Postural and gait stability of a planar five link biped by simulation

Postural and gait stability of a planar five-link model of a biped is considered. Equations of motion, in which external torques appear explicitly are derived by d´Alembert´s principle. Postural stability is achieved at arbitrary equilibrium points by open and closed loop torques in order to create the equilibrium point and to make the equilibrium point stable. Television recording of angles and angle rates of all five segments of a human in normal walk is taken and used as reference input to the system in order to generate the open and closed loop torques needed for locomotion. It is shown that one equilibrium point and one set of constant feedback gains suffice. It is also demonstrated that this method can be utilized to compute the forces at the joints and the components of the applied torques as functions of the state of the system. Simulations results of the nonlinear system with linear feedback and added disturbances are presented. The two main applications of this work are in the design of powered prostheses for the handicapped and, more importantly, in nondestructive testing to estimate feedback gains utilized by human beings in standing and in walking.