On Tue, 8 May 2012, gene heskett wrote:

Date: Tue, 8 May 2012 16:52:37 -0400
From: gene heskett <[email protected]>
Reply-To: "Enhanced Machine Controller (EMC)"
    <[email protected]>
To: [email protected]
Subject: Re: [Emc-users] PID controller Q's

On Tuesday, May 08, 2012 04:42:52 PM andy pugh did opine:

On 8 May 2012 21:06, Dave <[email protected]> wrote:
> You have no Pgain, but Igain and Dgain.  That's a problem.  An all I
> and D loop is almost always unstable.

That depends….

For a spindle P gain is not much help, as you need a non-zero PID
output even when at the set speed (and when the error is zero). That
is why the Wiki example is all-I.

The page I am looking at right now says D-I are both 1.0.

Silly Q probably, but could the pid.0.command value also be sent to sum2.0.in0, and the pid.0.output sent to sum2.0.in1 to furnish the desired offset, allowing the pid module to work with a much more balanced (read closer to zero) output? To my simple mind, which ignores the latency of a 1 khz servo thread for all this, that does seem like it should be a workable scenario. Let sum2.0.output drive the pwmgen.0.value.

uneccesary as this is exactly what FF0 does


Peter Wallace
Mesa Electronics
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