Balance Control of Humanoid Robot with Foot Rotation

Balance maintenance under unexpected environment is a key requirement for safe and successful coexistence of humanoid robots in normal human environments. The motion of a humanoid robot includes a phase where the stance foot rotates about the stance toe when the humanoid robot comes to a small object on the ground. The equation of motion has the form of an underactuated system in this phase. The objective of this study is to propose a control strategy for preventing the humanoid robot from tipping over. First, the dynamical model of robot in the sagittal plane is employed and the controllability of the robot is analyzed. Then, the controller can be designed based on Linear Quadratic Regulator (LQR) optimal control theory. Simulation result shows the effectiveness of the proposed method.