Development of stiffness changeable multijoint cervical structure with soft sensor flesh for musculo-skeletal humanoids

In order to obtain adaptive motions from external forces in environments, a multijoint and soft structure is important for humanoids. Because adaptive motions represent response capabilities interacting with environments and contribute to safety aspects in the process of fitting in human society. Moreover, it is significant for humanoids to realize these motions not only in their hands but also in their whole bodies that include heads and necks. However, most neck structure of humanoids have two or three D.O.F. to behave as pan and tilt functions of cameras mounted in heads. From a point of realizing these motions, it doesn´t have enough range of movement. Furthermore, adapting to physical impacts and contacts from environments is almost impossible because many humanoids don´t have mechanical joint-stiffness changers or soft flesh covered with their whole bodies. To solve this problem, we develop a new musculo-skeletal neck structure having a function of mechanical stiffness adjustment as a inside soft structure and sensor flesh as a outside soft structure. In this paper, we describe the design of a musculo-skeletal neck structure and the results of movement experiments using a prototype of the proposed neck mechanism.