Non-Restricted Measurement of Distance during Level Walk

Abstract

Non-restricted and precise measurement of horizontal displacement during walk is discussed. Walking velocity is derived by the integration of horizontal acceleration which is measured by a sensor system attached to the subject's toe. The walking distance results from the integration of the walking velocity. The sensor system consists of a three dimensional accelerometer and a ceramic gyro. The accelerometer measures three dimensional acceleration of the toe and the gyro senses the angular velocity of pitching angle of the sensor system. The axis of the accelerometer pitches and yaws during walk. Pitching of the accelerometer generates the mixture of the acceleration of gravity to the measured acceleration and causes error in the integrated data. The angle of the sensor system is measured by integrating the angular velocity derived from the gyro and is used to estimate the horizontal acceleration corresponding to the axis of the accelerometer. Although the yawing is caused by the installation of the sensor system and the rotation of the foot, the size of the horizontal acceleration projected to the horizontal plane is hardly affected. The integration of the horizontal acceleration is performed in every stance phase. The integral constant of the horizontal velocity must be zero during the stance phase and that of the angle of the sensor system is derived from the horizontal acceleration. Experimental results show that the difference between the real distance that subjects walked and the estimated one is 0.2[%] for seven subjects on average. The estimated distance is hardly affected by careless placement of the sensor system to the foot and abnormal walk such as fixed leg or shuffling.