Backlash vibration suppression in torsional system based on the fractional order Q-filter of disturbance observer

Abstract

In this paper, a fractional order Q-filter 1/(Ts+1)/sup /spl alpha// is introduced to substitute the integer order Q-filter 1/(/spl tau/s+1)/sup n/ used in conventional disturbance observer for speed control of torsional system. The theoretical analysis and experimental results show that changing the Q-filter's order fractionally can give a more effective way to adjust control system's frequency and time responses than just tuning it among integer orders. The tradeoff between stability margin loss and the strength of vibration suppression is a common problem in torsional system control. By introducing fractional order control (FOC) approach, control system can be designed more straightforwardly since control system's frequency responses can be altered between integer order control (IOC) system's continuously, while less control parameters are needed to be decided. Design process and experimental results demonstrate that an "EASY & STRAIGHTFORWARD DESIGN" can be achieved by introducing FOC control design concept. For implementation of the fractional order Q-filter, broken-line approximation method is applied. Even the realization issues for fractional order controllers are somewhat problematic. Experiment results show that the controllers can actually be realized quite acceptably.