The Ultimate Guide to Actuators

Author: Robbie Dickson

Wikipedia: Robbie Dickson

Unlocking the power of actuators: The definitive guide to design, selection, and optimization

Did you know that there are hundreds of actuators in a typical car?, in fact, it is estimated there are over 50 actuators of many different types within a car that you never get to see. How about in the home? there are also many different types used at home for multiple applications and use cases. The point is that Actuators come in many different forms and types, they can use used to automatically turn the water on and of in a washing machine, to lift a TV out of a cabinet, or to operate that coffee machine every morning. The point is that Actuators have been around for decades in applications we all take for granted every day. 

FIRGELLI is a world leader, supplier, and manufacturer of Electric Actuators, we have been around for over 20 years and partner with thousands of customers for very specific applications in every industry you can imagine. Our focus is on creating devices that suit our customer's needs which is why we have one of the largest ranges of actuators possible. From Tesla to the Terminator we supply an insane range of companies with diverse product ranges and we do that globally. 

This Ultimate Guide to actuators is about educating people on everything that is an actuator. We will go into them in great detail and cover them from every angle. Our primary focus will be on electric actuators as this is our primary product range, however, we cannot forget about other types and we will cover them also, because its important to understand the pros and cons of all these different types regardless of whether we develop these other types or not. 

Electric linear actuators are devices that convert a source of energy into a physical-mechanical motion in a straight line (linear actuator) or a rotary motion (rotary actuator). They are different from hydraulic and pneumatic actuators, as they use either compressed air or fluid to make something move. They are also more reliable, require less maintenance, and are often less expensive, but let’s go into this in greater detail.

The operation of an electric actuator is achieved by converting the rotational motion of an AC or DC motor into a linear motion or rotary motion but geared down from a typical 2000RPM+ speed of a motor, to something more suitable for creating motion (linear or rotary) that can then be made useful to do something practical. By useful we mean increasing the torque by lowering the speed, a necessary process for any electric actuator. For linear Actuators, depending on the direction of the screw's rotation, the shaft attached to the screw (leadscrew) moves in a straight line, up or down, providing a push or pull effect on the load. Electric linear actuators can also be easily integrated with positioning feedback for precise control. DC voltage is typically considered safer than AC voltage, but Actuators are available in either source. 

Common types of Electric Actuators

There are several different styles of electric linear actuators available on the market, each with its own advantages and disadvantages depending on the specific application. In this article, we'll explore the three main styles of electric linear actuators: Inline, L-shaped, and Parallel, Rotary, and Track (slide actuator)

Inline Actuator

Inline electric linear actuators are a popular choice for applications that require high speed and force capabilities in a compact design. These actuators feature a motor and actuator rod that are aligned on the same axis, allowing for a streamlined design that saves space. Inline actuators do have a major disadvantage however, and that is that they tend to be longer than any other type of actuator, because the Motor and gearbox have to sit behind the drive leadscrew which requires the overall length to be longer, whereas most other actuator types the Motor can sit along the side of the main body.  The big advantage however is that they tend to be a much nicer design to look at, they appear sleeker and more attractive which makes them ideal for applications where they are seen. 

L-shaped Actuator

L-shaped electric linear actuators are another popular option, particularly for applications where space is limited. These actuators feature a motor and gearbox mounted at a right angle to the actuator rod, creating an L-shape. L-shaped actuators are often used in furniture automation, industrial automation, and automotive applications.

Parallel Actuator

Parallel electric linear actuators are perhaps the most common style of actuator designed for high force and precision applications and feature a motor and gearbox mounted parallel to the actuator body thereby allowing the overall length to be more compact. The drive mechanism is typically Spur gears which can make them noisier, but that's the trade-off for a more compact Actuator. 

Rotary Actuator

A Rotary Actuator is a type of actuator where the final drive motion is rotary instead of linear. In contrast, a Linear Actuator can be thought of as a rotary actuator with a leadscrew, drive nut, and rod, which converts rotary motion from a rotary actuator into linear motion via the leadscrew. Rotary actuators have a continuous driving motion in either direction, with no stops or limits unless a stopping component is added.

Rotary actuators are versatile and can be used by attaching something to the driving flange to create the desired motion in the final application. However, it's important to consider the torque and speed required for the application. As rotary actuators have angular force, they are selected based on torque and speed dimensions. It's worth noting that torque and speed trade-off against each other, so high torque results in lower speed, and vice versa. This is due to the way gear ratios work in any type of motion where there are gears between the driving motor and the final driving wheel.

