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Title:Impedance Control as an Emergent Mechanism from Minimising Uncertainty
Authors: Djordje Mitrovic ; Stefan Klanke ; Rieko Osu ; Mitsuo Kawato ; Sethu Vijayakumar
Date:Feb 2009
Publication Type:Other Publication Status:Other
Efficient human motor control is characterised by an extensive use of joint impedance modulation, which is achieved by co-contracting antagonistic muscle pairs in a way that is beneficial to the specific task. While there is much experimental evidence available that the Central Nervous System (CNS) employs such an impedance control strategy only few computational models of impedance control have been proposed so far. In this paper, we study the computational aspects of the generation of joint impedance control in human arm reaching tasks and we develop a new model of joint impedance control for antagonistic systems. We formulate an actor's goal of arm reaching by optimising a cost function that accounts for maximal positional accuracy and minimal energy expenditure. To account for shortcomings of previously presented optimal control models, that fail to model impedance control, we employ the concept of learned internal dynamics models in conjunction with a stochastic arm simulation model, that exhibits realistic signal dependent noise-impedance characteristics. When using this stochastic arm model for dynamics learning with a locally weighted learning algorithm, the produced noise or kinematic variability reflects the prediction uncertainty on the level of the internal model. Introducing this information into the stochastic Optimal Feedback Control (OFC) theory reveals that impedance control naturally emerges from an optimisation process that minimises for model prediction uncertainties, along with energy and accuracy demands. We evaluate our method in single-joint simulations under static reaching conditions as well as in adaptation scenarios. The results show that our model is able to explain many well-known impedance control patterns from the literature, which supports our impedance control model as a viable approach of how the CNS could modulate joint impedance.
2009 by The University of Edinburgh. All Rights Reserved
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Bibtex format
author = { Djordje Mitrovic and Stefan Klanke and Rieko Osu and Mitsuo Kawato and Sethu Vijayakumar },
title = {Impedance Control as an Emergent Mechanism from Minimising Uncertainty},
year = 2009,
month = {Feb},

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