Okuma LB15 100-4 Diff Alarm
I found 1 post from 2010 in search but did not resolve my issue. Anyway..
This machine is a mid 80's LB15 OSP5000-G control.
Problem: Z axis alarm out with 100-4 diff error. (Usually when cold. Machine does better at running temp)
When I move the machine manually (pulse wheel) I can feel the axis motion stop. When the axis stops the Z motor is showing a 120% load. On the "Extend Data" servo screen I can verify the DIFF error... Of course if I keep going it will eventually alarm out due to the tracking difference.
What I have done so far:
1. Checked lubrication
2. Checked for mechanical issues
3. Checked cabling
4. swapped the motor
5. swapped the SVC board
6. swapped the Drive
7. swapped the drive power supply
(luckly we had an old machine we parted out. However the parts ARE used.)
Right now I'm still getting the same issues. No better/No Worse. Any other ideas?
Re: Okuma LB15 100-4 Diff Alarm
I have an identical problem with one '85 Okuma LB15. When RAPA stops counting, I have two situations:
1. Motor load over 200%, even without belt, until DIFF is too big and I got 100-4 Diff Alarm
2. Motor load over 200%, even without belt, but the motor at one point jumps (DIFF under 5mm), and I got a Zaxis servodrive error, and I have to turn off the lathe to get out of this error. So far, after this jumps, I had to replace two times a power transistor in the drive.
Until now, I have done all geeserteg's steps, and for the moment I'm scratching my head.
Any ideas?
Re: Okuma LB15 100-4 Diff Alarm
Quote:
Motor load over 200%, even without belt
why did you took the belt away?
Quote:
I had to replace two times a power transistor in the drive
are you sure, that mechanically the axis moves smoothly with no obstacles?check all mechanical reasons of the stop and jump. What about tapered gibs?
Re: Okuma LB15 100-4 Diff Alarm
Algirdas,
Thank you.
I think I found the problem. The Z-axis motor is loaded approx. 55% at 6m/min. Above this velocity, Diff Alarm occurs.
Tracking back all problems, it sounds something like this:
1. on February, we changed the TAC bearings on Zaxis ballscrew.
2. on July, a small crash happened. Realigned the turret and replaced the lock washer on turret's axle.
3. on September, one power transistor on BDU drive died, after several Z-axis servoamp errors. (IOCS lit) Replaced it.
4. on November, again several Z-axis servoamp errors. The BDU was taken off, but found to be good. One of our engineers mounted it back, and bufff. The same transistor exploded(reversed B1 and E1 wires). replaced it. And another transistor dead. By chance, we had another one for spare and changed it again.
While the drive was taken off, I have checked again the TAC bearings, and found them to be worn (grease turned brown), probably due to miss-alignment after the crash. Changed them.
The lathe works, but under 6m/min and no G00. Changed the BDU with one from another LB15, but same result.
Today, after a lot of meditation, probably I found the problem: Too much grease in the TAC bearings. On monday, I will clean them and will see if this is the cause.
BTW, do you know what kind of VAC units was on LB15's from '89-'90? I bought one at an auction, and has the VAC drive missing. I want to buy one, but I don't know what type, as it seems to be a little bit smaller than the VAC's on the other LB15's that we have. Also, this lathe doesn't have the PSU above the CPU(probably inside),it has two BL-D 50A servo drives(smaller than BDU units), no tape-reader and load meters on the back, and the relay panel is replaced by a 2-level PCB.
Re: Okuma LB15 100-4 Diff Alarm
Did you megaohm the motor and cable set?
Re: Okuma LB15 100-4 Diff Alarm
No, I don't have one. With a multimeter is OK.
But I'm thinking that grease is the problem, because the load on the servo is raising proportional with the speed, and the error appear every time after raising the speed over 6m/min.
I made a program to move back and forth the turret with 6m/min and worked for 30min without error. When I raised the speed with 10%, bang. error.
With the same program, on other LB15's, the load is 5%, not 55%.
Re: Okuma LB15 100-4 Diff Alarm
it can't be because of "too much grease" if the grease is good. bad lubrication of linear guides; big wear of linear guides; significant misalignment of linear guides; and once again tapered gibs. Or maybe even some crack.
Re: Okuma LB15 100-4 Diff Alarm
Algirdas,
There is plenty of oil on the guides. It hasn't tapered gibs on z-axis, they are rectangular. No cracks, and load is uniform all over Z.
I think I made a mistake when greasing the bearings, because I have filled them 100% with grease, and the bearings must be filled partially(discovered this later ). The grease is a lithium one, and may be a little thick.
When I mounted those bearings on the ballscrew, the outer race was a little bit hard to rotate, even without preload, due to grease.
Re: Okuma LB15 100-4 Diff Alarm
check if it's possible to rotate the ball-screw by hand.
check if there is no the exctra clearance of the saddle - the saddle movement must be smooth, no skew.
Re: Okuma LB15 100-4 Diff Alarm
Yes, it rotates smoothly if I try to rotate it from the motor's pulley. If I try to rotate it from the ballscrew race by hand, it's a bit hard.
Re: Okuma LB15 100-4 Diff Alarm
Is the x axis drive the same as z? Might try swapping them, sounds to me like a bad drive or the turcite is gone on the z saddle. Grease may make it harder to move, but shouldn't cause this. It may heat up though. Did you re grind the collars, or at least double check the preload on the bearings? Those old ones typically need to be re fit with modern bearings.