Minimalistic control of biped walking in rough terrain

The compass gait model has been intensively studied for a systematic investigation of complex biped locomotion dynamics, while most of the previous studies focused only on the locomotion on flat surfaces. In order to take a significant step forward in the study of dynamic biped walking, the problem addressed in this paper is the minimalistic control architecture of the compass gait model for walking in rough terrains. This controller utilizes an open-loop sinusoidal oscillation of hip motor, which induces basic walking stability without sensory feedback. A set of simulation analyses show that the underlying mechanism of the minimalistic controller lies in the “phase locking” mechanism that compensates phase delays between mechanical dynamics and the open-loop motor oscillation resulting in a relatively large basin of attraction in dynamic bipedal walking. By exploiting this mechanism, we also explain how the basin of attraction can be controlled by manipulating the parameters of oscillator not only on a flat terrain but also in various inclined slopes. Based on the simulation analysis, the proposed controller is implemented in a real-world robotic platform to confirm the plausibility of the approach. In addition, by using these basic principles of self-stability and gait variability, we demonstrate how the proposed controller can be extended with a simple sensory feedback such that the robot is able to control gait patterns autonomously for traversing a rough terrain.