Design and analysis of output feedback force control in parallel turning

Abstract

Parallel machine tools (i.e. machine tools capable of cutting a part with multiple tools simultaneously but independently) are being utilized more and more to increase operation productivity, decrease set-ups and reduce floor space. Process control is the utilization of real-time process sensor information to adjust process parameters (e.g. feed, spindle speed) automatically in order to increase operation productivity and quality. To date, however, these two technologies have not been combined. This paper describes the design of an output feedback controller for a parallel turning operation that accounts for the inherent non-linearities in the force process. An analysis of the process equilibriums explains the system's stability behaviour for different design specifications and the reverse trajectory method is used to numerically determine the exact stability boundary. Effects of saturation on stability are also analysed, and from this sufficient conditions for global stability are obtained. Finally, the system is analysed for robustness to parameter uncertainties. Simulations and phase portraits are used to verify the developed theory.