How Does a Linear Actuator Work?

By Shizu Yamaguchi

Today we will be covering how a linear actuator works and defining the different types and component parts. We will also go over some important variables to consider when selecting a linear actuator for your application. Let’s jump in.

What is a linear actuator?

A linear actuator is a system that transforms the rotational, mechanical output of its motor into straight line motion.

What are the different types of linear actuators?

Mechanical actuators

These kinds of actuators allow you to manually translate rotary into linear motion by using a handle or control knob. The conversion from rotary motion into the linear motion of the actuator is done by a few different types of mechanisms: lead screw and belt drive.

Electro-mechanical actuators/electric actuators

These linear actuators are quite similar to mechanical actuators in that they also translate rotary into linear motion. However, instead of having a manual source of rotary motion, an electric motor is used to generate force.

There are many different kinds of electric actuators, with different manufacturers often applying their own proprietary designs.

Rod-style is one of the most common and simple designs of linear actuators. The shaft here retracts and expands. 

rod-style linear actuator
Fig. 1. Rod-style electric linear actuator, motor to the left, moving mechanism to the right. Photo: “Actuator” by Wikisity, licensed under CC BY-SA 4.0

Another linear actuator design is track-style. The overall length of this actuator does not change, making it well-suited for applications with space limitations.

Column lifts can be used as well for table and TV lifts.

Hydraulic actuators/hydraulic cylinders

These linear actuators are actuated by a hydraulic pump. The part being moved is a piston, which is inside a hollow cylinder. The piston is also attached to an external object. 

An offset is applied to liquid that is inside the pump, which leads to a force that displaces the piston. Then, the piston moves the external object it is attached to. This type of linear actuator can be expensive and consume a lot of space.

Pneumatic actuators

These actuators are similar to hydraulic actuators, except they use compressed air to generate force instead of liquid. One drawback of this type of actuator is that the air can be contaminated by its lubricants. This contamination can lead to downtime.

Piezoelectric actuators

The piezoelectric effect is used to generate force for this type of actuator. Essentially, the effect is a characteristic of certain materials that can translate voltage into material expansion. Although these kinds of actuators are able to attain very high levels of precision in terms of positioning, their range of motion is generally quite limited.

What are the different components of the different kinds of linear actuators?

Motor: This part of an electric linear actuator provides a source of energy or power to the system via the principles of electromagnetism. Its output is rotational motion, which the linear actuator system translates into linear movement.

Gears: These ridged circular metal objects translate rotational motion into further rotational motion in a lead screw.

Lead Screw: This elongated cylinder with threads partners with a nut to translate rotational motion into linear motion. A lead screw can be either attached to an enclosed shaft or a carriage.

Limit switch: This is a button that when pressed down or activated, leads to the shut off of the motor. The purpose of this object is to stop the linear actuator system from overheating or overextending.

Motor coupling: This is the part of the linear actuator that takes the rotor’s rotational action from the motor and continues that movement in another attached shaft. This shaft, in the case of an electric linear actuator, is a smoothed portion of a lead screw.

Carriage: Attached to the nut, this rectangular object is made of bearings that connect to a rail or two rails on either side. This part of a linear actuator connects to the load of an object.

Load: This is usually the part of the system that is being driven by the linear actuator. The load is also defined as the force applied to the actuator when it is not moving.

Controller: This computer program is what an operator uses to activate the different functions of an electric linear actuator.

So how do electric linear actuators work?

We will discuss the workings of both rod-style and track-style electric linear actuators.

Rod-style 

For rod-style linear actuators, the current that goes through its motor creates rotational movement of its rotor or shaft. That shaft turns gears that are connected to a lead screw and nut, which make up the shaft. The shaft takes the rotational movement of the gears and turns that motion into linear movement. As the lead screw turns, the nut is moved linearly, creating the desired straight line motion.

To create the back and forth motions of the lead screw, the polarities of the current running through the motor must be reversed. In order to ensure that the motor “knows” when to switch the direction of the current, a small switch is installed within the shaft of the actuator. This limit switch is also used to ensure that the motor gets shut off each time the full length of the shaft is extended and each time the shaft is brought back into its original position.  

Limit switches are installed close to the bottom of the shaft and midway through the top of the shaft. The nut triggers the limit switch by running into it essentially as it moves up and down the lead screw.

To learn more about how a linear actuator motor functions, please read this article.

Track-style

track-style linear actuator
Fig. 2. Track-style electric linear actuator, made by igus

For track-style linear actuators, the motor, via a direct current, creates rotational motion of its rotor shaft. That shaft is connected to a motor coupling, which does the work of taking the rotational motion from the motor and putting that same rotational motion into work in the attached lead screw and nut. As the lead screw turns, the nut moves up or down the lead screw. This nut is attached to a carriage, which in turn is usually connected to some kind of load or positioning item.

There are two different ways this kind of linear system can “know” when to stop the motor when the carriage has reached one end and needs to return back to its starting position.

The first way involves a controller. This item is a computer program that is connected to the motor. The controller communicates to the motor how many times it needs to rotate (for example, spinning 300 times) before it needs to reverse polarities. This way, a backwards or forwards motion of the carriage can be created on the linear actuator without the motor burning out.

Second, an optical sensor or mechanical limit switch can be used to indicate to the motor when the linear actuator carriage has reached the one end of the length of the actuator and when the carriage needs to be moved back.

How do you select the right linear actuator?

Here are some important factors to consider when selecting your linear actuator. (Much will depend upon your application requirements).

Energy source: Most linear actuator applications can do with a DC motor, EC/BLDC motor or stepper motor. Please see the following blog post for further details on linear actuator motors.

Precision level: Determine whether you require something heavy duty or something more precise and for what length of time that precision will be required.

Force: Ensure in advance that the weight that your actuator needs to move is appropriate for the amount of force your motor can output.

Stroke length/distance moved: Most manufacturers sell linear actuators of various lengths that are customizable.

Speed: This is usually the most important factor for people when selecting their linear actuator. Those linear actuators that are able to output high force would usually move slower than those outputting low force.

Operating environment: Consider whether you are working in a rough environment with dust, chemicals or humidity.

One great way to select the appropriate linear actuator for your application is to use an online tool. With basic variables in hand, such as the ones described above, the right system can be selected. igus® offers both online tools for mechanical linear actuators and for track-style (space-saving) electric linear actuators so you can easily configure your own that are based on your application’s requirements.

igus® makes highly engineered wear-resistant plastic components, such as plastic bearings and linear actuators with plastic sliding liners. Long, predictable service life, zero maintenance and low costs make igus® an ideal choice for engineers looking to design projects that last and save them money over time. You are welcome to visit us at www.igus.com or call us at 1-800-521-2747 about your upcoming project.

References:

Test and Measurements World, Accessed 16 June 2021, https://www.test-and-measurement-world.com/Terminology/Advantages-and-Disadvantages-of-Pneumatic-Actuator.html 

Progressive Automations, Accessed 19 April 2021, https://www.progressiveautomations.ca/pages/actuators.

Wikipedia, Accessed 19 April 2021, https://en.wikipedia.org/wiki/Linear_actuator.

Dickson, Robbie, 2019, Firgelli Automations, Accessed 20 April 2021, https://www.firgelliauto.com/blogs/news/how-does-a-linear-actuator-work.

2015, Accessed 20 April 2021, NBK, https://www.nbk1560.com/en/resources/coupling/article/couplicon-about/?SelectedLanguage=en#:~:text=Coupling%20is%20a%20component%20used,providing%20misalignment%20for%20the%20shafts

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