Multibody Simulation Model of Human Walking

Abstract A three-dimensional simulational model of a human walking is presented. The biped is anthropomorphic, i.e., its inertial and kinematical properties are similar to human ones. The biped consists of eight rigid bodies. Each leg consists of three parts: thigh, shank, and foot. The trunk is modeled as two rigid bodies connected by a revolute joint. The inertia properties of head and arms are included in trunk properties. Each leg has 7 degrees of freedom. The whole modelled biped has 21 degrees of freedom. The impact and friction effects are considered in the ground reaction force modeling. The ground is represented by a flat, rigid surface. The normal to the ground component of reaction force depends on penetration of the foot into the ground and on the velocity of this penetration. The tangential reaction is represented in terms of a pseudo-Coulomb friction model (in this model of friction there is no stiction phase, i.e., the bodies are moving relative to each other at a negligibly small velocity). The direction of friction force depends on the relative movement velocity; the magnitude depends on the friction coefficient, the normal force magnitude, and also (nonlinearly) on the relative velocity. The direct dynamic problem is solved. Human gait patterns, derived from measurements of human walking, are used to calculate the necessary driving torques. A simple closed-loop control algorithm for stabilizing the motion is applied. The control system of the biped is not engaged in the planning of the trajectory; this task is realized following the gait pattern. The main task of the control system is to modify slightly and instantaneously the prescribed gait to prevent the biped from losing stability. To account for the elasticity of human tissues, so-called wobbling masses are introduced to the model. Both rigid body and wobbling mass models are validated by comparing obtained results of simulations with measurements of human walking. Advantages and disadvantages of the direct dynamics approach to human walking analysis are discussed.