Chill roll harmonic drive control question

Hi all, I am presently trying to put an old Heidelberg-Harris M300's chill roll harmonic drive control to work. I have already put the infeed drive to work and it works really well. The problem I am facing is that the original dc motor does not run smoothly at the low speeds the production people want it to run.

I am going to replace the drive for a newer one. My question is: what is the regulation tolerance for this application? I can go from a simple open loop ac drive using a portion of the line speed as reference or can go as sophisticated as a servo drive following an encoder mounted on the machine.

I am an electronic engineer but not the process expert.

Any help would be appreciated.