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Stability Zones During Quiet Standing & Rapid Prototyping FES System for Walking and Grasping


T. Keller

Saitama, Japan, National Rehabilitation Center for Disabled.

The experiments performed in our laboratory revealed that able-bodied subjects use four different high-level control strategies to maintain stable quiet standing, and that there is a direct correlation between these control strategies and the position of the subject's center of pressure (COP). The overall COP area was divided into four zones: a high preference zone, a low preference zone, an undesirable zone and an unstable zone. Division of the COP surface into four distinct zones is a new concept which should enable researches designing standing prostheses to better understand the basic design requirements for such devices. Potential standing prostheses, that will be designed to provide stable and safe ``hand free'' quiet standing, should maintain the COP position in the high and low preference zones. A model that describes these four stability zones has been proposed. A rapid prototyping FES system was developed that allows a modular implementation of walking and grasping neuroprostheses. Different sensor systems for the control of the neuroprostheses and different control strategies can be tested and tuned on the same system. This concept is more flexible compared to other FES systems that are built with a fixed set of sensors and a limited number of control strategies. The rapid prototyping FES system consists of an eight channel constant current FES device for surface stimulation that is PC controllable, an eight channel data acquisition board and a closed-loop controller software programmed on a standard PC using LabVIEW. A graphical user interface allows a fast adjustment of all parameters, including the stimulation patterns, the sensor and controller settings. All parameters are stored in setup files and therefore allow a fast re-configuration of the neuroprosthesis to the individual subject's needs. The rapid prototyping FES system was used to design individual grasping or walking neuroprostheses for 9 SCI and 2 stroke subjects. In a second phase the individual settings were transferred to a portable FES system.

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Type of Publication:

(05)Plenary/Invited/Honorary Lecture

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