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Actuators - A motion controlled device. What are they, and how do they work?

What is an Actuator and what do they do?

An Actuator is a device that creates a type of motion, usually linear or rotary. To make an Actuator operate it requires an input energy source, usually electrical or hydraulic fluid, but can also be pneumatic which uses compressed air. The output motion is exerted in the form of a shaft turning or a rod extending or retracting, that once connected to something can make something move back and forth repeatedly as many times as you wish, without the need for human intervention. 

An actuator in principle can therefore be described as a device that converts energy into motion. Actuators are used in a wide range of applications, from robotics and industrial automation to transportation and aerospace. They are used to control and move mechanical systems and can be classified into different types depending on the type of energy they convert, such as electrical, pneumatic, or hydraulic actuators.



Some common types of actuators include linear actuators, which convert rotary motion into linear motion, and rotary actuators, which convert linear motion into rotary motion. Linear actuators are often used in applications such as industrial automation, robotics, and medical equipment, while rotary actuators are commonly used in applications such as valves, turbines, and pumps. We have written an extensive Blog about Linear Actuators 101 here

Electric Linear Actuators - type of actuator

Additionally, there are different types of actuators based on the technology they use such as:

  • Electric Actuators These are powered by electricity and can be further classified based on the type of electric motor used such as DC motors, stepper motors, and AC motors.
  • Pneumatic Actuator: These are powered by compressed air and are commonly used in industrial automation and robotics applications.
  • Hydraulic Actuators: These are powered by fluid pressure and are commonly used in heavy-duty industrial applications such as construction equipment and heavy machinery.

It's important to note that the choice of the actuator will depend on the specific application, including factors such as load, speed, and operating environment.

Selecting the ideal Actuator

When Purchasing an Electric Linear Actuator, there are a few things you must consider. Firstly Linear Actuators have 4 main characteristics, each of which has different importance levels to any application.  These are Stroke - Force - Speed - IP Rating.  Typically you would choose the ideal Actuator based on the Stroke first, then force, then speed. Remember the Speed and Force trade-off against each other. So this means that you can have a high force, but then the speed will likely be lower. If you want High speed, then the force will likely be lower. 

When selecting the ideal electric linear actuator, several factors should be considered, including:

  1. Load Capacity: The actuator should be capable of supporting the load that it will be moving. Consider the weight of the load and any other factors that may affect the actuator's ability to move it.
  2. Speed: The speed of the actuator should match the speed required for the application. This will depend on the specific use case and may involve trade-offs between speed and other factors such as force and precision.
  3. Stroke Length: The actuator should have a stroke length that is appropriate for the application. Consider the distance that the actuator needs to travel and any physical constraints that may limit the stroke length.
  4. Force: The actuator should be able to generate enough force to move the load and overcome any friction or resistance in the system. This may involve calculating the required force based on the load and the desired acceleration or deceleration.
  5. Precision: The actuator should be precise enough to meet the requirements of the application. This may involve considering factors such as accuracy, repeatability, and backlash.
  6. Environmental Factors: The actuator should be able to operate in the intended environment, taking into account factors such as temperature, humidity, and exposure to dust or other contaminants.
  7. Power Supply: The actuator should be compatible with the available power supply and voltage requirements of the application.
  8. Noise: The actuator should operate at a noise level that is acceptable for the application.
  9. Control Options: Consider the available control options, such as manual controls, programmable controllers, and sensors, and choose the one that best meets the needs of the application.

By carefully considering these factors, it is possible to select an electric linear actuator that will meet the specific requirements of the application, ensuring optimal performance and reliability.

Selecting the ideal Linear Actuator

Step 1. What stroke (extension) do you need:

The Stroke of an Actuator can also be called the extension. This is the distance of which the rod will move through and extend in and out. Usually, these are measured in Inches and can range from 1" (inch) stroke to around 40" Stroke. It's not normal to have Actuators with a stroke of longer than 40" to 50" due to the mechanical limitations of the leadscrew inside the Actuator that provides the pushing and pulling force.

