On Wed, 9 Feb 2011, Yi-Shin Li wrote:
> Date: Wed, 9 Feb 2011 22:21:45 +0800
> From: Yi-Shin Li <y...@araisrobo.com>
> Reply-To: EMC developers <emc-developers@lists.sourceforge.net>
> To: EMC developers <emc-developers@lists.sourceforge.net>
> Subject: Re: [Emc-developers] pid bug
>
> On Tue, Feb 8, 2011 at 11:26 PM, Peter C. Wallace <p...@mesanet.com> wrote:
>
>>
>> --- if ( ( tmp1 * pid->limit_state ) <= 0.0 ) {
>>
>> +++ if ( ( tmp1 * pid->limit_state * pid->igain ) <= 0.0 ) {
>> +++ if ( ( tmp1 * pid->limit_state (pid->igain ) <= 0.0 ) {
>>
>> Is a possible patch if negative PID values are to be allowed
>>
>> Based on the diagram of this page
> (http://en.wikipedia.org/wiki/PID_controller),
> negative PID gain may make the system diverge (unstable).
> In my experience with Mitsubishi and Yaskawa AC Servos, the PID gains are
> always positive.
>
> Why would you need negative I-gain?
You wouldn't just have IGain negative, you would have all gains positive or
negative.
The point is that its a convenient way to reverse the output polarity
especially if the output device does not have this ability. I could go either
way on this (if its not supported I do think it should be documented or
prevented)
> Would it be possible that the polarity for calculating error is
> mis-configured?
>
> --
> Yishin
>
Peter Wallace
Mesa Electronics
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