Force sensing is an important part of a motion-copying system. To achieve the high performance of the control system, high quality of force sensing is required. This paper focuses on suppressing harmonic disturbances in the force estimation to improve the performance of force sensing. A friction-free disturbance observer with a dither signal is applied for both motion-saving and motion-loading systems. The dither signal reduces the friction effect on force estimation and the friction-free disturbance observer eliminates the oscillatory signal on force estimation. Moreover, the friction-free disturbance observer achieves effective harmonics suppression in force estimation. All control algorithms are implemented in FPGA to achieve short sampling period, and enable a wider force sensing bandwidth. The effectiveness of the proposed method is verified by experimental results. © 2013 IEEE.