Re: [CAD_CAM_EDM_DRO] EMC Home and Limit Wiring

beer@... wrote:

> I have some questions about the Home and Limit switch wiring for EMC. (
> I'm a CNCPro user )
>
> >From what documentation I can find, it seems that three switches are
> envisioned for any single axis; one for Home, one for "Near" Limit and
> one for "Far" limit.
>
> In the case of a three axis system, then, it looks like nine switches
> are expected.
>
> It also appears as if the switches are designated for a series
> connection .. a Home loop, and two Limit loops.
>
> I GUESS I can understand how this might work when the HOME setting is
> asked for.
>
> Move X only until HOME is triggered, then back a bit until it's not
> triggered.
>
> Move Y only until HOME is triggered, then ...
>
> Move Z only ...
>
> But I don't understand the logic behind the -Limit and +Limit. Why
> should EMC care WHICH direction things are going when a Limit switch is
> activated. Just stop !

EMC will allow you to jog off the limit switch, but not jog further onto
the limit sw. So, it needs to know which one is tripped.

> And finally, is there no provision for an EStop switch ? Or is this a
> double-pole switch to be added to both Limit switch loops.

Well, it depends on what stepper drivers or servo amps/interface
you are using. The Servo to Go card has a particularly weird
watchdog timer to detect failure of the computer to update the DACs,
and I wanted to use that, as I didn't trust the PC, Linux, RT patch
and EMC to be as reliable as it has been. So, I built my own
E-stop controller, that manages the E-stop sensing and response
in hardware, to shut down the spindle and servo amps.

I have included similar features in my parallel port servo control
and my stepper rate generator.

There should be a parallel port pin in all versions of EMC that will
accept an external E-stop signal. You have to read the documentation
for the auxilliary I/O to see which pin has that function.

Jon