Generating Multimodal Textures with a Soft Hydro-Pneumatic Haptic Ring

Abstract

The growing adoption of extended reality (XR) has increased demand for wearable technologies that provide naturalistic tactile sensations while allowing users to interact freely with their environments using bare fingers. However, most existing wearable haptic devices support only a limited range of tactile modalities. Here, we introduce a soft haptic ring and a data-driven rendering methodology for generating multimodal texture sensations. The device integrates pneumatic and hydraulic actuation to render roughness, thermal, and softness cues on the proximal phalanx. The ring can generate forces up to 1.75 N, produce displacements up to 0.27 mm within a 30-300 Hz operating range, and modulate display temperature by up to 25 Celcius within 65 s. The rendering methodology modulates these cues based on the user's exploratory actions: the hydraulic actuator conveys perceived temperature during static contact, while the pneumatic actuator generates pressure and vibration cues to convey softness and roughness during pressing and sliding gestures, respectively. We evaluated the system in a user study with 15 participants who matched six virtual textures generated by the ring to their real counterparts and rated their perceived sensations using guided exploratory actions. Participants achieved an average texture-matching precision of 68% and an F1 score of 0.68. Adjective ratings confirmed that the ring produces distinct and perceptually rich stimuli across all rendered modalities. These findings demonstrate the potential of the proposed haptic ring and rendering methodology to deliver multimodal tactile cues away from the fingertip for immersive XR applications, enabling diverse tactile feedback while preserving natural physical interaction.