[padobranac]

Machine - V.M.C. - KIA KV25
Control - Fanuc 0M

The problem came out suddenly, without any change on machine/control.

When machine starts to rigid tap, it immediately starts buzzing very loud.
It makes few threads (aprox. 3 out of 10 on one workpiece), and than feed and spindle stop (at R level i assume), but it is still buzzing. When I push Reset button, buzzing stops.

Buzzing is heard also when spindle doesn't rotate, between holes.
Buzzing can be described as on very bad bearings.
Buzzing is not heard when rotating with M3 at any speed.

Spindle motor is connected to spindle directly, with hard connection.
Rigid tapping, with same nc code (M29+G84) worked well before.

Now if I replace M29 with M3, it works OK (without buzzing), but it is not rigid (synchronised) tapping now.

[padobranac]

My coworker says that it used to happen also in past,
but just occasionally, with less intensity,
and much silently.
And it newer stopped before.

[underthetire]

Sounds like a built in sensor needs adjustment, thats if it uses one.

[ad64075]

What does your spindle load meter read when you head the buzzing sound?

[sinha_nsit]

Try lower rpm.

[padobranac]

Sounds like a built in sensor needs adjustment, thats if it uses one.

That would be an sensor for reference of spindle?

Where this sensor should be, inside of the motor?

Manual adjustment (moving) or with parameters?

What does your spindle load meter read when you head the buzzing sound?

There is no spindle load meter on operator panel.
Maybe this could be seen in some parameter/diagnostic? 0M, I doubt.

Try lower rpm.

Tried, again same thing.
I tried lower and higher RPM,and also changed feed.
Buzzing is all the time the same.

[underthetire]

If it's the built in sensor, it should be on top of the spindle. It will have a fine pitch toothed wheel with a small pickup sensor. When those start to fail, or the adjustment gap is set wrong, the motor will buzz during rigid tap and orientation. Then you will start to get sensor alarms on the drive.

[padobranac]

If it's the built in sensor, it should be on top of the spindle. It will have a fine pitch toothed wheel with a small pickup sensor. When those start to fail, or the adjustment gap is set wrong, the motor will buzz during rigid tap and orientation. Then you will start to get sensor alarms on the drive.

Thank you for your answer, BUT:
- I don't get any alarms, since now (may be in the future)
- during the orientation (M19), there is no buzzing heard

"the adjustment gap is set wrong"
That is in some parameter?

[pmrairokn]

Padobranac,

Have you found a solution to your problem? I have the same problem. Can you share?

Thanks

[padobranac]

I haven't solved my problem because I didn't had any needs to make taping for last few months. Now I need this function so I tried something...

I tried to adjust gap between sensor and toothed wheel.
I reduced it, before it was from 0.10 to 0.15 mm and now it is from 0.05 to 0.07 mm.
Nothing changed. I think it should not be less than that.
Maybe it should be more, or less?

Few notes:

- I checked connectors and wires, everything seems OK.

- Buzzing happens only in rigid tapping mode (M29 Sxxx + G84),
M3/M4 works just fine

- this start to happen suddenly, there were no problems with rigid tapping before some time (using the same program)

- There are no alarms at all.

- Mostly it does perform program (tapping)-ofcourse with buzzing,
only rarely it stops in the middle of cycle and buzzing continues,
and I have to push restart, but no alarms come out

- M19 spindle orientation works fine.

- Buzzing is heard also when spindle is stopped (at R level)

- Buzzing is worse with lower RPMs (below 1500).

- When I try with 2000 RPM or more there is no buzzing while tapping,
just when starting and stopping of spindle (at R and at bottom).

- when machine starts rigid tapping cycle and approaching R level,
spindle is stopped, buzzing is present, and it vibrates (making small movements left/right, I feel it when I put finger on the spindle)

- some time ago we have changed bearings of spindle


PULSE GENERATOR
A20B-9000-0500

AC SPINDLE MOTOR
MODEL 2S, 8000 RPM
A06B-0752-B190

SPINDLE PCB
A16B-2201-0440/05B


What to do next,
just buy new pulse coder,
or there is any way to check if it is bad?

Thanks in advance for any help!

[underthetire]

.004-.006" would be normal. Don't have a calculator here to convert. Sorry.

[padobranac]

.004-.006" would be normal. Don't have a calculator here to convert. Sorry.

That is 0.10 - 0.15 mm, exactly as it was before my adjustment/reduction.

During this night I got another idea:
Maybe encoder of Z axis is bad - giving non-constant position,
and spindle tries to follow the Z axis....???

[pmrairokn]

Here is a youtube video of our machine with the same problem. I have heard it can be the servo drive giving a bad signal to the spindle servo, or a bad sensor giving a bad signal to the servo drive. The frequency of the sound doesn't change with RPM. It sounds like gear-knocking, although this is direct drive. I suspect the spindle is constantly being corrected and that is the sound of it being corrected (speed up/slowing down of spindle).

[ame=http://www.youtube.com/watch?v=URn-JKiicrw]Fanuc Robodrill[/ame]

[padobranac]

No ideas fot solving this problem? :idea:

[sansgp]

I sense, this problem bit tricky.. In a closed loop system, everything is a suspect, until you find out the culprit. We have to eliminate one by one. Let me try with my 2c...

A rigid tapping cycle synchronizes the machine spindle rotation and feed (usually Z axis) to match a specific thread pitch.

When the rigid tap cycle is commanded, the control treats the Spindle like a rotary 4th axis, same way it treats the X & Y axes. The method used is called electronic gearing, where the Z axis is electronically geared off the spindle encoder.

Rigid tapping requires an encoder (pulse generator) fitted to the spindle motor and an encoder on the spindle shaft. This allows precise position control of the spindle motor. Same applies to M19 also.

Check and confirm, the actual speed of the spindle is displayed on screen. Eg: If you command spindle at 1000 rpm, the display should show anywhere between 999 - 1001 or some values like that.

With the above facts, we may analyse that the sound on spindle could possibly from the synchronising effect with Z axis. ( I would assume so, because M19 or M03 / M04 commands seems smooth, no vibration sound)

Check if there is any vibration with the Z axis when it is moving slowly. ( you can feel the vibration by placing a hand on the body of the moving Z axis.).
It is also possible to bypass the Z axis linear scale and use only its encoder for positioning. You can use this option to eliminate the probable causes for vibration.

Check the 'following error' of Z axis and compare that with X and Y axis when they are in motion with a same feed rate. If these values are similar, then good. (you can view their values on the diagnostic page, parameter 801, 802 etc.)

Finally, As you have suspected, sound could be owing to dodgy encoder pulses?

[sansgp]

One more suggestion to add: Check whether the belt between the Spindle and the Motor is loose. Tighten if required. (normally it is a toothed one or a V shaped belt)

[pmrairokn]

Padobranac,

I noticed on my Robodrill that there is significant play at the spindle. On another, newer robodrill that we have, there is physically no play in the spindle. I sense that the problem is with the key mechanism that locks the servo motor to the spindle. It may be a woodruff style key or something else. Mine started making the noise at a lower volume at first, then increasing to current. This would make sense if something were breaking down such as a woodruff key.

Check to see if you have any play in the spindle when a tool is loaded.

[pmrairokn]

Our buzzing was solved by replacing the key linking the spindle to the servo motor. I think it was an 8mm x 7mm key, held in place by a set screw, while resting on another set screw to keep it from falling through.

The motor shaft keyway had some wear as well, so we machined a key to fit the worn keyways.

This solved our problem. Check the play in your spindle first.