During rewinding,it will occurs tension force sometimes large and sometimes small, it is hard to make its winding unwinding speed in constantly. As winding and unwinding process, web roller material's diameter is changed, so it is hard to working in same speed, or the web material will be broken. Normally unwinding speed is used to measure equipment's capability, and rewinding speed is controlled by tension force. To make sure the web material will not broken, so it adopts speed control mode.

It is improper to control braking force, because during rewinding process, web roller's diameter will be larger and larger, then its speed will be faster and faster when pull web material to make reel tight, tension force becomes larger. Reduce the tension force is to make rewinding speed slower. In actual application, mostly to control speed, seldom to control braking torque. I think in this working situation, control torque frequency converter is more expensive than regular ones. Braking torque has a relationship with tension force, but they are different. 

Nowadyas, in unwinding machine, the 3 inch 6 inch mechanical chuck is widely applied for paper roller holding and griping. At the same time, it will equipped with a pneumatic brake, such as DBK multiple disc brake, NAB pilot mounted brake for tension control, so as to make sure web material unwinding in a same speed and tension force.