Passivity based turning control of 3D biped robot with asymptotical stability

Once the concept of passive walking was appeared, control of biped robots based on dynamically stable periodic gaits around a stable limit cycle became of interest of many researchers and it has been further accelerated nowadays. The authors have previously shown that in addition to passive walking, a passive, biped walker could interestingly show asymptotically stable turning motion over a novel 3D surface called "helical slope". In this paper, based on passive turning concept, a control method would be offered which is effective for 3D biped robots. The approach is based on potential energy shaping that is usually applied for walking control. In the proposed method, asymptotically stable passive turning motions that are performed on a certain helical slope are projected to 3D motions over flat ground and along a circular path (which is the image of the helical slope on the ground). The biped model used in this study, is a 3D model of compass gait robot with flat feet and flexible ankles that could generated stable passive turning motions. The simulation results show the effectiveness of the proposed method as well.