Energy-Based Stability Measures for Reliable Locomotion of Statically Stable Walkers: Theory and Application

To plan safe, reliable walker motions, it is important to assess the stability of a walker. In this article, two basic modes of walker stability are defined and developed: stance stability and walker stability. For slowly moving, statically stable walkers, it is convenient to use the magnitude of the amount of the work required to destabilize a walker as a measure of the stability of that walker. Furthermore, as shown in this article, the com pliance of the walker and/or terrain can significantly affect the work necessary to destabilize the walker. Consideration of compliance and the two modes of walker stability leads to the definition and development of four energy-based stability mea sures : the rigid stance stability measure, the compliant stance stability measure, the rigid walker stability measure, and the compliant walker stability measure. (The rigid stance stability measure is identical to the energy stability margin reported in Messuri and Klein [1985].) Several examples are used to demonstrate the application and use of these stability measures in type selection, gait planning, and control of the walker. The outcome of the present work is a more complete approach to using stability measures to ensure reliable walker gait planning and control.