Design And Implementation Of Continuous Annealing Furnace Temperature Control System

Heat treating is the controlled heating and cooling of a material to achieve certain mechanical properties,such as hardness,strength and the reduction of residual stresses.Many heat treating processes require the precise control of temperature over the heating cycle.Accurate control of temperature is difficult because temperature measurement devices are strongly affected by reflected radiation in the furnace cavity.The furnace is often operating during transient temperature conditions,as control actions take effect very slowly compared to the rate of change of operational targets.The temperature controllers in operation have been developed using conventional control methods.There are,however,many situations where these controllers are not properly tuned and there is heuristic knowledge available on how to tune them while they are in operation.Because PID controllers are often not properly tuned,there is a significant need to develop methods for the automatic tuning of PID controllers.While there exist many conventional methods for PID auto-tuning,here we will strictly focus on providing the basic ideas on how to construct a fuzzy PID auto-tuner.In the thesis,it is proposed different methods of controlling the furnace temperature,including using cascade PID in NOF and RTF furnace.Then,a fuzzy logic controller structure with an efficient realization and a small rule base that can be easily implemented in existing industrial controllers was proposed.It was demonstrated the potential of FLC in hardware test in an industrial setting.It is achieved by implementing,in PLC,a classical control strategy and an adaptation mechanism to compensate for the dynamic changes in the system.The proposed fuzzy PID was applied to the temperature process,and the performance and robustness improvements were observed in different cases.Furthermore,the stability of the control system is investigated.