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From: nagle@netcom.com (John Nagle)
Subject: Re: PID Constants - Rules of Thumb?
Message-ID: <nagleD5t511.JGz@netcom.com>
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References: <ARMSTRON.95Mar19212607@ford.cs.ucdavis.edu>
Date: Tue, 21 Mar 1995 20:31:49 GMT
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armstron@cs.ucdavis.edu (Matthew Aaron Armstrong) writes:
>Does anybody have any black-magic rules of thumb for finding good Kp,
>Ki and Kd constants for a PID control loop (specifically, for
>controling a DC motor with PWM with an LM629 chip)? Most sources seem
>to say "larger constants lead to faster response times, but can also
>cause instability" but stop there.

      See if you can find a copy of "Control System Design Guide",
which is by a motor control expert.  The Zeigler-Nichols method works
well for motors.  It's a scheme where you let the system oscillate a bit,
measure the frequency, and calculate Ki and Kd relative to Kp.
I don't have the formulas handy, but they're in "Control System Design
Guide".

      For manual tuning, set all three constants to zero.  Then
turn up Kp until oscillation occurs.  Then turn up Kd until oscillation
disappears.  Adjust Kd until the system is critically damped; i.e. there's
no overshoot.  Then increase Ki until the steady-state error goes to zero
in a reasonable time.

					John Nagle
