How to ramp air pressure in pneumatic cylinder until load cell force is met.

BrockSamson

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Feb 2019
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I need to ramp up the psi on a pnuematic cylinder until the force on the piston, measured by a load cell, is met. Then I need the air pressure to stay at that psi and maybe compensate a little bit for drift.

This is what I was thinking, ramp function on micrologix 1400 using analog to control an electronic pressure regulator.

I need to keep it as low cost as possible and the speed, repition rate, accuracy all have wide margins.

Is this doable?
Is the programming going to be very difficult? I can program PLCs but have never done any type of variable control with feedback
Have any suggestions?

Thank you.
 
SMC's ITV series pressure regulators can take a 4-20mA signal and respond super quickly.
 
I have done this with hydraulics.
Do not use PID unless you want to wait a long time.

what I did.
1. test the system to see what pressure you need manually, several times.
2. use 85% of that number as the base number to start with.
3. for the first automatic cycle only!!
a. apply the base number output to the pressure regulator.
b. wait 1 second and test the load.
c. increase the load b x counts until the load is reached.
d. store this number at the base for the next part
4. continue with the cycle
5. on the next cycle, apply the new setpoint.
6. after 1-2 seconds, look at the load and adjust the output up / down by x amount of the error
7. continue.

by the 5th or 6th cycle, you should be within /- 5 lbs or better.

as I said, this was with hydraulics, and worked very well.
the hotter the oil got, the faster the system got to pressure.

hope this helps,
james
 
The most accurate and fastest way to do this is with a RMC75E but since the cost needs to be low and the specifications aren't that tight, I would stick to the pressure regulator and put up with whatever performance you will get.

I/we have probably done more of these systems than anybody. I can tell you what the problems will be.
1. The pressure regulator only regulates the pressure on one side of the piston. Is the pressure on the rod side of the piston constant? If not the pressure on the cap side of the piston will need to change as the pressure on the rod side changes.
2. The pressure regulator will get to a desired pressure/ force eventually but a lot depends of the volume of air that the pressure regulator needs to fill or exhaust.

I need to ramp up the psi on a pnuematic cylinder until the force on the piston,
How much force?
How much volume?
The programming should be simple but the results may not be good depending.
 
For a kinda like system I used a Festo VPPE proportioning valve and a low friction 32mm x 200mm Festo cylinder. Both worked very well together.
 
I would think some kind of pwm controller would work.
I had an electronic boost controller (turbocharger) that was fast and accurate. It controlled air pressure. I "think" it used pwm.
Don't know what kind of hardware you'd need, but it just came to mind.
 
Hi....What we don't know of is the overall volume of air between your confinement valve and the chamber end which at that point compresses obviously "quickly". Nor do we know of whether this cylinder really moves 9 you notice "speed control". Speed control of what? What amount of volume is engaged with this?

I can just think that your controller is genuinely enormous contrasted with the volume of the air in the chamber and henceforth can compress it rapidly. As indicated above essentially all you need to do in this case is send the air through a type of limitation, either fixed (opening plate/Restriction hole) or some kind of factor limitation ( needle valve). When the pressing factor arrives at your necessary power at that point open the detour and afterward on the off chance that you need more air to make the cylinder move you will not be limited.
 
For a kinda like system I used a Festo VPPE proportioning valve and a low friction 32mm x 200mm Festo cylinder. Both worked very well together.

Airpel also makes low friction cylinders that I've used in the past for something similar. A standard cylinder won't likely work well...
 

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