Derivation of Floor Reaction Force by Estimation of Equivalent Acceleration Using Frequency Analysis

Abstract

The purpose of this study is to estimate floor reaction forces from measured body part accelerations. A three-dimensional motion analysis system is used for the measurement. In the proposed method, equivalent acceleration is used to derive the floor reaction force. The equivalent acceleration is derived from the equilibrium relationship between the inertial force of the whole body and the floor reaction force. In other words, the equivalent acceleration is the floor reaction force that is made dimensionless by dividing the floor reaction force during walking by the whole body mass. To estimate the equivalent acceleration, a motion mode function that represents the relationship between the acceleration of each measured body part and the equivalent acceleration is created in advance by frequency analysis. Once the equivalent acceleration is estimated, the floor reaction force can be derived by a simple force balance calculation. Therefore, it is possible to estimate the floor reaction force using only the acceleration of one body part. Results of walking experiments, the equivalent acceleration was estimated from the acceleration of the head, and the floor reaction force could be derived with high accuracy.