Anyone who has worked in manufacturing long enough will tell you that compressed air has been used to move machinery for a very long time. Pneumatic actuators tend to be the go-to for many manufacturing processes requiring medium to high output and for good reason. Most facilities nowadays have access to compressed air lines already, and pneumatic actuators are economical, easy to install and maintain, and generally last a long time. So why is it that (just like with cars) electric has become an increasingly popular option over the past few years?

What is an electric actuator?

Electric actuators are just as they sound, motion devices that are powered by an electric motor, usually either a stepper or a servo. They come in many shapes and sizes, with many being similar in form factor to existing pneumatic cylinder designs such as extruded body, round body, rodless, and thruster style. Others may be more purpose-built, featuring a long, extruded body carriage or multi-axis designs with 2 or 3 actuators integrated into a system. Besides form factor, drive type is one of the biggest considerations when selecting an electric actuator. The two most popular types of electric actuator drives are belt and screw drives.

Ever consider replacing pneumatic actuators with electric actuators

Electric actuators come in many different shapes and sizes, including rodded, rodless, thruster type, table type, as well as belt, screw, and rack and pinion driven single and multi-axis carriages.

Belt Drive

Belt drive systems use a tensioned belt to convert the rotational motion of an electric motor to a linear motion used by the actuator. Belt drives excel when high speeds and long travel distances are required, such as in light-duty pick-and-place applications and 3D printers. Since the belts are flexible, they are well-suited for multi-axis systems, where one belt can be used to control two axes. The drawbacks of belt drives, however, include reduced payload capabilities and increased maintenance compared to other types of drives, requiring periodic adjustments to belt tension to function correctly. They are also less durable than other types of actuators, as oils and debris can drastically reduce the life of the belts.

replacing pneumatic actuators with electric actuators

Belt drive actuators excel at moving low loads at extremely high speeds. Belts also allow for the unique ability to control two axes with one belt, making them perfect for high speed, multi-axis gantries.

Screw Drive

Screw drive actuators use a rotating screw shaft and nut to move an actuator. Screw drive actuators can either use a ball screw, meant for high precision, low load applications, or a trapezoidal screw, meant for high force, low precision applications. The pitch, or the steepness of the screw can also be changed, with a larger pitch allowing for higher speeds and a shorter pitch allowing for higher force output. The biggest drawback to screw drive systems, however, is their limited speed and travel distance. If a screw shaft is too long or spinning too fast, it can experience a phenomenon called ball screw whip, where the shaft will begin to distort in the center, similar to a jump rope, which can damage or destroy the actuator.

replacing pneumatic actuators with electric actuators

Screw drive actuators can be configured with a trapezoidal screw (left) for high force output or with a ball screw (right) for high precision applications.

Benefits of Electric Actuators

Electric actuators are becoming an increasingly popular option over traditional pneumatic actuators for the following reasons:

Multi-Positioning

Perhaps the most obvious benefit of an electric actuator is its infinite positioning and adjustability. Most pneumatic actuators have only two positions; extended and retracted, (although multi-position cylinders are capable of having 3, 4 or even 5 positions.) Electric actuators on the other hand, have the benefit of being able to position themselves at any spot along its stroke of travel, allowing actuators to be finely tuned and changed as processes change.

Electric actuators also allow for advanced movement profiles, such as varying speeds, adjustable force output, and positioning in space relative to an XYZ coordinate system that would be impossible with pneumatic actuators.

Accuracy and Precision

As anyone who has worked with pneumatics will know, air tends to be very hard to control. For one, factors such as operating pressure, temperature, and humidity can all affect the speed and force of a pneumatic cylinder. In the case of multi-position cylinders, the compressible nature of air means that the repeatability of intermediate positions is questionable at best.

Electric on the other hand, is much easier to control, and as electric motors typically use either stepper or servo motors, they have the benefit of high accuracy, high repeatability movements as well as torque control, resulting in consistent movement and force output in every cycle.

Force Output

The force of a pneumatic cylinder can be found by multiplying the area of the bore by the operating pressure of the system. This means that force output can only be increased by either raising air pressure (resulting in more air consumption) or installing a larger bore cylinder (slowing the movement speed and taking up more space).

Electric actuators benefit from much higher power density, meaning that a similarly sized electric actuator will output significantly more force than a pneumatic cylinder. Additionally, electric actuators can also utilize gearboxes to increase force output even further at the cost of speed if required, making them capable of extremely high force outputs, more efficiently and in a smaller form factor than pneumatic actuators.

replacing pneumatic actuators with electric actuators

Force output comparison between pneumatic and electric actuators of the same size. Electric actuators have the benefit of significantly higher output forces in the same form factor when compared to pneumatics.

