I have a strange problem while referencing CNC machine equipped with840DSinumerik controller.

Machine configuration:

CNC Sinumerik 840Dthat controls six axis via drivers SimoDrive 611.

Problem statement

The machine is working and has been referencing a certain way for over 15 years. It’s gantry Y-axis has two motors Y1 (master) and YG (slave), The problem I am facing is that whenever I try to reference the machine, while referencing Y-axis the Y-axis (Gantry) sways either right or left by a random value. This tilt in Y-axis is verified by the mechanical level meter and is also reflected electronically by the motor loads i.e. one of the motor on Y-axis is loaded heavily. Mechanical assemblies have been checked and verified and no looseness or play has been found. It is also pertinent to mention that gantry axis changes position only when it is referenced. And after referencing, it keep the same position all the time while moving up / down, unless it is referenced again.

I tried to mechanically level the gantry axis and then reference the machine but as soon it completes the Y-axis reference cycle it tits either left or right.

The machine has two measuring systems. optical linear encoders and builtin motor encoders. Along Y-axis it has same configuration with 2 x linear encoders(Heidenhain AE LB382C315 420-04)and 2 x motor encoders (Heidenhain Encoder ERN 1387 - 2048).

The parameters related to referencing as per my knowledge are stated as under:

34010 0

34020 4000

34040 300

34050 0

34070 2000

34090 0.0

34100 -69.0, 0

Please help me out in rectifying the problem?

Thanks in advance

PISCEAN 2010

Is this same problem mentioned in Gantry Axis changes position at the time of reference topic?

 Yes, the problem stated here with electrical perspective. 

Just to add, at reference point of Y axis we checked the readings of both measurement scales, the 2 x  linear encoders reading difference is negligible while the difference between 2 x motor encoders is significant. 

We have changed the Y1 (master) and YG (slave) drives as well as motors. But the problem still persist.