Control Tension by Controlling Brake Current
In a magnetic particle brake or clutch, torque is proportional to coil current. If coil current can be held constant, tension can be maintained in applications such as unwind stands, wire feed, and paper or film converting.
An ideal tension control would maintain coil current at a desired set point, and compensate for changes in the brake coil’s resistance (caused by heating) and input supply voltage.
In some applications closed-loop control is desired. A sensor provides a feedback signal proportional to tension. A dancer arm is typical of tension sensors.
In other applications it may be appropriate to allow the operator to manually set tension. Open-loop control can also be established using a roll diameter sensor.
In either case, the goal is to maintain constant coil current in the magnetic particle brake or clutch.
An example of a constant current (or torque) tension control is Regent Controls’ 8129.
● Accepts 0-10 VDC or 4-20 mA control signals
● Independent adjustments for Gain and Offset
● Use in closed-loop or open-loop tension control systems