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An electric actuator is a device used to provide actuation for secondary equipment using an electric motor. The output of this type of actuator may be linear or rotary, and, in the case of rotary actuators, can produce more than one complete rotation. Most linear electric actuators make use of a gear arrangement to extend and retract the actuation arm. Rotary types also use gears, cams, or direct connections to transfer motion depending on the application torque requirements. Electric actuators are used in a wide range of applications including controllers for doors and vents, valves, and machining processes.
An actuator may be thought of as a remote switch used to produce a fairly wide range of motion. They are used in applications where many switching or actuation functions are required in remote locations, in environments where it would be hazardous for an operator to work, and in applications requiring high-torque outputs. Actuators use various power sources, including compressed air, high pressure oil, and electric motors. The electric actuator utilizes an internal alternating current (AC) or direct current (DC) electric motor, and provides its actuation as a linear or rotary output. When stepper motors are used, these actuators can return extremely accurate actuation for precise engineering applications.
Linear electric actuator types provide a straight-line action used to open and close vanes, shutters, or doors, and move parts of machinery during operation. The high-speed rotation of the motor is translated into a slower and more powerful linear movement via a gear arrangement or lead screw. Linear actuator gears are generally worm or rack-and-pinion types, although ball and screw mechanisms are sometimes used. Lead screw actuators use a rod threaded with a coarse, square thread which revolves in a nut with a corresponding thread. As the rod rotates, the nut moves up and down its length to supply the necessary linear motion.
The rotary electric actuator generally supplies low-speed, high-torque rotary actuation of valves and machine processes. An electric rotary actuator does not have the same range of output limitations typical of rotary hydraulic actuators and can supply an infinite number of turns during any given cycle. This makes them ideal for applications such as gate valve actuation, where valves may require several hundred turns to fully open or close. Rotary electric actuators are usually geared to produce higher torque values at lower speeds. Both rotary and linear electric actuator variants generally employ travel limit switches that control their range of actuation.
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