6Mb 401 Alarm upon Spindle Start or Accelleration

[Deltic_Engine]

I have an old VMC with a GN/Fanuc 6Mb, circa 1982.
(Yea thats right, in my backyard - I like to tinker).

The 3ph power is being supplied by a new 30hp rotary Converter.

Everything is working great (All 4 axis) except getting
a 401 alarm upon splindle accelleration or decelleration.
It is a 10~15hp servo-driven spindle (More specs avail).

Example:
An M03 S100 Command works OK.
Upping the rpm from there to S200 Works.
In increments of 100rpm things are OK, all the way
up until 900~1100 rpm, where it gives me a 401.

OR if I try to go strait from zero rpm to say, S300,
it will trigger the same 401.

Ingeneral, it seems to trigger the 401 anytime
the spindle motor is accellerated or decellerated
in any brisk (read: 'Usable') fashion.

The controller's 401 diag screen lists all zeros.
There are no alarm lights on the PCBs staying on after the 401.

The only evidence that anything has happened is the
401 alarm screen and that all the Velocity Control boards shut down.

the GN/Fanuc Manual is of little help. It does not really cover
spindle motor controls or the spindle servo drive electronics.

Sound familiar to anyone out there?
Thanks in advance.
Jeff

[Al_The_Man]

I would suspect that the very high spindle accel. current is possibly dropping the artificial phase voltage enough to cause a fault to be sensed in the spindle drive, possibly in the third phase in general and this in turn is being sensed by the other parts of the system also.
I believe there were different spindle drives used on the 6 systems, usually DC spindle with analogue control. AFAIK there is no accel. parameters that can be adjusted as there is in the servo's.
You may have to try adjusting the gain control on the spindle drive, or finding other creative ways to accel. the spindle.
For that size of spindle the accel. current can be very high.
Al.

[Deltic_Engine]

The 30hp Rotary Phase Converter I am using is
putting out 245~255VAC 3-phase.

The input options of my 10hp (DC Servo Spindle) mill
are 220VAC, 230VAC or 380VAC.

I had PG&E check my line voltage. I thought it seemed high.
The 1-phase input measures 123V, 122v, (245V)
as measured by my PG&E guy.
He claims this is "excellent".

Questions:
1: When every 3-Ph appliance in the world seems to
specify 220V~230V, why should PG&E consider
245V as "excellent"?

2: Is 245V~255V from the converter considered high?

3: One seemingly knowledgable web site in Europe claims
that the intentionally higher line voltage ups your utility bill
and that is the main reason why most people's line voltages
are on the high side.
However the PG&E Guy claims just the opposite, that
a higher voltage will lower your bill. So, - Who is right?

4. I have read that one of the 3 legs off a rotary converter
is very suseptable to going under voltage when under load,
so that particular leg should ideally not be serving the
electronics side of a CNC system. Anything to this?

This all relates to a problem I am having:
Even though I am running a 10hp (max) spindle with a
giant 30hp rotary converter, the velocity boards of
the CNC (Fanuc 6MB) will shut down (alarm 401) IF the spindle motor
is accelerated OR decellerated in more than 100rpm increments.
All of the otrher motion control axis works fine/no other errors.

Thanks to all.

[Deltic_Engine]

Update from original Posting:
Although I had already wired the machine with the
correct phase rotation, The rotary phase converter
that converts single to 3-phase has, as most rotary converters do,
a 'Wild Leg', or one leg that can drop in voltage substantially.
I simply shifted the 3 main power input wires over (musical chairs)
so that the wild leg was not feeding the electronics side of the system.

Wala! still same phase rotation, but now I can go strait from
0 rpm to about 3500 rpm without incurring the 401 alarm.

However that solves only 60% of the problem.
Basically, I still need to reduce the spindle startup jolt so that it
does not trip the 401 at all.
This means I need to slow the accelleration and decelleration rate
of the spindle motor.

The spindle seems very abrupt indeed.
On a CNC Mill, there is no reason to suddenly accel/decel a servo spindle
motor up and down in rpm abruptly. There is plenty of time for a spindle to
accel/decell before or after any tool change or operation.
On this particular mill there are at least a couple full seconds available
for that purpose in any scenario that I can imagine.

