7.1 Reaction forces at the foot supports during bipedal stance

During bipedal stance, Ergoniza Intelligent considers between two and four active contact points between the feet and the floor. The number depends on whether effective contact exists at the heel, the metatarsal area, or both parts of each foot.

For static equilibrium to exist, the resultant of the reactions at the supports must be equal and opposite to the resultant of body weight and the external forces. In addition, the sum of the moments produced by all forces and external moments must be zero. The position of the center of pressure already incorporates the effect of these external actions; therefore, the resultant of the vertical reaction components must pass through that point. When no external loads, forces, or moments are applied at the hands, the center of pressure coincides with the vertical projection of the body center of mass.

When four contact points exist, the equilibrium equations alone do not determine a unique distribution of the reactions: four vertical components remain unknown, but there are only three independent equilibrium conditions. Ergoniza Intelligent completes the system using the geometric criterion described in the following sections. When fewer contact points exist, the procedure is adapted to the available supports.