Re: know your limits

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

Ian, Bill

(comments mixed in)

On Thu, 15 Mar 2001, Ian wrote:
> Hi Bill,
<s>
>However, I now realise that none of the axes
> finishes up at 000.000 as each has to move away to let the next one home (do
> you have to actually home each axis separately...

Yes.  But the good news is that once the axis finds its switch and moves
away to the distance set by

    HOME_OFFSET =                   0.10

then it will set that position to the value in

    HOME =                          0.000

> or is there a command which
> will send 'em all home at once?). 

This is commonly done with the stg board but can't be done with the parport
stuff as it is currently written.  I believe that someone mentioned that
they were trying to hack together a parport that had no limits but used
those pins for each axis home.

> I'm thinking here of running a second operation
> program on a part machined part, i.e. part machine it then home the axes,
> change tool and run a second program to work again on the same part.

If you're not loosing steps, there would be no need for the home operation
between.  In fact, one report has it that homing with large backlash numbers
leads to some strange homing behaviors.  Home with a micro switch can lead
to values in a +- 0.002 inch range at best.   This might be a disaster for
the fine work that you want to do. 

Adding a optical interupter to the motor shaft so that you get the home
signal at the same step pulse each time will give better accuracy.  You
could turn on the interupter lamp with the micro and pull down the parport
pin with the output transistor.  If you use this arrangement, a few steps
would be all that would be required to get the axis off the home switch and
ready for you to home the next axis.

Glad to hear about your progress.  Will there be some pics in the works?

Hope this helps.

Ray