An actuator is a component of a machine that is responsible for moving or controlling a mechanism or system, by converting energy into motion. It is the mechanism by which a control system acts upon an environment. It can be a simple system, such as fixed or electronic, or software-based, such as robot control.
Motion is usually created by air, electricity or liquid. The types of motion created by actuators are linear, rotary or oscillatory.
The most common types of actuator are as follows:
Pneumatic actuators convert energy formed by a vacuum or compressed air at high pressure into either linear or rotary motion. The advantage of this type of actuator is that has a quick response time as the power source doesn’t need to be stored in reserve. Large forces can be produced from relatively small pressure changes.
Hydraulic actuators consist of a cylinder or fluid motor that uses hydraulic power to drive mechanical operation. The motion output can be linear, rotary or oscillatory. The cylinder consists of a hollow tube along which a piston can slide. Despite having limited acceleration, a hydraulic actuator can exert considerable force as liquids are virtually impossible to compress.
Hydraulic actuators can be either single acting – when fluid pressure is applied to one side of the piston only – or double acting – where pressure is applied on both sides.
An electric actuator is powered by electrical energy converted by a motor. Electrical energy is used to actuate equipment such as multi-turn valves. Its advantage is that it is one of the cleanest forms of actuator as no oil is required.
 Thermal or magnetic
These actuators tend to be compact, lightweight and with high power density. They are actuated by applying thermal or magnetic energy.
A mechanical actuator functions by converting rotary motion into linear motion to execute movement. It involves gears, rails, pulleys, chains and other devices to operate. An example is a rack and pinion mechanism.
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