Actuator: the "muscles" of robots and devices

An actuator is a device that creates motion or force: an electric motor, a servo, a hydraulic or pneumatic cylinder. If sensors are a robot's senses, actuators are its muscles.

Actuators are a robot's muscles

In plain words

Your brain decides to lift your arm, but your muscles do the lifting. Robots work the same way: the program decides, and the actuators move. Even your smartphone has tiny actuators: the vibration motor and the little motors that move the camera lenses for focusing and stabilisation.

How it works

The actuator receives a command from the controller - a signal to "turn", "extend" or "press".
Electric actuators turn current into rotation or linear motion.
Hydraulic and pneumatic ones use liquid or air pressure - they are very powerful.
A gearbox is often added to a motor to increase force and reduce speed.
Position sensors report back how far the actuator has moved.

Tiny actuators inside a smartphone

Where you'll see it

In robots (joints of robotic arms and humanoids), drones (propeller motors), cars (power windows, brakes), smartphones (vibration motor, autofocus, optical stabilisation) and smart homes (electric locks, blinds, water valves).

Does it matter when buying

In smartphone specs you see them as "optical image stabilisation" or a "linear vibration motor". In robots, the quality of the actuators determines strength, precision, smoothness and battery life. Actuators are among the most expensive parts of humanoid robots.

Myths

Myth: An actuator is just a motor. Reality: A motor is one type. There are also hydraulic, pneumatic and piezoelectric actuators and "artificial muscles".
Myth: The more powerful the actuator, the better the robot. Reality: What matters is the balance of force, weight, precision and power use.

FAQ

How is an actuator different from a sensor?

A sensor perceives; an actuator acts.

How many actuators does a humanoid robot have?

Usually several dozen - in every joint and in the fingers.

Are there actuators in a watch?

Yes, the vibration motor for notifications is an actuator too.