Hello forum,

I'd like to ask you experts a question because I am slightly confused...
We just acquired a job and, as part of the automation supply, we need to develop a positioning strategy for a big machine on rails.

Imagine a big box on wheels, 4 at the corners that are driven (G120) plus two idlers in the mid point of the sides.

The driven wheels motors all have incremental encoders on the motor side connected to the drive directly.
Two of these wheel however are also equipped with a profinet absolute encoder on the load side of the drive unit going to the PLC.

I wanted to use the positioning technology objects but I don't see how it is possible to use both the incremental encoder on the motor for speed control on the motor side AND the absolute encoder for the positioning.

The profinet absolute encoder would be acquired by the PLC (S7-1518F) and it's signals dropped in a DB for use in an External Encoder TO.

But I have no idea how to proceed from here...

Should I make the 2 absolute encoders the only available encoders to the front positioners and then act on the 2 rear wheels with the speed feedback of the 2 front wheels?

I'm open to suggestions :-)

Fabio B.

There's a lot in this link that will help:

SIMATIC Technology - Motion Control: Overview and Important Links

Speed setpoint to the CU250S-2

Encoder from TM Count 

See, different encoders for speed loop (it does CU250S with attached motor encoder) and position loop with PLC and encoder on TM pulse module.