Reliable control during current loop failure using ETF for position servo system including disturbance observer

A reliable control method is proposed for multiple loop control systems. If a feedback loop fails (e.g., as a result of a sensor breakdown), the control system develops an unstable fluctuation. To cope with this problem, the proposed method uses an equivalent transfer function (ETF) for active redundancy compensation after loop failure. The ETF is used to maintain the transfer function of the entire system the same before and after loop failure. In this study, the characteristics of a reliable control system that uses an ETF were examined experimentally. A position servo system including a disturbance observer is used in the experiment. In case of feedback loop failure, the control system could not be stabilized using the disturbance observer alone; however, the ETF stabilized the control system after feedback loop failure.