I searched the messages i have from the list, and seen this... hope
it helps, not sure if something new has been implimented since this
message.
date Mon, Oct 29, 2007 at 5:22 PM
subject Re: [Emc-users] zero motion homing in program
mailing list emc-users.lists.sourceforge.net
Unfortunately, emc doesn't handle the repeating nature of rotational
axes very well. I feel that the ultimate solution is for an A-axis
traverse move to always move less than one revolution, even if the axis
is "wound up" by a move to A3600. If this approach is adopted, then
unwinding would be as simple as:
G0 A0
.. but that's for the future, not for today.
For now, I you can use G92 offsets for this purpose. If you program
"G92 A0", then the G92 coordinate system offset is modified so that the
current position of the A axis is now called 0.
If you use this method, I recommend adding G92.1 (cancel and zero G92
offsets for all axes) in the preamble of all your gcode files.
Otherwise, the first "G92 A0" in your program will erroneously apply
offsets for other axes that were previously set, even in a previous run
of emc.
Another caveat when using G92 offsets in this way is that if you are
actually at A3599 when you issue "G92 A0", subsequent moves will be
offset by one degree.
Finally, when you use this approach you have to make sure that the
machine coordinate (the "wound up" coordinate) never reaches the limits
set for the A axis in the inifile.
You might also consider using relative coordinates, so that your command
is in effect the number of revolutions to move, rather than the angle to
move to."
On Wed, Sep 30, 2009 at 3:54 PM, Alan Battersby
<alan.batter...@ntlworld.com> wrote:
> Hi everyone,
>
> If I make a full turn from 0 to 360 degrees say on the C axis, I want
> then to reset the coordinate system back to angle zero degrees in order
> to save an "unwinding" movement that occurs if I make a rapid move back
> to zero. For a couple of rotations I could use g54 etc but there is
> obviously a limit to this method. Perhaps I could use g92 but can it be
> cumulatively used over and over again?
>
> I envisage cutting paths which require several depth and width passes
> and this is multiplicative so 3 width passes and 4 depth passes gives 12
> rotations to be unwound when the path is complete in order to go onto
> the next path and that is with the pattern cut in a single rotation. I
> can generate patterns that take up to 20 rotations to complete.
>
> So I am wondering which is the best way of resetting back to the
> original zero position and can I avoid multiple unwindings? On should I
> think in terms of many smaller programs run sequentially?
>
> My apologies If this is an obvious beginners question I admit it I am,
> band I could not see anything obvious in the emc documentation.
>
> Thanks
> Alan
>
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