When do you choose hydraulic transmission, pneumatic transmission, or electrical transmission?

1.When the power to weight ratio requirement is high, hydraulic transmission should be used because the working pressure of the hydraulic system can be higher (such as 32MPa or higher), so the corresponding transmission power to the weight ratio of the actuator (hydraulic cylinder, hydraulic motor) is larger. The ratio of the power that can be transmitted by electrical or pneumatic transmission to the weight of its actuator (electric motor, cylinder) is relatively small (for example, the weight of a hydraulic motor is only 10% to 12% of that of an electric motor of the same power). Therefore, hydraulic transmission should be selected in situations where power to weight ratio requirements are high.

2. For light load high-precision position control, it is advisable to use electrical transmission as much as possible. In situations where the load is not large and high control accuracy is required, 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 wires are used). The corresponding hydraulic and pneumatic transmission require hydraulic or air sources, and the establishment of hydraulic and air sources is much more complex than power supply. Electrical transmission can also achieve high control accuracy. Therefore, when the load is not large and the accuracy requirement is high, electrical transmission should be chosen first.

3. When the load is large and the response requirements are fast, pneumatic transmission should not be used because the pressure of pneumatic transmission cannot be too high (usually the air pressure is not greater than 1MPa), so the driving load force should not be too large. In addition, due to the compressibility of gases and their large capacity, their response is slower. Therefore, when fast dynamic response is required, pneumatic transmission cannot meet the requirements.

4. It is recommended to use hydraulic transmission hydraulic system when continuously variable speed and wide speed range are required. As long as the flow rate is adjusted, the goal of variable speed can be achieved. Generally, stepless speed change can be achieved using a speed control valve, and the adjustment range is also relatively large. For example, the speed control range of a hydraulic system can reach over 200, while the speed control range of an electric motor is only about 20.

5. When low speed and high stability are required, pneumatic transmission should not be used. Due to the low pressure, the load should not be too large. Relatively speaking, the proportion of friction in the total load is larger than that of hydraulic or electrical transmission. Moreover, there is a significant change in friction force at low speeds (especially when dynamic friction and static friction are mutually (or repeatedly) converted). Therefore, at low speeds, pneumatic equipment is prone to crawling, and due to the compressibility of gas, crawling is even more pronounced. Therefore, in situations where low speed stability is required, pneumatic transmission should not be used, and hydraulic transmission should be used instead.

6. Linear reciprocating motion should be driven by pneumatic or hydraulic transmission. As the output of the electric motor is a rotational motion, if a load is required to perform linear reciprocating motion, a mechanical mechanism (such as a gear rack mechanism) must be added to convert the rotational motion output by the electric motor into linear motion. Hydraulic cylinders or cylinders generally perform linear reciprocating motion, so they can directly drive the load to perform linear reciprocating motion, making the structure simple.

7. Systems that require high stiffness should not use pneumatic transmission. Due to the high compressibility of gas, the stiffness of pneumatic systems is smaller than that of hydraulic systems. Therefore, systems that require high stiffness should not use pneumatic transmission, but rather hydraulic transmission.

8. In situations where high efficiency is required, pneumatic and hydraulic transmission should not be used. As the flow regulation of hydraulic and pneumatic systems is mostly throttling, the resistance loss is large, and therefore the efficiency is low. Generally, the overall system efficiency does not exceed 50%. Even if volumetric speed regulation is used, the total efficiency will not exceed 85%, while the total efficiency of electrical and gear transmission systems can often reach over 90%. Therefore, electrical transmission is suitable for fields that require high efficiency, and hydraulic or pneumatic transmission is not suitable.

9. Electrical and hydraulic transmission should not be used in situations of ultra high speed rotation or reciprocating motion. Pneumatic transmission should be used to make the electric motor rotate at high speed. A speed increasing gear device must be added, and when the speed increasing ratio is large, the volume is large and the friction force is also high. Hydraulic transmission is also not easy to achieve too high operating speed. Only pneumatic transmission can have high flow rates due to its small gas viscosity and resistance. Therefore, the movement speed can be very high. For example, the speed of the pneumatic inner grinding head can reach 100000 r/min, and the impact frequency of the pneumatic rock drill can reach 3500 reciprocating times per minute.

10. In situations with low speed and high torque, pneumatic and electrical transmission should not be used. Hydraulic transmission is preferred for situations with low speed and high torque. Pneumatic transmission is not easy to obtain high torque, while electrical transmission is not easy to obtain stable low speed (additional acceleration and deceleration must be added). Only by using low-speed and high torque hydraulic motors in hydraulic transmission systems can the requirements of low-speed and high torque be achieved, with a minimum stable speed of 1 r/min and a maximum torque of over 40000 N · m.

11. In situations where overload protection is required, pneumatic and hydraulic transmission hydraulic transmission and pneumatic transmission systems can be easily implemented with safety valves for overload protection. And after the overload ends, it can automatically continue to operate without the need for a restart. However, the overload protection device for electrical or mechanical transmission is relatively complex, and it often needs to be restarted after the overload ends.

12. In situations where the transmission ratio is strictly required, pneumatic and hydraulic transmission should not be used because the internal and external leakage of the hydraulic system varies with the working pressure and temperature, making it difficult to maintain a constant transmission ratio. As for pneumatic transmission, due to the high compressibility of air, it is more difficult to maintain a constant transmission ratio. So hydraulic and pneumatic transmission cannot maintain strict transmission ratios like mechanical transmission.

13. Hydraulic transmission is not suitable for long-distance power transmission, as the power transmission of hydraulic transmission is achieved through pipelines. Therefore, the length of the pipeline will be very long during long-distance transmission. The installation and layout are inconvenient and the cost increases. In addition, long pipelines also result in significant power loss. So it is best to use electrical transmission when transmitting power over long distances.

14. In harsh environments, hydraulic transmission should not be used. In winter, temperatures can reach below minus 25 ° C. Even if anti condensation hydraulic oil is used, hydraulic equipment for field operations cannot work reliably. If working under these conditions, it will cause varying degrees of damage to the parts in the pump and the hydraulic cylinder seals. Hydraulic transmission is generally not suitable for harsh environments such as flammable, explosive, dusty, and watery environments. The viscosity of hydraulic oil is related to temperature, and the higher the temperature, the lower the viscosity. Therefore, when the temperature changes greatly, the viscosity also changes greatly, and the corresponding system leakage also changes greatly. At the same time, the flow resistance of the pipeline also changes significantly (because the flow resistance is proportional to the viscosity). Therefore, when the temperature changes significantly, the originally set parameters also undergo significant changes, resulting in temperature drift. Reduce the control accuracy of the system accordingly.