A linear actuator is a type of actuator (a mechanism that creates a mechanical motion) that create motion in a straight line, i.e. pushes or pulls. They can be found in all kinds of industrial machinery, as well as in common pieces of technology like valves or hydraulic car jacks.
If you’re building a robot, you will most likely want to use some sort of linear actuators. They are the simple mechanisms that will allow your robot to move, push, and perform other interactions with physical objects. In robotics, linear actuators are primarily used to move appendages like arms, legs, and head, but in more sophisticated machines they sometimes perform more precise operations like moving artificial eyes and lips.
Actuators used in robotics vary greatly in size and in appearance, but all of them share some qualities.
Types Of Linear Actuators
As with every technology, there are several subtypes of linear actuators. Each one has its own advantages and disadvantages, but generally, all of them can be used in robotics.
1. Pneumatic actuators
Being the oldest type of actuators, pneumatic actuators were very popular a while ago, but these days they are largely replaced by newer technologies. Pneumatic actuators are still in use, but they are quite unwieldy when compared to the other actuator types on this list, and also require frequent maintenance works.
2. Electric actuators
Smaller and more reliable than pneumatic ones, electric actuators open a huge number of possibilities for robot-building. They can last for a really long time and fit even into the smallest robot. Electric actuators are particularly useful in a situation when safety and reliability are especially important, such as in the case of robots designed to work in the medical field.
Certain types of electric actuators may be especially interesting for those engineers or even hobbyists who are building their own robots from scratch, as they greatly reduce the long-term cost of a project, and require less maintenance compared to their pneumatic analogs.
3. Piezoelectric actuators
While the phenomenon of piezoelectricity has been known and studied since the 18th century, piezoelectric actuators are a relatively new technological development. Piezoelectricity is a special type of electric charge that builds up in some materials when they are put under mechanical stress. Actuators that use this technology are usually extremely precise, but also tend to be very pricey, so for an average engineer, they may not be the best way to choose.
Examples of Simple Linear Actuators Usable in Robototechnics
There are too many ways to use a linear actuator to name all of them, but we selected several mechanisms that can be interesting to integrate into a robot.
The simplest example of a pneumatic muscle is a braided mesh tube with its ends clamped and a skinny balloon inside of it. When we inflate the balloon, it can’t expand along its length, and so expands radially and cause the braid to contract, pulling the tube’s ends together.
That’s the way human muscles works, but with robots, it can be used to further extent.
This mechanism may sound simple, but with proper materials, it can be utilized to a great effect.
With scotch yokes, you can turn the rotation motion provided by your robot’s motor into linear motion. This linear actuator consists of a rod with a rectangular cut in a “yoke” in the middle of it. A rotating wheel with a pin is inserted into the rectangular slot, and its turning causes the rod to move back and forth.
This technology is widely used in different reciprocating mechanisms.
Probably the simplest actuator, the pneumatic cylinder uses the force of pressurized gas (usually air) to apply a force. This was once a very popular actuator technology, as pneumatic cylinders are durable, strong and environment-friendly, and once pressurized are able to hold chosen position for an indefinite period of time without applying any additional force. However, they aren’t so widely used now that more effective actuators are available.
This mechanism can still present some interesting technical solutions, especially if you are new to robotics and want to begin with something simple.
Solenoids are a type of electric coils that can push or pull an iron plunger when energized. The plunger can also be spring-loaded, so once solenoids stop being energized it will return to its original position. This technology can be found in electric locks, such as those used in security doors and cars, as well as in old doorbells.
Motorized Threaded Rods
To make this simplest linear actuator, you will need only a threaded rod, a drill, and several matching nuts. Alternatively, you can use a stepper motor instead of a drill, which will make the mechanism more precise.
Linear actuators are used in robot-building from the very beginning, and things are definitely not going to change in the near future. As the use of robots in different areas become more and more widespread, the technologies that are used in robotics evolve and become more complex. We’ve already seen how pneumatic actuators were replaced by electrical ones, and more likely than not we’ll see how those will be replaced by piezoelectric actuators in their turn.
Linear actuators that are currently available on the market vary greatly in terms of size, cost, and capabilities, so it’s not that hard to find something that suits your needs.
Among different types of linear actuators, the best choice for the average project is to use electric actuators. The combination of reliability, affordability and low maintenance cost makes them very attractive to smaller companies and groups. However, if you want to build a robot capable of very precise manipulations and have the necessary resources, choose piezoelectric actuators instead.
Don’t be shy to apply simple yet effective technical solutions of your own design, such as those presented above as examples, because using your imagination is never a bad idea. And remember that for anything you can’t build from scratch, there are always online stores.