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An Introduction To Actuators: Part I

An Introduction To Actuators: Part I

Adam Morissette
Adam Morissette
PA Engineer
An actuator is a motor that transfers energy from whatever is powering it into motion. This explanation may sound simplistic, but at heart that's what it does. Within that simplicity lies a great deal of utility; the majority of modern devices that involve motion of any kind could not exist without these components. For example:

In NASA's Mars Rover: It's full of actuators. The most important power the wheels and the sample collection tool. They are so important that NASA actually tests to double their rated specifications and lifetimes before signing off on them.

In Your Car: Have power locks or power windows? Those are linear motors providing all that motion. Cruise Control? Same thing. The modern automobile has over 100 actuators in it, helping you steer, brake, adjust your mirrors, pop your headlight covers, adjust your seat, trim the air vents, or even just to make the windshield wipers move. And in the trunk you probably have a car jack, which is another kind of linear device.

In Your Robots: Just about every robot you've ever seen requires linear motion tech to function. Moving the arms, legs, eyes, and head. Honda's ASIMO robot contains three very powerful ones to allow it to walk. And yes, this includes the Roomba.

In Your Movies: Nearly every mobile prop in a Hollywood film has actuators in it, including robots. When a car flies in the air after an explosion? That's usually a really big actuator that's triggered at the same time as the explosion, sending that thing flying.

In Your iPhone: Inside every vibrating phone is a mini-actuator, which rattles back and forth rapidly to create that signature buzzing.

The list could go on and on. The problem with these devices is that they do so much, and in so many different ways, that's it hard to wrap your head around how they actually work. Let's revisit the original definition: A motor that transfers energy from whatever is powering it into motion. After reading some of the examples above that should hopefully make more sense; the iPhone takes battery power and makes an actuator fire rapidly within it, the result is a back and forth vibratory motion. The new Mars Rover 'Curiousity' takes energy from a Plutonium mini-generator, and uses it to power the devices in the wheels, resulting in forwarding motion. The Hollywood stunt car flipper takes energy from a compressed gas (usually nitrogen) and moves once, very powerfully, causing the car to fly into the air. All of these examples use different power sources, fire off the actuator at different rates, and all have markedly different effects. A simpler description would be a linear cylinder is a thing that makes other things move.

How does it work?

There are as many kinds of actuators as there are automation applications for them, but each of them is based around one of the classic simple machines (screw, wheel and axle, lever, wedge, pulley, etc.). Examining each of these in detail would take quite a while, and is beyond the scope of this article. Instead, let's jump straight into the screw design.

The way it works is you have a screw, and on the screw is a nut. By holding the nut still in one hand, and turning the screw with the other, you are generating linear motion in the screw itself (e.g. it travels back and forth in a straight line depending on which direction you are turning it). This is an elegant solution because you are converting rotational motion (the force exerted on the screw) into linear motion (the screw bolt traveling through the nut), in a remarkably small space. There's also a lot of flexibility present, since you can change the pitch of the screw threads, the length of the bolt, the size of the nut, etc.

The classic machine example above translates easily into modern engineering. Instead of holding the nut tight with your hand, it's encased in a tubular mounting that moves up and down with the nut. Instead of turning the screw with your other hand, it can be linked up to simple 12 volt DC electric motor. The motor turns the screw, the screw in turn moves the nut up/down its length. You now have a basic device that can be used in a variety of ways.

This article is Part I of a continuing series; Read next part here.

Can you guess how many actautors were used to make this entire process a reality?

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