Everything You Need to Know About Linear Actuators
This article will give you a basic understanding of how actuators work and the terminology used to describe them. When you understand the basics it will be much easier for you to select your own electric linear actuator.
What is an Actuator?
An actuator is a device that requires an energy source input and an external signal input. These inputs create an output usually in the form of motion that can be either rotary or linear. For the purposes of this article we focus on Actuators that create linear motion, however we have created a much more detailed article that specifically focuses on Actuators in general, to view that go here "Actuators"
To help you further we have created an article called “Don’t Buy a Linear Actuator Until You Read These Five Steps.” This can help you avoid the many pitfalls of buying an electric linear actuator online.
We have also created a calculator that can be used to calculate what type of linear actuator you may need for a specific application. Simply enter some basic details into the calculator and the results will be shown. Click here for the Linear Actuator Calculator
Video Demonstration of an Actuator
What is a Linear Actuator?
An electric linear actuator is a device that converts the rotational motion of an AC or DC motor into linear motion. It can provide both push and pull movements.
This movement makes it possible to lift, drop, slide, adjust, tilt, push or pull objects with the simple push of a button. Just consider all the possibilities with a product that can do all this work for you at the touch of a button! and to make it even more attractive these Electric Actuators are incredibly easy and safe to install and set up. Today there are hundreds of millions of Actuators used in the world to perform many different tasks. We always say a Linear Actuator is ideally suited to applications that are the 3-D's Dirty, Dull, or Dangerous. However with the advancement of home automation we now find them been used extensively in the home and office to perform novelty tasks such as TV and Projector Lifting, Desk lifts, speaker pop outs and also kitchen appliance lifts.
Additionally, linear actuators allow the operator to have full control over the safe and accurate motion control they provide. They are energy efficient and have a long lifetime with little or no maintenance.
Installing an electric linear actuator is very easy compared to hydraulic or pneumatic systems. They also take take up much less space and are significantly cheaper than hydraulic and pneumatic actuators as they have no pumps or hoses.
An electric linear actuator consists of a DC or AC motor, a series of gears and a lead screw with driving nut that pushes the main rod shaft in and out. This is in essence what all linear actuators consist of. All that changes from actuator to actuator is the motor size, the gearing and the leadscrew. Some other electronics help to determine the amount of stroke limit switching and positional feedback options, but basically, an actuator is nothing more than a motor, some gears and a leadscrew.
What is a Lifting Column?
Lifting columns are another form of linear actuator. Typically, they provide a longer stroke because they have multiple stages. This allows them to expand and contract in a longer length than when they are fully closed. Another way to put it is that a column lift is an actuator within an actuator.
Another advantage of a column lift is that the linear guiding is built into the structure of the actuator and does not need adding externally. Linear actuators usually don’t cope well with side loading (we discuss that later). Column lifts have their guiding system built in which is why they are better for some applications over others.
What is a Micro Linear Actuator
Micro Linear Actuators or Mini Linear Actuators are used in applications where space is limited or the stroke of the actuator required is small. Perhaps you need to move something small or not very far then 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 Linear Actuator is that forces tend to be allot smaller due to the smaller Motors that drive them
The Benefits of Electric Linear Actuators Over Hydraulic Systems
Electric linear actuators are the perfect solution when you need a simple, safe and clean movement with accurate and smooth motion control. You can choose actuator systems for adjustments, tilting, pushing, pulling and lifting with fairly high forces.
A hydraulic system is capable of immense forces, but those systems require high pressure pumps, high pressure valves and piping, and a tank to hold all that hydraulic fluid in. So, if you have a lot of space and money is no object then hydraulics could be the way to go.
The hydraulic actuator uses fluid to push a piston backwards and forwards, whereas an electric linear actuator uses an AC or DC motor to drive a lead screw. The lead screw is fitted with a nut that runs up and down the lead screw, converting rotary motion into linear motion.
There are drawbacks to using hydraulics from an operating standpoint. The main one being control. You have very little precision control when it comes to these systems.
