عنوان مقاله [English]
A mechanical system is called a walker if it has multiple contact points with the ground, with which they regularly connect and disconnect to obtain a displacement of the whole body. The major problem of the walker system is balance maintenance. When the system has two feet, balance maintenance would be more complicated. A humanoid robot is one example of bipedal systems. So far, many studies have been carried out on the balance maintenance of humanoids, and different criteria have been presented, such as; Center Of Gravity (COG) and Zero Moment Point (ZMP). The main condition of balance is placing the COG or ZMP in a specific area called the stability region. In some studies, the stability region has been stated as being a convex hull of the contact points of the feet. In this method, a polygon with minimum sides is specified as the stability region, which contains all the contact points. In other studies, the stability region has been defined as a maximum polygon, which contains the soles. Also, in other studies, the stability region has been obtained using equations of motion. In these studies, the stability region has been considered an obvious subject or has been presented complicatedly. In this paper, a new and simple method is presented to obtain the stability region. At first, the equations of equilibrium for a humanoid robot are considered to obtain the main relation for description of the stability region. Also, the contact forces are calculated using the Coulomb friction. Then, the stability region for the general position of the legs is achieved. In order to evaluate the obtained stability region, the kinematical parameters of a humanoid robot are considered using a simulated model in Visual Nastran software.