Track Actuator - Slide Actuator

The Track Actuator, also known as the Slide Actuator, operates differently from other actuators as it doesn't have a shaft or rod that slides in and out of the actuator's end. Instead, a carriage slides along the main body or track of the actuator. This unique design makes it ideal for specific applications, such as massage chairs or industrial assembly lines where the track needs to slide something in and out repeatedly.

One significant advantage of this type of actuator is its versatility when it comes to installation. The carriage or nut, as they're sometimes called, have various threaded holes that make it easy to attach things to them. Additionally, it's possible to install more than one carriage on the same track, which increases strength and rigidity.

How to Choose the Right Electric Linear Actuator

When selecting an electric actuator, it is crucial to consider the specific requirements of your application. With various actuator models, such as parallel, L-shaped, or inline motors, available for a wide range of applications, choosing the right one can be challenging. We have written a separate article specifically on the subject of the different types of electric actuator styles here. 

Comparison of Different Actuator Systems: Pneumatic, Hydraulic, and Electric

Actuators are essential components in the manufacturing and automation industry. They are used to create movement in machines and systems, converting energy into motion. There are several types of actuator systems, with the three most common being pneumatic, hydraulic, and electric. We will discuss each actuator system's characteristics, advantages, and drawbacks, and compare them with one another.

Pneumatic Actuator System

Pneumatic actuator systems are widely used in the industry due to their low cost and simplicity. They consist of a simple piston inside a hollow cylinder, which moves in a linear motion. These actuators require air compressor, regulator, and an air cylinder to hold pressure. When pressure is applied to the cylinder, the piston moves, creating the necessary linear force. Retraction can be accomplished by either a spring-back force or by providing fluid to the opposite side of the piston.

One of the major drawbacks of pneumatic actuators is that it is difficult to achieve position accuracy. Mid-stroke positioning requires additional components and user support, making it challenging to achieve the desired results. Additionally, pneumatic actuators have a limited load rating compared to hydraulic and electric actuators.

Hydraulic Actuator System

Hydraulic actuator systems are known for their ability to produce very high forces and long strokes. They use an incompressible liquid supplied by a pump to move the cylinder in a linear motion. These actuators consist of two essential components: a control device, such as variable throttles or paired slide valves, and an actuation component, such as a piston or controlling valve slide. They are capable of very high forces and long strokes but are not programmable.

Hydraulic actuators are explosion-proof, shock-proof, and spark-proof, making them suitable for hazardous environments. However, they are also very complex, requiring a high-pressure pump, high-pressure regulators, and a hydraulic fluid reservoir. The hydraulic fluid leaks and disposal can also be challenging and require maintenance.

Electric Actuator System

Electric actuator systems are highly precise, making them suitable for high-speed, force, precision, and controlled acceleration and deceleration applications. These actuators convert the rotational force of a motor into linear movement, using a screw to create a push/pull effect. By rotating the actuator's screw via the motor, the nut will move up and down in a linear motion. Electric actuators are also programmable, offering flexibility in motion control capabilities with an electronic controller.

Compared to hydraulic and pneumatic actuators, electric actuators are the most reliable and require almost zero maintenance. They are also environmentally friendly and have minimal effects. However, they have a limited ability to handle shock loads, which can cause mechanical damage. They are also slow to high, but highly correlated to force, meaning high speed will mean low force, but low speed means high force capabilities.

Comparison of Characteristics

In the table below, we have summarized the characteristics of each actuator system. Electric actuators are the simplest and most cost-effective option, Pneumatic come in second, but they have limited load ratings, and are difficult to achieve position accuracy. Hydraulic actuators are capable of producing very high forces and long strokes, making them suitable for heavy-duty applications, but they are complex and require maintenance. Electric actuators are the most reliable and precise, but they are limited in handling shock loads.

When it comes to efficiency and operating costs, electric actuators are the clear winner, with low operating and maintenance costs. Pneumatic actuators have moderate purchase and operating costs, while hydraulic actuators have high purchase and operating costs. However, hydraulic actuators have a long lifespan, making them a cost-effective solution in the long run.