Step 2. Consider the speed required:

The speed of the actuator is directly related to the gear ratio inside of it. A high gear ratio will slow down the speed of the rod that extends in and out of the actuator but also increases the force dramatically. Actuators range from forces as low as a few lbs to a few thousand pounds. Another way to get more speed and force is to make the motor larger. So if you have a large-diameter DC motor, it can spin faster and give more force. So, it's also notable that size also trades off with speed and force too, just to complicate things further.

Step 3. Consider the Force required:

Much like step 2, in this step, you have to think about what speed you can live with if you need a high force Actuator. The higher force will mean slower speed and vice versa. When considering the force requirements for selecting the ideal actuator, several factors should be taken into account, including:
  1. Load Weight: The weight of the load that the actuator will be moving is a key factor in determining the force required. The actuator should be able to generate enough force to overcome the weight of the load, as well as any friction or resistance in the system.
  2. Acceleration and Deceleration: The required force will also depend on the acceleration and deceleration rates needed for the application. If the load needs to be moved quickly, a higher force may be required to achieve the desired acceleration.
  3. Distance and Speed: The force requirements will also be affected by the distance that the actuator needs to travel and the speed at which it needs to move. A longer stroke length or faster speed will require more force.
  4. Inertia: The inertia of the load and the actuator itself can also affect the force requirements. If the load has high inertia, a higher force may be needed to get it moving, while a lower force may be sufficient to maintain its motion once it is moving.
  5. Friction and Resistance: Friction and resistance in the system can increase the force requirements, as the actuator will need to generate enough force to overcome these factors in addition to moving the load.
  6. Safety Factors: It is also important to consider any safety factors when determining the force requirements. A higher force may be necessary to ensure that the load is moved safely and securely, without any risk of damage or injury.

By taking these factors into account, it is possible to select an actuator with the appropriate force capabilities for the specific application, ensuring optimal performance and reliability.

Step 4. IP rating:

The IP rating is the level of weather protection an Actuator has. A higher IP rating means the actuator can withstand more harsh environments such as rain and temperatures. A high IP rating of 66, is considered a very good outside type of weather application Actuator. However, for indoor use, an IP rating of 42 is adequate. When considering the IP (Ingress Protection) requirements for selecting the ideal actuator, several factors should be taken into account, including::
  1. Environment: The environment in which the actuator will be used is a key factor in determining the required IP rating. Consider factors such as temperature, humidity, dust, and water exposure.
  2. Location: The location of the actuator within the system can also affect the IP requirements. If the actuator is located in a high-risk area, such as near a water source or in an area with high levels of dust, a higher IP rating may be required.
  3. Regulatory Requirements: Regulatory requirements may also dictate the minimum IP rating required for the application. Be sure to check any relevant regulations or standards to ensure compliance.
  4. Expected Lifespan: The expected lifespan of the actuator can also be a factor in determining the required IP rating. If the actuator is expected to be in service for a long period of time, a higher IP rating may be necessary to ensure durability and longevity.
  5. Maintenance Requirements: Consider the maintenance requirements for the actuator and how the IP rating may affect maintenance procedures. For example, a higher IP rating may make it more difficult to access and service components inside the actuator.

By considering these factors, it is possible to select an actuator with the appropriate IP rating for the specific application, ensuring that the actuator will operate reliably and safely in the intended environment.

Step 5. How to mount the Actuator

So now you have the Actuator, but how do you mount it? All actuators come with what's called a Clevis on each and of the unit. This is where you connect the actuator to some type of bracket. For our Actuators, each actuator has a certain size of bracket that fits on both ends. Some actuators have special brackets to fit over the body of the actuator, but these can have restrictive movement effects on the actuator during motion. 

Step 6. What other factors may I need to consider:

There are other factors that you need to think about when selecting the ideal Actuator. Voltage, for example, may be important. Typically Actuators come in 12 or 24vdc as standard. How about Feedback control? If you need positional control of the Actuator then you may need an Actuator that has some level of feedback like a hall sensor, optical sensor, or even a Potentiometer built into the actuator. These devices all provide a feedback signal so that a controller knows its position at any time. This is needed for applications where you need more than simple end-to-end control. We have written another blog post dedicated just to this topic of Feedback actuators here.

