J. Van Doornik and T. Sinkjær (Denmark)
parallel manipulator, human gait analysis, posturography,robotics
A hydraulically actuated platform with four degrees of freedom was designed and implemented to be able to apply controlled perturbations either in freely walking or quietly standing human subjects. The platform surface measures 60x60 cm. The platform has four degrees of freedom: translation along the longitudinal and sagittal axis, and rotation around the sagittal and transversal axis. To apply plantar flexion or dorsi flexion perturbations, the center of rotation can be preset to align the ankle joint. The ranges of motion are limited to 10 cm for translational perturbations, or 10 for rotational perturbations. The platform is actuated by a construction of four parallel hydraulic cylinders, each controlled by their own PID loops. Between platform surface and surrounding floor, there is necessarily some space to allow for the motions. This space has been minimized to allow for subjects walking over the platform with only one foot stepping on it. The remaining space has been covered with a construction of metal plates, which is designed to follow the platform movement passively, and at the same time is able to carry the weight of one person. Initial experiments have been successfully carried out on both walking and standing subjects. The system has proven to be stable in operation and produces highly repeatable perturbations.
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