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

A reliable control method is proposed to cope with an unstable fluctuation caused by a loop failing in a multiple-loop control system. In this study, reliable control was applied to a Position servo system that was made to examine the reliable control method in an industrial machine and study its characteristics. The system uses an equivalent transfer function (ETF) for active redundancy compensation after a loop failure and has a fault detection and isolation scheme for the loop failure. The principle of the transfer function is that when a sensor is broken down and the sensor information cannot be acquired, the transfer function of the system differs from a transfer function of the normal system, hence the compensator (the ETF) that conforms the transfer function of the failing system to the transfer function of the normal system stabilizes the failing system. The ETF compensates for the failure of a system using software such that the failing system continues to be in control by switching the normal control program to the control program including compensation for the failing. In this study, the system including the ETF is analysed experimentally.