A joint torque sensing technique for robots with harmonic drives is proposed. Elasticity of harmonic drives is utilized to measure the joint torque. The technique provides joint torque sensing without reducing the stiffness of the robot and changing the mechanical structure of the joints. A finite-element analysis of flexsplines, which are flexible thin cups made from steel in harmonic drives, is performed. The analysis shows that a special configuration of strain gauges on the flexspline has to be employed to eliminate errors in sensor information due to rotations of wave generators. Characteristics of the torque sensor are examined experimentally. The linearity and the dynamic response are almost the same as those of a conventional sensing technique. Both theoretical and experimental investigations support the validity of the proposed sensing technique.
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