Introduction

Fundamental part of university education is to create connection of theoretical approaches with experimental or simulation methods for verification. Illustration of practical physical models is cardinal important for experimental exercises engineering, for comparing the computer simulation tasks with practical experiments and with realtime measured signals from technological aggregates. The improvement of theoretical findings is done by physical experimentation during the education process. The laboratory stands allow easy understanding of the various technologies and its control [7-10].

In most devices, technological process is performed by winding different types of materials. The most typical machines of this group are coiling machines in textile production, in the paper processing, wire making industry and etc. Technological process in these devices usually requires constant tension of the winded material (textile, paper, wires, threads and so on) at various velocities [1-5].

The universal stand of the winding band was design in department of control technologies at Kaunas University of Technology (Lithuania) for the educational and scientific purposes. The stand allows demonstrating and investigating the process of the winding band by controlling its tension in two ways. First method is done by measuring the diameter of unwinding roll or by measuring the length of the band loop. The second method is implemented by direct measurement of tension force of the band.

Disadvantage of the first method is that it is able to ensure correct control of the tension force only in the stabilized case. Determining the tension by the dancer loop length, the length of the loop should be somehow measured by the distance meter. In this case, the length of the loop is proportional to the tension force; however the tension of the spring and mass of the rolls of loop forms oscillating chain with the small damping coefficient. Damping of the oscillating motion should be performed by using electronic control devices by introducing the signals of the change in velocity of the length of loop and its derivative into the control system or by using the mechanical dampers [1]. For this reason, additional devices and equipment are required. It is obvious, that the best rewinding system should be the system with the direct measurement of tension force of the band. Therefore, the stand is designed in this way and investigated in this work.

This work is organized as follows: the structure of the lab stand is presented in the second chapter. The development of mathematical model of the lab stand is presented in the third chapter. The results mathematical modeling and real measurements are presented in the fourth chapter. The conclusions are presented at the end of the article.

Structure of the lab stand for tight band coiling

The tight band coiling system is a variation of the classical structure of the web coiling. The designed lab stand exactly imitates industrial coiling process at reduced size. The path of the band movement on the stand might be observed in the Fig. 1. The braking torque of the unwinding roll 1 is controlled by electromagnetic friction clutch. The unwinding roll 1 (Fig. 1) reel is mounted on the LENZE electro magnetic braking clutch [11] of type 14.512 with 14.422 control unit 5 used for controlling the breaking torque. The braking torque is adjusted by changing the current in the clutch windings trough the controllable rectifier 5 (Fig. 1).

The linear velocity of the band is controlled by the frequency converter with electrical drive EVS9322ES 3, 4 (Fig. 1). The angular velocity of the roll 3 (Fig. 1) is stabilized by using the feedback signal of linear velocity of the band. The tension force of the band is measured by the deformation transducer on the freely moving roll 2 (Fig. 1). Deformations are transformed into the electrical signal, which are proportional to the tension force of the band.

Regulator PCTRL2 of tension of the band is implemented inside the frequency converter 4 (Fig. 1). The desired tension force of the band is passed to the controller trough the connected computer. The feedback signal of the tension force is fed directly to the frequency converter. For the parameters observation and control the blocks with control devices 6) and measurements 7 (Fig. 1) are used. 