A bioinspired hybrid robotic joint for safer physical human-robot interaction

Clinical Snapshot

Key Findings

• P Value: Not reported; no inferential statistical testing performed

• Effect Size: Isometric force: 400 N at 240 kPa; stretchability: 80 mm; PAM density: 0.3 g/cm³; angle control RMSE: <2°; overshoot: <1%; rise time: <1.3 s; stiffness range: 0.054–0.076 Nm/deg

• Primary Outcome: Proof-of-concept validation of a single-DOF bioinspired hybrid robotic joint using TPU pneumatic artificial muscles in antagonist configuration with independent position and stiffness controllers

• Nnt Or Sensitivity: Not applicable (engineering proof-of-concept study; no NNT, sensitivity, specificity, or hazard ratio calculable)

• Confidence Interval: Not reported

Clinical Application

Bench-level feasibility is demonstrated for a single-DOF prototype. Clinical feasibility requires multi-DOF integration, wearable form factor development, biocompatibility testing of TPU in prolonged skin contact, pneumatic supply miniaturisation, and extensive safety validation. These are acknowledged as future work and represent substantial engineering and regulatory hurdles. In Australia, any wearable robotic medical device would require TGA registration as a Class IIb or Class III medical device under the Therapeutic Goods Act 1989, depending on intended use and risk classification. Rehabilitation robotics aligns with RACGP and ACI (Agency for Clinical Innovation) frameworks for technology-assisted rehabilitation. PBS listing for robotic rehabilitation devices remains limited in Australia; the NDIS may be a relevant funding pathway for assistive wearable robots. No Australian-specific data are presented in this study. The TPU material used would require TGA-compliant biocompatibility assessment (ISO 10993 series) before any human application. Not yet applicable to any clinical population. Potential future relevance to patients requiring upper-limb wearable robotic assistance (e.g., post-stroke rehabilitation, spinal cord injury, neuromuscular disease) and to occupational exoskeleton users. Human trials are a prerequisite before any clinical application.

Abstract

In many robotic applications, such as humanoids, wearable robots or supernumerary limbs, there is a growing shift from rigid, traditional mechanisms toward softer, more compliant systems. This trend is driven by the need for safer physical human-robot interaction and the ability to operate in unstructured environments. In this work, we present a hybrid approach to controlling a single-degree-of-freedom robotic joint that combines a rigid frame with soft pneumatic actuators to enable both precise and versatile interaction. The joint is bioinspired, as it is powered by a couple of actuators mounted in an antagonist configuration, such as the human elbow. A key innovation is the design of pneumatic artificial muscles using thermoplastic polyurethane, which achieve high isometric force (400 N at 240 kPa), significant stretchability (80 mm), and low density(0.3gcm-3), making them competitive with state-of-the-art alternatives. Two model-free controllers were developed to independently regulate joint position and stiffness. Angle control achieved high precision (<2∘RMSE) with minimal overshoot (<1%) and fast response (rise time<1.3s). Stiffness control modulated joint compliance across a range of 0.054-0.076 Nm deg-1, with the expected trade-off of reduced workspace. A final proof-of-concept demonstrated the concurrent use of both controllers to modulate the joint's dynamic behavior in response to external disturbances. While future work will address multi-DOF coordination and wearable integration, this study represents a foundational step toward safe, adaptable robotic actuation through the combination of rigid structures and soft actuation.

References

1. 1.Dimonte, G., Gandolla, M., & Proietti, T. (2026). A bioinspired hybrid robotic joint for safer physical human-robot interaction. Bioinspiration & Biomimetics. https://doi.org/10.1088/1748-3190/ae72db