Re: [CAD_CAM_EDM_DRO] Home / Limit switches

I used 12 digital inputs, wiring a seperate switch to each
input on my little grizzly mill. The one things I still need to do is
integrate
the E-stop functions between the grizzly spindle motor controls and my
CNC controls... (I'm actually thinking about ditching the grizzly
controls so I
could control spindle speed (perhaps position too!) Anybody done this?

Back to the limit/home stuff:

Contact with any of my limit switches will
1) Tell EMC that we've hit a limit (and since each limit input is
unique, EMC knows which limit was hit.

EMC will put the system in ESTOP and stop the program (I assume,
I'm
still working on running my first program, just been using it
manually ;) )
2) Disconnect all power to all actuators, and trigger the E-Stop
input.

My switches have both NC and NO terminals.
The common is grounded, and my EMC digital inputs are pulled high
using
resistor networks on my digital I/O card. When a limit switch is
contacted, the
NO terminal (feeding the EMC limit input) is pulled low, telling
EMC about the
limit condition.

The NC terminal is used to control the power into the system (via
relay). If any
limit is hit (that is, the NC terminal is no longer connected to
ground, either because
a limit condition or a wiring fault) the relay providing
amp/actuator power will
not toggle and power will be removed. This will "safe" the
system even if software
control is dead. (Although I found that I will cause an amp
fault if I hit a
physical end of travel(since the following error is greater than
128 encoder counts),
which is a nice third round of protection.

So on my system, the "home" switch is really important- Otherwise I'll
be guessing at
my initial position every time, as homing off of a limit switch is not
possible.

A question to the group:
I found when doing my E-stop circuitry and sequencing that it would
probably
be much simpler if I threw a PLC I had laying around at it. Of
course, then
I'd be relying on more software/hardware to E-stop, which is of
course, questionable
depending on the application. I used to do aerospace software, did
a lot of
fault handling stuff, and was wondering what the feelings of people
with more
CNC experience were.


Finally,
A HUGE THANKS to Jon, Smoke, Alan, Ray and Ballendo (and everyone
else!) that
helped me out with my G code questions. I'm going to try cutter
compensation
tommorow, but the work offsets and G92 were just what I was looking
for! This
group has some first class talent!

I'll send out a URL when I finish my mill web site.

Thanks,
murph


Carlos Guillermo wrote:

>
> Les -
>
> I was referring to LPT s/w-type CNC controls that (IIRC) refer to
> having inputs for 3 switches per axis. Do people actually use all
> 3?
>
> Carlos Guillermo
> VERVE Engineering & Design
>
> -----Original Message-----
> From: Les Watts [mailto:leswatts@...]
> Sent: Thursday, January 25, 2001 11:23 AM
> To: CAD_CAM_EDM_DRO@egroups.com
> Subject: Re: [CAD_CAM_EDM_DRO] Home / Limit switches
>
> >Does anybody out there omit the home switch?
>
> In other machines I did not use a home switch per se.
>
> I reverse direction on hitting the limit switch and stop on the
> first index pulse. That is soft home.
>
> That is most common with servos.... perhaps you are refering to
> steppers.
>
> Leslie Watts
> L M Watts Furniture
> Tiger, Georgia USA
> http://www.rabun.net/~leswatts/wattsfurniturewp.html
>
> Welcome to CAD_CAM_EDM_DRO@...,an unmoderated list for the discussion of shop built systems, for CAD, CAM, EDM, and DRO.
>
> Addresses:
> Post message: CAD_CAM_EDM_DRO@egroups.com
> Subscribe: CAD_CAM_EDM_DRO-subscribe@egroups.com
> Unsubscribe: CAD_CAM_EDM_DRO-unsubscribe@egroups.com
> List owner: CAD_CAM_EDM_DRO-owner@egroups.com, wanliker@...
> Moderator: jmelson@... timg@... [Moderator]
> URL to this page: http://www.egroups.com/group/CAD_CAM_EDM_DRO
> bill,
> List Manager
>
> FAQ: http://www.ktmarketing.com/faq.html