Electric Actuators vs. Fluid Cylinders
A comparison of technologies for an engineer
If you deal with engineering and motion as a discipline, you have concerns such as position, speed, acceleration, and force control. Whether you are picking, packing, or pushing – the systems you design must be reliable. One of the building blocks of any motion system is an actuator. This blog post is going to look at linear actuators, specifically, comparing the technologies of (1) electric actuators vs. (2) fluid cylinders. Electric actuators can often be an ideal technology to replace old hydraulic or pneumatic cylinders.
A comparison discussion is almost always better when we can get a bit more specific. For the purposes of this discussion of electric vs. hydraulic vs. pneumatic let’s assume we’re talking about stationary shop equipment. You are probably controlling your motion on this equipment with some sort of industrial controls. Push buttons, switches – maybe in concert with a PLC. Making those assumptions, you can compare on the grid below:
- Electric Actuators (Pros & Cons)
- Hydraulic Cylinders (Pros & Cons)
- Pneumatic Cylinders (Pros & Cons)
- Total Cost of Ownership
- Positioning: Offers extremely precise and highly controllable positioning; infinite flexibility.
- Speed: Great for high speed applications.
- Acceleration: Yes, rapid acceleration while maintaining efficiency.
- Force Control: Great control options. Can offer very high forces, even though hydraulics are typically associated with higher forces (more on this below).
- Efficiency: Approximately 75 to 80%.
- Positioning: Requires servo-hydraulic system to achieve better motion control capabilities.
- Speed: Can be slow; multiple cylinders on one system can create problems or limitations.
- Acceleration: Not ideal; multiple cylinders on one system can create problems or limitations.
- Force Control: Yes, high force density per cylinder size, but pressure fluctuations can affect control and repeatability.
- Efficiency: Low. Approximately 40 to 55%; requires constant pressure in the form of wasted stored energy.
- Positioning: Rely on control valves, cylinders, and sensors with limiting positioning abilities.
- Speed: Can be very fast but is limited by available air supply
- Acceleration: High accelerations are available.
- Force Control: Force is based on available air pressure but air is very compressible so force is limited.
- Efficiency: Very Low. The average facility, estimates show, has 30 to 35% air leakage
- Maintenance: Electric actuators are typically sized for life of application, the components come greased for life. Leaks are frequently identified in hydraulic and pneumatic systems causing unnecessary energy consumption, reduced equipment performance, decreased reliability, increased fluid costs, and increased housekeeping. Maintenance costs for electric actuators are much lower than fluid cylinders.
- Contamination: Hydraulic Oil Leaks: According to the National Oceanic and Atmospheric Administration (NOAA), more than 90 million gallons of Hydraulic products enter the environment each year. The risk of contamination is much lower with electric actuators.
- Noise Pollution: Electric actuators offer a quiet operation, a better option for employee safety. Compressors and hydraulic pumps can be a major source of noise on the plant floor.
A QUICK REVIEW:
Positioning: Electric actuators offer better precision, positioning, and flexibility. Winner = electric actuators
Speed: For any application requiring more than 1m/s (meter per second), Winner = pneumatic and electric actuators. For all other applications, we can call it a tie.
Acceleration: Winner = pneumatic and electric actuators.
Force Control: Calling it a no decision. Short answer; it depends. Hydraulics can offer HUGE forces, but may have difficulty controlling them. Electric actuators offer much better options for controlling forces and are catching up with options for large force loads (more on this below).
Efficiency: electric actuators are almost twice as efficient as fluid cylinders. Winner = electric actuators
What’s there to compare? This is just the way we’ve always done it…
Let’s back it up a step. Why do we use either of these systems? To create movement and to create force. You need to move an actuator forward X inches. You need it to push with lateral force Y. An engineer will have most of these parameters when designing a piece of equipment. In your day to day challenges, you may need to consider movement strokes or large forces beyond what might be considered “normal”.
LONG STROKE + FORCE CONTROL + HIGH FORCE + FLEXIBILITY
As you extend the length of a stroke of motion, balance and repeatability can suffer exponentially. Let’s look at an example of an electric actuator that can offer a stroke of up to 60”. You need your motion application to be precise and you need to maintain accuracy. Sometimes you need to combine precision and accuracy with high forces. Let’s look at an example of an electric actuator that can offer forces up to to 13,000 lbs.
- Long Stroke: Four (4) body sizes with stroke lengths from 18 to 60 inches (457 to 1,524 mm)
- Force Control: Positional accuracy of +/- 0.0004″/ft (+/- 0.0102mm/300mm) for roller screw actuators or +/- 0.002″/ft (+/- 0.051mm/300mm) for ball screw models
- High Force: Maximum force/thrust up to 13,039 lbf (58,001 N)
- Flexibility: Your choice: ball or roller screw selections
- Flexibility: Optional IP67 linear actuator configuration available to protect against dust and moisture
- Suitable for valve actuation, punch press, injection molding applications and more
Heavy duty high force actuators
This short 2 minute video helps illustrate the comparison of technologies:
We’re not saying never ever use fluid cylinders
Keep in mind, we’re just reviewing technology options here. In the real world, it may or may not make more sense to simply have a piece of equipment that uses a hydraulic cylinder and swap in a new hydraulic cylinder of the same type. Not every application requires a re-engineering of motion components. If you want to keep using hydraulic cylinders, check out the options available from Enerpac. These cylinders can offer a simple solution for large force requirements.
Take another look at electric actuators
If the reason you are still using hydraulic and/or pneumatic cylinders is because “This is just the way we’ve always done it” then you should consider learning more about electric actuators. Then can offer a low-maintenance and energy efficient option for engineers. If you want to learn more about electric actuators you can:
This post is part 1 of 2. Part 1 is Engineering Efficiency with Electric Actuators. Part 2 is Trouble-free Maintenance with Electric Actuators.
Are you designing industrial or commercial equipment? Do you face a decision between fluid cylinders and other options? Have you looked at the total cost of ownership? Does a replacement make sense for you?