How to Connect the Actuator

There are many ways to connect the Actuator, and this will depend on what type of control you have or need. A simple rocker switch control is by far the easiest way to connect one, but you may also want a remote control as another form of control. For positional control, you may need a more detailed connection. Typically most Electric actuators, offer a 2 wire configuration for connecting to power or a switch. +/- voltage are the wires leading from the actuator, and reversing those wires to the power source is what makes the actuator change direction. This process is called "reversing the polarity". A rocker switch does that for you inside the switch.

Two Wire Actuator connection methods:

The most common type of Actuator is a 2 wire system. simply connecting these wires directly to a power supply (usually 12vdc) will make the actuator move, and reversing the wires will make the actuator move in the opposite direction. A rocker switch is what does this for you, so connect the 2 wires from the actuator to the switch and connect the 2 wires from the power source to the switch and you are done. Our switches all have the wiring diagrams on each product page to make this simple

Feedback actuator wiring methods:

Actuators that have built-in feedback will have more wires. Typically 2 extra wires and in some cases 4 extra wires. These wires will need to go to the correct location. Hall sensor and Optical sensor actuators are usually wired up the same. A potentiometer actuator which always has only 3 wires will be the one that's a little different. All FIRGELLI feedback actuators have the wiring diagram printed onto the actuator. 

The term Actuator comes from the act of Actuating something, in other words, to Actuate is to operate something. So to simplify the expression of what it does, an actuator reads a signal and then it actuates, or it operates. Actuators are typically part of an overall system or machine or device integrated into something larger to produce useful work in some form. It is a component within that machine that does something by making it move. 

For an actuator to work, it requires an energy source input, usually electrical energy. It also requires an external signal input in some form to tell the actuator what to do, and then the device Actuates. The output is usually in the form of a motion that can be either Rotary or Linear that's used to achieve the desired outcome in a system. The funny part is that some Actuators use other Actuators to make them operate. For example, a hydraulic linear Actuator would use a solenoid Actuator to open and close the high-pressure fluid into the main piston of the Actuator. So, as you can see these devices are used in so many places and applications. 

actuators in cars

Let's look at a typical example of an actuator system used in our everyday lives. The heating in a car has both hot and cold temperature settings, as well as a fan with different force levels. The temperature setting is controlled by an actuator that regulates how much air flows over a heat exchanger. That actuator controls the airflow position, the more it flows over the heat exchanger the hotter the air is, conversely, the further away it is from the heat exchanger the cooler it is. 



actuators in cars

History of Actuators

Actuators have been around for over 100 years and their name came from what they do, they Actuate something. That is, they move something by opening or closing, pushing or pulling, lifting or dropping, etc. The most common type of actuator that you use every day is the solenoid actuator to lock and unlock your car door, or an electric linear actuator used to open and close the trunk in a car. Those are very common types of Electro-mechanical actuators that are used extensively in our daily lives. Before electricity was created, they were still made but would be human-controlled, such as a latch on a door.

What do they do?

As established, an actuator converts energy into motion but it also can help control that motion and energy.

The variables in an actuator system are the type of energy, amount of input, and speed of motion. What will always be consistent is the need for some sort of energy source and the production of mechanical motion. Actuators also work using the same components although these will look different depending on the type of actuator and its function.

Power source

The power source, as discussed, can be electric, air or gas, water or another type of energy source but these are the most common in the operation of actuators.

Power converter

The power converter carries power from the power source to the actuator in line with whatever units or measurements are detailed on a controller or in its design.

A hydraulic proportional valve is one example of a power converter used on the water - a mechanical part to let in or shut off the water so water flow is in line with the rate of input and the desired motion output.

Electrical inverters are another example, which is often used in industry to convert direct current electricity to alternating current electricity. They can look like rectangular electronic drives or circuits.

Actuator Definition

An actuator is a device that converts energy into motion or mechanical force. It is a component of a system that is responsible for controlling or moving a mechanism or system. Actuators are used in a wide range of applications, from small devices like smartphones and automobiles to large machinery in manufacturing plants and aerospace. They come in different types, including hydraulic, pneumatic, electric, and mechanical, and can be used to control various parameters, such as position, velocity, force, and acceleration. Actuators play a crucial role in the operation of many modern systems and are a fundamental component in fields such as robotics, automation, and control engineering.


