How to decide between a pneumatic and an electric actuator
During my last visit to the PLC production site of Siemens in Amberg, their operations manager told me that they are planning to replace the traditional pneumatic cylinders from the products lines. As a response to my question why they are thinking of this change, he said that electric actuators are easier to install and maintain. In addition they are more quite during operation, so will reduce the noise of the production line.
This made me think that pneumatic actuators will be replaced by electric actuators over the next years, which would have a quite huge impact on the big pneumatic players like Festo, SMC, Parker or Norgren. I was curious to understand a bit more around this “trend” and actually spotted that there are already a lot of debates and forums covering this in the World Wide Web. The below article summarizes my findings, which will highlight the pros and cons of both technologies.
The most important fact in advance. There is no clear answer whether it is better to use a pneumatic or an electric actuator. Like many of life´s decisions, the answer to this question typically begins with: “Well, it depends…”
Pros and cons of pneumatic actuators
It is a matter of fact, that pneumatic actuators provide more force than any other actuator technology, except hydraulics. The other main advantage is the high speeds which are possible with pneumatic actuators. These two values can be easily adjusted independently by using either pressure relief valves for the force and/or flow regulators for the speed which is another key advantage of this technology.
There are two other factors which speak for pneumatic actuators. The first is the low cost per unit, where the smallest cylinder sizes start somewhere in the area of 10 GBP, the other factor is the small footprint. The very small dimensions are a result of very limited control and adjustment options the cylinder provides directly.
This links perfectly into one of the disadvantages of pneumatic actuators which is the costs of the relatively expensive infrastructure that is required for pneumatic systems. The whole thing usually starts with a compressor that provides the compressed air, followed by a FRL (filter, regulator and lubricator) to prepare the air in the composition required for the devices which are actually supplied with it. This air is stored in a reservoir which is used as a buffer between the compressor and the consumer. The typical consumers of prepared, compressed air are valves and actuators. To complete the set of components typically uses in pneumatic systems, also switches, regulators, silencers, hoses, fittings and monitoring devices like pressure gauges or pressure sensors should be mentioned.
Considering the above it is obvious that the overall costs of a pneumatic system to drive an actuator can be quite expensive. In addition the devices used in the pneumatic system need to be maintained on a regular basis. According to the Department of Energy, 24 percent of the annual cost of compressed air is due to maintenance, equipment and installation while 76 percent is due directly to the cost of electricity for the compressor.
Pros and cons of electric actuators
One of the key advantages of electric actuators is the precise control and positioning. This allow easy implementation in existing machines and systems at low operating costs. Having the electronics separate from the actuator supports easy maintenance and minimal replacement costs. Another key differentiator is the very low noise of electric actuators compared to pneumatic actuators.
There are different versions of electric actuators available. Usually they all consist of a ball, acme or roller screw connected via a coupler to an electric motor. As the screw turns it moves the piston. The piston is connected to a rod or a carriage that moves the load.
Some variants use timing belts with two pulleys which allow very high speeds. These actuators are often used in robots.
The performance and costs of an electric actuator varies by the materials and the technical principle used for the actuator.
Electric actuators usually use stepper or servo motors – sometimes also AC motors or brushed DC motors in combination with limit switches if position accuracy is less critical. Stepper motors are the most economical choice when accurate positioning is required, but only suitable for applications where lower speeds are sufficient. Integrated encoders are recommended in the stepper to avoid the possible loss of synchronisation with a controller. The most precise option is an electric actuator that uses a servo motor. This will guarantee best performance, with superior precision and highest speeds – however, it is also the option with the highest cost per unit.
Electric actuators typically start at costs around 500 GBP – whereas miniature versions are available below 100 GBP already.
I hope the above helped to understand the core differentiators of the two technologies and supports you to narrow your decision.
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I think to add to this is that the precision , speed and response of control needs to be considered
With Electric actuators (Direct Screw or Belt), the significant latency in the control loop would be from the control system itself, not the electromechanical parts so when the correct position is detected it can stop very accurately and quickly once the control signal indicates it is a set point,
With Pneumatic there is stored energy in pipes and infrastructure due to driving pressure after the control valve that could cause errors in positioning or additional oscillation of position due to overshoot (If in a linear system) , this could also be seen as slow down of positioning if the overshoot is compensated for in a PID controller for instance.
Pneumatic would be used for solenoids like grippers and clamps in industry etc where it is either activated or not and not part of a linear position system (Typically). It is cheap and relatively clean and most of all, pretty safe and inert with the right gases.
Hydraulic provides the best of POWER and control due to the fact that the liquids are not compressible and can exert masses of power to the device being moved often found with lifting devices, Diggers, Steering and rotational systems etc where power and precision may be needed but not too much speed. This comes at the cost of expensive infrastructure, additional safety requirements and messy maintenance (Thousands of PSI in Hydraulic OIL pressure are not uncommon in large equipment)
Electric provides the finer control and precision including much power if needed as found with CNC Machines, Robotic assembly machines etc. Electric also provides an almost instant response to controls (Within the limitations of the inertia of the item being moved). It is clean and relatively cheap and safe.
Just something else to consider :)