Hello John,
On Sat, 02 Jun 2007 11:09:26 -0400
John Kasunich <[EMAIL PROTECTED]> wrote:
> Abel Michael wrote:
> > Hello List,
> >
> > I have a question about the usage the axes A and B in EMC, can I use
> > them in the same way as the linear axes X and Y?
> > Is there another possibillity to control 4 independent axes in EMC?
> >
> If the above (output points at some time intervals) is really all you
> want to do, you don't need g-code or most of EMC. By splitting the
> shape into points at specific time intervals, you are doing the job of
a
> trajectory planner. Converting that into g-code, so you can send it
> through EMC's interpreter and trajectory planner, seems strange.
>
> If you are using g-code, it seems like you might as take advantage of
> EMC trajectory planner - use arcs and lines in your g-code, not just
> periodic samples.
>
> On the other hand, if you'd really prefer to generate a sequence of
> points in your program, you can use HAL tools to send that sequence to
> the motors (stepper or servo, your choice).
>
> There is a hal component called "streamer", which works with a user
> space program called halstreamer. You load the streamer component,
> then do "cat myfile >halstreamer" (or pipe the output of your program
> directly to halstreamer.) Each line in "myfile" is just a series of
> numbers (in ascii format). Halstreamer converts the lines to binary
> and writes them into a FIFO. Then streamer reads the FIFO and writes
> the values to HAL pins in a realtime thread. It would be quite easy
> to stream a new set of values every millisecond. As long as cat and
> halstreamer keep the FIFO from running dry, the duration of a run is
> limited only by disk size.
>
> Once in HAL, you can do anything you want with the values,
specifically
> you can route them to stepgen modules, or to a PID loop driving a DAC
> and then a servo motor, or any other motion control solution that
works
> with EMC.
>
Using hal as base seems to be a very interesting aproach. It might save
lots of work (and trouble) to switch to hal instead of updating my own
realtime cutter. I'm really astonished hal seems to provide lots of
functions that I could use directly instead of implementing them myself.
I will keep this in mind.
> In your case, each line would have four values, for the four linear
> axes. You might want to add some additional values - you could use
> other HAL pins to turn your hot-wire power on and off for example.
>
That belongs to the plan,too ;)
> The decision to use EMC vs. HAL alone would be based on any other
> requirements you have besides basic motion control. If you want a
> GUI, then you want EMC proper. Likewise, the HAL only approach won't
> have any provisions for homing axes, unless you build those provisions
> into your HAL configuration. The HAL version also doesn't explicitly
> coordinate the motion of the axes - but it sounds like your Python
> program does that already.
Especially homing axes would be very nice to have. It happens quite
often that the cutting process is stopped manually. At this time this
means that the machine has to be justified again to the next start
position which is always annoying.
Thanks a lot for your extensive answer.
> Regards,
>
> John Kasunich
Best regards
Michael
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