8-DoF biped robot with compliant-links

Abstract

This paper proposes a new design of an 8-degree of freedom (DoF) biped robot with compliant links and its optimum trajectory generation for walking. The shanks of a biped are replaced by compliant links. Compliant links of different thickness are used to find optimum walking trajectory and the work done is compared for different cases. Compliant links are modelled using the pseudo-rigid body model (PRBM), in which a single compliant link is divided into two rigid links connected by a pin joint and a torsional spring at the joint. Gait trajectory is generated for continuous walking by defining the hip and swing foot ankle trajectories with respect to the stance-leg ankle. Different constraint conditions are taken into consideration to ensure continuity and smoothness of the walking trajectory in a straight path. The dynamic equations of motion of the bipeds are derived using the Euler–Lagrangian method and the work done for both rigid and compliant biped are obtained. The genetic algorithm (GA) is used to optimize the trajectory to minimize the work done. For dynamic balance of the biped, the zero-moment point (ZMP) method is used. By varying the thickness of compliant link and other gait parameters, various gait trajectories are simulated and compared based on the work done and balance. Experiments were carried out in which a biped robot with compliant links was made to follow the optimal trajectories and the experimental results are compared with simulation results.