50 Winder program featuresTension controlThe Tension control function provides control over tension on a material surface. Ifthere is a load cell or a dancer available in a control section, then stable tensioncontrol is maintained with the embedded PID-controller.Due to complexity of process a number of tuning tools are used to make the controladaptive and suitable in possible situations. The Stall function helps starting themachine smoothly and avoids over-regulation at slow speeds. The adaptive P-gainand integration time in combination with the adjustable trimming options helps tuningthe controller to remain stable with a constantly changing roll diameter.When no feedback device is available, the drive is still capable of estimating essentialprocess parameters and produce stable tension control in open loop. Features suchas Friction compensation, Inertia compensation and precise material propertysettings enable achieving best possible result.The objective of the tension control is to maintain the tension of the web, that is theforce applied to the web. The motor speed and torque must change as a function ofthe web speed and roll diameter.Motor torque = Tension reference × Roll radiusSee chain diagram for Tension control on page 664.SettingsParameter groups 77 Tension/Dancer control (page 429) and 78 Winder PIDcontroller (page 436) Open loopIn this mode, feedback from the web is not required. The tension of the web iscontrolled by calculating the torque reference of the motor, which is the product of theuser-given tension reference and the actual roll radius. The tension control PI isdisabled. Inertia and friction compensation can be used to improve the tension controlaccuracy.The drive is running as speed controlled; the torque limits of the speed controller arecontrolled by the tension control. To ensure that the drive is always running againstthe calculated speed controller torque limits, the application adds an overspeedreference to the final speed reference. The amount of overspeed reference isadaptable with parameters.Since tension feedback from the web is not available, accurate web data is aprerequisite for successful tension control. Therefore, the friction and inertiacompensation should be set up carefully when the Open loop tension control is used.The Open loop tension control is suitable especially for non-stretchy materials whichdo not set extremely high requirements for the tension.
