LB15

[alandudley]

If I run the spindle on my LB15 at 2000 rpms or above I get a 103/104 alarm when I stop the spindle even if I do it manually by hitting the stop button. Since 103/104 is a axis encoder alarm I do not understand why it would do that as the axis are not moving just the spindle. Does any one have a suggestion as to what may be the problem? Do you think it has anything to do with the regen since it only does it when it is decelarating?
Thank you for your help!

[neilw20]

The axis encoder is used for threading. Tacho generator is on end of motor. The encoder and the tacho signal probably don't agree, with the design limits.

Is it braking at the full current? It sounds like the full deceleration being commanded but is not happening correctly. In the LC15 there is a tacho generator on the end of the motor spindle. Very fragile wire in armature. Careful.

The tacho brushes: I found this were worn, and spindle control was erratic until the brushes were replace. Surface condition of commutator is important, and my problem was brush bounce. Is there any squealing noise from the tacho?

I found spare brushes in side the control cabinet. That was nice find

Reducing the speed in two steps might be a good workaround until you have identified the cause. I do suspect the tacho generator, if the LB15 has one, needs service.

6 or 8 years back since I was involved with it.

[alandudley]

Thank you very much I will check the tach. I haven't had the machine long and I have been running stainless at slow speeds so the problem just showed up when I started running some aluminum. I tried slowing the spindle down to 1000 before stopping and it works most of the time but I would like to fix it properly if I can I just didn't know here to look since the alarm is showing up for the x or z axis even when the axis's are not in motion. It does get up close to 100% power when braking from 2500 rpms and that seems to be where it is most prevalent but it still doesn't happen every time. Again thank you for your help!

[neilw20]

Just step down the speed a few times before stopping.
S2000
P0.5
S1500
P0.5
S1000
M5

Not sure about the time delay units. can't remember, but without the speed steps, with look ahead may still cause the problem.
You could also use use a small Z or X move between the changes.

100% power during braking is normal. If not 100% then the tacho is almost surely the problem.

It is not related to motion X, or Z, really, but in the whole scheme of things the spindle axis is not what is commanded, so the interpolator, says the axis motion is not as commanded.

Easy to slip off the end of the motor shaft, after removing brushes.
Very fragile wires - mine had a broken one to the commutator.
I had to regrind the commutator after making a mandrel for it.
Concentrically must be perfect!!!
Any irregularities will cause brush bounce, and makes threading impossible.
Ask an expert if you are not sure. Bet they are expensive.

Nice solid machine, with slightly peculiar controls.

Always start off with the feed knobs at 0 or 10% and you will never crash it.

Love the power. Generates more swarf than 2 teenagers can keep up with. hahah. and they thought it would be an easy day.

[alandudley]

Thank you sir for the information. I did not think about stepping the speed down with delays between the steps. That is a good idea and should rectify my problem until I get a chance to remove the encoder and repair it.

[mfgbydesign]

Perhaps changing the mode to Feed Per Minute instead of Feed Per Rev. before stopping the spindle?

[underthetire]

What year LB15? If it has the Okuma VAC unit, they are very sensitive to impedance on the incoming power lines during spindle decel. Usually caused by an aftermarket transformer. Usually it will come up with a voltage flutter alarm though.

[alandudley]

I think it is an 84 model. I have only had it a few months. I have been running stainless at slow speeds and haven't had any problems but now I am running aluminum at around 2000 rpms and when I try to stop the spindle to make a tool change I get the 103 X or 104 Z errors randomly. The longer it runs the more frequent the errors. I used the suggestion below and found that I have to drop the speed in 500 increments with a 1 second delay between steps to stop the problem. I am using a 30 hp cnc rated converter from phoenix converters so you are probably correct that it is a noise problem. Last night I was thinking about moving the phases around to see if maybe that would matter. I am not sure if it will do anything since power to the machine actually comes from it's own transformer anyway. I would think the transformer on the machine would not be sensitive to which leg of the phase went where. Is it important which leg that the generated phase goes too? My voltage is around 245 so I did change the tap on the transformer when I first put the machine in. Could that casue a problem. I am sure that the generated leg probably droops a little when the load is high. Thank you for your time and suggestions!

[neilw20]

It is all rectified to DC, so the phasing is not important.

Because it is a phase controlled bridge, it is only meaningful to measure the bus voltage at full speed.

Carefully measure the rectified bus voltage and see that it stays within spec.

The filter capacitors may becoming aged and losing capacitance.

Be careful. They remain charged, to dangerous voltages for a long time after power is removed.

When fully discharged, measure the capacitance, (which might be a new learning curve) and see that it is no more than 10 or 15% down on the labeled value.

There are many techniques to measure them at low voltage.

[underthetire]

One that old would probably have the Fanuc spindle drive, not the Okuma one. Should be a toggle switch on the spindle drive itself, the drive is actually mounted to the door i believe on those. Set the toggle switch to match your incoming voltage, either 200-220 or 220-240. This should be off the machine transformer voltage. The other thing to check is spindle belts. IF they are loose, i have seen the drive unit try to stop the spindle but the belts slip enough to not let the spindle drop RPM enough, so when the drive releases the dynamic braking, the spindle will actually cause the motor to speed back up. These are just suggestions BTW, the early machines alarms don't always mean what you think they mean.

Noise isn't so much of an issue on incoming power, as resistance in the transformer/line. During dynamic braking on some Okuma models, they put the extra energy back in to the incoming power line during decel. With a phase converter to a transformer, i would think there would be a high impedance. This was more of an issue with the Okuma VAC type A and VACII, and VACIII models. Yours should be Fanuc.

[alandudley]

WOuld that be measured at the transformer?

[underthetire]

Ideally you would want to measure it right at the spindle drive. Should be, R,S,T on the drive. U,V,W, go to the motor.