Simulation Study on Acquisition Process of Locomotion by Using an Infant Robot

Abstract

Locomotion is one of the basic functions of a mobile robot. Using legs is one of the strategies for accomplishing locomotion. The strategy allows a robot to move over rough terrain. Therefore, a considerable amount of research has been conducted on motion control of legged locomotion robots. This chapter treats the motion generation of an infant robot, with emphasis on the emergence of crawling locomotion. In the future, a walking robot that can carry out various tasks on unstructured terrain will be required. The walking robot is required to achieve real-time adaptability to a changing environment. However, the mechanism from which the adaptive motion pattern emerges is not clear. Recent biological research and psychological research on acquisition of motion have made great contributions and have given crucial hints as to how to overcome such problems. During spontaneous motion, such as crawling or straight walking, a lot of joints and muscles are organized into a collective unit to be controlled as if this unit had fewer degrees of freedom, but at the same time to retain the necessary flexibility for a changing environment (Bernstein, 1967). Gesell pointed out the principles of motor development in human infants (Gesell, 1946). According to that research, some developmental principles in the acquisition of ontogenetic activities can be observed. One is directional trends in the acquisition of ontogenetic activities; others are functional asymmetry in ontogenetic activities and self-regulation in ontogenetic activities. In addition, various studies have been made on the acquisition of motion especially that of locomotion (Newell, 1990; Thelen et al.,1986,1987; Clark et al.,1988; Burnside, 1927; Adolph, 1997; Savelsbergh, 1993). Moreover, the development of motions has been proposed as being a dynamic interaction between the nervous and musculo-skeletal systems. Rhythmic motion is generated by a central pattern generator (CPG) in the spinal cord (Grillner, 1977,1985). Sensory feedback from the contact sensors or joint angle sensors tunes the oscillation condition of the CPG and makes the locomotion stable in limit cycle (Taga, 1991,1994). Furthermore, biological researches on mode transition of the locomotion according to the situation or variance of the environment are actively going on (Ijspeert, 2001). Based on these biological facts, research has been conducted to clarify the mechanism for humans' acquisition of motion (Yamazaki, 1996; Hase, 2002; Ni et al., 2003; Endo et al., 2004, Kuniyoshi et al., 2004).