Episode #28: How To Convert From Pneumatic and Hydraulic Actuators To Electric?

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The Motion Control Show

We often talk to customers about the idea of replacing their fluid power, whether it's pneumatics or hydraulics, with electric.  It's pretty easy in concept, but there are definitely some things to be aware of when talking about that crossover.  I'm Corey Foster at Valin Corporation, let's see what we can learn.

First thing is the controls: how easy is it to replace the pneumatics with the electric?  Well, there are some manufacturers that actually make it pretty simple.  Here is a diagram of using a single or double solenoid.  And one manufacturer shows how easy it is to change with their controls  and their actuators over to electric from pneumatics.  So that part is actually not all that difficult.  The logic can still be the same in the PLC.  The wiring could be very similar or even the same. 

pneumatic cylinder
This diagram right here shows a pneumatic cylinder with some sensors on them to go back to the PLC.  So you've got the outputs, yo u have the inputs, you have the power, and if we change that over to electric this box here doesn't change.  The PLC, the inputs and outputs doesn't change, the power doesn't change, and then that connector just goes here to a little built-in controller to the actuator.  So the controls can actually be very simple, no big deal.

What's different about the mechanics?  Fluid power is Force = Pressure x Area.  That's the most basic equation for sizing fluid power.  Force equals the pressure times the area.  Electromechanical also has an equation for force, but it's Mass x Acceleration.  Notice that there's no acceleration taken into account here for fluid power, but there is for electromechanical.  So, if you really care about the move profile, then pneumatics and hydraulics are probably not your right solution in the first place.  But it tends to raise questions on choosing the right electromechanical solution that you didn't have to consider with fluid power. 

Fluid power is really "bang bang!"  It accelerates up, hits the hard stop, and it stops.  "Bang bang" back and forth between the two hard stops.  There's no control of deceleration, or acceleration for that matter, and it uses hard stops and bumpers to stop.  The force is constant, which is what causes that acceleration, but it varies with the pressure.  So, if you need a certain amount of force at 60 PSI and you only have 50 PSI, you don't get as much force as you'd want.  And the force density is sometimes important when talking about fluid power.  It's not really specified or anything, but I call it “force density” because it's the amount of force you get out of the package size of the actuator itself.  Pneumatics and electric are about the same with the usual 60-80 house PSI.  I have seen applications where someone's using 100 PSI on an actuator and pneumatics can get a little bit more out of its force density with that.  But, usually the average is in that 60-80 PSI range and it makes them about the same.  Hydraulics on the other hand, because it's using fluid as opposed to gas to move the actuator, can get a lot more force out of the package.  So, if somebody is trying to replace hydraulics with electric, that package size is probably going to become an issue.  It's really difficult to compete against hydraulics with electric.  If size doesn't matter, then electric can certainly replace hydraulics as well usually. 

For electric, we really prefer sizing and controlling using controlled stops, so we have an acceleration and deceleration.  And if we want really smooth motion to make it less jerky, we can actually even do an S-curve, a more controlled acceleration and deceleration.  You just can't do that with any fluid power solution.  We tend to frown on slamming into the hard stops because that wears down the actuators faster.  They're not designed for it, so we try not to do that.  The force varies when using electric as needed in order to make the move.  That's why it's more efficient, unless you want a specific force to push against something, like capping or pushing two parts together, but you can do that through programming.  Back to the force density, the motor sticking out or wrapping around here could be an issue depending upon your sizing and converting from the fluid power over to the electric. 

Something I've also noticed over the years is that when sizing and selecting pneumatics, people tend to buy and try.  "I think that this actuator will work.  We'll try it."  And if it's not large enough, they go ahead and swap it out for a larger one and get more force as needed.  Usually these are sitting on a shelf so the lead time is pretty low and you can get them pretty quickly.  Whereas with electric, we really tend to analyze the application, resize it, and then wait for the delivery, because everything is made to order for the most part, so that lead time often catches people off guard and they don't want to wait for it.  "I'm used to just buying and trying it."  Well, we're used to sizing and designing things properly in order to make sure we can actually do the move that's needed. 

Cost: right up front, pneumatics pretty much always costs less up front.  The electric options cost less in the long run, but a lot of people have a hard time taking that into account and that cost comparison really depends on what you include. 
  • What's your assumed efficiency? 
  • What are your electric costs? 
  • Do you still need the air generation and air prep?
  • Or your hydraulic power unit?
  • How often do you have to replace those fluid power actuators? 
  • Does cycle time matter? 
These are all factors in the cost and why people might want to switch over. 

And you might still be wondering, "Why would somebody want to change from fluid power over to electric?"  Well, right off the bat you get…
  • More control which can lead to…
    • higher throughput
    • less waste
    • faster cycle times with electric 
  • Efficiency
    • you don't have any air leaks
    • the electric is more efficient than the fluid power options
    • it leads to less energy consumption
  • Lower maintenance
    • Oftentimes, the fluid power actuators have to be replaced on a yearly basis or more often because of that "bang bang!" 
    • With electric we don't have to do that.  There's less mechanical wear and tear. 
  • A lower total cost of ownership
    • The electric just costs less to operate, and that might be why you or other people want to look at changing from fluid power over to electric. 

If you have any questions about this, want to consider changing from your fluid power to electric, want to talk over options or have any ideas or questions, feel free to reach out to us at Valin.com.  You can send an email AutomationSupport@valin.com.

I'm Corey Foster at Valin Corporation, I hope this helps.  

If you have any questions or are just looking for some help, we're happy to discuss your application with you.  Reach out to us at (855) 737-4716 or fill out our online form.