Impact modelling and analysis of the compliant legged robots

Abstract

The dynamics of the compliant legged robots are commonly characterized by the spring loaded inverted pendulum model. In this article, a new model is presented for the impact of the compliant legged robots. Compared with the spring loaded inverted pendulum model, the new model provides a means to take into account the factors such as the sliding of the terminal, the vibrations of the leg with distributed compliance and variation of the nonlinear contact force. The effectiveness of the model is validated by the finite element program LS-DYNA from the velocity and energy point of view. Based on the method used, the influences of the parameters, such as the incident angle, width, thickness and Young’s modulus of the flexible leg on the dynamic characteristics of the robot, are analysed. It is found that the post-impact vertical velocity of the robot decreases with the increasing incident angles, and increases approximately linearly with the width and thickness, while the variation of Young’s modulus of the flexible leg has little effects on it. The same is true of the energy loss ratio during the impact. All the parameters investigated are more intuitive than the stiffness described in the spring loaded inverted pendulum model and can be utilized directly for the optimization design and locomotion control of the compliant legged robots. In addition, the vibrations and multiple impacts can be predicted by the proposed model to reduce the energy loss.