Non-time Reference Gait Planning and Stability Control for Bipedal Walking

In this increasingly aging society, the needs for robots to assist human activities in daily environments such as offices, homes, and hospitals are growing rapidly. In such environments originally designed for human beings, biped robots, which have almost the same mechanisms as a human, present many advantages than wheeled robots like obstacle avoidance capabilities for its possibility of discontinuous contact with the ground, which allows the robot to step over obstacles and climb stairs. Biped walking robots have been in the research and development phase and biped robotics field has attracted a growing number of researchers during the last decades. Since the great success of the biped robot P2 developed by Honda in 1996(Kazuo, et al, 1998), more and more researchers focus their studies on biped robot, and have achieved many progresses. Honda has developed P3 and ASIMO afterwards. The latest version ASIMO can walk smoothly like a human being. As the most famous researcher on biped robots, Waseda University has developed many prototypes, their latest biped robot WABIAN can even make emotional gestures (Hashimoto, et al 1998). Although Sony is a new comer in biped robot researches, the excellent performances of Sony Dream Robot series biped robots have won good reputations, the latest robot SDR-4X can walk, dance, even stand up by itself after falling down. As a joint research platform in Japan, HRP-2 has realized co-operations with human such as lifting a desk in cooperation with people (Tanie, et al, 1999). Although performances of those biped robots are exciting and impressive, progresses in theoretical analysis are far behind prototype developments, a stable biped walking remains a highly demanding task for its high degrees of complexity, coupling, highly nonlinear, and unstable. Generating a desired gait for dynamic locomotion of biped robots is one of the important research areas in the study of biped robots. The simplest method to generate a desired trajectory for a biped robot is called the inverted pendulum mode (Kajita, et al, 1995). It is based on the assumption that all the links of the biped robot but the hip link have a negligible mass, thus the hip link representing the sole mass of the biped robot, and that the biped robot contacts with the ground at a single invariant point on the sole in each cycle of the single-support phase. The trajectory obtained with the inverted pendulum mode, however, compromises locomotion stability due to the fact that the link masses, such as a foot, that are assumed to be negligible are not in fact negligible at all. An alternative method O pe n A cc es s D at ab as e w w w .ite ch on lin e. co m