Vibration based under-actuated bounding mechanism

Abstract

Today's robots are able to perform very limited locomotion tasks by consuming high energy although animals are able to carry out very complicated but stable locomotion tasks using less control inputs and energy. Therefore, it is important to understand the principles of animal locomotion in order to develop efficient legged robots. This paper presents a U-shape visco-elastic beam mechanism that is able to run like a bounding animal when it is actuated by a simple pendulum at the torsional resonance frequency of the elastic body. A simple physical model has been developed to investigate the dynamics of the mechanism and the natural body dynamics of quadrupeds. In the mechanism, a small rotating mass was attached to a DC motor which was mounted on the center of the spine. When this motor is actuated at around the torsional resonance frequency of the elastic body, the robot starts to move and it exhibits a self-organized locomotion behavior. The self-organized locomotion process of the robot does not require any central authority, sensory feedback or external element imposing a planned motion. Comparing the bounding locomotion of the beam mechanism with those of well-known quadrupeds such as a horse, greyhound and cheetah, it can be concluded that the pendulum-driven U-shaped visco-elastic beam displays kinematic behavior similar to a horse, in terms of both experimental and simulation results. Interestingly, this bounding locomotion occurs only if the shape ratio and the actuation frequencies of the beam are close to those of the fastest quadrupeds.