Ok, so I read a bit more, and what I assume were absolute encoders are in fact an absolute encoder and a multiturn encoder. Together they give the position information (wich is what machine centers have). They have a battery backup for power loss. What I still don't know is if they continue reading with the battery or only holds the last position known.
If that 's the case, would it be possible to park the motor at a full step so it will keep that position at power loss?
So to sumarise, we have angle and turn count, knowing the pitch of the screw we can calculate the position at start. After that it keeps working open loop as always.
I found this: https://www.ichaus.de/PV1M1
What do you think?