Non-restricted measurement of walking distance

Vertical walking distance is discussed. The horizontal distance is estimated by using the three dimensional acceleration of the subject´s toe. Considering the movement of the foot, it is assumed that only the pitch angle of the foot changes and that the velocity of the foot is never negative. A three dimensional accelerometer is fixed to the subject´s toe and measures the acceleration during the swing phase of the foot. A piezoelectric gyro is used to estimate the angle of the foot and to calculate its horizontal acceleration. The horizontal distance is obtained by integrating the horizontal acceleration twice each step. The vertical distance is calculated by integrating the change of atmospheric pressure during ascent or descent. A band pass filter is applied to reject natural changes of the atmospheric pressure and sensor noise. The integration of the output of the filter produces a value corresponding to the vertical distance. Experiments were performed in a horizontal corridor and on some stairs. The results show that the error of the horizontal distance estimated is less than 5.3% and 0.0% on average, and the vertical distance is less than 11.1%