Dear all,

I am investigating this issue for quite some time now on a Cincinatti Milacron Arrow 750.

The Z-axis is not moving with the Z-axis BDS4 servo amplifier ("driver").

However, Z-axis BDS4 driver is moving X and Y-axis perfectly fine (they are not as heavy). This tells me that the Z-axis BDS4 driver should be working OK.

Also, X and Y BDS4-drivers move Z-axis (slowly, but they do, up & down with about the same speed - could be a setting in the software). This confuses me! It doesn't make too much sense to me. So I took a lot of measurements, found out that the servo PWM-signals (Ma,Mb,Mc) of X and Y-axis BDS4's are around 51% duty cycle whereas the Z-axis PWM-signal's duty is only around 30-43% max.

Could the lower PWM duty cycle be the ONLY reason? If that would be the case, then why the X-axis BDS4 driver (currently on Z-axis servo) is only moving slowly at 51% PWM duty? According to the owner of the machine, everything is automatically being lubricated, although the machine was standing for a few years now.

This is a "Goldline Brushless P.M. Servomotor" by Cincinatti Milacron on the Z-axis.

The DC-resistance of the windings of the Z-servo is 3x 1.7 Ohm whereas for X and Y-servos the DC-resistance is 3x 4.5 Ohm. This could be correct as the motor should be more powerful and all 3 are equal.

We have taken out the mechanical brake at the back of the servo to rule out issues with that (for all our tests).

The Z-axis can now be turned even by hand from the back of the servo with a pair of pliers.

The tool holder is sitting on a block of wood. As we were able to lift up the Z-axis just now, using the X-servo amp (BDS4), we left a gap of about 0.5-1 cm, then turned off the power. The Z-axis dropped on the wood immediately (as expected). So why the Z-axis BDS4 driver wouldn't move the Z-axis down at least?

So I guess all that is left now:

1) doubt the owner about the machine being fully lubricated, although still moving by X/Y-BDS4's and by hand + able to drop by itself
2) the 3 windings of the Z-servo are shorted in a strange way so all 3 show same low resistance of 1.7 ohms each
3) the magnet inside the Z-servo lost its magnetic fields over that past nearly 30 years

More measurements in the attached table (resolver, DC bus etc.).

Hope someone could give me some advice on this please.

Thank you!

Tom