Actuators are not the trendiest subject to be written or talked about in the same way that artificial intelligence (AI) and automation have grabbed the world's attention. However, they are a fundamental part of our lives, and are a widely used device that probably makes its way into every facet of your existence and its importance in the modern world can't be under-estimated. In some ways, it goes hand in hand with AI and other cutting-edge technology of the day, particularly where robotics is concerned.
In fact, actuators are the linchpin for making a robotic arm move once an energy source — electrical — is provided. Every time you drive a car, actuators are operating in the engine by controlling airflow and creates torque, a rotational energy force, which then manages the speed and fuel use of your vehicle.
Actuators are even found in small objects like electric switches and household devices like the TV lift to help you mount the television, or a recliner you put your feet up on at the end of the day. Such critical devices with wide-ranging applications deserve some knowledge on what they are, how they're made, where you can find them, and how you operate them.
This e-book runs through the fundamentals of actuators and provides a critical overview of the concepts behind actuators and the forces that drive them. You will learn about the main types of actuators and their various applications across industries. By the end of this book, you will understand how actuators operate, how you connect to them and move things. You will also come to know how to select one for the specific function you want.
It is time to appreciate the role actuators play in our modern world and their place in the future.
What Is an Actuator?
An actuator is the part of any machine that lets it create motion. Just like the muscles in the human body allow legs, arms, fingers, and other parts to move, the actuator is the component that enables movement in mechanical apparatus.
It does this by converting incoming energy and signals into a mechanical force. This incoming force can be electric, pneumatic (air), or hydraulic (water), while the outgoing motion can be rotary or linear.
Actuators are thus present in everything around us, from the access control systems on our doors to the robots doing the heavy lifting at the local warehouse. Even our mobile phones have actuators to create vibrations when they're turned on silent.
Linear Vs. Rotary Actuators
Linear actuators produce linear motion, which means they can move backwards or forwards between a set straight trajectory for a limited distance.
Rotary actuators create rotary motion around a circular plane and are not limited by distance. It can keep revolving around the annular dimension for as long as it needs.
Linear and rotary actuators can come in different forms depending on how they're powered and both can use hydraulic, pneumatic, or electrical energy sources. As such, each type will come with its unique set of advantages and disadvantages.
Water, Air or Electricity?
Electric actuators are motor-driven and tend to trigger other circuitry functions. They are powered using an electrical current and typically used within control systems. These types of actuators carry numerous benefits: they are simple to build or apply, carry minimal noise, and are cost and energy-efficient. Their downsides are that they are low speed and inappropriate for heavy loads.
Hydraulic actuators, on the other hand, can handle a burden of over 10 kilonewtons. A typical hydraulic actuator is a piston-like actuator comprised of a cylinder, piston, and spring. It also requires a hydraulic supply and return line and stem. They can handle high-force applications and don't need to be located near their pumps and motors while retaining the same power. They do have disadvantages, however, in that they can leak fluid, which can cost them efficiency and cause potential damage. They also need various ancillary parts like release valves, hoses, tanks, and regulators.
Pneumatic actuators sit somewhere in between electricity and hydraulic in terms of capability and can handle small to large loads. Pneumatic actuators use compressed air or gas to move a piston along a hollow cylinder and build pressure to move the load. Pneumatic actuators are generally lauded for the fast motion they create but like hydraulic actuators, they require complementary parts like valves, tubes, and a compressor.
Choosing an Actuator
Selecting the right actuator requires detailed consideration as there is no one-size-fits-all model and the type of actuator — linear pneumatic, electric rotary, rotary pneumatic, etc — depends on the industry and the application.
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.
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.
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.
From the mundane to the heavy-duty, there is an actuator used in so many everyday applications, mostly hidden from view, but doing work in some form or another.
How Are Actuators Made?
As established, an actuator can help convert 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.
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.
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.
The 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.
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.
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.
How Actuators Work
In reductive terms, an actuator is a type of motor that introduces and stops motion. While we associate motors with being electrically driven, they can also be controlled mechanically, manually, and via software. We can delve a little further into the mechanics of the different types of motors.
Rotor and Stator Assemblies
Rotor and stator assemblies are circular coils and windings in the motor. The easiest way to associate rotor and stator and understand what they do is to think of rotor – rotational, and stator — stationary.
In an electric motor, a current is induced when the stator assembly receives a voltage, which travels to the rotor assembly. Their interaction creates a magnetic field and, consequently, motion. Where electric motors are concerned, there are two types: AC motors and DC motors that move at constant or variable speeds, respectively.
AC motors vary the speed of motion they produce according to the frequency of voltage going in. An AC motor can be an induction motor or synchronous motor, which means it has one or two excitation systems (that provide current to the rotor), respectively. The former means the rotor moves slower than the stator, while they move in synchronization in a synchronous motor.
There are many other differences between induction and synchronous motors but a key one is the principles on which they work with electromagnetic induction behind the workings of induction motors and magnetic locking key to synchronous motors.
