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###### Transformation Application of SB70 Inverters in Winding of Stainless Steel Sheets

Nitrogen bright annealing furnace – Put the stainless steel sheets into the nitrogen bright annealing furnace for high-temperature treatment to soften the sheets before subsequent processing series to form finished product. This procedure is of crucial importance in its impact on quality of the products, and therefore has high requirement. It generally consists of several components: unwinding motor, before the pressure roller motor, S club motor, winding motor, etc. The unwinding motor, front roller motor, S roller motor has power of 5.5 kW and the winding motor has power of 30 kW. Operation process of system – A roll of stainless steel sheet is led by the unwinding motor into the annealing furnace through the front roller; after high-temperature heating treatment, and then led by S roller motor, and wound by winding motor. During the work process, the constant linear speed of each part is constant, which has important effect on the subsequent processing of the products. It is shown as follows:

Fig. 1 Schematic Wiring Diagram of Winding Stainless Steel Sheets

Before the transformation, traditional inverter synchronization method is previously used for control. However, frequency conversion control can only guarantee synchronization of S roller motor and winding motor in speed. For the winding motor part, with the increase of winding turns, the outer diameter is gradually enlarged, and its linear speed is required to be unchanged; therefore, it is actually constant tension between the two. To maintain a constant speed, the operator must always measure the linear speeds of S roller motor and winding motor, and according to the difference of the measured speeds, manually change the frequency of S roller inverter and winding inverter to adjust the linear speeds of the two in order to achieve consistent linear speeds. As it is difficult for manual operation, which cannot achieve constant tension control or constant linear speed control for winding stainless steel sheets, and thus cannot maintain a constant tension, the excessive large tension and tautly deformed steel sheets or excessive small tension and loosely deformed steel sheets are often the results, affecting the quality of the products. Moreover, the previous winding system has the following drawbacks: 1. As each power point receives non-uniform force, the system can not run in the same linear speed; 2. S roller motor is liable to slip at low speeds; 3. Overload and stalling often occur to the winding motor; 4. In material feeding and discharge, it is difficult to control.

Under the existing conditions, for the winding motor, with the increase in volume diameter, as long as the S roller motor and winding motor can always maintain constant linear speed (i.e., constant tension), the technological requirements of the winding system is satisfied. For this, in the original system, frequency-conversion speed regulation is adopted for transformation. As the unwinding motor is at the front stage, the requirement in tension control is not high; therefore, transformation will only be made on the S roller motor and the winding motor. The S roller motor of the system will adopt SB70G5.5 kW. Between the S roller motor and winding motor, there is a flexible connection for stainless steel sheets. If the winding motor has linear speed higher than that of S roller motor, the S roller motor will be in power generation state, and therefore, the inverter needs to be provided with external braking resistor. Winding motor adopts SB70G30KW, while the inverter adopts vector control without PG and uses the rich arithmetic logic unit of SB70, and through connection of internal computing unit, to increase torque limitation on the basis of the speed control. Torque limitation value is given directly by the internal arithmetic unit, based on 100% of the 2.5 times of the motor rated torque.

The analog output frequency of S roller SB70G5.5 kW is used as the given value of the linear speed to supply the winding motor, and by regulating the gain and offsetting of corresponding input signals of the inverter as linear speed signal, to carry out the calculation, limitation of the torque, in order to achieve constant linear speeds of the S roller motor and winding motor. The schematic wiring diagram of the inverter is shown in Figure 2:

Fig. 2 Schematic Wiring Diagram of Tension Control Inverter

For S roller inverter, the setting is relatively simple. For frequency setting, the potentiometer setting and external control starting is configured. Emergency stop button that has combined movement with the winding motor is provided in case of emergency stop. In just starting the winding motor, inching function is needed, and therefore, inching function is provided. In inching, torque limitation is switched by the analog switch in the inverter to make the torque limitation to be 100% in inching.

The scheme has been used to make transformation for winding of the four nitrogen bright annealing furnace and has been successfully applied. After transformation, with the constant-tension winding, the precision of processing is high, and the product quality is greatly improved. It is safe, reliable and of stable performance, and improves production efficiency. The system is not provided with tension sensor. The speed encoder realizes the control of linear speeds and constant tension of S roller and winding motors, which has won favorable praise from the users who have expressed high recognition and satisfaction of the excellent and powerful function of SB70 inverters.

