Re: The guts of Circular Interpolation

Pete,

It would halp to know what is your desired "end result". Is it
academic, or to help you understand a certain control, or do you want
to WRITE a circ interp routine? Because the "best" links and info to
give will depend on this, IMO.

There are at least several ways to perform circ interp, and more than
a few websites. Help me narrow your request so I can give you truly
useful advice. (because when I was looking for the same thing; I
found I had to do a LOT of "wading"...

Ballendo

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Pete Miles" <petem@o...>
wrote:

> I am looking for either a website or some literature that explains

in

> detail what happens inside a CNC controller when executing a

circular

> interpolation command, either G01 or G02.
>
> It is my understanding that a CNC actually breaks up the arcs into

a

> set of smaller linear moves so that the cordal deviation with the
> line segment and the arc are within the tolerance spec set in the

Amp.

>
> These small line segments have a set of coordinates and a velocity.
> Which causes both axis of the machine to move. But prior to

moving,

> it needs to calculate the accelerations and decelerations,

distances

> to move based on the acceleration values, adjusting the straight

line

> velocities so that the tool gets to the end of the small sub line
> segment at the right time so as to maintain (or try to) velocity
> through the entire arc.
>
> Now all of these tiny little calculations take time, and are

repeated

> many times during a single G02/G03 command. Then all these
> calculations have to match up with the servo update clock, and when
> things like jerk, acceleration, and velocity on an axis become
> limiting factors, things have to slow down.
>
> What I am looking for is how all this is calculated. Does the CNC
> controller do all the work, is the servo controller involved with
> some of the calculations.
>
> Any info would be appreciated.
>
> Pete Miles