Re: [CAD_CAM_EDM_DRO] Re: I'm curious

This reminds me of a difficult problem I had years ago on a CNC lathe
that was closed loop. It was a very old controller so we won't go
into details. In any event the X-axis was in the habit of loosing 2
to 3 microns of real position every time the lathe completed a cycle.
This was eventually traced down to a relay inside the spindle
controller.

The reality is that closed loop is very much the ideal situation but it
does not gaurantee anything with respect to electrical noise. In
fact closed loop systems just have more places for noise to impact the
system.

Dave


mpictor wrote:

>And what if there is noise on the line, and the Gecko ignores a step
>or steps when it shouldn't? That isn't closed loop! You can look
>all you want with an oscilloscope, but you'll never account for all
>possibilities. True closed loop won't either, but it will result in
>fewer mistakes.
>
>Your new system works 30-40% better than what it replaced? Well,
>well. New technology works better than outdated technology. What a
>suprise.
>
>Mark
>
>--- In CAD_CAM_EDM_DRO@yahoogroups.com, Erie Patsellis <erie@s...>
>wrote:
>
>
>>And I contend, a properly tuned (o'scope, critically damped) Gecko
>>
>>
>when
>
>
>>run within the power limits of the attached motor will exhibit far
>>
>>
>less
>
>
>>than 128 counts of following error, and even then, only on rapids.
>>
>>
>I
>
>
>>typically see about 4-5 counts error (~ 1/2 thou) or so, far less
>>
>>
>than
>
>
>>the allowable following error for rapids on the "name brand"
>>
>>
>closed loop
>
>
>>controllers. IF I get a following error with a Gecko, I'm either
>>accelerating too fast or otherwise have exceeded the capabilities
>>
>>
>of the
>
>
>>motor. On a typical system, 128 counts is somewhere in the areo of
>>
>>
>12.8
>
>
>>thou following error, did I mention on rapids? If you are getting
>>greater than 128 counts of error on a G1 move, there is something
>>seriously wrong with your tuning or you're using too small of a
>>
>>
>motor.
>
>
>>The geckos are closed loop, a pulse received indicates to the
>>
>>
>drive that
>
>
>>it has to move one count, it corrects the position. Gecko's work,
>>
>>
>and
>
>
>>quite well, most of the machines I retrofit have 'conventional'
>>
>>
>closed
>
>
>>loop controls, against common logic, a Mach2/Gecko system
>>
>>
>typically
>
>
>>rapids 30-40% faster, cuts smoother, and is about twice as
>>
>>
>productive
>
>
>>versus pre retrofit. and these particular routers are not small,
>>
>>
>the
>
>
>>smallest I work on is a 6x10, my personal test bed is an 8'x12'
>>
>>
>router.
>
>
>>The argument is mostly semantics, as I, you, and many others on
>>
>>
>the
>
>
>>list, work within the performance envelope and get qute good
>>
>>
>results. I
>
>
>>do on the other hand, have no hesitation in moving up to the
>>
>>
>larger AC
>
>
>>servos, if the budget and performance needs justify it.
>>
>>
>>erie
>>
>>
>>
>>
>
>
>
>
>
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