Everything you need to know about linear Actuators
This blog will help you understand all the terminology used, and to give you an understanding on how a Linear Actuator actually works and operates. When you understand the basics, it makes it much easier for you to select your own Electric Linear Actuator.
Firstly however lets define what an Actuator is?
An Actuator is a device that requires an energy source input, an external signal input, both of which then create an output usually in the form of a motion that can be either Rotary or Linear.
For the purpose of this Article we will focus more on a Linear Motion Actuator.
To help you further we have created an article called “Don’t by a Linear Actuator until you read these 5-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 show. Click here for the Linear Actuator Calculator
What is a Linear Actuator?
An electric linear actuator is a device that converts the rotational motion of a AC or DC motor into linear motion – that is, it will provide both push and pull movements.
By pushing and pulling it is possible to lift, drop, slide, adjust, tilt, push or pull objects, simply by pushing a button.
Additionally, Linear Actuators provide a safe and clean movement with accurate motion control that you, the operator have full control over. They are energy efficient and have a long lifetime with little or no maintenance.
Installing an actuator is very easy compared to hydraulic or pneumatic systems and they take up much less space, as they have no pumps or hoses. They are also significantly cheaper than Hydraulic or Pneumatic Actuators for the same reason.
An electric linear actuator consists of a DC or AC motor, a series of gears and a Lead screw including a driving nut that pushes the main rod shaft in and out. This is in essence what all Linear Actuator consist of, and all that changes from Actuator to Actuator are the motor size, the gearing and the leadscrew. Some other electronics help to perform 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, that allows them to expend and contract in a longer length than they are when fully closed. Another way to put it is that a Column Lift is an Actuator within an Actuator.
One other 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 Actuator usually don’t cope well with side loading (we discuss that later). Column Lifts have their guiding system build into the Lifts which is why they are better for some applications over others.
Why use an Electric Linear Actuator instead of say Hydraulic?
Electric linear actuators are the perfect solution when you need 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, where as 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. And that is control. You have very little precision control when it comes to these systems.
A 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 fulfill 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 hatch
- Slide out steps
- Snow plow adjusters
- Hidden doors
- Solar panels
- Sliding doors
- Sliding window treatments
- Farming implementations
- Animatronics and Robotics.
Industrial applications include:
- Damper control and height adjustable work stations
- Home Automation such as moving TV’s or Projectors.
What is the difference between Static Load and Dynamic Load?
You may see on our Spec sheets we mention both of these. Dynamic, working, 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 puling force. Side loading or cross loading should be avoided. But in these situations we suggest to customers to use linear Slide rails or guide rails in their system, to be able to handle any side loading, and rely on the Actuator to provide the pure push and pulling work.
Is side loading permissible on Linear Actuators?
Side loading, or radial loading is a force applied perpendicular to the linear actuator center-line. Eccentric loading is any force whose center of gravity does not act through the longitudinal axis of the actuator. Both side loading 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.
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 limit switches are important because it prevents the Actuator from burning and stalling the motor when it reaches the end of 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 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 in 12v typically. 24v motors are used for more industrial applications or in high force Actuators. 24v is more efficient for higher force applications
The AC Motors will be either 220-240 VAC 1-phase motors, 220-240/380-415VAC 3-phase motors (50/60Hz) or 24VDC motors.
Are Linear Actuators available in different speeds?
Linear actuators are available in a variety of linear speeds and a standard list is detailed with each product. All that will change in the Actuator to achieve different speeds is that the gearing will change. But please note when the gears are changed to get a different speed then so too will the force. 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.
What type of mounting do the Linear Actuators have?
The linear actuators generally have a mounting points we call clevises at each end of the actuator to allow a pivoting movement. There are a number of options, double clevis as 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. IP54 offers basic protection such as dust, and a higher IP66 rating offers a water proof protection and 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’s 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 over loading due to amplification of force.
Can two or more Linear Actuators be synchronized?
Small differences in motor speed 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 and that feedback data is sent to a controller where that controller then calculates how to make actuators run together regardless of their loading or speed differences. Feedback Actuators include Potentiometers, Optical sensors, or Hall sensors.
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 much more details overview on how a Linear Actuator works, we created this article "Inside a Linear Actuator - How an Actuator works"