Hello, all,

We have a Bridgeport/Romi EzPath lathe at work that has a "rumble"
in the Z axis servo. I tweaked some pots on the servo amp and
got it to quiet down so that the machinist is real happy with it,
but I think it could be better. First, I have no idea what those
pots do, as the labels are beyond cryptic. There are 3 pots there,
VC, BL and CC. I'm guessing that maybe VC is velocity loop
compensation, and CC is current loop compensation. This machine
has the SEM motors typical on the Bridgeport machines, and drives
the leadscrew by a coarse toothed belt. I'm wondering if the belt
is wearing or needs the tension adjusted?

Anyone have a servo adjustment procedure for these? (It has the
servo amps that are roughly 4" square boards mounted on a bent
piece of metal, with the power transistors mounted on the bent
part. No sign of a manufacturer or model number on them.

Thanks,

Jon

On Mon, 09 Jan 2006 23:08:51 -0600, Jon Elson
wrote:

Hello, all,

We have a Bridgeport/Romi EzPath lathe at work that has a "rumble"
in the Z axis servo. I tweaked some pots on the servo amp and
got it to quiet down so that the machinist is real happy with it,
but I think it could be better. First, I have no idea what those
pots do, as the labels are beyond cryptic. There are 3 pots there,
VC, BL and CC. I'm guessing that maybe VC is velocity loop
compensation, and CC is current loop compensation. This machine
has the SEM motors typical on the Bridgeport machines, and drives
the leadscrew by a coarse toothed belt. I'm wondering if the belt
is wearing or needs the tension adjusted?

Anyone have a servo adjustment procedure for these? (It has the
servo amps that are roughly 4" square boards mounted on a bent
piece of metal, with the power transistors mounted on the bent
part. No sign of a manufacturer or model number on them.

Thanks,

Jon
=============
Ancient wisdom says "if it works *DON'T* f*** with it.

Updated version is "the better is the enemy of the good."

Uncle George

On Mon, 09 Jan 2006 23:39:09 -0600, F. George McDuffee
wrote:

On Mon, 09 Jan 2006 23:08:51 -0600, Jon Elson
wrote:

Hello, all,

We have a Bridgeport/Romi EzPath lathe at work that has a "rumble"
in the Z axis servo. I tweaked some pots on the servo amp and
got it to quiet down so that the machinist is real happy with it,
but I think it could be better. First, I have no idea what those
pots do, as the labels are beyond cryptic. There are 3 pots there,
VC, BL and CC. I'm guessing that maybe VC is velocity loop
compensation, and CC is current loop compensation. This machine
has the SEM motors typical on the Bridgeport machines, and drives
the leadscrew by a coarse toothed belt. I'm wondering if the belt
is wearing or needs the tension adjusted?

Anyone have a servo adjustment procedure for these? (It has the
servo amps that are roughly 4" square boards mounted on a bent
piece of metal, with the power transistors mounted on the bent
part. No sign of a manufacturer or model number on them.

Thanks,

Jon
=============
Ancient wisdom says "if it works *DON'T* f*** with it.

Updated version is "the better is the enemy of the good."

Uncle George

Indeed.

Im a machine tool tech by trade. And I make money on machines that had
someone with a screwdriver and far too much time on their hands.

Unless you know Exactly what you are doing...as George said so
eloquently..dont **** with it. If you got it running without a rumble.
(probably loop gain)...count your blessings and dont go for the gold.

Though..I could sure use the work.

Gunner

The aim of untold millions is to be free to do exactly as they choose
and for someone else to pay when things go wrong.

In the past few decades, a peculiar and distinctive psychology
has emerged in England. Gone are the civility, sturdy independence,
and admirable stoicism that carried the English through the war years
.. It has been replaced by a constant whine of excuses, complaints,
and special pleading. The collapse of the British character has been
as swift and complete as the collapse of British power.

Theodore Dalrymple,

On an old Acroloc, we had a rumble in "Y". Solved it by cleaning the
tachometer brushes. They were at the rear of the drive motor. Ten years ago.
Memory fades...


