Page - 160 - in Adaptive and Intelligent Temperature Control of Microwave Heating Systems with Multiple Sources

5. ExperimentalResults rubbersetup, it isreasonabletobelievetheycanachieveasimilartem- peraturehomogeneityusingtherealCFRPprepregs. The target temperature curve defined in the experiments is shown by figure 5.22. Consideringthesafety issueandthereliabilityof thevac- uumbagging, themaximumtarget temperature isset tobe100◦Cand the temperature increasing rate is 8◦C/min. The target temperature curve is defined as shown in figure 5.22, which is similar with the target temperaturecurveusedinrealCFRPcuringprocess [PPW+02]. A typical control performance of PID is shown in figure 5.23. The control period used in the PID controller is ∆t= 1.5 s. In figure 5.23, the first temperature T1 is used as the controlled temperature. For the controlled temperature T1, it can be perfectly controlled by the PID controller and it follows the target temperature curve closely during the entire heating process. However, the problem for the PID con- troller is that all other temperatures are not controlled at all. All dif- ferent temperaturecurveshavethesamechangingtrendandthetem- perature differences between each other are almost constant during the flat-temperature period. Although the final temperature window ∆T1and∆T2 (temperaturedifferencebetweenthemaximumandthe minimum temperatures) in the end of both flat-temperature periods (a)Workpieceusedin theexperiment. + + + + + T1 T2 T3 T4 T5 (b)Measuredtemperatures. Figure5.21. Pictureof theworkpieceandmeasuredtemperatures. 160