Re: [CAD_CAM_EDM_DRO] New question about limit and home switches

> I have a question about home and limit switches, and EMC. Let's say I
> have a machine with a 12 x 15 table. I want home to be the center if
> the table. The machine has limit switches on each axis and a home
> switch on the x and y axis positioned so that the table is centered
> when the home switches are tripped. The question is, what does EMC do
> if a home switch is tripped during a movement such that x would move
> from -4 to +4 and trip the home switch when it passes 0? The
> following code may help explain this:

If I understand correctly, you are asking what happens if you drive
over a home switch while running a program, subsequent to homing
the machine. The answer is nothing - the home switch only gets
looked at during homing. Running over a limit switch on the other
hand will shut the machine down.

It gets more complicated in that in the standard parallel port mapping
all the homes are connected together and all the limits connected
together, so after homing an axis you have to be sure it gets parked
away from its switch so you can home the next one. With an additional
I/O card these can be split out seperately.

Let me also mention that zero does not have to be the position of the
home switch. Usually machine design is to put the home switch near an
end of the axis travel so that the machine doesn't have to guess which
way to move to find it, and use an offset home value if you want zero
in the middle. But the machine may have to move farther to home this
way.

If the operator can insure that the axis is always positioned to the
same side of the sensor before the homing move, then putting the
sensor in the middle is faster.

I've run into this problem on a machine (not emc) which I am modifying
the software for at work, so I frequently have to restart the software
and rehome the machine before I can test it. Some of the axis are
quite long, and others quite slow, so one of these days I'm going to
reposition the sensors at the end of the more heavily used end of the
travel.

Chris