S.Y. Kim and D.J. Braun, Controllable Mechanical-domain Energy Accumulators, IEEE International Conference on Robotics and Automation, London, United Kingdom, pp. 7359-7364, 2023.

This paper presents a novel lockable compression spring that can store and release mechanical energy with high efficiency and precise control. The design uses a compact capstan clutch to lock elastic energy at any spring deflection, hold forces up to 1000 N, and release the spring in less than 10 ms with minimal control effort. The prototype achieves an 80% energy storage and return efficiency, comparable to efficient electric motors, while maintaining the form factor of a conventional spring.

Why it matters: Traditional springs cannot hold energy without external load, and existing lockable springs add complexity and inefficiency. This design provides a simple, efficient, and controllable way to accumulate and release energy, paving the way for energy-efficient spring-based actuators and next-generation robotic systems.