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

Thank you all for clearing things up for me a bit.You were very helpful.
Regards,
Jim
egroupscdh@... wrote:> From: caudlet

>
> --- In CAD_CAM_EDM_DRO@y..., Alan Marconett KM6VV wrote:
> > Hi Jerry, Jim,
> >
> > On the subject of "loosing position/counts", if the stepper(s) are
> > stopped abruptly with out deceleration, they WILL loose position
> (the
> Guys: I guess I am confused. I am trying to visualize a situation
> where I would want to continue on with a program that has just driven
> my table into the limit switches. At that point I think I would like
> to take a deep breath, move my table back to home then check the code
> that caused the problem. I understand the issue that once you lose
> your place with an open loop system you are pretty much SOL on
> getting things back to absolute 0,0,0. I always try to set my
> material up so I have a known reference point by using an edge feeler
> or conversly setting my machine to some 0,0 point and moving the
> material to be back at zero using the offset method.

That's a good question. I guess my answer would be that G-code programming
mistakes do happen. You are also assuming that 'homing' is an easy
operation. In my case, since my lathe is a converted manual lathe it does
not have an indexable tool post. To set the X axis zero I have to take a
test cut on scrap, measure it and set the axis to the appropriate value - a
real pain, so I endeavor to never 'position info'.

BTW: The E-Stop circuit should not contain any solid state logic between it
and the spindle relay and axis motor relay(s). Remember you want to
minimize the possibility of nothing happening when you hit the E-Stop
button - it may be part of your body in the way!

In my case the E-Stop circuit uses normally closed switches controlling a
relay for the spindle motor (between the VFD and the motor ... VFD control
circuits can fail) and a relay controlling power to the stepper drivers -
not and 'enable' signal but in the actual power circuit to the drivers (the
'enable' logic could fail). The E-Stop button (normally closed) is in the
'hold' circuit of the relays. Once hit, the button must be reset and then
another 'enable' button (normally open, momentary) pressed which again
enables the spindle and driver power relays.

This minimizes the components in the E-Stop circuit that might fail
endangering life and limb. One of the relays could stick but this would be
very rare.

Back on the subject of limit switches. On my B-port Series I that I
converted to Ahha I used the original table limit switches (one per axis) in
the E-Stop circuit (i.e.: Hard Limit) and added roller-arm microswitches for
the 'Soft Limits'.

Cheers,

Chuck Hackett
Omaha, Nebraska, USA



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