Actuator
액추에이터
The part that actually moves a robot's joints. It is the robot's muscle.
Overview
Even when a robot's brain decides "raise the arm," it is the actuator that makes the force and lifts it. The most common kind is an electric motor combined with a gearbox. When a lot of force is needed, oil pressure (hydraulics) is sometimes used instead.
A single humanoid contains dozens of actuators. They must be small and light yet strong, precise and long-lasting, so they are hard to make and take up a large part of a robot's price.
An everyday example
Compared with the human body, the brain is the AI, the eyes are cameras, and the muscles and joints are actuators.
Why it matters
How forceful and delicate a robot's movement is gets decided here. The more robots are sold, the more attention also goes to the companies that make this part.