The actuator is an essential and important part of the automatic control system. Its role is to accept the control signal sent from the controller, change the size of the controlled medium, so as to maintain the controlled variable in the required value or within a certain range. Actuators can be divided into three categories according to their energy forms. Pneumatic actuator uses compressed air as energy, which is characterized by simple structure, reliable action, stable, large output thrust, convenient maintenance, fire and explosion prevention, and low price. Therefore, it is widely used in chemical industry, paper making, oil refining and other production processes, and it can be conveniently used with passive instruments. Even when using electric meters or computer control, pneumatic actuators are still available when converting electrical signals through electric-gas converters or electric-gas valve positioners into standard air pressure signals of 20-100 kPa. The electric actuator has convenient energy use and rapid signal transmission, but the structure is complex and the explosion-proof performance is poor. Liquid actuator is basically not used in chemical, refining and other production processes, it is characterized by large output thrust.
At the gear level, the engine speed can be transmitted to the output bar by two sets of gears. The main reducer is completed by a planetary gear, and the secondary reducer is realized by a worm wheel, which is fixed in a central position by a set of strained springs. In the case of overload, that is, when the output rod exceeds the set torque of the spring, the central worm wheel will undergo axial displacement, fine-tuning of the switch and the signal device, to provide protection for the system. Subject to the coupling operated by the external change lever, the output lever is coupled to the worm wheel during the engine operates and is coupled to the hand wheel during manual operation. When the engine is not working, the engine can easily break the motor drive, and the hand wheel can be connected only by simply pressing the control lever. Since the motor drive is preferred over the manual operation, the reverse action automatically occurs when the engine starts again. This avoids opening the hand wheel when the engine is running, which is beneficial to protect the system.
