Ultracompact Joint Torque Sensor Units With Enhanced Resolution for Collaborative Robots

摘要

Measuring accurate force/torque is a key factor for the cooperative robot to realize human–robot collaboration tasks. However, integrating torque sensors into robot joints is still a challenge due to limitations including size, cost, and mismatched communication protocol. Moreover, the crosstalk errors from undetermined external forces and the sinusoidal effect from the harmonic drive (HD) make it difficult to measure torque accurately. This article proposed ultracompact joint torque sensor (JTS) units, addressing the contradiction of the cooperative robot to realize high-resolution force sensing while ensuring proper stiffness. To achieve these goals, a novel spoked structure with double holes is proposed to increase strains and improve stress concentration. Meanwhile, an optimization model is formulated to enhance the resolution with the desired stiffness. In addition, the torque ripple elimination method is introduced, which can properly handle the crosstalk suffered from the HD and thus accurately measure the interest torque. Finally, three sizes of JTS with different loads were implemented with the feature of modularization, lightweight, low cost, and easy to manufacture. Dynamic calibration was applied to a proposed JTS and the performance was also experimentally evaluated. Experimental results showed that the prototype can accurately measure the torque of interest in the range of 170 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{N}\cdot \text{m}$ </tex-math></inline-formula> while eliminating crosstalk, and the torque resolution of the small, medium, and large JTS is 0.02, 0.05, and 0.1 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{N}\cdot \text{m}$ </tex-math></inline-formula> , respectively, under the premise of ensuring the stiffness. These results and economic costs can promote the application of JTSs in collaborative robots.