Fanuc servo vibration noise Z-ax lathe

[richardfp4]

We just got a 1990 Puma 10S lathe with a Fanuc
15 controll. Overal state is good, it has about
9500 cutting hours and guides are fine.

The Motor of the Z-ax is a Fanuc 10S-2000 rpm
(same name as the Puma by coincidense) and it is making
a lot of noise, vibrations in the Z servo make the machine noisy.
Accuracy is fine but when you feel the servo it is really
vibrating unlike the same motor on the X-ax.
There are no error messages and accuracy is good.
I hope someone can give me some ideas about what
to check. I already changed the servo gain from 3000 to
1800 but this didn't make any difference.

Thanks
Richard

[underthetire]

Check the ballscrew thrust bearings. Binding there will cause servo problems. Check run-out on the B/S coupling, if all good pull the motor out and rotate by hand. Should feel smooth with no notchyness at all.

[richardfp4]

Oke thanks for your suggestions
I already checked the spindle bearing, it has no backlash
in Z direction but the ballscrew nut has backlash,
about .04 mm. I have seen machines with 0.1 mm balscrew
backlash with not any vibrations and noise in the servo at all.
But I will check the radial clearance of the spindle bearings
and the other things you suggested.

I also get an error 12 after switching on the fanuc display.
But there is another button that I have to press for about
2 seconds and after that the error 12 is gone and the hydraulic
pump starts.

I know error 12 but this error is not on the spindle drive display.

So could it be an error on the Z-ax servo drive? I cannot see
this message on the servo drive as there is no display on the
servo drive.
Could it be a half broken servo drive or should'nt it work at
all if it is a 12 error? Could a servo drive work if one of the
transistors is broken? I cannot see on what servo drive the
error 12 is as I only have a 2 digit display that shows errors.
On the display of the Fanuc 15TF there is not any alarm message
at all.

Thanks,
Richard

[underthetire]

You are confusing me. You said vibration on Z axis motor, yet you are checking spindle bearings and spindle drive ???

[richardfp4]

Oke I see this is confusing.
It is only about the Z bal screw, I called this spindle.
It is not about the Spindle with the chuck, that is all fine.

[fanucman]

is the x axis motor the same part number... if yes

swap the command and feedback cables to see if its the motor or drive

[richardfp4]

Oke good idea thanks.
I try that next week.

[richardfp4]

I have checked the bearings and couplings with a micrometer
and they seem to be fine. If I am pulling with about 300N
I only see 0.01 mm of deflection, it doesn't look like play.

I found something more. I enabled the setting to load the
default servo parameters. After that the Z-axis didn't work
anymore at all with a certain error message.

After searching I found the wrong motor was adjusted in the
Fanuc 15 settings.
After setting the right motor the Z-axis works again.

After loading the default servoparameters from Rom there are
vibrations when the Z-axis is moving and
before it was only when the Z-ax didn't move. So I guess parameters
definately have a big effect but simply changing the gain didn't
make any difference at all. The parameters that were changed because
of setting the correct motor sure have effect but it still isn't wright

I have many settings like current gain, Velocity gain, feed forward
position gain. I know what they do but I don't know where to start with tuning.
Trial on error could be very timeconsuming.

This is a Fanuc 15A and unlike a fanuc 15B which has waveform diagnosis function
this Fanuc 15A doesn't seem to have this.
So I wonder how I could check response of low level parameters apart
from listening to the vibrations.

If the motor is positioned and in servo loop and I pick the coupling and try to
turn it it starts with making a lot of noise and it vibrates with a high frequency.
You always feel some vibration when trying to displace a servo on power but
the Z-ax is just wrong when comparing to the X-ax.

I see in my parameter manual

For details on digital servo parameters, refer to HAC Servo Unit
Maintenance Manual (B–65005).

Could anyone please help me with this manual? Is it available
in PDF format?

Thanks
Richard

[richardfp4]

A Fanuc specialist fixed the problem.
There was an inertia ratio parameter, in the manual
they said if you don't know the exact value make it zero.
Other Fortune lathes with Fanuc 15 controll also have
this on zero.
The inertia ratio was adjusted to 0 and the current
gain was changed a bit. That made the servo absolutely
quiet again. The coupling seemed the cause in first
instance but after changing the parameters it was
absolutely quiet.