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Rotational Stability Index (RSI) point: postural stability in planar bipeds

Published online by Cambridge University Press:  12 October 2010

Goswami Dip  and
Vadakkepat Prahlad
Goswami Dip*
Affiliation:
Department of Electrical and Computer Engineering, National University of Singapore, 4 Engineering Drive 3, Singapore117576. E-mail: prahlad@ieee.org
Vadakkepat Prahlad
Affiliation:
Department of Electrical and Computer Engineering, National University of Singapore, 4 Engineering Drive 3, Singapore117576. E-mail: prahlad@ieee.org
*
*Corresponding author. E-mail: dip.goswami@ieee.org
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Summary

The postural stability of bipedal robots is investigated in perspective of foot-rotation during locomotion. With foot already rotated, the biped is modeled as an underactuated kinematic structure. The stability of such biped robots is analyzed by introducing the concept of rotational stability. The rotational stability investigates whether a biped would lead to a flat-foot posture or the biped would topple over. The rotational stability is quantified as a ground reference point named “rotational stability index (RSI)” point. Conditions are established to achieve rotational stability during biped locomotion using the concept of the RSI point. The applicability of the RSI point is illustrated through experimentation for the landing stability analysis of the bipedal jumping gaits.

The traditional stability criteria such as zero-moment point (ZMP) [M. Vukobratovic and B. Borovac, “Zero-moment point – thirty five years of its life,” Int. J. Humanoid Robot. 1(1), 157–173 (2004)] and foot-rotation indicator (FRI) [A. Goswami, “Postural stability of biped robots and the foot-rotation indicator (FRI) point,” Int. J. Robot. Res. 18(6), 523–533 (1999)] are not applicable to analyze biped's postural stability when foot is already rotated. The RSI point is established as a stability criteria for planar bipedal locomotion in presence of foot rotation.

Keywords

Internal dynamicsRotational stabilityRotational-stability index (RSI) point
Type
Articles
Information
Robotica , Volume 29 , Issue 5 , September 2011 , pp. 705 - 715
Copyright
Copyright © Cambridge University Press 2010

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