Actuator

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An actuator is a type of motor that is responsible for moving or controlling a mechanism or system.

It is operated by a source of energy, typically electric current, hydraulic fluid pressure, or pneumatic pressure, and converts that energy into motion. An actuator is the mechanism by which a control system acts upon an environment. The control system can be simple (a fixed mechanical or electronic system), software-based (e.g. a printer driver, robot control system), a human, or any other input.

History[edit]

Some of the earliest forms of actuation can be found as far back as Archimedes, who lived approximately between the years 287 B.C., and 212 B.C. What became known as Archimedes' screw was one of the first linear actuators used to haul water from boats.

Other early actuation methods included mechanisms with wooden screws designed to crush grapes into wine and olives into oil.

Types[edit]

Hydraulic[edit]

A hydraulic actuator consists of a cylinder or fluid motor that uses hydraulic power to facilitate mechanical operation. The mechanical motion gives an output in terms of linear, rotary or oscillatory motion. Because liquid is nearly incompressible, a hydraulic actuator can exert considerable force, but is limited in acceleration and speed.

The hydraulic cylinder consists of a hollow cylindrical tube along which a piston can slide. The term double acting is used when pressure is applied on each side of the piston. A difference in pressure between the two side of the piston results in motion of piston to either side. The term single acting is used when the fluid pressure is applied to just one side of the piston. The piston can move in only one direction, a spring being frequently used to give the piston a return stroke.

Pneumatic[edit]

Pneumatic rack and pinion actuators for valve controls of water pipes

A pneumatic actuator converts energy formed by vacuum or compressed air at high pressure into either linear or rotary motion. Pneumatic energy is desirable for main engine controls because it can quickly respond in starting and stopping as the power source does not need to be stored in reserve for operation.

Pneumatic actuators enables large forces to be produced from relatively small pressure changes. These forces are often used with valves to move diaphragms and so affect the flow of liquid through the valve.

Electric[edit]

An electric actuator is powered by a motor that converts electrical energy to mechanical torque. The electrical energy is used to actuate equipment such as multi-turn valves. It is one of the cleanest and most readily available forms of actuator because it does not involve oil.

Mechanical[edit]

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.

Examples and applications[edit]

In engineering, actuators are frequently used as mechanisms to introduce motion, or to clamp an object so as to prevent motion. In electronic engineering, actuators are a subdivision of transducers. They are devices which transform an input signal (mainly an electrical signal) into motion.

Examples of actuators[edit]

Circular to linear conversion[edit]

Motors are mostly used when circular motions are needed, but can also be used for linear applications by transforming circular to linear motion with a lead screw or similar mechanism. On the other hand, some actuators are intrinsically linear, such as piezoelectric actuators. Conversion between circular and linear motion is commonly made via a few simple types of mechanism including:

Virtual instrumentation[edit]

In virtual instrumentation, actuators and sensors are the hardware complements of virtual instruments.

Performance metrics[edit]

Performance metrics for actuators include speed, acceleration, and force (alternatively, angular speed, angular acceleration, and torque), as well as energy efficiency and considerations such as mass, volume, operating conditions, and durability, among others.

Force[edit]

When considering force in actuators for applications, two main metrics should be considered. These two are static and dynamic loads. Static load is the force capability of the actuator while not in motion. Conversely, the dynamic load of the actuator is the force capability while in motion. The two aspects are rarely have the weight capability and must be considered separately.

Speed[edit]

Speed should be considered primarily at a no-load pace, since the speed will invariably decrease as the load amount increases. The rate the speed will decrease will directly correlate with the amount of force and the initial speed.

Operating conditions[edit]

Actuators are commonly rated using the standard IP Code rating system. Those that are rated for dangerous environments will have a higher IP rating than those for personal or common industrial use.

Durability[edit]

This will be determined by each individual manufacturer, depending on usage and quality.

See also[edit]

References[edit]

  1. ^ Sclater, N., Mechanisms and Mechanical Devices Sourcebook, 4th Edition (2007), 25, McGraw-Hill

External links[edit]