Re: Polar Coordinates CNC?

--- In CAD_CAM_EDM_DRO@y..., "wenger2k" <wenger2k@y...> wrote:

> The application would be the same as any other - i.e. router/plasma
> application (4'x8' as practical size for discussion purposes).
>
> I would think that Linear moves in polar space would be roughly the
> same and no more complicated than arc/circular moves in cartesian
> space - would they?
>
> I think that a polar machine could be a more cost effective

approach

> given that you eliminate many of the most expensive components of

the

> system (the long axis

> Why hasn't this been done before? I don't know - I expect that the
> cartesian basis of g-codes themselves have preselected this to a
> degree.

It's been done many times. It is referred to as a rotary axis. If a
rotary axis is oriented parallel to a spindle (Z), it is identified
as a C axis. The complete range of movement can be defined as X-Z-C
coordinate triples. Since G-code by definition is the tool movement,
the entire coordinate system is covered by this. Several of the G-
code intrepreters can output rotary axis code. The problem with this
method of control is that the linear movements by definiiton are
approximated by tiny arc movements. Since most movement is linear,
the programs become quite large. 10 years ago it was a no-brainer as
the controllers could not process large programs. Today it may be
economically feasable to produce rotary code (polar to you) that can
be processed, and the result could be a machine with a linear and a
rotary axis. One draw back is that as the radius increases in size,
the machine accuracy decreases. This is not the case with dual
linear machines. a 3 place decimal degree is much more accurate at a
2 inch radius than it is at a 20 inch. You may need to spend more
than you would think to get a reasonable angular resolution at the
longest radius.

A 2000 line encoder, a 4 foot diameter would be 150.8 circumference.
yields .0754 inch per encoder line. This would not be too
practical. However, IF, (very big if) you could get a decent
circular rack at 4 foot diameter, you could get excellent resolution
from a stepper motor. Also might get some decent resolution from a
pully or gearbox setup for a center drive.

It's almost intriguing enough to start throwing a prototype
together. ;-)

Best Regards,

Fred Smith - IMService