Emergence of three-dimensional quasi-passive dynamic walking by excitation of lateral rocking (Influence of rocking motion and physical characteristics on gait transition)

This paper tries to clarify how rocking motion and body structure effect on the emergence of walking and the changes of the gait such as walking speed and the length of stride. Humans naturally exhibit adaptive performance in various environments. Moreover, they are able to adjust the gait for their purposes. The adaptive locomotion is generated not only with leg swing motion, but also the lateral rocking of the body, rotation of the center of mass, etc. Most previous researches have mainly mentioned the direct drive of the legs. On the other hand, one previous research has indicated interesting motion observation that the body motion in lateral plane will get to a dominant factor in the phase of low speed walking. According to the previous result, we propose an idea that the walking can be generated by an excitation of lateral rocking of the body without direct actuations of legs. Therefore, in this paper, we especially focus our attention on three-dimensional quasi-passive walking provoked by the rocking motion of the robot body in lateral plane. After developing a robot with an oscillator that excites rocking motion of the robot body in lateral plane, we confirmed the emergence of walking in the experiment. Next, we investigated the gait difference by changing the parameters of the rocking motion (amplitude, period) and the robot body structures (length of the leg, offset of the legs to forward). The experimental analyses indicate that the walking speed, robustness and consumption of energy are mainly correlation to the period of lateral rocking and the offset of the legs to forward. In summery, an appropriate combination between the period of rocking motion and structures of the robot body leads to control of the gait.