Problem- "over current/ field loss" on spindle acceleration or deceleration

[rolandkra]

Hello, I've copied this over to this forum from 5T and hope it gets a little more exposure.
I've moved my Nakamura lathe with Fanuc 5T controller to another property and let it sit for a year. I'm running it via a slightly small phase converter

It boots up properly but the spindle drive behaves badly

Following are the symptoms;

When I use the control panel to start the spindle, and the speed knob is in the lowest position, the motor turns on and makes a mild growling sound.

If I then turn the spindle speed knob quickly, the circuit trips and I get an alarm on the spindle drive board "over current/ field loss" after which I turn the power supply off then on again and re-boot the machine.

After starting the spindle again, when I turn the knob slowly to increase the speed, the motor follows but is a little rough sounding and it doesn't reach as high a speed as it used to nor accelerates as fast as it used to, ie: the motor doesn't keep up with the knob position. If the spindle is at 2000 RPM and I turn the knob to <full> (3000RPM) the spindle speed will increase over 20 seconds to only 2500 RPM . It sounds OK at that point.

If I press the spindle stop button at that point, or at any time when the spindle speed is above ~300 RPM, the circuit shuts down and I get the same alarm.

If the spindle is at any higher speed and I turn the knob quickly to reduce the speed, the circuit shuts down and I get the same alarm

If the spindle is running at high speed and I SLOWLY turn the knob to reduce the speed to around 300 RPM and then press the spindle stop button, the spindle stops as it should.

Would anyone be able to guide me on this problem?
How do I check phase sequencing /rotation?
regards, Roland

[cncdiag]

Swap any 2 phases of the incoming 3 phase power to the machine

[rolandkra]

Thanks cncdiag, I've done that but there's a drawing that has a warning attached stating that the phase sequence must be correct and I don't know how to check that.

If I'm correct, I can wire up in the following 6 ways. In each of the pairs of ways, one will be correct rotation and one will be reverse.

1) (line 1 to A), (2 to B), (3 to C)

2) (line 1 to A), (2 to C), (3 to B)
---------------------------------
3) (line 1 to B), (2 to A), (3 to C)

4) (line 1 to B), (2 to C), (3 to A)
---------------------------------
5) (line 1 to C), (2 to A), (3 to B)

6) (line 1 to C), (2 to B), (3 to A)

I've tried all six and think that I caused another problem. I'm running this with a rotary phase converter for which the manual states that if there is a control transformer attached, that it should go across two specific phases and that's going to take a bit of thinking about. I was hoping for an easier solution but this is the bed I've made.

regards, Roland

[gandp]

I have the same problem with accel and decel speeds on my fanuc 6t lathe as you are experiencing. Almost 4 years ago I posted my problem but got no where. No one can solve this. I had the SCR's replaced in the drive and that was a waste of money. Let me guess.........it's a Fuji Drive? And your lathe has no gearbox? I also have a 5t machine but it runs good. It's an early 5t. Says 1976 on the serial plate of the machine. I have three fanuc 6's in the shop. The 2 that don't run well on a RPC are the early 6's and the one that runs good is a 1984 machine and this machine has a gear box and the drive is something other than Fuji. My hunch, is that these early '80s Fuji drives don't like manufactured 3-phase current. Was your machine on a RPC before? I can use my machine but programming the speeds is a pain in the ass. It's better if I install a collet nose and take off the heavy chuck but I still have to watch how I program the spindle speeds. I get the "growling" noise on startup if I command a speed higher than 400 rpms. Once I get to that I then go to 800 and after that anywhere to 3000. Coming down I go to 1500, 900, 450, 200, dwell 1.5 seconds then M05. Sounds stupid but it works for me. I leave the collet chuck on it now. This machine ran flawlessly on utiliy 3-phase so its quite obvious it's the rpc or my power source. One fellow stated getting your transformer (on the pole) closer to your shop may help as he claimed a voltage drop from the pole could do this. I don't know. Sorry to take up any of your valuable time but I'll be watching your post. Please e-mail me back if you discover and/or solve this problem. Also, my tech who services my machines claimed we can take out these old drives and replace them with a VFD.

[hrh]

Most of the Nakamuras have FANUC DC Spindle servo units.

