ARX/ARMAX Modeling and Fractional Order Control of Surface Roughness in Turning Nano-Composites

Control of machining systems is important to ensure manufacturing quality. In this paper, multi input single output system of surface roughness generated during turning of Al/Mg/CNT composites was identified by ARX and ARMAX models of varying orders. The best of identified models were selected for control based on FIT, MSE, order, number of parameters and residuals. FPID controller was employed on the selected models to control output surface roughness. Of the three inputs, one was manipulated at a time keeping the other two constant at their mid levels based on experimental design. FPID parameter λ was also varied for improving controller performance. ARMAX model obtained better time domain characteristics as compared to ARX model. This result was especially evident for manipulated variables of feed rate and depth of cut, which effect surface roughness the most during machining.