Understanding Fluid Power: An In-Depth Look at Types of Actuators
Manufacturing products require a lot of efficient machinery and many times that equipment includes actuators. But different actuators are used for different applications. So, how do you know which actuator is best for your application? And what types of actuators are available, anyway?
Here is our guide to the two most common types of actuators — linear and rotary, the many variations of each, and their top applications.
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- Pneumatic Linear Actuators
- Hydraulic Linear Actuators
- Electric Linear Actuators
- Rotary Actuators
- Other Actuators
What is an Actuator?
An actuator is a device that makes something move — forward, backward, or at an angle — to a specified distance or number of degrees. Actuators are also used to slow, stop, and hold. They work by converting energy from a power source (air, liquid, or electricity) into force.
For example, an elevator goes up and down, but it also has to stop and wait at floors along the way. The doors open and close. In a processing plant, raw materials are conveyed along a complex path where they may be gripped, raised, turned, stamped, etc. until the final product is complete. Actuators, also called cylinders, make all these movements possible. Without them, automated equipment could not exist.
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Common Types of Actuators
There are two basic types of actuators, but there are numerous variations within each category. The two basic types of actuators are:
- Linear, those that move a load in a straight line either forward and/or backward or up and/or down, depending on the axis.
- Rotary, those that move a load in a circular or angled direction up to a full 360 degrees. (Some rotary actuators can actually continue spinning.)
Whether a linear or rotary actuator is best for a particular application depends on several factors including:
- Load type
- Holding power
While we can generalize about the pros and cons of different actuators in relation to each of these factors, the truth is that every industrial design project is unique in some ways. The more you know about the types of actuators and their capabilities, the easier it will be to identify the right one. (Sometimes, the right one is custom-designed.)
In this guide, we’ll take a closer look at the various types of linear and rotary actuators as well as a couple of other types that are sometimes used for industrial purposes.
Linear actuators are amazingly versatile because their operation is simple: the actuator moves a precise distance (measured in inches or millimeters), then stops. That means they can push and/or pull loads in a straight line, but that same essential motion can also be used to clamp, block, lift or lower, and eject something. Linear actuators are often paired with motors to operate pumps, valves, and switches.
Linear actuators can be powered by compressed air, hydraulic fluid, or electricity. Regardless of power source, they are reliable and cost-efficient to operate, though not necessarily under the same circumstances.
Pneumatic Linear Actuators
Pneumatic devices run off a compressed gas, usually air. The gas is pumped into one end of the cylinder and then pushed out the other end, pushing a piston forward. The piston drives the load. Pneumatic air cylinders are widely popular because compressed gas is commonly used for many purposes in industrial settings, so there is no need for a secondary power source.
There are four different styles of pneumatic actuators — rod, cable, rodless, and magnetically-coupled. They can be single- or double-acting. Single-acting actuators work in one direction only. They push the piston forward, then an internal spring or simple gravity return it to the original position. In a double-acting cylinder, force is used to move the piston (and, therefore, the load) in both directions.
Pneumatic Rod Linear Actuator: In this type of actuator, there is an internal rod, which extends outside the cylinder to move the load forward and then retracts. Typically, the rod and the bore are round. However, W.C. Branham makes a unique oval-bore version, which eliminates any chance the rod will become misaligned over time as it extends and retracts.
Pneumatic Cable Linear Actuator: As the name implies, cable-driven actuators use an internal cable instead of a rod to move the load. The cable fastens to the piston inside the cylinder but also extends outside, where it attaches to a pulley. Cable actuators are very efficient and function well where high repeatability is needed. They can also work with spring-assist for emergency stopping. As with all types of actuators, correctly sizing the device is essential.
Pneumatic Rodless Actuator: Rodless cylinders are a good choice where space is very limited because there is no rod to protrude from the cylinder as it extends. W.C. Branham’s DURATRK rodless cylinders can provide the same amount of force in about 45% less space. They can be spec’d in multiple bore sizes and lengths.
Pneumatic Magnetically-Coupled Linear Actuator: This style of actuator uses magnets instead of physical attachment to draw and retract the piston within the cylinder. The piston is sealed within a tube, which attaches to a carrier using magnetic force so that the piston and carrier move together as one. Magnetically-coupled cylinders are very powerful. They can be sized to move loads a very short distance or several feet. Because the piston is sealed inside, there is no danger of damage from external dirt, corrosive materials, or other harsh elements.
Pneumatic Air Actuator Applications
Pneumatic linear actuators are ideal for applications that require strength/high torque and speed but need a light-weight product. They can withstand temperature extremes from 250-degrees Fahrenheit to -40-degrees Fahrenheit as well as wet or harsh environments. They can be made of stainless steel to meet extreme standards such as those for food and beverage processing or semiconductor clean rooms. They are also a good choice for environments where safety may be a special concern because there are no motors to generate magnetic interference that could cause an explosion.
With pneumatic air actuators, there are no worries about contamination from leaking hydraulic fluid, which makes them an excellent choice for car washes as well as production plants.
They can streamline material handling when tasks involve a complex series of movements such as multiple starts and stops, high speeds, or changing speeds. Although all pneumatic linear actuators can provide precise movement, they can also be fitted with positioning sensors when even greater precision is needed. Branham’s oval bore models are especially valuable where precision is critical such as in medical device manufacturing.
Pneumatic air actuators are available in a wide range of sizes, styles, and configurations, can be used with a variety of mounts, and require minimal maintenance.
