Re:

On Sun, 08 Oct 2000, Donald wrote:
<s>
> Tim,
>
> This makes a good starting point but doesn't really explain how to
> hook up homing switches let's say. EMC uses one pin (pin 12(S5)) for
> input of homing. Where is the input coming from on the other side of
> the switches? How are the switches wired? Series, parallel, or
> series/parallel? It don't say. And I can't find anything that does
> say.

WIRING

For EMC using the parallel port for steppers, try this. Connect all of
your normally-open home switches in parallel. (normally-closed
would be in series) Connect one side to any pin 18-25 but be sure it is a
signal ground if you use an el cheapo cable. Connect the other side of the
switches to pin 12. The home wiring is done.

INI SETUP

During the setup of the EMC for homing, you will be dealing with the
following variables in each axis section of the ini file that you intend
to run.

HOME = 0.000
HOMING_VEL = 0.1
HOME_OFFSET = 0.1000
HOME_SWITCH_POLARITY = 1
HOMING_POLARITY = 1

Disclaimer - I always do things by trial and error. These procedures may
crash your machine into an end of travel if you are not quick enough on
the abort or estop. You can set the HOMING_VEL so that you will easily
have time to watch and press abort.

Hand crank each axis near the middle of travel so that no switch is
tripped. Start up EMC and turn the machine on. (estop off, machine on,
manual mode) You will need to do the following steps for each axis.

0 - Machine motion

This step assumes that you have jogged the machine and that it appears
to move to bigger numbers when you jog it in the direction that you think
should be positive. It may not be a jog+ that does this because jog
direction has a ini file polarity. We just need to know that axis plus
and minus change the numbers in the correct direction. If it does not,
you will need to change something on the wiring of motors, encoders, amps,
whatever.

1 - Polarity of home switches

HOME_SWITCH_POLARITY = 1

Press home for any axis. If the numbers for that axis turn green
immediately, reverse the home polarity in the ini file. If the axis runs
and keeps going press abort. Polarity should be correct.

2 - Polarity of initial home motion

HOMING_POLARITY = 1

When you press home did the axis move toward the switch. If yes, good. If
not reverse the polarity of axis motion. Now with motion toward the home
switch, press it by hand or screwdriver or whatever and see if motion
stops and the numbers turn green. If yes your system is correctly wired
and polarized.

3 - Home offset

HOME_OFFSET = 0.1000

This is the direction and distance that an axis will move after the home
switch has closed. When you use the stepper and parallel port definition,
you will need to home each axis with all others off from their home
switches. Put enough distance in here to get that axis back off the
home switch. I make this motion the opposite direction to the home
motion.

4 - Home position value

HOME = 0.00

This is the value that the axis will set and show when it has finally
reached the resting position after all of the above motion. You can set
this to any value that you think is right.

Repeat steps 1-4 for each axis. Make sure that the other home switches
are not left tripped from previous work.

Once you have set the home switches and value, you can set the soft limits
for each axis so that you will not overrun its real travel.

I think that linuxcnc.org would be happy to host drawings. They can be
placed in the dropbox by each contributor and someone (?) should/will
compile them into folders.

Ray