A Dual-Cam Parallel Elastic Actuator with Shared Gas-Spring Compensation for Humanoid Ankles

Abstract:To improve torque capacity and energy efficiency of humanoid ankles, this paper proposes a 2-DoF parallel elastic actuator (PEA). The main novelty of the proposed design lies in its dual-cam, single-gas-spring architecture, which enables torque compensation in both pitch and roll using a shared elastic element, thereby improving structural compactness compared with conventional multi-element compensation schemes. By leveraging parallel gas springs and customized cam modules, the proposed architecture provides dual-axis torque assistance tailored to specific task requirements. The second key contribution is the formulation of a coupled 2-DoF mathematical model that explicitly captures the interdependence between the two compensation units through the shared spring. Based on this model, an optimization-based design framework is developed to synthesize customized cam profiles from prescribed torque references, establishing a systematic link from task requirements to hardware realization. The complete lower-leg CAD integration is presented in detail. Static FEA and kinematic simulations confirm the design's feasibility and torque-relief effectiveness. The results highlight the proposed design as a compact, customizable solution for 2-DoF humanoid ankle torque compensation.

Accepted to IEEE AIM 2026. Copyright 2026 IEEE. Personal use of this material is permitted

Robotics (cs.RO)

arXiv:2608.30832 [cs.RO]

(or arXiv:2608.30832v1 [cs.RO] for this version)

https://doi.org/10.48550/arXiv.2608.30832 Focus to learn more arXiv-issued DOI via DataCite (pending registration)

https://doi.org/10.1109/AIM65483.2026.11658177 Focus to learn more DOI(s) linking to related resources

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