On Sat, 22 Dec 2012, Stephen Dubovsky wrote:
> Date: Sat, 22 Dec 2012 16:29:39 -0500
> From: Stephen Dubovsky <smdubov...@gmail.com>
> Reply-To: "Enhanced Machine Controller (EMC)"
> <emc-users@lists.sourceforge.net>
> To: "Enhanced Machine Controller (EMC)" <emc-users@lists.sourceforge.net>
> Subject: Re: [Emc-users] Pid saturated, was: Servo error
>
> Peter,
> I *FULLY* understand. My 8th paragraph states if the drive is poorly tuned
> (voltage mode = no tuning) and the poles are low in freq (bingo) the D is a
> bandaid. Voltage mode control doesn't hide/move the plant poles to a
> higher freq like current mode can. Its simpler but lower performance.
> Only so much bandwidth a single loop can get if it gets handed all the
> multi-order system resonances in one black box. Much better to handle each
> system order at a time (torque,speed,position). The D adds zero which if
> you put ontop of the next systems pole you can help things out. There are
> systems that it works in. Buts its a bandaid.
Um no, you dont. I was giving advice on how to tune a voltage mode loop, Your
advice does not apply in this context. Its very clear that you have not
actually tuned a voltage mode loop. D is absolutely needed for stability, A
voltage mode drive with velocity feed forward approximates a torque mode loop
(a second order system). Without a D term the solution to this system
function is a sine wave.
Peter Wallace
Mesa Electronics
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