efficiency will not exceed 85%, while the total efficiency of the electrical transmission and gearing system can often reach more than 90%, so the high efficiency requirements of the occasion are appropriate to use the electrical transmission, should not be used in the selection of hydraulic or pneumatic transmission, should be considered electrical transmission.
11. light load high-precision position control should try to use electrical transmission
In the load is not large but requires high control accuracy occasions, it is best to use electrical transmission, because the control accuracy of electrical transmission is higher, the power supply is easier to obtain (if the wire can be). Corresponding hydraulic transmission and pneumatic transmission requires a hydraulic source or gas source, the establishment of the hydraulic source and gas source is much more complex than the power supply, the electrical transmission can also obtain a high degree of control accuracy. Therefore, the load is not large and high precision requirements should be the first choice of electrical transmission.
12. Ratio requirements for strict occasions should not be used pneumatic and hydraulic transmission
As the hydraulic system of internal and external leakage with the working pressure and temperature changes, it is difficult to maintain a constant transmission ratio. As for pneumatic transmission, due to the compressibility of air, it is more difficult to maintain a constant transmission ratio. Therefore, hydraulic and pneumatic transmission is not as mechanical transmission can maintain a strict ratio.
13. Hydraulic drive is not suitable for power transmission over long distances
Since the power transmission of the hydraulic drive is realized by piping, the length of the piping will be very long for long-distance transmission. Therefore, the length of the pipeline will be very long for long-distance transmission. Installation is not convenient and cost increases. In addition, the power loss of the long pipeline is also large. Therefore, it is best to use electrical transmission to transmit power over long distances.
14. The use of hydraulic transmission is not suitable for harsh environments
Winter temperatures reach minus 25 ° C or less, even with anticondensation hydraulic oil, field operation of hydraulic equipment cannot work reliably. If working under these conditions, the pump parts and hydraulic cylinder seals will bring different degrees of damage. Flammable and explosive, dusty and watery environments are generally not suitable for hydraulic transmission.
Hydraulic oil viscosity and temperature, the higher the temperature, the smaller the viscosity. Therefore, when the temperature change is large, the viscosity change is also large, the corresponding system leakage change is also large, while the pipeline flow resistance change is also large (because the flow resistance is proportional to the viscosity). Therefore, the original tuning parameters in the temperature changes in the parameters of the larger changes are also large, resulting in temperature drift. The control accuracy of the system is reduced accordingly.