23 Jan 2018

A non-boring guide to actuators


Ever seen a Transformers movie? Well, who hasen’t? Have you ever wondered what makes the giant robots on the screen work, though? Apart from the power of imagination, they are able to move because of actuators!

But what are actuators? Where are they used? In this article, we will try to answer these, and other questions

What are actuators?

An actuator is a part of a machine that produces motion by converting one type of energy to another. In order to work, actuators require two things: a control signal and an energy source, which can be either pneumatic pressure, hydraulic fluid pressure, or electrical energy..

There are four main types of actuators, which we’re going to describe below.

Hydraulic actuators

Hydraulic actuators consist of a cylinder and a piston. Fluids are hard to compress, therefore such actuators can exert a huge amount of force.

In linear hydraulic actuators, fluid is used to extort or ease the pressure on the piston, which in turn generates linear movement.

When it comes to rotary hydraulic actuators, apart from a cylinder mechanism, gearing and output shafts are added to achieve a rotary movement.

Pneumatic actuators

Pneumatic actuators are very similar to hydraulic ones in terms of construction and features. The only difference is that they use air or gas pressure to generate movement.

Mechanical actuators

Mechanical actuators convert rotary to linear motion. A good example is the rack and pinion mechanism.

Electrical actuators

Electrical actuators are powered by an electrical current. They normally consist of a motor, a linear or rotary guide and a drive mechanism.

Electric actuators achieve a linear or rotary motion. The electric energy is converted into movement through mechanical transmission, electromagnetism or thermal expansion.

Applications of actuators

The most basic examples of actuators can be found all around us. One of the simplest examples is a retractable ballpoint pen. The mechanism that ejects the tip of the pen is a simple human-powered actuator with a spring that facilitates a return motion.

Car brakes are another application of actuators that can be found in our everyday life. In order for a car to stop, a driver pushes the brake pedal, which acts on the brake pads via a system of actuators, causing the car to stop. In this case, the human power input is the control signal and hydraulic pressure is the energy source.

Actuators can have some exciting hi-tech applications too! Recently, a team of Harvard scientists developed artificial muscles, which can be used in constructing robots. The simple construction design is based on origami structures and is very easy to make. The actuator in this structure is a mechanism that pumps air or fluid in or out causing the ‘muscle’ to contract or expand.

What is more, as the scientists claim, the materials for making such a ‘muscle’ can cost as little as $1!. The muscle can carry up to 1000 times its own weight. Imagine a person holding up a fully loaded truck – that can put things in a perspective! Going further – imagine what possibilities does the construction give for the future of robotics, which heavily rely on actuators in order to facilitate machine movement.

Each of the actuator types we’ve described earlier has its own, unique applications. It’s important to understand the differences.

Hydraulic actuators

Because of the huge amount of power, which can be produced with fluid pressure, hydraulic actuators are often used in the aerospace industry. Neither human nor other types of actuators can produce sufficient power, therefore hydraulic solutions are the best for this purpose.

Hydraulic actuators are also used in renewable energy devices as a means to capture energy and facilitate highly powerful and precise movement.

Other applications of hydraulic actuators include earth-moving equipment, factory automation devices and even rides at amusement parks.

Pneumatic actuators

Because air and gases are easier to compress than fluids, pneumatic actuators produce less power. They are used in automobile engines, nail guns, air compressors, pumps and various (as well as countless) industrial machines.

Mechanical actuators

Examples of mechanical actuators are: screws, wheels and axles (found in anchors) and cams. They are usually simple machines, often operated by human power.

Electrical actuators

Electrical actuator solutions are applied in many areas, from heavy duty construction and earth-moving equipment, factory automation, defense, agriculture and even medium-sized consumer products.

Actuators vs ball screws

Ball screws, similarly to mechanical actuators, convert rotary into linear motion. They are incredibly efficient, as the friction is reduced. Ball screws are, however, the more expensive option. They also require much more care than actuators, especially when it comes to lubrication and keeping the mechanism clean at all times. A tiny bit of dirt may drastically lower the efficiency or even destroy the whole mechanism.

Overall, ball screws are the efficient, expensive and high-maintenance solution.