Accumulating Energy in Assistive Springs using Bounded Force and Deformation: Theory, Mechanism Design, and Experimental Validation

Abstract

Springs can provide force to assist motor-driven robots or spring-augmented humans at zero net energy cost by recycling mechanical work during motion. However, humans have limited force and range of motion, and motors have a limited ability to produce force. These limits constrain how much energy a conventional spring can store and, consequently, how much assistance a spring can provide. This work introduces an approach to accumulating negative mechanical work in assistive springs over several motion cycles. It is shown that, by utilizing a novel floating spring mechanism, the weight of a human or robot can be used to iteratively increase spring compression, irrespective of the potential energy stored by the spring. Decoupling the force required to compress a spring from the energy stored by a spring could enable spring-driven robots and humans to perform physically demanding tasks without the use of large actuators and power supplies.