Re: servos, steppers, limit switches

This sounds like it could be more complex than I reckoned. I'm kind
of puzzled as t how the DeskCNC controller box has all 3 limit
switches AND the e-stop switch all wired in series according to teh
hookup diagram...

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Madhu Annapragada"
<mapr@c...> wrote:

> One way to zero (reset, home ) without limit switches is to run the

axis at

> a slow speed to a mechanical stop. The controller would determine

the

> mechanical stop by monitoring the encoder as you guessed. Once the

encoder

> stops counting, and if the encoder has an additional index (Z or

reference

> pulse), the controller would move back until it saw the index pulse

at which

> point it would stop the axis and set this as a zero or home

position. I am

> sure you can see the inherent disadvantage in this; one you have to

run the

> machine slowly so as to not damage the axis when you run against the
> mechanical end of motion. Second, if you do not have a index pulse

on the

> encoder, the repeatability of the zero position would not be very

good as

> the controller might either zero on the leading edge or the falling

edge of

> the A channel or the B channel. A index pulse on the other hand

gives one

> better repeatability.
> Madhu
>
> >-----Original Message-----
> >From: Brian Sherwood [mailto:lurch@m...]
> >i'm in the process of converting my taig to servos...and someone

told

> >me i don't need limit switches on a servo setup although the

stepper

> >setup has one at the max-value of each axis. the wiring diagram

for

> >the servo setup shows the limit switches wired in series with the

e-

> >stop switch.
> >
> >My first stupid newbie question is, how does a servo system ever do
> >a 'home' command to find out where it is without limit switches?

Or

> >does it just run to the end of travel and drop out when the encoder
> >stops encoding, then you set your known value for that axis to that
> >point, knowing the mechanical limits? Like, for example, if I know
> >my x-axis travel is 12 inches, do I just run it til it is against

the

> >stop and when it stops, I set x to 12 in the program and call it

done?

> >
> >Thanks in advance.
> >
> >Brian
> >