WAVE: Worm Gear-based Adaptive Variable Elasticity for Decoupling Actuators from External Forces

2025-09-26

AI Summary

Traditional robotic actuators struggle to simultaneously achieve tunable stiffness, force–position decoupling, and overload protection. To address this, this paper proposes WAVE—an adaptive variable-stiffness actuator based on worm-gear transmission. Its core innovation lies in exploiting the inherent irreversibility of worm gearing to physically decouple the drive motor from external contact forces, while integrating a pre-compressed spring to enable continuous stiffness modulation and impact energy absorption. A dedicated force–position separation control strategy is further designed, ensuring that motor torque asymptotically approaches zero when the joint remains stationary under external load. Experimental validation confirms the accuracy of the stiffness model and demonstrates wide-range, continuous joint stiffness regulation. In contact-intensive tasks, WAVE significantly enhances operational robustness and environmental adaptability while effectively preventing actuator overload damage.

Technology Category

• Intelligent Robots: Manipulation
• Humans and AI: Human-Aware Planning and Behavior Prediction
• Search and Optimization: Mixed Discrete/Continuous Search

Application Category

• Responsible Web: Machine-in-the-loop, human agency and autonomy
• Systems and Infrastructure for Web, Mobile and WoT: Energy management for devices in mobile Web and WoT environments
• Graph Algorithms and Modeling for the Web: Efficient manipulation of static and dynamic Web-related graphs

Abstract

Robotic manipulators capable of regulating both compliance and stiffness offer enhanced operational safety and versatility. Here, we introduce Worm Gear-based Adaptive Variable Elasticity (WAVE), a variable stiffness actuator (VSA) that integrates a non-backdrivable worm gear. By decoupling the driving motor from external forces using this gear, WAVE enables precise force transmission to the joint, while absorbing positional discrepancies through compliance. WAVE is protected from excessive loads by converting impact forces into elastic energy stored in a spring. In addition, the actuator achieves continuous joint stiffness modulation by changing the spring's precompression length. We demonstrate these capabilities, experimentally validate the proposed stiffness model, show that motor loads approach zero at rest--even under external loading--and present applications using a manipulator with WAVE. This outcome showcases the successful decoupling of external forces. The protective attributes of this actuator allow for extended operation in contact-intensive tasks, and for robust robotic applications in challenging environments.

Problem

• Decouples actuators from external forces using worm gear mechanism
• Enables continuous stiffness modulation through spring precompression control
• Protects system by converting impact forces into stored elastic energy

Innovation

• Worm gear decouples motor from external forces
• Spring converts impact forces into elastic energy
• Modulates stiffness via spring precompression length