The unwinder library can be used for mechanics with or without a dancer.
Almost all functions of the unwinder depend on the radius of the bobbin. The unwinder calculates the radius based on the rotation of the bobbin and the length of the foil taken by the feeder. When the unwinder controls a dancer mechanic, the amount of foil stored in the dancer buffer has to be considered. If the unwinder is used without a master connection, the length of the foil has to be calculated with the average feeder velocity. The accuracy becomes better with longer distances.
If the calculation of the radius is not exact enough, then the user can set the radius to another value at any time, which is determined for example by an external sensor. In addition, the mass of the bobbin is calculated for every new radius and the J-Load parameter of the drive is updated.
Master
For a better performance of the unwinder the feedback controller is assisted by a pre-controller. This pre-control mode connects the bobbin to the master axis, by using a cam. This cam is designed such, that the master movement does not cause a jerk on the foil. The feedback controller only has to compensate jerks that are caused by measurement errors of the radius and adjust the cam continuously.
Masterless
Without a master (dancer required), the pre-control is calculated with an average feeder velocity that is provided by the user. The material difference is compensated by the dancer. Consequently the average velocity has to be calculated over a feeder period, in which the material difference cannot be bigger than the buffer of the dancer.
In both configurations (with or without a dancer), a control loop is necessary to move the bobbin according to the feedback value. A three-step controller is mainly used for dancer applications and a PI controller (working as a torque controller) without it. This controller keeps the dancer in the middle position or moves it back after a jerk.
The feedback handler uses the value of the sensor (dancer or roll measurement) to calculate the control value. The user has to define the minimum and the maximum sensor value and the corresponding application values (length of the foil inside the dancer or tension on the foil). The configured reference value can be changed at any time. The feedback handler calculates a linear interpolation according to these parameters.
During operation a foil can tear. The machine should not be used anymore until this is fixed. Consequently, the unwinder has to monitor the feedback value of the dancer or the measurement roll.
The mass of the bobbin changes while the unwinder is moving. To keep the control loop of the servo axis stable, the J-Load parameter has to be updated during the operation. This is performed by the unwinder (using the mass of the bobbin).
