Controllable Mechanical-domain Energy Accumulators

TL;DR

This paper introduces a novel lockable compression spring with a capstan clutch that passively locks and unlocks under high force, enabling high-fidelity energy storage and release with efficiency comparable to electric motors.

Contribution

The paper presents a new lockable spring design using a capstan clutch that achieves high force locking, rapid unlocking, and high energy efficiency, addressing limitations of previous lockable springs.

Findings

Locks over 1000 N force at arbitrary deflections

Unlocks in less than 10 ms with minimal control force

Achieves 80% energy storage and return efficiency

Abstract

Springs are efficient in storing and returning elastic potential energy but are unable to hold the energy they store in the absence of an external load. Lockable springs use clutches to hold elastic potential energy in the absence of an external load, but have not yet been widely adopted in applications, partly because clutches introduce design complexity, reduce energy efficiency, and typically do not afford high fidelity control over the energy stored by the spring. Here, we present the design of a novel lockable compression spring that uses a small capstan clutch to passively lock a mechanical spring. The capstan clutch can lock over 1000 N force at any arbitrary deflection, unlock the spring in less than 10 ms with a control force less than 1 % of the maximal spring force, and provide an 80 % energy storage and return efficiency (comparable to a highly efficient electric motor operated at constant nominal speed). By retaining the form factor of a regular spring while providing high-fidelity locking capability even under large spring forces, the proposed design could facilitate the development of energy-efficient spring-based actuators and robots.