Actuator

The hydraulic actuator consists of cylinder or fluid motor that uses hydraulic power to facilitate mechanical operation. The mechanical motion gives an output in terms of linear, rotatory or oscillatory motion. As liquids are nearly impossible to compress, a hydraulic actuator can exert a large force. The drawback of this approach is its limited acceleration.

The hydraulic cylinder consists of a hollow cylindrical tube along which a piston can slide. 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. The term double acting is used when pressure is applied on each side of the piston; any difference in pressure between the two sides of the piston moves the piston to one side or the other.[3]

Pneumatic rack and pinion actuators for valve controls of water pipes

Pneumatic actuators enable considerable forces to be produced from relatively small pressure changes. 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. Moreover, pneumatic actuators are safer, cheaper, and often more reliable and powerful than other actuators. These forces are often used with valves to move diaphragms to affect the flow of air through the valve.[4][5]

Electric valve actuator controlling a ½ needle valve.

An electric actuator may provide the actuation force/torque in one of several ways. Electromechanical actuators may be used to power a motor that converts electrical energy into mechanical torque. Another approach is an electrohydraulic actuator, where the electric motor remains the prime mover, but provides torque to operate a hydraulic accumulator that is then used to transmit actuation force in much the same way that diesel engine/hydraulics are typically used in heavy equipment.

Electrical energy is used to actuate equipment such as multi-turn valves, or electric-powered construction and excavation equipment.

When used to control the flow of fluid through a valve, a brake is typically installed above the motor to prevent the fluid pressure forcing open the valve. If no brake is installed, the actuator gets activated to reclose the valve, which is slowly forced open again. This sets up an oscillation (open, close, open ...) and the motor and actuator will eventually become damaged.[6]

Twisted and coiled polymer (TCP) actuator also known as supercoiled polymer (SCP) actuator is a coiled polymer that can be actuated by electric power.[7] A TCP actuator looks like a helical spring. TCP actuators are usually made from silver coated Nylon. TCP actuators can also be made from other electrical conductance coat such as gold. TCP actuator should be under a load to keep the muscle extended. The electrical energy transforms to thermal energy due to electrical resistance, which is also known as Joule heating, Ohmic heating, and resistive heating. As the temperature of the TCP actuator increases by Joule heating, the polymer contracts and it causes the actuator contraction.[7]

Actuators which can be actuated by applying thermal or magnetic energy to a solid-state material have been used in commercial applications. Thermal actuators can be triggered by temperature or heating through the Joule effect and tend to be compact, lightweight, economical and with high power density. These actuators use shape memory materials such as shape-memory alloys (SMAs) or magnetic shape-memory alloys (MSMAs).

A mechanical actuator functions to execute movement by converting one kind of motion, such as rotary motion, into another kind, such as linear motion. An example is a rack and pinion. The operation of mechanical actuators is based on combinations of structural components, such as gears and rails, or pulleys and chains.

• Comb drive
• Digital micromirror device
• Electric motor
• Electroactive polymer
• Hydraulic cylinder
• Piezoelectric actuator
• Pneumatic actuator
• Screw jack
• Servomechanism
• Solenoid
• Stepper motor
• Shape-memory alloy
• Thermal bimorph
• Hydraulic actuators

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:

• Screw: Screw jack, ball screw and roller screw actuators all operate on the principle of the simple machine known as the screw. By rotating the actuator's nut, the screw shaft moves in a line. By moving the screw shaft, the nut rotates.
• Wheel and axle: Hoist, winch, rack and pinion, chain drive, belt drive, rigid chain and rigid belt actuators operate on the principle of the wheel and axle. By rotating a wheel/axle (e.g. drum, gear, pulley or shaft) a linear member (e.g. cable, rack, chain or belt) moves. By moving the linear member, the wheel/axle rotates.[12]

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

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.

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.

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.

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