[ungie]

Hello guys!
The machine: Okuma Eurocenter v50 (ESV4020) / Osp u10m
Made in Czeh Republic around 2002 (Electrical drawing number E-777/778)

A few days ago a colleague noticed that the spindle of the machine sounds strange.
As we've exmained the problem the summary is prettey strage.

1. When I put in for example S5600M3 the machine spins up to 5600 than slowly changes rpm about +-200 totally randomly. This change in rpm is not visible when we check actual rpm on the "block data" screen "Sr" value in the upper right corner, but clearly hearable by ear.
2. At the current job we use a dia 20mm 6 flute solide carbide roughing endmill at 21mm depth 6mm side cut at S1600 F580 we notice that the "Sr" value is dropping down from 1640 to 1580 as the tool goes into the material and rises back up to 1640 when the tool exits. (these parameters before this anomaly were creating ~50% spindle load which was never ever before a problem, now it is ~52%) At first run today the spindle slowed down so much that the it stopped(i'we failed to see this action).
3.At higher rpms the situation is the same i think. As we drill a dia 5,6 mm 15mm deep hole at 5600rpm and 780mm/min feed, fluctation is also observable on the "Sr" value and also noticeable by ear as the drill applies torque to the motor.
The machine at 8000 rpm shows "Sr" value of 8200 form its brand new state, which is proper. rigid tapping without floating holders at M3x0,5 formed thread holes were never a problem.
I dont know that the "Sr" value is read from the spindle by the sindle position encoder located on the side of the spindle and calculated to the real value (because the tiny differencial between the diameters of the motor wheel and the spindle wheel) or it is readed by the motor encoder inside the Sindle motor directly from the rotation of the motor shaft.
If I would know that I could guess about what to examine in the next step of debugging.
Can this be the result of clogged or unworking ventillation unit on the outside of the drive units? can this be a cause of a piece of dirt on the spindle position encoders gearwheel or the encoder itself is dying, or it is more likely the problem is at the motor encoder or some of the drive units are playing with Us?
Maybe there are somebody who can tell the causing source from this list of symptoms
Pleas take Your time to let me know what you think.
Anyway it would be nice to check out both of the encoders actual readed values. If there is a way to do that let me know please!
Any help appreciated
Ps: I can upload Electrical drawings on request

[doctorcnc]

Often when a motor driven by a servo or spindle drive lacks torque, the problem is the drive is missing 1/2 a phase going to the motor. Disconnect the spindle motor UVW wires from the drive, command a slow enough speed that the drive does not alarm off and then look at the 3 phase drive outputs (U,V,W) using drive bulk cap minus for your scope ground. All three phases should be swinging rail to rail about 300 VAC. Obviously there are lethal voltages present to do this test. Make sure you are qualified for the risk.
I doubt this is a encoder problem, unless there is an encoder belt slipping somewhere. The drive & control are monitoring for most encoder failures. Usually the motor encoder goes to the drive and the spindle encoder goes to the control. There should be a diagnostic page that shows raw spindle encoder feedback.

[fordav11]

I can second that opinion. it's definitely a spindle drive problem.
however they are really not easy to fix so you would be better either
getting someone from Okuma to look at it, or sending it out to a
repairer and have them test and repair it.

[mujkance]

Hello ungie,

I didn't worked at this type of machine, but I have experience with an Alfing machine and I have the same problem.

At the end I found out that problem was with clamping of tool because the clamped value was too small.
But it depends from the type of the machine and how it works.

By your story, I think it's problem with your drive, control card may be faulty.

Best regards,
Samir

[ungie]

In the end it turned out the problem was in the spindle belt slippage. The belts were worn out so they slipped even at proper tension