On Thu, 19 Apr 2007, Jon Elson wrote:
> Date: Thu, 19 Apr 2007 10:35:19 -0500
> From: Jon Elson <[EMAIL PROTECTED]>
> Reply-To: "Enhanced Machine Controller (EMC)"
> <[email protected]>
> To: "Enhanced Machine Controller (EMC)" <[email protected]>
> Subject: [Emc-users] Servo tuning problem
>
> This is mostly for John Kasunich, but anyone else with servo
> experience is welcome to chime in.
>
> My customer Stuart Stevenson has been having some problems
> with homing, so I had him send me his entire set of config
> files. When I got them, I saw that he had what appeared to
> me to be VERY unusual PID settings. When I run these on my
> machine, I see that the operation is "stable" but not accurate.
> By that, I mean that the machine continued moving for MINUTES
> after I took my finger off the jog key. The following error was
> in the realm of inches. Stuart says he has no following error
> to speak of, but I find that hard to believe.
>
> Here are his settings :
>
> P = 40
> I = 4000
> D = 0
> BIAS = 0
> FF0 = 0
> FF1 = 1
>
> INPUT_SCALE is 10000
>
> Having so much I term just seems wildly wrong to my experience
> tuning this PID scheme. I have noteced that the EMC2 D term is
> much more sensitive than it used to be.
>
> The servo interface is my PPMC analog servo board set.
> He is using Fenner drives from Servo Dynamics.
> I don't know whether they are set up for velocity mode or torque
> mode. Since this is so different from my setup, I'm thinking
> maybe he has his amps set for torque mode.
>
> Does anyone have any ideas what is going on, here?
>
> Jon
Well, torque mode needs more damping as there is less intrinsic damping in the
motor drive system, but those numbers still seem low on gain and really high
on damping.
It would be easier for me to understand if the PID units were normalized so
for example P is in units of A/Error = (Wm/S^2/We) (for torque mode)
Peter Wallace
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