A motion-copying system is characterized by its ability to preserve and reproduce the motions of a human operator. The performance of a motion-copying system based on bilateral control is affected by friction and harmonic disturbances. To improve the performance of this system, we propose a friction-free disturbance observer with a dither signal for both motion-saving and motion-loading systems. The dither signal reduces the effect of friction, while the friction-free disturbance observer suppresses oscillatory disturbances in force estimation. Moreover, the friction-free disturbance observer achieves effective harmonic disturbance suppression in force estimation. All control algorithms are implemented in a field-programmable gate array to achieve a short sampling period that reduces the controller execution time and enables a wider force-sensing bandwidth. The effectiveness of the proposed method is verified by experimental results.
2014 The Institute of Electrical Engineers of Japan