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Improving backdrivability in geared rehabilitation robots

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Abstract

Many rehabilitation robots use electric motors with gears. The backdrivability of geared drives is poor due to friction. While it is common practice to use velocity measurements to compensate for kinetic friction, breakaway friction usually cannot be compensated for without the use of an additional force sensor that directly measures the interaction force between the human and the robot. Therefore, in robots without force sensors, subjects must overcome a large breakaway torque to initiate user-driven movements, which are important for motor learning. In this technical note, a new methodology to compensate for both kinetic and breakaway friction is presented. The basic strategy is to take advantage of the fact that, for rehabilitation exercises, the direction of the desired motion is often known. By applying the new method to three implementation examples, including drives with gear reduction ratios 100–435, the peak breakaway torque could be reduced by 60–80%.

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Authors and Affiliations

  1. Department of Biomedical Engineering, The Catholic University of America, Washington DC, USA

    Tobias Nef & Peter Lum

  2. Center for Applied Biomechanics and Rehabilitation Research, National Rehabilitation Hospital, Washington DC, USA

    Tobias Nef & Peter Lum

Authors
  1. Tobias Nef
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  2. Peter Lum
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Correspondence to Tobias Nef.

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Nef, T., Lum, P. Improving backdrivability in geared rehabilitation robots. Med Biol Eng Comput 47, 441–447 (2009). https://doi.org/10.1007/s11517-009-0437-0

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  • DOI: https://doi.org/10.1007/s11517-009-0437-0

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