alarm 105 (z servo error to large)

[PilzMachine]

Hi all, I have a VF-4 that has alarm 105 going off all the time when we rapid at 100%. We turned it down to 50% and the problem went away for a few months but this morning it did a slow crash into the part. By a slow crash I mean that the C'bore tool we were using stalled out about.125 deeper than programed but didn't break the tool. (we were spot facing .010 dp) I have no idea if it didn't stop before the R value or if it fed straight thru the z value

Anybody else have this problem of a rapid z axis faulting out?
Thanks,
Joe

[underthetire]

Lost pressure in your counter balance ?

[Wizzard of H]

Check the load shown for the Z motor when at standstill.
If you have a counterbalance for Z, it should be under 20%
If you have a no counterbalance system, it should be under 70%.
But... those usually result in an "overload" alarm.
If the alarm occurs while cutting, make sure you are not asking more than it can do.
If the alarm occurs in a rapid move, maybe Z up, it might still be the counterbalance.

[haastec]

Not sure how old your machine is, but look at the size of the servo amps for X,Y, and Z. If Z axis is the same, (from left to right, X,Y,Z) swap the Z axis drive amp with X or Y and see if the problem moves to that axis.

Good luck!

[PilzMachine]

its a 2004 VF-4
it looks like I should be able to just switch the two plugs on z and y sevo boards rather than physically move the boards

[Brass Monk]

I have having a similar problem with my VF-3. It is a 2003 model. For the past year or so I haven't been able to use 100% rapid in the Z axis without it alarming out with a "Z axis servo error too large". So I have been using the machine with the rapid set to 25% just to get some work done. However, lately the machine will give an uncommanded movement in the Z axis while running a program, not much, just a couple of thou, but enough to gouge the part. Another anomaly occurs with the spindle at the Z home position, the spindle head will move a couple of thou in the Z+ and Z- position. The curious thing though is that even though I can physically see the spindle head "shuddering", the Z axis position readout on the screen does not change. I was lead to believe that the Z position readout on the screen is generated by the encoder on the top of the Z axis drive motor. When this occurs, the Z axis load indication goes from 30% to over 200%. This has happened only a few times but I am at a loss to figure out what is wrong. I have spoken with tech reps from both Haas and my local dealer and they haven't been able to come up with a definitive answer, just guesses. My machine doesn't have a counter balance, just the Z axis servo motor twisting a 40 mm ball screw. Occasionally I can detect a slight "vibration" or noise when I rapid up the Z axis, which lead me to believe that the problem may be in the ball screw or bearings. I checked the oil lines and then ways and screw seem to be getting oil, as there are no visible signs of wear. The Haas rep says that it is very rare for the Z axis motor to have a problem so it seems to have narrowed down to the ball screw. I don't want to change the screw unless I absolutely have to. I was quoted $1750 in parts and probably $1000 in labor.
The one thing that keeps nagging at me is the fact that the Z axis has moved uncommanded without it being displayed on the Z axis position readout on the screen. Kind of makes me think of a computer problem.
I am at a loss as to how I should go about fixing this thing. I wander if anyone else has had a similar problem. Any advice would be appreciated.


I am hoping that someone here on this forum can steer me in the right direction. I would appreciate any advice.

[Wizzard of H]

The most recently described symptom could be several things including the motor. A lot of this depends on what kind of motor.

1) Brush motor systems (before 1997) have not seen this kind of symptom but bad brushes might do it.

2) Brushless systems with Z axis brake might do this if the brake is mistakenly engaged. A broken cable would remove power from the brake and enage it.

3) Brushless system without brake (counterbalance) should not do that unless...

4) Brushless system with an encoder problem might jump to a high load but it usually followed by an encoder alarm. Check cabling and alarm history.

And some clarification: the axis position displays are not the actual readout from the encoder. They are the commanded postion. The difference is the servo error. The average error is always zero but the actual postion can change a small amount in response to forces like cutters.

[PilzMachine]

Just talked to a service tech who immediately told me to replace the motor.
Nothing more to say about it. He says that He's replaced so many in the past 5 years he won't even look at anything else.

Now I have to say he's kind of head strong (knowing him from the past) and maybe not looking at the total machine.

I'm talking to HFO in an hour or so and if they concur I'll order the motor and see if my problems go away.

I'll keep updating this post till it gets resolved

[PilzMachine]

Swapped the X and Z axis boards just now and the problem followed the board