A new solution for the control system of the cross cutter in the board factory

Abstract

Transversal cutters (flying shears) plants are used, among others, in continuous paper or cardboard production processes. In the technological processes of cardboard production, transverse cutters are located at their end, where the material (cardboard) in the form of a long strip is cut into shorter pieces (tabs). Continuity of the process requires that this cutting be done without stopping or slowing down the movement of the strip being cut. The basic technological requirements that should be met by the transverse cutter plant are:

•          Cutting the sheet to specified length;

•          High accuracy of the length of the cut pieces;

•          Quality cutting, without creasing, tearing, or crushing at the point of cutting.

In the operation of transverse cutters, the strip being cut reaches the flying shears at the desired speed, which is determined by the speed of rotation of a pair of rollers called the press (press drive). Flying scissors consist of two blades placed perpendicular to the movement of the tape, the length of blades corresponds to the maximum width of the tape being cut (shear drive). The shears mechanism ensures that the blades are at the same moment opposite each other and cut off part of the web. To ensure proper cutting with high quality of the cut (tab edges) the peripheral speed of the blades must be equal to the speed of the web at the instant of cutting.

The principle of operation of the cutter, whose control system will be described in this paper, is based on the variable speed of the motor (flying shears mechanism), which is directly coupled with the shears mechanism. The speed of the blades during one round (cutting cycle) changes, which is why the requirements for speed change dynamics, with the accuracy of speed and position synchronization in the period around the cutting, as well as the speed profile from one cutting to the next, are very demanding.

Latest PLC from the Technology series, with integrated PROFInet and PROFIBUS DP communication protocols, was used to implement the control system of the transverse cutter. Press and knife drives are powered by high performance series frequency converters with integrated vector control algorithm for servo drive. PROFInet communication is also used to connect digital and analog input and output signals, via modules grouped into six groups.

Frequency converters, whose communication with the PLC is realized by PROFIBUS DP communication, are used to power and control other drives (cart for changing the active unwinder - "rowing", decurling, elevator, forks and carts for change of pallets). PROFIBUS DP communication is also used for the integration of other "smart" devices (absolute encoders, web tension force measurement, etc.).