On Tue, 22 Apr 2008, jros wrote:
> Date: Tue, 22 Apr 2008 22:06:01 +0200
> From: jros <[EMAIL PROTECTED]>
> To: "Enhanced Machine Controller (EMC)" <emc-users@lists.sourceforge.net>
> Cc: "Casas Olcoz, Alberto" <[EMAIL PROTECTED]>,
> Alberto Casas <[EMAIL PROTECTED]>
> Subject: Re: [Emc-users] Very low PRM system.
>
> Hello, I use to read the list to get more insight on different aspects
> related to EMC.
> Right now we are facing some problems related to PID tuning.
>
> And when I have read this
>>
>> If you have a good analog velocity mode system you can get smooth
>> motion at
>> slow speeds without a high line count encoder.
>>
>
> I've remembered that apparently (eye is the tester, still no measures)
> our "tuned" PID is giving us smooth motion at relative high velocities
> (order of 100mm/s), but visible oscillations (0.1mm approx ) at low
> velocities (order of 1mm/s).
>
> I wonder if this effect can be related to a low resolution encoder, our
> encoders are able to give 10mm/4096 pulse spacial resolution.
>
> Also, we are controlling using torque (intensity), although the drive
> can be configured to accept velocity as command.
>
> The motor has a resolver internally, but the driver exports only
> quadrature signals ABZ -A-B-Z, that I plug directly to my motenc-100
> card.
>
> Can this imply that I can get a more smooth motion using driver
> configuration to accept velocity?.
>
> Any comments are welcome.
>
> Thanks
>
> Javier
.1 mm of error or noise works out to be about 41 encoder counts. This is not
well tuned especially at slow speeds. A well tuned system should be capable of
at least 10 times better whilst creeping along. Can you record the error with
HALscope to get a better look at whats going on?
Velocity mode may help, especially if the amplifier has a better velocity
input than the encoder (meaning it has a tachometer etc), but then you may
need to tune the amplifiers velocity loop as well.
>
Peter Wallace
Mesa Electronics
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