Walking Control Framework on Uneven Terrain Using Variable Stiffness Sole

Although many walking control frameworks have been developed to enable biped robots to walk stably on uneven terrain, the foot sole of the robot is also important. Inspired by that study, we have developed a Variable Stiffness Sole (VSS), which is able to adapt to the shape of the obstacles on the ground in Compliant Mode and provide robust support in Stiff Mode. Furthermore, we proposed a walking control framework on uneven terrain for a biped robot equipped with the developed VSS. The proposed walking control framework comprises a posture balance controller to stabilize the zero moment point from disturbances applied to the robot, an ankle torque/foot force controller for walking on uneven terrain, and a VSS controller to change the mode of the VSS. Finally, the proposed framework was verified through walking experiments of RoK-3 equipped with the VSS module on a single obstacle and uneven terrain with various obstacles.