Fanuc Servo Alarm

[herbmarkovit]

I just purchased a 1984 Kitamura MyCenter with a Fanuc 3m control. I have no documentation for this machine. When the machine powers up I get:
SERVO ALARM: 01 (overload)
I am using a Rotary Phase Converter
AC Input
L1-L3 202VAC
L1-L2 227VAC
L2-L3 209VAC
Relays On
EMS
2DLS
CR1

I would appreciate any suggestions you may have.

[Al_The_Man]

Check wether the thermal relay needs re-setting for that axis. It is often caused by motor overload when cutting, what size motors do you have as the motor current can be checked with a clamp-on meter.
Al.

[herbmarkovit]

I received a reply from Kevin:

Look at the servo drives, just below the circuit board you will see a red reset button. push this on all your drives.

My Answer to Kevin;
Thank you for the advice. The Z Axis needed to be reset. After resetting Z, I was able to move all axis (X,Y,&Z). After a couple of minutes the Z axis went out again. The guy that sold me the mill said that the Z axis would hunt once in a while. The machine has sat Idle in a warehouse for over 2 years. I did not get a chance to try jog. I would guess that I may have a bad DC Z axis drive servo. There were no red led's on the Z axis drive board (A20B-0009-0320/10d).

How can I turn the spindle on. The push buttons don't seem to operate. These are 5 buttons on the lower right of the control panel. The labeling on 1 & 2 (left) is worn off. The next 3 are: ccw-stop-cw.

[Dan Fritz]

The overload sensor will trip out on your Z servo if the motor draws too much current for too long a period of time. This overload sensor can trip if the motor is working too hard to either move the Z axis or hold it in position.

Many vertical machines have counter-balance mechanisms on the Z axis that takes the static load off the motor. If the counter-balance is working properly, the motor shouldn't have to work very hard just to support the weight of the Z axis while the machine is stationery. The motor should work the hardest when the axis is acellerating or decellerating, or when you're taking a heavy cut. Z servos are most likely to trip while pushing a large diameter drill into tough materials, because the thrust loads for a drill are quite high compared to other types of tools.

Check to see if you have a mechanical (counterweight with chain & sprocket) or possibly an air cylinder as a Z axis counter-ballance mechanism. I've seen broken or disconnected chains on mechanical counterballances, and it's possible that an air cylinder counterballance isn't getting enough pressure.

Another thing to watch for is lubrication. If the machine's been sitting for a while, be sure that the Z ways are getting some lube, and that the Z ballscrew is also well lubricated. It may seem that way lube wouldn't matter when the machine is not moving, but it does. The servo must "hunt" to keep the axis in position, and an unlubricated slide or ballscrew can place a large current load on the motor.

[herbmarkovit]

Thank You Dan. There is no Chain or counter balance that I can see. There is a Hydraulic reservoir, but I am not sure what is hydraulic? Not having any documentation makes this a bigger problem then it should be.

I may have a lube problem. I applied transmission oil to the vertical ways & Ball screw & manually ran the Z axis up & down for about 2 or 3 minutes before the servo alarmed again. I think I will try to blow out the lube lines & then try to fill them.

I have a clamp on ammeter but dont know what wire to check. The servo is rated for 12 amps, but dont see any wires big enough for 12 amps. The 12 amps must be a peak current available for a very short period of time.

[Al_The_Man]

A 12amp motor should be a 10M type DC, this is continuous rated current, the best type of clamp-on is the AC/DC type some come with a plug to attach to a meter on the Mv range (Fluke).
If the meter does not have a capture peak reading and it is momentary, it may be hard to catch. There are two DC leads that go to the motor also the AC three phase into the drive can be measured, they are probabally scr drives on that unit.
But if the current is hard to obtain, you may want to disconnect the motor from the load and run it free, another thing that is sometimes not regularly checked untill there is a problem, is the brushes on the motors, replace them if worn, it is cheap insurance.
Brushess can be obtained from Helwig Carbon for these motors.
On the lube problem, you cannot often blow the lines out as they have metering ports at each termination point, these should be replaced as they are hard to clean.
Al.

[Al_The_Man]

Originally Posted by herbmarkovit How can I turn the spindle on. The push buttons don't seem to operate. These are 5 buttons on the lower right of the control panel. The labeling on 1 & 2 (left) is worn off. The next 3 are: ccw-stop-cw.

Can you issue a S**** M3 (spindle clock-wise) in MDI mode?
Also to operate the spindle by the buttons, it depends how the OEM set it up, you may have to be in jog or a manual mode if fitted.
Al.

