On Wednesday 10 April 2019 12:47:23 John Dammeyer wrote:

> Hi Andy,
> See below.
> > -----Original Message-----
> > From: andy pugh [mailto:bodge...@gmail.com]
> > Sent: April-10-19 2:46 AM
> > To: Enhanced Machine Controller (EMC)
> > Subject: Re: [Emc-users] Leaving an axis out of the home sequence
> > AND (continued:)
> >
> > On Wed, 10 Apr 2019 at 04:49, John Dammeyer <jo...@autoartisans.com>
> >
> > wrote:
> > > Since my Harmonic Drive/STMBL are an AC Servo
> >
> > ...
> >
> > > The question then is whether or not the system, when starting
> > > can/will
> >
> > recognize an input which is a unit present signal.
> >
> > This is a solved problem :-) (I have exactly the same 4th axis as
> > you)
> >
> > I have a loop of wire on two spare pins on the connector where the
> > 4th axis plugs in to the machine:
> > This drives an input on the STMBL. The STMBL HV enable is only set
> > (HAL Logic) if this input indicates motor-present.
> My HP_UHU drives have that feature built in.  The encoder connector
> has to have a jumper to show the encoder is connected.  Probably to
> avoid a runaway condition.
> > I just accept having an A axis display even when the axis isn't
> > connected. And the machine will f-error if you try to move or jog
> > it.
> I'm testing with both MACH3 and LinuxCNC so I can write up a neat
> little conversion document that takes a parallel port BoB based system
> from MACH3 into LinuxCNC with minimal pain.  In the MACH3 system, on
> my CNC router, when I tell the open loop stepper controlled axis to
> home all that MACH3 does is zero out the DRO.
> But Gene has a home switch on his rotary indexer.  Now thinking about
> it I think the solution might be simple. When he pulls the indexer off
> the mill he has to unplug the encoder cable.  If he's using safe type
> limits then the switch is normally closed and a home (or limit)
> happens when it opens.

Exactly what I'm doing.  Except no endoder, stepper driven and likely 
needs a bigger motor, and more speed reduction to improve the holding 
power.  Thats a downright puny motor on it now, and I have a 270 oz/in 
currently holding down a stepladder step. 8 wire so slower top speed but 
easy on the psu. In fact I think I'll check and see if its shaft is 
compatible yet today.

> So run the home switch circuit through the encoder connector and wire
> the mating encoder connector to have the connection closed.  From the
> CNC controller perspective the system is already homed.

Thats not how lcnc homes. In fact if the switch is closed, it jogs away 
till it opens, THEN goes into the normal home search routine. I use that 
to advantage on the Sheldon to assure it actually searches for the 
switch closure.  By sensing the front gib, which is NOW a solid bar the 
width of the carriage, once it has approached the spindle and closes, it 
stays closed, At homing, it will back away to the right till it opens 
before the normal search begins.

I found this undocumented behavior when I put home switches on TLM. 
Putting in on the back of the bed because the screw is in the way on the 
front, and set the switch roller to touch the tapered gib holders bottom 
as it goes by. In fact I had to do a minor rebuild because I was sensing 
the bottom of the OEM gib, and the tapered holder is thicker.
> The only 
> problem will be if LinuxCNC uses a find home switch sequence, and then
> backs off so the switch just opens again before it declares it's home.
> In that case it would try to move off a non-existent home switch and
> try turning the indexer forever.  And perhaps that's again where that
> extra input comes in.  If the input is asserted then a home switch
> exists.  If it's not asserted then a home switch doesn't exist and he
> runs it like you run yours or I run mine.
> Again in the MACH3 situation, all I have to do is select the ports and
> pins menu selection under the config menu.  Select inputs and uncheck
> Home switch for A axis.  That also hits the software ESTOP and shuts
> power down to the drives when I click OK to save.  I can now unplug
> the A axis and remove it.  Then press the now blinking RESET button,
> power is back and a HOME command just clears the A axis DRO.  Simple. 
> No file editing.  No multiple config copies.
> That's what is really needed on LinuxCNC.
> John
> > It might be possible to load different configs depending on that
> > signal. A bash script can send halcmd commands to load the hostmot2
> > driver, start the threads, read a pin, and then run one of two or
> > more linuxcnc startups (after unloading Hostmot2 and realtime,
> > probably.)
> >
> > Maybe even an edited version of the LinuxCNC startup script:
> >
> > Personally I haven't cared enough about the vestigial axis to bother
> > :-)
> >
> > --
> > atp
> > "A motorcycle is a bicycle with a pandemonium attachment and is
> > designed for the especial use of mechanical geniuses, daredevils and
> > lunatics."
> > � George Fitch, Atlanta Constitution Newspaper, 1916
> >
> >
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Cheers, Gene Heskett
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
Genes Web page <http://geneslinuxbox.net:6309/gene>

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