Hydraulic Linear Actuators
Linear actuators that use hydraulic fluid can generate a tremendous amount of force and hold it almost indefinitely because fluid is virtually incompressible. In fact, a hydraulic actuator can produce 25 times more force than a similarly sized pneumatic actuator. However, hydraulic power can also perform subtly because that same fluid incompressibility allows for precise linear control.
Not only can a hydraulic actuator dish out the force, but it can also stand up to shock loads as well as dirty or otherwise harsh working conditions. Like their pneumatic cousins, hydraulic linear actuators can be single- or double-acting.
Hydraulic Rod Linear: It takes a lot of force to move, control, and hold the heaviest loads, and that’s where hydraulic rod actuators shine. Think elevator operation or a car carrier that has to lift and lower automobiles. Rod-style hydraulic cylinders can exert up to 5,000 psi (compared to a similar size pneumatic actuator that would provide just 100-200 psi).
Hydraulic Cable Linear: A cable style hydraulic actuator under low pressure can provide very smooth movement.
Hydraulic Actuator Applications
Hydraulic linear actuators are useful in a broad array of applications, especially various forms of material handling. They can move loads forward and back, clamp, press, lift, turn, and rotate items. They can stop loads and ensure no-fail hold. They are tough, reliable, and can be configured in many different ways to enable standardized equipment design. Perhaps surprising, hydraulic actuators can be quite compact in size and still deliver high-force performance.
You might think of them as the tortoise and pneumatic actuators as the more nimble hare.
Hydraulic systems can be self-contained, enabling mobility. This is why heavy-duty construction and shipyard equipment, forklifts, etc. use hydraulic actuators. In static manufacturing facilities, the system’s motor and pump can be located some distance away without sacrificing power.
Hydraulic systems require more maintenance than other types of actuators because there are more moving parts. Seals wear out and have to be replaced, and the potential of leaking fluid makes hydraulic cylinders inappropriate for applications where sanitation is critical such as clean rooms, food processing, and beauty product manufacturing.
Electric Linear Actuators
Electric actuators use a motor as their power source, so the process is somewhat more complex. In most pneumatic and hydraulic actuators, pressure moves a piston that moves the load. In an electric actuator, there is no piston, there is either a screw or a belt (similar to the cable in other actuators). The electric motor activates gears, which turn the screw or drive the belt to move the load. That means the motor must be an integral part of the actuator set-up, which requires more space.
On the other hand, electricity is universally available, whereas compressed air or hydraulic fluid systems may not be.
Electric actuators are more expensive to buy than other types, but they are less expensive to operate. They can be used alone or grouped to perform multiple tasks in sequence such as reaching, lifting, tilting, or rotating. Both screw-driven and belt-driven electric linear actuators can provide high-speed, precise, repeatable position control. And they are strong. They can generate force between 2,000 and 4,000 pounds.
Electric Belt Actuators: Electric actuators that use a timing belt are 90% efficient, easy to operate, and long-lasting.
Electric Screwdriver Actuators: Electric linear actuators that use a screwdriver are especially useful for high-thrust applications and where accuracy and repeatability are essential.
Electric Actuator Applications
Electricity is infinitely scalable and controllable, so electric linear actuators are a great choice for applications that require extreme precision. They can also be programmed electronically for remote operation. Due to their motorized operation, they are best for situations that require only a few cylinders. However, they are very versatile, making them valuable for tasks such as material handling, robotics, operating cutting equipment, positioning solar panels, raising and lowering heavy, hard-to-reach windows, and opening and closing valves.
Electric linear actuators are completely sealed, so they are clean to operate. That makes them a good choice for sanitary environments such as manufacturing of medical devices, semiconductors, and for food and beverage processing — applications where the process itself has to be pristine and where equipment is also subjected to harsh water and chemical washdown treatment.
Where linear actuators can move loads only in a straight line, rotary actuators can move them at virtually any angle or provide continuous spinning. Picture a conveyor with a swing gate that pivots into position to divert an item onto another conveyor, into a box, etc. Or an arm that lifts and turns the item onto its side as it moves forward.
Rotary actuators are often used in conjunction with linear actuators. They can be powered by either compressed air or hydraulic fluid systems.Back to top
Other Types of Actuators
When we discussed electric linear actuators, we mentioned belt and screw drive options. But there is another type of actuator altogether that is driven by a rack and pinion gears. In this system, a circular toothed gear, called a pinion, meshes with the teeth on a bar (the rack) as it rotates, converting that rotational motion into linear movement.
Rack and pinion actuators can drive very heavy loads, so they are often used in applications such as stairlifts and rack railways that run up and down a steep slope. Rack and pinion systems are also used to provide smoother steering in automobiles.Back to top
Because actuators go to the heart of the job, it can be virtually impossible (or impossibly expensive) to change them out once equipment is installed. That makes it all the more imperative that you make the right choices to begin with.
W.C. Branham manufactures several styles of pneumatic actuators, including our exclusive oval-bore model, as well as some types of hydraulic cylinders. All are available in numerous sizes and configurations. We’ve been in business for many years helping companies and design engineers find “solutions in motion” that exactly fit their needs. Visit our product page to learn more.
One thing we know for sure is that no two projects are the same. That’s why we don’t simply make and sell actuators, we provide as much advice and as many recommendations as you need. We are always happy to modify or completely custom-design a product.Back to top