Re: The math algorithm behind cutter compensation G codes

On Wed, 10 Aug 2005 14:32:19 GMT, Neat Trick <trick@xxxxxxxxxxxxxx>
wrote:

>On Tue, 09 Aug 2005 22:30:29 -0700, footy <footy@xxxxxxxxx> wrote:
>
>[snip]
>
>>starting the next one, or how big an arc. You might want to get ahold
>>of a copy of Computer Numerical Control by Warren S. Seams or something
>>similar.
>
>His name is Warren S. Seames and the book is more of an applied CNC book than a
>CNC systems engineering book. The OP is looking for algorithms to be applied
>inside the CNC system for cutter compensation look-ahead. Most of this kind of
>information is considered proprietary

Simple analytic geometry? Done by a simple computer?

>to the systems that are commercially
>produced and there is not much documentation to be found about how they do it.

Because it's so trivial.

>You are correct about how look-ahead will be a big part in how cutter
>compensation is handled in outside and inside corners

The inside (concave) has no options.
There are probably two ways to handle outside
(convex), depending.

Generally, just follow curves offset from the toolpath or
programmed motion/geometry by the value of the radius
comp.
IF the programmer needs circular interpolation about
a sharp external (convex) corner then a small radius
should be in the geometry. Than it becomes automatic
and NOT something for the control to randomly guess at
(programming intent).

>and the need for fill-in
>blocks to perform arcs around points of tangency etc.

See WSP posts.
Chmfers are also programmable by default in some
cases (control parameters).
Often used by 2D MDI programmers ...

>I would be very interested
>to see how Siemens handles it inside their 840D system.

Probably as mentioned above <G>.
--
Cliff
.

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