I have this problem on my machine.
It is Fanuc OM and machine DAH-LIH.

Everything is fine, machine is working and sudenly at one moment, z axis goes down and tool hits into table.
And display "434 servo alarm: Z axis detect error"

And after that i restart machine and everything is ok, and from time to time, it happens again.

What could that be?

Sorry if this is wrong forum