Re: [CAD_CAM_EDM_DRO] 3D Contouring - Loss of Accuracy

Hi Chuck,

The Flashcut controller generates the step & direction pulses to the
Geckos/ Rutex's directly - and is connected via a serial port to the PC.
I've tried several brands and types of parallel port cards with G-Code
Controller and also used port buffers/amplifiers to boost the signal
etc. I don't think it's related to the timing or level of the direction
pulse - if I understand you correctly. Also, I can run single axis
forward/reverse tests for similar times (e.g. an hour) and not lose
anything... Confusing eh?

I will think further about your suggested two axis "step" test - but
basically that's what contouring amounts to. I can generate the error
in whichever axis has the most movement (i.e. direction reversals,
accelerations etc.) either horizontal contouring (constant Z) or
parallel contouring (constant Y). I had previously thought it could be
a math problem - maybe not enough significant digits - but that doesn't
make sense when you look at the G-code - it has absolute XYZ
coordinates. The error occurs relative to a fixed datum such as a
switch closure or a nail head pointer.

Cheers, Peter



Egroupscdh (E-mail) wrote:

>Ok, I'm no expert here but I'll stick my neck out ...
>
>As I understand it you're using the parallel port in all cases. Could it be
>that the error is occurring during direction reversals only one step at a
>time?
>
>Possibly the edge of the 'direction' line is not correctly oriented with
>respect to the 'step' line.
>
>While watching the step and direction lines with your scope (dual trace I
>hope) you might try configuring a test case such as:
>
> -----
> |
> A |
> X ----- |
> I | | |
> S | | |
> ----- | -----
> A | | |
> | | |
> | -----
> |
> |
>
> AXIS B
>
>using different combinations of axis with and without motion in the third
>axis to see if the error shows up.
>
>You might also try purchasing a parallel port card and trying that.
>
>Cheers,
>
>Chuck Hackett
>"Good judgment comes from experience, experience comes from bad judgment"
>7.5" gauge Union Pacific Northern (4-8-4) 844
>Railroad: Camp Creek Railroaders, Waverly, Nebraska, USA (3000', 7.5")
>Home: Elkhorn, Nebraska (just west of Omaha)
>
>
>>From: Peter [mailto:prenolds@...]
>>
>>Hi all,
>>
>>I'm stumped! ....
>>I find is that running a large 3D file I gradually accumulate a small
>>error typically in one of the most active axes which often exceeds 0.3mm
>>or .012" after half an hour to an hour of running time. It is usually
>>in the same direction, but not always.
>>....
>>
>>Cheers, Peter
>>
>
>
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