Online biped walking pattern generation for humanoid robot KHR-3(KAIST Humanoid Robot-3: HUBO)

This paper describes an algorithm about online walking pattern generation method, sensory feedback controllers for walking of humanoid robot platform KHR-3 (KAIST Humanoid Robot - 3: HUBO) and experimental results. The walking pattern trajectories have continuity, smoothness in varying walking period and stride, and it has simple mathematical form which can be implemented easily. The gait trajectory algorithm is composed of two kinds of function trajectory. The first one is cycloid function which is used for ankle position in Cartesian coordinate space. Because this profile is made by superposition of linear and sinusoidal function, which has a property of slow start, fast moving, and slow stop. This characteristics can reduce the over drive at high speed motion of the actuator. The second one is 3(rd) order polynomial function. It is continuous in the defined time interval, easy to use when the boundary condition is well defined, and has standard values of coefficients when the time scale is normalized. Position and velocity values are used for its boundary condition. F/T (Force and Torque) sensors at the ankles of the robot and accelerometers at soles are used to compensate the input position profiles (in joint angle space and Cartesian coordinate space) for keeping its dynamic balance. They are to reduce unexpected external forces such as landing shock, and vibration induced by compliances of the F/T sensor structures, link frames and reduction gears, because they can affect seriously on the walking stability. We use real-time controllers such as ZMP (Zero Moment Point), vibration reduction, landing orientation, damping, landing timing and landing position controller according to its objectives. This trajectory and control algorithm is implemented for the free-walking of KHR-3.