A 2-DoF Switchable Variable Stiffness Actuator for Legged Walking Robots

The legged walking robots equipped with variable stiffness actuators (VSAs) show advantages in energy efficiency and various terrain. However, the energy cost to modulating and maintaining stiffness is still substantial, as the deflected spring and the stored potential energy would prevent stiffness modulation, requiring an extra amount of energy, especially for high stiffness output. In this article, we present a novel switchable variable stiffness actuator (SVSA) with 2 degrees-of-freedom (DoFs) for legged walking robots, capable of modulating output stiffness without changing potential energy stored in the spring and overcoming spring force, to perform energetically conservative legged locomotion. We introduce two independently controlled motors to drive both ends of a lockable spring along the shank and thigh, and the locking module consists of a globoid worm and worm gear for rigid locking, along with a solenoid to actively control the engagement of the spring with fast speed. Experiments validate the locking robustness and efficiency of the lockable spring, verifies the energy efficiency of the proposed SVSA. Finally, the applicability of the proposed SVSA to legged walking robot is comprehensively explored to propose an energy-efficient locomotion strategy.