Conclusion

In conclusion, choosing the right actuator system for your application requires careful consideration of your specific needs, as each has its advantages and disadvantages. Pneumatic, hydraulic, and electric actuator systems all have unique characteristics that make them suitable for certain applications. Pneumatic systems are ideal for simple applications that require high speed, while hydraulic systems are best suited for heavy-duty applications that require high force and long strokes. Electric systems are highly precise and reliable, making them the best option for applications that require accuracy and repeatability.

There are many components inside a typical electric actuator. Here are some of the common components that can be found inside an electric linear actuator:

1. Electric motor - provides the power to move the actuator's Rod or shaft in and out
2. Lead screw or ball screw - converts rotary motion of the motor into linear motion of the actuator's output rod
3. Encoder or limit switches - provide position feedback and limit the range of motion of the actuator to prevent damage or overloading
4. Housing or casing - contains and protects the internal components and provides mounting points for the actuator
5. Bearings - support the output rod and reduce friction during motion
6. Gearbox - reduces the speed of the motor and increases the torque output, allowing the actuator to move heavier loads or exert greater force.

Note that the specific components and their configurations may vary depending on the type and application of the electric linear actuator. The image below is a very high level picture that shows the main components.

 Want to see more detail inside an Actuator?

 In the image below you can see a typical FIRGELLI actuator and all of its components in much more detail. This level of detail is still missing many parts such as O-rings, wiring etc, as this would clutter the image far too much, so we removed some non-core components for easier viewing. 

The Motor

All electric actuators have a motor that is either AC or DC. Most are DC because they are safer to handle and DC can be controlled much easier. The size of the motor is what gives the actuator its power, and so larger motors mean more power and vice versa. 

When it comes to Motors there are two types, Brushed, and Brushless. A brushed motor, which is the most common type, is a type of DC motor that uses brushes (made of carbon or graphite) to transfer electrical power to the rotor (the rotating part of the motor). The basic components of a brushed motor include the stator (stationary part), the rotor (rotating part), and the commutator.

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The stator contains one or more coils of wire that are wound around a metal core. These coils are usually arranged in a circular pattern around the rotor. The rotor, on the other hand, consists of a shaft that is mounted on bearings and a series of wire windings or permanent magnets that are arranged in a cylindrical pattern around the shaft.

The commutator is a segmented cylindrical conductor that is mounted on the shaft and is connected to the rotor windings. The brushes make contact with the commutator, allowing electrical power to be transferred from the power source to the rotor.

When electrical power is applied to the stator coils, it creates a magnetic field around the rotor. The magnetic field interacts with the magnetic field produced by the rotor, causing the rotor to rotate. As the rotor turns, the commutator segments move past the brushes, switching the polarity of the current flowing through the rotor windings, which produces the torque that drives the motor.

The commutator segments are arranged in a specific pattern so that the polarity of the current in the rotor windings changes at the appropriate time during each rotation of the rotor. This switching of the current allows the motor to continue rotating in the same direction.

Brushed motors are relatively simple in design and construction, but they have some limitations. One of the main disadvantages is that the brushes and commutator wear over time, leading to increased friction and reduced efficiency. This wear can also generate sparks and cause electromagnetic interference. Additionally, brushed motors tend to be less efficient and have a lower power-to-weight ratio compared to brushless motors. However Brushed motors are more common, much lower price points, and much easier to control. This is why they are most commonly used in Electric Actuators. 

Below is a Brushless motor

A brushless motor (BLDC) uses a different configuration where the rotor is the rotating part, and the stator (fixed part) has the winding. The rotor in a BLDC motor typically consists of a series of permanent magnets arranged in a circular pattern around the shaft. The stator, which surrounds the rotor, has multiple coils of wire wound in a specific pattern. The stator windings are energized by an electronic controller that uses sensors to determine the position of the rotor magnets and control the flow of current to the stator coils, producing a rotating magnetic field that interacts with the permanent magnets on the rotor, causing it to spin.

The main differences between the two types of motors are:

1. Brushed motors require brushes to transfer power to the rotor, while brushless motors don't require brushes as the stator is the fixed part that has the windings.
2. Brushed motors tend to generate more electromagnetic interference and produce more heat due to the brushes making contact with the commutator, while brushless motors have no contact, producing less heat and electromagnetic interference.
3. Brushless motors have a higher power-to-weight ratio and are more efficient than brushed motors as there are no energy losses due to friction between the brushes and the commutator.
4. Brushless motors are typically more expensive than brushed motors due to the more complex electronics needed to control the motor.
5. The Lifespan of a Brushless motor is significantly longer because there are no points of contact between the commutator and brushes, in fact, the only worn parts are in the bearings which typically have very long lifespans. 

