Thread: Z-axis servo motor vibration on qtn-450

We have a 18 month old Mazak QTN-450 that recently starting making a high pitch noise coming from the Z-axis servo motor and later turned into a vibration of the Z-axis ball screw. This Vibration is transferring to the part during finish passes. We contacted Mazak and they said it would be more than likely the Servo Drive. We had a new identical machine come in and we swapped out the Servo Drive and the problem did not go away. On Mitsubishi's advice, we swapped an identical encoder, changed a few parameters that they recommended and again the problem still exist. The only thing we have not swapped out is the Servo Motor itself. Mitsubishi doesnt believe the motor is bad and are saying it may be in a mechanical bind.
However, we can turn the ballscrew by hand with ease.

Mazak wants $7,600 for the servo motor, but before we fork over that money I wanted to make sure there wasnt anything else we could try or test before doing that. Any suggestion would be welcomed.

what parameters did you change, i had the same problem have the parameters written down in the truck. I'll post them tonite.

Ok the parameter i changed was sv38 which is a notch filter. go into servo monitor page, get the axis to make the noise, watch the freq for that axis when it reaches its highest point write that number down. then put that number into sv 38, cycle power. my noise went away right away if yours is still there then do the same thing again to find highest freq then put that number in to Sv46.

Great. Thanks for your reply. We will try that and post back the results.

The electricals on a Mazak have a 2 year warranty! Servo motors count as electrical...

Problem found. After changing the parameters we were able to tame down the Z-axis servo noise that it was making, however our Z-axis movement still wasn't a smooth motion. We decided to start checking the bolts on the ball screw and found our problem. At the point were the ball screw bolts to the turret there are 4 bolts. We only had 1 loose bolt holding it all together. 3 of the Bolts had fallen out. 2 of the Threaded Holes on the plate were stripped out and we will have to buy a new one. I guess the Mazak guy that was supposed to check and see if these were tight was day dreaming that day. It's frustrating to spend $200k on a piece of equipment and have bolts falling out on you. Critical ones at that.

Glad to hear the parameters got rid of the noise. I've seen those bolts come loose but not on a new machine. Hope you can just replace bolts and that there is not something wrong with the screw.

Quality has definitely gone down at Mazak. Not only US built, but Japan and UK built as well. If it is close to the end of the month, the machine will ship ready or not. That is a "cash flow management strategy". Customers with million $ machines suffer the same fate.

How long did this machine run with the vibration? Maybe the frequency of vibration was able to loosen the bolts.

It's been about 2-3 weeks since we noticed the vibration, however, judging on how dirty 2 of the bolts that were sitting in the bed, I would say they fell out a while back. I'm not certain, but wonder if the loose Z-axis nut was causing an extra load on the Servo motor and causing the noise.