Beege

"Jon Elson" wrote in message
...
Hello, all,

We have a Bridgeport/Romi EzPath lathe at work that has a "rumble"
in the Z axis servo. I tweaked some pots on the servo amp and
got it to quiet down so that the machinist is real happy with it,
but I think it could be better. First, I have no idea what those
pots do, as the labels are beyond cryptic. There are 3 pots there,
VC, BL and CC. I'm guessing that maybe VC is velocity loop compensation,
and CC is current loop compensation. This machine
has the SEM motors typical on the Bridgeport machines, and drives
the leadscrew by a coarse toothed belt. I'm wondering if the belt
is wearing or needs the tension adjusted?

Anyone have a servo adjustment procedure for these? (It has the
servo amps that are roughly 4" square boards mounted on a bent
piece of metal, with the power transistors mounted on the bent
part. No sign of a manufacturer or model number on them.

Thanks,

Jon

Beege wrote:

On an old Acroloc, we had a rumble in "Y". Solved it by cleaning the
tachometer brushes. They were at the rear of the drive motor. Ten years ago.
Memory fades...


Well, I've never been inside an SEM motor, so I don't know what sort of
tach brushes they use in there. I'm pretty sure it is a traditional DC
brush
tach. The silver wire brushes usually don't need any attention until the
completely wear in two, and then cleaning won't be much use. Cleaning
them before that point would require nothing harder than a stream of
alcohol, as the wires are hair thin.

This one definitely sounds like a servo loop problem, and the Bridgeport
guy has been out several times at $500 a pop to do the same thing.

Jon

Gunner wrote:

On Mon, 09 Jan 2006 23:08:51 -0600, Jon Elson
wrote:



Indeed.

Im a machine tool tech by trade. And I make money on machines that had
someone with a screwdriver and far too much time on their hands.

Unless you know Exactly what you are doing...as George said so
eloquently..dont **** with it. If you got it running without a rumble.
(probably loop gain)...count your blessings and dont go for the gold.


Well, since I designed and built my own PWM velocity servo amps, I do have
some familiarity with the conventional velocity servo. (My amps have NINE
adjustable pots on them, which makes them a bit of a nightmare. Three
sounds a lot better.) We definitely feel it is better, and he will
probably not
be bothered by surface finish issues until the damn vibration comes back
in a few months. I was hoping to get some experience from other users of
the same machine, as it seems to be a fairly popular model. If we have
to retension the toothed belt, or even replace it every year, that won't be
a problem. But, I'd like to know if there is a stated procedure for that.
(I don't have a good feel for how much radial load the SEM motors are
comfortable with.) Obviously, if this keeps needing adjusting in the same
direction, we are compensating for SOME change in the system, probably
mechanical. Maybe it is the wearing-in of the Z ballscrew, as the preload
decreases, the friction, and therefore the damping, decreases, and the loop
tends toward less stability.

Though..I could sure use the work.



Well, I think the travel time would be a problem. You're in California,
IIRC.
We're in St. Louis, MO. Also, if you don't know this machine, the manual
information supplied by Bridgeport is a joke. There is a wiring diagram.
That's IT! It was enough for me to figure out which servo amp was the Z
axis, that's all I was able to get from it.

Jon

On Tue, 10 Jan 2006 13:59:32 -0600, Jon Elson
wrote:

If we have
to retension the toothed belt, or even replace it every year, that won't be
a problem. But, I'd like to know if there is a stated procedure for that.
(I don't have a good feel for how much radial load the SEM motors are
comfortable with.) Obviously, if this keeps needing adjusting in the same
direction, we are compensating for SOME change in the system, probably
mechanical.

Some belts stretch with time & service.
--
Cliff

On Tue, 10 Jan 2006 13:59:32 -0600, Jon Elson
wrote:

Bridgeport

Jon,
Wait for invntrr to post again or Email him.
--
Cliff