Since the electric motor invention, engineers have been searching for ways to use their principle of operation to generate linear motion instead of rotary motion, as seen in rotary actuators. In the past century or so, they've devised a variety of ways to make this happen.
The most common method of creating linear motion is using jackscrews, which, in essence, screw-like those that raise a car's chassis when turned. Jackscrews exist in everything from boat winches and elevators to printing presses and conveyor belts.
But if you're still confused about what defines linear actuators, you aren't alone. That's why we're tackling this confusing topic and explaining it to you once and for all. We've come up with a guide that'll give you all the information in a simple, easy-to-understand manner.
What Is a Linear Actuator?
Linear actuators are simple electromechanical devices that turn electrical power into linear motion instead of rotational actuators. Linear actuators tend to be more compact, accurate, and reliable than rotary actuators, making them the ideal solution for many applications that involve linear motion.
Linear actuators also have the distinct advantage of requiring fewer gears or other components to convert rotary motion into the desired amount of linear motion. For example, some jackscrews need several gears to generate one inch of linear motion. Linear actuators need only two or three components at most.
Linear actuators can turn a simple push or pull into an arc that'll extend as far as your arm will allow. In fact, the versatility and simplicity of linear actuators make them a favorite among industry professionals.
How Do Linear Actuators Work?
Linear actuators are simple electromechanical devices that rely on an electric motor and a threaded rod. The threaded rod connects to the object that moves in a line. At the same time, the engine causes rotary motion inside the threaded rod. As the rod turns, it moves along an axis. Simple as that!
Linear actuators consist of two primary sections: a telescopic section and a drive section. The telescopic section consists of two metal bars (called "action" and "drag") which slide along one another when moved by the motor inside them. The drive section contains a motor and an attached threaded rod. The motor turns, driving the threaded rod along inside the telescopic section.
As the threaded rod moves, it causes actuating motion in the action/drag bars, moving them along an axis (hence "linear actuator"). Yet, the precision of linear actuators relates to the action/drag bar design and their embedded motors, so this is where picking the right actuator comes into play.
What Are the Types of Linear Actuators?
Linear actuators exist as four main types, according to the way they're powered. The four types are electromagnetic, pneumatic, hydraulic, and piezoelectric. These actuators can be active or passive, with the former relying on electrical power and the latter having no power source.
At first, you might think that it's a negative thing actuators aren't more generalized in their function. But the fact that there are so many types will only benefit you in the long run. As different industries have encountered various problems. They have devised their own solutions using new types of linear actuators to better handle their unique challenges.
The result is a bunch of different types of actuators that fit specific needs and issues. This in itself is a massive benefit since it allows each type of linear actuator to serve its own purpose and do it better. Here's a breakdown of how each type of actuator works and what they set out to achieve.
Electromagnetic actuators use an electric current for their operation. The principles behind electromagnetic actuators are like those for electromagnetism, driving motors, or solenoids. The current drives a wire wrapped around a ferromagnetic material such as steel, which twists and pushes against the drag bars.
When a current happens, it generates a magnetic field that attracts other ferromagnetic materials such as iron. Once the current stops flowing, the magnetic field gets weaker, and the iron core flies out of the cylinder. This principle allows electromagnets to pick up metal objects, so electromagnetic actuators' linear motion changes by switching direction.
For it to work, there must be a spring mechanism that keeps tension on the wire to "fling" the core and return it to its original position. As you can imagine, this is where the resilience of linear actuators comes into play. They are far more durable than you might think.
Pneumatic actuators share the same functionalities as pneumatic tools. These serve the same form and functions as various types of tubes, cylinders, and valves. Pneumatic actuators work by using compressed air or fluids to power things like pistons. When air or liquid is introduced into the cylinder, it pushes on a piston which causes it to move.
It's important to remember that pneumatic actuators are usually simpler and more compact than hydraulic ones, making them an excellent option for at-home applications. Yet, they're typically limited by the gas's most extensive pressure or fluid to drive the piston. Also, they need more maintenance and care than other types of linear actuators.
To use a pneumatic actuator, you simply need to start air or fluid flow through the working cylinder. Remember that air-powered linear actuators are almost always paired with an electric pump to provide an air supply when needed.
Hydraulic actuators are rams that can be used for such tasks as lifting or moving heavy objects. They consist of a cylinder and piston submerged in oil, which provides resistance due to their viscosity.
