RE: home/limit switches - combined

["Tim Goldstein" <timg-at-ktmarketing.com>]

I was having a problem understanding how homing worked as it seemed to be
buggy to me. I contacted Fred Proctor and following is his explanation.
Found out that it worked fine, I just didn't understand it and had the
values set wrong.

Tim
[Denver, CO]

The way homing works is that motion proceeds at the [AXIS_#] HOMING_VEL
speed in the direction specified by [AXIS_#] HOMING_POLARITY until the
home switch trips. The polarity of the home switch is set by [AXIS_#]
HOME_SWITCH_POLARITY. Then, the axis position at the trip point is saved
and motion is aborted. Once the move stops, a move back to the saved
trip point plus any offset in [AXIS_#] HOME_OFFSET is done, and the axis
position is set to the value specified by [AXIS_#] HOME.

With HOME_OFFSET and HOME set to 0, the homing sequence would look like
this:

1. slow jog toward home switch.
2. switch trips.
3. jog decelerates and move terminates shortly after home switch.
4. jog back to switch trip position.
5. position set to 0, and digits turn green.

With HOME_OFFSET set to -0.1 (sign depends on value of HOMING_POLARITY),
and HOME set to 3.0, the homing sequence would look like this:

1. slow jog toward home switch.
2. switch trips.
3. jog decelerates and move terminates shortly after home switch.
4. jog back to point 0.1 units past switch trip position (to get off
switch if you need to)
5. position set to 3.0, and digits turn green (lets you specify 3.0 as
home for this axis).


Fred Proctor

>
> ----- Original Message -----
> From: Matt Shaver <mshaver-at-erols.com>
>
> > If the software limits don't stay relative to machine zero, then that's
> > a bug that needs to be fixed. You might try G92, rather than G10L2Pn, as
> > a workaround until this can be fixed.
>
> I had some time to play around with the machine again tonight and I could
> not get the soft limits to do what I thought they did before -
> they seem to
> stay at machine zero with g1 l2 p#  or g92.  This is good - but I feel bad
> now for saying they were moving.  I'm sorry bout that.  I think what I was
> seeing was actually due to the homing problem I have.
>
> It seems like the backlash setting is the culprit.  If I enter
> 0.0 backlash
> everything is perfect - homes to the swich - backs off 0.1 to get off the
> switch and stops.  I can press 'home' repeatedly and it stops within .001"
> each time.
>
> If I enter my .014 backlash it gets confused.  I'll home it, set the
> incremental jog to .001, hit the jog and it moves .063!  After that first
> move it moves .001 each time but here is where it gets wierd, if I home it
> again it'll home offset almost .200 instead of .1.  I'll try the
> incremental
> .001 jog and it'll go over .1.  Now if I try to home again I get
> the message
> "- limit exeeded' (my soft limit is -0.15) I haven't got a clue whats
> wrong - either I got something wrong with my system or everybody else is
> using zero backlash ball screws and doesn't see the problem.  Could you
> maybe set some backlash on your machine and see if you get this wierd
> behavior too?
>
> Thanks...
>
> Joel
>
>