Investigation of a Novel Continuously Rotating Knee Mechanism for Legged Robots

This paper presents a novel continuously rotating knee mechanism for legged robots. Specifically, the mechanism presented is used on NABi (Non-Anthropomorphic Biped). Legged robots with traditional humanoid design often have human-like leg configurations that require complex motion planning and high number of degrees of freedom for locomotion. NABi however, has a unique leg configuration that increases stability and balance while simplifying mechanical design and motion planning. A novel knee joint design that allows the robot's shin (tibia) to rotate a full 360 degrees continuously will allow the robot to walk over large obstacles such as a tall doorsill or climb stairs easily. In normal conditions, the robot uses a bipedal walking gait, however in certain scenarios, the rotating knees become beneficial. This paper presents the findings from the observations of a series of experiments performed for two specific example scenarios. Examples include going over a barrier (doorsill) and ascending stairs. With an initial plan to perform motion analysis and trajectory planning on the above locomotion types, we observe that careful planning and trajectory generation is not the optimum method to approach this problem. It is rather preferred to treat the locomotion method as a continuous motion that passively adjust based on variable factors such as robot geometry, torque output, and friction properties.