Actuator

An actuator is a component that is capable of moving and controlling a mechanism or system. It requires a control signal and a source of energy, generally electrical power, but could also be hydraulic power. The control signal is usually a low-energy electric voltage or current. When it receives a control signal, an actuator responds by converting the energy into mechanical motion.

Thus, digital or analog signals from processors, or even directly from sensors, can act as control signals for an actuator and change the state of the machine they are controlling.

Actuators generally provide controlled and limited movements or positioning. The two basic motions are linear and rotary. Linear actuators convert energy into straight-line motion, typically for positioning applications. They usually have a push and pull function. Rotary actuators convert energy to provide rotary motion. Each actuator type has versions for different power configurations and comes in many styles and sizes depending on the application.

One of the most common types of rotary actuators is the servomotor. While a motor rotates continuously and fully in one direction, a servomotor rotates in small increments in either direction depending on the control signal provided. For example, in an electric airplane, a motor will drive the propeller which rotates continuously in one direction. But a servomotor (acting as an actuator) will move the control surfaces (ailerons, rudder, and elevators) which need small, controlled movements in both directions.

Servomotors are also used in robots, to move parts of the robot in small movements in multiple directions.

This is a schematic of a linear actuator. When the electric current is passed through the coil it creates a magnetic field that pulls up the armature and the stem. When the current stops, the spring pushes the armature and stem back down.