In DC motors, the rotor assembly tries to align with the stator but is prevented by the commutator — a type of rotary electrical switch. The rotary assembly, therefore, continues to rotate while the stator is stationary and helps regulate speed.
Stepper and servo motors are examples of DC motors that are both electromechanical devices that convert a digital pulse or voltage into rotational movement or displacement. Their performance can depend on the load size, and required speed.
Pneumatic motors are driven via vacuum or compressed air to produce linear or rotational motion. Air pressure and flow determine its speed or torque. Some common pneumatic motors include the rotary vane, axial or radial piston, turbine, V-type, and diaphragm.
Positional accuracy is something that might be cited in relation to actuators — the ability to achieve the command position. Different types of motors will have different positional accuracy capabilities. Pneumatic motors are better for applications where positional accuracy is less important.
Hydraulic motors use pressurized fluid, often water, to move a piston through a tube. The pressure of the fluid and flow rate determines torque or speed. The flow rate is determined by the size of the motor's orifice, the difference in pressure between its inlet and outlet, and fluid temperature.
However, hydraulic motors are not known for producing high speeds and typical applications are in construction and mobile equipment.
Main Types of Actuators
Actuator types vary according to the energy source, the type and speed of movement required, and its function. Actuator types do evolve and develop but it is helpful to understand the basics around some common actuators in use.
Electric Linear Actuator
Electric linear actuators use electrical energy to produce motion in a straight line using a piston that moves backwards and forwards triggered by electric signals. They produce pulling, pushing, ejection, or lifting movements. Their motors produce high-speed rotational motion with a gearbox that reduces speed or impact.
Electric Rotary Actuator
Electric rotary actuators use electrical energy to produce rotational movement, either for continuous motion or towards a fixed angle. They involve the combination of an electric motor, multistage gearbox, and limit switch. It creates rotation and torque when the current enters a magnetic field and from the force produced.
Hydraulic Linear Actuator
Hydraulic linear actuators use water pressure or other pressurized fluid to generate straight movements. They can produce torque strong enough to move external objects, hence their industrial applications. Hydraulic actuators consist of pistons that move in one direction and a spring that produces the reverse motion. There are also double-acting hydraulic actuators in which pressures comes at both ends to move the piston back and forth for more uniform motion.
Hydraulic Rotary Actuator
Hydraulic rotary actuators use pressurized fluid to rotate mechanical parts. They come in the form of circular shafts with keyways and tables — like a bolt — to mount other components. The shaft, which can be single or double, rotates when its teeth connect to the grooves in the piston and changes linear movement to rotational.
Pneumatic Linear Actuator
Pneumatic linear actuators use compressed air to create motion by moving pistons back and forth or by pushing and pulling a carriage through a driveway or tube. Springs are used to bring the piston back. Alternatively, fluid is sometimes used at the opposite end to push it back. Pneumatic linear actuators can produce high speed and torque for short distances and are resistant to opposing pressure like wind or explosions.
Pneumatic Rotary Actuator
Pneumatic rotary actuators use compressed air to create oscillation and they commonly use rack and pinion, scotch yoke, and vane design actuators. For example, rack and pinion actuators use compressed air to push a piston and rack in a linear motion that turns into a rotary movement in a pinion gear and output shaft.
Piezoelectric actuators utilize piezo material with electrical currents. Piezo materials are materials, such as ceramics, that expand and contract when touched by an electric charge producing energy. They are known for short, frequent, and fast response movements.
Choosing the Right Actuator
Needless to say, there are a great many actuators used in different fields and they won't all be suitable for your purposes. Here is a quick guide on finding the right one.
Assess Movement Type Required
By now, you'll realize the main two types of movement are linear and rotary. Depending on the function, you'll know if decisive linear movements are needed or if you require more dynamism in the resulting function. You may also want to consider, however, how far you want that movement to take place — short/sharp movements, or continuous etc.
Energy Input Considerations
Electrical actuators are very common and are gaining capabilities for an increasingly diverse series of functions. The requisite electrical current may not always be practical, however, in which case you can turn to hydraulic and pneumatic actuators eliminating the need for high voltage input.
Should You Consider Precision?
Precision levels were mentioned before and in some motors, you will need to achieve a precise command position. A "general" rule is that heavy-duty work can bypass the need for precision but smaller, intricate and delicate tasks will require greater accuracy, such as in picking and handling. That consideration will bear significantly on the actuator you choose.
What Force is Best
The broad objective of an actuator is to move something but the force required depends on how heavy or large the subject is. Keep in mind the dimensions of the objects your actuator must move so that you choose one with adequate load capacity.
How Far Must the Object Move?
Are small strokes needed to move the object or does it have to be lifted or transported relatively long/high distances? Any actuator will produce a stroke length that should be considered when choosing one for your desired purpose.
What Speed of Motion Do You Want
Actuator speed is a fairly important consideration and actuators that need higher force will often be slower than those generating a lower force. Actuator speeds are measured in distance per second.
