Re: [CAD_CAM_EDM_DRO] re:Digitizing

Roland gets around this by explaning how to set up the digitizing using
several steps. The top can be digitized first, then the sides and then the
bottom. They even explain a pretty good way of acomplishing it. And,no, I
haven't taken apart the probe on my machine...it's to new to be voidding the
warranty.

I do have an idea the might solve the "angle" problem a bit though....just
need to get it down "on paper" to see how it looks and how easy that would
be to build. Part of it would come from having the circuit break under very
little probe movement.

Smoke

>Picture digitising an older model truck (with a steep front
>windshield angle). As the probe moves down, it will be
>stressed 'sideways', and since it only "opens" the circuit in
>the 'up/down' direction, it is reasonable to think that the downward
>motion will continue until either the sideways component binds or
>bends something, or the single axis switch(of the probe) is tripped.
>At different probing points (on the 'grid'), the effect may be
>increased if the probe has a ball tip. At other probe points, the
>effect will be worse with a pointed tip probe (like the roland). Can
>you visualise this?
>
>The point is (pun intended) 'sliding down' the surface, moving
>slightly sideways as it goes, either binding or 'clicking' at some
>arbitrary point (due to the single axis actuation). Allow the probe
>to 'click' in any direction and the problem disappears... The
>sideways component of the vector(the sloped surface being probed)
>will open the switch.
>
>Next problem with "grid" based probing. Visualise a 'stepped' surface.
>(one step up, like this:
> oo__________
> ___________| Real part
>
>The o's represent the probe tip in two grid point positions (up
>position shown).
>
>You can see that the first one has not reached the vertical step (it
>will probe down until it hits the flat surface below). The second is
>poised directly above the vertical step. It will probe til it reaches
>the upper flat plane. The result of these two probed points will
>define this:
> oo__________
> _________/ Probe Data-derived part
>
>Clearly not an accurate representation of the probed surface!
>
>My guess is that the 'extra' moves your Roland does is based on some
>algorithm designed to minimise this sort of error (whether it's a
>GOOD algorithm is a DIFFERENT question :-) )
>
>Now instead, if the program drops down to the 'flat',Clears itself by
>moving up one step, then begins moving toward the next grid point, it
>will 'sideways trip' at the vertical wall. If the program is smart
>enough to remember which direction it was moving when it tripped (and
>using the concept of PRIORITY axis I mentioned earlier. i.e., clear z
>first) it will move 'up' to 'clear' the probe input, which will not
>happen until the top is reached (assumes a truly vertical surface).
>At THIS point,(those puns again) the program 'should' data-log the
>position, even tho it's NOT on the grid! Then TRY to complete the
>move to the next grid point. In THIS case, we'll get there(since the
>surface is flat) and begin the downward(priority movement first)probe
>again...
>
>Even better it will 'log data' at both the top AND bottom of the
>vert. wall, but this will require some 'smarts' to recognise
>the 'shape' that the probe is moving over, based on the 'tripped'
>points. A pre-processor which logs ALL 'trips', then analyses whether
>they should be output to the 'logged' file... Sort of a 'look-behind'
>to see which of the 'stops' are worth 'remembering'...
>
>This means the grid points will be the MINIMUM number of probe points
>logged, and that features lying BETWEEN grid points are recognised.
>
>Hope this helps.
>
>Ballendo
>
>
>
>
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