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Author

Kang, Sang Hoon
Robotics and Rehab. Engineering Lab (R2EL)
Research Interests
  • Rehabilitation Robotics & Mechatronic Tools, Biomechanics for Rehabilitation, Human Limb Impedance Estimation, Assistive and Healthcare robotics, Robust Motion/Force Control

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Stochastic estimation of human arm impedance under nonlinear friction in robot joints: A model study

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Title
Stochastic estimation of human arm impedance under nonlinear friction in robot joints: A model study
Author
Chang, Pyung HunKang, Sang Hoon
Keywords
Arm impedance; Dynamic compliance; Friction; Impedance control; Stochastic estimation
Issue Date
201005
Publisher
ELSEVIER SCIENCE BV
Citation
JOURNAL OF NEUROSCIENCE METHODS, v.189, no.1, pp.97 - 112
Abstract
The basic assumption of stochastic human arm impedance estimation methods is that the human arm and robot behave linearly for small perturbations. In the present work, we have identified the degree of influence of nonlinear friction in robot joints to the stochastic human arm impedance estimation. Internal model based impedance control (IMBIC) is then proposed as a means to make the estimation accurate by compensating for the nonlinear friction. From simulations with a nonlinear Lugre friction model, it is observed that the reliability and accuracy of the estimation are severely degraded with nonlinear friction: below 2. Hz, multiple and partial coherence functions are far less than unity; estimated magnitudes and phases are severely deviated from that of a real human arm throughout the frequency range of interest; and the accuracy is not enhanced with an increase of magnitude of the force perturbations. In contrast, the combined use of stochastic estimation and IMBIC provides with accurate estimation results even with large friction: the multiple coherence functions are larger than 0.9 throughout the frequency range of interest and the estimated magnitudes and phases are well matched with that of a real human arm. Furthermore, the performance of suggested method is independent of human arm and robot posture, and human arm impedance. Therefore, the IMBIC will be useful in measuring human arm impedance with conventional robot, as well as in designing a spatial impedance measuring robot, which requires gearing. © 2010 Elsevier B.V.
URI
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DOI
http://dx.doi.org/10.1016/j.jneumeth.2010.02.021
ISSN
0165-0270
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