Re: [CAD_CAM_EDM_DRO] Power Brownouts

echnidna wrote:

>Hi Group,
>I live in an area where occaisional disruptions occur to the electricty power grid. Is there any way to protect cnc machines from a power failure when part way through a machining cycle. A UPS is practical for the computer itself but the high cost of a very large unit to accomodate the routers (and dust collectors) isnt practical.
>
>I want to prevent damage to the machine and the job in progress.
> And hopefully be able to restart at the point where the machining was interupted.
>
>

Does your system use encoders/servos or steppers? If it uses encoders,
then keeping the computer (cnc
control) powered up through a UPS will allow it to keep track of
position when the mains power
goes out. A small dip in the line power while a servo machine is
running will often not be
noticed at all, unless the machine was running at rapid traverse rate,
and then it wouldn't
mess up a cut. If the outage is longer than the servo drive or VFD
driving the spindles can
take, they should force an E-stop condition, and the program should be
able to continue from
that point once the rest of the machine is back on. If your routers run
directly off the
line power, you need some sort of power dip detector to put the control
into E-stop. A
120 V relay with the NO contacts wired into the E-stop chain would
probably work.

I had a pretty long blackout (for a machine with no UPS anywhere) once
while running my
mill. It was long enough that it got totally dark, and I was reaching
behind me for where I
knew I had a flashlight when the power came back on. I was amazed to
note that the axis
servo drives and the spindle VFD rode through the outage without
tripping offline. The
computer rode through it, too, which was only a slight surprise. The
outage was over 1/2
second, at least.

Anyway, with open-loop steppers (no encoders) then you have the choice
of powering them
with a UPS or accepting that any power outage will cause the position
reference to be lost.
At least, if the CNC control is made aware of the condition through the
E-stop chain, and
the control has a UPS, then you will know the program block where it
stopped, and can
restart the program at that point after rehoming the axes.

Jon