[guhl]

machine works
Z axis gets stopped
401, 421 alarms appear
meanwhile, on position screen Z axis readings run in "-" direction
and in diagnostic parameter 801 I see position error runs in "+" direction
if I push Estop Z axis readings get stopped, but positin error goes on
if I disconnect encoder, situation is the same, but controller shows "axis disconnect"

[Stupidav]

Sounds to me like that axis has physically come to a stop but the Motor and encoder is still running. Have you looked to see if this is the case?

If so depending on the drive; example Ball Screw, the Nut quite possibily is broken or even the screw itself.

[guhl]

I disconnected encoder, but the case was the same

[Aaron liang]

You can try to modify the prameters of 505.