So, on a GN/Fanuc 6Mb, HOW do I change the accel/decel map for the spindle?
I have looked in the book at all the parameters, but the only
parameter I find that might do this is parameter 140, or 'SANGN',
which is the spindle gain adjustment.

If I suceed in changing the accel/decell map, There is one more
parameter I might have to adjust to compensate for a longer
accel/decel map: 062 'SCTTIM', the delay timer between the speed change
command given and the moment the speed is to be checked/verified by
the controller.

Am I missing any other ways to adjust accel/decel on the spindle?
Beaing a SERVO spindle I would expect there to be a dedicated adjustment
for this, just as there is on all the other motion control axis.

Thanks

[Al_The_Man]

Originally Posted by Deltic_Engine Beaing a SERVO spindle I would expect there to be a dedicated adjustment for this, just as there is on all the other motion control axis. Thanks

What do you mean by 'Servo Spindle' ASFAIK the 6 will not control the spindle as a C axis, you can however have threading and CSF if a lathe or spindle position for tool change, but this is not Servo action.
Al.

[Deltic_Engine]

The spindle motor is a Servo-type. Says so on the label.
"Porter Peerless 10hp DC Servomotor" and does have a
wired-up encoder.
So it sounds like they are not driving it as a servo, but simply
taking advantage of the encoder on it for feedback?

That would explain its' jolting from 0~3500rpm in an instant.
And apparent lack of a velocity control board for it.

If so, maybe I can just try adding some big capaciters or something
else to act as a line buffer????

[Al_The_Man]

What spindle amplifier is on it? Most have pots on the board that can be adjusted, more sophisticated types have a keypad/parameter setting on the spindle drive.
Al.

[Deltic_Engine]

OK, The Spindle servo drive board is an old Sweo 0028-033

The Sweo board does have independent pots for Accel/Decel.
Both pots were cranked to the max.
When I turned them down full soft, the problem cleared up
(temporarily) I was able to go zero to 6,000rpm and back
without the fault (yippie!).

However the 'slowest' accelleration the adjustment provides
still results in only about 1/2 of a second to go from
zero to 6,000 rpm. That is to say, not all that much of
a difference from what it was doing before, but enough to
fix the problem (until things warmed up, that is):

This first test was done in the morning (60 degF).
Whereas by noontime I was getting the fault again.
By late afternoon it was about as bad as it ever was
(zero to a measely 200 rpm was producing the 401 alarm again).

And by late afternoon it would not even go up to 4,000rpm
at all, even in 100 rpm increments.

Interestingly, none of the Sweo board's fault lights come on.
It seems the fanuc boards are more sensitive than it is;
Although their lights simply all go out (no fault lights).

I also tried adjusting the Sweo's 'gain' pot, but that had no effect on
the problem, other than to cause jerkiness when too far away
from its original setting.

So back to square one. Perhaps it is something still out of spec,
but not sure why the problem seems so temp sensitive.
Input voltages from the RPC are pretty consistant through the day.

I have searched for an 'accell/decel' add-on card like
Sabina offers for it's DC servo drives:
http://j.b5z.net/i/u/2129619/i/optioncards/1410.pdf
It 'conditions' the digital speed input signal from the machine's
main controller into an adjustable digital ramp-up for the
DC servo driver board.

I have inquired with them as to if it could also work with
the old Sweo board. It seems possible.

However perhaps more likely I would upgrade the driver board
to a newer design that allows more accel/decel adjustment?

I any case, I suspect the Sweo board more than anything so far.

[Deltic_Engine]

OK, it seems the Accel/Decell pots on the Sweo Spindle Board were 'disabled'
So adjusting them was ineffective.

But there is also a pot that is labeled 'Current Limit' that can be turned down to limit
the total amps drawn by the spindle motor (upon accel/Decel and chip cutting).

I had seen the pot before, but presumed it was just an alarm setpoint instead.

Sure enough, the pot was cranked to full amps. I turned it down quite a bit
and although the accel/decel is still pretty quick, I can now go from
0~6,000 rpm and back without any more 401 alarms.

Its a 10hp spindle, so I will still have plenty of power to hog some chips out
of the small Aluminum & Ren-Shape projects I have.

Thanks to all!!