Human Body Modeling for Ground Contact Force Estimation of RoboWalk

Abstract

RoboWalk is a lower limb rehabilitation robot for Human body weight assistance. To achieve a proper design of RoboWalk, there is a need to understand the dynamics of human and foot contact forces with the ground that is the focus of this paper. In fact, an important component of human-Robo Walk forward dynamics simulation is foot-ground contact modelling. Different models have been proposed to simulate the contact of the foot with the ground. In this study, the dynamic equations of human body is developed with 19 degrees of freedom, while three points of collision with the ground are considered for each foot. Next, the kinematics information obtained from the experimental data are introduced to the dynamical equations, and the joint torques are estimated by solving the inverse dynamics of the human model. The results are compared to the experimental data for model validation. However, it is assumed that the numerical value of the foot contact model parameters are not available, so the pelvis is constrained in such a way that the human model foot does not hit the ground. Therefore, these uncertain parameters does not affect the validation results. Next, a model is selected from the existing models to express the foot contact behavior with the ground, while such models should provide stable walking with selecting the appropriate parameters. To determine the shear and normal contact force, numerical values of the parameters are required while these values depend on the shoe and the ground material and surface. Then, the path traveled by the pelvis in the human dynamic model was compared with the path of the actual pelvic motion and their difference was used to form a cost function to determine the parameters. In the next step, by choosing appropriate values for the contact parameters of the foot and the springs and the damping of the toe joint, the path of the pelvis becomes closely identical to the actual pelvis motion. Finally, after the human gait stabilized, the developed dynamics model is compared with the experimental data.