###### Application of SLANVERT SB70 Series Inverter in Film Winder

Common film winding in industry mainly includes cloth, paper, plastic film, etc., which requires high tension accuracy. Roll diameter varies greatly. Tension requirement is variable with the increase of the roll diameter, thus tension taper control is required to prevent reel damage or internal folds. By setting existing functions and fully making use of arithmetic unit and counter, SLANVERT SB70 Series Inverter can realize the tension control required by film winding. The solution is as follows:

Main setting frequency of the corresponding slave machine (winder) is calculated from the running frequency of the master machine (processor) representing film linear speed and the real time roll diameter of the wound film and taken as the feedforward. Meanwhile, PID regulator is used to control the film tension PID output. Setting frequency is continuously modified and the modified frequency is considered as the setting frequency of the winding motor. The control method by combining feedforward and feedback is high in control accuracy and many tension control dedicated inverters uses the method.

Part I Calculation of setting frequency of winder

Users need to know three values: initial roll diameter, final roll diameter, and paper thickness. Based on the three values, calculate the following values required for parameter setting:

If the final roll diameter of film is 1000mm, initial roll diameter of 100mm, and film thickness of 0.05mm, then:

Percentage of initial roll diameter, D_{0}=100/1000=10%;

Setting value of counter =1000/(0.05×2)=20000;

Preset value of counter = 100/(0.05×2)=2000.

At this moment, the count value of the counter (with setting count value as 100%) is equivalent to an output signal of a roll-diameter sensor, i.e. real-time roll-diameter value D (with final roll diameter as 100%).

Considering the frequency of master machine as F_{0}, frequency of slave machine as F, and current roll diameter as D (with final roll diameter as 100%), we know:

F_{0}×D_{0}=F×D；

It is able to calculate that: F=F_{0}×(D_{0}/D);

First, calculate the value of D_{0}/D through arithmetic unit 3; and then calculate the value of F_{0} (i.e. AI1) through arithmetic unit 2, which is multiplied by the output of arithmetic unit 3 so as to get the value of F. At this moment, the result of arithmetic unit 2 is just the main setting frequency of the winder, so the frequency setting channel for the winder is set as the setting of arithmetic unit 2. By this, the setting of main setting frequency of winder is complete.

Part II Setting Calculation of PID

With the method of close-loop tension control, the setting value of PID shall be set as tension value required by users. However, tension value required by users is a value continuously decreasing with the change of roll diameter rather than a constant, i.e. tension has a taper. Refer to Fig. 2.

Fig. 2 Tension Taper Sketch

Tension taper formula is as:

T=T_{0}×[1-K×(1-D_{0}/D)]

=T_{0}×(1-K)+T_{0}×K×(D_{0}/D)

Wherein, T refers to the actual ideal tension value (with the maximum tension value of the tension sensor as 100%);

T0 refers to initial tension value (with the maximum tension value of the tension sensor as 100%);

K refers to tension taper parameter, within range of 0-100%;

D_{0} refers to initial roll diameter (with final roll diameter as 100%);

D refers to real-time roll diameter (with final roll diameter as 100%);

Wherein T_{0}×(1-K) and T_{0}×K are constant.

Then calculate the value of T_{0}×K×(D_{0}/D) through arithmetic unit 4, wherein the value of D_{0}/D is the result of arithmetic unit 3 and T_{0}×K is digital setting, and then calculate the value of T through arithmetic unit 1, i.e. T_{0}×(1-K)+T_{0}×K×(D_{0}/D), wherein the value of T_{0}×K×(D_{0}/D) is the result of arithmetic unit 4 and T_{0}×(1-K) is digital setting.

At this moment, the result of arithmetic unit 1 is the real-time tension value required by users, and the setting channel of PID is set as the setting of arithmetic unit 1. By this, the setting of setting channel for PID is complete. Arriving here, the design of tension control solution is complete.

Site running condition is as: after the master machine begins to start, the slave machine receives the start signal and begins to start and continuously regulate output frequency according to the change of roll diameter and the feedback of tension sensor so that tension sensor can change with the roll diameter change as per tension taper requirement at reference position and the winding motor can always run steadily. During deceleration, tension sensor has no large deflection till the stop. In the whole process, no deformation or relaxation happens.