Robust control of multistage printing systems

Printing errors (e.g. doubling) in multistage printing machines are mainly caused by web tension fluctuations, which arise from excessive rotation non-synchronization errors among the driven rollers in different stages (units). Therefore, the critical task in printing quality control is to attenuate web tension variations. In this paper, a robust H∞ control strategy is proposed to attenuate tension fluctuations when the system is subject to disturbances and variations in speed or other operating conditions. Three system robustness properties are analyzed by using structured singular value analysis (μ-analysis). A systematic investigation is taken to analyze the impacts of different parameter variations on system robustness, with a purpose of providing a reference for achieving robust stability in a multistage printing system. The effectiveness of the proposed robust H∞ controller is evaluated by both simulation and experimental tests.