Re: Pulse Gen

PhilC wrote:

> ----- Original Message -----
> From: "Wally K" <cnc4me@...>
> <snip>
> >
> > Thanks for the reply Phil. I do not think the external pulse circuit
> > has to do complicated things like circular interpolation. Why not
> > let the computer do that. Just have the external circuit generate
> > the stepper pulses.
> >
>
> Actually circular interpolation is not very hard at all. Ever heard of the
> Bresenham Circular Interpolation Algorithm? Just a few shifts and adds...

But, the Bresenham algorithm(s) are specifically optimized for a discrete
grid, and want to pass through every point along one axis in the path.
This is great for drawing solid lines, circles and ellipses, etc. on a
raster screen, but really doesn't apply well to a machine tool path.
In that, you may want to skip over intermediate 'pixels' at high speed,
or spend some time 'between' them when moving very slowly. The
Bresenham algorithms would be cumbersome for this kind of purpose.
Simple trig is all you need to compute smooth paths at any velocity.
When you project the trajectory to a certain point in time over the
path, you then round off to the nearest discrete position based on
machine resolution, and go there. Although this works best with
floating point computations, that is no big impediment as it once
was.

Jon