Re: E-Stop and Overtravel Switches...

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

Gene

Great stuff!  I agree with all of it.  I wonder if you would be willing to
work this up for part of the machine I/O wiring and safety section of the
EMC handbook.  I'd be happy to help you with it.  

What I've done with the backplotter.ini file is to open those lines so that
they don't trip up the virtual machine with floating voltages on the
printer port when there is no real machine there.  I really should have put
a disclaimer there that says, "don't try this with a real machine at home!"
 Although some will anyway.

Thanks for the post.

Ray



At 02:46 PM 1/30/2000 -0500, you wrote:
>
>
>Ray Henry wrote:
>> 
>> 
>> I set the home switches so the control thinks they are closed.  I set the
>> overtravel so the machine thinks they are open.  Not having them connected
>> should not make a difference.  I've read about folk on the list who never
>> hook some of these things up.
>> 
>> Get back to me cause I love a good fight. (read problem)
>> 
>
>
>     Hi Ray,
>
>      I would like to point out that the industrial machine tools all
>(as far as I know) have the home switches, and especially the overtravel
>switches, set for constant voltage sensing.  In other words, they have
>to have a complete circuit when NOT actuated (closed, open on
>actuation).  I repair these machines on a daily basis.  The reason for
>wiring them like this is vibration of the machines sometimes loosens
>wires, and a loose wire is an open circuit at times.  The theory is that
>if the wire is loose, the machine will go into overtravel no matter
>where it is physically and shut down machine operation until fixed.  A
>loose wire will become a nuisance, I will be called, and I will have to
>find the loose wire.  It saves a lot of ballscrews, blown fuses, and
>overheated motors.  Home switches and overtravel switches wired not to
>constantly detect voltage (open, closed on actuation) can loosen up and
>the machine won't stop, no matter if you want it to or not.  I only
>point this out for people who might not realize the difference.
>
>     You mention E-Stop notification to the computer.  This is good, but
>I would also like to point out (as you know) that the E-Stop switch
>should not rely on the computer to shut down the axis drives.  Those
>drives should be wired seperately to the E-Stop switch so no matter what
>the computer is doing, the axis will stop.  Open up the relay
>(contactor) that supplies power to the motors.  The computer can
>energize this relay through the normally closed (non-actuated) E-Stop
>switch.  When you are tossing parts all over the shop, you want that
>sucker to stop.