Actuators are devices that cause a machine or another linked device to operate. In a way, you can consider actuators to be the “muscles and tendons” in mechanical and electrical systems. In simple terms, a rotary actuator uses a rotary motion while a linear actuator goes in a path (contrary to the name, the path is usually but not always a straight line.)
Of course, this can be overly simplistic, as in practice there are countless different types of rotary and linear actuators. In many cases, linear and rotary actuators are connected through levers and pulleys to translate motion and transmit force, so at times it is less clear whether a device is a linear or rotary actuator.
In practice, whatever the end result of the different actuators in an assembly determines whether it is rotary or linear. For instance, a component that uses a linear actuating component to move a rotary actuator is still normally defined as a rotary actuator as the assembly outputs a rotational force.
By way of example, screws are considered to be simple linear actuators, converting rotary motion into forward motion. Rack and pinion assemblies can be either, depending on what force is being outputted.
Both linear and rotary actuators also come in several types. They can be powered by pneumatics, hydraulics, magnets, electricity, vacuum, materials expansion, human power, among many others. No type is necessarily better than the other, and it’s all dependent on the design of the device as well as its application.
Common examples of rotary actuators
Here are a few rotary actuators you’re likely to find around your home:
Electric motors come in several different varieties and are used in a wide array of household items. They are used in fans, food processors, air compressors, and clocks. Hundreds of them may also be present in your vehicle as well. Notably, they are essential for conventional turbine-based power generation systems.
Fluid pressure gauges
Typical gauges for fluid pressure in vehicles and other applications use a simple rotational actuator that uses the pressure of the fluid to move an indicator marking.
Both vehicles and mechanical watches use combinations of rotating gears so that the power provided to the assembly is translated to different forces and speeds as needed by the application.
Ball and roller bearings
These are used in virtually all heavy equipment to reduce friction and help support axial and radial loads.
Common examples of linear actuators
Here are a few types of linear actuators you may be interacting with on a day-to-day basis:
Sliding doors and windows
These can be very simple systems based on human power, as you might find in your home, or fairly complex such as those found in the power windows in your car.
Reciprocating power tools such as jackhammers, hammer drills, and reciprocating saws use linear actuators to allow their type of motion.
While most engines are ultimately rotary actuators because they are meant to turn wheels, propeller screws, or electric generators, the pistons in your engine are, of course, a type of linear actuator.
While relatively simple individually, when combined, rotary and linear actuators can be used to perform a variety of incredibly complex functions — most of which we take for granted. Both types of actuator are critical to how modern devices function and virtually everything with moving parts will employ both types of actuators in their design.
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