Re: thanks, NC subprograms and tangential axis

[Jon Elson <jmelson-at-artsci.wustl.edu>]

Max Heise wrote:

> Hi Everybody,
>
> first thanks go out to Jon Elson for his reply on April, 12th.
>
> My Machine is now running fine for about 2 weeks.

Great!  Glad I could help.

<snip>

> My next questions are:
> 1.
> What would I have to change to add NC subprogram call to the rs274 emctask ?

I think this could be quite hard.  The interpreter is fairly complex, and any
branching
or procedure calling breaks the lookahead machanism.  It would take some careful
study to this.  I think one reasonable restriction to start with would be that
subprograms or branches would only be permitted when there was no motion
in progress.  That might be doable by a mere mortal.  Putting subroutines into
sections of programs where motion is going on would be a lot harder.

>
> And 2.
> My current setup has 2 linear and an angular axis.
> As this machine is cutting carton, the knife mounted on/controlled by the third
> angular axis has to be tangential to the moving direction of the 2 linear
> axes(x/y). If this is not done, the carton will tear because the knife will just
> scratch, not cut.

The easiest way to deal with this is to wait for angular axes to be fully supported.

(Right now, angular axes are only supported under manual control, but this is
supposed to be in the works.)  Once that happens, I think you could write
a small program to read the X and Y moves in an RS-274 program and compute
the angle for straight moves.  If you ever need to do arcs, you could compute the
angular rate of the arc, and program the angular axis to move at that rate.
This program would then write out a modified RS-274 program, with the
knife angle added to the X and Y moves.

> Would I have to change to add this ? Is is OK if I compute the position of the
> angular axis about 10 times a second. So is it possible to do this in the PLC ?
> Were do I have to have a closer look at ?

Because the user interface is not running in real time, it is always quite a ways
behind the machine.  Trying to control the knife outside of the real-time
portion would be very difficult.

Jon