S.Y. Kim and D.J. Braun, Variable Stiffness Floating Spring Leg: Performing net-zero energy cost tasks not achievable using fixed stiffness springs, IEEE Robotics and Automation Letters, vol. 8, no. 9, pp. 5400-5407, 2023.
This paper introduces a new variable stiffness spring design that combines force amplification with energy conservation. Unlike conventional springs, which have fixed force-deflection behavior, or typical variable stiffness springs, which require energy to adjust stiffness, the proposed design remains energetically conservative while offering customizable stiffness. The authors present the theory of these springs and demonstrate their effectiveness in a cyclic lifting task that demands high force but no net energy, a task not achievable with traditional springs.
Why it matters: Many tasks in daily life and industry, such as standing from a chair or moving heavy objects, require force but little to no net energy. Motors consume energy even in these cases, creating inefficiency. Energetically conservative variable stiffness springs provide a way to handle such tasks with minimal energy use, enabling more capable and efficient assistive devices, exoskeletons, and industrial robots.