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Actuators 101: What are they, and what does an actuator do

What is an Actuator and what does an actuator do?

What is an actuator? An Actuator is a device that requires an energy source input usually electrical energy, an external signal input in some form to tell the actuator what to do, and then the device actuates. The output in the form of a motion can be either rotary or linear and is used to achieve the desired outcome in a system.

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. 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. 

what is an actuator

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 actually 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 does an actuator 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 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

What is an actuator? A actuator is a physical-mechanical device that performs the conversion. It can look different depending on what type of input/output you are working with and hoping to produce.

In a door handle, the actuator is a plastic box with plungers attached to it. A hydraulic actuator, however, is made up of metal pistons. For an actuator to be effective, its design must effectively transform energy and is tailored as such.

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

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 Actuator 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 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.

robotic actuators

Solar power: Linear actuators are used to move solar panels to their optimal position for capturing the right exposure of sunlight to harness solar power energy.

Agriculture: In particular, hydraulic linear actuators can handle heavy loads involved in farming. Electric actuators could also find use in more delicate agricultural tasks.

Common Uses of Rotary Actuators

Industrial use/valve actuator: Rotary actuators are generally used when you need a torque energy force. Rotary valve actuators are thus used in various industrial machinery where valve operation is necessary, frequent, and is otherwise difficult to access. They are especially used within the oil and gas industry.

Pick-and-place handlers: As robotic picking is increasingly replacing manual picking, its capabilities must also more accurately match human movement. Rotary actuators, including miniature ones for finer movements, can achieve this.

Mobile construction equipment: Using rotary actuators within the mobile construction industry can be useful where there is limited rotational energy and more compact solutions are required.

Aerospace: In aerospace, a rotary actuator can convert high-speed low torque motion into low-speed, high-torque motion, which could be needed on the trailing edge flap on an airplane wing or the bomb bay on a military aircraft.

Subsea applications: Specialist rotary actuators such as for underwater use are also in production for various functions happening at sea, whether that's engineering or for use within water-submerged vehicles.

actuator applications

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.

Types of Actuators

Solenoid Actuators

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. 

type of actuator

Piezo Actuators

 

These actuator's 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 their force is very high, this means that you can amplify the expansion of the Piezo stacks to get more movement, but 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 Actuators

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 that 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 the other direction. 

Pneumatic

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 actually be very small and compact in size 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 using 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 in 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, forklifts trucks, tractors, etc.

hydraulic Actuators

How do they work?

Hydraulic Actuators use high-pressure fluid to push a piston backward and forwards 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

A rotary actuator is an actuator that produces a rotary (spinning) motion, which makes them ideally suited to opening and closing valves. There are many different ways to create rotary motion and thus many ways to create a rotary Actuator. The differences come in from the type of application. For example; In the picture below you can see that rotary motion is being created by a rack-and-pinion style movement where the "rack" is being controlled as a piston. The piston can be either hydraulically controlled or pneumatically controlled. So, what would the difference be? If the rotary actuator below is hydraulically controlled then the forces exerted could be huge, which could suit industrial applications requiring large forces to open and close a valve. If this rotary actuator is pneumatically controlled, then the actuator may require less force to rotate the main shaft, which will, in turn, be used to perform the required tasks. 

rotary actuators

Rotary Actuator 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

Servo Rotary Actuator

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 is 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 an Actuator?

A 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 actually 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 a actuator, just on a small scale.

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

actuators

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 iti 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

Electro-Mechanical Linear Actuators.

With Electric Linear Actuators, rotary motion from an AC or DC motor is converted to linear motion via a Leadscrew. A Leadscrew is basically 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.

linear actuator a type of actuator

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 in order to create that linear motion.  The more torque that is able to be applied to the leadscrew, the more linear force will be available for the sliding rod. 

There are different ways to create the torque in an actuator. Adding gear between the motor and the leadscrew 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 Linear 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 on how an Electric Linear Actuator works, we created this 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.

micro actuators

Summary

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 microactuators can be powered by small 12v power sources with great accuracy and precision for robotics and small applications. For more details on Acuators, 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.

electro mechanical linear actuators

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