[herbmarkovit]

Thank you Al, I wrote a little program to send all axis to 0 & to turn on the spindle. Everything appears to work except for the Z overload alarm which occurs after a few minutes. It looks like disconnecting the DC servo (10M) from the drive could be a good sized job from the looks of the coupleing. The incoder & key under the yellow cap looks ok. I think my problem is either high current from a bad servo motor or high current from excessive friction due to lack of lubrication. I do have a clamp on ammeter to check the current. I will let you know.

[Dan Fritz]

One thing I forgot to mention before was that many Z axis motors have electric brakes inside them. The brake is activated by REMOVING the power from the brake coil, which is usually 100 volts AC. When you turn the control on and the servo comes up ready, the brake is supposed to get power and release so the motor can turn easily. If the brake is stuck, or if it's not getting power, you'll have a motor that's fighting it's own brake. That'll trip the overloads pretty fast.

Also, if you have an ocilloscope, you can see the current feedback on CH11 on the Z axis servo board. These older Fanuc servos were 3-phase full-wave SCR drives, and they work pretty well when they're tuned up.

If you look at CH11 on the servo board with a scope, you will see a series of "bumps" that match up with the 3-phase current. You'll see 3 phases of 60-cycle bumps, which means 180 bumps per second on the scope. These bumps get taller and shorter depending on how much current is going to the motor. A flat line at 0 volts means no current, and bumps that range up to +10 or -10 volts means full current forward (or reverse). At jog speeds, these bumps shouldn't be much more than one volt either way. You will be able to compare the current feedback on the Z axis with the X and Y axes to see if things are normal. A scope display that shows two bumps and a "gap" indicates a blown fuse, a bad SCR, or a missing phase. I don't think this is your problem, because you would probably be blowing the other fuses rather than tripping the overload sensor.

The overload sensor is monitoring the DC current to the motor, not the AC current into the SCRs. A shorted motor could also do this, so also look for things like coolent goo in the motor, carbon brush dust from worn-out brushes, etc.

Here's a simple test you can perform (if you're careful!). Start with the power off, and:

1) Put a set of wooden blocks under the Z axis to keep it from dropping very far (leave them loose, but don't let things move down more than an 1/8 inch or so).

2) On the back of the Z servo amplifier, you will find some fuses. Pull them all out. Do not remove the X or Y fuses, just the Z fuses. If you have small motor (0 or 5 size) you will only have 3 black plastic 15A indicator fuses. If you have a larger motor (10, 20, or 30 size) you will have 3 cartridge fuses and 3 1.3A indicator fuses in parallel. In that case, remove all 6 fuses.

3) Turn the CNC on and observe the Z axis. If it slowly drifts downward, the ballscrew is turning easily (that's good). If it drifts a bit too far, you'll get an "Excess error" alarm in the Z axis. This would be normal, but you'll have to turn the CNC off/on again to continue with the test. If the Z ballscrew still can't be rotated by hand, you've either got a stuck brake, an unlubricated ballscrew, or a set of dry ways. Your mission is to find out which one is causing the friction.

The fact that the Overload sensor keeps tripping out indicates that the Z axis is just too hard to move. I'll bet there's a mechanical or lube problem that's making that Z motor work too hard.

[herbmarkovit]

Hi Guys THANK YOU for all your advice.

I found the Line from the auto luber to the manifold on the Z axis disconnected. The ferrule was bad. I replaced the ferrule & am now trying to lube the machine.

I can move the Z axis up & down for a few minutes before it starts "moaning" (sounds like the hydraulic pump). I wish I knew what the hydraulics are for.

We have a hurricane coming here tomorrow morning & we may leave. I will work on the mill after the hurricane passes.

[herbmarkovit]

The saga continues. I am still working on the problem. It is not a lubrication or mechanical problem. I removed the 10M DC Servo Motor After I placed a Block of wood under the spindle (very good idea-without this the spindle would have crashed). The brake has 105 VDC as soon as "power on" is applied but the servo still alarms when I try to operate the Z axis. I could not find any fuses on the servo drive card (circuit breakers behind PCB). I am in the process of removing the brake disc from the servo motor. I will try to run it without the brake later in the week. The CNC does not have a hydraulic system. The tank of fluid is for the Spindle Bearing Chiller.

[Al_The_Man]

If you have the motor off and want to do limited testing on the bench to check for noisey operation and brake drag is to rig up a dc voltage to operate the brake by using a 120vac outlet with a 5amp rectifier in one lead and feed it to the two wires of the brake, Check the polarity of the brake voltage when on the machine and hook up with the same polarity just in case they have a reverse diode fitted on the motor.
Then see if the shaft turns free by hand. If every thing sounds and feels OK, hook up a car battery to the DC motor leads and it should run at around 50~100 rpm, reverse the leads for the opposite direction test. Obviously take care to ensure the 120v from the socket is well taped up or insulated. Rough running or excess current can usually be detected.
Al.