Reliable Control Using Equivalent Transfer Function for Position Servo System

In this paper, a reliable control method is proposed for a position servo system using multiple loops. The position servo system has two minor-loops which are a speed loop and a current loop. If one minor feedback loop fails, such as a case of the speed sensor break down, the position servo system becomes unstable. To cope with this problem, the proposed method uses an equivalent transfer function (ETF) as an active redundancy compensation after the loop failure. The ETF is designed so that it does not change the transfer function of the whole system before and after the loop failure. Therefore, the stability of the position control system using this proposed method is guaranteed even if the speed feedback loop fails or the current feedback loop fails. The effectiveness of this proposed method is confirmed by the experimental results