Table 2: Initial and final motor speed and interstand tension

Stand/Zone	1	2	3	4	5
Stand Speed (RPM)	130 (125)	109 (115)	220 (226)	300 (292)	295 (302)
Interstand Tension (PSI)	40.2 (0)	-177.6 (0)	-250 (0)	239.6 (0)	-205.4 (0)

The tension control system coordinately controls the interstand tension of each interstand zone in a repetitive and interval mode. After 5 billets, all interstand tensions are brought to very insignificant values. After 18 billets, all interstand zones are brought to a tension-free status. Table 2 also shows the final speeds of roughing stands and the final values of interstand tensions (data in the parentheses).

To evaluate the transient performance of the control system, Figs. 4 and 5 show the overall armature current and motor speed responses of the selected stands 4 and 5. The response curves are for 20 rolled billets. Fig. 6 is an enlarged view of partial responses of Stand 5 for the last 5 billets. It can be seen that the armature current of each stand traces well its reference value after a few billets. Note that the current impacts while the billet is hitting on or leaving the controlled stand or hitting on its downstream stand are inevitable in the rolling process and not handled by the control system.

The current reference of a stand represents the armature current of that stand in the forward-tension-free status. It is sampled for every billet and may include a backward tension. Hence, the current reference is not fixed until all interstand zones become tension-free as seen in Figs. 4 and 5.

From the speed responses, one can see that the stand reference speed is automatically adjusted to make its own match the speed of the downstream stand. The instantaneous drop and rise of actual speed occurring while the strip is hitting on or leaving the controlled stand are unavoidable and not controlled by the tension control system. There is a leading speed compensation designed to reduce the speed drop from stand impact to an acceptable extent. One can clearly see the speed auto- adjustment process from the first half of the enlarged partial speed response of Fig. 6.

 

Conclusion

Looperless interstand tension control of roughing rolling mills remains a hard-to-resolve problem. This paper proposes a successful multistand fuzzy tension control system for a roughing rolling mill. Test results on a virtual rolling mill show that the proposed technique has made it possible to realize a satisfactory multiple stand tension control of roughing rolling process.

Acknowledgement

This work was supported by the Natural Sciences and Engineering Research Council of Canada (NSERC) through Collaborative Research and Development Grant CRDPJ 234028-99, and by Materials and Manufacturing Ontario Collaborative Research Grant IC403. The authors would like also to thank the assistance of Quad Engineering Inc. in providing test facilities and for useful comments.

 

References

[1] R. Takahashi, “State of the art in hot rolling process control”, Control Engineering Practice, 9 (2001), pp. 987-993, 2001.

[2] H. Katori, R. Hirayama, T. Ueyama and K. Furuta, “On the possibility of looperless rolling on hot rolling process”, Proc. 1999 IEEE International Conference on Control Applications, vol. 1, pp. 18-22, 1999.

[3] G. Li, “Decoupled intelligent tension control”, Technical Report, ITC.3 (internal), Ryerson University, Jan. 2002.

[4] T. Hesketh, Y. A. Jiang, D. J. Clements, D. H. Butler and

R. van der Laan, "Controller Design for hot strip finishing mills", IEEE Trans. Control System Technology, vol. 6, no. 2, pp. 208-219, 1998.

[5] H. Imanari, Y. Morimatsu and K. Sekiguchi, “Looper H-infinity Control for Hot-strip Mills” IEEE Trans. Ind. Appl., vol. 33, pp. 790-796, May/June 1997.

[6] Y. Seki, K. Sekiguchi, Y. Anbe, K. Fukushima, Y. Tsuji and S. Ueno, “Optimal multivariable looper control for hot strip finishing mill,” IEEE Trans. Industrial Applications, vol. 27, no. 1, pp. 124- 130, Jan.-Feb., 1991.

[7] M. Shioya, N. Yoshitani and T. Ueyanma, “ Noninteracting control with disturbance compensation and its application to tension-looper control for hot strip mill", Proc. 1995 IEEE 21st International Conference on Industrial Electronics, Control and Instrumentation, IECON 1995, vol. 1, pp. 229-234, 1995.

[8] F. Janabi-Sharifi and J. Fan, "Self-tuning fuzzy looper control for rolling mills", Proc. 39th IEEE Conference on Decision and Control, vol. 1, pp. 376-381, 2000.

[9] F. Janabi-Sharifi, "Neuro-fuzzy looper control with T- operator and rule tuning for rolling mills: theory and comparative study", Proc. 27th IEEE Annual Conference Industrial Electronics, IECON 2001, Nov. 2001, Denver, Co., pp. 58-63, 2001.

[10] L. Winitsky and R. Li, “Virtual rolling mill for real time control system tuning, operator training and rolling mill simulation”, Association of Iron and Steel Engineer, 1999.

[11] I. Shpancer and W. Kinsner, "A study of a tension control system architecture for Manitoba rolling mills", Research Project Proposal 0037-002 (internal), 1983.

Current (A) 120

Speed (rpm) 240

 

 

100

 

235

 

 

80

230

 

 

60

 

225

 

40

 

 

220

20

 

 

215

0

 

 

-20

 

0           500         1000         1500        2000         2500         3000         3500

 

Time (s)

 

210

 

0           500         1000         1500         2000         2500         3000         3500

 

Time (s)

 

Current (A) 140