Re: [Emc-developers] Shared home and limit switches

[Jason C. <jas...@mu...>]

Jeff,
	Only problem is see is that if the homing direction is not towards
the home position the axis will travel until it hits the hard stop. You
still need to have the limits to stop damage.
Jason

-----Original Message-----
From: emc...@li...
[mailto:emc...@li...] On Behalf Of Jeff
Epler
Sent: Tuesday, 27 February 2007 11:08 AM
To: emc...@li...
Subject: [Emc-developers] Shared home and limit switches

<twice2> on IRC has been trying to set up a machine which uses a single
parport pin for limit and home switches.  It looks like he's run into an
emc2 bug: when he's homing X (for instance), when the limit switch opens
it will cause a fault on the Y and Z axes (their limit switches weren't
disabled for homing)

I think that if we have a pin 'axis.N.homing' which is TRUE when homing
and FALSE when not homing, the necessary 'limit ignoring' behavior can
be built in HAL.  In this case, the logic would be 
    limit-switch = shared-switch and (no axis is homing)
which could be built from a number of 'and' and 'not' components.

An alternative is to add more smarts inside the motion controller
(something like: if this axis and the homing axis are both SHARED and
IGNORE_LIMIT, ignore limits on this axis) but for some reason I don't
like this idea as much.

Thoughts?  Can we change 'axis.N.homing' to a pin to 2.1.2?  (It's
currently available, but as a parameter)

Jeff

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