Re: homing and axis errors

[Ray <rehenry-at-up.net>]

On Thu, 14 Sep 2000, you wrote:
> Hello,
> 
> I have been playing around with my little homebrew
> setup some more, and I learned something curious.  I
> once saw that I could home my single axis, and it
> would not respond to jog changes, but it would show
> position changes on the EMC display when I turned the
> shaft.  

I'd guess that the EMC was still trying to home the axis and was ignoring
your jog commands.

>I was unable to reproduce this (I wasn't able
> to get the axis to home and go green) till tonight. 
> My setup has no switches whatsoever.  What I found was
> (by checking between the actual and comand positions)
> on startup all axes are yellow.  I highlight axis 0
> (the only one I have), and click "home".  It appears
> to do nothing when the actual machine position is
> displayed.  the display is yellow, and reads 0.0000. 
> When I look at the commanded position, it keeps
> increasing in the positive direction.  If I let it go,
> it hits 20.000 then drops.  Eventually I get the
> following error message:

You can be thankful that you didn't define a 100' machine in the ini or
you'd have been there all night watching the thing run to the end.. ;-)

> minimilltaskintf.cc 938 Error on Axis 0
> Maximum software limit on axis 0 exceeded

This means that the EMC never saw the home switch inputs as closed.  If
you define them as closed in the ini file, It should always see them as
closed.  

Is this homebrew axis a closed loop?  In other words does the EMC drive a
motor that drives the the encoder.  If it is not, you will rapidly
confuse the EMC when you command a position change because it is watching
the encoder position and expecting to see the change that it commanded.
 
> Then it goes green (homes?)  after which I can turn
> the shaft and see the position change.  If I click
> home again, the axis goes yellow, but the commanded
> position seems to decrease and settle to 0.0000, and
> turn green again.

Yep.  Grean means homed.  The momentary return to yellow is a
normal reaction to a second home command.  With recent releases, a home
command sets the EMC to an un-homed condition.  It will remain un-homed
until is has found the home position that you define.

> Does anyone have any idea why it won't home properly? 
> I used the code from the stg module, and uncommented
> the #defines for no limit switches and no home
> switches.

If this is a closed loop I'd guess that you do not have tight enought
control of the loop.  You need to do some tuning.  If it is not a closed
loop, I'd rig some kind of  connection so that the motor drives the
encoder, set up emc so that it knows distance, and start tuning.

Ray