"Ignoramus28517" wrote in message
...
On 2010-06-27, Joseph Gwinn wrote:
In article ,
Ignoramus31989 wrote:

Just wanted to do a little sanity check.

The question is about wiring power for all motive power (XYZ and
spindle) on this Bridgeport CNC mill.

The mill will be wired for single phase, with spindle motor on a VFD.

My current plan is as follows.

1. The CNC PC would be fed with incoming power without ANY regard for
any switches. When I need to shut it down I would type "sudo shutdown".
I
will use this PC for many other shop purposes.

2. Have a switch (original switch on the door) be the first control of
incoming power to the mill (besides the PC, see 1)

3. Have all incoming power go through two fuses.

4. Jon's PPMC control box will be powered by 220v (more like 243 VAC
in reality). So any one fuse that blows, would cut the power to PPMC
control box.

5. Servo power supply, as well as power to the spindle VFD, will be
provided through a contactor.

6. Regular start and stop buttons would simply send signals to
software via PPMC.

7. The motive power contactor is actuated by a solid state relay built
into PPMC, but its control line will also go through a relay
controlled by estops, so that pressing ESTOP automatically cuts all
power to any moving equipment. I may need an extra relay in the estop
circuit, so that ESTOP not only cuts off motive power, but also sends
a signal to the control box and thus to the software that estop
occurred.

What I like about this approach is that it is relatively idiot proof
(estop means stop regardless of any software mistakes), and yet by
preserving power going into PPMC, I can keep track of my position
etc. It also keeps the PC going.

The minus is that in case of estop, the motors will coast to stop
instead of braking. But it is more simple.

Does this make any sense?

In addition to all the good points made by others, I would add one thing:
Ensure that if prime power is lost and later regained, all motion will
stop and
stay stopped until you give permission.

I am pretty sure that if power is lost, EMC will lose contact with the
PPMC controller and will go into some sort of emergency mode.

I have l1 and l2 go through fuses and will make sure that ppmc runs
from both legs of incoming power, not just form one leg.

I would also go through your design and ask the question for each and
every
component: what happens if this fails (stuck on, stuck off, or stuck
open)? I
particularly liked the part about busted encoders breaking machines as
the
servos manfully tried to achieve the unachievable.

I agree totally.

i

You can separate the power to keep power on the controls and encoders, but
kill power to the drives and things that cause motion and can cause injury
to people or equipment. As long as you keep the controls and encoders
powered up, you will keep the positions and shouldn't have to re-home,
unless there is an error. If there is an error in the encoder feedback
circuits it would be difficult to tell if you lost position information
because you had to hit an e-stop. I try to give power to controls and
feedback or input circuitry but kill power to outputs, motors, valves,
contactors, etc. If you had a robotic airplane, if things went wrong, would
you be better off to turn the robot off (or turn the flight data recorder
off) or leave it on so you can later see what went wrong. For the morons
that made up the "Kill all power" rules, does an aircraft kill power to the
flight data recorder, ie the black box? If not, why not, and why should
power be killed to a machines recorder (controls) if it is only recording
data, ie inputs, no outputs? Or to put it another way, I agree with "hands
off" but I disagree with brain off.

RogerN