When the current passes through, heat is generated and reduces the viscosity of the surrounding oil. The resulting decrease in resistance makes it easier to push down the piston against the oil's resistance.
When you use a hydraulic linear actuator, a fluid (generally oil or water) is pumped into the cylinder, forcing it to expand. This process is controlled by a valve and causes an attached object to move relative to the ground.
Piezoelectric actuators work on the principle of piezoelectricity, which is the electric charge that accumulates in certain materials when they're put under mechanical stress or pressure. For example, if you crumple up some aluminum foil, it'll generate an electric charge, and you will create a spark if you touch it.
It turns out that this process can produce linear motion rather than electric charges as well. The way it works is that crystals are attached to both sides of the material, and then the voltage is applied across them. One of the crystals acts as an electrode and makes electrons flow in one direction through the material. In contrast, the other crystal makes them move in the opposite direction.
Piezoelectric actuators are typically found in such applications as stereolithography machines and printers, where exact positioning and precision are paramount to success.
What Are Linear Actuators Used For?
Linear actuators are widely used in several applications, but they all have one thing in common. It may sound obvious, but they can make an object move linearly.
That may not seem like a big deal. Still, when you consider how many things need linear movement to be effective, it makes sense that the need for this kind of device is so prevalent everywhere. You can see examples of linear actuators everywhere in everyday life, from inside the home to the world's most giant warehouses and manufacturing facilities.
Linear Actuators in the Home
A typical household uses for linear actuators include garage doors, gates, and the drapes in your living room. The mechanisms are lightweight and compact enough to fit conveniently into the homes of non-manufacturing sector consumers. Linear actuators are also commonly found in drive-thru windows and at bank teller windows.
Most people don't realize that they are included as part of everyday items such as doors, garage doors, and windows. Yet, these devices are commonplace in what you might consider high-end construction materials due to their versatility.
They serve the same purpose at the end of the day, just on different economies of scale. Here's some more detail on how these linear actuators work around your house.
Garage Doors and Iron Gates
Linear actuators are a small but essential element in the large, hulking machines that open and close garage doors. Linear actuators are used to push a large, heavy door opener back and forth to open the garage door.
Suppose you've opened up your garage door manually and looked inside at all the parts. In that case, you may have seen the electric motor connected by a chain to a pulley system that opens the door.
TV Mounts and Stands
TV mounts and stands probably aren't the first thing that comes to mind when you think about linear actuators, but they're doing an essential job. These are used to adjust your television angle with minimal effort. They're most typically used in hotels to make it easier for housekeeping to clean and change hotel televisions' channels. Still, you'll find them in some household mounts too.
Another example of this is in your car. Cars use linear actuators as a part of their braking system. The driver's brake pedal is connected to a push rod that runs down to the master cylinder. This is where hydraulic fluid pushes against pistons inside the cylinder, which causes shoes on each wheel to expand.
Linear Actuators in Industry
Linear actuators come with many applications in industrial settings within manufacturing plants. For example, in manufacturing, linear actuators act as pressure chambers. These then generate high-pressure water jets to cut, shape, or drill materials such as stone, aluminum, steel, and concrete.
But they are generally used for lifting and transportation. In a warehouse, they're used to lift heavy objects such as pallets or containers from one place to another. They may also be found in other distribution-type settings. In these settings, they raise, lower, and push large through the plant or from one dock to another.
Linear actuators can also be found in the application of assembly lines, where they are tasked with moving individual pieces of the assembly line along its cycle. Below are some more specific use cases of linear actuators from the assembly line.
Conveyor systems use linear actuators to transport materials. There are a variety of conveyor systems that perform a variety of functions. A belt conveyor uses a series of pulleys or rollers to move items horizontally. The electric motor powers the roller device, which moves along the track to deliver items.
Strapping machines use linear actuators to bundle items together via strapping tape. This machine consists of clamps, a drive head, and an end effector that makes the final connection. The end-effector also makes it possible to attach the ends of the strapping tape to the corresponding side.
Pick and Place Robots
These robots are designed to pick up objects from a shelf and place them into another container. This is an important task that assists humans with their daily jobs. There are two types of robots used in this application. The first type is designed to handle rigid objects like boxes. In contrast, the second type (micromanipulators) takes care of delicate items like sandwiches or hamburgers.
Linear Actuators Used for Automation
One of the biggest crossover industries for linear actuators is automation, whether industrial or for technical and scientific purposes. For example, robotic arms often need a linear actuator for precise movements of the arm. In this case, the devices are used to lift and lower the objects in a controlled manner.
