Hydraulic servo control bouncing

[unsyndicated]

Hello,

I'm trying to control a Moog G631 Electro-Hydraulic Servo Valve with a DoMore H2 using a F2-4AD2DA card, and linear position sensor  I can get it to "work" but not well, it moves in the direction I want when I want but it is very far from constant. It overshoots the SP then oscillates when the cylinder is not bottomed out. I thought using a PID and auto-tuning would be the trick but it never seems to even out.  I do not believe it is a hydraulic issue as it has no problem moving the cylinder.  Its an extrusion process with the plastic helping to "lift" the cylinder.

[BobO]

Are you using PI or PID? The derivative term can cause issues.

How noisy is the input data?  That one can be troublesome, because filtering adds delay, but noisy data causes other issues, particularly with fast processes and ones using derivative terms.

How fast is the process? If the analog delay in and out is too large a percentage of the process time constant, that can make difficult to get stable.

[Controls Guy]

Second to everything BobO said, plus try manual tuning.

I often like manually tuned results better than auto-tune (how do you know the guy that codes the auto tune wants the loop to run the way you want it to?),  plus with less variables in play you can better see what the issue is, I sometimes find.

[unsyndicated]

I was trying to use PID, I'll change that tomorrow.

The input seems to be fairly noisy.  I'm not concerned if filtering adds a delay, I can adjust with timers.

each cycle is about 15 seconds divided into four sections/timers.  Need a certain set point for one of the ones in the middle (4 secondsish) then the other three are the same.

I'm apprehensive to attempt to manually tune as i'm not the most experienced. 

[ADC Product Engineer]

Use Auto Tune to get it close and then tweak it.  Start with adjusting "P" so to get the overshoot so that it isn't a big hump.  Next adjust "I" to try and get the overshoot/undershoot to even out.  This is the basic idea of manual tuning.   I would bet you can find a few dozen videos on Youtube showing how to tune a loop manually.  They might not be explicitly for BRX, but the principle is the same for most all PID controllers.

[Controls Guy]

Agreed.   As long as you don't do anything radical and start moving the gains in from the right direction, you won't break anything.