Adaptive Control of Harmonic Drives Based on Virtual Decomposition

Harmonic drives are interesting for robotic applications due to their attractive properties such as high reduction ratio, compact size, low mass, and coaxial assembly. However, the high friction and the dynamics of the flexspline are the main issues that significantly challenge the control systems. In this paper, an adaptive controller capable of adaptively compensating the friction, while incorporating the dynamics of the flexspline, is developed in both joint torque and joint-position control modes. The virtual decomposition control approach allows the dynamics of harmonic drives to be controlled separately from the conventional dynamics of the robots. Adaptive friction compensation and flexspline dynamics based control are the two main contributions of this paper. The L₂/L_infin stability and the L ₂-gain-induced H_infin stability are guaranteed. Experimental results demonstrated in both time and frequency domains confirm the feasibility of the proposed approach