Re: Polar Coordinate based CNC

Lee:

I've been doing some preliminary work on this, and it's like a lot
of engineering problems in that optimizing for one variable makes
another one squirt out. But there's some promise there.

The big advantages are that only rotary joints are required, and
that the load paths can usually be shorter (not in all cases
though). The chips stay out of the motion stuff as a bonus.

The big drawback is that since the coordinated motion to generate a
+1" move in X (say), changes depending on where you are on the table -
the machine must be initially calibrated to some absolute angles.
This is the Achilles Heel, since the degree of precision required to
do that is pretty sobering.

No insurmountable problems, but at the end of the day it seems
easier just to get along with the good old prismatic joints. So nice
and linear.

Someday I'll get around to building a prototype to test the idea.
As another poster pointed out, it puts the metal where it counts to
build the work envelope.

Dave Kowalczyk
Everett WA
TurboCNC software --> http://www.dakeng.com

> > ----------
> > > From: Lee Wenger <wenger2k@y...>
> > >
> > > What all would have to happen to allow a CNC machine to
> > be based on a polar coordinate system rather than a
> > rectangular one. The big benefit to me would be that the
> > single most expensive component of a router/plama type of
> > system is the slides and drive components (the screws or
> > rack/pinon not the motor itself) for the longest axis (for
> > systems of the size/type I have in mind this would be to
> > move a gantry). But I assume that would mandate a change
> > to the controller so it could interpret g-codes as polar
> > coordinates. Are there any controller packages out there
> > currently that support polar-coordinates?
> >
> >