RE: [CAD_CAM_EDM_DRO] Re: Help a confused newbie out please

> From: Jim Brown
>
> I thought that a limit stop was the same function as an Estop
> condition for the controller program. I didnt know that they
> were 2 seperate things.Told ya I was a newbie!

We all started there! :-)

> So an Estop will cause you to lose position sync,and it stops
> movement abruptly?

Yes, at least with the Ahha controller. I assume that this is true of all
'open-loop' setups (i.e.: where you don't have physical table feedback via
scales, etc.)

> Does a limit stop cause a position sync loss also? How does it
> stop the travel.....abrubptly also?(Im using steppers until I
> learn more, then Ill advance to servos)

Sync is not lost on a 'limit' stop with Ahha because it brings things to a
stop in a controlled manner. This is by using deceleration as opposed to a
dead stop. Remember that the mechanical system (table, screw, motor
armature, etc.) all have mass and can not stop instantly. So if you are
driving the axis at a high rate and you stop the step pulses the inertia of
the system will likely cause the motor to turn some number of steps that
were not commanded by the controller - hence the controller no longer
'knows' where the table really is.

> I had planned on using micro switches with rollers on them,
> that would act as a limit stop as the table/saddle swept
> them. I just didnt know where to place them(ie, before the
> actual travel limit or at the end of travel)

Depends on your control system: if it brings things to a controlled stop
after hitting a limit then you must allow enough 'over travel' room past the
switch (for the worst case -i.e.: fastest axis speed) before the physical
end of motion is hit. If your system stops immediately upon hitting a limit
switch you can probably get away with no (or very little) over travel room
but if it's an open-loop system you'll probably have to re-home things to
get back in sync.

Also be sure that once the limit switch is hit it remains activated even in
the over travel area otherwise bad things can happen.

> Regards,
> Jim

Cheers,

Chuck Hackett
Omaha, Nebraska, USA