Design and development of a compact small-scale spherical gear mechanism with manipulability-based singularity avoidance

Multi-degree of freedom (DOF) robotic systems, particularly those with seven or more DOFs similar to the human arm, have the potential to significantly expand the functional range and versatility of robotic manipulators. The spherical gear mechanism, known as Active Ball Engagement Mechanics (ABENICS), serves as a novel joint element that enables the integration of multiple rotational axes at a single point, resulting in a more compact structure with increased degrees of freedom. This study focuses on the design and validation of a miniaturized spherical gear mechanism, featuring a spherical gear with a module of 1.5 mm and an outer diameter of 51 mm. The study discusses its mechanical design, operational performance, and manipulability-based motion control strategy for effective singularity avoidance. Furthermore, a driving gear-based angular feedback system utilizing hall-effect sensors is introduced for homing, demonstrating improved performance and reliability compared to the previously implemented IMU-based homing approach. Experiments were conducted to assess the mechanism’s motion range, positional error, singularity avoidance, and homing performance, all of which were successfully validated. The results confirm the potential of this miniaturized mechanism to enable more compact, efficient, and functional robotic systems. Finally, the study demonstrates the application of the developed mechanism as a wrist joint attached to a robotic arm, capable of carrying a 250 g payload during a pick-and-place task.