Zappa, a Compliant Quasi-Passive Biped Robot with a Tail and Elastic Knees

Abstract

Bipeds are complex hybrid dynamical systems mixing both continuous and discrete-event phenomena (Hurmuzlu et al., 2004). The main characteristic of biped walkers is the abrupt kinematic change between the swing phase and the stance phase together with dynamical impacts. The main problem is how to achieve a rhythmical or periodical walk. Another difficulty of these robots is their high power requirement and, consequently, high energy consumption, which limits their autonomy. It can be attributed to the high number of actuated joints, and because energetic studies are not typically considered during the movement’s planning. Different studies focusing on the construction of locomotion controllers for completely actuated legged robots are found in the literature. These studies aremainly oriented to solve trajectory generation problems for the active control centered approach. In (Boeing & Braunl, 2004) the authors show there is an example of this methodology showing that an impedance control is better than the computed torque method. However, the conventional approach has been questioned by researchers inspired by biomechanical models (Kuo, 2007; McMahon, 1984). The discovery of McGeer about passive dynamic walking by building a biped without any motors or sensors (McGeer, 1990), opens the doors to a new design concept based on morphological considerations. Moreover, the interaction betweenmorphology and control is a topic of actual researches and debates in robotics (Pfeifer & Bongard, 2007). Therefore, exploiting the intrinsic passive dynamics has many advantages compared to the classical two-part methodology (trajectory generation and active controller). Two of them are the energy consumption reduction (the energetic cost is produced in step-to-step transitions) and the simplicity of control (low computational cost). Nevertheless, some theoretical and practical studies (Collins & Ruina, 2005) show that it is difficult to achieve the complex dynamics exhibited by humans and animals taking into account only the properties of simple passive-dynamic walking, but might help in the design of walking robots. In (Fumiya & Pfeifer, 2006) the authors show how to exploit the above mentioned passive properties of biped robots with the incorporation of sensors. 15