[rajappa]

I have a Okuma LB 15 lathe with OSP5000L-G control and Fanuc AC spindle drive type A06B-6055-H208 with top pcb type A20B-1001-0120. In this machine, spindle do not have power at low rpm (600) in high gear. When I checked the motor current, it has already reached its maximum current of 40 Amps and because of that, the spindle speed drops and finally stops. It is working normal at higher speeds in high gear. Also, at low gear, it works ok. I have seen the rpm shown on the monitor and spindle drive different. Spindle drive shows 50 % more speed than the rpm shown in monitor both in low and high gear. The spindle drive works ok until its rated motor current of 40 amps. At that time, I see the input current to drive is about 13 Amps. Can anybody suggest any solution for this problem ?

[underthetire]

What do you mean no power? The speed indicated on the drive is motor, not spindle speed. If your overloading in high gear, switch to low. Those are only 15hp peak machines.

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[neilw20]

Buried in the back of the cabinet, hopefully, there are some spare brushes.
Also small ones for tacho generator on end of motor shaft.
DON'T dismantle tacho, as it is FRAGILE (unless you are a confident instrument repair person)
Might be the brushes on the tacho generator.
I found the commutator on the tacho gen needed to be reground as brush wear beyond limits had caused damage.
Don't even try to cleanup the commutator by hand. You will probably make it worse! Very critical for correct operation especially threading.
I am guessing this, as I repaired a LC15 (i think it was) or was that LC20.
Long time ago.

Machine normally accelerates and brakes right on the current limit to stopped. Either gear.

[underthetire]

Lb 15 with that Fanuc drive should be an AC motor and no tacho.

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[rajappa]

Thanks for replies. It has got Fanuc AC Motor Model 8 - 3 phase 220V - 7.5 KW (Cont) / 11 KW (30 Min) rating. So, no brushes / commutators. It is true, if the gear is changed to low gear, it works. But, earlier, the spindle can take 3mm cut at 600 rpm in high gear. But, now, it can not take even 1 mm cut for the same job / material. At 0.8 mm cut , spindle load is shown 100 % / 110 % in the monitor. Also current drawn by motor is checked 40 Amps, which is the maximum allowed for this motor. In this machine, there is hydraulic problem in changing the gear. It takes long time to change gear. So, the particular job is done at high gear. It was working in this condition for long time. After some outsider attend to some fault in spindle drive, this problem started. The original spindle parameters got erased in spindle drive. Since there was no back up, new set of parameters are entered. Is there any chance, due to wrong parameters, this problem can arise ? Max rpm for this motor is 4500. But, it goes upto 6000 in spindle drive display. Spindle gear ratio is 1: 4 ( Low to High). So, I am able to calculate the ratios between spindle speed and motor speed. I have seen the current drawn by three phases of motor same. I have not checked the motor insulation. I do not doubt the motor. Will thee be any problem in drive ? If so, what can be the fault ?

[underthetire]

Yes, parameters can make a big difference. Those Fanuc drives were pretty common on the LB15s, I'm sure someone has the correct ones. The only other thing is a transistor module may be on its way out, but typically that shows up when trying to start the spindle.

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[Algirdas]

Check the wiring first. It could be messed up during intervention.

Is there any chance, due to wrong parameters, this problem can arise ?

try to find correct modulation frequency. I can't figure out what else can make current through the motor grow at your case.

[fordav11]

if it worked before and the parameters were lost then surely it's a parameter issue and the actual machine is ok.
you just need to put the parameters back to how they were before they were lost.
then the problem is solved.

[rajappa]

Thanks for replies. I got parameters and explanation for each parameter in a website. But those parameter values are not for this machine. Already, I changed parameter value for No 15 from 40 to 55 to increase the maximum spindle speed from 3000 to 4200 in high gear and 700 to 1000 in low gear to achieve the maximum rated speed. But the value 40 is correct, since it reflects 40X100 = 4000 rpm of motor. It was showing earlier max motor rpm in drive about 4500 and now it shows about 6000. I think, there is an encoder in motor connected to drive and another in spindle connected to system. Since there was no problem with system earlier, I can take spindle rpm shown in monitor as correct. I have not checked yet the spindle rpm and motor rpm with a tachometer. From the parameter description details I got, I can not find any parameter related to motor current. I will search in internet for right parameters for this machine. As Mr Underthetire mentined, there is a chance of transistor module partially defective. But the current drawn by all the three phases are same. First, I look for original parameters. If I can not get, I will initiate a thread and also contact the maker for this. I do not know whether maker can help in this, since it was attended by maker's representative earlier.