The human vestibular system senses linear and angular movements using inertial principles. It is an important sensory organ in human postural control. The availability of micro-mechanically produced inertial sensors, measuring acceleration and angular velocity, enables small tri-axial inertial sensor systems to provide movement information comparable to the human vestibular system. These sensors have high potential for application in human movement analysis.

The advantage of inertial sensing is that it enables movement to be assessed by taking measurements at a single point, without requiring a reference. The disadvantage is that several movement quantities are represented in one signal (e.g. inclination and acceleration), and these cannot generally be distinguished.

This paper reports progress in the development and application of movement sensors at the University of Twente and Roessingh Research and Development. A tri-axial accelerometer and tri-axial angular velocity sensor (i.e. a rate gyroscope) have been combined in a new inertial sensor, which measures forces acting on a single mass. Algorithms have been developed for optimal estimation of relevant movement quantities, on the basis of signals from a tri-axial inertial sensor. Applications for sensing ambulatory human movements using such sensors will be discussed.

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