What is the Operating Environment?
Actuators are frequently used in industrial applications as well as the more orderly environments of indoor labs and workshops. If you are operating within a particularly rugged environment, ensure the actuator you choose is rated well for protection.
How Will You Mount It?
Actuators can be mounted in different ways. For example, a dual-pivot mounting system allows the device to swivel or turn while extending and retracting. A stationary mounting system keeps the actuator more secure in one place.
There are other considerations when selecting the right actuator but the above guide should help narrow down options.
Assessing Actuator Performance
Part of selecting the right actuator, or deciding if it is the right actuator once you have chosen one, is assessing its performance.
There are various performance metrics relevant to an effective actuator. Here are a few to consider.
Torque or force
Torque, which you will hear of a lot in relation to actuators, is the twisting force that speaks to the engine's rotational force. You can consider it as simply "force" but either way it is key to actuator performance. Two metrics are relevant to torque or force — static and dynamic loads. Static load force is relational to the capacity of the actuator when it is at rest while dynamic loads refer to capacity when the actuator is in motion.
Speed considerations will vary depending on the function of the actuator and so should be considered in relation to your requirements. Higher weighted loads will naturally be slower. However, a good way of comparing speed performance metrics is to look at the actuator's speed when it is not carrying any load, as long as it has the capacity to carry the types of objects relevant to its required function.
Durability is very much a consequence of actuator type and design. Heavy-duty actuators will be naturally more durable, such as hydraulic actuators, and so will naturally perform better for industrial uses. All other things considered, the actuator should have a good design with components that fail to wear easily and are sized well. If you're newly introduced to actuators and mechanical engineering, bear in mind assessing this metric comes with experience. There are centers, however, that carry out push-pull tests and assess quality and safety, which can be helpful when procuring an actuator.
Energy efficiency is important for a multitude of reasons, not least for sustainability and environmental considerations and also costs. As a rule of thumb, less required energy to get an actuator to carry out its function is a good indicator of performance.
Connecting an Actuator
The types of actuators and the functions they relate to are broad. It follows, there is unlikely to be a blueprint or universal instruction manual when it comes to connecting actuators.
However, a common actuator, electric linear actuators, are relatively simple to connect and can be useful in varied household functions. Here is a rundown of connecting one to a device or a control mechanism like a rocker switch.
Connecting to a Device
Some electric linear actuators have four pins that are easily connected to your device. In this instance, the process is as easy as plugging in the actuator and walking away.
If your actuator does not come with the four pins included, you can buy a four-pin connector, available in six-foot and two-foot lengths.
Connect the connector to the actuator by finding the wires, which are hopefully exposed. You need to twist the wires to the connector before plugging it in. Use electrical tape to cover any exposed wires. If you can't find the wires or there is not enough, you can cut back the rubber for better give to connect to the connector.
The actuators may have different colored wires to the connector. If the actuator has red and black wires and the connector has brown and blue, for instance, connect red to brown and black to blue. If it has a red-blue combination, connect red to brown and blue to blue. If the actuator wires are red and yellow, connect red to brown wire and yellow to blue.
Connecting to a Rocker Switch
Rocker switches are the easiest way to control a linear electrical actuator either via a momentary rocker switch — those that move when the button is pressed — or a non-momentary switch, which can be switched between an "extend" movement, "retract" movement, or "off."
To connect a rocker switch, you will need a 12VDC battery or a 110VAC/220VAC to 12VDC power adapter in addition to your switch and actuator.
Connect the negative power to the third terminal of the rocker switch and use the second wire to connect terminals 3 and 4. The positive power of the power source connects to terminal 6 of the switch while the second wire connects terminal 6 to terminal 1. Connect the wires from terminals 2 and 5 to the actuator, which should now give you a working controller.
This is a simple, yet common example of connecting an electric linear actuator that has diverse uses.
Mounting an Actuator and Setting it In Motion
Once you connect your actuator to the device or controller, you need to mount it, ready for use. There are two methods for this — dual pivoting and stationary mounting, as mentioned earlier.
Dual Pivot Mounting
Fixing an actuator on a platform that allows it to pivot involves using a mounting pin or clevis fixed to each bracket on each end of the actuator. A cross pin slides through the bracket and actuator to connect the two, we call these mounting brackets. The actuator can pivot around each pin, which means the actuator can shift alongside the object it is moving, allowing a little more dynamic function. A very common application of this type of mounting method is seen on doors allowing them to swing open and closed.
Stationary mounting involves fixing the actuator to a shaft mounting bracket and allows the actuator to create push or pull motions from a set position. This is how a button is mounted, for instance.
In both mounting methods, it is also important to make sure the mounting apparatus can handle the actuator's load as undue load could damage the actuator or cause it to veer off-kilter.
It is also important to consider the environment you are operating your actuator and any propensity to dust or water. Like any mechanical device, your actuator, mount, and ancillary components require maintenance. If you look after your actuator and take time to understand its capability and mechanisms, it could serve you for a long time.