Mechanical load

The mechanical load is a physical stress or opposing force on the system working against the energy the actuator produces. As such, it induces the system to produce more power.

An everyday example of this interplay can be seen when a car is driving uphill. The tilt or slope is a load the engine works against, so, to move, the car must increase its speed. In mechanical engineering, a mechanical load can be worked in as part of the system design.

Controller for an Actuator

The controller is a device that activates the actuator and controls the output, guiding its direction, force, and its longevity. It stops the system from working on its own devices and allows limits at both ends of the conversion, which the operator can oversee.

It could be an electric, electronic, or mechanical device, and could look like a button, lever, switch, or dial. But there are many different examples when it comes to operating an actuator.

actuator controller

Different Applications

Whether you're looking at linear or rotary actuators, their list of applications is endless. They're likely to be in some device around you, including your mobile phone. Without them, many industrial applications would be far less efficient.

Common Uses of Linear Actuators

Material handling: Manufacturing plants and warehouses no doubt have a use for material handling systems in which linear actuators are incredibly useful for effective and quick control and processing of goods, including conveyor belt systems.

how actuators are used

Cutting equipment: Using a machine for cutting protects human safety when dealing with repetitive tasks involving sharp or dangerous equipment. Linear actuators can power machines for accurate slicing, including wood, glass, or card.

Raw materials processing: Examples of using actuators in raw material processing are glass/ceramic furnaces or marble/wood-working machines and, coupled with trending automation capabilities, they can operate more efficiently and accurately.

Robotics: Robotics is a classic and obvious example of where linear actuators are used and their rise in use means more innovations and variety seen here.

actuators in robots

From the mundane to the heavy-duty, there are many types of actuators used in so many everyday applications, mostly hidden from view, but doing work in some form or another.

Different Types

Solenoid Actuator

Sticking with the Automotive, let's explore another very common actuator type, and that is the Solenoid Actuator. Solenoids work like a relay; they take in an electrical current and create an electromagnetic field. It is that magnetic force that then makes a rod move in and out. Typically, the higher the magnetic field that's supplied to the solenoid actuator, the more force it creates, and visa-versa. These are very simple on/off type actuators, which means very few control options. For example, solenoid actuators have no real control over speed or force, and also a very limited stroke length. It is rare to find a solenoid Actuator with more than 2" (inches) of stroke.

solenoid actuators

The central locking on car doors is the most common type of solenoid Actuator used. they simply connect and disconnect the latch from the door handle. The control mechanism is also very simple; a single pulse of 12v DC electricity is sent to the solenoid to actuate it, and a spring makes it return.

Below is a typical solenoid actuator, as used in most cars. If they look unfamiliar, it's because most people don't see inside the door panels of a car. 

types of actuator

Piezo Actuator

These actuators' movement comes from being energized by voltage and they require very large voltages to make them expand and contract, typically over 200V. The Piezo material is a type of ceramic, it is very brittle and will have many layers with metal plates between each layer so each piezo stack gets energized.

Large amounts of voltage are required for a very small change in length, typically a Piezo will only expand by about 1% of its size, but its force is very high, this means that you can amplify the expansion of the Piezo stacks to get more movement, but a trading force for distance. The amplification could be done mechanically, such as with a lever, but Piezos are typically used in applications where you need very high precision and control. They are most commonly used as fuel injectors for cars, where the Piezo actuator controls the fuel volume entering the cylinder; where the control level needs to be down to the microns (one-millionth of a meter). 

Piezo Actuators

Pneumatic Actuator

These types of actuators use pressurized gas or air in a cylinder created by a high-pressure pump to move a piston to create linear motion. Like hydraulic actuators, the design of a pneumatic linear actuator has been around for a long time. An air compressor is used to pressurize the air or inert gas in a tank, and  high-pressure air is used to make the actuator's piston slide in and out. Once the piston in the actuator has reached the end of the travel, a valve switch is then moved to open the valve to the other end of the actuator where again high-pressure air then pushes the piston in the actuator in the other direction. 


The benefits of using pneumatics are:

    1. High speed is possible and is controlled by the pressure valve and volumetric capacity of the system.
    2. Fairly high forces can be achieved.
    3. Little sound is emitted apart from the pump pressurizing the tank.
    4. Very long strokes are possible.
    5. Extremely high cycle reliability and durability.
    6. The Actuators can be very small and compact since they are quite simple in construction. 