The Important parts - the Clevis

A clevis (sometimes spelled "clevice") is a mechanical fastener that is used to join two objects together, typically a rod or shaft to a load or linkage. It consists of a U-shaped metal bracket with holes at the ends of the arms that allow for the attachment of a pin or bolt. The clevis can be used to transmit forces or motion between the objects while allowing for some degree of rotation or pivoting. Clevises are commonly used in various industrial applications, such as in the construction of machinery, vehicles, and aircraft. They can also be found in hydraulic and pneumatic systems, where they are used to attach cylinders, pistons, or other components to a load or actuator.

Below is an image of the Clevis on both the Rod end (the part that moves) and the motor end (the part that stays fixed into place)

The purpose of the Clevis ends of an Actuator is that one end stay fixed (usually the motor end) and the rod end which is the part that extends in and out has a clevis mount too. The U-shaped brackets that fit on both ends use a round pin and this allows the bracket to rotate around one axis. This is very important because as an Actuator is pushing something open and closed, the actuator also changes the angle, without it being able to rotate around at least one axis the system would fail. 

Overload Protection 

Some Actuators come with a built-in overload current protection system called a Thermistor.  

A thermistor is a type of resistor whose resistance varies with temperature. The name "thermistor" is a combination of "thermal" and "resistor". Thermistors are commonly used in electronic circuits as temperature sensors, in which their resistance changes with temperature are measured and used to determine the temperature of the surrounding environment.

There are two types of thermistors: positive temperature coefficient (PTC) and negative temperature coefficient (NTC). PTC thermistors have a resistance that increases with increasing temperature, while NTC thermistors have a resistance that decreases with increasing temperature.

Thermistors are made of semiconductor materials such as metal oxides, which have a high sensitivity to temperature changes. The resistance-temperature relationship of a thermistor is non-linear, which means that the resistance change is not constant with temperature. The relationship between resistance and temperature can be approximated by a mathematical equation called the Steinhart-Hart equation.

Thermistors are used in a wide range of applications, including temperature measurement and control in electronic circuits, temperature compensation in oscillator circuits, and protection of electronic devices from overtemperature conditions. They are also used in automotive, HVAC, and medical applications for temperature sensing and control. FIRGELLI has them built into one of our Actuator models for the customer who likes this feature. 

Not all actuators have thermistors built in because to reset the Thermistor once it kick in, you have to remove the load that caused the cut-out to begin with and then reverse polarity to the actuator. This can be very easy to do with a control program, but for an analog setup with just a power supply and a switch, it may not be best suited. But this type of safety is very effective and ideal for applications where children or fingers could be injured otherwise. 

Different features of the actuator can affect its speed and load capacity, including voltage, leadscrew type, and motor specifications. Here are some of the features and their effects:

1. Voltage: The voltage supplied to the actuator affects the speed and torque that can be produced. Higher voltages typically result in higher speeds and torque. However, using higher voltages may also result in higher power consumption, and may require more expensive power supplies and controllers. The choice of voltage for a DC motor depends on the application requirements and constraints. Here are some benefits and drawbacks of using 12V, 24V, and 48V DC motors

2. Leadscrew type: The leadscrew is responsible for converting rotary motion from the motor into linear motion of the actuator. Different types of leads crews can affect the speed and load capacity of the actuator due to the friction they each create. ACME lead screws are less expensive and can handle heavier loads, but have lower efficiency and may produce more heat. Ball screws, on the other hand, are more efficient and have higher speeds, but can be more expensive but still have high load capacities.

3. Motor specifications: The motor is responsible for providing the power to move the actuator. Different motor specifications can affect the speed and torque that can be produced. Higher RPM motors can produce higher speeds but may have lower torque, while higher torque motors can handle heavier loads but may have lower speeds. The size and weight of the motor can also affect the overall size and weight of the actuator.

Here's a table summarizing some of the features, pros, and cons of different AC electric actuator components:

The lifespan of an actuator is not only affected by its internal components but also its ability to withstand environmental intrusions such as solid objects and liquids. To ensure our electric actuators have long-lasting durability, FIRGELLI adds a protective seal around their exterior.