Total Operating Cost

Contrary to popular belief, compressed air is not free. In fact, the US Department of Energy estimates the cost of compressed air at anywhere between 18 and 30 cents per 1,000 cubic feet of air, depending on the cost of power per kw and the efficiency of the air compressor. This means that a continuously running actuator requiring 1.5 cfm of air costs anywhere between $11 and $19 a year.

While electric actuators obviously still require power to function, they are significantly more efficient than an equivalent air compressor, with typical servo and stepper motors achieving around 75% power

efficiency. In contrast, the US Department of Energy estimates found that the typical efficiency of a compressed air system to be between 10% to 15%. This means that the same size pneumatic actuator from earlier, if converted to electric, will only use between one fifth and one eighth of the power, resulting in an approximated operating cost of between $1. 30 and $3.80 a year. This reduction in operating cost means that electric actuators can be significantly cheaper to run long term when compared to a similarly sized electric actuator.

Benefits of Pneumatic Actuators

While electric actuators have become an excellent alternative to pneumatic actuators in recent years, they do still have some drawbacks. Here are some factors for when pneumatic actuators may still be a better choice over electric:

Lower upfront Purchase Cost

While electric actuators may have the potential for great cost savings in the long run, the unfortunate truth is that upfront cost can sometimes be a dealbreaker. Compared to a similarly sized pneumatic actuator, an electric system will generally cost about ten times as much. This is due to the increased complexity of the drive and guide systems, as well as the cost of supporting hardware such as motor drives, cabling, and controls. For budget-oriented projects or smaller applications where pneumatic cylinders require a negligible amount of air, the payoff of energy savings with electric may not be worth it, making pneumatic cylinders still a very viable option.

Simplicity

There is still something to be said for simplicity in the world of automation. Pneumatic actuators are a prime example of this, essentially consisting of a piston in a tube that moves from one end to the other. This makes them a great option for when simple, non-precise, A to B movement is needed, such as opening the lid on a container or acting as a part stop on a conveyor belt. In these cases, electric actuators may be overkill, complicating the design of a machine and increasing the upfront cost of the project to the extent that the benefits of electric may not be fully realized.

In addition, on the controls side electric actuators can quickly use up IO on a PLC or require fieldbus communication, which a PLC may not have. In contrast, pneumatic actuators generally only require two outputs for extend and retract movements and one or two inputs dedicated to cylinder switches, making pneumatics a more viable option for smaller projects which may only have access to a basic, brick style PLC.

Durability

Whether your machinery is designed to make automotive parts or baked goods, most manufacturing processes require actuators to perform in extreme environments for millions of cycles without failure. Industrial environments have many hazards, such as extreme heat or cold, water or chemical sprays, or even the overzealous forklift driver, and actuators must be designed to withstand the harshest of these environments. Electric actuators, while usually built to take the beatings of everyday industrial use, tend to be less resistant to extreme environments when compared to electric. In particular high and low temperature environments tend to be a weakness of electric actuators, as most have an operating temperature of between 35 and 170-degrees Fahrenheit.

Pneumatic actuators on the other hand, are limited only by their seal material, with specialized cylinders being able to handle temperatures from -40 to over 600 degrees Fahrenheit. Pneumatics also tend to fare better in wet and dirty environments as electric actuators (particularly belt drives) contain delicate electronics which are more easily damaged. It is important to consider an actuator’s ingress protection (IP) rating and operating temperature range when dealing with extreme environments, as this can drastically affect the overall lifespan of the actuator.

Closing thoughts

Comparing electric actuators to pneumatic isn’t always an apples-to-apples comparison. Of course, no one would ever design a 3D printer using pneumatic actuators or use electric actuators in a 300-degree injection mold; there will always be applications where one is better than the other. For processes requiring more than two positions, high precision, or large force outputs, electric is definitely worth considering. On the other hand, if an application needs an actuator to be simple, economical or is exposed to extreme environments, pneumatic actuators tend to still make more sense. For anything in between, it is worth calculating the ROI of using electric actuators over pneumatic to realize the potential long-term cost savings of switching to electric.

Whichever style actuator your next project requires, our team at EFP is here to help with all your pneumatic and electric actuator needs. Not sure which would be best for your application? Contact us today to talk with our in-house experts!