Development of stable and energy-efficient bipedal walking robots - challenges in stability analysis and stability criteria

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BACKGROUND: Stability is the primary requirement for bipedal walking. Two distinguished yet relevant stability criteria (Lyapunov's stability and transient stability) are often used, but suffer from two drawbacks: lacking a tool for Lyapunov's stability analysis and overly stringent transient stability criteria. Such drawbacks cause high energy consumption of bipedal robots and prohibit stability analysis of many engineering systems. It is paramount to address the above issues and to develop adequate methodologies for stability analysis. RESEARCH PROGRAM: My research focuses on developing constructive tools for Lyapunov's stability analysis and new transient stability criteria for energy-efficient bipedal robots. The concept of Lyapunov exponents will be extended for stability analysis of nonlinear engineering systems. To ensure the generality, three distinct physical systems, namely a passive walker, human subjects walking on the treadmill and a durability testing system of machinery, are selected for the research. A less stringent transient stability criterion will also be developed based on the concept of ground reference points and the extended virtual contact surface. A passive dynamic walker, a simple mechanism, which can walk on a ramp remarkably similar to human gait without actuators, will be used. Such natural gait is stable and energy-efficient. A passive walker is more suited for developing new transient stability criteria than using human subjects in that it is simple in structure and has low measurement errors. Both theoretical and experimental approaches will be used. SIGNIFICANCE: The research can directly impact on the development of stable and energy-efficient bipedal walking robots. Its impact is beyond developing bipedal robots in that it advances the stability analysis and control of many real-world engineering systems.