Drawbacks of pneumatic are:

  1. Additional equipment is required such as a tank and high-pressure pump.
  2. The entire system can not be allowed to leak if the system fails.
  3. Air is a compressible gas, meaning when a pneumatic actuator is moving a high force, there is always a lag because the gas/air will naturally compress first before it moves the piston inside the actuator. This means there will be a lag in the system. Hydraulic Actuators do not have this problem.
  4. Very low positional control is achievable. Watch the video below where we use Lego to demonstrate the lack of control compared to a mechanical Actuator, and use a DTI (Dial Test Indicator) to show the difference

Where are they used?

They are used where high-speed motion is required, upwards of 30 inches per second. Once installed they are hard to move from one place to another as they require a lot of installation time. These Actuators are found on the assembly lines of manufacturing factories as they are ideal for performing millions of cycles with no maintenance, and they can move very quickly. 

Hydraulic Actuators

Hydraulic Actuators operate exactly the same way as Pneumatic actuators, except instead of using high-pressure air or gas they use a non-compressible liquid called hydraulic fluid. Because the fluid is non-compressible it has a huge advantage over pneumatics, these systems are capable of immense forces. This is why you see them used exclusively on heavy-duty construction equipment like diggers, dump trucks, forklift trucks, tractors, etc.

hydraulic Actuators

How do they work?

Hydraulic Actuators use high-pressure fluid to push a piston backward and forward where the switching is done through valve switches. These systems require high-pressure pumps, high-pressure valves and piping, and a tank to hold hydraulic fluid in. So, if you have a lot of space and money and require a very high amount of force, hydraulics could be the way to go.

The benefits of using hydraulic actuators are:

  1. Moderate speed is possible and is controlled by the pump speed.
  2. Extremely high forces can be achieved. 
  3. Very long strokes are possible.
  4. Extremely high cycle reliability and durability.
  5. The Actuators can be very small and compact in size since they are quite simple in construction. 

The Drawbacks are:

  1. Control. Hydraulic Actuators have very little precision control.
  2. Hydraulic fluid is required for the system to work, and the fluid is very toxic. If the system fails, it could leak.
  3. When the hydraulic pump is operating it can be very noisy, and the higher the required force, the louder the noise.
  4. Hydraulic fluid relies on predictable viscosity, so it does not flow smoothly through pipes and valves, etc. This requires additional energy to push fluid at high pressure through pipes and fittings. As a result, hydraulic systems are very inefficient to operate and use, especially in varying climates.
  5. Price. These systems are expensive to buy and install. 

Rotary Actuators

Another type of rotary actuator is servo motors and stepper motors. These are electrically controlled actuators that have a constant rotational movement and also offer very precise rotational control. These types of actuators are commonly used in Robotics and consumer electronics where rotational movement and torque is produced by a rotary motor. The speed is reduced and torque is increased by a gear system to create the rotary motion. To get precise control, the actuator will have a sensor that measures position. This is usually in the form of a hall sensor or encoder that sends a signal back to the 'brain' to translate into a position. A great feature of servo motors is that they can be made very small and used in very tight places.

rotary actuators

The principle:

The motion produced by these types of actuators may be either continuous rotation, as seen in an electric motor, or movement could be a fixed angular rotation. With a rotary actuator that's pneumatically or hydraulically controlled they are more likely to be a fixed angular rotation type, this is because the rack or piston that rotates the main shaft can only move so far and so the rotational movement is restricted by the linear stroke available. If more rotation is required, the piston would need to slide further, and a different gear ratio is used to translate the motion. 

rotary actuator gear ratio

Rotary Servo

Another type of rotary actuator is a servo motor and stepper motor. These are electrically controlled actuators that have a constant rotational movement, and also offer very precise rotational control. 

Servo rotary Actuator

These types of actuators are commonly used in Robotics and consumer electronics where rotational movement and torque are produced by a rotary motor. The speed is reduced and torque increased by a gear system to create the rotary motion. To get precise control, the actuator will have a sensor that measures position. This is usually in the form of a hall sensor or encoder that sends a signal back to the 'brain' to translate into a position. A great feature of servo motors is that they can be made very small and used in very tight places. 

