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

In this paper, a fractional order Q-filter 1/(Ts+1)^α is introduced to substitute the integer order Q-filter 1/(τs+1)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.