An electric linear actuator has a long lifetime with little or no maintenance at all. This ensures a very low total operating cost compared to other systems.
Electric actuator systems are quiet, clean, non-toxic and energy efficient. They fulfil the ever-increasing demands and legislation concerning environmentally sound equipment.
What Are Some Real-World Examples of What a Linear Actuator Can Do?
Linear actuators move things and we have seen thousands of applications over the years.
Some examples of practical automation applications are:
- Motorized hatches
- Kitchen appliance lifts
- Throttle control
- Marine engine hatches
- Slide-out steps
- Snowplow adjusters
- Hidden doors
- Solar panels
- Sliding doors
- Sliding window treatments
- Farming implementations
- Animatronics and robotics
Industrial applications include:
- Damper control and height-adjustable workstations
- Home automation such as moving TVs or projectors
What is the Difference Between Static Load and Dynamic Load?
You may see on our spec sheets both static and dynamic load. Dynamic, or lifting load, is the force that will be applied to the linear actuator while it is in motion. Static load, sometimes called the holding load, is the force that will be applied to the linear actuator when it is not in motion. The dynamic load is what you need to move something and the static load is what you need to then keep that something in place.
In What Direction Can Loads be Applied to Linear Actuators?
Linear actuators can be used in tension, compression or combination applications. We refer to this as the pushing or pulling force. Sideloading or cross-loading should be avoided. In a situation where side loading cannot be avoided, we suggest to customers to use linear slide rails or drawer slides in their system. The slide rail can handle much more side loading than the actuator. By reducing side load the linear actuator can perform its maximum pushing and pulling force.
Is Side Loading Permissible on Linear Actuators?
Sideloading, or radial loading, is a force applied perpendicular to the linear actuator centerline. Eccentric loading is any force whose center of gravity does not act through the longitudinal axis of the actuator. Both sideloading and eccentric loading should always be avoided as they can cause binding and shorten the life of the linear actuator. However, if you use a drawer slide in the application this will greatly impact how much loading can be applied. By placing the object you are moving on a drawer slide it allows the weight to be carried by the slide instead of the actuator taking all the weight. Another option when you are dealing with side loading is to use a track actuator.
Do Linear Actuators Have Limit Switches?
Most linear actuators come with limit switches built into them. The type of limit switches available varies with each product range. These include electro-mechanical, magnetic proximity and rotary cam. Limit switches are normally pre-set on actuators to stop the actuator stroke when it gets to its full extension and full retraction. The purpose of using Limit switches in Linear Actuators are to prevent the Actuator from stalling once it gets to the end of its mechanical limit. If the Actuator stalls, the motors still try to keep going that will eventually result in the Motor burning out. This is why Actuators typically have built in Limit switches, to switch off the electrical power to the motor once it gets to the end of stroke. Reversing polarity then allows the actuator to change direction.
Limit switches are important because they prevent the actuator from burning and stalling the motor when it reaches the end of the stroke. The limit switch simply cuts power to the motor.
External limit switches allow you the flexibility to set the limits of travel in your system to fit your particular application. The customer is responsible for properly setting the limit switch in the unit. If the limit switches are not set or are improperly set, the unit may be damaged during operation.
What is an adjustable limit switch Linear Actuator?
Actuators with built in Limit switches are not adjustable because they are set at the factory as they are been assembled. However FIRGELLI® have developed the worlds first externally adjustable limit switch Actuator (Patent Pending) that allows the user to be able to adjust the final inch of travel of the Actuators stopping position. We have written a separate article just on this clever new device here "How does an Adjustable limit switch actuator work". This new product makes it very easy to adjust the final end stroke of the travel to help with the applications installation process. In most cases it unlikely the application requires an exact fixed stroke length, or in some cases the stroke may need to be adjusted over time, which is where this type of Linear Actuator would come in extremely handy. In many cases the application requires its stroke to be adjusted over time to account for shrinkage or wearing in or an application over time. So having a Linear Actuator that has built in adjustable limit switches would really help to keep things going smoothly. The video below shows how this type of Actuator works.
