Abstract: Parallel variable stiffness actuators are disclosed. The parallel variable stiffness actuator can comprise a spring and a variable-stiffness mechanism. The variable-stiffness mechanism can be configured to modulate a stiffness of the parallel variable stiffness actuator. The parallel variable stiffness actuator can further comprise a direct-drive motor arranged in parallel with the spring. A force of the direct-drive motor can be applied directly to a load. Resonant energy accumulation methods implemented by a parallel variable stiffness actuator are also disclosed. A stiffness of a spring can be changed when there is no energy stored by the spring. A resonant energy accumulation method where a force of a direct-drive motor can be applied in resonance with the oscillatory motion, while the stiffness of the parallel variable stiffness actuator can be changed to keep the amplitude of the oscillatory motion nearly constant.

Abstract: Various examples of systems, methods, and applications of variable stiffness springs are described. In one example, a variable stiffness joint apparatus can include a torsional spring; a variable stiffness mechanism comprising a self-locking mechanism and a linkage system, the self-locking mechanism comprising an auxiliary spring; and an actuator in communication with the auxiliary spring of the self-locking mechanism. When the actuator changes position, a force is applied to the auxiliary spring by the actuator and a stiffness is adjusted at an energy cost that is independent of the stiffness of the spring and the energy stored by the spring. In another example, a self-adjusting variable stiffness mechanism can include a compression spring. The energy stored by compressing the compression spring and the mechanism can self-adjust a stiffness to enable energy accumulation using a same maximal compression force which is not dependent on the energy accumulated in the spring.

Abstract: The present disclosure relates to a parallel variable stiffness actuator. The parallel variable stiffness actuator can comprise a spring and a variable-stiffness mechanism. The variable-stiffness mechanism can be configured to modulate a stiffness of the parallel variable stiffness actuator. The parallel variable stiffness actuator can further comprise a direct-drive motor arranged in parallel with the spring. A force of the direct-drive motor can be applied directly to a load. The present disclosure further relates to a resonant energy accumulation method implemented by a parallel variable stiffness actuator. A stiffness of a spring can be changed when there is no energy stored by the spring. A resonant energy accumulation method where a force of a direct-drive motor can be applied in resonance with the oscillatory motion, while the stiffness of the parallel variable stiffness actuator can be changed to keep the amplitude of the oscillatory motion nearly constant.