An overview of the underactuated biped robots

This paper presents an overview on underactuated biped robots. Firstly, background, latest research and characteristics of underactuated biped robot are introduced. Secondly, the model of underactuated biped walking system is described. And then the stability criterion based on hybrid zero dynamics theory and the Poincaré map is discussed. Meanwhile, commonly used methods for off-line gait planning and control strategies are analyzed. Finally, several open problems need further research and the development directions are indicated and discussed.