Accuracy improvement of built-in torque sensing for Harmonic Drives

Built-in torque sensing for Harmonic Drives is attractive since it maintains mechanical characteristics of the gear while providing detection of the transmitted torque. Torque sensing by using strain gauges has been studied, but is not widely used yet due to a relatively high signal fluctuation, which is generated by the gear operation. Characteristics of the signal fluctuation are analyzed in this paper, and a method to effectively compensate the signal fluctuation is proposed. The signal fluctuation is perfectly compensated by adjustment of the strain gauge sensitivities. A minimum number of strain gauges needed to compensate the signal fluctuation is derived. The experimental result with three strain gauges compensating the basic frequency component of the signal fluctuation is shown.