Re: Digest Number 12

Jon and members:

I just tried this URL for Server to Go and it works, so here it is:

http://www.iglou.com/servotogo/

Have a great day all

Don Hughes

Jon Elson wrote:

>
> From: Jon Elson <jmelson@...>
>
> Mike Romine wrote:
>
> > From: Mike Romine <mromine@...>
> >
> > Jon wrote:
> >
> > > A dedicated
> > > card (currently ISA) with quadrature encoder counters and servo DACs
> > > interfaces to the motion hardware.
> >
> > Who makes this card? Is this the 'servo2go' card I have heard mentioned
> > on this list?
>
> Yes, exactly. their URL is : http://www.servotogo.com/ but it didn't work just
> now when I tried it.
>
> >
> > > I don't know what jerk control is - do you mean backlash compensation?
> >
> > Jerk control is limiting the rate of change of acceleration. I was not
> > thinking of the right thing when I wrote that as jerk control is part of
> > the feedback loop (you feedback 3rd derivative of delta position), not
> > feed forward. Actually, it sounds like the EMC control system needs
> > some work if the PID filter is not working and you are using feed
> > forward to compensate (feed forward is an open loop compensator).
>
> Yes, it does. Their PID doesn't keep history, it just uses error from the
> last sampling period. Real PID needs you to compute the integral term
> from a history of some previous samples, at least 5 or 10. many also use
> several previous samples to build a trend for the differential term. These
> things usually require a rolling buffer of previous error samples.
>
> Still, I'm cutting metal with accuracy approaching the machine's basic
> accuracy, so I have no complaint about the CNC. Tool deflection
> is probably my most significant error, now!
>
> Jon
>
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