Is a Relay a type of Actuator?

Relay is also sometimes considered to be a form of Electrical Actuator, meaning the relay actuates an electrical signal or connection. Even though this may sound like an electrical component with no moving parts, it does have a moving component to it. A relay is a magnetically charged coil that opens and closes a connector via an electromagnetic field. So, technically, it is a form of an actuator, just on a small scale.

For this article, we will focus more on Linear Actuators. This example is intended to illustrate how the term "Actuators" is very broad and can cover Rotary Actuators, Solenoids, and other types too. 


Converting rotary motion from a servo motor to linear motion

 converting rotary motion from a servo motor into linear motion

Because rotary servo actuators are so commonly used and relatively inexpensive to buy, it has become a popular way for people to create linear motion. Through simple linkages and some form of linear guiding system, it is possible to create linear motion. The stroke that results will be directly proportional to the lever arm length as seen in the picture above. The longer the arm from the servo actuator, the longer the stroke will be; however, the downside is that the force will be reduced because the torque is proportional to the arm length. 

Below torque equation for rotary actuators

torque equation for rotary actuators


With Electric Linear Actuators, covered in a separate blog article here, the rotary motion from an AC or DC motor is converted to linear motion via a Leadscrew. A Leadscrew is a helical gear machined onto a Rod. As the Leadscrew rotates from to the motor, the nut (as shown in yellow below) slides up and down the leadscrew in a smooth linear motion, translating rotational movement into linear movement - Hence the name "Linear Actuator". This is very different from a solenoid actuator, which is still a form of Linear Actuator, but in the industry, engineers typically differentiate the two by calling them "Solenoid Actuators" and "Linear Actuators" even though both output linear motion.


With Electric Linear Actuators, having different length Leadscrews gives you different stroke lengths. Turning the leadscrew faster or slower with the motor gives different linear speeds. The more force from the motor that can be applied to the leadscrew means more force is given to the nut that slides up and down the Leadscrew. The nut is attached to the Rod and the Rod that is what you see and attach to the mounting bracket to create that linear motion. The more torque that can be applied to the lead screw, the more linear force will be available for the sliding rod. 

There are different ways to create torque in an actuator. Adding gear between the motor and the lead screw is the most common method; the higher the gear ratio, the more force is created. There is a trade-off: higher forces mean lower speed, conversely, higher speed means lower force. Additional speed for a given force would require a larger input motor, which is physically bigger and draws more current to function; both the size and the power make it more expensive.

Electric Actuators

An electric actuator is a device that converts the rotational motion of a motor into linear motion, or takes electrical current to create an electromagnetic field and uses magnetism to force a metal object away from its magnetic field. While these types are very different, they share the same name and both provide actuation.  This means they all provide both push and pull movements in either a linear or rotational movement. 

For a more detailed overview of how an Electric Linear Actuator works, we created the article "Inside a Linear Actuator - How an Actuator works"

If you are looking to purchase an electric linear actuator we have created an article called “Don’t buy a Linear Actuator until you read these 5-steps” this can help you avoid some common problems before spending any money.

Micro Linear Actuators

 Micro Actuators or Mini Linear Actuators are used in applications where space is limited or the required stroke of the actuator is small. Perhaps you need to move something tiny a very short distance, a Micro Linear Actuator would be ideal for such an application.  Typically Micro Actuators' strokes are 10mm to 100mm and are very compact in size.  One of the downsides of a Micro Actuator is that forces tend to be a lot lower due to the small motors built into them.

exploded view of an actuator


Actuators come in many different types, from rotary to linear, hydraulic and pneumatic, solenoid, and electro-mechanical. Each type has an ideal application. Large industrial rotary actuators that are hydraulically driven are great for opening huge oil-pipe valves, and micro-actuators can be powered by small 12v power sources with great accuracy and precision for robotics and small applications. For more details on Actuators, we have written a white paper that goes into a little more depth in the world of actuators. Please read that article here

FIRGELLI®  actuators are specially designed and produced with high-quality materials to give you the perfect balance of power, control, and price to build your automation systems.

Check out our Actuators here

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