The main difference is that linear actuators must withstand high amounts of wear and tear from daily use in the automation world. A motorized linear actuator must be able to work over and over again without breaking. These devices often have to lift heavy objects as well, which can weigh upwards of 1,000 pounds!
Because these machines are often involved in the manufacturing process and specialist research, it's vital that they don't collide with other bits of the machinery or with people who may be nearby. That's what makes this technique so suitable, as it can provide the exact movements required.
Automated Guided Vehicles(AGV)s
AGVs are essential to the warehouse system because they help move larger packs around the facility. An AGV is a small vehicle used in environments where the workers need to get things from one place to another. As you can imagine, these vehicles are vital in industrial settings where the workers need to transport heavy loads over long distances.
The AGV moves along a track made up of conveyor belts and used sensors to determine if the route is exact or if there's an obstacle ahead of it, like a forklift. It uses stop-and-go technology and is used primarily for delivering items. Still, it can also be used for carting large bins out of the warehouse as needed.
When AGVs are being operated by an operator, they are often referred to as "ride and drives." When they are fully automated, they are referred to as a "moving walkway" or "robot conveyor." The big difference is that once it has reached its destination in the moving walkway, it must be able to detect the location and stop itself from gliding away.
Linear Positioning Table
Linear table systems use linear actuators to control the position of a table supported by wheels or rollers. The linear actuator will supply the force required for top-down positioning (i.e., moving the object to its starting point). These systems are available in 2-axis and 3-axis configurations.
2-axis systems will move the table in a back and forth fashion, while 3-axis systems can move the table upwards and downwards and left and right.
One of these tables' main uses is for staking items onto a substrate, which requires the linear actuator to lift up when retracting and lower down when advancing. It also has to supply the necessary retracting force to keep the object in place, which is why it's essential to choose the right linear actuator.
Users can also control how a linear positioning table moves by controlling how much force they apply using a control panel or computer. By making small adjustments, users can ensure that their objects are in the exact position they want them to be without wasting time.
Printing Machines and CNC Machines
Linear actuators are used extensively in printing machines where they're typically called servos. They are used for the printing machine's automated tasks, including moving belts, lifting print heads, and moving the carriage on a CNC machine.
CNC machines use linear actuators to position the bit wherever it needs to be for milling or cutting. These must be set at exact angles. Otherwise, they can cause damage to other parts of the machine. In fact, many printers use several servos to achieve more intricate movements for printing purposes.
The linear actuators are also used to move the print head relative to the moving bed during the printing process. And, though this may seem like a simple task, it's actually not, as many factors need to be considered.
How fast you advance or retract depends on how quickly you want it to print and how much weight is on the bed. Also, you must consider the speed at which any other parts of the assembly are moving.
When Not to Use a Hydraulic Linear Actuator
Suppose you find yourself looking for a way to move a heavy object or something of moderate size. Still, you don't want the acceleration and deceleration effects. In that case, a linear actuator is probably not the ideal solution. This is because linear actuators mostly rely on hydraulic pressure and can only apply force to an object if there is enough time for it to generate pressure.
Hobbyists have also seen these limitations. Hobby users of robotics find them too slow to power the main motors for a robot's legs or arms. Instead, they are best suited as smaller actuators that control joints or do other tasks where speed isn't as critical. The hobbyist will often use a servo motor in conjunction with the linear actuator to change direction and/or speed.
Thus, linear actuation is excellent for precise, controlled movements where extreme precision and consistency are necessary. But it's not ideal for rapid changes in direction or heavy lifting applications. This drawback is something that all linear actuators have in common, and you should consider these when evaluating them.
Linear Actuators Are Everywhere
The uses for linear actuators are almost endless. They occur everywhere, from the production lines of shipping and manufacturing centers to the cars we drive throughout our daily lives.
No matter where you look, you'll find that there's some form of the linear actuator in use. These machines are the beating heart of countless machinery pieces that we all rely on to get things done every day.
The best way you can use a linear actuator is to match it up with your application. Take into account what tasks it will have to do and what kind of force exerts upon it. This will help you work out the lifting weight, how fast it needs to move, and if it's strong enough for your needs.
If you're working on a product that you know needs an actuator, whether you know which type or not, get in touch today for a quote, and let's see how we can lift your project to new heights!