Singularity lock mechanism based on rolling spool dynamics

In robotics, locking mechanisms are crucial in reducing energy consumption of devices such as manipulators. One type of locking mechanism that is widely utilized is the singularity-type locking mechanism. This device is designed such that its degree of freedom decreases at the singular point, allowing it to support large external forces for extended periods with minimal energy input. However, conventional singularity-type locking mechanisms face challenges in designing singular points. In this study, we propose a novel singularity-type locking mechanism based on rolling spool dynamics (called spool paradox). This innovative device applies a curved trajectory to the spool paradox, enabling the arbitrary design of singular points by adjusting the shape of the curve. Through a developed theoretical model and experiments, we demonstrated the capability of our proposed mechanism in locking external forces with minimal energy input. Furthermore, we applied the proposed mechanism to 1-DOF robotic arm and confirmed its motion.