A known winding device of the initially described type, with a corresponding control system, for producing wound rolls whose hardness can be influenced in a predetermined manner, will now be described on the basis of the schematic view shown in FIG. 1.
FIG. 1 illustrates a central contact winding device. In this winding device the web 1 being wound is introduced by means of a contact roller 2 contacting the winding tube 3, or to the film roll 4 that forms on this winding tube, and is wound onto the film roll 4; the contact roller is positioned against the circumference of the film roll 4 that is forming. Positioned in front of the contact roller is a web tension measuring roller 5, which measures the tractive force of the film web running over the contact roller 2. The web tension measuring roller 5 forms a web loop or diverts the web 1, so that the tractive force can be determined from the tension exerted on the web tension measuring roller 5 by the incoming and outgoing portions of the web. Assigned to the web tension measuring roller 5 is a receiver 6 for the measured data, which feeds a signal corresponding to the measured tractive force of the web to a control device, for example, a computer 7. This computer 7 compares the signal obtained from the receiver 6 as an actual value with a desired value stored in the computer 7. If the two signals differ, the speed of the direct-current motor 8 driving the contact roller 2 will be controlled in a positive or negative fashion, specifically in such a way that the actual value fed from the receiver 6 to the computer corresponds to the desired value.
Since the diameter of the film roll 4 increases with the winding time, the motor 9 driving the winding tube 3 and the film roll 4 forming on it must also be regulated according to the increasing diameter of the film roll 4. This is provided for in that a sensor 10 monitors the winding tube 3 or the pins or journals supporting the winding tube 3, and the sensor 10 determines the actual diameter of the film roll 4 by means of the counted revolutions of the winding tube 3. This value provides a measure for changing the torque of the winding motor 9. The torque of the winding motor 9 is controlled accordingly. Thus, the torque of the motor 9 is changed in accordance with the diameter of the film roll that is forming and in accordance with the desired winding characteristics, while the speed of the motor 8 which drives the contact roller 2 is also controlled.
As described, a winding device operating as a central contact winding device is shown in FIG. 1, in which both the contact roller and the winding tube on which the web is wound are driven and both are in continuous contact with each other.
In a different system, the contact roller 2 is moved away from the winding tube 3, or the wound roll 4 that forms on this tube, and is positioned at a distance from the tube. Winding of this kind is referred to as "central gap winding". This mode of operation is always preferred when highly sensitive films must be wound, which run the risk of being damaged by contact pressure from the contact roller.
If the wound rolls are wound by a central gap winding method, the winding motor 8 and the motor 9 driving the contact roller 2 are controlled in the manner described above. A different type of control has not previously been thought possible, inasmuch as the web tension between the winding tube 3, or the film roll 4 forming on the tube, and the displaced contact roller could not be measured, as it was impossible to house measuring devices in the immediate area. If the known winding device described in FIG. 1 is operated as a central gap winding device, the torque of the winding motor is controlled according to the increasing diameter of the wound roll 4 that is in the process of forming in such a way that the desired winding characteristic is obtained. Controlling the torque of the winding motor is only able to provide the desired winding characteristic in a very imprecise fashion, however, so that controlling the torque of the winding motor is no longer adequate for the increased demands with respect to the characteristic of coil hardness in the case of wound rolls with sensitive types of film.