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Modeling of a closed-loop controlled laser machining process with different control strategies

In designing classical controllers it is necessary to assume that the parameters of the system are reasonably well known. However the ablation process involves inherent nonlinearities and significant uncertainties in the model parameters, which are one of the main problems for designing an appropriate controller. Nonlinearities occur e.g. due to the chemical processes or due to the changing the absorption or the gas flow. The concentration of added oxygen to the assisting gas stream influences the system behavior significantly. It will be shown that the nonlinearities depend on the process parameters. A simplified nonlinear process model based on an analytical investigation is presented and discussed. To get a glimpse of the time constants, nonstationary investigations are carried out. The best way to control such a complex nonlinear system is to use an input-output map. This can be settled with an experimental off- loop identification or by fuzzy inference. A fuzzy controller itself has a nonlinear behavior and allows designing an appropriate controller without any mathematical model of the process.