Type Synthesis and Kinematic Analysis of a 2-DOF Shape-Morphing Wheel Mechanism for Step-Overcoming

This study presents a novel shape-morphing wheel that enables to not only traverse flat ground quickly in a circular configuration but also overcome obstacles like steps effectively in a transformed configuration. The proposed wheel mechanism has two degrees-of-freedoms (DOFs) to change its wheel radius and the tilting angle of its lobe simultaneously in response to obstacles of various sizes. The kinematic requirements for the 2-DOF shape-morphing wheel mechanism are first defined. Then, the proper mechanisms for the proposed wheel mechanism are exhaustively searched. As a result, five mechanisms are selected in combination with four-bar mechanism to synchronize the motions of wheel lobes. From the kinematic viewpoints including the singularity, transformation range and interference, the characteristics of selected mechanisms are analyzed extensively, and a novel 2-DOF shape-morphing wheel mechanism has been successfully constructed.