Electric Actuator replacement for pneumatic

[DaveCr]

Hi, I am working on a project to replace a pneumatic cylinder which is used for to close an impulse sealing jaw with an electric linear actuator. AFAG actuator is to be used but there is a problem with how can it be calibrated. The old pneumatic cylinder has the gauge calibrated each year. For the electric actuator the slide moves to a position and then it closes to a pressure. this pressure is a percentage of the overall force of the actuator. The tolerance is +/-5%. I feel we don't need to calibrate an electric actuator but has anyone had an issue like this before?

 

[MikeHalloran]

I have no basis for believing that a force actuator needs no calibration just because it is 'electric'.

Mike Halloran
Pembroke Pines, FL, USA

 

[DaveCr]

HI Mike, I was going to use a load cell to verify the force once a year. I have heard pressure sensitive paper may be used but I have never seen it used in any application

 

[prex]

A pneumatic cylinder is a force actuator, an electric one is a displacement actuator; you can't reliably set a force on the electric actuator without a closed loop control.

prex
[URL unfurl="true"]http://www.xcalcs.com[/url] : Online engineering calculations
[URL unfurl="true"]http://www.megamag.it[/url] : Magnetic brakes and launchers for fun rides
[URL unfurl="true"]http://www.levitans.com[/url] : Air bearing pads

 

[DaveCr]

Hi prex, we are using it in a heat sealing application where temperature is most important. we know from our old process that the force has a large window. The electric actuator is unreliable but it says it is accurate to +-5%. We could not fit a load cell in the application for closed loop control therefore we hope to perform a check regularly to check it. As you say it is unreliable therefore our check will be out by +-5%. We did think about a electric actuator with pneumatic head. We need a solution for when this new machine arrives

 

[roydm]

The electric actuator will be very slow when compared to the pneumatic one.
I gather you are trying to use it to get a certain force, easy to do with a pneumatic.
Perhaps you can incorporate a spring and set the electric actuator to stop at a fixed point thus compressing the spring to give the force required.

 

[MintJulep]

You need to step back and take a wider view of things.

You have stated:

" we know from our old process that the force has a large window" How large? What happens if the force is too low? What happens if the force is too high?

" The old pneumatic cylinder has the gauge calibrated each year." But does anyone ever look at the gauge? If they do, do they make any adjustments? The gauge, in and of itself, has no effect on your process.

" I was going to use a load cell to verify the force once a year." and "we hope to perform a check regularly to check it" What will you do if you check and it's out of tolerance? What if it's out of tolerance, but your process is just fine? More importantly, what if your process goes bad 3 months after you do the check? Will anyone know?

The key is to establish the actually force limits that the process can tolerate. Then notice that "tolerate" is the root of "tolerance".

It's possible to take roydm's excellent suggestion of a driving to a fixed position against a spring and design a simple and robust device that also almost no chance of ever "going out of tolerance" as long as the actuator gets to position.

Failure to get to position can be easily detected and trigger an alarm.