DISG: Driving-Integrated Spherical Gear Enables Singularity-Free Full-Range Joint Motion

Dexterous joints have attracted interest in the field of robotics. This article presents a driving-integrated spherical gear (DISG) that enables entire spherical meshing and active driving between two spherical gears, forming a dexterous multidegrees of freedom rolling contact joint. The DISG consists of a pair of spherical gears and an omnidirectional internal driver. The spherical gear shape is a combined projection of the conventional planar gear profile in the longitudinal and latitudinal directions, which can mesh and be driven over the entire sphere. An actively driving magnet and a passively following magnet are magnetically connected across the spherical gear and together form the internal driver, enabling arbitrary connection points throughout the sphere. In all configurations, one spherical gear can roll in all directions on the surface of the other. Furthermore, we analyze the kinematics of DISG and prove that the DISG-based dexterous joint has good kinematic characteristics, such as singularity-free and full-range workspace. We verify the theoretical and physical characteristics of DISG in a series of experiments on the prototype. We also compare DISG-based joints to other joint actuators and show that DISG-based joints have advantages in dexterity, motion range, compactness, and lightweight.