An actuator, by definition, is any device that controls or causes another device to move or operate. In principle, an actuator converts a control signal into mechanical action, like what happens in an electric motor or the read/write arm assembly of a hard disk drive.
The control signal can be pneumatic, electric, hydraulic, thermal, or mechanical in nature, but nowadays typically actuators are being driven by digital control signals via the use of software solutions.
There are actually many different variations of actuators available today, but here are some of the common ones:
There are three main types of actuators, although they can be differentiated further into other subtypes:
An electric actuator can produce the force or torque actuation in several different ways, but the main principle is that electrical energy is used to actuate the movement. This is mainly done by using an electric motor and a control system to convert electrical energy into torque or linear force.
We can also combine electric energy with other types of energy to perform the actuation. For example, an electrohydraulic actuator works by using an electric motor to provide torque to operate a hydraulic accumulator to produce the actuation force.
The most important advantage of electric actuators over the two other types is the fact that it can be used to produce very precise actuation and movements.
For example, a mechanical hard disk drive uses an actuator to read and write data from a spinning disk at extremely high speeds in excess of 7,200 RPM.
A stepper motor can produce rotation that moves a certain ‘step’ for each actuation. Stepper motors are common devices where position feedback is not needed and actuation steps are predefined an not likely to change.
Servo motors are used in applications that require a more granular or precise actuation. A servo motor can be commanded to a precise location using sensor feedback such as an encoder.
Here are some common uses of electric actuators in industry.
Pneumatic actuators utilize gas or pressurized air to actuate the movement. This is mainly performed by using a piston or diaphragm that keeps the air in the upper portion of the cylinder. In turn, air pressure will force open the piston to move the valve stem or rotate the valve control.
Many types of pneumatic actuators exist and can produce either linear or rotary motion. Pneumatic cylinders can be single or double-acting actuators.
Pneumatic actuators are typically used in main engine controls due to the nature of pneumatic energy. Pneumatic energy doesn’t need to be stored in reserve to perform the actuation, so can quickly respond in starting and stopping. Pneumatic energy is also safer, cheaper, and can be extremely powerful.
Examples of pneumatic actuator implementations include:
Hydraulic actuators, as the name suggests, utilizes the force from pressurized fluid or liquid (mainly oil) to create movement. This is typically done by using a cylinder barrel with a piston connected to a piston rod that moves back and forth.
Hydraulic actuators are based on the principle that fluids are incompressible, meaning, that a pressure change is equal in all directions in a closed system. This is known as Pascal’s Principle.
The basic idea of a hydraulic actuator is to use two pistons in separate hydraulic cylinders, and the hydraulic fluid can freely travel from one cylinder to the other.
When a force (the signal) is applied to one of the cylinders, the piston will move and then transmit the force through the fluid to move the other piston, creating the actuation.
The demonstration in the image above shows how a smaller piston with a much smaller input force can be utilized to drive or “actuate” a large piston resulting in a much larger output force.
Examples of hydraulic actuator implementations include:
Actuators can be used in any applications that require controlled, precise movement and/or force.
Motor actuators are typically used when circular/rotary motions are required but are also often utilized in linear implementations by transforming circular to linear motion with a lead screw or other means.
Actuators are often used in industrial and manufacturing applications, and in devices like pumps, valves, and switches that require controlled movements.
Below are common actuator types, their implementations, and their advantages/disadvantages:
| Types | Characteristics | Use Cases |
| Ball-screw actuators | Offers great mechanical advantage by producing high axial output force for high torque input, but has limited stroke and speed. | Transportation (including aerospace), military, industrial |
| Brush DC motor actuators | Brush motors offer very robust and durable design, but typically expensive and complex to implement | Consumer-grade appliances, factory, automated devices. |
| Acme-screw actuators | Very simple to implement and versatile, but not very durable due to sliding wear | Heavy-duty equipment, consumer products (especially low-cost ones), transportation |
| Rod-style actuators | Hygienic due to its sealed motion components, but offer high force output. Relatively expensive | Medical applications, food processing/sorting, consumer-grade products |
| Belt-and-pulley actuators | Very high speed and longer strokes, but not very precise (need guiding equipment) | Conveyor belts |
| Linear motor actuators | Fast and precise, but relatively expensive | Semiconductors, medical, and other applications that require very high precision |
| Planetary roller-screw actuators | Fast and precise, but relatively complex installation | Aerospace, semiconductor, and other applications that require very high precision |
Standard actuators have only two positions to allow the actuation: open and close. For example, a piston in a hydraulic actuator can be positioned in a fully open position (i.e. up) and a fully closed position (i.e. down).
In a 3-position actuator, as the name suggests there is a third, intermediate position. For example, a 3-position pneumatic actuator can have an operation of 0°- 45°- 90°, with the 45° position as the third, intermediate position, or 0°- 90°- 180° with 90° as the intermediate position.
The intermediate stop position is typically adjustable, so, for example, a 45° can provide 20°, 30° positions, among others, while 90° actuators can provide 20°, 30° 50°, 75°, and so on. This is typically performed by adjusting the external nuts of the actuator (usually outside the two end-caps).
3-position actuators are used in dosing, exact filling, and any other kinds of applications where the intermediate stop position is needed.
To fully understand how 3-position actuators work, let’s check the images below.
In this example of a pneumatic actuator, the air is supplied to port 2 and port C and is exhausted at port 4 to achieve the fully-open position. The air in port 2 generates force to the internal piston to continue the opening actuation.
The air is supplied simultaneously to port 2 and port D, while exhausted at port 4 and port C. The air supplied to port D moves the pistons to the center position, while the rods stop these pistons in the desired intermediate position as adjusted by the user.
The closed position is achieved when air is supplied to port 4 and exhausted at port 2.
We hope we’ve answered some of your questions with respect to what an actuator is and explained some of the more common actuator types. If you enjoyed this article and would like to become a member of the site, you can register here completely free.
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