Leg stiffness adaptation for running on unknown terrains

The ability of biological locomotors to rapidly and stably traverse unstructured environments has inspired the development of numerous legged robotic platforms. While strides have been made in negotiating terrains cluttered with obstacles, dealing with surface property variations has received less consideration. This work presents a leg stiffness control strategy that estimates the surface compliance and adjusts the leg stiffness in order to maintain a nominal locomotion behavior while allowing for stable transitions between surfaces of up to three orders of magnitude differences in ground compliance. Implementation of this technique with high-bandwidth variable stiffness actuators that are currently being developed will expand the range of legged robotic platforms to environments with sudden and significant changes in terrain characteristics.