Which products are affected?
Tension Control Template V2.0, V2.2, V3.0
What happens?
If the unwinder is operated in motor mode the torque of the unwinder oscillates between the setpoint torque of the friction compensation and zero. This means that the tension on the material is not constant. In case of sensitive materials to be wound it may happen that a web break occurs.
When does the problem occur?
The behaviour only occurs in case of overcompensated unwinders working in motor mode.
An unwinder must operate in motor mode if only due to the friction inside the plant a larger tensile force would have an effect on the material than defined by the tension setpoint. If, in this connection, overcompensation occurs, e.g. due to an incorrectly set friction characteristic, the automatic torque reduction avoids that the unwinder is accelerated in unwind direction. This torque reduction basically works like a P controller using the value from C3222 as gain factor.
With the presetting C3222 = 100 the torque reduction does not work as described in the documentation but in most applications too aggressively.
Possible diagnostics?
The intervention of the automatic torque reduction is signalled with the g_bAutoTorqueLimitationActive=TRUE template. If the winder starts to oscillate in this operating status the parameter C3222 should considerably be reduced (e. g. C3222 = 20 instead of C3222 = 100). As a result, the oscillations should be reduced.
Short-term measures/recommendations?
Overcompensation should be avoided by specifying the friction/acceleration torque values correctly. The automatic torque reduction uses a gain of C3222 = 20 so that in case of overspeed resulting from setpoint (from line speed) plus double speed offset (C3107 = 5 %) a compensation torque is not added anymore.
Evaluation:
Due to a parameter setting which is only suitable to a limited extend, the winding drive may oscillate if a specific operating point of the unwinder is reached. As a result, sensitive web materials to be wound may be damaged. The behaviour occurs during commissioning and can easily be avoided by modifying the parameter set.