What Type of Motors do the Linear Actuators Use?
Linear actuators are available with AC or DC motor variants. However, each range has preferred standard types. DC motors are the most popular and are typically 12 volt. 24 volt motors are used for more industrial applications or in high force actuators where they are more efficient.
The AC motors will be either 220-240 VAC 1-phase motors, 220-240/380-415 VAC 3-phase motors (50/60Hz) or 24VDC motors.
Are Linear Actuators Available in Different Speeds?
This video below is a quick introduction to all the main features on our Premium Linear Actuators.
Linear actuators are available in a variety of linear speeds and a standard list is detailed with each product. To achieve differing speeds the gearing on the actuator will change. Please note, when gears are changed to affect speed, force will be changed as well. Force and speed always trade-off against each other.
What is the Duty Cycle Capability of a Linear Actuator?
Duty cycle rating for a linear actuator is generally expressed as a percentage of “on-time” (the ratio of on-time to total time) or as distance traveled over a period of time. The duty cycle rating is expressed differently for different actuator types. For a more detailed discussion of duty cycle, see the blog post "What is Duty Cycle in a Linear Actuator?"
What Type of Mounting do the Linear Actuators Have?
The linear actuators generally have mounting points we call clevises at each end of the actuator to allow a pivoting movement. There are a number of options. Double clevis is standard but typically each actuator has its own standardized mounting bracket that you would use.
What Type of Enclosures do the Linear Actuators Have?
Linear actuators have different IP ratings. The lower the number, the lower the protection is. For example, IP54 offers basic protection such as dust and IP66 offers a waterproof protection and is ideal for outdoor use. This chart below shows the IP rating of each of Firgelli's linear actuators. We also wrote a separate blog post just on the topic of linear actuator IP ratings here.
Is Back-driving Possible in Electro-mechanical Linear Actuators?
Unless otherwise stated, back-driving is possible in all electric linear actuators. Back-driving is when a force is applied that is greater than the static force, allowing the actuator shaft to move without any power applied to it. Actuators that use a ball screw are normally fitted with an electrical brake (typically motor mounted) to prevent the load from back-driving the actuator.
Can a Linear Actuator be Run Into a Hard Stop?
We don't recommend applications that have possible hard stops because it can lead to the actuator becoming jammed. Examples of jamming include over-travelling the limit switches and jamming the nut and screw internally at the extreme ends of the stroke or driving the actuator against an immovable object and thus overloading the actuator severely.
What Are the Common Factors in the Failure of a Linear Actuator?
Improper loading, improper installation, excessive duty and extreme environments may contribute to premature actuator failure. The most popular by far is overloading due to amplification of force.
Can Two or More Linear Actuators be Synchronized?
Small differences in motor speed in identical actuators is fairly normal. And different actuator loading may cause the units to get out of synchronization very easily. The units cannot, therefore, be guaranteed to run in synchronization. For exact synchronization a closed-loop control system is recommended. This is possible using an actuator with built in feedback. The feedback data is sent to a controller and the controller then calculates how to make the actuators run together regardless of their loading or speed differences. Feedback actuators include potentiometers, optical sensors, or hall sensors. Our blog post "Achieving Synchronized Motion Using Firgelli Linear Actuators" provides more detailed information on this topic.
Are the Actuators Lubricated for Life?
Linear actuators are grease lubricated for the internal parts of the actuator including gearbox assemblies and the leadscrew and nut assemblies. The actuators are greased for life.
In the temperature test, the actuators are tested to operate in extreme temperatures as well as to endure rapid changes in temperature. In most cases, tests are performed on the actuator to withstand going from a +100°C environment to -20°C repeatedly and still maintain full functionality.
For a more in depth look at how a linear actuator works, we created this article "Inside a Linear Actuator - How an Actuator Works."