Actuators play a central role in the function of many automated machine systems and have been a staple in the aerospace industry for years. These devices control the movement of nearby machine elements by using one of several methods. In order to fully gain an understanding of how actuators are used in automation and other machines, it is necessary to learn the operating principles behind the various actuator types. In this blog, we will cover all the different variants of mechanical actuation, including linear, electric, magnetic, pneumatic, and others.
Actuators can be classified by the type of motion they provide or by their energy source. Most commonly, actuators are chosen based on their motion first, with other factors playing a minor role. We will now dive deeper into the two types of motion actuators provide.
As the name suggests, linear actuators provide motion on one axis, which may either be horizontal, vertical, or diagonal. The two most common moieties that may be found are rod-style and track-style. Rod-style actuators contain a pneumatic or electric-powered motor, which creates rotational movement upon a central shaft. As the shaft spins, it drives several gears to convert rotational motion into linear. In order to reverse the direction of the assembly, the motor must be equipped with a switch that is sensitive to the current being applied. As a result, loss of power or pneumatic pressure will cause the actuator to return to the resting position.
Track-style actuators are popular for industrial automation applications, owing to their higher precision capabilities. Instead of relying on an external shaft, these devices pair a motor with a coupling element capable of producing rotational motion. The coupling is also attached to a lead screw and nut, which drives a carriage to the desired position. Track-style actuators determine their direction and final position through one of two means. A controller-based approach utilizes a computer that keeps track of the number of coupling rotations and compares it with a defined set point. After reaching that set point, the system will automatically reverse its direction to avoid motor burnout or inadvertent collision. Alternatively, an optical sensor or mechanical limit switch may be used to control motion. These modalities are commonly employed in automation settings.
Rotary actuators are used to facilitate rotational motion or produce torque without displacement. Like linear actuators, these devices have two typical configurations. The rack-and-pinion actuators contain a gear that is acted upon by linearly-moving pistons. This gear is attached to an output shaft which is the actual component coming into contact with the target. Alternatively, vane-type actuators rely upon pneumatic or hydraulic pressure to automatically turn valves, dampers, or lifting equipment. These devices do not rely upon gears or linearly moving elements, helping extend their operational lifespan.
Both linear and rotational actuators may rely upon hydraulic power to provide motion. Although slower than other power sources, hydraulic actuators can readily deliver significant amounts of force from a nominal input. They can also support power transmission over long distances with ease due to hydraulic fluid compressibility. However, the hydraulic fluid must be regularly inspected for cleanliness and signs of leaking since contamination can severely decrease its efficacy.
Relying on compressed gas to create mechanical movement, pneumatic actuators are accurate and reliable devices. They are also markedly safer than other power options since their function is not dependent on ignition or electricity. As a result, pneumatic actuators are usually the first choice for any application dealing with flammable materials, such as natural gas.
Similar to pneumatic power, electric actuators deliver accurate and reproducible results. This fact makes them a viable choice for precision applications. They are also immune to the leakage and efficiency drops that plague hydraulic actuators.
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