Overcurrent / Field -loss is a very typical but troublesome problem.
Usually caused by poor connections between the spindle control PCB and the drive unit.
Improper firing signals: Repair PCB or replace with fully functional PCB. Expert repair required!!!
Tacho-generator brushes are badly worn or the commutator needs to be undercut and cleaned.
Poor insulation of the spindle motor due to the carbon dust buildup.
Replace or "service" the contactor inside drive unit (poor contact causing single phase condition)

Blown input fuses (sometimes the flag fuses don't blow out because the PCB fuse circuit is damaged and therefore you won't know if the fuses are blown unless they are measured)
Faulty current detector.
Check phase sequence and waveform with an oscilloscope...

The fact is, please contact a properly experienced person who KNOWS the quirks of these drives and how to properly adjust the settings. The youngsters have NO IDEA.

Careful with VSD units with open loop systems. Response for speed variation is 10x slower than closed loop systems and you will end up with variations on threading jobs..

[rolandkra]

Hello gandp, it does sound like the same problem and your solution of using speed steps in the program is one that I thought about but I'm glad to hear that it works. I'll try your pause before turning off as well. Your other helpful fix of using a much lighter spindle nose sounds good, I hadn't thought about the mass. My lathe is different in that it has a Fanuc controller with Fanuc drives and a 3 speed gear box which can only be changed while stationary, but on that thought I could use a lower gear for nearly all of my work as I rarely go over 2000 RPM and that would decrease the load on acceleration.
I'd be wary of the VFD thing for threading.
Somehow I think something has fallen off or been upset in the move but at least with your method I can work it until I fix it.

I've just seen your other post about drive longevity and it sounds like a good idea for those of us in low production environments. Perhaps someone here can suggest a way of varying the acceleration ramp on the board rather than programming all those "steps"
regards, Roland

[rolandkra]

Thanks hrh, I am hoping that poor connections are the source of the problem and I'll try what you suggest. My Nakamura does have a Fanuc DC spindle servo unit.

I understand your comment about the "expert repair" but have found that, at least around on the east coast of Australia, there are very few people who still know these machines.

[QUOTE]
Improper firing signals: Repair PCB or replace with fully functional PCB. Expert repair required!!!
Tacho-generator brushes are badly worn or the commutator needs to be undercut and cleaned.
Poor insulation of the spindle motor due to the carbon dust buildup.
Replace or "service" the contactor inside drive unit (poor contact causing single phase condition)

Blown input fuses (sometimes the flag fuses don't blow out because the PCB fuse circuit is damaged and therefore you won't know if the fuses are blown unless they are measured)
Faulty current detector.
Check phase sequence and waveform with an oscilloscope...
[QUOTE]

[cncserveng]

If it is a DC drive, you should check the brushes and commutator. The comm should be clean without a deep groove. The brushes should be at least 12 - 16mm long and not chipped.

you may have a field weakening or field motor winding problem, check the wiring and field coil is a 100 or so Ohms and not shorted to ground..

[salmve]

Hello rolandkra and others.

Happy New Year!

Have you read this thread?
http://www.cnczone.com/forums/fanuc/...dle_drive.html

I havent got solution to the problem but with warming/freezing method lathe has worked over two years now.

Just now i have 11kw 3phase motor and VFD waiting for assembly. Combination is wired and new motor is running beside the old motor.

Vekku

[rolandkra]

Thanks Vekku, happy New Year to you and the others too.
I've just read the post that you suggested, very promising.

Will check out my machine from that point of view

How accurate is your VFD and motor for threading?
regards, Roland

[Indmach]

Hi Guys
I have Daewoo puma 10 cnc lathe with fanuc 6t control I have figure out why there is a field loss on these dc drives.
1st check the semi conductor fuses
2nd check all the fuses on the drive the small black if there is a white mark in the small hole than take a fuse and open it than use small thin wire an use solder gun and put the little and fix it rather than buy a new one.
3rd when turn the machine on in the moring let the spindle run at slowest RPM for 15 to 30 minutes by doing this you are warming the drive and spindle drive.
4th check if the machine is level its not shaking when changing speed.
5th clean the comentetar of Dc spindle drive motor.
6th not to use over G76 S400 and not to use more than 1500 RPM
if use 2500 rpm make sure your g76 is less than 250
That's what I have found and it is working fine for me I don't do production but I use it as a manual lathe by making 12 prgms and calling them sub its faster than manual lathe Since my machine is big I use it for big parts over 6" to 12"
Good luck
Ron @ Industrial Machining Inc
in Windsor Ontario Canada

[Indmach]

sorry G96 not G76